Lameness Associated with the Stifle and Pelvic Regions - · PDF fileLameness associated with the stiﬂe may be acute or ... (TS). Large muscle mass may prohibit palpation of the greater

Lameness Associated with the Stifle and PelvicRegions

Sue J. Dyson, VetMB, PhD

Author’s address: Centre for Equine Studies, Animal Health Trust, Lanwades Park, Bury Road,Kentford, Newmarket, Suffolk CB8 7UU. © 2002 AAEP.

1. Introduction

The reciprocal apparatus of the hindlimb meansthat similar lameness characteristics are shared bymany causes of hindlimb lameness in both the prox-imal and distal parts of the limb. It is rarely pos-sible by evaluation of gait alone to identifyaccurately the source of pain causing lameness, al-though a combination of clinical signs may lead theclinician to suspect a site of pain. It is only throughthe diligent use of local analgesic techniques thatthe source of pain can be reliably determined, andinterpretation of these is not always straightfor-ward. To my knowledge, there have been no epide-miological studies investigating the relativeincidence of different sites of pain causing hindlimblameness, and any such study would be heavily de-pendent on the accuracy of diagnosis. It is my im-pression, after 22 yr of lameness investigation, thatlameness ascribed to the pelvic region is often over-diagnosed. In my opinion, comprehensive clinicalexaminations combined with local analgesic tech-niques are often under utilized, in part because ofthe inherent dangers of hindlimb lameness investi-gation. Thus, pain causing lameness in the moredistal parts of the limb is often overlooked. How-ever, in my experience these dangers are overem-phasized and in a large proportion of horses

thorough clinical examinations and local analgesictechniques are possible with minimal risk, providedthat horses are quietly and appropriately re-strained. Over a 3-yr period (January 1999 to De-cember 2001, inclusive) I investigated 318 horses of2 yr of age or older with hindlimb lameness in whicha definitive diagnosis of the source of pain was es-tablished; 49 horses (15%) had lameness associatedwith the stifle region and only 29 horses (9%) hadlameness associated with the pelvic region. Horsespresenting with restricted hindlimb impulsion andback stiffness, which were ultimately diagnosedwith sacroiliac joint pain, were excluded from thisassessment. A further 22 horses (6% of 340) withunilateral hindlimb lameness were evaluated in thisperiod and a definitive diagnosis of the source ofpain causing lameness could not be established, de-spite thorough clinical examination, comprehensivelocal analgesic techniques and nuclear scintigraphicexamination. These figures, based on a referralpopulation of horses and restricted to horses 2 yr ofage or older, may overestimate the incidence of up-per hindlimb lameness in the general horse popula-tion. In my opinion it is critical to be able toreliably perform perineural analgesia of the tibialand fibular nerves in order to exclude definitivelythe hock region and distal parts of the limb as po-

AAEP PROCEEDINGS � Vol. 48 � 2002 387

IN DEPTH: UPPER HIND LEG LAMENESS

NOTES

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Proceedings of the Annual Convention of the AAEP 2002

tential sources of pain causing lameness, bearing inmind that it is frequently only possible to achieveimprovement in lameness, rather than its completealleviation. The purposes of this paper are to de-scribe an approach to the diagnosis of stifle andpelvic injuries and some of the more common causesof lameness, and to highlight some of our currentlimitations in diagnosis. It focuses on horses of 2 yrof age and older and, therefore, does not considerconditions more prevalent in immature horses, suchas juvenile osteochondrosis.

2. Anatomy

Accurate knowledge of functional anatomy is crucialfor understanding the role of the stifle in the recip-rocal apparatus of the hindlimb. Detailed knowl-edge of anatomy is also essential for interpretationof radiographic, ultrasonographic, and nuclear scin-tigraphic images and for understanding the limita-tions of diagnostic techniques. However, it isbeyond the scope of this paper to discuss anatomy indepth.

3. History

Lameness associated with the stifle may be acute orinsidious in onset and may or may not be associatedwith localizing clinical signs. History of a kick orhitting a fixed fence mean that a fracture must beruled out. Although osteochondrosis (OC) is usu-ally manifest in immature horses, it may not becomesymptomatic until later in life. History of lamenessthat is variable in severity may be suggestive of asubchondral bone cyst (SBC). Difficulties in get-ting up from lying down may be associated witheither stifle or pelvic region pain. Pelvic injury in amature athlete is a comparatively unusual cause oflameness, except as the result of trauma due to afall, rearing, and falling over backwards, and becom-ing cast in the stable or sustaining an injury duringtransport. When there is no history of trauma, di-agnosis can be difficult and it is frequently necessaryto exclude all possible sources of pain in the distallimb before focusing on the pelvic region.

4. Clinical Examination

Visual Assessment and Palpation

Some horses with stifle pain tend to stand with thestifle rotated outwards. Visual inspection may re-veal distension of the femoropatellar (FP) or medialfemorotibial (MFT) joint capsules. Detectable dis-tension of the lateral femorotibial (LFT) joint is un-usual. A horse with severe stifle pain may standbearing weight only on the toe of the foot. It iseasiest to palpate the stifle joint if the horse is fullyload bearing, with the limb in a normal position,neither protracted or retracted. I grasp the horse’stail with one hand and palpate with the other, firstlocating the tibial crest and then moving proximallyto assess the patellar ligaments, the collateral liga-ments of the FT joint and the joint capsules. En-

largement of the medial patellar ligament mayreflect previous medial patellar desmotomy. Firmpressure should be applied to all soft-tissue struc-tures and bony prominences to see if pain can beelicited. It can be helpful to rock the horse’s weightfrom one hindlimb to the other and to observewhether the patella remains relatively stable in po-sition, or moves jerkily. Repeated upward pressureon the patella may be resented by horses with de-layed release of the patella. The limb is picked upand flexion is assessed. Some horses with stiflepain pick up the limb exaggeratedly, avoiding max-imum flexion of the stifle (Fig. 1). The ligamentousand bony structures are palpated again. In my ex-perience, the use of other manipulative tests of thestifle to assess integrity of the cruciate ligaments isof no value. Abduction of the limb may cause painassociated with injury of the medial collateral liga-ment of the FT joint, but this is a nonspecific test,which is also resented by some clinically normalhorses.

Clinical assessment of individual structures of thepelvic region by visual examination and palpation isnot easy, especially in warmblood and draft breeds,because of the large muscle mass of the hindquar-ters. It is frequently only possible to palpate thetubera coxae (TC) and tubera sacrale (TS). Largemuscle mass may prohibit palpation of the greatertrochanter of the femur. Atrophy of the hindquar-ter musculature is nonspecific and can reflect disusedue to pain arising anywhere in the limb, although

Fig. 1. Exaggerated lifting of the limb during flexion.

388 2002 � Vol. 48 � AAEP PROCEEDINGS




atrophy of the muscles around the tail head oftenreflects injury to the tuber ischium, or local nervedamage. Asymmetry of the height of the TS is acommon finding in horses in full work, free from lame-ness, although may be seen in association with poorperformance or alterations in hindlimb gait. Alter-ation in muscle mass in the proximity of the TS cansuperficially give a false impression of asymmetry ofthe TS themselves (Fig. 2). Asymmetry of the TCmay reflect a previous injury unassociated with ongo-ing pain. Poor muscle development in the lumbarregion and over the hindquarters may make the TSand the summits of the spinous processes of the lum-bar vertebrae appear abnormally prominent. Thismay reflect the way in which the horse has beenworked, or may reflect disuse muscle atrophy associ-ated with pain.

The pelvic region should be appraised visually andpalpated systematically and, although preliminaryassessment is usually best performed in the stable,for accurate evaluation of symmetry of the muscu-lature and bony elements of the pelvic region thehorse should be standing completely squarely be-hind, on a firm, level surface with the horse lookingstraight ahead. In a horse with severe lamenessthis may not be possible, because the horse may be

unwilling to load fully the lame limb. Careful dif-ferentiation should be made between muscular andbony asymmetry. Marked muscular atrophy canmake accurate assessment of symmetry of the pelvicbones difficult. In order to evaluate accurately thelevelness of the TC, it is necessary for two assistantsto place an index finger on the craniodorsal aspect ofeach tuber coxae, and extend the finger horizontally,or to mark the TC with tape. Elevation of the tailmay be necessary to identify muscle atrophy aroundthe tail head, which may be seen in association witheither nerve damage, or injuries of the ipsilateraltuber ischii (TI).

Assessment of symmetry when the horse is un-willing to bear weight evenly on both hindlimbs isnot easy, but particular attention should be paid tothe way in which the limb is positioned. An abnor-mally straight limb may reflect luxation of the cox-ofemoral (CF) joint and secondary upward fixation ofthe patella. The greater trochanter of the femur ofthe lame limb may appear higher than that of thecontralateral limb.

The muscles of the lumbar and pelvic regionsshould be assessed carefully to identify any area ofabnormal muscle tension, pain on palpation or un-usual firmness. Firm stroking of the muscles

Fig. 2. (A) Symmetry of the bony prominences of the pelvis and the overlying musculature. (B) Atrophy of the right glutealmusculature, but symmetry of the bony prominences. (C) Atrophy of the left gluteal muscles and apparent asymmetry of the tuberasacrale. The left tuber sacrale appears higher than the left. The horse had a left ilial wing stress fracture.





firstly with a finger and then with a blunt-endedobject, e.g., artery forceps, is useful to determinewhether either muscle spasm or muscle fascicula-tion are induced. Palpation of the caudal musclesof the crus is also important because abnormal painor tension can reflect either primary muscle injury,or an injury of the ipsilateral TI.

Firm pressure should be applied to the bony prom-inences to see if pain can be induced, or an abnormalreaction such as marked sinking on the hindlimbswhen pressure is applied to the TS. Both TCshould be grasped simultaneously and the horserocked from side to side to determine whether crep-itus can be detected by palpation or auscultation,bearing in mind that the absence of crepitus does notpreclude the presence of a fracture.

Careful, systematic examination of the pelvic ca-nal region per rectum is also indicated in order toassess the aorta and iliac arteries, the psoas muscu-lature and the caudal aspect of the ilial shaft, andthe pubis and ischium.

Manipulation of the limb may be resented if there ispain associated with the CF joint, but generally theresponses to flexion of the limb, protraction, retraction,or abduction are rather nonspecific. A horse withpain associated with the sacroiliac (SI) joints or a CFjoint may be reluctant to stand on one limb, with theother limb raised and may behave very awkwardly inanticipation of discomfort. However, this is a nonspe-cific reaction and it must be borne in mind that somehorses present difficulties in picking up the hindlimbsin the absence of any sign of lameness or poor perfor-mance. Difficulties in picking up hindlimbs may bedue to reluctance to accentuate weight bearing on thelamest limb, reluctance to flex the lame limb or psy-chological. If the horse is a shiverer, unilaterally orbilaterally, the response to hindlimb flexion can bedifficult to assess.

Gait Assessment

Lameness associated with the stifle region is oftennot significantly different in character from lame-ness associated with pain arising in the more distalparts of the limb. Some horses rotate the stifle ofthe lame limb outwards. Horses with an unstablemeniscus or severe desmitis of a collateral ligamentof the FT joint may show increased discomfort whenturned in small circles. Severe lameness associ-ated with a fracture may result in the horse bearingweight only on the toe. There is often a reducedheight of arc of foot flight, resulting in a variabledegree of toe drag. Lameness may be worse withthe affected limb on either the inside or outside of acircle on the lunge. Bilateral stifle pain may resultin poor hindlimb impulsion rather than overt lame-ness. Mild lameness is usually accentuated by rid-den exercise, especially when the rider sits on thediagonal of the lame limb, but this is nonspecific andtypical of many horses with hindlimb lameness.Proximal limb flexion (hock flexion test) often in-creases lameness, but a negative response does not

preclude stifle pain. A very marked response toflexion is usually more likely to reflect stifle thanhock pain. Holding the limb behind the horse inthe shoeing position, by supporting the crus, withoutundue flexion of the hock, nor pressure on the fet-lock, may accentuate stifle pain in some horses(Fig. 3).

The degree and character of lameness associatedwith the pelvic region depends on the underlyingcause. Fractures or luxation of the CF joint resultin acute onset, severe lameness. Lameness associ-ated with other lesions in the pelvic region may bevariable in degree, both between horses with similarlesions, and within and between examination peri-ods. Pain associated with the CF joint frequentlyresults in the horse moving on three tracks with thenonlame limb being placed between the two fore-limbs, i.e., the horse is drifting away from the lamelimb. On the lunge the horse may be inclined tobreak to canter, rather than move with adequatehindlimb impulsion, but this is not specific for pelvicpain, and is typical of many hindlimb lamenesses.Pain associated with the CF joint, or the greatertrochanter of the femur sometimes results in thehorse carrying the lame limb in canter. Lesionsassociated with the SI joints may result in the horsecrossing over each hindlimb at the trot, i.e., plaiting,but this is not seen in all horses. The horse maymove with reduced hindlimb impulsion, rather thanovert lameness. This restriction in gait may bemuch more obvious when the horse is ridden. Al-

Fig. 3. Stifle flexion test.





though acute fractures of the TI invariably causelameness, chronic injuries may result in loss of per-formance (e.g., jumping to the right), rather thanovert lameness.

The response to flexion tests is rather nonspecific.Bear in mind that increased weight bearing on onelimb, caused by flexing the contralateral limb, mayaccentuate lameness in the weight-bearing limb.Turning the horse in small circles, inducing rota-tional forces on the CF joint, may accentuate lame-ness associated with the CF joint.

Ridden exercise is invaluable in horses presentingwith a history of poor performance, reduced hind-limb impulsion, or low-grade lameness, because fre-quently the lameness is accentuated. Some horseswith SI pain, or pain associated with new bone onthe caudal aspects of the wings of the sacrum willshow extreme reluctance to go forward freely.However, care must be taken to differentiate thesehorses from those with bilateral hindlimb lameness,thoracolumbar pain, recurrent low-grade exertionalrhabdomyolysis and those performing poorly due tothe rider, due to previous poor schooling or to acombination of boredom and an unwillingtemperament.

5. Local Analgesia

If there are obvious clinical signs of stifle pain, e.g.,distension of the medial FT joint capsule, exagger-ated lifting of the limb during flexion and outwardrotation of the stifle, or there has been knowntrauma to the stifle region, it may be reasonable toproceed directly to radiography and ultrasonogra-phy. However, in many horses with stifle pain lo-calizing clinical signs are absent or equivocal, andlocal analgesia is essential to determine the sourceof pain, bearing in mind the limitations of intra-articular (IA) analgesia.

The stifleIntra-articular injection of the FP joint may eitherbe performed alone, or in conjunction with the me-dial and lateral FT joints. Although in a significantnumber of horses there is communication betweenthe FP and each of the medial and lateral FT joints,this is not a consistent feature.1 Diffusion of mepi-vacaine to all compartments of the stifle after injec-tion of one compartment has been demonstrated,2

but the concentration of mepivacaine achieved maybe inadequate to provide pain relief. In my experi-ence, unless there is definitive clinical suspicion of astifle problem involving a specific compartment,blocking each joint independently may result in anoverall false-negative result, whereas if all threecompartments are blocked simultaneously, lame-ness may be significantly improved. If there is ob-vious distension of a joint capsule then it may beindicated to block a single compartment. The re-sponse to IA analgesia is often delayed and a posi-tive response is sometimes not evident until up to 90min after injection.

I prefer to inject the stifle joints with the horserestrained in stocks. Most horses resent needlepenetration of the skin, rather than advancement ofthe needle and injection, and therefore in the major-ity there is little advantage to be gained by placingsubcutaneous blebs of local anaesthetic solution.It is important that the horse remains fully weightbearing on the limb to be injected, so it may behelpful in some horses to pick up the ipsilateralforelimb. In many horses the horse’s attention canbe adequately distracted by application of a nosetwitch and stroking the ipsilateral forelimb. If thehorse is very difficult, sedation for injection can beconsidered, provided that the lameness is of moder-ate to severe in degree. Sedation with xylazine andbutorphanol is recommended. The effect of theblock cannot be assessed for approximately 30 min,but because the effect of mepivacaine usually lastsfor 2 to 3 h, delay in assessment is not a problem.Sedation is not appropriate if lameness is only mild,because it may induce a mild, persistent bilateraltoe drag, which can confound interpretation. A 3–4cm 20-gauge needle is used for each joint and 20 mlof mepivacaine.

In my experience, the response to perineural an-algesia of the tibial and fibular nerves may be de-layed for up to 2 h in some horses, especially ifperformed by an inexperienced clinician, with inac-curate placement of the local anaesthetic solution.It is therefore advisable that at least 2 h shouldelapse between performing these blocks and IA an-algesia of the stifle to avoid misinterpretation.

FP joint

Technique. The FP joint may be approachedfrom the cranial or lateral aspects. For the cranialapproach, palpate the tibial crest and the middleand medial patellar ligaments. The needle is in-serted between these ligaments and directed ob-liquely proximally or horizontally at an angle ofapproximately 45° – 90° to the skin. The depth ofinsertion depends on the thickness of the overlyingpatellar fat pad. Unless the joint capsule is dis-tended it is unusual to retrieve synovial fluid usingthis approach. At least 20 ml of mepivacaineshould be injected.

The lateral approach is more likely to yield syno-vial fluid.3 The needle is inserted caudal to thelateral patellar ligament, approximately 5–6 cmproximal to the lateral edge of the proximal tibia,perpendicular to the long axis of the femur. Theneedle is inserted until it meets bone and is thenwithdrawn slightly.

Interpretation. IA analgesia of the FP joint isnot specific because it usually communicates withthe MFT joint. Intra-articular analgesia is gener-ally not required in juvenile cases of OC, becauseclinical signs are usually obvious. However,chronic OC can result in poor hindlimb action, ormore obvious lameness in mature horses and in





these cases localizing clinical signs may be less ob-vious. In such horses, IA analgesia usually pro-duces some improvement in lameness, but thedegree of improvement may only be slight. Flat-tening and subchondral bone sclerosis of the lateraltrochlea of the femur can be identified radiographi-cally in both clinically normal horses and those withhindlimb lameness. Thus, the significance of suchlesions can be difficult to determine. The patellarligaments are periarticular or extra-articular struc-tures. Injuries of the middle patellar ligament oc-curs most frequently, but IA analgesia of the FPjoint usually results in little or no improvement inlameness.

MFT joint

Technique. The MFT joint is approached be-tween the medial patellar ligament and the medialcollateral ligament of the FT joint, approximately 2cm proximal to the tibia. The needle is directedhorizontally, perpendicular to the skin. Synovialfluid may appear spontaneously in the needle hub ifthe joint capsule is distended, but otherwise it maynot be possible to retrieve synovial fluid. There isusually no resistance to injection. If injection isimpossible, partially withdraw the needle and redi-rect the needle caudally and proximally to avoid themedial meniscus.

Interpretation. See below.

LFT joint

Technique. The LFT joint is approached eitherbetween the lateral patellar ligament and the longdigital extensor tendon, or between the long digitalextensor tendon and the lateral collateral ligamentof the FT joint. The needle is inserted horizontallyapproximately 2 cm proximal to the proximal tibia.It is unusual to retrieve synovial fluid.

Interpretation. It is unusual for pain associatedwith the stifle to be eliminated completely by IAanalgesia. It is therefore important to be fullyaware of the degree of lameness before injection, sothat mild to moderate improvement is not missed.SBCs in the medial femoral condyle are often asso-ciated with a variable degree of lameness, withinand between examination periods. Improvementin lameness associated with a SBC in the medialfemoral condyle following IA analgesia is very vari-able. Other osseous cyst-like lesions (OCLLs), e.g.,in the proximal tibia, respond inconsistently to IAanalgesia. Lameness associated with mensicaltears, meniscal ligament tears or damage to a cra-nial or caudal cruciate ligament is usually signifi-cantly improved. However lameness due to acruciate ligament injury often has a delayed re-sponse due to the position of the cruciate ligamentsbehind the synovial membranes separating the me-dial and lateral compartments of the femorotibialjoint. The improvement in lameness due to osteo-

arthritis (OA) of the FT joint is also variable.Slight improvement should be regarded as signifi-cant. Lameness due to injury to either one of thepatellar ligaments or the collateral ligaments of theFT joint, or the fibula, is usually not affected.

CF jointTechnique. IA analgesia of the CF is technicallydifficult, because in many well-muscled, maturehorses it is impossible to palpate the bony land-marks and, therefore, their position must be deter-mined ultrasonographically. The horse should bestanding reasonably squarely, bearing weightevenly on each hindlimb. The needle is insertedbetween the greater and lesser protuberances of thegreater trochanter of the femur. A 14-cm 18-gaugespinal needle is required. It is preferable to insertthis through a subcutaneous local anaesthetic bleb.The needle is directed from caudally at an angle ofapproximately 30° to the long axis of the horse andadvanced slightly distally. The aim is to direct theneedle along the axis of the femoral neck. Bear inmind that the CF joint is situated vertically abovethe stifle joint. Synovial fluid may be aspirated insome, but not all cases. Thirty ml of mepivacaineshould be injected. Lack of resistance to injection isnot a good indicator that the needle is correctlypositioned. Extra-articular deposition of local an-aesthetic solution may result in temporary obtura-tor nerve paralysis, which completely confoundsinterpretation of the block.

Interpretation. Lameness associated with theCF joint in mature horses is comparatively rare.In the presence of advanced OA there may be afalse-negative response.

SI jointBy using a 9–18 cm needle inserted abaxial to themidline at the lumbosacral space, between the TS,and directed approximately 20° caudally, local an-aesthetic solution (20 ml per side) can be infiltratedaround the caudal aspect of the SI joints. Thisimproves clinical signs in many horses, sometimesdramatically, but in my experience a negative re-sponse does not preclude the presence of significantSI joint disease. Improvement is usually apparentwithin 15–20 min after injection. Sciatic nerve pa-ralysis is a potential complication, although in myexperience is rare. Localized patchy sweating oversemitendinosus and transient ipsilateral partialperineal paralysis has been seen in one horse.

Serum Muscle Enzyme Concentration

Measurement of serum concentration of creatine ki-nase (CK) and aspartoaminotransferase (AST) is in-valuable for the diagnosis of both acute and chroniccases of rhabdomyolysis (tying up). In chroniccases it may be necessary to compare resting levelswith concentrations reached after maximum exer-cise. Peak levels of CK are likely to occur 3 h after





exercise. If a horse has had a tying-up episodewithin the last 4–5 d AST levels will almost invari-ably be raised. Some horses with chronic recurrentproblems will have constantly elevated levels of bothCK and AST. The degree of elevation of muscleenzyme concentrations may show a poor correlationwith the severity of clinical signs.

Diagnostic Imaging

Radiography

Radiographic examination of the stifle requires aminimum of lateromedial, caudolateral-craniome-dial oblique and craniocaudal views.4 Flexed lat-eromedial views may give additional informationabout the proximal aspect of the tibia and the troch-lear ridges and femoral condyles and permit moreaccurate evaluation of the apex of the patella. Cra-nioproximal-craniodistal oblique views of the flexedstifle are essential for the diagnosis of some patellarfractures.

Flattening of the lateral trochlear ridge, with nor-mal subchondral bone opacity or some sclerosis, is areflection of OC, but may be clinically silent in amature horse (Fig. 4). A slight depression in out-line of the cortical bone of the medial femoral con-dyle with normal subchondral bone opacity can beseen as an incidental radiological abnormality.The fibula ossifies from one or several centers andtransverse or oblique lucent lines may persist be-tween ossification centers, and should not be con-fused with a fracture.

Radiographic examination of the pelvic region of ahorse can be performed either with the horse anes-thetized and positioned in dorsal recumbency, or inthe standing position. Because the advent of nu-clear scintigraphy and diagnostic ultrasonographythe indications for radiographic examination havereduced. If pain inducing lameness has been local-ized to the CF joint, radiographic examination isindicated to determine the nature of the pathologyand, hence, prognosis. High-quality radiographscan only be obtained with the horse positionedin dorsal recumbency under general anesthesia.Evaluation of the SI joints can be difficult because ofthe superimposition of abdominal viscera. Identifi-cation of new bone formation on the caudal aspect ofthe joint, or irregular joint-space width are poorprognostic indicators. Nuclear scintigraphic exam-ination gives accurate information about bone turn-over, but anatomical detail is less well defined;therefore, radiography of a suspected acetabularfracture may be indicated at least 6 wk after theonset of lameness to determine whether or not asuspected fracture involves the CF joint, which mer-its an extremely guarded prognosis for return to fullathletic function in a mature horse.

Radiographs of the CF joint obtained in the stand-ing position may be satisfactory for confirmation ofluxation of the joint.

Diagnostic UltrasonographyDiagnostic ultrasonography of the stifle is readilyperformed by using a 7.5- or 10-MHz linear trans-ducer and permits evaluation of the collateral liga-ments of the FT joint, the patellar ligaments, thejoint capsules of the FT and FP joints, the bonesurfaces, the cranial mensical ligaments and partsof the meniscal cartilages.5–7 It is possible to viewlimited parts of the cruciate ligaments with a sectortransducer, but little diagnostic information can beacquired. Ultrasonography is most useful for iden-tification of soft-tissue injuries of the stifle, but maybe more sensitive than radiography in determiningthe extent of periarticular osteophyte formation inassociation with OA.

Diagnostic ultrasonography of the pelvic region canbe performed either transcutaneously, or per rectum.8

The choice of transducer frequency depends on thestructures to be imaged. Transcutaneous evalua-tion of the bony elements of the pelvis and the deepmusculature requires a 5- or 3.5-MHz transducer,depending on the size of the horse, whereas evalua-tion of the dorsal sacroiliac ligaments, the sublum-

Fig. 4. Flattening of the lateral trochlear ridge of the femur(arrows), an incidental finding in a 10 year old Grand Prixshowjumper that never had lameness referable to the femoropa-tellar joint.





bar musculature, the ventral aspect of the lumbarand sacral vertebrae and the aorta and iliac arteriesis better performed by using a 5.0- or 7.5-MHz trans-ducer. Evaluation of nerve roots per rectum maybe best achieved by using a 10-MHz transducer.

Diagnostic ultrasonography is useful in the eval-uation of fractures, assessment of muscles and theSI ligaments, determination of blood-vessel patency,assessment of the lumbar vertebrae and their artic-ulations, and evaluation of nerve roots.

Nuclear ScintigraphyNuclear scintigraphic examination of the stifleshould ideally include both lateral and caudal views.Careful positioning of the gamma camera and longacquisition times, preferably by using a motion cor-rection program, are essential for diagnostic qualitycaudal views. Acquisition of too few counts mayresult in lesions being missed. Scintigraphic exam-ination may be negative in association with primarysoft-tissue injuries, such as meniscal tears, cranialmeniscal ligament desmitis, and cruciate injury.With good-quality scintigraphic images, medial fem-oral condyle SBCs can generally be seen scinti-graphically. OC in mature horses is oftenscintigraphically negative. A retrospective study ofhorses with lameness improved by IA analgesia ofthe stifle and scintigraphic findings showed a ratherpoor correlation in a significant proportion of horses(Table 1).9 False focal regions of increased radio-pharmaceutical uptake (IRU) sometimes occur(Fig. 5).

Nuclear scintigraphic evaluation of the pelvic re-gion is useful for the identification of fractures,

stress reactions in bone, increased bone modelingassociated with OA and other bony lesions, evidenceof recurrent exertional rhabdomyolysis (RER) (insome, but not all cases), evaluation of blood flow inthe aorta, iliac and femoral arteries, and assessmentof the SI joints. Sensitivity of the technique is inpart dependent on the angle of the gamma camera tothe area of interest and the degree of overlying mus-cle mass. It is important to recognize that somelesions may be bilateral; therefore, recognition of thenormal scintigraphic appearance of the region inhorses of different ages and involved in differentdisciplines is important. Bear in mind those super-ficial bony structures such as the TC and TS willalways appear “hotter” than deeper structures.Unilateral muscle atrophy may also confoundinterpretation.

Complete evaluation of the pelvic region requiresdorsal views of the SI joints, oblique views of the ilialwings, caudodorsal and caudal views of the tuberaischii, and lateral views of the CF joints. Caremust be taken in interpretation of the appearance ofthe SI joints because there are age-related changesthat occur in normal horses (Fig. 6).10 Swayingmovement of the horse during image acquisition canresult in images that mimic abnormalities and theuse of a motion-correction program is invaluable.

Diagnostic ArthroscopyDiagnostic arthroscopy is an invaluable tool for in-vestigation of stifle pain in the absence of obviousradiological changes, and is the only method of de-finitive diagnosis of some stifle injuries; however,access is restricted and only limited amounts of the

Table 1. Clinical Features, Response to Local Analgesia, and Results of Radiographic, Ultrasonographic, Scintigraphic, and ArthroscopicExamination of 24 Horses with Stifle Pain January 1998 to August 1999a

Clinical FeaturesResponse to IA

Analgesia Radiology Ultrasonography Scintigraphy Arthroscopy

Joint effusion, 2 Positive, 14 OCLL, 4 Middle patellardesmitis, 3

Generalized IRU, 5 Mild cartilage damage,4

Abnormalflexion, 12

Equivocal, 5 OC, 2 Joint effusion, 3 IRU femoralcondyle, 3

Cranial meniscalligament tear, 2

Enlarged medialpatellarligament, 1

Negative, 2 OA, 2 No abnormalitydetected, 12

Cranial cruciateligament tear, 2

Favored limb atrest, 1

Not performed,3

Modeling in regionof intercondylareminence oftibia, 4

Not performed, 6 IRU proximal tibia,2

Meniscal tear, 1

Stifle rotatedoutwards, 2

Modeling ofpatella, 1

IRU cranioproximaltibia, 4

Abnormal cartilage, 1

Lameness No abnormalitydetected, 11

IRU patella, 2 Not performed, 14

Mild, 8Moderate, 14 Negative, 7Severe, 2

aFemotibial joint pain, 6; OCLL, 4; middle patellar ligament desmitis, 3; osteochondrosis, 2; osteoarthritis, 2; cranial meniscalligament desmitis, 2; cranial cruciate ligament desmitis, 2; meniscal tear, 1; abnormal cartilage, 1; focal lesion caudal femoralcondyle, 1.





joint can be assessed by using both cranial and cau-dal approaches.11–13 In some horses several low-grade lesions may be identified concurrently, none ofwhich appears compatible with the degree of lame-ness seen clinically. In other horses with obviouslesions of, e.g., the medial meniscus, other lesionsare present concurrently, so comprehensive evalua-tion of all of the joints is essential to obtain mostaccurate prognostic information.

Differential Diagnosis

A breakdown of diagnoses for 71 horses, 2 yr of ageor older, with stifle pain examined between January1998 and December 2001 is summarized in Table 2.Lameness associated with pain arising from thefemorotibial joints was most common.

The stifle

OsteochondrosisAlthough OC is a developmental abnormality of car-tilage and bone, in some horses clinical signs may

Fig. 5. Lateral scintigraphic view of the stifle. There is focalincreased radiopharmaceutical uptake in the cranioproximal as-pect of the tibia, but lameness was unrelated to the stifle.

Fig. 6. (A) Dorsal scintigraphic view of the pelvic region of anormal 3 year old Thoroughbred. Note the clearly demarcatedtubera sacrale. (B) Dorsal scintigraphic view of the pelvic regionof a 10-year-old Thoroughbred cross. Note that in this olderhorse the definition between uptake in the tubera sacrale and thesurrounding sacroiliac joint region is less distinct than in theyounger horse (A). However in both (A) and (B) there is left rightsymmetry.





not be manifest until maturity. Generally clinicalsigns in an adult are less obvious than in a horse lessthan 2 yr of age. Effusion of the FP joint is avariable feature. Horses with bilateral OC maypresent with poor hindlimb action rather than overthindlimb lameness. Lameness associated with amobile fragment may be episodic in nature and mayonly be apparent performing particular movements.Occasionally, a fragment that was previously immo-bile and clinically silent may become dislodged bytrauma causing lameness. There is a positive re-sponse to IA analgesia of the FP joint, althoughhorses with flattening of the lateral trochlear ridgeassociated with tightly adherent but highly abnor-mal articular cartilage may show only slight im-provement. Radiological abnormalities includealtered contour of the lateral and/or medial troch-lear ridge of the femur, and alterations in subchon-dral bone opacity, with or without one or moremineralized fragments. Concurrent evidence of OAwarrants a guarded prognosis. Treatment is by ar-throscopic removal of fragments and debridement ofloose cartilage.14 Prognosis in these horses is fa-vorable, but those with a cobblestone appearance tothe articular cartilage, which is well adhered to theparent bone, have a more guarded prognosis.

Subchondral Bone Cyst of the Medial FemoralCondyleSubchondral bone cysts of the medial femoral con-dyle are consistent in their pathological appearance,having a fibrous cyst lining. Well-defined radiolu-

cent lesions elsewhere do not always have a consis-tent structure and are therefore referred to asosseous cyst-like lesions (OCLLs). SBCs may occurunilaterally or bilaterally and usually cause acute-onset lameness of variable degree, both betweenhorses and within individual horses, from day to dayor during an exercise period.15 There appears to belittle correlation with the size or duration of the SBCand the degree of lameness, although very largeSBCs, especially those close to the medial epicondyleof the femur, are generally associated with severelameness and the horse may have difficulties in get-ting up from lying down. There is generally nopalpable effusion of the FT joint. The response toIA analgesia is very variable: in some horses lame-ness is dramatically improved, whereas in otherslittle difference is seen. Diagnosis is based on ra-diographic identification of a SBC and either local-ization of pain causing lameness to the MFT joint orexclusion of other potential sources of pain. Inhorses that do not respond to IA analgesia, nuclearscintigraphy is sometimes helpful. No treatment isuniformly successful. Treatment options includeintra-lesional injection of corticosteroids, arthro-scopic debridement, with or without installation of acancellous bone graft, rest, or work combined withnonsteroidal anti-inflammatory drugs.16–19 Choiceof treatment is dependent on the age of the horse, itsintended use, the size and shape of the cyst, andresponse to previous treatments. Pre-existing ra-diological evidence of OA warrants a more guardedprognosis. I favor arthroscopic debridement andinstallation of a bone graft in horses that do notrespond to conservative management, assumingthat the shape of the cyst neck will hold the graft inplace. A recent experimental study showed no ad-vantage of grafting,20 but in my clinical experienceresults have been more favorable than curettagealone.

Dimples

Flattening or a depression in the outline of the me-dial, or less commonly the lateral, femoral condylecan be seen in the contralateral limb of a horse witha SBC, and in a mature horse these are generallynot progressive. However, these lesions can beseen alone and, if there is alteration in the underly-ing subchondral bone opacity, there may be associ-ated lameness (Fig. 7). There are usually nolocalizing clinical signs. Lameness is usually im-proved by IA analgesia. Diagnosis is based on ra-diography. Arthroscopic exploration may or maynot reveal abnormalities of the overlying articularcartilage. Often there is a wrinkling or in-folding ofthe cartilage at the typical site of a SBC. Suchlesions may be associated with either sclerotic sub-chondral bone or less commonly sugary type bone.Debridement or forage has resulted in clinical im-provement, but a limited number of horses havesubsequently developed SBCs.

Table 2. Distribution of Lesions in 71 Horses, 2 yr of Age or Older,with Stifle Pain Examined Between January 1998 and December 2001

FT joint paina 20Tibial stress fracture 10Medial femoral condyle SBC 5OCLL proximal tibia 5Medial meniscal tear 4Cartilage defect FT joint 4OA 4Cranial cruciate desmitis 3Middle patellar desmitis 3Intermittent upward fixation of the patella 3OC 3Tear of cranial meniscal ligament 2Fracture of tibial crest 1Fracture of medial trochlea of femur 1Fracture of fibula 1Permanent upward fixation of patellab 1Fragment FT joint 1

aHorses designated as “FT pain” had pain localized to one ormore FT joints, in which no abnormality was identified radio-graphically, ultrasonographically, or arthroscopically (10 horses;minor cartilage abnormalities or minor fraying of a cranial me-niscal ligament were considered of questionable significance tothe presenting lameness). Fifteen horses had focal or diffuse IRUin the stifle region.

bAlso had luxation of the CF joint secondary to a comminutedilial shaft fracture.





Other OCLLsOCLLs occur in the lateral femoral condyle or theproximal tibia. In my experience, the most com-mon location is the proximomedial aspect of the tibia(Fig. 8). These are usually well-defined unilocularlesions, often surrounded by a sclerotic rim. Five of6 adult horses with OCLLs of the proximal tibia hadmedial lesions, that were considered to be secondaryto OA.21 In my experience, there may or may notbe radiographic evidence of OA when clinical signsare first recognized. Lameness is variable in de-gree and is generally, but not invariably, improvedby IA analgesia. Successful treatment by surgicaldebridement has been recorded,21 although in myexperience the prognosis in mature horses isguarded.

Less well-defined OCLL are sometimes seen in amore central location distal to the intercondylar em-inences of the tibia usually in association with acranial meniscal insertional injury or cranial cruci-ate ligament injury (Fig. 9).

Osteoarthritis and Other Cartilage andSubchondral Bone LesionsOsteoarthritis is characterized radiographically byperiarticular osteophyte formation. Osteophytesare usually first seen on the cranioproximal aspectof the tibia. There is some variation in shape of thetibial plateau between horses, so careful comparisonwith the contralateral limb is indicated. Horsesusually show some response to IA analgesia, but thedegree of improvement in lameness is rather vari-able. Diagnosis is based on radiography. Nuclearscintigraphy is often equivocal or negative. Somehorses respond satisfactorily to IA medication withhyaluronan and corticosteroids, although repeated

treatments are often required. Arthroscopic explo-ration is often rather unrewarding, because carti-lage changes are often worst on the tibial plateau,an area that is largely obscured by the meniscalcartilages. The prognosis depends on the degree ofOA and the athletic expectations for the horse.Many horses are suitable for pleasure riding, butcannot cope with more demanding pursuits.

In some horses with FT joint pain, but no detect-able radiological change, localized cartilage lesionsare identified in focal regions of either the medial orless commonly the lateral femoral condylea,22–23.In my experience, these lesions vary in appearance,size, and location, and may be traumatic in origin.Some horses have responded to debridement or IAmediation, whereas in others lameness has beenpersistent. Eleven horses had dimples, wrinkling,or in-folding of the articular cartilage at the typicalsite of a SBC opening in the medial femoral con-dyle.22 This cartilage was not firmly attached tothe subchondral bone. Four horses had more gen-eralized cartilage fissuring and irregularities.Treatment by surgical debridement had a good out-come in six of seven horses with focal lesions, but theprognosis for more widespread lesions was poor.

Intra-articular Pain, but No Identifiable CauseThere is currently a group of horses that eludesdefinitive diagnosis of the cause of lameness, despitelocalization of pain to the FT joints. These horseshave no identifiable radiological or ultrasonographicabnormality. In some, there is a diffuse increaseduptake of radiopharmaceutical in the stifle region.No lesions compatible with the degree of lamenessare identifiable arthroscopically; however, the limi-

Fig. 7. Caudocranial radiographic view of the stifle of a 7- year-old dressage horse, with left hindlimb lameness alleviated byintra-articular analgesia of the medial femorotibial joint. Notethe flattening of the medial femoral condyle and the region ofsubchondral bone sclerosis (arrows).

Fig. 8. Caudocranial radiographic view of the left stifle of aGrand Prix showjumper with moderate lameness. There is alarge well-circumscribed osseous cyst-like lesion (arrows) in theproximomedial aspect of the tibia. Note also the osteophyteformation on the medial aspect of the proximal tibia.





tations of arthroscopic examination must be borne inmind.

Desmitis of the Collateral Ligaments of theFT JointDesmitis of the medial or lateral collateral ligamentof the FT joint is usually the result of trauma.24

There is usually localized soft-tissue swelling, and

with acute injury pain on palpation. There may beassociated effusion of the FT joint. Stressed radio-graphs are helpful in severe injuries to assess thedegree of joint laxity. The extent of the lesion canbe determined ultrasonographically. There is usu-ally enlargement of the ligament, with disruption ofits normal architecture. The origin and insertionshould be inspected carefully for the presence of anyavulsion fragments. In more chronic injuries theremay be entheseous new bone at the origin or inser-tion of the ligament. Sometimes desmitis occurs inconjunction with other injuries,25 so the entire jointshould be carefully appraised radiographically andultrasonographically. Treatment is by conserva-tive management and prognosis depends on the se-verity of the original injury. Some horses make acomplete functional recovery, but with severe inju-ries the prognosis is guarded.

Cruciate Ligament InjuryTears of the cranial (CrCrL) and less commonly thecaudal (CaCrL) cruciate ligament usually occur inthe mid body, or close to the insertion.26–30 Com-plete rupture is very unusual. Diagnosis is depen-dent on arthroscopic identification of a lesion,although in chronic cranial cruciate injuries newbone cranial to the intercondylar eminence of thetibia may be seen. This entheseous new bone isbest identified in flexed lateromedial views. Theremay be effusion in the medial FT joint. Lamenessis variable in degree and is usually improved by IAanalgesia, although the response may be slow.Lesions of the CaCrL are often best seen from theMFT joint, and lesions of the CrCrL may be bestevaluated from the LFT joint, although it may benecessary to debride the synovial covering of thecruciate ligament to evaluate it properly. In somehorses with cruciate ligament injury the synovialseptum between the medial and lateral FT joints ispartially disrupted. The ligaments should be bothinspected and probed. Some horses have obviousdiscoloration and fibrillation of the ligament,whereas in others the extent of fiber disruption isonly determined by probing. The prognosis is de-pendent on the severity of the original injury.Twenty-one of 28 horses (78%) with Grade 1 lesionsmade a full functional recovery, but only 6 of 17horses (35%) with grade 2 lesions were able to re-sume full work and no horses (of 4) with a grade 3lesion became sound.31

Meniscal TearsMeniscal tears vary in their configuration, some be-ing sagittal plane splits through the axial aspect ofthe mensicus, whereas others are transverse splitsthat can involve up to two thirds of the menis-cus.32,33 Tears extending longitudinally from thecranial meniscal ligament into the meniscus withminimal separation are categorized as grade 1.Tears involving the cranial axial pole, the full extentof which can be evaluated are categorized as grade 2,

Fig. 9. (A) Lateral scintigraphic image of the right stifle of a 7year old Warmblood dressage horse with right hindlimb lamenessthat was partially improved by intra-articular analgesia of themedial and lateral femorotibial joints. There is intense focalincreased radiopharmaceutical uptake in the proximal tibia. (B)Caudocranial radiographic view of the right stifle. There is alarge rather poorly defined osseous cyst-like lesion (arrows) distalto the intercondylar eminences of the tibia.





and severe lesions, the full extent of which cannot bedetermined are grade 3.33 Medial meniscal lesionspredominate. Lameness is usually moderate to se-vere. There is generally effusion of the affected FTjoint. Lameness is improved by IA analgesia Some,but by no means all, mensical tears can be identifiedultrasonographically (Fig. 10). Radiographic evi-dence of narrowing of the FT joint space, dystrophicmineralization of the mensicus or OA are all poorprognostic indicators. Definitive diagnosis re-quires arthroscopic examination; it may or may notbe possible to evaluate the full extent of the tear,depending on its location and configuration. Thisalso influences the ability to debride lesions (Fig.

10). Prognosis depends on the severity of injury.Fifteen of 28 horses (54%) with grade 1 lesions re-sumed full work. Seven of 14 horses (50%) withgrade 2 lesions returned to athletic function afterdebridement. However, severe grade 3 lesionshave a guarded prognosis, with only 2 of 8 horses(25%) making a functional recovery.33

Meniscal Ligament DamageTearing of one of the cranial meniscal ligaments, orless commonly recognized, a caudal mensical liga-ment results in instability of the mensicus and lame-ness. Lesions may occur in isolation or inconjunction with meniscal tears. Minor fibrillation

Fig. 10. (A) Longitudinal ultrasonographic image of the medial meniscus of an 8 year old event horse gelding with distension of themedial femorotibial joint capsule and moderate lameness, partially improved by intra-articular analgesia. Proximal is to the left.There is a anechogenic split through the medial meniscus. (B) Arthroscopic image of the medial femorotibial joint showing the tornmensicus. (C) Post mortem examination showing the bucket handle tear through the medial meniscus.





is often seen arthroscopically, but is often not aprimary cause of lameness. There is invariably ef-fusion and moderate to severe lameness. Lame-ness is improved by IA analgesia. In some horseslarge rather poorly defined radiolucent zones areseen distal to the intercondylar eminence of the tibiaassociated with chronic cranial meniscal ligamenttrauma. Such changes have also been seen in as-sociation with chronic cranial cruciate ligament in-jury. Minor tears have a favorable prognosis, buttears resulting in meniscal instability have a poorprognosis.

Intermittent Upward Fixation or Delayed Releaseof the PatellaA horse that has locked the patella is easy to recog-nize, but intermittent upward fixation or delayedrelease can be much more difficult to identify, be-cause of its episodic nature. Abnormal jerky move-ment of the patella may be seen as the horse movesover in the stable, or when it decelerates from canterto trot, or from trot to walk, or when walking downa steep incline. Repeated delayed release of thepatella can cause stifle soreness, and unwillingnessto work, although overt lameness is unusual.Warmblood horses with straight hindlimb conforma-tion appear to be predisposed. Treatment aims toincrease fitness of particularly the quadriceps mus-cles, and to improve bodily condition when neces-sary. A change in foot angle may be beneficial.The use of internal blisters is sometimes helpful.34

Desmotomy of the medial patellar ligament shouldbe considered a last resort.

Fragmentation of the Apex of the PatellaFragmentation of the apex of the patella is recognizedas a potential sequel of medial patellar ligament des-motomy,35–37 causing mild to moderate lameness,which is often associated with effusion of the FP joint.Lameness is improved by IA analgesia of the FP joint.Diagnosis is based on radiographic evidence of model-ing or fragmentation of the apex of the patella, bestseen on a flexed lateromedial view. Radiographs mayunderestimate the degree of bony and cartilaginousabnormality. Treatment is by arthroscopic debride-ment and the prognosis is favorable.

Desmitis of the Patellar LigamentsDesmitis of the patellar ligaments has probablybeen underdiagnosed. Middle patellar desmitis oc-curs most often, either alone or together with desmi-tis of the lateral patellar ligament.38 Seven of ninehorses were show jumpers. With acute injury theremay be mild periligamentous soft-tissue swellingand pain on palpation of the ligament in the flexedposition, but in more chronic injuries there may beno localizing clinical signs. Lameness, which var-ies from mild to severe, is partially improved by IAanalgesia of the FP joint in a small proportion ofhorses. Lesions of the middle patellar ligamentmay be associated with abnormal movement of the

patella, or previous medial patellar ligament desmo-tomy. There are usually no radiological abnormal-ities. Lesions occur at the origin, mid-body, orinsertion and are identified ultrasonographically(Fig. 11). There is usual focal loss of echogenicityand poor fiber pattern. Insertional lesions of themiddle patellar ligament may be associated withincreased radiopharmaceutical uptake (IRU) in thecranioproximal aspect of the tibia. To date, horseshave been treated conservatively and the prognosisfor return to full athletic function without recurrentinjury has been guarded.

FracturesPatella. Fractures of the patella are usually theresult of direct trauma, either a kick, or hitting afixed fence, resulting in sudden onset severe lame-ness.39,40 Lameness often improves quite quickly,but mild to moderate lameness persists. In theacute stage, before development of periarticular softtissue swelling, it may be possible to palpate a dis-placed fracture fragment. Pain may be elicited byfirm palpation of the medial aspect of the patella.The most common fracture configurations are small,displaced pieces from the base of the patella, readilyseen in a lateromedial radiographic view, or frac-tures of the medial pole of the patella. Displacedfragments from the medial pole of the patella may beseen in lateromedial projections, but their origincannot be determined. Skyline projections of theflexed stifle are required to determine the origin ofthe fragment and to identify nondisplaced fractures.Fractures of the base of the patella heal satisfacto-rily when treated conservatively and have an excel-lent prognosis. Fractures of the medial pole of thepatella must be treated by surgical removal, becauseeven if nondisplaced initially, these fractures be-come displaced and secondary OA is an inevitablesequel.39 Most fractures can be treated by arthro-scopic removal,41 although large fragments mayneed to be removed via an arthrotomy incision cen-tered over the fragment. The prognosis for returnto full athletic function is excellent.

Femoral Trochleas. The femoral trochleas arealso vulnerable to external trauma, especially ahorse hitting a fixed fence.40,42 Fracture of a troch-lear ridge of the femur may occur concurrent with afracture of the medial pole of the patella, so even ifan obvious lesion is seen in a lateromedial radio-graph, a skyline projection should also be obtained.There is usually acute-onset severe lameness asso-ciated with distension of the FP joint capsule. Di-agnosis is made radiographically. Treatment is byarthroscopic removal of the fracture fragments andthe prognosis is good.

Femoral Condyles. Small chip fractures arisingfrom the femoral condyles can also result from ahorse hitting a fixed fence, in turn resulting inacute-onset severe lameness. Radiographic exami-nation often reveals the fracture fragment(s), but it





may not be possible to determine its origin. Mosthorses respond favorably to arthroscopic removal ofthe fragments.

Tibial Crest. Fracture of the tibial crest is usu-ally the result of trauma, such as hitting a fixedfence.40,43–46 Most fractures are orientated ob-liquely, from craniodistal to caudoproximal, but arenonarticular. Fractures may be nondisplaced, ordisplaced cranioproximally. There is usuallyacute-onset severe lameness, with mild, localizedsoft-tissue swelling and focal pain. Diagnosis ismade radiographically. Both conservativea,46 andsurgical management40,43–45 have yielded good re-sults, with return to full athletic function. Surgicalmanagement by internal fixation of large fragments,or removal of smaller fragments, results in morerapid recovery, and may be preferable for large dis-placed fragments.

Intercondylar Eminence of the Tibia. Frac-ture of the intercondylar eminence of the tibia is anunusual injury.48–50 It is generally not associated

with cruciate ligament injury, because the cranialcruciate ligament inserts cranial to this eminence.Lameness is moderate to severe and is usually as-sociated with effusion of the MFT joint. Lamenessis improved by IA analgesia and diagnosis is con-firmed radiographically. Treatment is by arthro-scopic removal of the fracture fragment or, if large,repair by internal fixation. Prognosis is favorable,provided that there are no other concurrent injuries.

Stress Fracture of the Proximocaudal Tibia.Stress fractures of the tibia occur unilaterally or bilat-erally almost exclusively in young Thoroughbred flatracehorses, resulting in acute onset severe lameness,that rapidly resolves with rest. Bilateral stress frac-tures may be present, despite unilateral lameness.There are usually no localizing clinical signs. Thereis usually no response to IA analgesia, although, sur-prisingly, there are anecdotal reports of occasional pos-itive resultsb. Diagnosis is usually reliant on nuclearscintigraphy. The caudoproximal aspect of the tibiais a predilection site in Thoroughbreds in Europe.

Fig. 11. (A) Transverse and (B) longitudinal (proximal is to the left) ultrasonographic images of the middle patellar ligament of a 6year old warmblood showjumper, with left hindlimb lameness and mild intermittent upward fixation of the patella. Hypoechogeniclesions within the middle patellar ligament are consistent with desmitis.





Radiographs may reveal pre-existing periosteal or en-dosteal callus, or occasionally a fracture line. Mosthorses respond satisfactorily to conservative manage-ment of rest for 3–5 mo.

Fibula. Fractures of the fibula are comparativelyunusual, but cause acute-onset moderate to severelameness. There are usually no localizing clinicalsigns and the response to IA analgesia of the FP orFT joints is generally negative. Diagnosis dependson nuclear scintigraphic and radiographic examina-tions (Fig. 12). Most fractures occur in the mostproximal aspect of the fibula and are associated withintense, focal IRU. Radiographically care must betaken not to confuse a normal lucent line betweenseparate ossification centers as a fracture. Conser-vative treatment is usually successful, but lamenessis slow to resolve and radiographic healing may take4–6 mo. Five of five horses made a complete func-tional recovery.a

Injury to the Origin of the Gastrocnemius Mus-cle. Injury to the origin of the gastrocnemius mus-cle on the distal caudal aspect of the femur is rare51

and has been associated with a gait abnormalitycharacterized by outward rotation of the calcaneusand inward rotation of the toe of the lame limb.Diagnosis has been based on scintigraphic identifi-cation of intense IRU in the distal caudal femur.In some horses, periosteal new bone has also beenidentified radiographically. Three of four horsesreturned to full athletic function after prolongedrest.51

The Pelvis

In 29 horses, 2 yr of age or older, with hindlimblameness associated with pelvic pain, examined be-tween January 1999 and December 2001, SI jointpain and ilial stress fractures were the most com-mon diagnosis (Table 3).

FracturesThe incidence of stress or fatigue fractures of thepelvic region in the mature horse is very low, exceptin horses which race over fences, which have a sig-nificant incidence of ilial stress fractures. The ma-jority of fractures are the result of external trauma,e.g., a fall.

Stress Fracture of the Ilial WingStress fractures of the ilial wing in mature athletes areseen almost exclusively in horses that race over fences.Lameness is usually acute in onset and severe, al-though may resolve rapidly with rest. There is usu-ally rapid atrophy of the ipsilateral glutealmusculature. The tuber sacrale of the affected sidemay appear lower. It is unusual to be able to elicitpain by palpation.

Diagnosis may be confirmed by nuclear scintigra-phy. Oblique views of the ilial wings are required.If the fracture is complete and involves the dorsalsurface of the ilial wing the fracture may be demon-strable ultrasonographically.

Treatment by box rest and controlled exercise for3 mo usually results in complete recovery, unless thefracture involved the SI joint. The training pro-

Fig. 12. (A) Lateral scintigraphic image of the left stifle of a 12 year old riding horse with moderate lameness unaffected by any localanalgesic technique. There is focal intense increased radiopharmaceutical uptake over the proximocaudal aspect of the tibia andfibula. (B) Caudocranial radiographic view of the stifle. There is a fracture of the proximal aspect of the fibula (arrow).





gram should be reviewed to identify any factors pre-disposing to injury.

Fracture of the TIFracture of the TI sometimes occur in event horses,which fall when jumping up onto a bank. They mayalso occur in any horses as a result of a fall on theflat. However, they have also been recognized inhorses from other disciplines, with no known historyof trauma. There is usually acute-onset relativelysevere lameness. Mild, localized swelling is easilyoverlooked, unless the TI is suspected as a siteof injury. The ipsilateral semimembranosus andsemitendinosus muscles are usually sore to palpa-tion. Atrophy of the muscles around the tail headoften develops within 7–10 d. Usually there is nopalpable crepitus. In more chronic cases pain onpalpation may not be evident, although the TI mayappear asymmetrical, and the lameness may be onlymild or moderate.

Diagnosis of a fracture of the TI can be confirmedwith nuclear scintigraphy (Fig. 13). Dorsal obliqueand caudal views are useful. There is usually bothan increased uptake of the radiopharmaceutical andan abnormal pattern of uptake.a,52 In some cases itmay be possible to determine whether the fracture iscomplete and if it has become significantly dis-placed. Discontinuity of the bone outline may alsobe confirmed with diagnostic ultrasonography.Radiographic examination can be performed, but ismost easily done with the horse under generalanesthesia.

Treatment by restriction to box rest usually re-sults in a satisfactory outcome, although very occa-sionally sequestration of the fracture fragmentoccurs, necessitating surgical removal.

Occasionally a horse presents without obviouslameness, but with reduced performance and a ten-dency to jump drifting consistently to one side, dueto pushing off unevenly with each hindlimb. Thishas been in association with reduced muscle devel-opment over one of the TI, and increased uptake oftechnetium 99m MDP in the TI. The outline of theTI appears irregular ultrasonographically.

Fracture of the Greater Trochanter of the FemurFracture of the greater trochanter of the femur is anunusual injury, causing severe lameness. There isa tendency for the fracture fragment to be displacedcranially, due to the pull of the attachments of thedeep and middle gluteal muscles.

There are usually no localizing clinical signs, un-less the horse is very poorly muscled and the greatertrochanter is readily palpable. The diagnosis isbased on nuclear scintigraphic examination, with orwithout diagnostic ultrasonography. The progno-sis for return to athletic function with conservativetreatment is guarded.

Fracture of the SacrumFractures of the sacrum may be complete or incom-plete and result in bilateral hindlimb lameness.If the fracture is complete the contour of the hind-quarters when viewed from the side changes, so thatthere is abnormal angulation of the rump. Theremay be associated neurological signs, including flac-cid paralysis of the tail, reduced sensation aroundthe tail head, urine dribbling in a mare, and loss ofanal tone. The onset of neurological signs may bedelayed for several weeks after the primary fracture.The fracture may be palpable per rectum. The frac-ture may be confirmed both radiographically andwith diagnostic ultrasonography per rectum. The

Fig. 13. Dorsal oblique scintigraphic image of the tubera ischiiof a Thoroughbred cross Irish draught horse with left hindlimblameness, which was unaltered by any local analgesic tech-nique. Lameness had developed following a fall whilst beingshod. There is an abnormal shape of the left tuber ischii, withfocal increased radiopharmaceutical uptake, compatible with adisplaced fracture.

Table 3. Distribution of Lesions in 29 Horses with Hindlimb LamenessAssociated with the Pelvic Region, January 1999 to December 2001

SI joint diseasea 10Ilial stress fracture 7Fracture or enthesopathy of the third trochanter

of the femur 3Fracture of a TI 4Dorsal SI desmitis 2CF joint OA 2Luxation of the CF joint, secondary to a

comminuted ilial shaft fracture 1

aSI joint disease was also diagnosed in an additional 27 horsesthat presented with poor performance, back stiffness and pain,and poor hindlimb engagement.





prognosis for return to athletic function is veryguarded.

Recurrent Equine Rhabdomyolysis “Tying Up”The spectrum of clinical signs associated with recur-rent equine rhabdomyolysisi (RER) ranges enor-mously. A horse may present with mild bilateralhindlimb stiffness, or loss of freedom of action,which may deteriorate slightly with work, withoutthe horse becoming unduly distressed, but some-times having a prolonged recovery period after work.Such horses may have no palpable firmness of thehindquarter musculature, nor pain induced by firmpalpation and a normal pattern of sweating. Thehorse may be able to compete, but perform belowexpectations. These clinical signs are not unique toequine rhabdomyolysis and may be seen in horseswith severe thoracolumbar discomfort associatedwith impinging spinous processes or OA, or painassociated with the SI joints.

Alternatively, a horse may start to jump poorly,e.g., during the cross-country phase of a 3-d eventand pull up with a unilateral hindlimb lameness,with no localizing clinical signs, and which resolveswithin 24 h. In contrast, a different horse mayhave recurrent acute onset, severe episodes, oftenprovoked by competition, e.g., during the speed andendurance phase of a 3-d event, which may be so badas to result in recumbency.

The incidence of RER depends to some extent onthe discipline in which the horse is involved, occur-ring most commonly in racehorses, endurancehorses, and event horses. It is relatively unusualin show jumpers and dressage horses, but occasion-ally occurs in competitive Thoroughbred-type po-nies. In all these horses the results of musclebiopsies usually indicate that there is no evidence ofabnormal glycogen metabolism as in polysaccharidestorage myopathy, which occurs more commonly indraft and draft cross-breeds and Quarterhorses.There is evidence in the Thoroughbred that RERmay be an heritable condition, as an autosomal re-cessive trait with variable expression.53 A familialtrait has also been observed in some part Thorough-bred event horses.a However, many cases in both3-d event horses and endurance horses do not be-come apparent until the horse is middle aged, oreven older. The condition is manifest more fre-quently in mares than in stallions or geldings.

Diagnosis is based on measurement of raised se-rum muscle enzymes (CK and AST) after exercise.The degree of muscle-enzyme elevation frequentlydoes not correlate with the severity of clinical signs.Interpretation is not always straightforward be-cause asymptomatic endurance horses frequentlyhave extremely high levels of CK and AST duringand after a ride. Horses with low-grade RER,which occurs daily, will often have constantly raisedlevels of CK and AST, even if rested.

Nuclear scintigraphy can be useful in horses withlow-grade hindlimb stiffness and poor performance,

to validate a suspected diagnosis of RER,54 to eval-uate blood flow to the hindlimb musculature,55 andto exclude any other concurrent musculoskeletal le-sions. In association with RER in some, but not allcases, abnormal uptake of technetium 99m-MDP isseen in the affected muscles in the bone phase of thescan, appearing usually as diagonal streaking, butin more severe longstanding cases there may belarge areas of intense uptake of the radiopharma-ceutical in the affected muscles. Lesions are notrestricted to the gluteal muscle mass, but may alsoaffect quadriceps, biceps femoris, semitendinosus,semimembranosus, and longissimus dorsi muscles.Lesions may be symmetrical or asymmetrical.However, normal uptake of the radiopharmaceuticaldoes not exclude RER.

Muscle biopsy is used to determine whether thereis any evidence of polysaccharide storage myopathy.Feeding a high-fat and low-carbohydrate concentra-tion diet in these horses may reduce the frequencyand or severity of attacks after a period of 3–6 mo.56

Measurement of fractional excretion of electro-lytes (sodium, potassium, calcium phosphorus, andchloride) can be useful to identify those individualsthat seem unable either to absorb, or to utilize nor-mally, specific dietary electrolytes, and which mightbenefit from dietary supplementation.57,58 For ac-curate interpretation of results, it is important thatthe horse is consuming its normal diet and has re-covered from any recent acute attack of equine rhab-domyolysis when blood and urine samples arecollected. A mid-stream urine sample should becollected, preferably freely voided rather than acatheterized sample. Results are only valid if se-rum creatinine is within the normal range and thefractional excretion of creatinine is normal. Resultsshould be compared to the normal ranges for a horseon a similar diet, because results for horses eating anoat- and hay-based diet are different for those on acube-based diet, or a diet high in alfalfa. Fractionalexcretion ratios for potassium will tend to be high ifthe horse is allowed access to pasture. Low values forfractional excretion ratios for sodium or calcium indi-cate that the diet should be supplemented with sodiumchloride, or either calcium carbonate or calcium glu-conate, respectively. Appropriate dietary supple-mentation may help to prevent further attacks.

Management practices may also help to preventattacks in some horses. These include daily workwith a long slow warm-up period, turn out as muchas possible, and avoidance of undue stress, espe-cially in highly strung, nervous individuals. How-ever, some cases, especially those resulting in dailylow-grade clinical signs that are not stress provoked,prove intractable to successful management.

Muscle InjuryMuscle soreness is frequently unassociated with anyrecognizable histopathological changes within themuscle and is often secondary to some other cause oflameness, due to the altered way in which the horse





is moving. Muscle soreness can often be induced byoveruse of an undertrained muscle, and can result inlocalized soreness and stiffness for several days.Focal intense muscle spasm and pain can cause sud-den-onset reduction in performance and, if primary,is usually relieved by manipulation to relieve themuscle spasm, producing rapid amelioration of clin-ical signs.

Focal muscle soreness associated with localizedswelling may be due to intramuscular haemorrhage,muscle fiber tearing, or rhabdomyolysis. Diagnosisof the cause may be determined by measurement ofserum muscle enzyme concentrations and by ultra-sonographic evaluation. Haemorrhage will resultin an area of diffuse increase in echogenicity withinthe muscle. This should be differentiated from hy-perechogenic regions that are the result of chronicmuscle fibrosis. Serum muscle enzyme concentra-tions are usually not elevated in those cases ofhaemorrhage, muscle fiber tearing, or fibrosis.

Damage to deep muscles of the hindquarters isdifficult to identify because there are frequently nolocalizing clinical signs to alert the clinician to thepossible site of damage. Thermographic evaluationcan be useful to help to identify superficial muscleinjury.

Some horses with reduced performance have painon palpation of the psoas muscles per rectum. Thismay be primary or secondary to lumbosacral, or SIpathology and is an indication for nuclear scinti-graphic evaluation of the pelvic region and ultra-sonographic examination of the lumbosacralvertebrae.

Fibrotic MyopathyFibrotic or ossifying myopathy usually involves thesemitendinosus and semimembranosus muscles, re-sulting in a pathognomonic gait at the walk. Thecranial phase of the stride is abruptly halted and thefoot is slapped to the ground. Clinical signs areusually sudden in onset. Careful clinical examina-tion usually reveals a region of palpably firm mus-cle. Ultrasonography is used to determine theextent of fibrosis or mineralization. Treatment bytenectomy of the tendon of origin of semitendinosushas been very successful in my experience.

Less commonly recognized are more minor muscletears, associated with localized muscle soreness, de-tectable by careful palpation. There are no charac-teristic gait abnormalities. In some, but not allhorses, structural abnormalities of the muscle maybe identified ultrasonographically.a

SI Joint InjuryThe diagnosis of SI joint disease has tended histor-ically to be a “dustbin diagnosis,” frequently madeby exclusion, when the clinical signs could not beexplained by any other condition. The high inci-dence of pathological degenerative lesions found inthe SI joints of Thoroughbred racehorses59 and inmixed-breed horses60 indicates that degenerative

disease of the SI joint is likely to be a significantclinical problem, but definitive diagnosis remainsdifficult.

Pathological changes of the SI joint include lip-ping, cortical buttressing, and osteophyte formation,together with enlargement of the joint surfaces.These are thought to be a response to chronic insta-bility of the joints, although no evidence of ligamen-tous laxity has been identified.60,62 Erosion of thearticular cartilage may also occur, but joint anky-losis has not been documented. A positive associa-tion has been recognized between the severity of theimpingement of thoracolumbar dorsal spinous pro-cesses and lumbar transverse processes, and theseverity of SI lesions and also between the severityof articular process degeneration and the degree ofSI pathology.

A separate entity of entheseophyte formation atthe site of attachment of the SI ligaments has beendescribed unassociated with pathology of the SIjoints.62 Their clinical significance has not beenwell defined, but I have recognized this condition inseveral dressage horses with severely restrictedhindlimb impulsion and back stiffness.

Subluxation of the SI joint is comparatively veryrare62,63 and is the result of acute, traumatic disrup-tion of the dorsal SI ligament and the SI joint cap-sule. It should be differentiated from an acute ilialwing fracture, resulting in depression of the ipsilat-eral tuber sacrale.

The prominence of the TS varies between horsesand in part reflects the conformation of the back andhindlimbs. However, poor development of the ep-axial muscles in the lumbar region, due to the horsenot using its back and hindlimbs properly, maymake the TS appear more prominent. Poor muscledevelopment may either be a reflection of pain, or ofthe horse’s previous training: if the horse hasnever been asked to engage the hindlimbs properlyand work through its back, these muscles will not bewell developed.

Many apparently clinically normal horses havesome degree of asymmetry of the height and orshape of each tuber sacrale. Careful clinical ap-praisal of a small proportion of these horses mayreveal subtle hindlimb gait abnormalities, and milddiscomfort induced by either pressure applied overthe TS, or picking up one hind limb and swaying thehorse on the other. These findings are more likelyto be detected in horses that are not fully fit, and areoften ameliorated when the horse is fitter and hasgreater muscle support. They may reflect mild in-stability of the SI joints, but are not necessarilysynonymous with degenerative change.

Osteoarthritis of the SI joints may be present de-spite symmetry of the TS. It is usually a bilateralcondition and is rarely associated with unilateralhindlimb lameness. It often manifests as reducedperformance, failure to properly engage the hind-limbs, and back stiffness. Signs are often markedlyaccentuated when the horse is ridden. In mild





cases, the loss of hindlimb power and lack of supple-ness through the horse’s back may be much easierfor the rider to feel than for an observer to appreci-ate. Gait irregularities may be most apparent asthe horse changes direction through a tight circle.Specific movements such as half pass, or sequenceflying changes may be difficult. The horse may be-come progressively more unwilling to work undersaddle.

A comprehensive clinical evaluation is essential topreclude other conditions that may present simi-larly, such as bilateral distal hock joint pain. Itmay be necessary to preclude the hindlimbs as apotential source of pain by performing perineuralanalgesia of the tibial and fibular nerves and IAanalgesia of the FT and FP joints of one hindlimb, tosee if lameness becomes apparent in the contralat-eral limb.

Nuclear scintigraphic examination may facilitatediagnosis both by helping to preclude the presence ofother significant causes of poor hindlimb action andby giving a positive indication of abnormalities ofthe SI joints.10,64 Profile analysis and quantitativeevaluation by using regions of interest are requiredfor accurate diagnosis.10 The results should ideallybe compared with horses of both similar age andwork history, because there appears to be significantvariability between clinically normal horses. Thisappears to be both an age- and discipline-relatedchange. In a normal horse, uptake of the radio-pharmaceutical is bilaterally symmetrical. Exces-sive motion during image acquisition can result inimages that are not of diagnostic quality and maymimic abnormalities. Therefore, images ideallyshould be acquired dynamically and a motion-cor-rection program should be used.10 Abnormalitiesare recognized as both abnormal patterns of uptakeof the radiopharmaceutical and abnormal ratios ofuptake between each SI joint region and a standardreference site (Fig. 14). Care must be taken to dif-ferentiate between uptake in the TS and uptakeassociated with the region of the SI joints.

Radiographic examination requires general an-aesthesia and can be frustrating because superim-position of abdominal viscera can precludeevaluation of the SI joints. However, detection ofjoint-space irregularities or spur formation on thecaudal aspect of the joints are poor prognosticindicators.

Ultrasonographic examination should be per-formed both transcutaneously to evaluate the dorsalSI ligaments8,65 and per rectum,8 to eliminate pa-thology of the lumbosacral vertebrae.

Management is essentially palliative and progno-sis is generally inversely correlated with the sever-ity of clinical signs. Local infiltration of asclerosing agent, P2G, or a combination of cortico-steroids (methyl prednisolone acetate, 200 mg) andSarapin appears to provide relief in some horses.Some horses benefit from treatment with nonsteroi-dal anti-inflammatory drugs, which provide partial

pain relief enabling the horse to work better anddevelop increased muscle strength. Daily work onthe lunge by using side reins or a chambon, togetherwith exercise in a cage horse walker in which thehorse is free and not tied, and no ridden exercise forseveral weeks may be of significant benefit. Acu-puncture therapy helps some horses. The responseto shock-wave treatment is currently being as-sessed. Affected horses should be maintained inwork at all times, in order to maintain muscularfitness.

SI joint disease may occur in association withother conditions; therefore, careful appraisal of thewhole horse is essential if a successful managementstrategy is to be achieved. Nuclear scintigraphicevaluation should include the thoracolumbar region.Concurrent impingement of dorsal spinous pro-cesses (DSPs) in the mid or caudal thoracic or cra-nial lumbar regions may occur, with or withoutassociated pain. Infiltration of local anesthetic so-lution between, or around, the impinging DSPs maybe necessary to determine their contribution to theclinical problem. Careful evaluation of the syno-vial articulations, especially close to the thoracolum-bar junction, is also important. Occasionally SIdisease has been seen together with OA of the cox-ofemoral joints. This warrants a very guardedprognosis.

Desmitis of the Dorsal SI LigamentDesmitis of the dorsal SI ligament has been recog-nized in horses that have presented with back painor unilateral hindlimb lameness, with or withoutfocal pain on palpation.8,65 In my experience, in anacute injury there is usually localized heat andswelling, with a variable degree of lameness. Usu-ally lesions have been restricted to one side and havebeen characterized ultrasonographically by enlarge-ment of the ligament and disruption of normal ar-chitecture, with hypoechogenic regions seen intransverse images and loss of parallel alignment ofechoes in longitudinal images. Rarely, there maybe entheseophyte formation on the tuber sacrale.Such lesions have been seen either alone or in con-junction with other causes of back pain.

New Bone on the Caudal Aspect of the Wing ofthe SacrumA small number of mature competition horses usedfor dressage or show jumping have presented withinsidious onset loss of hindlimb action, progressingto unwillingness to maintain a proper trot. Thesehorses have appeared considerably worse when rid-den compared to evaluation in hand or on the lunge.The horses have shown abnormal sensitivity to pal-pation in the general areas of the SI joints. How-ever, careful analysis of nuclear scintigraphicimages has shown relatively normal uptake of theradiopharmaceutical in the region of the jointsthemselves, but increased uptake abaxial to thejoints. The horses have responded very poorly to





treatment with nonsteroidal anti-inflammatory orother analgesic drugs. Postmortem examinationhas revealed spurs of new bone on the wings of thesacrum just caudal to the auricular surface, but notinvolving the SI joint itself. This has been seen inassociation with fusion of the transverse processes ofcaudal lumbar vertebrae and osseous proliferationinvolving intervertebral foramina or synovialarticulations.a,62

Aorto-Iliaco-Femoral Thrombosis

Aorto-iliaco-femoral thrombosis is a relatively un-common cause of exercise induced hindlimb lame-ness of variable severity.66 Clinical signs may besudden and severe in onset, or subtle initially andslowly progressive. Horses of all ages may be af-fected. The incidence is higher in male horses thanmares. The pathogenesis is unknown.

Fig. 14. (A,B,C) Dorsal scintigraphic images of the pelvic region of 3 warmblood dressage horses, all of which had poor performance,and variable degrees of restricted hindlimb impulsion and hindlimb gait irregularities when ridden. The gait was markedly improvedby infiltration of local anesthetic solution around the sacroiliac joint region in all horses. Note the variation in radiopharmaceuticaluptake in the 3 horses and compare with Fig. 6B.





Clinical signs vary depending on the site(s) ofthrombus formation, its size, and the degree of ves-sel occlusion. Lesions occur most commonly at theterminal aorta, but may also involve both the inter-nal and external iliac arteries and the femoral ar-teries, either unilaterally or bilaterally. Lesionsrestricted to the femoral artery have not been docu-mented. In mild cases, the horse may present withpoor performance, early fatigue, or slight loss ofhindlimb action during a work period. If the le-sion(s) is predominantly unilateral the horse mayshow episodic hindlimb lameness, induced by work.In more advanced cases, there may be progressiveshortening of hindlimb stride with exercise, followedby the development of distress and sweating, exceptover the hindlimbs. If the horse is allowed to stop,it may repeatedly flex its hindlimbs and stamp thefeet to the ground. The affected limbs feel cool anddelayed filling of the saphenous veins may be seen,with reduced pulse amplitudes in the dorsal meta-tarsal artery. Clinical signs usually resolve if thehorse is allowed to stand still for a few minutes.

In advanced cases, it is usually possible to palpatea thrombus per rectum in the terminal aorta, whichfeels abnormally firm. Pulses in the iliac arteriesmay be reduced or absent. In less advanced cases,diagnostic ultrasonography is required to identifythe lesion. Ultrasonography is also useful to deter-mine the extent of the lesions.67 Examination ofpart of the femoral artery can be performed trans-cutaneously on the medial aspect of the crus.68

Doppler ultrasonography of this part of the femoralartery can help to determine if a more proximallesion is present.c

First-pass radionuclide angiography can be usedto determine blood flow in the aorta and iliac arter-ies,55,69 and also the femoral arteries.a However,the sensitivity of the technique for detection of sub-tle lesions has yet to be determined.

The aims of treatment are to try to prevent fur-ther thrombus formation and to develop a collateralblood supply for adequate perfusion. There are noavailable drugs that will alter a pre-formed throm-bus. Treatment rationale has been based on painrelief, and the use of anti-inflammatory drugs, plate-let inhibitors, anthelmintics, fibrinolytic agents, andanticoagulant drugs. Those most commonly usedinclude phenylbutazone (2.2. mg/kg BID for 2 mo),aspirin (5 mg/kg SID for several months), and isox-suprine (1 mg/kg BID for 3 mo). Successful treat-ment is presumably based on the development of aneffective collateral blood supply.

I have successfully managed some mild cases withlong-term aspirin therapy, but more severe cases areusually refractory to treatment. Only 2 of 29horses returned to their former athletic function,with resolution of clinical signs, following medicaltreatment.66 Surgical removal is feasible,70 al-though the rate of recurrence is quite high.

Coxofemoral Joint

The CF joint is relatively rarely a source of paincausing lameness in the horse.

Osteoarthritis. Osteoarthritis of the CF joint isan unusual cause of hindlimb lameness in the horse,usually occurring unilaterally, but occasionally bi-laterally. It may occur secondary to dysplasia, rup-ture of the teres ligament or trauma.

Lameness varies from moderate to severe. Thehorse will both resent flexion of the limb and beunwilling to stand on the limb for long periods withthe contralateral limb picked up. The degree ofgluteal muscle disuse atrophy may be more thanthat associated with pain in the more distal part ofthe limb. Lameness may be characterized by a ten-dency for the horse to move on three tracks. IAanalgesia usually results in improvement in lame-ness, but it is rarely alleviated fully.

Nuclear scintigraphic evaluation may be helpfulin highlighting the CF joint as abnormal, especiallyif the results of IA analgesia are equivocal. How-ever, it is important to be aware that loss of muscleover the hindquarter of the lame limb may confoundinterpretation and it is, therefore, important to eval-uate ratios of uptake of the radiopharmaceutical inthe region of the CF joint and another standardizedlocation and compare this with values for normalhorses. Be aware that the uptake associated withthe CF joint is much less than that of the cranial andcaudal parts of the greater trochanter of the femur.

Definitive diagnosis of OA requires radiographicexamination and high-quality radiographs can onlybe achieved with the horse in dorsal recumbency,under general anesthesia. Abnormalities includeperiarticular osteophyte formation, new bone forma-tion along the femoral neck, lucent zones in thesubchondral one of either the acetabulum or thefemoral head, and loss of congruity between theacetabulum and the femoral head (Fig. 15). Careshould be taken not to confuse the depression in thefemoral head and underlying radiolucent zone at thesite of insertion of the teres ligament as a lesion.

IA medication of a CF joint with radiographicabnormalities has yielded disappointing results.The prognosis for return to athletic function isguarded.

Luxation of the Coxofemoral Joint, with orwithout Secondary Upward Fixation of the Pa-tella. Luxation or subluxation of the CF joint is anunusual injury. It can occur as a primary injury orsecondary to an unstable fracture of the ilial shaft.The trauma causing luxation can also result in ar-ticular fractures of the acetabulum. Permanentupward fixation of the patella may develop as asequel, due to the displacement of the femur. Thefemur is displaced proximally; therefore, the greatertrochanter of the femur appears higher on the lamelimb. However, this can be very difficult to assessbecause the horse is usually reluctant to bear weight





on the limb. Upward fixation of the patella results inan abnormally straight hindlimb stance and an inabil-ity to flex the limb. The diagnosis can be confirmedby radiography and with high output X-ray machinesdiagnostic radiographs can be obtained with the horsestanding; however, it may be difficult to determine ifthere are concurrent fractures. The prognosis forathletic function is hopeless.

Rupture of the Teres Ligament. Rupture of theteres ligament is the result of trauma. It has beenseen in a horse that tried to get up prematurely fromgeneral anesthesia while the limbs were still re-strained in hobbles. Lameness is severe, with thehorse being unwilling to bear weight on the limb.Secondary OA rapidly ensues. Definitive diagnosisis only possible postmortem. The prognosis for ath-letic function is hopeless.

Displacement of the Femoral Head. Displace-ment of the femoral head has been seen occasionallyin young horses with severe lameness and reluc-tance to bear weight on the limb. Diagnosis is con-firmed radiographically. The prognosis is hopeless.

Fracture or Enthesopathy of the Third Trochanterof the FemurFracture of the third trochanter of the femur is arelatively unusual injury, resulting in acute-on-set, severe lameness that often improves quiterapidly with box rest. In a lean, poorly muscledhorse it may be possible to elicit pain by palpation,but in a well-muscled warmblood type this is usuallynot possible. There are no particular gait charac-teristics. Nuclear scintigraphy is particularly valu-able for tentative diagnosis of a fracture.There is intense, focal IRU (Fig. 16). Diagnosismay be confirmed radiographically, but good-qualityradiographs can only be achieved under general an-esthesia. Fractures are often longitudinal, occur-ring at the base of the trochanter. There is usuallyminimal displacement. Diagnostic ultrasonogra-phy has not been useful in my experience in helpingto confirm the presence of a fracture. It is possiblethat some horses with IRU in the region of the thirdtrochanter have enthesopathy of the attachment ofthe superficial gluteal muscles, but I have not beenable to confirm this ultrasonographically. Treat-ment is box rest for 2 mo, followed by walking exer-cise for another month. Healing may occur byeither osseous or fibrous union. Prognosis is good.

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Fig. 15. Ventrodorsal radiographic view of the left coxofemoraljoint of a 9-year-old National Hunt racehorse. There is model-ling of the cranial and caudal margins of the acetabulum (whitearrows) and the cranial articular margin of the femoral head(black arrow).

Fig. 16. Lateral scintigraphic image of the right coxofemoraljoint region of a 7-year-old warmblood dressage horse with acuteonset severe right hindlimb lameness, that rapidly improved.Lameness was not altered by any local analgesic techni-que. There is intense focal increased uptake of radiopharmaceu-tical associated with the third trochanter of the femur.





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