Management of concurrent patellar luxation and cranial cruciate ligament rupture using modified tibi

PAPER

OBJECTIVES: To evaluate a novel surgery aimed at managing concur-

rent medial patellar luxation (MPL) and cranial cruciate ligament

(CCL) ruptures in dogs weighing more than 30 kg.

METHODS: Tibial plateau levelling osteotomy (TPLO) and femoral

trochleopasty were performed. The principal tibial fragment was

laterally translated by 3 to 6 mm and was externally and abaxially

rotated to create a wedge measuring 1·5 to 2·5 mm at the medial

and cranial aspect and 1 to 3 mm at the medial and distal aspect

of the tibial plateau fragment. The fragments were stabilised with a

narrow TPLO plate.

RESULTS: Thirteen surgeries were performed in 12 dogs with a mean

weight of 39·8 kg. The mean postoperative tibial plateau slope

was 8·1°. Additional surgery was required in two cases, one due

to failure of fi xation and another due to screw breakage. The mean

lameness score was 3·5 (out of 5) before surgery, 0·7 after 8 to 12

weeks, and 0·3 at fi nal follow-up. Median follow-up was 1115 days

(range, 270 to 2040 days). No patella luxated after surgery.

CLINICAL SIGNIFICANCE: MPL and CCL ruptures may be successfully

managed by performing a TPLO and simultaneously altering the rela-

tionship of the principal and tibial plateau fragments during surgery.

INTRODUCTION

Cranial cruciate ligament (CCL) ruptures and medial patellar luxations (MPL) are common causes of hind limb lameness in dogs and may occur concurrently (DeAn-gelis and Hohn 1970, Hayes and others 1994, Aragon and Budsberg 2005, Pow-ers and others 2005). MPL is considered a predisposing factor for CCL rupture (Wil-lauer and Vasseur 1987). MPL is primarily found in small and toy breeds (dogs weigh-ing <20 kg) but large breeds (weighing >20 kg) represent 9% to 35% of all MPL patients (Prister 1972, Remedios and oth-ers 1992, Johnson and others 2002, Arthurs

Management of concurrent patellar luxation and cranial cruciate ligament rupture using modifi ed tibial plateau levelling

and Langley-Hobbs 2006). Surgical man-agement options for dogs with clinical MPL disease include soft tissue proce-dures, including lateral imbrication of the fascia lata, stifl e joint derotational sutures, cranial sartorius muscle release and hard tissue procedures, such as wedge or block trochleoplasty, and tibial crest transposition (Roy and others 1992, Johnson and others 2001, Johnson and others 2002, Arthurs and Langley-Hobbs, 2006). Several of these procedures are routinely combined to address MPL in dogs. Trochleoplasty and tibial crest transposition have been recom-mended in large breed dogs to reduce the likelihood of recurrence of MPL (Gibbons and others 2006). However, complication rates of 18% to 29% have been reported in large breed dogs (Arthurs and Langley-Hobbs 2006, Gibbons and others 2006). Osteotomies of the femur or tibia have been advocated to manage angular and rotational deformities of the femur and tibia, including varus deformities of the femur and internal rotation of the tibia (Swiderski and Palmer 2007, Roch and Gemmill 2008). CCL ruptures occur in dogs of all sizes. They are managed with intracapsular or extracapsular stabiliza-tion techniques. Surgical alterations of the tibial plateau, such as tibial plateau level-ling osteotomy (TPLO), are now popular when addressing CCL ruptures in large and giant dog breeds (Slocum and Slo-cum 1993, Kim and others 2008). When MPL and CCL ruptures occur concur-rently, both conditions must be addressed to regain normal stifl e joint function. This may be achieved using staged surgical pro-cedures (that is, TPLO followed by MPL management several weeks later) or by combining several surgical procedures in a single event. During the TPLO proce-dure, the curved cut of the tibial plateau preserves the tibial crest. If a tibial crest transposition is required, an additional osteotomy is necessary which requires additional fi xation and may decrease

ANKE LANGENBACH AND DENIS J. MARCELLIN-LITTLE*

Journal of Small Animal Practice (2010) 51, 97–103DOI: 10.1111/j.1748-5827.2009.00854.x

Accepted: 1 September 2009; Published online: 11 January 2010

Veterinary Surgical Center, Vienna, VA 22180, USA

*Department of Clinical Sciences, College of Vet-erinary Medicine, North Carolina State University, Raleigh, NC 27606, USA

Presented in part at the ACVS Symposium, Chicago, IL (October 2007) and the ECVS Annual Scientifi c meeting, Basel, Switzerland (July 2008).

Journal of Small Animal Practice • Vol 51 • February 2010 • © 2010 British Small Animal Veterinary Association 97

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A. Langenbach & D. J. Marcellin-Little

98 Journal of Small Animal Practice • Vol 51 • February 2010 • © 2010 British Small Animal Veterinary Association

the stability of the proximal portion of the tibia and lead to tibial crest avulsion (Priddy and others 2003, Kergosien and others 2004). To reduce patient morbidity and accelerate postoperative recuperation, it would be advantageous to combine the management of MPL and CCL ruptures without increasing the invasiveness of the surgical procedure. We proposed that we could manage CCL ruptures and MPL by displacing the osteotomised tibial plateau in relation to the principal tibial fragment during TPLO, mimicking a tibial crest transposition and realigning the quad-riceps mechanism. The purpose of this study was to prospectively evaluate the combined MPL and CCL stabilisation in large breed dogs.

MATERIAL AND METHODS

Dogs were included in this study if they were presented for hind leg lameness, had cranial cruciate ligament ruptures and MPL, weighed more than 30 kg, and were seen at the Veterinary Surgical Center in Vienna, Virginia (USA) between January 2001 and December 2006. Twenty-fi ve dogs undergoing TPLO in our hospital were randomly selected as case controls to compare the age of patients at the time of surgery in both groups.

Clinical evaluationAll dogs had a physical, orthopaedic, and radiographic evaluation. Preopera-tive complete blood count and chemistry were performed on all dogs. Lameness was graded subjectively as described by Impellizeri (2000). A numerical rating scale (NRS) with 5 levels of lameness severity was utilized per the following: 0 = no detectable lameness at a walk or trot, no detectable lateral weight shift at a stance; 1 = no detectable lameness at a walk or trot and minor lateral weight shift at a stance; 2 = lameness at a walk or trot without hip hike; 3 = lameness at a walk or trot with hip hike; 4 = non-weight bearing at a trot; 5 = non-weight bearing at stance or walk. MPL was graded by Putman’s grading system with grades 1 to 4 (Single-ton 1969). Written consent was obtained from all clients.

Radiographic evaluationMediolateral stifl e radiographs were pro-duced with the stifl e and hock held at 90° allowing for both joints in the radiographic projection. The radiographic beam was centred on the stifl e. A craniocaudal pro-jection was produced also, including hock and stifl e in the exposure. The beam was centred on the stifl e.

Preoperative radiographs were produced immediately before surgery, postopera-tive radiographs immediately following. These radiographs were produced with the patients anaesthetised. Radiographs were produced in the same manner at four and eight weeks post surgery and at other reevaluations, but under sedation. The tibial plateau slope (TPS) was mea-sured on preoperative and postoperative radiographs using the method proposed by Slocum (Baroni and others 2003). The orientation of the femoral trochlea in rela-tion to the distal portion of the femoral shaft as seen on craniocaudal radiographs was measured.

SurgeryInhalation anaesthesia was performed after endotracheal intubation using iso-fl urane as an anaesthetic agent. Epidural analgesia was administered preoperatively in four patients at L7/S1 using a combina-tion of bupivicaine (Marcaine (5 mg/ml), Hospira, Inc., Lake Forest, IL) (1 ml/4·5 kg) and morphine (Morphine Sulfate (15 mg/ml), Baxter Healthcare Corpora-tion, Deerfi eld, IL) (0·11 mg/kg) deliv-ered through a 0·9-mm diameter, 6-cm long diamond point spinal needle. The remaining nine procedures the patients received a 3-ml intra-articular injection of bupivicaine (5 mg/ml) with epinephrine (Marcaine with epinephrine (5 mg/ml and 0·0091 mg/ml), Hospira, Inc., Lake Forest, IL) (0·0091 mg/ml). All patients received an intravenous dose of cefazolin (Cefazolin (reconstituted to 100 mg/ml), Watson Laboratories, Inc., Corona, CA) (22 mg/kg IV) that was repeated at 90-minute intervals when necessary. The durations of surgery and anaesthesia were recorded.

A craniomedial approach to the stifl e was performed, followed by complete stifl e joint exploratory arthrotomy. A ruptured CCL and MPL were confi rmed in all cases

and remnants of the CCL were removed. In cases where a meniscal tear was pres-ent the torn portions were removed, while in cases where the meniscus was intact a meniscal release was performed. A wedge resection trochleoplasty and a cranial sar-torius muscle release were performed. The TPLO procedure followed (Slocum and Slocum 1993). The jig was removed after completion of the curved cut. The surgeon and an assistant levelled the tibial plateau to the desired level and aligned the quad-riceps mechanism by performing three alignment alterations beyond plateau lev-elling. With the patella reduced and facing cranially, the principal tibial fragment was externally rotated along its long axis until torsion between the patella and the tibial tubercle was eliminated (fi rst alteration). This created a 1·5- to 2·5-mm gap between the medial and cranial aspect of the oste-otomised tibial plateau fragment and the tibial crest on the principal tibial fragment (Fig 1). Gaps were measured intraopera-tively using a sterile ruler. The bow-legged appearance (genu varum) was addressed by aligning the femoral shaft, patella, tibial tubercle, tibial shaft and hock. This was done by laterally translating the tibial crest in relation to the osteotomised tibial plateau fragment by 3 to 6 mm (second alteration) and by abaxially rotating the distal portion of the tibia to create a 1- to 3-mm wide gap between the medial and distal aspect of the osteotomised tibial pla-teau fragment and the principal tibial frag-ment (third alteration). There was no gap between the cranial or distal aspect of the osteotomised tibial plateau fragment and the principal tibia fragment on the lateral aspect of the tibia. The displacement of the principal tibial fragment in relation to the tibial plateau fragment resulted in a lateral transposition of the tibial crest (Fig 2) and realigned the mechanical axis of the pel-vic limb. A stainless steel bar was used to confi rm the alignment of the femur and tibia. The tibial plateau was secured with a 1·55-mm-diameter Kirschner wire passed from the proximo-lateral tibial crest to the caudal central tibial plateau. The patella was checked for stability. Plate contour-ing for this procedure differed from typi-cal TPLO procedures. Bending irons were used to create an approximately 30° angle between the third and fourth screws and


Modifi ed tibial plateau levelling

tablet), Novartis Animal Health US, Inc., Greensboro, NC) (1 to 2 mg/kg PO q 24 hours), two patients were admin-istered tramadol hydrochloride (Tra-madol Hydrochloride (50 mg tablet), Caraco Pharmaceutical Laboratories, Ltd., Detroit, MI) (2 mg/kg PO q 12 hours) in addition to deracoxib, and two separate patients were administered Acepromazine Maleate (25 mg tablet, Boehringer Ingel-heim Vetmedica, Inc., St. Joseph, MO) (1 to 2 mg/kg PO q 12 hours) for sedation. Patients were discharged to owners the day after surgery.

Follow-up evaluationPatients’ follow-up included a 7- to 10-day reevaluation and suture removal, 4- and 8- to 12-week reevaluation with radiog-raphy of the stifl e. An additional reevalu-ation with radiographs was performed in 12 of 13 patients more than six months after surgery and a phone interview was conducted with the owner and referring veterinarian of the remaining patient. Outcome was considered excellent if no lameness was present, good if grade 1 or 2, fair if grade 3 and poor if grade 4 or 5 lameness was present at fi nal reevaluation.

RESULTS

Twelve consecutive client-owned dogs: three Labrador retrievers, three Labrador retriever mixed, two golden retrievers, two greater Swiss mountain dogs, one Dalma-tian and one husky mixed were included in this study. One dog was operated bilat-erally with staged procedures. These pro-cedures were considered as independent procedures in this report. The mean age at surgery was 3·6 years (median age, 2 years; range, 1 to 10 years). By compari-son, the mean age of control dogs under-going TPLO in our hospital was 5·5 years. There were nine male neutered dogs and three female spayed dogs in the study. The mean weight was 39·8 kg (range, 30·3 to 49 kg). The mean preoperative lameness grade was 3·5 out of 5 (range, 2 to 5). The mean preoperative TPS was 26° (range, 20 to 34°). The mean orientation of the fem-oral trochlea in relation to the distal por-tion of the femoral shaft was 9° of varus (range, 5 to 12° of varus).

FIG 1. Front view of the stifl e joint of a dog with MPL and CCL rupture before (A) and after realign-ment (B). Genu varum is initially present. The tibial plateau fragment is tilted forward to decrease the TPS (arrow). The alignment of the quadriceps is improved by rotating the principal tibial frag-ment externally (in relation to the osteotomised tibial plateau fragment), by laterally translating the principal tibial fragment and by displacing its distal portion abaxially (arrow). This displacement creates an open wedge on the medial aspect of the tibia between the cranial aspect of the osteot-omised tibial plateau and the tibial crest and between the distal aspect of the osteotomised tibial plateau and the tibial shaft

medially twisting the cranial aspect of the proximal portion of the plate (Fig 3). The contoured TPLO plate was applied and secured with six screws: three distal cortical and three proximal cancellous screws. The Kirschner wire was removed. The stifl e was checked for patella stabil-ity, quadriceps alignment and absence of cranial tibial thrust. The area was lavaged followed by a multi-layer closure using monofi lament absorbable (PDS, Ethicon, Inc., Somerville, NJ) and non-absorbable (Ethilon, Ethicon, Inc., Somerville, NJ) sutures. The stifl e joint was iced following surgery and then bandaged with a modi-fi ed Robert Jones bandage. The bandage was removed the following morning and the stifl e was iced again. Analgesia was provided in eight patients with morphine (0·44 mg/kg) combined with aceproma-zine (Acepromazine Maleate (10 mg/ml),

IVX Animal Health, Inc., St. Joseph, MO) (0·02 mg/kg) given ½ intramuscularly and ½ intravenously and in four, a constant rate infusion of morphine (3 ml/kg/hour IV for 8 hours) was administered. The CRIs were reduced sequentially by 50% at each of 8, 12 and 16 hours. Oral anti-biotics and analgesics were provided the morning following surgery. Nine patients were administered cephalexin (Cephalexin (250 mg and 500 mg capsules), Ranbaxy Pharmaceuticals, Inc., Jacksonville, FL) (22 mg/kg PO q 12 hours) and four patients were administered cefpodox-ime proxetil (Simplicef (200 mg tablet), Pharmacia & Upjohn Company division of Pfi zer, Inc., New York, NY) (5 mg/kg PO q 24 hours) for a seven-day antibiotic course. Ten patients were administered the non-steroidal anti-infl ammatory drug (NSAID) deracoxib (Deramaxx (100 mg



FIG 2. Craniocaudal radiograph of the stifl e joint of a 1·5-year-old neutered male Labrador Retriever with a grade 3 MPL and CCL injury before (A) and immediately after simultaneous management of the stifl e joint instability and patellar luxation (B) using a modifi ed tibial plateau levelling procedure. The patella is luxated and the tibial crest is on the medial aspect of the tibia on the preoperative radiograph. The patella is reduced and the tibial crest is centred on the postoperative radiograph

FIG 3. Artist rendering based on left plates used to perform a standard TPLO procedure (A) and for the combined management of patellar luxa-tion and CCL rupture described in this report (B). The plate used for conventional TPLO is contoured to the surface of the medial aspect of the proximal portion of the tibia, forming approximately a 20° angle. The plate used to stabilize the tibia of the dogs in this study has an increased concavity in its proximal portion, forming approximately a 30° angle. The cranial aspect of its proximal portion is medially twisted

MPL was present in all dogs with six grade 2 and seven grade 3 MPL. All stifl es had complete CCL ruptures as deter-mined by physical examination and con-fi rmed during stifl e surgery. One surgeon (AL) performed all surgeries. The mean (±sd) durations of surgery and anaesthe-sia were 69 ± 17 minutes and 122 ± 34 minutes, respectively. All dogs received a single narrow 3·5 mm plate from one of three sources: nine Slocum plates (3·5 mm TPLO plate 224TL3.5-R/L or 225TL3.5-R/L, Slocum Enterprises, Eugene, OR), three Veterinary Orthope-dic Implants plates (3·5 mm TPLO plate, Veterinary Orthopedic Implants, South Burlington, VT), and one Securos plate (3·5 mm TPLO plate 9107401010R or 91077401011L, Securos, Fiskdale, MA) were used. The mean postoperative TPS was 8·1° (range, 2 to 14°). The median time to follow-up was 1115 days (range, 270 to 2040 days). The mean TPS at the time of reevaluation was 9·8° (range, 2 to 15°).

Although all dogs had bilateral stifl e disease, 11 dogs had MPL/TPLO surgery

on one stifl e but one dog had MPL/TPLO surgery on both stifl es, nine months apart. Eight dogs had only MPL on the contra-lateral leg. Five of these eight patients had standard MPL surgery on the opposite leg. Three had no surgery on the opposite leg, despite existing MPL during the study period. Three dogs had CCL on the other side and two received a TPLO surgery and one a standard extracapsular repair.

Eleven of 12 dogs were alive at the end of the study period. The mean postopera-tive lameness score was 0·7 out of 5 (range, 0 to 2) 8 to 12 weeks after surgery and was 0·3 out of 5 (range, 0 to 2) at long-term reevaluation. There was no recurrence of MPL.

One dog weighing 49 kg fell down a fl ight of stairs chasing a cat two weeks after surgery. He broke all proximal screws, fractured his fi bular head and reluxated his patella. A second procedure with stabi-lisation of the tibial plateau using a TPLO plate and bilateral external fi xation device was necessary. He developed a postopera-tive wound infection that was treated with enrofl oxacin (136 mg Enrofl oxacin tablets,

Bayer HealthCare LLC, Shawnee Mission, KS) (5 mg/kg PO q 12 hours) and amoxicil-lin trihydrate/clavulanate postassium (Cla-vamox (375 mg tablet), GlaxoSmithKline, Research Triangle Park, NC) (12·5 mg/kg PO q 12 hours), as well as septic arthritis that was treated with amikacin (Amikacin sulfate (50 mg/ml), Phoenix Pharmaceu-tical, Inc., St. Joseph, MO) (10 mg/kg IV q 24 hours), ampicillin (Ampicillin (reconstituted to 250 mg/ml), American Pharmaceutical Partners, East Schaum-burg, IL) (10 mg/kg IVq 8 hours) and ceftriaxone (Ceftriaxone sodium (recon-stituted to 350 mg/ml), Roche Labora-tories, Inc., Nutley, NJ) (25 mg/kg IM q 24 hours). He recovered and improved his grade 5 lameness to grade 3 at eight weeks and grade 2 at three months post surgery. The external fi xator was removed 56 days later and plate and screws were removed at 251 days post the initial TPLO with MPL surgery. He was reevaluated for a right forelimb lameness and elbow pain at



suture removal, 261 days post surgery. No pelvic limb lameness was present at that time. He was euthanatised 605 days post surgery after acute onset tetraparesis, neck pain, and anorexia.

Another dog had plate and screws removed at day 293 because of a mild pain response to palpation. All but a por-tion of the broken most proximal screw were removed. That screw fragment was removed 591 days after surgery because of potential interference with the lateral collateral ligament. Two patients had inci-sional complications and healing occurred uneventfully.

DISCUSSION

Our results show that MPL and CCL rup-ture correction using a modifi ed TPLO procedure and trochlear wedge resection may be performed successfully in large dogs with grade 2 or grade 3 MPL. The outcome assessment methods in this study were limited to joint palpation and visual assessment of lameness. Lameness was addressed with a subjective numerical scale. The use of a force plate would have increased the objectivity of our outcome assessments (Waxman and others 2008), but was unavailable in our practice. Sub-jectively, this procedure is not more tech-nically challenging than either procedure alone and may be performed without major technical diffi culty. This proce-dure appears technically simpler than the combination of a TPLO with a transpo-sition of the tibial crest and it does not require two osteotomies and the creation of a small crest fragment that could avulse in the postoperative period. The proce-dure requires simultaneous alignment of the quadriceps mechanism and rotation of the tibial plateau. This is achieved by moving the principal tibial fragment later-ally and abaxially while rotating it exter-nally. The successful realignment of the tibia leaves an open wedge, medially. As a consequence, the plate used to stabilise the proximal portion of the tibia is used in buttress fashion. The specifi c mechani-cal consequences of this form of fi xation have not been assessed experimentally. Buttress fi xation of bone fragments is less stable than fragment apposition using

interfragmentary compression (Hulse and Hyman 1991, Prayson and others 2001, Marcellin-Little and others 2008). Few reports have compared the complication rate after fi xation of bone fragments with buttress or compressive fi xation. In one randomised study of unstable trochanteric fractures in 233 people, failure of fi xation occurred after 9% of buttress fi xations and after 19% of compressive fi xations (Buciuto and others 1998). The acute failure of fi xation and screw breakage seen in the two cases in this report may have resulted from the fact that buttress fi xa-tion was used. However, the low incidence of mechanical failures for the patients and the absence of tibial plateau fragment “roll back” in this report suggest that the stabil-ity of buttress fi xation is acceptable. Even though all patients in this report received a single narrow plate, a broad plate or sec-ond plate could be added to the fi xation to lower the likelihood of mechanical failure. Three different narrow plates were used in this report. The fi rst nine cases received original TPLO plates (3·5 mm TPLO plate 224TL3.5-R/L or 225TL3.5-R/L, Slocum Enterprises, Eugene, Oregon). Because of concerns regarding the material properties of these plates (Boudrieau and others 2006), plates from two other man-ufacturers were used in four cases. While we felt that the overall alignment of the operated limb was improved in all cases, we did not objectively evaluate the impact of the surgical procedure on the shape of the pelvic limb when dogs were stand-ing or using goniometry, radiography or computed tomography. Such assessments would be necessary to assess the impact of this procedure on the mechanical axis of the pelvic limb.

Mean postoperative TPS (8°) was slightly larger that the proposed TPS of 5° (Slocum and Slocum 1993). One patient in this report was undercorrected (14°) because of the perceived diffi culties and risk of fi bular fracture during correction. This patient was free of lameness at reeval-uation. In vitro studies demonstrate that cranial tibial thrust is neutralised at 6·5° (Warzee and others 2001, Reif and others 2002). In one report, good outcomes after TPLO were present in dogs with postop-erative TPS ranging from 0 to 14° (Robin-son and others 2006).

All dogs in this study had mild to mod-erate varus angulation of their femoral trochlea in relation to the femoral shaft (genu varum), as seen on their craniocau-dal radiographs and from their bow-legged stance. Because the mean (±sd) femoral varus angulation of the dogs in this report (9 ± 2°) was similar to the angulation measured in nine mixed breed dogs free of orthopaedic problems in a previous report (9 ± 2°)(Dudley and others 2006), it is not possible to ascertain whether the dogs in this report had true deformities of the dis-tal portion of the femur and whether these potential femoral deformities impacted the development of patellar luxations and CCL ruptures. None of the dogs managed during the study period had grade 4 MPL. While the surgical procedure described in this report could possibly be performed in dogs with grade 4 MPL, the presence of more severe angular and rotational femoral and tibial deformities may require additional corrective procedures, such as a distal femoral osteotomy (Swiderski and Palmer 2007, Roch and Gemmill 2008).

The patients in this report had a mean age of 3·6 years. They represented approxi-mately 3% of TPLO patients in our hospi-tal. They were in average two years younger than the control dogs undergoing TPLO. They were also younger than dogs undergo-ing TPLO in other reports, who had a mean age of 4·7, 5·0 and 6·2 years ( Pacchiana and others 2003, Priddy and others 2003, Stauffer and others 2006). The younger age of the dogs in our report may be due to the fact MPL is a developmental con-dition likely to affect young patients and, if MPL predisposes dogs to CCL rupture, then such rupture is more likely to occur in a younger population of dogs than that suffering from CCL rupture alone.

The 12 patients in this report had bilat-eral stifl e disease. Eight patients (67%) had bilateral MPL. The reported rate of bilat-eral MPL is approximately 50% (Alam and others 2007). Our rate was higher, possibly because of the long-term pro-spective nature of this study. Four patients (33%) had bilateral CCL rupture. This is in agreement with the reported rate of bilateral CCL rupture (Doverspike and others 1993).

A jig is used to prevent malalignment in normal hind legs during TPLO procedure



(Slocum and Slocum 1993). It also acts as a guide during TPLO performed on dogs with CCL rupture and internal torsion of the tibia, varus or valgus tibial deformities. In our study, we felt that complete quad-riceps alignment was not possible with the jig in place and we decided to perform the correction without the jig. While the absence of a jig could lead to iatrogenic axial or rotational malalignment, the very focus of this procedure was on realigning the tibia. We felt that the good long-term clinical outcome supported our realign-ment method. Using preoperative CT planning or intraoperative fl uoroscopic image intensifi cation could increase the precision of this tibial realignment method. TPLO performed without a jig did not appear to lead to axial or rota-tional malalignment in two recent reports (Bell and Ness 2007, Schmerbach and others 2007).

The reported complication rate of TPLO has ranged from 19% to 28% (Pacchiana and others 2003, Priddy and others 2003, Stauffer and others 2006). The reported complication rate after MPL surgery in large breed dogs has been reported to be 29%, with 10% of patients having major complications such as patel-lar reluxation or implant failure (Gibbons and others 2006). The heaviest dog in our study had implant failure and patel-lar reluxation due to a traumatic event. This complication occurred during a fall that resulted in fi bular fracture, fracture of the top three screws and reluxation of the patella. An additional surgical proce-dure was required to stabilise the stifl e. The patient recovered and improved to a grade 2 lameness, three months after sur-gery. Proper client compliance with con-fi nement is important after surgery. The use of a broad plate or the addition of a second plate could lower the likelihood of such mechanical failure in patients placing large loads on their operated legs in the early postoperative period. We now use broad plates on patients weighing more than 41 kg with tibiae that can accommo-date the larger plate.

One patient was referred for poor prog-ress after extracapsular stabilisation of a CCL-defi cient stifl e joint. This patient also had an MPL. While MPL was not diagnosed in that patient before the origi-

nal surgery, it is likely that the MPL was developmental and did not result from the extracapsular stabilisation because of the distal portion of the femur had a varus angulation and because the wound closure of the fascia lata was intact when evaluated during the second surgery. It is possible, however, that MPL was secondary to the CCL stabilisation in that dog. MPL has been reported to result from CCL stabili-sation (Arthurs and Langley-Hobbs 2007). In that report including 32 patients, MPL after CCL stabilisation was considered challenging and a variety of management methods were used. The reluxation rates ranged from 35% to 100% and were lower with tibial crest transposition, sulcoplasty and tibial realignment. The overall suc-cess rate was 79%. We cannot conclude whether the procedure evaluated in this report would be appropriate to manage patients with failed CCL stabilisation and MPL.

We conclude from this report that MPL and CCL ruptures may be simultaneously managed in large dogs by externally rotat-ing, by laterally translating and by abaxi-ally displacing the principal portion of the tibia during the TPLO procedure. The geometric and mechanical features of this corrective surgery could be optimised using in vitro experiments.

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Management of concurrent patellar luxation and cranial cruciate ligament rupture using modified tibi