Popliteal Tendon Transposition for Stabilization of the Cranial Cruciate Ligament Deficient Stifle Joint in Dogs: An Experimental Study

Veterinary Surgery 24:465-475. 1995

Popliteal Tendon Transposition for Stabilization of the Cranial Cruciate Ligament Deficient Stifle Joint in Dogs:

An Experimental Study

ERIC MONNET, DVM, MS, Diplomate ACVS, PETER D. SCHWARZ, DVM, MS, Diplomate ACVS, and BARBARA POWERS, DVM, PhD, Diplomate ACVP

Popliteal tendon transposition was performed in five dogs with surgically induced cranial cruciate ligament rupture. After a lateral approach to the stifle joint, the popliteal tendon was severed distal to the sesamoid bone and transposed cranially onto the tibia1 crest to mimic the sagittal orientation of the cranial cruciate ligament. The origin of the popliteal tendon on the lateral femoral condyle was preserved. Lameness was not clinically detectable 2 months after surgery. At 6 months postoperatively, there was minimal radiographic and histopathologic evidence of degenerative joint disease in the stifle joints that had underwent surgery. There was no gross or microscopic evidence of meniscal damage found at necropsy 6 months after surgery. Biome- chanical studies are warranted before recommending the procedure. OCopvright I995 by The American College of Veterinary Surgeons

HE TREATMENT of dogs with ruptured T cranial cruciate ligaments remains contro- versial. In one study, dogs weighing less than 15 kg that did not undergo surgical repair had a recovery rate of 85.7%, whereas dogs weighing more than 15 kg had a recovery rate of only 19.3%.' Numerous surgical techniques have been reported in both the human and veterinary literature for stabilization of joints with a ruptured cranial cruciate ligament. The reported success rate (defined as return to good or excellent function), regardless of the surgical technique used, ranged from 85% to 93%.2-9

Intra-articular repair techniques attempt to mimic normal anatomy and stifle biomechanics; however,

if autogenous tissues are used, a protracted period of restricted activity is required to allow revascular- ization and strengthening of the graft.6%'0-12 With ac- tive dogs, this is not always possible. On the other hand, extra-articular techniques allow early limb usage, but they do not preserve normal stifle biomechanics." Transposition of the fibular head and lateral collateral ligament is reported to have excellent clinical results,13 but is associated with a significant number of intraoperative complication^'^^'^ and the effect on joint kinematics has been ques- tioned. Advancing the fibular head cranially and putting the lateral collateral ligament in tension alters joint mechanics and rotates the tibia externally in relation to the f e m ~ r . ' ~ . ' ~

From the Department of Clinical Sciences and the Department of Radiology and Radiation Biology, College of Veterinary

This work was supported by a Basic Science Research Grant, United States Department of Agriculture Animal Health and Disease

Presented at the 21st Annual Conference of the Veterinary Orthopaedic Society, Snowbird, UT, February 27, 1994. Address reprint requests to Eric Monnet, DVM, MS, Department of Clinical Sciences, College of Veterinary Medicine and

Biomedical Sciences, Colorado State University, Fort Collins, CO 80525. OCopyright I995 by The American College of Veterinary Surgeons

Medicine and Biomedical Sciences, Colorado State University. Fort Collins, CO.

Program.

016 1-3499/95/2406-0004$3.00/0

46 5

466 POPLITEAL TENDON TRANSPOSITION IN DOGS

The popliteal muscle is a strong triangular muscle that lies within the popliteal space and covers the caudo-lateral joint capsule and proximal caudal- third of the tibia. It is covered caudally by the gastrocnemius and superficial digital flexor muscles. It originates on the distal surface of the lateral condyle of the femur and crosses under the lateral collateral ligament of the femorotibial joint. The tendon of the popliteal muscle inserts cranially on the lateral femoral condyle. The popliteal muscle flexes the stifle and internally rotates the tibia.

It is our hypothesis that cranial transposition, in tension, of the popliteal tendon would provide an alternative method for stabilization of the cranial cruciate ligament deficient stifle joint, with the potential advantage of preserving normal biomechanics of the stifle joint. This experimental study evaluates the ability of transposition of the popliteal tendon to stabilize the cranial cruciate ligament deficient stifle joint and to determine the effect that the procedure had on the structures of the joint.

MATERIALS AND METHODS

Five mature mixed-breed dogs, weighing between 20 and 30 kg, were subjected to unilateral cranial cruciate ligament excision and joint stabilization by popliteal tendon transposition. Preoperatively, the five dogs received a complete physical, orthopedic, and neurological examination. The contralateral stifle joint was used as a negative control. All the animals were treated in a manner consistent with the United States National Institutes of Health Guide for the Care and Use of Laboratory Animals and the Animal Welfare Acts (US PL 89-544; 91-579; 94-279). l 5

Each dog was premedicated with atropine, aceproma- zine, and oxymorphone. Anesthesia was induced with thiopental, and maintained with oxygen and halothane during the procedure. The limb to undergo surgery was randomly selected.

With the dog in dorsal recumbency the hindlimb was prepared for aseptic surgery according to standard procedures. The cranial cruciate ligament was isolated through a lateral parapatellar incision, transected, and excised. The joint capsule was closed using 2-0 poly- dioxanone (Maxon, Davis and Geck, American Cy- anamid Company, Wayne, NJ) in a cruciate suture pattern.

The lateral retinacular fascia was separated from the joint capsule and retracted caudally to expose the lateral collateral ligament and the caudal part of the femorotibial

joint capsule. The peroneal nerve was identified and pro- tected throughout the surgery. The gastrocnemius muscle was retracted caudally to expose the musculotendinous junction of the popliteal muscle. The tendon of the popliteal muscle was bluntly dissected and isolated from the overlying collateral ligament (Fig 1). The tendon was then transected at a point distal to the level of the sesamoid bone, which is located at the level of the musculotendinous junction, and dissected free from the underlying joint capsule (Fig 2). The dissection was continued to the level of the tendons origin on the femoral condyle (Fig 3). The proximal part of the cranial tibial muscle was elevated to expose the tibial tuberosity cranial to the tendon of the long digital extensor muscle. A no. 5 polyester (Ticron, Davis and Geck, American Cyanamid Company, Wayne, NJ) suture was placed in the distal part of the tendon, proximal to the sesamoid bone of the popliteal tendon, using a Krackow pattern (Fig 4).16 The suture was then passed through a tunnel drilled in the tibial tuberosity (Fig 5 A-B). The lateral half of the tunnel was over-drilled to allow incorporation of the sesamoid bone in the proximal tibia (Fig 5C). With the tibia in external rotation and the stifle in a slightly flexed position, the suture was tightened through a button on the medial side of the tibial tuberosity. The suture was tightened until the drawer motion was completely eliminated. The stability of the joint was tested in a cranio-caudal direction. Using 0 poly- dioxanone, the lateral fascia was imbricated with a “vest- over-pants’’ suture pattern. The subcutaneous tissue and skin were closed in routine fashion. Postoperatively the limbs were supported in a padded bandage (Robert Jones dressing) for 2 weeks. Analgesics (oxymorphone) were given as needed throughout the immediate postoperative period.

Fig 1. Anatomy of the popliteal muscle and tendon and its relationship with the gastrocnemius muscle and lateral collateral ligament. (Reprinted with permission from Miller’s Anatomy of the Dog, ed 3, by Evan 1993).

MONNET, SCHWARZ, AND POWERS 467

in degrees: using the table plane as a reference and the orientation of the calcaneus to measure the angle), range of motion (goniometer in degrees: aligned with the lon- gitudinal axis of the femur and the tibia), circumference of the thigh at mid-femur (flexible tape ruler in milimeters), and mediolateral diameter of the femorotibial joint at the level of the distal end of the patella in ex- tension (caliper in milimeters). Radiographs (mediolateral and cranio-caudal views) were made preoperatively of both stifle joints, immediately postoperatively for the surgical side, and then of both stifle joints every month. The contralateral stifle joint was radiographed to evaluate changes from overuse of the leg and for comparison. Radiographs were evaluated blindly by a board certified radiologist for signs of degenerative joint disease and joint effusion using a subjective scoring sys- tem (Table I ) . Cytological analysis of synovial fluid from both stifle joints was performed preoperatively and monthly thereafter. Two board certified orthopedic surgeons, unfamiliar with the surgical technique, evaluated the dogs 6 months after surgery without prior knowledge of which stifle joint had undergone surgery. Lameness when walking and running, crepitus, range of motion, and drawer motion were evaluated.

Dogs were euthanatized with an intravenous overdose of pentobarbital 6 months after surgery. Each stifle joint was macroscopically evaluated and photographed. Spec- imens of articular cartilage (surgical and contraletral joints) were taken from predetermined sites on the femoral condyle (medial and lateral condyle), trochlear groove, and the tibial plateau for histopathologic analysis. Spec- imens were processed in paraffin, sectioned, and stained with hematoxylin and eosin and safranin-0. Each histological specimen was evaluated and a score determined according to the modified Mankin Score for osteoarthritis

?

Fig 2. The popliteal tendon is transected distal to the sesamoid bone (dotted line).

The five dogs were evaluated weekly for the first 4 weeks and then monthly until 6 months postoperatively. Follow-up evaluations consisted of an orthopedic examination plus evaluation of limb usage when walking, running, and climbing stairs. Surgical procedures and follow-up examinations were performed by the same investigator. At each follow-up, both stifles were measured for cranial drawer motion (ruler in millimeters), internal rotation of the tibia in 90" flexion (goniometer

Fig 3. The popliteal tendon is dissected free from the underlying joint capsule to the level of its femoral origin (arrow). (P, patella; S, sesamoid bone of the popliteal tendon; T, tibial crest).


i

Fig 4. Modified locking loop suture pattern (Krackow pattern) preplaced in the distal part of the popliteal tendon. The popliteal sesamoid bone is distal to the suture.

(Table 2)'' The medial meniscus and a full thickness sample of the joint capsule were obtained and similarly processed for histopathologic analysis. The popliteal tendon and the sesamoid bone-bone interface were studied histologically.

Statistical analysis included a nonparametric test (Wil- coxon signed rank test P <: .05) to compare the surgical side with the control side.

RESULTS

No complications were encountered during the surgical procedure in any of the dogs. Oxymorphone (0.1 mg/kg subcutaneous) was used as needed postoperatively to control pain.

Clinical Evaluation By 2 weeks postoperatively, all dogs were

weight-bearing but lame when walked. At 4 weeks

they were lame but weight-bearing when running. Two months postoperatively, none of the dogs showed gait abnormalities and were considered clinically normal. There was no difference in the diameters of the thigh and the stifle at any time during the study when the surgical side and the control side were compared. None of the dogs showed any signs (eg, pain, discomfort, lameness) that could be related to the lack of a functional popliteal muscle in the limb that underwent surgery.

At 6 months postoperatively, the orthopedic eval- uators were unable to detect which limb had undergone surgery while watching the dogs walk or run. Mild crepitus and drawer motion were detected in the experimental stifle joint of each dog during orthopedic examination.

Drawer Motion

Cranial drawer motion was evaluated monthly in both the stifle joint that underwent surgery and the control stifle joint. Two weeks postoperatively, drawer motion (measured in millimeters) was significantly increased in the stifle joints that underwent surgery when compared with the control stifle joints (Fig 6). Drawer motion was always more pronounced when the joint that underwent surgery was held in 90" flexion. After 1 month, there were no further change in cranial drawer motion in the joint that underwent surgery but was increased when compared with the control stifle joints (median: 5 mm; range: 2 to 5 mm versus median: 0 mm; range 0 mm, respectively).

Range of Motion

Range of motion in the experimental stifle joints was significantly decreased postoperatively when compared with the unoperated stifle joints. No dif- ferences were noticeable at the 1, 2, and 3 month postoperative evaluations, but the range of motion was significantly decreased at 4 and 6 months after surgery (Fig 7).

Internal Rotation

The degree of internal rotation, determined at 90" of flexion, was measured in both femorotibial joints for comparison. Internal rotation of the stifle joint


Fig 5. (A) The no. 5 polyester suture is passed through a pre- drilled hole in the tibial crest (S = sesamoid bone). (B) The hole in the tibial crest is cranial to the tendon of the long digital extensor muscle. (C) Notice the partial overdrilling of the lateral tibial crest to allow incorporation of the sesamoid bone in the tibial crest. The suture is tied on a button.

of the limbs that had undergone surgery was significantly decreased immediately postoperatively (Fig 8) but was not significantly different from the control side after 1 month.

Synovial Fluid Analysis

Synovial fluid analysis from the stifle joints that had undergone surgery showed a mild mononuclear


Table 1. Radiographic Scale Used to Grade the Amount of Degenerative Joint Disease and Joint Effusion

on Follow-up Radiographs

6.0 surgical sun r. -I

Degenerative Joint Disease Score

None Mild Moderate' Severe

Joint Effusion None Mild Moderate Severe

0 2 6

10

0 2 6

10

inflammatory response during the 6-month study period. The white cell count remained below 2,000

0 5 4 - 0 1 s 3.0 I U Pre Pos 2W 1M 2M 3M 4M 6M

TIME

Fig 6. Drawer motion in millimeters, before and after surgery, and at 2 weeks, 1 ,2 ,3 ,4 ,6 months. Asterisk indicates statistically significant difference between the surgical and the control side (P < .05).

Radiographic Evaluation All of the experimental joints developed radio-

graphically evident osteoarthrosis by 1 month after

Table 2. Modified Mankin Score Used to Grade the Amount of Histopathologic Changes Caused by Degenerative Joint

Disease in Cartilage Samples

Score

Normal Surface irregularities Pannus plus surface irregularity Clefts to transitional zone Clefts to radial zone Clefts to calcified zone Complete disorganization

Normal Diffuse hypercellularity Cloning

Hypocellularity No hypocellularity Superficial Transitional Radiate

Normal Slight reduction Moderate reduction Severe reduction No dye noted

Cells

Matrix staining (safranin-0)

0 1 2

gression was not observed (Fig 9, 10, 11). Dog 3 showed sesamoid displacement at 1 month.

Gross and Histopathologic Examination

Pannus type reactions were not evident macroscopically on the femoral condyle in either expen- mental or control stifle joints. Mild chondromalacia was present on the lateral femoral condyles in all experimental joints and the joint capsule was thicker when compared with the control side. The large

160.0 - 150.0 - 140.0 - 130.0 - 120.0 -

110.0-

Cmtroi Side

Surgical Side p-- Surgical Side

Pre P m 2 W 1M 2M 3M 4M 6M

TIME

Fig 7. Range of motion in degrees, before and after surgery, and at 2 weeks, 1,2,3,4,6 months. Asterisk indicates statistically significant difference between the experimental and the control side (P < .05).

MONNET, SCHWARZ, AND POWERS 47 1

55.0 1 Control Side

35.0

30.0 Surgical Side

Pre Pos 2 W 1M 2M 3M 4M 6M

TIME

Fig 8. Internal rotation in degrees, before and after surgery, and at 2 weeks, 1 ,2 ,3 ,4 ,6 months. Asterisk indicates statistically significant difference between the experimental and the control side (P < .05).

polyester suture used in dog no. 5 was broken and the suture was loose in dog no. 3. Histopathologic evaluation of the cartilage showed surface irregularities, occasional chondroma formation, and hypocellularity of the tangentional zone in 4 out of 5 experimental stifles. One experimental joint showed moderate structural damage characterized by clefts into the radiate zone. The modified Mankin scores for the stifle joints that underwent surgery were significantly different when compared with the control stifles (median score for surgical side: 17/60; range: 6.5 to 21.5 versus 3.5/60; range: 2 to 12.5, respectively). A mild decrease in glycosaminoglycan content was noticed on safranin-0 staining in the superficial and transitional zones in the stifle joints that underwent surgery when compared with the control stifle joints (median score: 2 of 16; range: 1 to 4.5 versus median score: 1.5 of 16; range: 0.5 to 3, respectively). Synovial membranes showed villous hyperplasia, chronic inflammation, and fibrosis in all of the stifle joints that underwent surgery. No meniscal abnormalities were evident on macroscopic or microscopic examination.

The popliteal tendon on the surgical side showed increased cellularity and vascularity. Cells present were mostly fibroblasts. There was increased glycosaminoglycan content between the collagen fibers. In dogs nos. 1 and 5 there was fibrocartilaginous metaplasia in the tendon.

The sesamoid bone was resorbed either partially or completely in all experimental stifle joints. 0s- teoclasts in resorption lacunae were present in the partially resorbed sesamoid bone. When the remnant of the sesamoid bone was present, it was surrounded

by fibrous tissue without evidence of bone union between the sesamoid bone and the tibial crest. Ex- cellent fusion of the popliteal tendon collagen fibers into the tibial crest, creating tissue anchorage of the tendon, was consistently present. There were zones similar to those described for attachments of normal tendon or ligament to b ~ n e . ' ~ , ' ~ The zones were composed of ligament, fibrocartilage, mineralized fibrocartilage, and bone. The bone-tendon interface was distinguished by a tide mark. No inflammatory cells or indications of remodeling were noticed at the bone-tendon interface (Fig 12). The sutures through the tibial crest were surrounded by bone and firmly anchored.

DISCUSSION

The major objective of surgery for cranial cruciate ligament rupture in the canine stifle joint is reestab- lishment of stability. Popliteal tendon transposition limited cranial drawer motion but preserved normal internal rotation of the tibia during flexion of the femorotibial joint. The surgical technique is simple. Because transposition of the popliteal tendon is an extra-articular technique, it eliminates placement of foreign or autogenous material in the joint. Dogs rapidly regained clinical use of their limbs (within 4 to 6 weeks). However, force plate analysis was not available to objectively evaluate the weight-bearing ability of the dogs after surgery. Based on visual examination of all five dogs during walking and running, experienced orthopedic surgeons were unable to distinguish gait abnormalities between the experimental versus control limbs. Therefore, the authors

14.0 1 W

0 a

:: 2 2

a 0 n a

U 0

U

12.0 lo.ol 8.0

Control side . Pre Pos 2W 1M 2M 3M 4M 6M

TIME

Fig 9. Radiographic evaluations according to the grading scale, before and after surgery, and at 2 weeks, 1,2,3,4, and 6 months. Asterisk indicates significant difference between the experimental and the control side (P < .05).


evident at follow-up in all dogs in our ~ tudy . ' -~ , '~ Cranio-caudal instability was evident 2 weeks postoperatively and remained unchanged at I month. Instability may result from breakdown at the bone- graft attachment or from stretching of the graft, similar to that found with intra-articular autograft techniques.'2,20 Until 4 weeks postoperatively, the attachment of autogenous tissue grafts to bone is weak. ' Intra-articular grafting techniques may fail postoperatively because of inadequate fixation of the graft.20,2' The immediate stability of the bone-ligament interface is important.20,2' A major advantage of the fibular head transposition technique is that creation of a new bone-ligament interface is not required.21 A cancellous bone screw with spike washer or staple, which would improve stability in the immediate postoperative period, could have been used as alternative fixation techniques for the popliteal

Fig 10. Cranio-caudal radiograph of the stifle joint underwent surgery 6 months ago.

believe that from the clinical and owner standpoints, transposition of the popliteal tendon results in an acceptable outcome. However, signs of degenerative joint disease were present on follow up radiographic and histological evaluation 1 month after surgery presumably because of instability.

In this study, the popliteal tendon was transposed onto the tibia1 crest cranial to the long digital extensor muscle. In that position, the popliteal tendon seems to mimic more closely the orientation of the cranial cruciate ligament than does the lateral collateral ligament after fibular head transposition. No anatomical or functional studies have been performed to confirm this observation.

Similar to the findings of other reported investi-

stabilization techniques, there was drawer motion gations of intra-articular and extra-articular stifle ~i~ 11. Mediolateral radiograph of the stifle joint that under-

went surgery 6 months ago.


Fig 12. Photomicrograph of a bone-tendon interface showing incorporation of the tendon fibers into the bone matrix (T, tendon; FC, fibrocartilage; TD, tide mark; B, bone), hematoxylin and eosin stain; original magnification X 100.

tendon.22 However, because of the position of the popliteal tendon on the tibial crest (cranial to the long digital extensor muscle), the authors believed there was insufficient tendon material present to ad- equately anchor the graft. The Krackow suture pattern, used to anchor the popliteal tendon graft, was recently reported to have decreased maximum strength, total energy and stiffness when compared with the locking loop pattern for tenorrhaphy of a flat tendon.23 In the surgical technique reported herein, incorporation of the sesamoid bone in the suture pattern may prevent slippage of the suture from the tendon and increase maximum strength. Only dog no. 3 showed postoperative displacement of the sesamoid bone, which was most likely caused by stretching or tearing of the tendon by the suture material. Early postoperative use of the limb may also stretch the tissue.22 Drawer motion remained the same after 1 month, probably because of fibrosis of the periarticular tissues. Over time, because of its hypertrophy, the joint capsule becomes a primary structure for stabilization of the stifle joint.” How- ever, we do not believe that the limited joint capsule reaction was the only reason for the increased stability. Long-term studies of experimental transection of the cranial cruciate ligament reported continued instability, even with increased joint capsule thick- n e ~ s . ~ ~

Meniscal damage was reported recently in 25% and 50% of dogs that underwent experimental cranial cruciate ligament transection and stabilization using fibular head transposition during a 4 and 10

month study period, respectively. The amount of drawer motion also increased with time.14 Meniscal injury was not evident in our 6-month study. The authors hypothesize that the absence of meniscal damage was caused by improved joint kinematics after popliteal tendon transposition. It has been well documented that cranio-caudal instability of the stifle causes medial meniscus i n j ~ r y . ’ ~ . ~ ~ The menisci are restraints to drawer motion in the stifle; however, they provide minimal amount of cranio-caudal stability during full weight-beanng.26

Extra-articular techniques limit internal rotation and therefore interfere with the tibial “screw home” mechanism during flexion of the ~tifle.~’~’ By trans- posing the lateral collateral ligament in a cranial position and under continuous tension, fibular head transposition eliminates this mechanism.’ With the medial and lateral collateral ligaments in tension, fibular head transposition eliminates rotation and the gliding motion of the stifle during flexion, which transforms the stifle into a pure hinge-type joint.21 In this study, internal rotation was not preserved immediately after surgery; however, it returned to normal by 2 weeks, which corresponded to the time mild drawer motion was detected. The drawer motion may be related to stretching of the tendon of the popliteal muscle or breakdown at the bone-tendon interface. The mild histological remodeling (hy- percellulanty and hypervascularity) and degenerative (fibrocartilaginous metaplasia) changes observed in the popliteal tendon support the likelihood of tendon stretching from chronic repeated tearing. Histolog- ically, the bone-tendon interface in the tibial crest was equivalent to a normal bone-tendon interface, with a tide mark found between the new bone and the fibrotic tissue emerging from the bone. Similar tide marks are found in certain ligament insertion sites where fibrocartilage provides a transition between soft tissue and Several studies have reported that tendon, when used either as an autograft or allograft substitute for the cranial cruciate ligament, becomes well incorporated in bone, and its insertion site matures to resemble fibrocartilage over time.27-29 If motion at the bone-tendon interface occurred immediately postoperatively, histopatho- logical evidence of this should have been found.

After cranial cruciate ligament repair, radiography has been found to be more accurate for evaluation ofjoint biology than assessing the degree of lameness or drawer m ~ t i o n . ~ . ~ ’ Whether a cranial cruciate lig-


ament stabilization technique maintains normal joint biology can be determined by evaluation of secondary joint disease or further progression of the secondary joint disease present at the time of surgery. In a recent study on radiographic evaluation after intra-articular stabilization, degenerative joint disease progressed until 12 to 18 months, even when the dog was reported normal by the owner.3 Osteo- phytes have been detected as early as 3 weeks after cranial cruciate ligament rupture.’ In the present study, radiographic evaluation showed only mild osteoarthrosis and mild joint effusion in all five experimental stifles.

Minimal changes in the articular cartilage and no meniscal damage were noticed in our five dogs after 6 months. The authors believe this is related to increased stability provided by transposition of the popliteal tendon. Chondromalacia, which appears early in degenerative joint di~ease,~’.’~ was macroscopically evident but mild in our study dogs by 6 months after surgery. Irregularity in the tangential or superficial layer with cloning of the chondrocytes was the most common structural lesion identified. Glycosaminoglycan content was slightly decreased in the superficial layer of the cartilage. These changes were mild, indicating minimal degenerative changes.

Transposition of the popliteal tendon represents an alternative to the fibular head transposition technique and has the advantage of preserving internal rotation of the tibia during flexion of the femorotibial joint. This technique is easy to perform and results in early return to usage of the limb with minimal degenerative joint disease. Biomechanical testing is necessary to evaluate the strength of the popliteal tendon when compared with the cranial cruciate ligament and the lateral collateral ligament. A pro- spective randomized clinical trial is indicated to further evaluate the popliteal tendon transposition technique with naturally occurring cranial cruciate ligament rupture in dogs. The fate of the tendon fixation site also warrants further study.

ACKNOWLEDGMENT

The authors thank Dr R.D. Park, DVM, PhD, Diplo- mate ACVR for his expertise in radiographic evaluation, and Drs E.L. Egger, DVM, Diplomate ACVS and D.L. Piermattei, DVM, PhD, Diplomate ACVS for their as- sistance in the clinical evaluation of the dogs.

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Documents

Popliteal Tendon Transposition for Stabilization of the Cranial Cruciate Ligament Deficient Stifle Joint in Dogs: An Experimental Study