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Veterinary Forum November 2008 (Vol 25, No 11)

Surgical Update — Uncommon Cause of Lameness

by Aaron Wehrenberg, DVM, Rebecca Spivack, VMD, Mary Palmer, DVM, MS, DACVS

    Editor's Note: This is an unusual injury that was well diagnosed by the radiologist and surgeon. An astute observer once opined, you "see what you know." A bony fragment in the stifle is most often associated with a cruciate injury but other less common injuries can cause a similar radiographic appearance. It is sometimes necessary to consider the "zebras" in the differential diagnosis.— Don R. Waldron, DVM, DACVS, Column Editor

    Maggie, a 19-week-old, female Great Dane, was referred with an approximately 3-week history of lameness affecting the left pelvic limb. The owner was unable to recall any trauma in Maggie's recent past. Physical examination found a bright, alert, active puppy. All vital signs were within normal limits. Maggie was mildly weight bearing and held her left pelvic limb out from midline. Palpation of the left stifle indicated moderate-to-severe effusion with no cranial drawer or tibial thrust.

    The referring veterinarian had taken radiographs of the left stifle and had noted effusion in the stifle. A small radiopaque fragment consistent with bone was noted on the cranial caudal and lateral views of the left stifle and appeared to be centrally located in the stifle (Figure 1). The radiographs had been reviewed by a radiologist, and a diagnosis of proximal long digital extensor tendon avulsion had been made.

    On referral, surgical treatment to re-attach the avulsed bone fragment was discussed with the owners, who consented to surgery.

    The results of preoperative blood work were within normal limits, and the patient was placed under general anesthesia using isoflurane and a morphine-ketamine constant-rate infusion for pain control. Before proceeding with surgery, preoperative radiographs again confirmed the avulsed fragment from the long digital extensor fossa (Figure 2). Interestingly, the digits of the left paw could be flexed completely while the hock was being straightened and the stifle flexed (Figure 3), further substantiating a diagnosis of long digital extensor tendon avulsion.

    Stifle exploratory surgery was performed through a lateral arthrotomy. On entering the joint, a large amount of dark blood-tinged synovial fluid was encountered. The site at which the fragment had avulsed from the extensor fossa was clearly visible. The origin of the tendon consisted of a large, fibrous piece of tissue with a small fragile osseous fragment attached (Figure 4). Because the bone fragment was so small, it could not be reattached using pins or screws.

    Repair involved first excising the avulsed fragment and then suturing the tendon to the lateral joint capsule using nonabsorbable suture material consisting of 1-0 prolene. The long digital extensor tendon was oriented in its normal anatomic plane (Figure 5). Thorough stifle exploration revealed no additional abnormalities. Closure of the stifle arthrotomy was routine.

    After surgery, the digits no longer had the abnormal flexion while the hock was straight and the stifle flexed as noted preoperatively. The left pelvic limb was placed in a modified Robert-Jones bandage while the patient was in a normal standing position.

    The following day, the patient was released and the owners were advised to restrict Maggie's activity for 2 weeks. At the 2-week follow-up, the bandage was removed and the incision had healed well. Maggie was walking well at that time, and the owner was instructed to continue to restrict activity to leash walks for an additional 4 weeks.

    Discussion

    Dogs with proximal long digital extensor tendon avulsion can have varying degrees of lameness, ranging from marked lameness to no apparent lameness other than a clicking sound — similar to a meniscal click — while walking.1 Anatomically, the long digital extensor tendon originates at the extensor fossa located cranial on the lateral aspect of the femoral condyle.2 It extends from inside the stifle joint distally along the lateral aspect of the tibia and hock to insert on digits II and V.2 The primary function of the long digital extensor tendon is to flex the hock and extend the digits.2

    This orthopedic condition tends to occur in immature large- to giant-breed dogs after low-grade trauma2 that may not be noticed by the owner, as occurred in this case.

    Diagnosis requires radiography, along with palpation. Being able to flex the digits while the hock is straight and the stifle is flexed is a clear indication that mechanical function to the long digital extensor has been lost.2 Avulsion of the origin of the cranial cruciate ligament in an immature dog may appear radiographically similar (i.e., stifle effusion and avulsed bone fragment within the stifle joint); however, no cranial drawer should be elicited in dogs with trauma to the long digital extensor tendon.

    Surgical repair is necessary with proximal long digital extensor tendon avulsion. This may be accomplished by using a screw with or without a washer or Kirschner wires to hold the avulsed fragment in reduction or, as occurred in this case, by suturing the tendon in an appropriate anatomic position.2 Postoperative care consists of protecting the repair with external coaptation for 2 to 3 weeks and then physical rehabilitation for 1 to 2 months.2 Overall, these patients have a good prognosis if the avulsion is diagnosed and treated early after trauma.2

    About the Column Editor

    Dr. Waldron is professor of surgery in the department of small animal clinical sciences at Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, Va. He also is a member of the Veterinary Forum Editorial Board.

    1. Piermattei DL, Flo GL, Decamp CE. Brinker, Piermattei, and Flo's Handbook of Small Animal Orthopedics and Fracture Repair, ed 4. Philadelphia: WB Saunders; 2006:624.

    2. McKee WM, Cook JL. BSAVA Manual of Canine and Feline Musculoskeletal Disorders: The Stifle. Gloucester, United Kingdom: British Small Animal Veterinary Association; 2006:58-60.

    References »

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