Library: Article (Featured Medical Case)

Title: Patellar Luxation: Distal Femoral Osteotomy
Date: 7/1/10

Detail: "Brody" a 6 ½ year old male Cockapoo (figure 1) presented for surgical consultation of bilateral medial patellar luxation (right grade II/IV; left grade III/IV) with concomitant right cranial cruciate insufficiency. His pertinent history included a total of 5 attempted surgical procedures (New York State) for correction of patellar luxation between the two stifles -- all resulting in failure to stabilize the patella - with a more recent episode of non-weight bearing lameness to the right pelvic limb. There was no known trauma witnessed or suspected, and Brody's condition had not improved with rest and NSAID's. Plain film radiographs demonstrated mild-moderate bilateral stifle DJD and effusion with distinct and excessive femoral varus (bow-leggedness) of the left distal femur. Physical examination confirmed both medial patellar luxation, and cranial cruciate insufficiency.

Limb alignment radiographs of both femurs (figure 2) demonstrated normal physiologic varus of the right femur at 5 degrees and excessive varus of the left femur at 14 degrees. Some reports consider greater than 12 degrees as above the threshold of physiologic varus. However, practically as long at excessive varus angles are not accompanied by patellar luxation (some bulldogs can approach 20 degrees of varus without concomitant patellar luxation), few veterinary orthopedists will pursue definitive correction. An important exception to this rule would be the presence of cranial cruciate insufficiency -- which, in addition to a functional cruciate repair (TPLO, TTA) may additionally require correction of the femoral varus to properly overcome the abnormal forces occurring in these bowlegged stifles even in those without overt patellar luxation.

On Brody's right stifle, we elected to repair the acquired and congenital deficits in a conventional manner: open arthrotomy for cruciate ligament debridement, menical inspection - trochlear wedge recession, tibial tubercle transposition, medial release and lateral imbrication. Furthermore, the cranial cruciate ligament was addressed with a lateral fabellar suture through a tibial bone tunnel. Recovery from this procedure, in spite of some mild, sub-clinical recurrence of the patellar luxation, has been good. Once the recovery from the right stifle repair was fully rehabilitated, the patellar luxation on the contra-lateral left limb began to become symptomatic, and in an effort to reestablish quadriceps integrity, and in order to protect the cranial cruciate ligament from potential damage, a realignment procedure was elected.

In the case of Brody's left stifle, and especially given that multiple conventional attempts had been performed in order stabilize the patella, we recommended and performed a femoral realignment - or distal femoral corrective osteotomy (DFO). This involves an open arthrotomy and a combined medial and lateral approach to the distal femur, a lateral closing wedge osteotomy, and application of a specialized plate fixation (DFO plate). Essentially, this procedure results in a 'straighter' femur, or a more realigned quadriceps mechanism. In Brody's case, we elected to place one of our new Fixin (conical coupling) plates (figure 3), resulting in a correction to 5 degrees of varus (figure 4 & 5). In addition, a very proximal medial release, and lateral imbrications were performed, along with the more standard wedge recession and transposition of the tibial tubercle. All of these reconstructions resulted in satisfactory quadriceps alignment and function.

At this stage, Brody continues to rehabilitate well, and a near normal return to pre-injury activity and status is anticipated. Brody illustrates the complexity with which some more routine orthopedic conditions may present. We commonly see bilateral patellar luxation, and fairly regularly see patients with concomitant cranial cruciate insufficiency. However, Brody represents a situation in which both conditions were further exacerbated and worsened due to an excessive variation of normal physiologic varus. Additionally, rather than a Cockapoo, we would more commonly expect such excesses in varus with: Labrador retrievers, American pitbull terriers and other brachycephalic and bull-breeds. Although complex, Brody's condition appears to be well addressed with a combination of limb straightening and more conventional techniques to achieve patellar stability.

For consultation, and advice on these challenging orthopedic conditions, please do not hesitate to contact any of the surgeons of Veterinary Surgical Centers . We look forward to hearing from you.

John J. Haburjak, DVM Diplomate American College of Veterinary Surgeons

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