Bilateral distal femoral trochlear block migration after medial patellar luxation surgery in a dog.

The objective of this study was to describe management of a 2-year-old neutered male mixed breed dog with bilateral trochlear block recession migration with unilateral revision surgery. This is a rarely reported complication of a common surgical procedure. A 3D model segmented from a computed tomography scan using Mimics was performed before surgery to help determine whether surgical reduction of the osteochondral trochlear block fragments was feasible and preoperative press fit was acceptable. Subsequently, the trochlear block fragment in the left stifle was surgically reduced. During surgery, the osteochondral fragment was maintained in reduction with a transcondylar Kirschner wire because of imperfect press fit. The right stifle with trochlear block migration was treated medically. Short-term follow-up examination at 5 and 8 weeks revealed improvement in lameness after surgery. 3D modeling was also used to investigate potential underlying causes for bilateral block recession migration which was determined to be multi-factorial with excessive sulcoplasty depth being an important reason promoting risk of migration. During planning for femoral trochlear block recession sulcoplasty, it is important for the cut to be deep enough to help minimize risk of reluxation of the patella. However, press-fit of the osteochondral fragment is impaired when the depth of the recession sulcoplasty is excessive.