BACKGROUND: Patella alta is the proximal displacement of the patella within the femoral trochlea. Previous studies have identified an association between patella alta and patella luxation. Distalisation of the tibial tuberosity has been recommended to establish proximodistal alignment of the stifle extensor mechanism with the underlying femur in dogs affected by patella alta. However, a recent canine ex vivo study found stifle extensor mechanism load increased significantly following tibial tuberosity distalisation. Generation of excessive load within the stifle extensor mechanism was avoidable by performing a combined transverse femoral ostectomy and tibial tuberosity distalisation.
CASE REPORT: Two dogs presented with acute onset left hindlimb lameness and medial patella luxation. The left patellar ligament length to patella length ratio was 2.37 and 2.39 in each dog (reference range 1.33-2.06), consistent with patella alta. No other stifle abnormalities were identified. Proximodistal stifle extensor mechanism alignment was corrected with a combined transverse femoral ostectomy and tibial tuberosity distalisation. The postoperative ratio of the distance between the proximal pole of the patella and femoral condyle to patella length ratio (A : P) fell within the corrected reference range (1.52-2.44). Follow-up orthopaedic examination and postoperative radiographs at 10-12 weeks demonstrated clinical bone union of the femoral ostectomy and tibial tuberosity distalisation sites. No evidence of medial patella luxation or lameness could be detected.
CONCLUSION: A combined transverse femoral ostectomy and tibial tuberosity distalisation technique resolved medial patella luxation with patella alta in two dogs. Additionally, the normal A : P reference interval should be corrected to 1.52-2.44.