Canine medial patellar luxation - Review

Authors: 
K. L. Perry L. M. Déjardin
J Small Anim Pract. 2021 Feb 18. doi: 10.1111/jsap.13311.

Despite being one of the most commonly diagnosed causes of canine hind limb lameness, the pathogenesis of medial patellar luxation remains incompletely understood. Most cases are considered developmental with anatomical deformities leading to failure of the stifle extensor mechanism. These include coxa vara, coxa valga, reduced anteversion angle, distal external femoral torsion, excessive distal femoral varus, internal proximal tibial torsion, proximal tibial valgus, tibial tuberosity medialisation, patella alta and shallow trochlear groove. The diagnosis of medial patellar luxation is generally easily made during an orthopaedic examination, however, assessment of the associated limb deformities can be challenging.

While radiography remains the most common method for assessment of limb deformity in dogs, accurate characterisation of three‐dimensional structures from two‐dimensional radiographs is limited, particularly for tibial deformities. CT is advantageous in facilitating the precise qualification and quantification of skeletal abnormalities contributing to the luxation. This is critical in planning correction of said deformities and in achieving accurate realignment of the quadriceps mechanism.

Dogs presenting with lameness secondary to medial patellar luxation are candidates for surgical intervention. Techniques used to realign the extensor mechanism and improve patellofemoral articulation congruity include femoral trochleoplasty, tibial tuberosity transposition laterally and/or distally, corrective osteotomies of the femur and tibia and soft tissue balancing techniques. Every case should be carefully evaluated to identity all abnormalities and develop a comprehensive plan that addresses each of them.

Complication rates following medial patellar luxation surgery vary extensively but can be reduced following accurate measurement of conformational deformities and subsequent tailored corrective surgery.