The effect on patellofemoral joint stability of selective cutting of lateral retinacular and capsular structures

Patient selection for lateral retinacular release (LRR) and its efficacy are controversial. Iatrogenic medial subluxation can occur with inappropriate LRR. The aim of this study was to determine the reduction in patellofemoral stability with progressively more extensive LRR. The force required to displace the patella 10mm medially and laterally in nine cadaveric knees was measured with and without loading of the quadriceps and iliotibial band. The knee was tested intact, then after progressive release beginning proximal to the patella (PR), the mid-level between the proximal and distal limit of the patella (MR) where the fibres are more transverse, then distally till Gerdy's tubercle (DR) and finally the joint capsule (CR). Both medial and lateral stability decreased with progressive releases, larger for the medial. The MR caused a significant reduction of lateral stability between 30 degrees and 90 degrees of knee flexion. There was an 8% reduction in medial stability at 0 degrees flexion with a complete LRR (DR). A comparable reduction in medial stability in the loaded knee at 20 degrees and 30 degrees flexion was obtained with MR alone, with no further reduction after DR. A capsular release caused a further reduction in medial stability at 0 degrees and 20 degrees and this was marked in the unloaded knee. In extension, the main lateral restraint was the joint capsule. At 30 degrees flexion, the transverse fibres were the main contributor to the lateral restraint.