Functional assessment of outcome of surgery to correct patellofemoral instability in human patients

A case-control study with 6 months of patient follow up. This study sought to determine if surgery followed by rehabilitation for patellar instability could restore normal gait function. A previous study has established abnormalities in gait pattern and joint congruence in patients with a history of patellar instability. We hypothesised that surgery for patellofemoral instability would improve knee function. Eight human patients (mean age 29, range 17-42) who were awaiting patella stabilisation surgery (5 tibial tuberosity osteotomy, 2 medial patellofemoral ligament reconstruction, 1 trochleoplasty) were compared against eight normal Controls (mean age 28, range 19-31). Patients were assessed pre-operatively and six months after surgery by biomechanical gait analysis. Gait trials involved simultaneous collection of kinematic and force data. Patients were grouped into two subgroups pre-operatively based on knee joint net moment during stance, and their joint moments during stance pre- and post-operatively were compared against the Control subjects. In pre-operative gait analysis, four patients (P1) produced some extensor moment in early stance and four (P2) demonstrated a severe gait deficiency with failure to generate a knee extensor moment during stance. Normalisation in gait pattern was observed in all patients post-operatively. Those who had the most severe gait abnormality (P2) demonstrated the most improvement in their knee joint moments. Improvements were observed in the milder (P1) cases, but these were less dramatic. Patella stabilisation by surgery can restore normal gait function. Normalising the anatomy of the knee extensor mechanism is the objective of surgery. Normal anatomy facilitates the rehabilitation objectives of optimising extensor function during the weight-bearing phase of gait.