Technical Errors during Medial Patellofemoral Ligament Reconstruction Could Overload Medial Patellofemoral Cartilage

BACKGROUND: The influence of reconstruction of the medial patellofemoral ligament on the patellofemoral force and pressure distributions has not yet been investigated. HYPOTHESIS: Technical errors can cause tension to develop within a reconstructed medial patellofemoral ligament, which will adversely alter the normal patellofemoral force distribution by increasing the load applied to the medial cartilage. STUDY DESIGN: Controlled laboratory study. METHODS: Four computational knee models were used to simulate knee function from 30 degrees to 90 degrees of flexion with (1) an intact medial patellofemoral ligament, (2) an anatomically correct reconstruction using a double hamstring tendon autograft, (3) a 5-mm proximally malpositioned femoral attachment site, (4) a graft that is 3 mm shorter than the intact medial patellofemoral ligament, and (5) combined proximal malpositioning and a short graft. RESULTS: The results were similar for the intact and anatomically reconstructed medial patellofemoral ligament. Proximal malpositioning of the femoral attachment and using a short graft increased the graft tension during flexion, which decreased the lateral force and the lateral tilt moment acting on the patella. When a short graft was combined with proximal malpositioning, the compressive force applied to the medial cartilage at least doubled at low flexion angles, which increased the peak medial pressure by more than 50% at low flexion angles. CONCLUSION: When the medial patellofemoral ligament is reconstructed, small errors in graft length and position can dramatically increase the force and pressure applied to medial patellofemoral cartilage. CLINICAL RELEVANCE: Overloading the medial cartilage after medial patellofemoral ligament reconstruction could lead to degradation, pain, and arthrosis.