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Patellofemoral Contact Area and Pressure after Medial Patellofemoral Ligament Reconstruction

Background It is not known whether nonisometric femoral graft attachment diminishes the effectiveness of medial patellofemoral ligament reconstruction. Purpose To determine whether a nonisometric femoral attachment point is associated with differences in contact area and pressure in the patellofemoral joint as compared with an isometric attachment point. Study Design Controlled laboratory study. Methods Eleven cadaveric knees were amputated and secured in a loading fixture. The quadriceps tendon was clamped 5 cm above the proximal pole of the patella and fixed to a plate. Colinear compressive forces were applied. Forces were set to achieve isometric quadriceps moments at 30°, 45°, 60°, and 90° of knee flexion. Contact areas and pressures were measured using a sensor system. Initially, isometric reconstruction was done using the known isometric femoral attachment point of the posterior medial epicondyle. The attachment was then revised in each specimen to the known nonisometric femoral attachment of the adductor tubercle. Results Before medial patellofemoral ligament reconstruction, average facet patellofemoral contact area and pressure generally increased with angle of knee flexion. With few exceptions, initial versus postprocedure data and isometric versus nonisometric contact area and pressure data did not differ significantly at any angle tested. Percentage contact area and contact pressure in the medial facet did not differ significantly from the initial percentage for either attachment, and no difference was found in the percentage medial contact area or pressure for isometric versus nonisometric attachment at the angles tested. Conclusion Use of the nonisometric attachment point of the adductor tubercle in medial patellofemoral ligament reconstruction did not appear to alter knee contact area or contact pressures as compared with isometric femoral attachment at the posterior medial epicondyle. Clinical Relevance In medial patellofemoral ligament reconstruction, patellofemoral contact area and pressure may not be adversely affected by use of the nonisometric femoral attachment point used in this study.