Pressure and contract-surface measurements within the femoropatellar joint and their variations following lateral release.

The Pressure Measurement Foil (PMF), of Prescale, developed by the Fuji company permits the determination of the contact surfaces and of the pressure pattern within the femoropatellar joint. We measured contact surfaces and pressure distribution between patella and femoral condyles at different degrees of knee joint flexion before and after a lateral release. At a external load of 1000 N, only 12% of patellar surfaces established contact in extension, which was increased to 25% on flexion of 120 degrees. Superimposition of all function-related contacts showed that contact was established with the entire patellar surface. With increasing degree of flexion the mean pressures across the pressure zones showed only minor variations, owing to the flexion- dependent enlargement of the contact surfaces. Lateral release does not influence articular mechanics; it was at least not possible to change the retropatellar pressure to any measurement extent by releasing the lateral patellar connection.