We analyzed the mechanism of patellofemoral joint instability, using new parameters by Computed Tomography. Knees with PFJI consisted of four knees with recurrent patellar dislocation and eight knees with patellar subluxation. Twenty seven normal knees were also evaluated. A CT scan was taken at the level of the femoral epicondyle, the tibial tuberosity and the ankle joint both in full extension and at 30° of flexion. The tibial tuberosity in knees with PFJI was significantly positioned laterally compared with that in normal knees in full extension. At 30° of flexion, it was positioned in the normal range. When recurrent patellar dislocation and patellar subluxation were compared, tibial tuberosity in knees with recurrent patellar dislocation was significantly positioned laterally compared with patellar subluxation.
A CT scanning at two different angles should be performed to evaluate patellofemoral joint instability.
