Assessment of patellar maltracking using combined static and dynamic MRI

Between January 1995 and Jul 1997, 474 patients with anterior knee pain resistant to conservative treatment were referred for MR of the knee. The MR examination consisted of routine sequences with an additional patellofemoral dynamic examination using a technique that has been developed at this institution. The dynamic study examines both knees simultaneously, with the patient supine and the quadriceps loaded. No gating or restraint apparatus is needed. Patellar subluxation or tilt was present in 188(40%) of cases, bilateral in 104 and unilateral in 84 cases (right 39, left 45). It was classified as mild in 51%, moderate in 39% and severe in 10%. Subluxation was more prevalent in females than males (42% vs. 37%) and this was most obvious in the severe group where 68% were female. In 90 knees selected at random, four measurements of patellofemoral morphology were obtained using reconstructed images from a volume gradient echo sequence. These measurements were correlated with the degree of subluxation or tilt. A tibial tubercle distance greater than 20 mm, a femoral sulcus angle greater than 150 degrees, sulcus depth less than 4 mm were specific for subluxation but no measurement proved to be sufficiently sensitive to preclude a tracking study. MRI can be used to define more precisely the anatomy of the extensor mechanism and its relationship to the femur and tibia, in both a static and dynamic setting. In this way, patients with anterior knee pain can be classified more accurately and the outcomes of treatment more reliably assessed.