Assessment of patellar maltracking using combined static and dynamic MRI

Between January 1995 and Jul 1997, 474 patients with anterior knee pain res istant to conservative treatment were referred for MR of the knee. The MR e xamination consisted of routine sequences with an additional patellofemoral dynamic examination using a technique that has been developed at instituti on. The dynamic study examines both knees simultaneously, with the patient supine and the quadriceps loaded. No gating or restraint apparatus needed. Patellar subluxation or tilt was present in 188(40%) of cases, bilateral in 104 and unilateral 84 cases (right 39, left 45). It was classified as mild 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 gr oup where 68% were female. In 90 knees seat random, four measurements of pa tellofemoral morphology were obtained using reconstructed images from a vol ume gradient echo sequence. These measurements were correlated with the deg ree 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 m m were specific for sublaxation but no measurement proved to be sufficientl y sensitive to preclude a tracking study. MRI can be used to define more pr ecisely the anatomy of the extensor mechanism and its relationship to the f emur 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.