Patellar motion analyzed by kinematic and dynamic axial magnetic resonance imaging in patients with anterior knee pain syndrome.

Ten consecutive patients (12 knees), all women, with anterior knee pain syndrome participated in the study. The patellofemoral joints were examined with the knee in 0 degrees, 10 degrees, 20 degrees, and 30 degrees of flexion. At each knee position, kinematic and dynamic, an axial magnetic resonance (MR) image was used to focus on the sagittal plane, followed by an axial image focused through the middle of the patella. Ten healthy volunteers (20 knees) with no history of previous or current knee problems or anterior knee pain also underwent MRI scanning following the same procedure. Three angles were measured: patellar tilt angle (PTA), sulcus angle (SA), and congruence angle (CA). For statistical analyses, we used the Mann-Whitney U-test. Compared with the control knees, five patterns of malalignment were identified. The most frequently observed was tilt and lateralisation, with elevated CA and decreased PTA. In extension, the average CA for this group was 22 degrees and PTA -4.8 degrees vs -8.1 degrees and 14.3 degrees for control knees respectively. Contraction of the muscles caused tilt of the patella in symptomatic knees. This decrease of the PTA was statistically significant in extension (P < 0.05) and in 10 degrees of flexion (P < 0.05). Contraction of the thigh muscle increased CA in 30 degrees of flexion. This lateral pull was statistically significant (P < 0.05). There were no statistically significant differences of SA between the groups, regardless of muscle contraction or flexion angle. At 30 degrees of flexion, muscle contraction increased CA and decreased PTA. In our opinion, imaging in the first 30 degrees of flexion with thigh muscle contraction is necessary for a correct diagnosis.