Knee joint anterior malalignment and patellofemoral osteoarthritis: an MRI study

Objectives To evaluate patellofemoral congruency measurements on MRI and correlate the findings with severity of ipsilateral osteoarthritis. Methods We retrospectively reviewed 650 consecutive knee MRI examinations from 622 patients divided into two age groups: a parts per thousand currency sign50 and > 50 year-old. The femoral sulcus angle (SA) and depth (SD), lateral patellar displacement (LPD), lateral patellofemoral angle (LPFA), tibial tubercle-trochlear groove (TT-TG) distance and Insall-Salvati index as well as the grade of focal cartilage defects (ranging from I to IV) in the patellofemoral region were assessed in each subject on axial and sagittal fat-saturated intermediate-w MR images. Results A significant difference exists between normal and knees with patellofemoral joint osteoarthritis regarding SA (p = 0.0002 and < 0.0001), SD (p = 0.0004 and < 0.0001), LPD (p = 0.0014 and 0.0009) and LPFA (p = 0.0002 and 0.0003) in both age groups (a parts per thousand currency sign50 and > 50 respectively). Significant correlation was found between grading of cartilage defects and SA (rho = 0.21, p = 0.0001 and 0.443, < 0.0001), SD (rho = -0.198, p = 0.0003 and -0.418, < 0.0001), LPD (rho = 0.176, p = 0.0013 and 0.251, 0.0002) and LPFA (rho = -0.204, p = 0.0002 and -0.239, 0.0005) in both age groups. Conclusions Knee joint anterior malalignment is multivariably associated with patellofemoral osteoarthritis. Key Points MRI is an excellent method to evaluate knee alignment and articular cartilage damage. Significant associations exist between alignment parameters and osteoarthritis of the patellofemoral joint. The "sulcus angle" and "sulcus depth" were the most valuable osteoarthritic markers.