Patellofemoral joint pain is one of the most common pathologies observed in orthopedic clinics. It is widely held that abnormal joint mechanics play a causative role in the development of anterior knee pain and that chronic patellofemoral joint pain may lead to cartilage degeneration, arthritis and permanent disability . However, the relationship between joint kinematics and clinical symptoms remains unclear. We applied a new magnetic resonance imaging (MRI)-based method to assess three-dimensional patellar tracking during loaded knee flexion to determine whether anterior knee pain is associated with abnormal joint kinematics.
The symptomatic and matched knees of 60 subjects (20 cases with anterior knee pain and clinical evidence of patellar malalignment; 20 cases with anterior knee pain and no clinical evidence of patellar malalignment, and 20 controls matched for age, gender and physical activity level) were imaged through a range of loaded knee flexion using a validated MRI-based method . Using this novel evaluation tool, the motion of the patella relative to the femur was determined as a function of knee flexion angle. Group values through a common range of knee flexion were compared using analysis of variance.
In the control group, the normal pattern of patellar motion is increasing medial rotation, tilt and shift as the patella approaches the trochlear groove during loaded knee flexion (from 19° to 28°). In the group with pain and clinical signs of malalignment, the patella is translated 2.6 mm more laterally and rotated 1.3° more medially (P < 0.001). Statistically, differences in patellar kinematics are observed between the control group and the group with pain and no clinical evidence of malalignment; however, the magnitude of the differences are all within the range of the accuracy and repeatability of the technique with the exception of the decreased distance between the patella and femur (P < 0.001).
This MRI-based method detects a normal pattern of patellar kinematics that is consistent with previous reports  and detects abnormal kinematics in subgroups of individuals with anterior knee pain. In the cases with pain and clinical evidence of patellar malalignment, the increased lateral shift and medial rotation is consistent with weakness of the vastus medialis oblique muscle, which has been linked with patellofemoral joint pain previously. Our results do not support the notion that increased lateral tilt is associated with patellofemoral joint pain. In the cases with pain and no clinical evidence of patellar malalignment, the closer positioning of the patella relative to the femur may reflect a decrease in cartilage thickness. Of note is that in most cases the pattern of patellar motion was similar to that for the controls. Longitudinal studies using this novel MRI-based method will aid in determining the link between knee pain and joint mechanics.
Supported by grants from Canadian Institutes of Health Research (CIHR), NSERC, and Physiotherapy Foundation of Canada. Salary support was awarded by The Arthritis Society/CIHR (Research Fellowship, NJM) and the Canadian Arthritis Network (DRW).
J Bone Joint Surg Am 1982, 64:147-152. PubMed Abstract