Patellofemoral joint kinematics in individuals with and without patellofemoral pain syndrome.

BACKGROUND: Patellofemoral pain syndrome is a prevalent condition in young people. While it is widely believed that abnormal patellar tracking plays a role in the development of patellofemoral pain syndrome, this link has not been established. The purpose of this cross-sectional case-control study was to test the hypothesis that patterns of patellar spin, tilt, and lateral translation make it possible to distinguish individuals with patellofemoral pain syndrome and clinical evidence of patellar malalignment from those with patellofemoral pain syndrome and no clinical evidence of malalignment and from individuals with no knee problems. METHODS: Three-dimensional patellofemoral joint kinematics in one knee of each of sixty volunteers (twenty in each group described above) were assessed with use of a new, validated magnetic resonance imaging-based method. Static low-resolution scans of the loaded knee were acquired at five different angles of knee flexion (ranging between -4 degrees and 60 degrees). High-resolution geometric models of the patella, femur, and tibia and associated coordinate axes were registered to the bone positions on the low-resolution scans to determine the patellar motion as a function of knee flexion angle. Hierarchical modeling was used to identify group differences in patterns of patellar spin, tilt, and lateral translation. RESULTS: No differences in the overall pattern of patellar motion were observed among groups (p>0.08 for all global maximum likelihood ratio tests). Features of patellar spin and tilt patterns varied greatly between subjects across all three groups, and no significant group differences were detected. At 19 degrees of knee flexion, the patellae in the group with patellofemoral pain and clinical evidence of malalignment were positioned an average of 2.25 mm more laterally than the patellae in the control group, and this difference was marginally significant (p=0.049). Other features of the pattern of lateral translation did not differ, and large overlaps in values were observed across all groups. CONCLUSIONS: It cannot be determined from our cross-sectional study whether the more lateral position of the patella in the group with clinical evidence of malalignment preceded or followed the onset of symptoms. It is clear from the data that an individual with patellofemoral pain syndrome cannot be distinguished from a control subject by examining patterns of spin, tilt, or lateral translation of the patella, even when clinical evidence of mechanical abnormality was observed.