Consistency of patellar spin, tilt and lateral translation side-to-side and over a 1 year period in healthy young males.

The purpose of this study was to determine the consistency and symmetry of in vivo measures of patellar spin, tilt, and medial/lateral translation in healthy knees. Patellofemoral joint kinematics were measured bilaterally through a range of loaded knee flexion in 10 active males (aged 19.0 (0.57) years) at baseline, 6, and 12 months using a validated magnetic resonance imaging method. Effects due to time and limb were determined using ANOVA. Variation over 12 months and from side-to-side was summarized as the average of the mean absolute deviations of the measures at 1 degrees increments of knee flexion for corresponding loading cycles for each knee. The measures did not differ over time (p>0.52) or side-to-side (p>0.17). The mean intrasubject variability over the three time points was < or = 1.17 (0.3) degrees for spin and tilt and < or = 0.83 (0.61) mm for lateral translation. The mean intrasubject variability between limbs was 2.14 (1.29) degrees for spin, 0.46 (1.96) degrees for tilt and 1.29 (1.28)mm for lateral translation. The consistency of measures of normal patellar motion over a 1 year period supports application of this methodology to evaluate changes in patellar motion in longitudinal studies involving patient populations.