Relationship between Patellar Tracking and the Screw-home Mechanism of Tibiofemoral Joint

ObjectiveTo demonstrate the effect of the screw-home motion on the stability of the patellofemoral joint, and investigate its mechanism of regulation of patellar tracking. MethodsTwenty volunteers who met the criteria were examined. All subjects had axial computed tomography (CT) scanning performed on bilateral knees at 0 degrees and 30 degrees of flexion. Scanning began above the femorotibial articulation and femoral trochlear groove, and moved sequentially down to the level of the anterior tibial tubercle. The following measurements were obtained: tibial rotation relative to the femur (TRRF), tibial tuberosity-trochlear groove (TT-TG) distance, lateral patellar displacement (LPD), patellar tilt angle (PTA), and congruence angle (CA). We assessed the change (Delta) in each variable at both flexion angles, and analyzed this to investigate the corresponding relationship between the patella, the femur, and the screw-home mechanism. The differences between the values measured at 0 degrees and those measured at 30 degrees flexion were analyzed using the paired sample t-test. The differences between men and women were analyzed using the t-test. Pearson's correlations were performed to determine the relationship between Delta TT-TG distance and Delta LPD, Delta PTA and Delta TRRF, and Delta CA and Delta TRRF. ResultsThere were 10 women and 10 men enrolled in the present study, with an average age of 25years and an average body mass index of 21.8kg/m(2), and all volunteers had no history of knee injuries. Compared with measurements taken at 0 degrees flexion, TRRF at 30 degrees flexion was significantly increased, and the PTA, CA, LPD, and TT-TG distance were significantly decreased (all P < 0.01). There was no difference between men and women at 0 degrees and 30 degrees flexion, respectively (P < 0.01). In this respect, there was no sex difference, but the change was greater for men than for women. Both Delta PTA and Delta CA demonstrated significant correlation with the TRRF (both P < 0.01); a significant correlation between Delta LPD and Delta TT-TG distance was also demonstrated (P < 0.01). ConclusionsAs the tibiofemoral joint rotated, the patellofemoral joint became more stable and aligned, which indicates that the screw-home mechanism plays an important role in regulating patellofemoral joint alignment.