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

Abstract

Objective: To demonstrate the effect of the screw-home motion on the stability of the patellofemoral joint, and investigate its mechanism of regulation of patellar tracking.

Methods: Twenty volunteers who met the criteria were examined. All subjects had axial computed tomography (CT) scanning performed on bilateral knees at 0° and 30° 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 (Δ) 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° and those measured at 30° 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 ΔTT-TG distance and ΔLPD, ΔPTA and ΔTRRF, and ΔCA and ΔTRRF.

Results: There were 10 women and 10 men enrolled in the present study, with an average age of 25 years and an average body mass index of 21.8 kg/m² , and all volunteers had no history of knee injuries. Compared with measurements taken at 0° flexion, TRRF at 30° 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° and 30° flexion, respectively (P < 0.01). In this respect, there was no sex difference, but the change was greater for men than for women. Both ΔPTA and ΔCA demonstrated significant correlation with the ΔTRRF (both P < 0.01); a significant correlation between ΔLPD and ΔTT-TG distance was also demonstrated (P < 0.01).

Conclusions: As 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.

Keywords: Kinematics; Patellar tracking; Patellofemoral joint; Tibiofemoral joint; “Screw-home” mechanism.

Figure 1

Measurement of tibia tuberosity‐trochlear groove (TT–TG) distance and tibial rotation relative to the femur (TRRF). (A) TT–TG distance: the distance between the axial section depicting the deepest part of the trochlear groove (a) and the center of the tibial tuberosity (b), while ensuring that the measurement was parallel to the posterior condylar axis of the femur; (B) TRRF on axial computed tomography scan: the angle (α) between the line (c) drawn through the posterior border of the proximal tibia and the line (d) drawn through the two most posterior points of the posterior femoral condyles. F, femur; T, tibia.

Figure 2

Measurement of patellar tilt angle (PTA) and congruence angle (CA). (A) PTA, the angle (β) between the line intersecting the widest part of the patella (a) and the line tangential to the anterior surfaces of the femoral condyles (b); (B) CA, the angle (γ) between the line bisecting the sulcus angle (c) and the line connecting the apex of the sulcus to the lowest aspect of the patella ridge (d).

Figure 3

Measurement of lateral patella displacement (LPD). Line a connects the lateral and medial femoral anterior condyles. Line c is perpendicular to line a through the peak of femoral condyle, and line b is parallel with line a through medial edge of the patella, and LPD is defined as the distance from b to c.

Figure 4

Bar chart illustrates the angle of tibial rotation relative to the femur (TRRF) at 0° and 30° flexion between men and women.

Figure 5

Bar chart illustrates the patellar tilt angle (PTA) at 0° and 30° flexion between men and women.

Figure 6

Bar chart illustrates the congruence angle (CA) at 0° and 30° flexion between men and women.

Figure 7

Bar chart illustrates the distance of tibia tuberosity–trochlear groove (TT–TG) at 0° and 30° flexion between men and women.

Figure 8

Bar chart illustrates the lateral patella displacement (LPD) at 0° and 30° flexion between men and women.