Influence of knee flexion angle and weight bearing on the Tibial Tuberosity‐Trochlear Groove (TTTG) distance for evaluation of patellofemoral alignment

PURPOSE: The aim of the present study was to investigate the influence of knee flexion and weight bearing on the Tibial Tuberosity-Trochlear Groove (TTTG) distance. MATERIALS AND METHODS: Magnetic resonance imaging of the knee was carried out in 8 healthy volunteers. An open 0.25 T scanner equipped with a C-shaped permanent tilting magnet allowing examinations in weight-bearing conditions was used for the present investigation. A 3D gradient-echo sequence with axial slice orientation was obtained in a lying and an upright position with the knee straight and at 30° of knee flexion. The medial, central and lateral trochlear heights as well as the TTTG were determined. RESULTS: The mean medial trochlear height was 76.2 ± 4%, the central trochlear height was 72.2 ± 3%, and lateral trochlear height was 82.9 ± 3 %. The mean TTTG distance was 11.6 ± 4.4 mm in lying position at 0° knee flexion and 7.3 ± 2.9 mm (n.s.) at 30° knee flexion. Under weight bearing, the mean TTTG was significantly smaller at both 0° knee flexion 6.3 ± 3.2 mm (p = 0.040) and 30° knee flexion 4.9 ± 3.9 mm (p = 0.006) compared to the lying position with 0° knee flexion. CONCLUSION: Tibial Tuberosity-Trochlear Groove distance depends on both knee flexion angle and weight bearing. The latter only seems to be of relevance in full extension.