The effect of knee flexion and rotation on the tibial tuberosity-trochlear groove distance

The purpose was to measure the effect of flexion and additional rotation of the femur relative to the tibia on the tuberosity-trochlear groove distance (TT-TG) in the same subject in 20 cadaveric knees joint. In 20 human adult cadavers, formal fixed knees (age: 81.9 years, SD 12.3; 10 female) CT scans were performed in extension and 30A degrees of flexion as well as in neutral, maximal possible internal (IR), and external rotation (ER). On superimposed CT scan images, TT-TG was measured in each position. TT-TG measurements were correlated in all knee positions. TT-TG in full extension/neutral rotation was 7.8 mm (SD 3.4, range, 2.4-15.3). TT-TG in full extension and IR was significantly lower, and TT-TG in full extension and ER was significantly higher than in neutral rotation (5.4 +/- 2.3 vs. 10.9 +/- 4.8 mm; P < 0.001). IR and ER varied between 1.0A degrees-7.6A degrees and 0.2A degrees-9.2A degrees, respectively. TT-TG in 30A degrees flexion/neutral rotation was 3.9 mm (SD 1.8, range, 1.3-7.8), which was significantly lower than in full extension and neutral rotation (P < 0.001). TT-TG in 30A degrees flexion and IR was significantly lower, and TT-TG in 30A degrees flexion and ER was significantly higher than values obtained in neutral rotation (2.7 +/- 1.2 vs. 6.5 +/- 3.4 mm; P < 0.001). IR and ER in 30A degrees flexion varied between 0.6A degrees-10.7A degrees and 1.9A degrees-13.0A degrees, respectively. Flexion as well as rotation of the knee joint significantly alters the TT-TG. These results may have wider clinical relevance in assessing TT-TG and further decisions based on it.