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 30° 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 1.0°–7.6° and 0.2°–9.2°, respectively. TT–TG in 30° 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 30° flexion and IR was significantly lower, and TT–TG in 30° 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 30° flexion varied between 0.6°–10.7° and 1.9°–13.0°, 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.