*3.3.9 Tibial Tuberosity-Trochlear Groove (TT-TG) Distance*

Computed Tomography scan can help in identifying lateralization of the tibial tuberosity, as measured by the TT-TG distance. An axial CT image demonstrating the femoral trochlear groove is superimposed on an axial image of the tibial tuberosity. A line is drawn on this superimposed image along the posterior margins of the femoral condyles. Two lines are then drawn perpendicular to this line, one bisecting the femoral trochlear groove and the other bisecting the anterior aspect of the tibial tuberosity. The distance between these two lines determines the extent of lateralization of the tibial tuberosity. A normal TT-TG distance is around 9 mm. A TT-TG distance >20 mm is considered abnormal. Values greater than 9 mm have been shown to identify patients with patellofemoral malalignment with a sensitivity of 85% and specificity of 95% [71].
