Correlation of the tibial tuberosity–trochlear groove distance with the Q-angle

Purpose The Q-angle has been used for years to quantify lateralization of the patella. The tibial tuberosity–trochlea groove distance (TT–TG distance) was introduced to analyse patellar tracking. Does a significant correlation exist between these two parameters? Do other significant interrelations exist between the Q-angle/TT–TG distance, torsion of the femur and tibia, the frontal axis, overall leg length, gender, former patellar dislocation, BMI? Methods One hundred knees in 55 patients with patellofemoral symptoms were included in a prospective study. All patients underwent clinical examination, including measurement of the Q-angle. A torsional CT was obtained from all patients. Results The correlation coefficient was 0.33/0.34 (left/right leg), showing that the TT–TG distance tends to rise in direct ratio to a rising Q-angle. Thus, a significant correlation was found ( p = 0.017). Femoral and tibial torsion had a positive effect on the TT–TG distance, but showed no significant correlation. Leg length had a significant effect on the TT–TG distance ( p = 0.04). The frontal axis had a nonsignificant influence on the Q-angle or TT–TG distance. On average, the Q-angle in women was 2.38° greater than it was in men, but the difference was not significant. Conclusion A significant correlation was noted between the Q-angle and the TT–TG distance. Both depend on various parameters and must be assessed for the analysis of patellofemoral maltracking. The Q-angle did not differ significantly between men and women; thus, the conclusion is that no different ranges need not be used. Level of evidence Diagnostic study, Level III.