Using magnetic resonance imaging (MRI) as an aid to better define the center of patella and tibial tubercle in determining quadriceps angles

Background: A full-length standing scanogram (FLSS) can be difficult to measure a quadriceps angle (Q-angle). The trochlear groove (TG) and tibial tubercle (TT) normally cannot be inspected. Purpose: The purpose of this retrospective study was to use magnetic resonance imaging (MRI) of knees to aid in accurately defining the TG and TT on FLSS radiographs. Methods: Sixty consecutive adult patients (29 men and 31 women; average, 46 years) took knee MRI for ligament or meniscus injury. A standardized patellar center was defined as the deepest point of the TG on a transverse MRI film along the femur trans-epicondylar line (TEL). The distance from this point to the lateral femoral cortex and the TEL were measured. The TT was chosen at the insertion of patellar tendon (the lowest margin) revealed on a transverse MRI film. Then, the distance from the TT to the lateral tibial cortex and the tibial diameter at this level were measured. Results: The standardized patellar center was at a point 42% from the lateral end of the femur TEL. The TT was 2 cm distal to the articular surface, and 37% from the lateral end of the tibial diameter. There was no statistical significance between men and women for the location of the TG and TT (p ＞ 0.05). However, men had more distal insertion of the TT (22.2 mm vs. 19.6 mm, p ＜ 0.001). Conclusion: A Q-angle may be more accurately defined on a FLSS by using MRI to aid localizing the TG and TT.