Patellar Dislocations: Does Knee Flexion Affect the TT–TG Distance?

Patellar dislocations are not only painful but also significantly impact physical function and quality of life. A key factor in assessing the risk of recurrence is the tibial tuberosity–trochlear groove (TT–TG) distance: higher values are linked to patellofemoral instability and may indicate the need for surgical procedures such as tibial tubercle medialization.

Originally measured on X-rays and later on CT scans (≥20 mm considered pathological), TT–TG is now often assessed using MRI during routine knee evaluations. However, current guidelines recommend whole-leg rotational imaging to detect femoral or tibial deformities, which can increase costs and patient burden.

This study investigated whether knee flexion affects TT–TG measurements, comparing conventional knee MRIs taken at 20°–30° of flexion with whole-leg rotational MRIs acquired near full extension. Findings confirmed the hypothesis: measurements obtained in near-extension were significantly higher, highlighting the importance of accurate patellofemoral alignment assessment to prevent recurrence and optimize surgical planning.

In short: Knee flexion can substantially alter TT–TG readings, and overlooking it may underestimate the risk of patellar instability.