Editorial Commentary: The entry point-trochlear groove (EP-TG) angle measures lateralization of the proximal trochlear entry point in patients with patellar instability.

Patellar instability is a complex orthopedic condition, occurring at an incidence of 23.2 per 100,000 person-years, and resulting from a combination of osseous and soft tissue factors. Osseous abnormalities associated with patellar instability include trochlear dysplasia and a lateralized tibial tubercle. Evaluation of these factors includes dysplasia evaluation using the DeJour classification, and the tibial-tubercle-to-trochlear-groove distance (TT-TG) to evaluate relative lateralization of the tibial tubercle. Three-dimensional modeling has advanced the evaluation of complex trochlea geometry and patellar tracking. Evaluation of the TT-TG distance through flexion, dubbed the radial TT-TG (rTT-TG) distance, shows rTT-TG distances are notably larger than traditional TT-TG measurements, with increasing grade of dysplasia associated with a more pronounced difference between measurements. The entry point-trochlear groove (EP-TG) angle may help more accurately describe the morphology of the proximal trochlea and aid in planning or assessing osseous correction with a trochleoplasty. The EP-TG angle may also be of use as a variable to determine when an isolated medial patellofemoral ligament reconstruction (MPFLR) may fail and require osseous correction. A lateralized proximal trochlea entry point is associated with recurrent patellar instability.