Patellar Dislocation

Patellar dislocation refers to displacement of the patella from the trochlear groove, almost always laterally. The first dislocation is typically traumatic, occurring in adolescents and young adults during sports involving cutting, pivoting, or jumping. The medial patellofemoral ligament (MPFL) is disrupted in 90-100% of cases, often at its femoral attachment.

Anatomic predisposing factors include trochlear dysplasia (most important), patella alta (high-riding patella), increased TT-TG distance (tibial tubercle-trochlear groove >20 mm indicates lateral malalignment), excessive femoral anteversion, genu valgum, and generalized ligamentous laxity. Recurrence rate after first dislocation ranges from 15-44%, with risk factors including young age (<14 years), trochlear dysplasia, contralateral instability, and inadequate rehabilitation.

Acute management focuses on reduction (often spontaneous), assessment for osteochondral fragments (occur in 5-50% of dislocations, requiring CT or MRI), and short-term immobilization. Non-operative treatment with brace and physical therapy is appropriate for first-time dislocators without large osteochondral fragments. Surgical indications include large displaced osteochondral fragments, recurrent dislocations (≥2), and high-risk anatomic factors. Surgical options include MPFL reconstruction (most common, with autograft hamstring or quadriceps tendon), trochleoplasty for severe trochlear dysplasia, tibial tubercle osteotomy (TTO) for patellar alta or increased TT-TG, and lateral release for tight lateral retinaculum (rarely indicated alone).