Epidemiology
- Peak incidence in adolescence
- Lateral dislocation in almost all cases
Aetiology
- Twisting injury on a planted foot with valgus and external rotation
- Risk factors include trochlear dysplasia, patella alta, raised TT-TG and ligamentous laxity
Anatomy
- MPFL is the main restraint to lateral translation in early flexion
- MPFL femoral attachment lies close to the distal femoral physis
Clinical Features
- Spontaneous reduction is frequent
- Haemarthrosis and medial retinacular tenderness
- Positive apprehension test
Investigations
- AP, lateral and skyline radiographs
- Scrutinise for osteochondral fracture
- MRI for chondral injury and MPFL tear
- Measure TT-TG, patellar height and trochlear dysplasia (Dejour)
Management
- Closed reduction by knee extension
- Short period of brace immobilisation followed by early physiotherapy
- High redislocation rate, especially in younger patients
- Arthroscopic or open fixation of large osteochondral fragments
- Removal of small loose fragments
- MPFL reconstruction for recurrent instability, with physeal sparing technique in skeletally immature patients
- Guided growth or tibial tubercle procedures are avoided before physeal closure
Complications
- Recurrent dislocation
- Patellofemoral arthritis
- Stiffness after prolonged immobilisation
- Femoral physeal injury from MPFL tunnels
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.