Mechanism
- lateral displacement of patella after contraction of quadriceps against a flexed knee
Risk Factors
- young, female
- obesity
- high-riding patella (patella alta)
- knock-knees (genu valgum)
- Q-angle (quadriceps angle) increased
- shallow intercondylar groove
- weak vastus medialis
- tight lateral retinaculum
Clinical Features
- knee catches or gives way with walking
- severe pain, tenderness anteromedially from rupture of capsule
- weak knee extension or inability to extend leg unless patella reduced
- +ve patellar apprehension test
- patient apprehensive when examiner laterally displaces patella
- often recurrent, self-reducing
Investigations
- x-rays: AP, lateral, skyline view of patella
- check for fracture of medial patella and lateral femoral condyle
Treatment
- non-operative first
- knee immobilization x 4-6 weeks (Zimmer Splint)
- progressive weight bearing and isometric quadriceps strengthening
- if recurrent
- surgical tightening of medial capsule and release of lateral retinaculum
