Patella Dislocation

Aetiology

  • Can occur with a direct blow or sudden quadriceps contraction with a flexing knee
  • Most common in teenagers, higher incidence in females
  • Always dislocates laterally

Risk factors

  • Ligamentous laxity/hypermobility
  • Increased Q-angle - genu valgum, femoral neck anteversion
  • High riding patella
  • Hypoplastic lateral femoral condyle
  • Lateral quads insertions or weak vastus medialis

Clinical presentation

Symptoms

  • Clear history of patella dislocating laterally
  • Often self-relocating

Signs

  • Pain medially (from torn medial patella retinaculum tendon)
  • Effusion (haemarthrosis)
  • Patella apprehension test positive

Investigations

X-ray

  • Lipo‐haemarthrosis occurs with characteristic x-ray appearance
  • A small opacification may suggest osteochondral fracture

Management

  • May spontaneously reduce when the knee is straightened or rarely may require to be manually manipulated back into position (reduction with knee extension)
  • Aspiration (rarely) - if intractable pain and very swollen
  • Brace
  • Physiotherapy

Complications

  • When the patella dislocates, the medial patellofemoral ligament tears and osteochondral fracture may occur as the medial facet of the patella strikes the lateral femoral condyle
  • The risk of recurrent dislocation after first time dislocation is around 10%
    • Physiotherapy to strengthen the quadriceps may help
    • Patients with recurrent dislocaton may benefit from surgery - lateral release, MPFL reconstruction
    • The risk of recurrent instability decreases with age