Harvey's Garden

Patellar dislocation

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2 min read

Epidemiology & Risk Factors

  • Demographics: Young athletes (10–20 yo), females > males.
  • Mechanism: Pivoting/twisting on a flexed knee (valgus stress + external rotation) or direct medial trauma.
  • Risk Factors:
    • Patella alta, trochlear dysplasia, ↑ Q-angle (genu valgum).
    • Ligamentous laxity (Ehlers-Danlos).
    • Vastus medialis obliquus (VMO) weakness.
    • Prior subluxation/dislocation (highest risk for recurrence).

Clinical Features

  • History: Audible “pop,” rapid swelling/hemarthrosis, severe anterior knee pain, giving-way sensation.
  • PE:
    • Gross deformity: Patella displaced laterally; knee held in flexion.
    • Medial tenderness: Along the Medial Patellofemoral Ligament (MPFL).
    • Patellar Apprehension Test: Positive (pain/fear with lateral force on patella at 20–30° flexion).

Diagnosis

  • Initial: Plain Radiographs (AP, Lateral, Sunrise) → r/o osteochondral fractures, confirms reduction.
  • Confirmatory / Advanced: MRI → gold standard for MPFL tear, chondral lesions, or loose bodies.
  • Arthrocentesis: Lipohemarthrosis (fat-fluid levels = intra-articular fracture).

Differential Diagnostics

  • ACL Tear: Diff by (+) Lachman/Drawer tests; patella normally positioned; intra-articular pop.
  • Tibiofemoral Dislocation: Diff by gross limb deformity, multiligament tears; requires urgent popliteal artery assessment (ABI, CTA).
  • Quad / Patellar Tendon Rupture: Diff by inability to straight-leg raise, palpable tendon gap (quad rupture = patella baja; patellar rupture = patella alta).
  • Meniscal Tear: Diff by (+) McMurray test, joint line tenderness, delayed joint effusion (24 hrs).

Management

  • Acute (First-line):
    1. Closed Reduction: Medially directed pressure on patella while gently extending the knee.
    2. Post-reduction X-ray: Rule out associated fractures and verify relocation.
    3. Conservative Care: Brief immobilization (hinged brace in extension 1–2 wks) → PT focused on VMO strengthening + RICE/NSAIDs.
  • Surgical (Second-line / Refractory):
    • Indications: Osteochondral fracture / loose bodies, irreducible dislocation, or recurrent instability.
    • Procedure: Arthroscopic fragment removal/fixation, MPFL reconstruction.

Complications

  • Recurrent dislocation/instability (most common; 30–50%).
  • Patellofemoral osteoarthritis.
  • Intra-articular loose bodies causing joint locking.

Graph View

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