Patella Injuries
Patella injuries range from simple, nondisplaced fractures to complex comminuted or intra‑articular fractures with disruption of the extensor mechanism. They commonly result from a direct blow to the anterior knee (fall, dashboard injury) or an indirect tensile load - sudden forced knee flexion against a contracted quadriceps.
Because the patella is integral to the extensor mechanism and the patellofemoral joint, assessment must focus on fracture pattern, articular congruity and the ability to actively extend the knee.
Mechanism and common fracture patterns
- Direct impact commonly causes comminuted or stellate fractures and may produce open injuries.
- Indirect tensile load (eccentric quadriceps contraction) typically produces transverse fractures through the mid‑patella and carries risk of extensor‑mechanism disruption.
- Patellar dislocation (usually lateral) may produce osteochondral fragments from the patella or trochlea.
- Patterns to recognise include transverse, vertical, stellate/comminuted, osteochondral fragments, and in children the sleeve avulsion.
Clinical assessment
Presentation
- Acute anterior knee pain, swelling and a tense haemarthrosis are common findings.
- Focal patellar tenderness is usually present; a palpable step or gap may be detectable.
- Inspect the skin for bruising, skin compromise, open wounds or threatening skin tension.