Extensor Mechanism Rupture

The extensor mechanism of the knee constitutes of the tibial tuberosity, the patellar tendon, the patellar, the quadriceps tendon and the quadriceps muscles

Aetiology

  • More common in the middle age population who play running or jumping sports
  • The patellar tendon or quadriceps tendon can rupture with rapid contractile force which can occur after lifting a heavy weight, after a fall or spontaneously in a severely degenerate tendon
  • Patellar tendon ruptures tend to occur in a younger age group (<40) with quadriceps tendon rupture in older patients (over 40)
  • Can be associated with blunt or penetrating trauma

Risk factors

  • Previous tendonitis
  • Steriod use/abuse
  • Chronic renal failure
  • Ciprofloxin - quinolone antibiotics can cause tendontitis and can risk tendon ruptures
  • Diabetes
  • Rheumatoid arthritis

Clinical presentation

Symptoms

  • Knee pain and weakness

Signs

  • Unable to straight leg raise
  • Palpable gap in the extensor mechanism
  • Partial tears can also occur which may have some extensor mechanism function but reduced power

Investigations

  • X-ray - may show an effusion or patella sitting in the wrong place (high in PT rupture, low lying in quads rupture)
  • USS or MRI may show partial/complete tear
  • Obese patients the gap may not be obvious and ultrasound may determine the extent of the injury

Management

  • Requires urgent surgical repair with follow up physio to gradually increase ROM
  • Small partial tears of the quadriceps may be treated by immobilisation and physio
  • Steroid injections for tendonitis of the extensor mechanism of the knee should be avoided due to high risk of tendon rupture