Patellar Injuries

Description

• Usually caused by twisting on a flexed knee
• Direct trauma is a less common cause
• Lateral dislocation of the patella is most common, with the patella displaced over the lateral femoral condyle
• Uncommon dislocations include superior, medial, and intra-articular dislocation

• Direct trauma:
  • Most common mechanism
  • Direct blow or fall on patella, i.e., dashboard injury
  • Usually results in comminuted or minimally displaced fracture, or open injury
• Indirect forces:
  • Excessive tension through the extensor mechanism during deceleration from a fall, i.e., landing on feet from fall from moderate height (can also cause patellar tendon rupture)
  • Avulsion injury from sudden contraction of the quadriceps tendon
  • Usually results in transverse or displaced fracture (often both)
• Types of patellar fractures:
  • Transverse: 50–80% (usually middle or lower third of patella)
  • Comminuted (or stellate): 30–35%
  • Longitudinal: 25%
  • Osteochondral

• Usually caused by forceful eccentric contraction of quadriceps muscle on a flexed knee during deceleration (e.g., jump landing and weight lifting)
• Often occurs in older athletes:
  • Microtrauma from repetitive activity

Etiology

• Risk factors for patellar dislocation:
  • Lower extremity malalignment (i.e., knock knee etc.)
  • IT band tightness
  • Generalized joint laxity
  • Deficient vastus medialis
  • Lateral insertion of patellar tendon
  • Shallow patellar groove
  • Patella alta (high-riding patella)
  • Below the knee amputation
• Common injury in adolescent athletes, especially girls
• The younger the patient at the time of initial dislocation, the greater the risk of recurrence

• Male:female ratio 2:1
• Highest incidence in those 20–50 yr old

• Peak incidence in third and fourth decades:
  • Often in athletes
• Risk factors:
  • History of patellar tendinitis
  • History of diabetes mellitus, previous steroid injections, rheumatoid arthritis, gout, systemic lupus erythematosus
  • Previous major knee surgery

• Microtears of tendon matrix from overuse
• Seen in high jumpers, volleyball and basketball players, runners