Description

• Pain in or around the patella that is aggravated with increased patellar loading (e.g., prolonged sitting, squatting, kneeling, or ascending/descending stairs); not attributable to other causes
• Synonyms: anterior knee or retropatellar pain syndrome, chondromalacia patellae, runner’s knee
• System(s) affected: musculoskeletal

Epidemiology

Prevalence

• Incidence between 2007 and 2011 in the United States was approximately 6%.
  • 55% of patients were female
  • More cases were identified in the Southern portion of the United States, compared to other regions of the country (1).
• In a military population, prevalence of 12% in males and 15% in females (2).

Etiology and Pathophysiology

Increased patellofemoral joint loading, which is often multifactorial (3):

• Patellar malalignment or maltracking (3)
• Abnormal anatomy (e.g., patella alta, trochlear dysplasia) (3)
• Quadriceps asymmetry, weakness and/or tightness (3)
• Hamstring tightness (3)
• Laxity of the patellofemoral joint or a tight lateral retinaculum (3)
• Increased hip joint internal rotation (3)
• Altered tibiofemoral joint mechanics (3)

Risk Factors

• Activities such as running, squatting, and climbing up and down stairs
• Sudden increase in activities
• Female gender
• Dynamic valgus
• Patellar instability
• Quadriceps weakness
• Foot abnormalities (e.g., pes pronatus, rearfoot eversion) (1)
• In adolescents: increased hip adduction strength, although this may represent increased activity level
• Previously considered risk factors, now of uncertain significance: age, height, weight, body mass index, body fat, Q angle, and hip weakness

General Prevention

Strengthening and stretching exercises, particularly hip abductors and terminal extension of the quadriceps

Commonly Associated Conditions

• Overuse
• Knee ligament injury/surgery
• Patellar tendinopathy
• Prolonged synovitis
• Iliotibial band friction syndrome