Knee Pain



A common outpatient complaint with a broad differential

  • Knee pain may be acute, chronic, or an acute exacerbation of a chronic condition.
  • Trauma, overuse, and degenerative change are the frequent causes.
  • A detailed history, including patient’s age, pain onset and location, mechanism of injury, and associated symptoms, can help narrow the differential diagnosis.
  • A thorough and focused examination of the knee (as well as the back, hips, and ankles) helps to establish the correct diagnosis and appropriate treatment.



  • Knee complaints account for 12.5 million primary care visits annually.
  • The incidence of knee osteoarthritis (OA) is 240 cases per 100,000 person-years.


  • The knee is a common site of lower extremity injury.
    • Patellar tendinopathy and patellofemoral syndrome are the most common causes of knee pain in runners.
  • OA of the hip/knee is the 11th cause of global disability and the 38th most common cause of disability-adjusted life years (DALYs).

Etiology and Pathophysiology

  • Trauma (ligament or meniscal injury, fracture, dislocation)
  • Overuse (tendinopathy, patellofemoral syndrome, bursitis, apophysitis)
  • Age (arthritis, degenerative conditions in older patients; apophysitis in younger patients)
  • Rheumatologic (rheumatoid arthritis [RA], systemic lupus erythematosus [SLE])
  • Crystal arthropathies (gout, pseudogout)
  • Infectious (bacterial, postviral, Lyme disease)
  • Referred pain (hip, back)
  • Vascular (popliteal artery aneurysm, deep vein thrombosis)
  • Others (tumor, cyst, plica)

Risk Factors

  • Obesity
  • Malalignment
  • Poor flexibility, muscle imbalance, or weakness
  • Rapid increases in training frequency and intensity
  • Improper footwear, training surfaces, technique
  • Activities that involve cutting, jumping, pivoting, deceleration, kneeling
  • Previous injuries

General Prevention

  • Maintain body mass index <25 kg/m2.
  • Proper exercise technique, volume, and equipment; avoid overtraining.
  • Correct postural strength and flexibility imbalances.

Commonly Associated Conditions

  • Fracture, contusion
  • Effusion, hemarthrosis
  • Patellar dislocation/subluxation
  • Meniscal or ligamentous injury
  • Tendinopathy, bursitis
  • Osteochondral injury
  • OA, septic arthritis
  • Muscle strain

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