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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 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 11th cause of global disability and 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
- 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
- Maintain normal body mass index.
- 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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