Knee Pain

Description

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.

Epidemiology

Incidence

• 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.

Prevalence

• 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