Description

Knee pain is a common complaint in the outpatient setting with a broad differential.

• Knee pain may be acute, chronic, or an acute exacerbation of a chronic condition.
• Trauma, overuse, and degenerative conditions are frequent causes.
• Obtaining a detailed history, including patient age, pain onset and location, mechanism of injury, and associated symptoms, can help narrow the differential diagnosis.
• A thorough but focused exam, including examination of the hips, is key to making a correct diagnosis and determining appropriate treatment.

Epidemiology

• Knee pain accounts for 1.9 million primary care visits annually.
• The incidence of knee osteoarthritis is 240 cases/100,000 person-years (1).

• The knee is the most common site of lower extremity injury among runners (2):
  • Patellofemoral syndrome is one of the most common diagnoses.
• Osteoarthritis (OA) is one of the leading causes of disability in the US.

Risk Factors

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

General Prevention

• Maintain normal body mass index; lose weight if obese.
• Use appropriate exercise training principles.
• Correct strength and flexibility imbalances.
• Proper activity-specific techniques, equipment (i.e., jumping and landing, knee pads)

Etiology

• Trauma (ligament or meniscal injury, fracture, dislocation)
• Overuse (tendinopathy, patellofemoral syndrome, bursitis, apophysitis)
• Age related (arthritis, degenerative conditions, apophysitis [young])
• Rheumatologic (rheumatoid arthritis [RA], gout, pseudogout)
• Infectious (bacterial, postviral, Lyme disease)
• Referred pain (hip, back)
• Other (tumor, cyst)

Commonly Associated Conditions

• Fracture, contusion
• Effusion, hemarthrosis
• Patellar dislocation/subluxation
• Meniscal injury
• Ligamentous injury
• Tendinopathy
• Bursitis
• Osteochondral injury
• Arthritis
• Septic joint
• Muscle strain