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Osteoarthritis, Knee

For further information, see CMDT Part 41–06: Musculoskeletal Injuries of the Knee

Key Features

Essentials of Diagnosis

  • Degeneration of joint cartilage

  • Pain with bending or twisting activities

  • Swelling

  • Loss of active and passive range of motion in severe osteoarthritis (OA)

General Considerations

  • Cartilage loss and OA symptoms are preceded by damage to the collagen-proteoglycan matrix

  • The etiology of OA is often multifactorial including

    • Previous trauma

    • Prior high-impact activities

    • Genetic factors

    • Obesity

    • Rheumatologic or metabolic conditions

Demographics

  • The incidence of knee OA in the United States is 240 per 100,000 person-years

  • The prevalence of OA will likely grow to 70 million persons by 2030 as the number of persons over age 65 years increases

Clinical Findings

  • Pain in the affected joint with loading of the joint or at the extremes of motion.

  • Swelling, grinding, catching, and locking

  • Pain can also produce the sensation of "buckling" or "giving way" due to muscle inhibition (Tables 41–4, 41–5, and 41–6)

  • As the joint degeneration becomes more advanced, the patient loses active range of motion and may lose passive range of motion as well

  • As the condition worsens, patients have an increasingly limited ability to walk

    • Symptoms include pain with bending or twisting activities and going up and down stairs

    • Swelling, limping, and pain while sleeping are common complaints, especially as OA progresses

Table 41–4.Differential diagnosis of knee pain.
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Table 41–4. Differential diagnosis of knee pain.

Mechanical dysfunction or disruption

 Internal derangement of the knee: injury to the menisci or ligaments

 Degenerative changes caused by osteoarthritis

 Dynamic dysfunction or misalignment of the patella

 Fracture as a result of trauma

Intra-articular inflammation or increased pressure

 Internal derangement of the knee: injury to the menisci or ligaments

 Inflammation or infection of the knee joint

 Ruptured popliteal (Baker) cyst

Peri-articular inflammation

 Internal derangement of the knee: injury to the menisci or ligaments

 Prepatellar or anserine bursitis

 Ligamentous sprain
Table 41–5.Location of common causes of knee pain.
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Table 41–5. Location of common causes of knee pain.

Medial knee pain

 Medial compartment osteoarthritis

 Medial collateral ligament strain

 Medial meniscal injury

 Anserine bursitis (pain over the proximal medial tibial plateau)

Anterior knee pain

 Patellofemoral syndrome (often bilateral)

 Osteoarthritis

 Prepatellar bursitis (associated with swelling anterior to the patella)

 “Jumper’s knee” (pain at the inferior pole of the patella)

 Septic arthritis

 Gout or other inflammatory disorder

Lateral knee pain

 Lateral meniscal injury

 Iliotibial band syndrome (pain superficially along the distal iliotibial band near the lateral femoral condyle or lateral tibial insertion)

 Lateral collateral ligament sprain (rare)

Posterior knee pain

 Popliteal (Baker) cyst

 Osteoarthritis

 Meniscal tears

 Hamstring or calf tendinopathy

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