Osteoarthritis

Description

• Progressive loss of articular cartilage with reactive changes at joint margins and in subchondral bone
• Primary osteoarthritis (OA)
  • Idiopathic: categorized by clinical features (localized, generalized, erosive)
• Secondary OA
  • Posttraumatic
  • Childhood anatomic abnormalities (e.g., congenital hip dysplasia, slipped capital femoral epiphysis [SCFE], Legg-Calvé-Perthes disease)
  • Inheritable metabolic disorders (e.g., Wilson disease, alkaptonuria, hemochromatosis)
  • Neuropathic arthropathy (Charcot joints)
  • Hemophilic arthropathy
  • Endocrinopathies: acromegalic arthropathy, hyperparathyroidism, hypothyroidism
  • Paget disease
  • Noninfectious inflammatory arthritis (e.g., rheumatoid arthritis [RA], spondyloarthropathies)
  • Gout, calcium pyrophosphate deposition disease (pseudogout)
  • Septic or tuberculous arthritis
  • Femoral acetabular impingement (FAI)
• System(s) affected: musculoskeletal
• Synonym(s): osteoarthrosis; degenerative joint disease (DJD)

Epidemiology

• Symptomatic OA most common in patients >40 years
• Leading cause of disability in patients >65 years
• Predominant sex: male = female
• 90% of hip OA is primary.
• Hip OA is more common in whites.

• ~60 million patients
• Increases with age; radiographic evidence of OA is present in many patients >65 years old.
• Moderate to severe hip OA in 3–6% of whites; <1% in East Indians, blacks, Chinese, and Native Americans

Etiology and Pathophysiology

• Failure of chondrocytes to maintain the balance between degradation and synthesis of extracellular collagen matrix. Collagen loss results in alteration of proteoglycan matrix and increased susceptibility to degenerative change.
• Biomechanical, biochemical, inflammatory, and immunologic factors contribute to cartilage loss. Attempts at repair most commonly manifest as osteophyte formation.

• Up to 65% of OA may have a genetic component.
• The heritability of end-stage hip OA is up to 27%.
• Twin studies in women show 50% (hip, knee) to 65% (hip) heritability rates of OA.

Risk Factors

• Increasing age: >50 years
• Age as a risk factor is greatest for hip and knee OA.
• Hand OA is most common in postmenopausal women.
• Obesity (weight-bearing joints); BMI >35
• Small critical shoulder angle (<30°) can predispose to shoulder OA.
• Trauma, infection, or inflammatory arthritis
• Female gender (knee and hand)