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How Osteoarthritis Develops

Patient-friendly explanation of how osteoarthritis develops - from healthy cartilage to worn joints - including what happens inside the joint, why it causes pain, and what drives disease progression

πŸ“…Last reviewed: January 2025πŸ₯Bones & Joints

πŸ“–What is How Osteoarthritis Develops?

Patient-friendly explanation of how osteoarthritis develops - from healthy cartilage to worn joints - including what happens inside the joint, why it causes pain, and what drives disease progression

πŸ”¬What Causes It?

  • MECHANICAL STRESS - excessive or abnormal loading damages cartilage cells (chondrocytes) and extracellular matrix
  • CARTILAGE BREAKDOWN - death of chondrocytes leads to loss of proteoglycans and collagen, cartilage loses ability to withstand load
  • INFLAMMATORY CASCADE - damaged cartilage releases inflammatory molecules (cytokines) that further accelerate breakdown
  • SUBCHONDRAL BONE CHANGES - bone underneath cartilage thickens (sclerosis) and develops cysts, losing shock-absorption capacity
  • SYNOVIAL INFLAMMATION - joint lining becomes inflamed (synovitis), producing more inflammatory molecules and causing pain and swelling
  • OSTEOPHYTE FORMATION - bone spurs grow at joint margins attempting to stabilize joint but causing pain and stiffness

⚠️Risk Factors

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You may be at higher risk if:

  • AGE - strongest risk factor: 10% prevalence under age 45, 50% over age 65, 80% over age 80 (cartilage repair capacity declines with age)
  • OBESITY - doubles knee OA risk, triples hip OA risk (every 5kg weight loss reduces knee OA risk by 50%)
  • PREVIOUS JOINT INJURY - fracture involving joint surface increases OA risk 7-fold, ACL tear increases knee OA risk 5-fold
  • GENETICS - 40-65% of OA risk is hereditary (specific genes affecting cartilage metabolism, collagen structure)
  • GENDER - women more prone to knee and hand OA (especially post-menopause - hormonal factors), men more prone to hip OA
  • OCCUPATION - jobs requiring repetitive kneeling/squatting double knee OA risk, heavy lifting increases hip/spine OA risk
  • JOINT MALALIGNMENT - bow-legged (varus) or knock-kneed (valgus) deformity concentrates load on one side of joint
  • MUSCLE WEAKNESS - quadriceps weakness increases knee OA risk 3-fold (muscles normally absorb shock and protect cartilage)
  • INFLAMMATORY ARTHRITIS - previous rheumatoid arthritis or septic arthritis damages cartilage, predisposes to secondary OA

πŸ›‘οΈPrevention

  • βœ“Maintain healthy weight throughout life - obesity in 20s-40s increases OA risk in 50s-70s
  • βœ“Regular low-impact exercise to maintain muscle strength and joint mobility (walking, cycling, swimming)
  • βœ“Avoid high-impact activities and sports injuries when possible - previous ACL tear increases knee OA risk 5-fold
  • βœ“Prompt treatment of joint injuries - anatomic reduction of fractures, ligament reconstruction if needed
  • βœ“Correct joint malalignment early (bow-legged or knock-kneed) before arthritis develops
  • βœ“Occupational modification if job requires repetitive heavy lifting, kneeling, or squatting
  • βœ“Genetic counseling if strong family history (40-65% of OA risk is hereditary) - can't change genes but can modify risk factors