What are the main causes of knee arthritis?

Main Causes of Knee Arthritis

The main causes of knee osteoarthritis include age-related degeneration, genetic predisposition, previous knee trauma, obesity, and joint malalignment, with traumatic knee injuries being a significant contributor to post-traumatic osteoarthritis. 1

Primary Risk Factors

Constitutional Factors

• Age is a significant risk factor, with nearly 50% of people developing symptomatic knee OA by age 85 1
• Genetic predisposition plays a substantial role, with heritability estimates ranging from 0.39-0.65 according to twin studies 1
• Female gender is associated with higher prevalence of knee OA, potentially due to hormonal factors 1

Mechanical Factors

• Previous knee trauma significantly increases the risk of developing osteoarthritis 1, 2
• Various single and multistructure knee injuries increase the odds of symptomatic OA with moderate-certainty evidence 2
• Specific injuries with increased OA risk include:
  • Cruciate ligament injuries (ACL tears) 2
  • Collateral ligament injuries 2
  • Meniscal injuries, particularly those requiring meniscectomy 2
  • Chondral (cartilage) injuries 2
  • Patellar/tibiofemoral dislocations 2
  • Knee fractures 2
  • Multistructure injuries (e.g., ACL with meniscal injuries) 2

Biomechanical Factors

• Joint malalignment that causes abnormal mechanical loading contributes to cartilage degeneration 1, 3
• Muscle weakness, particularly quadriceps weakness, is both a risk factor and consequence of knee OA 3
• Reduced joint proprioception affects joint mechanics and stability 3

Metabolic Factors

• Obesity is a significant modifiable risk factor for knee OA 3, 4
  • Being obese at age 20 increases the risk of developing severe knee OA by 3.5 times 4
• Heavy physical activity, particularly occupational stress, increases risk by 2-3 times 4

Post-Traumatic Osteoarthritis

• Post-traumatic OA accounts for approximately 12% of all OA cases globally, affecting about 36 million people 2
• Very-low certainty evidence suggests increased odds of structural OA related to:
  • ACL reconstruction with cartilage injury (OR=2.31; 95% CI 1.35 to 3.94) 2
  • ACL reconstruction with partial meniscectomy (OR=1.87; 95% CI 1.45 to 2.42) 2
  • ACL reconstruction with total medial meniscectomy (OR=3.14; 95% CI 2.20 to 4.48) 2
• Inflammation plays a key role in post-traumatic OA development, potentially aggravated by hemarthrosis (bleeding into the joint) 5

Pathophysiological Mechanisms

• Articular cartilage degeneration is the primary pathological feature of knee OA 1
• Osteoarthritis represents an imbalance between destructive and synthetic processes in cartilage 6
• The disease process involves:
  • Decreased concentration and viscosity of synovial fluid 6
  • Underlying inflammation of the synovium 6
  • Damage or reactive changes in the subchondral bone 6
  • Complex interactions of cells and soluble mediators including cytokines, growth factors, inflammatory mediators, and chondrodegradative enzymes 6

Clinical Implications

• Prevention efforts should focus on implementing evidence-based injury prevention programs 2
• Addressing modifiable risk factors is crucial, particularly:
  • Minimizing unhealthy adiposity 2, 3
  • Strengthening quadriceps muscles 2, 3
• Early diagnosis and treatment are essential to prevent further joint destruction and maximize functional ability 7

Common Pitfalls in Understanding Knee OA

• Overemphasis on the perceived value of early ACL reconstruction for reducing OA risk, when evidence suggests otherwise 2
• Failure to recognize that OA can affect younger adults, not just the elderly 3
• Neglecting to address modifiable risk factors such as obesity, muscle weakness, and biomechanical issues 3