What causes osteoarthritis in the knees?

Causes of Knee Osteoarthritis

Knee osteoarthritis has a multifactorial etiology that includes both constitutional factors (aging, sex, obesity, genetics) and local mechanical factors (trauma, occupational stress, and joint alignment). 1

Constitutional Risk Factors

• Age: Prevalence increases significantly with age, with nearly 50% of people developing symptomatic knee OA by age 85 1
• Sex: Women have higher prevalence (13%) compared to men (10%) in those aged 60 years or older 2
• Obesity: One of the strongest modifiable risk factors, with risk increasing progressively as BMI increases 3
  • Compared to individuals with BMI 24.0-24.9 kg/m², those with BMI ≥36 kg/m² have 13.6 times higher risk of knee OA 3
  • Weight reduction of 5 kg could potentially prevent 24% of surgical cases of knee OA 3
• Genetics: Significant genetic component with estimates from twin studies showing heritability of 0.39-0.65 1
• Reproductive variables: Hormonal factors may contribute to the higher prevalence in women 1

Local Mechanical Risk Factors

• Previous trauma: Joint injury significantly increases risk of subsequent OA development 1
• Occupational and recreational stress: Repetitive joint usage, particularly activities involving squatting and kneeling 4
• Joint alignment: Abnormal mechanical loading due to malalignment contributes to cartilage degeneration 1
• Meniscectomy: Prior meniscal surgery increases risk of knee OA 3
• Muscle weakness: Particularly quadriceps weakness can contribute to joint instability and OA progression 2
• Joint laxity: Excessive movement within the joint can accelerate cartilage wear 2

Pathophysiology

• Articular cartilage degeneration: Primary pathological feature characterized by focal loss of cartilage 1
• Bone changes: Marginal and central new bone formation (osteophytes) 1
• Inflammatory processes: Cytokines and other inflammatory mediators contribute to cartilage breakdown 4
• Mechanical forces: Abnormal loading patterns accelerate joint degeneration 4
• Metabolic factors: Leptin and other metabolic mediators may influence cartilage metabolism 4

Risk Factor Interactions

• The combination of obesity with other risk factors creates synergistic effects that dramatically increase OA risk 3
• Individuals with obesity, Heberden's nodes, and previous knee injury have a 78-fold increased risk compared to normal-weight individuals without these factors 3

Clinical Implications

• Early identification and modification of risk factors, particularly obesity, can significantly reduce disease burden 3
• Weight management should be a priority for patients at risk of knee OA or with early disease 3
• Patients with history of knee injury or meniscectomy should receive targeted preventive interventions, especially if overweight 3
• Understanding the multifactorial nature of knee OA is essential for developing comprehensive prevention and treatment strategies 1, 5