Risk Factors for Knee Arthritis
The primary risk factors for knee osteoarthritis include age, female sex, obesity, genetics, previous knee trauma, and occupational activities involving repetitive knee stress—with obesity and previous knee injury being the most important modifiable factors to address for prevention. 1, 2
Non-Modifiable Risk Factors
Age is the strongest predictor, with nearly 50% of people developing symptomatic knee OA by age 85, and risk increasing substantially in women after menopause. 2
Female sex confers higher risk than male sex, likely due to hormonal factors. 1, 2
Genetics account for 39-65% of knee OA heritability based on twin studies, with first-degree relatives of OA patients having an odds ratio of 2.57 for developing the condition. 3, 2
Previous knee trauma dramatically increases OA risk with moderate-certainty evidence, including:
- Cruciate ligament injuries (ACL/PCL)
- Collateral ligament injuries
- Meniscal tears
- Chondral injuries
- Patellar or tibiofemoral dislocations
- Knee fractures
- Multistructure injuries 1, 2
Post-traumatic OA accounts for approximately 12% of all OA cases globally (36 million people), with very-low certainty evidence showing increased structural OA risk after ACL reconstruction combined with cartilage injury, partial meniscectomy, or total medial meniscectomy. 2
Modifiable Risk Factors
Obesity (BMI ≥25 kg/m²) is the most critical modifiable risk factor. Weight loss of ≥10% significantly reduces knee compressive forces (by approximately 200 N) and inflammatory markers (IL-6 levels), while improving pain and function. 1, 4
Occupational factors including repeated knee bending, heavy lifting, and working in certain job fields that stress the knee joint increase risk. 1
Quadriceps weakness and poor muscle function around the knee contribute to abnormal joint loading and accelerated cartilage degeneration. 2, 5
Joint malalignment creates abnormal mechanical loading patterns that promote cartilage breakdown. 2
Prevention Strategies
Weight management is paramount—patients with BMI ≥25 kg/m² should lose weight, with a target of ≥10% body weight reduction to meaningfully reduce knee joint forces and inflammation. 1, 4
Exercise programs should include:
- Strengthening exercises (particularly quadriceps)
- Low-impact aerobic activity
- Neuromuscular education
- Self-management programs 1
Both land-based and aquatic programs are effective when performed 3-5 sessions per week for 8-12 weeks, with each session lasting approximately 1 hour. 6 Exercise does not accelerate OA development when trauma is avoided, and actually reduces pain and disability in those with established disease. 7
Injury prevention programs should be implemented to reduce the incidence of all knee trauma, as no clear treatment targets exist to prevent OA after knee injury occurs. 1
Common Pitfalls
Do not recommend acupuncture, glucosamine, or chondroitin—these have strong evidence against their effectiveness. 1
Do not assume early ACL reconstruction prevents OA—evidence does not support this belief, and managing patient expectations about surgical timing is important. 1
Do not confuse adolescent overuse injuries (like Osgood-Schlatter disease) with adult OA risk factors, as these are distinct conditions with different pathophysiology. 8