What is osteoarthritis?
Osteoarthritis is characterised by the gradual breakdown of cartilage — the smooth tissue covering joint surfaces — combined with changes in the underlying bone and surrounding soft tissues. It is not simply 'wear and tear' in the traditional sense; inflammation, metabolic factors, and mechanical loading all contribute to its development and progression.
The most commonly affected joints are the knees, hips, hands and spine. Symptoms include joint pain (typically worse with activity and better with rest in early stages), stiffness (particularly in the morning or after rest), swelling, and reduced range of motion.
Risk factors
Age — the strongest association
OA prevalence increases dramatically with age: from approximately 10% in those under 45 to over 50% in those over 65. However, age is a proxy for cumulative exposure to risk factors, not an inevitable biological destiny.
Obesity
Obesity is the most modifiable risk factor. Each additional unit of BMI above the healthy range increases knee OA risk by approximately 11%. The mechanism is partly mechanical (increased joint loading) but also metabolic — adipose tissue produces inflammatory cytokines that directly drive cartilage degradation.
Previous joint injury
Joint injury — particularly ACL (anterior cruciate ligament) tears and meniscal injuries — dramatically increases OA risk. Studies show that 50–60% of people with significant knee injury develop OA within 10–15 years.
Genetic factors
Family history is significant — OA has a heritability of approximately 40–65%. However, genetics is not destiny; modifiable factors can override genetic predisposition to a significant degree.
Elite athletes in high-impact sports have increased OA risk due to injury and extreme loading. But recreational exercise at moderate intensity is actually protective — it builds the muscle support that reduces cartilage loading per step, maintains healthy cartilage nutrition, and reduces the obesity-related inflammatory component of OA risk.
Prevention and management
Weight management
For overweight individuals, weight loss is the highest-impact OA prevention and management intervention. A 5kg weight loss reduces the force on the knee by approximately 20kg per step (due to the mechanical lever arm effect).
Exercise
NICE recommends exercise as first-line management for knee and hip OA — ahead of medication. Aerobic exercise and strengthening exercise both reduce pain and improve function, with effects comparable to or exceeding NSAIDs in some trials.
Surgery
Knee arthroscopy (keyhole surgery) for OA is no longer recommended by NICE — multiple RCTs have shown it is no better than sham surgery or physiotherapy for most OA presentations. Joint replacement remains highly effective for severe, function-limiting OA.
Exercise (strengthening + aerobic), weight loss where appropriate, and education (understanding the condition reduces anxiety-driven pain amplification). These are the evidence-based first-line treatments — and they work better than most people expect.
OA risk factors and their modifiability
| Risk Factor | Impact | Modifiable? |
|---|---|---|
| Obesity (BMI>30) | Very high — strongest modifiable factor | Yes — weight loss highly effective |
| Previous joint injury | High — 50-60% OA within 15 years | Partially — injury prevention key |
| Age | Very high — OA doubles every 10 years | No — but rate is modifiable |
| Female sex | Moderate — OA more common and severe | No |
| Muscle weakness | High — poor support increases loading | Yes — resistance training effective |
| Occupational loading | Moderate — kneeling/squatting work | Partially |
| Family history | Moderate — 40-65% heritability | No — but lifestyle modifies expression |
Frequently asked questions
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