Prevalence of knee osteoarthritis features on magnetic resonance imaging in asymptomatic uninjured adults: a systematic review and meta-analysis

Key points

1. 01Overall pooled prevalence: cartilage defects 24%, osteophytes 25%, bone marrow lesions 18%, meniscal tears 10% in asymptomatic uninjured knees
2. 02Prevalence rises sharply with age for cartilage defects (11% under 40 vs 43% at 40 or older) and meniscal tears (4% vs 19%)
3. 03Bone marrow lesions were the most common finding in younger adults and did not increase significantly with age
4. 04MRI sequence type and physical activity level influenced prevalence estimates substantially
5. 05Imaging findings alone should not drive treatment decisions, as they are often normal age-related changes

How it was conducted

Design

Systematic review and random-effects meta-analysis (PRISMA-compliant, PROSPERO registered CRD42016053969)

Databases searched

EMBASE, Medline, CINAHL, SPORTDiscus, Web of Science, Scopus; inception to 24 October 2017

Included studies

63 studies (46 cross-sectional, 17 longitudinal) from North America, Australia, Europe, Asia, and Africa

Participants

4751 adults (5397 knees); all asymptomatic with no history of knee injury or surgery

Primary outcomes

Pooled prevalence of cartilage defects, meniscal tears, bone marrow lesions, and osteophytes; stratified by mean age under 40 vs 40 or older

Age stratification

Studies split at mean age 40 years to reflect known increase in degenerative changes after that threshold

What they found

• Overall pooled prevalence of cartilage defects: 24% (95% CI 15% to 34%; I2=97.8%)
• Cartilage defects under 40 years: 11% (95% CI 6% to 17%); 40 or older: 43% (95% CI 29% to 57%)
• Cartilage defect prevalence increased 14.4% per 10 years of age (95% CI 9.0% to 19.9%, p<0.001)
• Overall pooled prevalence of meniscal tears: 10% (95% CI 7% to 13%; I2=87.2%)
• Meniscal tears under 40 years: 4% (95% CI 2% to 7%); 40 or older: 19% (95% CI 13% to 26%)
• Meniscal tear prevalence increased 3.2% per 10 years of age (95% CI 0.2% to 6.1%, p=0.036)
• Overall pooled prevalence of bone marrow lesions: 18% (95% CI 12% to 24%; I2=95.6%)
• Bone marrow lesions under 40 years: 14% (95% CI 6% to 24%); 40 or older: 21% (95% CI 14% to 31%); age increase not statistically significant (p=0.076)
• Overall pooled prevalence of osteophytes: 25% (95% CI 14% to 38%; I2=98.2%)
• Osteophytes under 40 years: 8% (95% CI 0% to 25%); 40 or older: 37% (95% CI 22% to 53%)
• Osteophyte prevalence increased 10.2% per 10 years (95% CI 1.7% to 18.7%, p=0.021)
• In weight-bearing sport athletes under 40, bone marrow lesion prevalence was 30% (95% CI 17% to 45%) vs 3% (0% to 11%) in general population studies (p<0.001)
• Medial meniscal tears (14%, 95% CI 8% to 20%) were significantly more common than lateral tears (5%, 95% CI 2% to 8%) in adults 40 or older (p=0.009)
• Meta-regression estimated approximately three-quarters of asymptomatic adults aged 70 years would have a cartilage lesion

Limitations

• High unexplained between-study heterogeneity remained even after meta-regression (I2 up to 98%)
• BMI could not be assessed as a moderator because half of included studies did not report it
• Most studies were small (median 27 participants); many used asymptomatic controls as comparators for diseased cases rather than population-representative sampling
• Compartment-level data were not uniformly reported; when whole-knee data were unavailable the highest single-compartment prevalence was used, potentially under-representing true whole-knee rates

Why it matters

For patients

If your MRI shows a meniscal tear or cartilage change and your knee does not hurt, this finding is often a normal part of ageing rather than the cause of any future problem.

For clinicians

Knee OA features on MRI are highly prevalent in pain-free uninjured adults, so these findings must be interpreted alongside clinical symptoms before recommending surgical or other interventions.

For readers

This meta-analysis provides age-stratified reference rates that can anchor clinical reasoning and help set appropriate patient expectations when reviewing knee MRI reports.