Objectives To assess the extent to which knee extensor strength and weight in adolescence are associated with knee osteoarthritis (OA) by middle age.
Methods We studied a cohort of 40 121 men who at age 18 years in 1969/1970 underwent mandatory conscription in Sweden. We retrieved data on isometric knee extensor strength, weight, height, smoking, alcohol consumption, parental education and adult occupation from Swedish registries. We identified participants diagnosed with knee OA or knee injury from 1987 to 2010 through the National Patient Register. We estimated the HR of knee OA using multivariable-adjusted Cox proportional regression model. To assess the influence of adult knee injury and occupation, we performed a formal mediation analysis.
Results The mean (SD) knee extensor strength was 234 (47) Nm, the mean (SD) weight was 66 (9.3) kg. During 24 years (median) of follow-up starting at the age of 35 years, 2049 persons were diagnosed with knee OA. The adjusted HR (95% CI) of incident knee OA was 1.12 (1.06 to 1.18) for each SD of knee extensor strength and 1.18 (1.15 to 1.21) per 5 kg of body weight. Fifteen per cent of the increase in OA risk due to higher knee extensor strength could be attributed to knee injury and adult occupation.
Conclusion Higher knee extensor strength in adolescent men was associated with increased risk of knee OA by middle age, challenging the current tenet of low muscle strength being a risk factor for OA. We confirmed higher weight to be a strong risk factor for knee OA.
- knee osteoarthritis
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Contributors Conception and design of the study: ME and AT. Data collection: ME and ST. Statistical analysis: AT. Data interpretation: all authors. Drafting of the manuscript: AT. Critical revision of manuscript and acceptance of the final version: all authors.
Funding We would like to acknowledge the support from the Swedish Research Council, Kock Foundations, Österlund Foundation, Crafoord Foundations, the Swedish Rheumatism Association, the Faculty of Medicine Lund University and Region Skåne.
Competing interests None declared.
Ethics approval the Regional Ethical Review Board in Lund, Sweden.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The data are not available for sharing because of privacy and integrity issues protected by the Swedish law.