Risk factors for knee replacement due to primary osteoarthritis, a population based, prospective cohort study of 315,495 individuals
1 Orthopaedic department, Telemark Hospital, Skien, Norway
2 Section for Preventive Medicine and Epidemiology, University of Oslo, Oslo, Norway
3 Norwegian Institute of Public Health, Division of Epidemiolgy, Oslo, Norway
4 Orthopaedic department, Oslo University Hospital, Oslo, Norway
5 Faculty of medicine, University of Oslo, Oslo, Norway
6 The Norwegian Arthroplasty Register, Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway
7 Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway
8 Department of Surgical Sciences, Faculty of Medicine and Dentistry, Bergen, Norway
BMC Musculoskeletal Disorders 2014, 15:217 doi:10.1186/1471-2474-15-217Published: 23 June 2014
Osteoarthritis (OA) of the knee is a common and disabling condition. We wanted to investigate the modifiable risk factors Body Mass Index (BMI) and physical activity, using knee replacement (KR) as a marker for severely symptomatic disease, focusing on the interaction between these risk factors.
315,495 participants (mean age 43.0 years) from national health screenings were followed prospectively with respect to KR identified by linkage to the Norwegian Arthroplasty Register. Data were analysed by Cox proportional hazard regression.
During 12 years of follow up 1,323 individuals received KR for primary OA. There was a dose–response relationship between BMI and heavy labour, and later KR. Comparing the highest versus the lowest quarter of BMI, the relative risk was 6.2 (95% CI: 4.2-9.0) in men and 11.1 (95% CI: 7.8-15.6) in women. Men reporting intensive physical activity at work had a relative risk of 2.4 (95% CI: 1.8-3.2) versus men reporting sedentary activity at work, the corresponding figure in women being 2.3 (95% CI: 1.7-3.2). The effect of BMI and physical activity at work was additive. The heaviest men with the most strenuous work had a RR of 11.7 (95% CI: 5.9-23.1) compared to the ones with the lowest BMI and most sedentary work. For women the corresponding RR was 15.8 (95% CI: 8.2-30.3). There was no association between physical activity during leisure and KR.
We found that a high BMI and intensive physical activity at work both contribute strongly to the risk of having a KR. As the two risk factors seem to act independently, people with strenuous physical work with a high BMI are at particularly high risk for severely disabling OA of the knee, and should be targeted with effective preventive measures.