Background: The association between obesity and knee osteoarthritis, and specifically the role of obesity as a risk factor for knee osteoarthritis has been well documented. A systematic review and meta-analysis by Blagojevic et al. in Osteoarthr Cartil 18(1):24-33, (2010) examined 36 papers reporting on BMI and found that all studies demonstrated obesity and being overweight to be risk factors for knee osteoarthritis. The effect size for obesity as a risk factor for knee OA was reported to be I² = 97%, and the random effects pooled odds ratio for obesity compared to normal weight was 2.63 with a 95% CI of 2.28-3.05.
Objective: This review summarises recent findings involving the association between knee osteoarthritis and obesity: the potential mechanisms of the link between the two disease states; and the potential benefits of weight loss on obese, knee osteoarthritis patients.
Methods: Studies for inclusion in our report were identified using: MEDLINE; EMBASE; PUBMED; Cochrane Central Register of Controlled Trials; CINAHL; and reference lists of relevant articles.
Main results: A number of recent studies involving the association between obesity and knee osteoarthritis have since been published. A large, population-based prospective study (n = 823) conducted by Toivanen et al. with a follow-up of 22 years found that the risk for knee osteoarthritis was 7 times greater for people with BMI ≥ 30 compared to the control of people with BMI <25. A prospective cohort study of the Norwegian population by Grotle et al. that followed 1,675 patients reported that BMI >30 was significantly associated with osteoarthritis of the knee, with odds ratio of 2.81, and 95% CI of 1.32-5.96. Lohmander et al. found that in a large cohort study of 27,960 patients from the Swedish population, the relative risk for knee osteoarthritis (fourth quartile compared to first quartile) was 8.1, with a 95% CI of 5.3-12.4. Finally, a case-control study from Holliday et al. with 1,042 knee osteoarthritis patients and 1,121 matched controls reported that the adjusted odds ratio for knee osteoarthritis in patients with BMI >30 was 7.48 with 95% CI of 5.45-10.27.
Conclusion: Recent prospective studies demonstrate obesity as a primary risk factor for incident knee osteoarthritis. The potential mechanisms to link obesity and knee osteoarthritis, as both a biomechanical and metabolic condition are strongly linked. It has been established that weight loss for obese patients with knee osteoarthritis is clinically beneficial, for pain reduction, and for improved function. The exact mechanism linking obesity and osteoarthritis is complex; however, it is our opinion that further evidence supporting the link between the two diseases will be useful in providing clinicians and researchers with targets for physical therapy and pharmacological management of obese patients with knee osteoarthritis.