The incidence of osteoarthritis (OA) is greater in the knee than in other joints and is increasing. This could be because of an increase in the applied loads on this joint or because of a change in the alignment of the knee joint. The aim of this review was to determine the effects of being overweight on knee joint OA. Moreover, it aimed to determine whether a change in body weight by diet or exercise influenced the loads applied on the knee joint and decreased the incidence of knee OA. A systematic literature search was carried out to find the literature published on the effects of joint loading and being overweight on knee OA in databases such as Medline, PubMed, Embase, Web of Sciences, Scopus, and Google Scholar. The key words such as knee OA and loading, knee OA and joint contact forces, knee OA and body weight were used to determine the effects of joint loading on knee OA. The quality of the studies was evaluated by use of Downs and Black tool. There were 15 studies on the effects of joint loading, overweight, and obesity on joint contact force and knee OA symptoms and three studies on the effects of weight loss, exercise, and intensive diet intervention on joint loading. The quality of these papers varied between 9 and 20. The results of this review showed that obese subjects are at high risk of knee OA because of change in alignment of the knee joint and also overloading of the joint. Use of approaches such as diet and exercise may decrease the loads applied on the joint and decrease the incidence of knee OA.
