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factors for symptomatic OA of the knee in women. They identified a significant association with a previous knee injury, arthritis of the feet, heavy smoking, being overweight, and various occupational activities. They went on to show that having a BMI ≥ 25 before the age of 40 tended to significantly increase the risk of symptomatic OA of the knee in women.30 OA of the knee is thought to develop because of the effect of local factors acting in a systemic environment.28 Cooper et al31 found that certain risk factors, including obesity, previous knee injury, and a history of regular participation in sports, had a greater effect on the initiation of OA of the knee rather than on its radiological progression. These findings are consistent with the concept that OA of the knee is initiated by injury to the joint, but progression occurs because the intrinsic capacity for repair of the host is impaired. Perhaps, in the obese, there is also an inability of the articular surface and subchondral bone to recover from the effects of persistently increased loading. Treatment It would appear to be obvious that knee pain and OA are strongly associated with an increased BMI. One should then be able to conclude that weight loss may reduce these symptoms. However, there is little prospective information to substantiate this assumption. In the Framingham Knee Osteoarthritis Study, 64 women with symptomatic knee OA were compared to women without the disease, and the authors found that weight-change significantly affected the risk for the development of OA of the knee.32 They found that a reduction in BMI of two units or approximately 5.1 kg over a ten-year period decreased the odds of developing OA by over 50%. Unfortunately, their results did not address the effect of weight loss after the onset of symptoms. Interestingly, weight gain was only associated with a slightly increased risk of OA of the knee, which was not statistically significant. One problem with this study was the need to rely on patients reporting the onset of symptoms that had occurred many years previously. Other problems that arise when studying the relationship between knee pain and OA in the obese patient include the difficulty patients have in achieving or maintaining significant weight loss, the prolonged time it takes to achieve weight loss, and the difficulties associated with following this particular subgroup of patients in the long term.33,34 Non-operative. Non-operative treatment of obesity includes behaviour modification and pharmacological and medical treatment. Recent studies have shown that the treatment of obesity by moderate to severe dieting in combination with behaviour modification can sustain twothirds of weight loss one year later.34 Pharmacological treatment has been found to be expensive and largely ineffective with a high rate of recidivism. A trial of 182 obese patients comparing two popular weight-loss preparations, orlistat and sibutramine (the latter product now withdrawn in many parts of the world), found both to be associated with significant weight loss when combined with diet and exercise.35 However, non-compliance in 80 patients (44%) and rebound weight gain afterwards proved to be a considerable problem.35 This makes it imperative both for the overweight patient and their clinician to appreciate that obesity is a chronic problem requiring long-term compliance. Interestingly, non-compliance was associated with a higher initial body weight, previous anti-obesity therapy, the number of concurrent medications, and medical comorbidities. Recently, Messier et al36 in a sample of 252 patients aged ≥ 60 years, with OA of the knee and a BMI ≥ 28, reported the results of the first prospective randomised trial showing that modest dietary weight loss in combination with moderate exercise leads to significant improvement in self-reported measures of knee pain and function and measures of mobility. They showed that a 5% weight-loss over 18 months resulted in an 18% improvement in function. When a change in diet was combined with exercise, the patients under study achieved a 24% improvement in function and better mobility. Of note was the fact that there was little difference in the radiological height of the medial and lateral joint space between the groups studied. Non-impact loading exercises, including those on a stationary bicycle and in water, are essential as they minimise the load transmitted through the knee joint while providing effective exercise. To date, the effect of weight loss on OA of the knee remains speculative; one particular criticism of the aforementioned study is that participants were encouraged to ‘continue all medication and other treatments as prescribed’.37 Surgically-assisted weight loss. Surgical treatment for obesity has been shown to have a favourable effect on cardiovascular risk factors including the incidence of diabetes and health-related quality of life.38,39 Loss of weight of between 5% and 15% produces significant improvements in cardiovascular and metabolic health, and weight loss of 10% over six to 12 months is seen as a realistic goal for individuals trying to lose weight.40,41 Apart from a reduction in axial load transmitted through the weight-bearing surfaces of the lower extremities, improved mental well-being and increased physical activity in those who have
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