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Orthopaedic Surgery, 59 Executive Park South, Atlanta, Georgia 30329, USA. Correspondence should be sent to Dr M. S. Sridhar; e-mail: michaelsridhar@gmail.com ©2012 British Editorial Society of Bone and Joint Surgery doi:10.1302/0301-620X.94B4. 27648 $2.00 J Bone Joint Surg Br 2012;94-B:433–40. Received 25 May 2011; Accepted after revision 3 November 2011 Given the growing prevalence of obesity around the world and its association with osteoarthritis of the knee, orthopaedic surgeons need to be familiar with the management of the obese patient with degenerative knee pain. The precise mechanism by which obesity leads to osteoarthritis remains unknown, but is likely to be due to a combination of mechanical, humoral and genetic factors. Weight loss has clear medical benefits for the obese patient and seems to be a logical way of relieving joint pain associated with degenerative arthritis. There are a variety of ways in which this may be done including diet and exercise, and treatment with drugs and bariatric surgery. Whether substantial weight loss can delay or even reverse the symptoms associated with osteoarthritis remains to be seen. Surgery for osteoarthritis in the obese patient can be technically more challenging and carries a risk of additional complications. Substantial weight loss before undertaking total knee replacement is advisable. More prospective studies that evaluate the effect of significant weight loss on the evolution of symptomatic osteoarthritis of the knee are needed so that orthopaedic surgeons can treat this patient group appropriately. In September 2011, the United Nations General Assembly on non-communicable diseases met in New York to discuss the global obesity pandemic.1 In 2008, a systematic analysis of epidemiological studies across 199 countries had shown that 1.46 billion adults worldwide were overweight and 502 million obese.2 In the United States, the age-adjusted prevalence of obesity (body mass index (BMI) ≥ 30 kg/m2 ) in 2007/8 was 32.2% in adult men and 35.5% in adult women, with 1988 of 2750 (72.3%) adult males and 1798 of 2805 (64.1%) adult females having a BMI ≥ 25 kg/m2, suggesting that more than two-thirds of the American population was overweight.3 A 2010 report estimated that the total annual cost of obesity to the United States economy was in excess of $215 billion, and that this was probably twice as much as that spent on adults of a healthy weight.4 Recently, a simulation model projected that there would be 65 million more obese adults in the United States and 11 million more in the United Kingdom by 2030; this would be equivalent to 26 to 55 million quality-adjusted years of life lost for the two populations.5 The combined medical costs for the treatment of preventable diseases caused by obesity are expected to increase by $48 billion/year to $66 billion/year in the United States and £1.9 billion/year to £2 billion/year in the United Kingdom by 2030.5 In the United States, it is estimated that there is radiological evidence of osteoarthritis (OA) of the knee in over 13 million (37%) of those aged ≥ 60 years, over four million (12%) of whom are symptomatic and report restricted activity.6 The prevalence of OA is greater with increasing age and BMI,2 in women, and in some ethnic groups. The risk of OA of the knee is increased by almost four-fold (3.87) in obese women and nearly five-fold (4.78) in obese men, whereas the risk in overweight women and men is 1.89 and 1.69, respectively7 ; where a BMI between 25 and 29.9 is considered overweight and 30 to 34.9 obese. In 2007, more than 350 000 patients underwent total knee replacement (TKR) in the United States,8 and this number is expected to increase exponentially over the next two decades.9 Not infrequently, the orthopaedic surgeon is the first person to discuss obesity and weight loss with the patient. In 1999, Galuska et al10 reported that only 42% of obese patients were advised by their physician to lose weight, but those who received advice were more likely to make an attempt to do so. Given the growing prevalence of obesity and its association with OA of the knee, orthopaedic surgeons need to be familiar with the 434 M. S. SRIDHAR, C. D. JARRETT, J. W. XEROGEANES, S. A. LABIB THE JOURNAL OF BONE AND JOINT SURGERY pathophysiology, evolution, and management of the obese patient with degenerative knee pain. Pathophysiology Although the exact mechanism by which obesity causes degeneration of articular cartilage remains unclear, recent studies have investigated the contribution of mechanical, humoral and genetic factors. Mechanical factors. Maquet and Pelzer11 showed that two to five times the body weight of an individual is transmitted across the knee joint during the course of the day. The reactive forces across the patellofemoral joint rise from three times body weight when climbing or descending stairs to seven to eight times body weight while squatting.12 It stands to reason that excess weight increases the load borne by all parts of the joint, potentially overwhelming the articular cartilage simply from axial loading or as a result of repeated microtrauma, leading to wear and damage. In a study by Messier et al,13 142 sedentary overweight, and obese older individuals with radiologically proven OA of the knee underwent three
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