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obese group, operating times were longer and their time to return to work was more delayed than a matched cohort of nonobese patients despite having less physically demanding jobs.53 Overweight women have been shown to have a poorer quality of life and are less satisfied after arthroscopic knee surgery than women of normal weight.54 Knee arthroplasty. Kurtz et al55 have estimated that by 2030 the rate of TKRs performed each year will be nearly seven times that in 2005. Most patients presenting for a TKR are obese,56-58 and joint replacement surgery is often discouraged. Obesity is generally considered a contraindication for unicompartmental knee replacement.59 In a series of 79 minimally invasive medial unicompartmental replacements, a BMI > 32 predicted failure and decreased survivorship.59 Dewan et al60 focused on a subgroup of patients with morbid obesity in order to study the relationship between BMI and outcome after TKR. The KSSs were calculated for 67 patients with a BMI < 30, 71 patients with a BMI from 30 to 39, and 31 patients with a BMI > 39. At a mean follow-up of 5.4 years (2.2 to 14.6) they found that for most outcomes, there was no difference between the BMI groups and although the samples had not been balanced with regard to age and ethnicity, the patients with the lowest mean age were in the highest BMI group. However, there was a significant increase in the rate of patellar radiolucency in the highest BMI group. The authors recommended close monitoring of TKRs in patients who are morbidly obese, especially with regard to the patellofemoral compartment.60 Although it has been previously debated whether increased weight affects the outcome after TKR,61,62 the literature clearly reports an increased risk of peri-operative complications in obese patients, which include an increased risk of intra-operative injury to the medial collateral ligament, wound dehiscence and infection, pulmonary atelectasis, thromboembolic events, and loosening of the components and failure.63 Foran et al64 compared the clinical and radiological data from 78 TKRs in 68 obese patients with data from a matched group of non-obese patients. The proportion of knees with a KSS ≥ 80 points at a mean of 80 months was 88% (69 of 78 knees) in the obese group, which was significantly lower than the 99% (77 of 78 knees) seen in the non-obese group. Furthermore, the morbidly obese subgroup had a significantly higher rate of revision than the non-obese group. The authors concluded that any degree of obesity, defined as a body mass index ≥ 30, has a negative effect on the outcome of TKR. In a study that compared 326 TKRs in those with a BMI > 30 with 425 TKRs in patients with a BMI < 30, the rate of focal osteolysis (radiolucency) was found to be five times that of control subjects when the BMI exceeded 40, although ten-year survivorship rates showed no appreciable difference.65 In this same study, the revision rate in the obese group was 4.9% (16 patients) compared with 3.1% (13 patients) in the non-obese group. At a mean follow-up of nearly 76 months, the mean increase in International KSS was comparable between the two groups. The authors pointed out that while one would expect a poorer outcome following joint replacement from increased body weight as a result of greater biomechanical force generated, differentiation between weight and obesity is important, as the former is an absolute measure while the latter is relative. Whereas body weight may be predictive of increased failure, BMI may not.66 Furthermore, the authors were cognisant of the work by McClung et al,67 which showed that a higher BMI in patients undergoing arthroplasty of the hip and knee was associated with a lower activity level, possibly reducing the amount of polyethylene wear, which is a manifestation of use rather than time elapsed. In a recent prospective cohort study of 291 patients undergoing a revision TKR, Mulhall et al68 found that both increased body weight and BMI were significant predictors of reduced implant survivorship and resulted in less improvement in functional and quality of life outcomes six months after a revision TKR.68 The reasons for failure of the prosthesis were not significantly different between the obese and the non-obese group, but the obese patients were more likely to have specific comorbidities. Styron et al69 recently reviewed 162 patients who had undergone a TKR and found that morbid obesity was not significantly associated with a slower return to work. In their prospective cohort, they found that the factors that predicted a delayed return to work were the receipt of Workers’ Compensation, having a physically demanding job, and having less pain pre-operatively. Patients who were self-employed, those with a ‘sense of urgency about returning to work’ and those employed at a ‘handicap-accessible workplace’ returned to work earlier. Women, despite being far more likely to be obese, returned to work sooner than their male counterparts.69 Return to work included return to part-time jobs. The study did not address socioeconomic or regional variations, but it was quite telling that motivation on the part of the patient, regardless of obesity, was crucial to a timely return to work. While the study described above stressed patient motivation as critical to functional outcome, patient expectations continue to
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