The impact of obesity on weight change and outcomes at 12 months in patients undergoing total hip arthroplasty

Objectives: To establish the rate of clinically significant weight change after 12 months in patients who have had a primary total hip arthroplasty (THA); to identify patient characteristics that predicted weight loss or gain; and to compare clinical and functional outcomes between obese and non-obese patients.

Design, setting and participants: Prospective study of 471 patients who underwent THA between 2006 and 2007 at St Vincent’s Hospital, Melbourne, a university-affiliated tertiary referral centre. Patients were classified as non-obese, obese and morbidly obese, and were assessed using the Harris Hip Score (HHS) and 12-item Short Form Health Survey (SF-12).

Main outcome measures: Incidence of weight loss or gain 12 months after surgery; preoperative patient variables predictive of weight change; functional and quality-of-life outcomes and rate of adverse events at 12 months; differences in outcomes between obese and non-obese patients.

Results: 194 patients (41%) were obese or morbidly obese. At 12-month follow-up, 18 obese or morbidly obese patients (9%) had lost ≥ 5% of their preoperative weight and 118 patients (25%) had gained ≥ 5% of their preoperative weight. No preoperative predictor of weight loss was identified, but weight gain was associated with lower preoperative SF-12 mental health scores (odds ratio [OR], 0.98 [95% CI, 0.96–0.99]; P = 0.04). There were no significant differences between obesity groups in improvement in HHS or SF-12 physical health scores. Improvement in SF-12 mental health scores was greater in obese (+ 3.6 [SD, 12.2]) and morbidly obese (+ 3.7 [SD, 9.4]) patients than in non-obese patients (– 0.1 [SD, 11.7]) (P = 0.01). Compared with non-obese patients, the odds of a postoperative complication were significantly greater in obese patients (OR, 1.81 [95% CI, 1.05–3.11]) and morbidly obese patients (OR, 5.77 [95% CI, 2.10-15.86]).

Conclusion: Clinically significant weight loss in obese patients after THA is uncommon. Obese and morbidly obese patients experience comparable reduction in pain and improvement in function after THA, but the risk of complications in the first 12 months after surgery is significantly greater than the risk in non-obese patients.