60 – RELATIONSHIPS AMONG BMI, SELF REPORTED COMPLICATIONS, FUNCTIONAL OUTCOMES AND SATISFACTION FOLLOWING ELECTIVE, PRIMARY HIP AND KNEE REPLACEMENT: RESULTS FROM A CANADIAN REGIONAL JOINT REPLACEMENT REGISTRY

Abstract

Purpose: There remains some debate over the impact of obesity on complications and function following total joint replacement. The purpose of this study was to examine the relationship between BMI, self reported complications, function and satisfaction using data from a large prospectively collected dataset.

Method: A total of 5364 procedures with complete one year post operative data were obtained from a Canadian joint replacement registry for analysis. Self reported complications after one year included re-operation, DVT, PE, dislocation and infection requiring antibiotics. BMI was classified as either non-obese (BMI30kg/m2). Satisfaction was collapsed into dichotomous categories: satisfied or unsatisfied. Pre and post operative scores from the Oxford 12 were also included.

Results: The mean age of the total hip replacement (THR) group was 67.1 yrs (+/−11.8) with a mean BMI of 29.8 (+/−6.4). The total knee replacement (TKR) group’s mean age was 68.2 yrs (+/−9.99) with a mean BMI of 33.0 (+/−7.0). Ninety percent (90.6%) of THR patients were satisfied one year after surgery compared to only 81.9% of TKR patients (p< 0.0001). For TKR patients, larger BMI was associated with both satisfaction and self-reported complications; obese patients reported being satisfied 82.4% of the time versus non-obese at 76.9% (p=0.037). Complication rates for obese TKR patients were 11.9% and 7.9% for non-obese (p=0.064). For THR patients, a similar relationship did not exist between BMI and satisfaction; however, it was observed for complications. Obese patients reported a complication rate of 7.4% versus 4.2% (p=0.02) for non-obese. Improvements in Oxford 12 scores were noted across all groups; mean improvement was 22 points in the THR group and 15 points in the TKR group, irrespective of BMI. Improvements in Oxford 12 scores were associated with complications; THR patients reporting complications showed mean improvements of 17 points versus 23 for those who did not (p< 0.0001). TKR patients reporting complications had mean improvements of 10 points versus16 for those who did not (p< 0.0001). Satisfaction was also related to Oxford 12 score; THR patients who were unsatisfied demonstrated an Oxford 12 improvement of only 9 points versus 24 points for the satisfied patients (p< 0.0001). Unsatisfied TKR patients demonstrated an improvement of only 4 points compared to 18 points for satisfied patients, (p< 0.0001).

Conclusion: THR patients were younger and more satisfied than TKR patients. There appears to be a positive relationship between BMI and complication rates for both TKR and THR. A larger BMI was related to increased satisfaction in TKR, it was unrelated in THR. Satisfaction was related to degree of functional improvement which, in turn, was curtailed by complications. It is therefore prudent to advise patients to reduce BMI prior to surgery to mitigate complications; however superior or equivalent satisfaction rates and positive functional improvement can be expected post surgery.