Abstract
Aim
To evaluate the association of BMI and improvement in patient-reported outcomes after TKA.
Methods
Knee replacement outcome data for procedures carried out over an eight month period was extracted from a regional arthroplasty register in the UK. Data was available before surgery and 12 months after. We analysed the impact of overweight on post-operative change in the Forgotten Joint Score − 12 (FJS-12) measuring joint awareness and the Oxford Knee Score (OKS) measuring pain and function using five BMI categories (A: <25, B: 25–29.9, C: 30–34.9, D: 35–39.9 and E: >40).
Results
We analysed data from 431 TKA patients with a mean age of 70.1 (SD=9.2 years) and 54.5% being female. Frequency of the BMI categories in our sample were as follows: A) 15.8% with a BMI<25, B) 32.8 % with a BMI 25–29.9, C) 27.7% with a BMI 30–34.9, D) 16.5 % with a BMI 35–39.9, and E) 7.1 % with a BMI above 39.9. Data analysis showed a statistically significant association (Z= 12.10, p=0.02) of BMI with post-operative improvement in the FJS-12 from pre-surgery to 12 months: A) + 37.9 points (Cohen”s d= 1.67); B) + 40.3 points (Cohen”s d= 1.67); C) + 34.0 points (Cohen”s d= 1.54) D) + 29.7 points (Cohen”s d= 1.29) and E) + 23.5 points (Cohen”s d= 1.24). Post-operative change in OKS did not show a statistically significant association with the BMI categories (Z=1.24, p=0.872).
Conclusions
Our study shows that obesity has an impact on improvement after TKA in terms of joint awareness, with overweight patients being at higher risk of less benefit from surgery. Whereas the FJS-12 showed a substantial difference in the recovery process, the postoperative improvement measured with the OKS was comparable for patients in the different BMI categories. This highlights that outcome scores may differ in their ability to capture the impact of BMI on postoperative recovery.
