Abstract
Aim
To compare the results of total knee replacement in a consecutive series of morbidly obese patients (body mass index (BMI) > 40 kg/m2) with a matched group of non-obese (BMI< 30 kg/m2) patients.
Methods
41 consecutive total knee replacements performed in morbidly obese patients were matched pre-operatively with 41 total knee replacements performed in non-obese patients for age, sex, diagnosis, type of prosthesis, laterality, knee score and function score components of the Knee Society Score (KSS). All patients were prospectively followed up and the post-operative KSS, radiographs, complications (superficial wound infection, deep joint infection, deep venous thrombosis, peri-operative mortality) and five-year survivorship compared for the two groups. No patients were lost to follow-up (mean follow-up in morbidly obese: 38.5 (range 6-66) months; non-obese: 44 (range 6-67) months).
Results
The mean knee score was inferior in the morbidly obese group compared to the non-obese group, but the difference only approached significance (p=0.08). The mean function score was significantly inferior in the morbidly obese group compared to the non-obese group (p=0.01). Total knee replacements performed in morbidly obese patients were associated with a significantly higher incidence of radiolucent lines on post-operative radiographs (29% vs. 7%, p=0.02) and a significantly higher complication rate (32% vs. 0%, p=0.001). The five-year survivorship based on revision and pain as endpoints was 72.3% (95% Confidence Interval (CI) 52.1%-92.5%) for the morbidly obese group compared to 97.6% (95% CI 92.9%-100%) for the non-obese group (log-rank test, p = 0.02).
Conclusion
In a subgroup of obese patients who are morbidly obese, the results of total knee replacement are poor. These patients should be advised to lose weight prior to surgery or be warned of the inferior results before proceeding with surgery.
