Abstract
Purpose
To investigate the effect of obesity on functional outcome following total ankle arthroplasty.
Method
We identified 43 obese patients (46 ankles) (BMI > 30kg/m2), using a prospectively collected database of total ankle arthroplasties. Inclusion criteria included: (a) Post-traumatic or inflammatory arthritis; (b) Minimum two-year follow-up, (c) Coronal plane deformity less than 10 degrees. Exclusion criteria: (a) Co-morbidity affecting physical function; (b) Recent total joint arthroplasty.
American Orthopaedic Foot and Ankle Society (AOFAS), Ankle Osteoarthritis Scale (AOS) and SF-36 questionnaires were used preoperatively and at latest follow-up. Revision was defined as any intervention requiring replacement of part or whole of the prosthesis.
A control group of non-obese individuals (BMI 18.5–29.9kg/m2) was devised matching for age within 10 years, gender, diagnosis, implant and length of follow-up (within 1 year). From the original group of 46 ankles, we matched 28 ankles, thereby constructing two groups for comparison (matched obesity and control).
Results
From the original obesity group (n=46, mean BMI 34.7, age 65.1 years and follow-up 3.5 years), four patients were lost to follow-up. There were 10 revisions (21.7%) including five for liner exchange, four full component and one revision to fusion. Statistically significant (p<0.001) improvements were detected with all outcome measures (AOFAS, AOS and SF-36).
In the matched obesity and control groups we used 11 STAR, 11 Mobility and six Hintegra implants. Delayed wound healing affected one patient in each group. In the matched obesity group (mean BMI 35), there were six revisions (three liner exchange, three full component) (21.4%), at a mean of 3.2 years. One patient was lost to follow-up (known to be revised). Statistically significant improvements were noted with all outcome measures.
In the control group (mean BMI 26.1), there were three revisions (two liner exchange and one full component) (10.7%), at a mean of 2.3 years. All patients were followed-up. Statistically significant improvements were associated with all outcome measures except the mental component summary of the SF-36 (52.2 to 54, p=0.37). The same score pre-operatively was lower in the matched obesity group (45 vs. 52.2, p=0.193).
Overall, no difference was found in mean outcome score improvement between groups. In the matched obesity group, the mean pre-operative AOS pain score was higher (58.8 vs. 46.5) (p=0.016), as was the preoperative AOS disability score (68.4 vs. 58.5) (p=0.082). The mean post-operative AOS pain and disability scores were also higher, although not reaching significance (p=0.096 and p=0.241 respectively).
Conclusion
Obesity is associated with greater functional and psychological preoperative burden, although the overall improvement in functional outcome is comparable to non-obese matched controls. Obese patients can expect a significantly higher revision rate (21.4% vs 10.7%) within five years of surgery.
