The effect of BMI on long-term outcomes after operatively treated ankle fractures: a study with up to 16 years of follow-up

Background: Ankle fractures are a common injury and the main cause of post-traumatic ankle arthritis. The prevalence of obesity is increasing worldwide, and this population is known to have poorer short and midterm outcomes after ankle fractures. Our objective is to assess long-term patient-reported outcomes in patients with operatively treated ankle fractures, and the effect of BMI on these results using the new and validated patient-reported outcome questionnaire, the Manchester Oxford foot and ankle questionnaire (MOXFQ). Methods: We performed a retrospective review of all ankle fractures treated operatively in a ten-year period from 2002-2012. The MOXFQ and SF-12 were sent to all patients and were obtained, on average, 11.1 years after surgery (range 5.3-16.2 years). Results: Two thousand fifty-five ankle fractures were reviewed, of which 478 (34%) patients completed the questionnaires. The mean age was 48.1 ± 15.5 years, 52% were men and the mean BMI was 26.1 ± 4.5 kg/m2. Of the 478, 47% were of normal weight, 36% were overweight, and 17% were obese. Overall, 2.1% were type A, 69.9% B, and 24.9% type C fractures. There were no significant differences in the type of fracture between the BMI groups. Comparing obese and non-obese patients, there were large differences in MOXFQ pain (33 ± 29 vs. 18.7 ± 22.1, effect size 0.55), and function scores (27.3 ± 29 vs. 12.5 ± 21.1, effect size 0.58). No differences in complications and reoperations rates were observed. The BMI value at surgery correlated more strongly with the MOXFQ pain score than the BMI at follow-up (Spearman's Rho 0.283 vs. 0.185, respectively). Conclusion: These findings reveal that obese patients have significant worse long-term outcomes, namely increased pain, poorer function, and greater impairment in everyday life after an operatively treated ankle fracture. Moreover, pain and function linearly declined with increasing BMI. Our findings appear to indicate that increased BMI at surgery is an important contributor to adverse outcome in the operative management of rotational ankle fractures. Level of evidence: III.