Can body mass index influence the fracture zone in the fifth metatarsal base? A retrospective review

Background Fifth metatarsal base fracture are a common occurrence in the orthopaedic practice. Literature on the epidemiology of such fractures is scarce. The aim of this analysis was to study the relationship between Body Mass Index (BMI) and the zone of the fifth metatarsal base involved by the fracture. Methods Data on adult patients who have been diagnosed with isolated fifth metatarsal base fracture were gathered at our Institution (blinded for review). Age, sex, height, weight and injury mechanism were collected from electronic medical records. Fractures were classified according to the Lawrence and Botte classification (Zone 1, 2 and 3) by three independent reviewers. Results From March 2016 to December 2018, 149 patients (109 women and 40 men) have been diagnosed with fifth metatarsal base fracture. Average age and BMI at the time of injury were 51.9 (SD 17.1, range 18–84) and 24.0 (SD 3.8, range 16.4–36.7) respectively. Fracture distribution was 63.8% in zone 1, 23.5% in zone 2, 12.7% in zone 3. 12.1% of patients had a BMI < 20 kg/m2, 57.7% between 20 and 24.9 kg/m2, 22.2% between 25 and 29.9 kg/m2 and 8.0% over 30 kg/m2. No statistically significant differences attributable to sex (p = 0.774) or age (p = 0.379) were found between different zones of fracture. Average BMI was found to be higher in the zone 3 (26.1 ± 4.7 kg/m2) fracture group than in zone 1 (23.7 ± 2.9 kg/m2) (p = 0.031). Conclusion The prevalence of proximal diaphysis (zone 3) fractures rises proportionally with BMI in our sample study. BMI appears to have an impact on fifth metatarsal base fractures pattern.