Beware the Boxer's Fracture Imposter: Where Does the Metaphysis End and the Diaphysis Begin?

Fractures of the fifth metacarpal are a common injury. In children, they are often stable and heal uneventfully, including after closed reduction. Fractures of the metacarpal diaphysis, conversely, tend to be unstable and may require surgical intervention. It is unclear at what point fractures of the fifth metacarpal fracture should be considered unstable. We identify the location at which a fifth metacarpal fracture is at risk for surgical intervention. A two-year retrospective cohort analysis of all children (age ≤18) with fifth metacarpal fractures presenting to a Pediatric Plastic Surgery clinic was performed. Clinical and radiographical data were acquired from electronic medical records. Fracture location and fracture angulation were measured, descriptive statistics were performed, and multivariable logistic regression was used to identify predictors for surgery. Ninety-eight patients met criteria for review. Mean patient age was 14.0 years (SD 2.2), and 95% were male. Forty-two (44.2%) patients underwent closed reduction, and 12 (12.2%) patients were recommended for surgery. Increased fracture angulation on initial lateral radiograph (OR: 1.08 (1.03-1.14 95% CI), p = 0.006) and more proximal fractures (OR: 0.92 (0.86-0.98 95% CI), p = 0.008) were identified as independent predictors for surgery. Fractures occurring proximal to 70% of metacarpal length resulted in accurate detection of those requiring surgery with 72.4% sensitivity, 75.3% specificity, 95.5% and 27.6% negative and positive predictive value, respectively. In pediatric fifth metacarpal fractures, increased fracture angulation and those occurring proximal to 70% of the metacarpal length were independent predictors for surgery.