Nail Fit: Does Nail Diameter to Canal Ratio Predict the Need for Exchange Nailing in the Setting of Aseptic, Hypertrophic Femoral Nonunions?

OBJECTIVES To evaluate patient-independent risk factors for aseptic femoral hypertrophic nonunion requiring exchange nailing, with particular reference to the fit of the nail at the isthmus within the canal. DESIGN Retrospective case control study. SETTING Level 1 trauma center. MAIN OUTCOME MEASUREMENTS Between 2008 and 2012, 211 patients without any patient-dependent risk factors for nonunion were treated with a locked reamed intramedullary nail for a femoral shaft fracture. Twenty-three cases went on to hypertrophic nonunion requiring exchange nailing (treatment group) and 188 cases went on to union (control group). Patient-independent risk factors for exchange nailing were documented. RESULTS Patient-independent risk factors for exchange nailing were poor fracture reduction [Odds ratio (OR): 11.5, 95% confidence interval (CI), 4.0-33.4, P < 0.001], open fracture (OR: 7.6, 95% CI, 3.0-19.6, P = 0.004), Winquist classification of 4 (OR: 4.4, 95% CI, 1.9-6.7, P = 0.016), and poor nail fit (OR: 10.3, 95% CI, 5.1-28.4, P < 0.001). Multivariate analysis revealed nail fit as an independent predictor of femoral nonunion requiring exchange nailing (OR: 11.4, 95% CI, 6.9-15.2, P < 0.001). Moreover, we found a direct relationship between increasingly poor nail fit and increased risk of exchange nailing, with the criterion occurring at a nail fit ratio