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 <70%.

CONCLUSION: When proceeding to femoral fracture reamed intramedullary nailing, we recommend a minimum nail fit of 70% at the isthmus and ideally 90% or more, to avoid surgical reintervention.

LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.