Who is in danger? Impingement and penetration of the anterior cortex of the distal femur during intramedullary nailing of proximal femur fractures: Preoperatively measurable risk factors

BACKGROUND: Intramedullary nail (IMN) perforation through the cortex of the distal femur is a risk of intramedullary stabilization of proximal femur fractures. This study was performed to identify information that is available before operation that can pick out patients at risk for this complication. METHODS: A retrospective review of records and roentgenograms of 150 patients treated with intramedullary stabilization of a proximal femur fracture during a 4-year period at a Level I trauma center was performed. The position of the tip of the IMN in the distal femur was measured on postoperative lateral roentgenograms and grouped into anterior, middle, or posterior one third positions. Patients in whom the tip of the nail contacted or penetrated through the anterior cortex were designated as having cortical impingement. RESULTS: Nail tip position was in the anterior one third of the distal femur in 71 (47%) of 150 patients, and 38 (25%) of these patients fit the definition for cortical impingement. The radiographic femoral angle of incidence strongly correlated with an anterior nail tip position (p < 0.0001) and cortical impingement (p < 0.0001). Shorter patients were also more likely to have cortical impingement (p < 0.005), and patients less than 160 cm in height had a 49% likelihood of impingement. A starting point in the posterior one third of the greater trochanter increased the likelihood of having an anterior nail tip position as well (p < 0.007). CONCLUSION: Of the 150 patients in whom an IMN was used for stabilization of a proximal femur fracture, 71 (47%) had the distal part of their nail positioned in the anterior one third of the distal femur. Patients who are shorter and/or had an increased femoral bow as measured on a lateral roentgenogram are more likely to have an anterior nail tip position or cortical impingement. Posterior starting points should be avoided to prevent this complication. LEVEL OF EVIDENCE: Prognostic study, level III; therapeutic study, level IV.