Healing of Atypical Subtrochanteric Femur Fractures After Cephalomedullary Nailing: Which Factors Predict Union?

OBJECTIVES: The purpose of this study was to determine the healing rate and time to union of atypical subtrochanteric fractures treated with cephalomedullary nailing. DESIGN: Retrospective review, descriptive, and analytic study. SETTING: Six level 1 trauma centers. PATIENTS/PARTICIPANTS: The study included 42 patients with 48 displaced, atypical, bisphosphonate-associated subtrochanteric femur fractures who underwent surgical intervention. INTERVENTION: Cephalomedullary femur nailing. MAIN OUTCOME MEASUREMENT: The main outcome measures were radiologic healing and time to union. RESULTS: The primary healing rate after cephalomedullary nailing of bisphosphonate-associated subtrochanteric femur fractures was 68.7% (33/48 patients). Mean time to union was 10.7 months. Malalignment was determined using the differences in neck-shaft angle (the difference between the normal side and the surgically repaired side) and sagittal angulation. These all proved to be significantly correlated with failure and delayed healing time. The cutoff points for neck-shaft angle, difference in neck-shaft angle, and sagittal angulation were 125.6, 4.4, and 5.5 degrees, respectively (receiver operating characteristic curve analysis). CONCLUSIONS: The healing rate of atypical subtrochanteric femur fractures treated with cephalomedullary nailing is lower than that previously reported for atypical femur fractures. The quality of fracture reduction proved to be the most important factor in bony union and time to union. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.