Analysis of risk factor for nail breakage in patients with mechanical failures after proximal femoral nail antirotation in intertrochanteric fractures.

Breakage of the intramedullary nail is a rare complication after proximal femoral nail antirotation (PFNA) in intertrochanteric fracture treatment. The purpose of this study was (1) to investigate the frequency of nail breakage among the patients who were treated for mechanical failure after PFNA for intertrochanteric/pertrochanteric fracture, and (2) to determine the risk factors for nail breakage in PFNA treatment of intertrochanteric fracture.To identify mechanical failure after internal fixation using PFNA, we retrospectively reviewed the data of 35 patients (35 hips) who required reoperation after PFNA with a helical blade for intertrochanteric/pertrochanteric fracture between June 2005 and June 2018.We evaluated the frequency of breakage of PFNA and compared the demographic and radiologic parameters between the breakage and control (non-breakage) groups. We also compared the lever arm for the load of stress from the fulcrum according to the centrum-collum-diaphyseal (CCD) angle of blade by using reverse design technique.Among the 25 patients with mechanical failure after PFNA except 10 patients with peri-implant infection and osteonecrosis, 7 (28.0%) showed breakage of PFNA at average of 8 months (range, 5-13 months) after index surgery. A larger horizontal offset (the horizontal distance from the lateral surface of the IM nail and the medial tip of helical blade) was associated with an increased risk of nail breakage. A CCD angle of 130° has a shorter lever arm for the load of stress from the fulcrum, meaning a higher stress for nail breakage, although there was no association between CCD angle and breakage of the nail.Our study suggested that higher horizontal offset and a higher CCD angle can increase the risk of breakage of the PFNA nail at the aperture for the helical blade.