Rewriting the tip apex distance for the proximal femoral nail anti-rotation

Abstract

Introduction: The proximal femur nail anti-rotation (PFNA-II) (Synthes GmbH, Oberdorf, Switzerland) is the most commonly used implant for intramedullary nailing of unstable intertrochanteric fractures in our centre. However, mechanical failure of the bone with respect to the implant is a cause of concern due to its significant morbidity especially in the elderly. To date, factors for fixation failures are not well defined in the literature. This study aims to evaluate the factors that predispose to cut out of the PFNA implant and to provide a guide for surgical fixation.

Patients and methods: This study was a retrospective analysis of 340 patients who underwent PFNA-II insertion from 2011 to 2013 in our centre. Intraoperative image intensifier images were used for calculation of tip apex distance, neck shaft angles, determination of Cleveland zones. Demographic data was collected on patients age and gender. The fractures were classified based on AO-OTA classification (Marsh et al., 2007) [1]. Patients were followed up for a minimum of 4 months and union of the fracture or until a complication occurred. Risk ratio for cut out was also compared with each statistically significant variable to determine the cut-off point.

Results: The incidence of cut out was 6.7% Tip apex distance, neck shaft angles and female gender were statistically significant for cut out. The study found that tip apex distance beyond 27mm increased the risk of cut out. Neck shaft angles less than 128° also increased the risk of cut out. Posterior and superior blade position in the femoral head and AO 31A3 fractures trended towards significance for cut out but were not statistically significant.

Conclusion: To avoid cut out, one should aim for a tip apex distance of not more than 27mm and preserve a neck shaft angle of more than 128°. Risk stratification of the patient allows the surgeon to take greater caution in the post-operative period to detect early cut out.

Keywords: Cut out; Neck shaft angle; PFNA; Tip apex distance.