Potential pitfalls of lateral radiographic assessment of the nail position in the distal femur.

INTRODUCTION

Antegrade nailing of proximal femur fractures is a widely accepted treatment that relies on lateral radiographs to assess distal nail positioning. However, the distal femur is trapezoidal in cross section, consequently standard lateral radiographs may be insufficient. This study aimed to utilise 3D modelling to virtually assess the accuracy of lateral radiographs in defining the position of a femoral nail in the distal femur, specifically considering distal cortical encroachment.

MATERIALS AND METHODS

Three-dimensional models of a commonly used nail, were positioned in 3D models of 63 femora, generated from CT scans. Lateral projections, representative of lateral radiographs, were generated and measurements of the closest point distance between the distal nail and anterior inner cortex were recorded. Axial slices through the model at the same distal position were produced for any nails located in the canal's anterior 1/5th and used to quantify the shortest nail to anterior cortex distance.

RESULTS

A significant (p = 0.000) difference exists between the positions of the nail in the lateral projection (- 1.7 ± 1.24 mm) compared with axial position (- 0.23 ± 1.41 mm) with reference to the inner cortical surface. In the lateral projection, 30 nails were located in the canal's anterior 1/5th, of these, 14 nails were identified in the axial position as perforating the inner cortex, with four also perforating the outer cortex surface.

CONCLUSION

Femoral nails are often anteriorly located in the distal femur and reviewed using lateral radiographs. However, this research demonstrates that owing to the geometry of the distal femur, a lateral radiograph may be inadequate for determining the true position of a femoral nail within the distal femur. Accurately assessing the position of femoral nails may help to address and prevent thigh pain, and iatrogenic fracture or perforation which have been associated with anterior positioning.