Femoral Intramedullary Nails: Classification, Design and Clinical Relevance
Intramedullary nailing is the treatment of a femoral shaft fracture by placing a load-sharing implant within the medullary canal, usually with proximal and distal interlocking to control length, alignment and rotation. For examination purposes, femoral nails are best classified by their anatomical entry point, anatomical region treated, locking configuration, design characteristics and intended use. Understanding these features is essential not only for selecting a nail, but also for understanding why a nail may become stuck, bent, or broken in a non-united fracture.
1. Basic anatomical and biomechanical orientation
The adult femoral canal is not a uniform cylinder. It is generally widest in the metaphyseal regions and narrowest at the isthmus, with anterior bowing in the sagittal plane and variable coronal-plane curvature. The medullary canal is also often eccentric in the distal femur. Therefore, a nail must have an appropriate radius of curvature, diameter and length; an excessively straight or large nail may resist insertion or cause cortical perforation.
A femoral nail functions primarily as a load-sharing device. Interlocking screws prevent shortening, rotation and telescoping, while the nail provides relative stability and maintains alignment. In a simple transverse fracture, controlled axial loading…