Comparative Evaluation of a Positive-Locking Antirotation Mechanism in the Design of Telescopic Nails for Patients in the Growth Phase

Abstract

The aim of this study is to develop an intramedullary telescopic nail that—in contrast to the current standard—is rotationally stable and firmly anchored in the bone proximally and distally, without containing any extraosseous components that may alter the surrounding soft tissue. Three prototypes for a positive-locking adapted telescopic intramedullary nail (PLATIN) were developed. In a series of biomechanical tests, the prototypes were compared with two Fassier–Duval telescopic nails, which represent the clinical standard. Axial pressure, torsion, and four-point bending measurements were carried out in a materials testing machine, with the telescopic nails implanted into composite bone. Tests were conducted without failure and up to failure. Specifically, the force required for telescoping, as well as torsional stiffness and bending stiffness, was investigated. Taking into account differences that were inherent in the materials, the prototypes showed similar results in the four-point bending tests. In the pressure tests, the prototypes required greater forces than the Fassier–Duval nails. The torsional stiffness was between 0.020 N·m/deg and 0.135 N·m/deg, depending on the diameter of the nail. Positive-locking effect was achieved by a hexagonal shape of an inner rod part and a hexagonal form-fitting outer tube part. Proximal and distal locking of the telescopic nail in the bone was performed by usage of K-Wires in specific arranged drill holes at the end of both parts. Based on these satisfactory results, the future clinical application of positive-locking irrotational telescopic nails can be expected. Furthermore, redesign or development of new designs for existing telescopic nails is recommended.