A mechanical and clinical evaluation of the Helix Wire for subcapital humerus fracture ostheosynthesis

The aim of this paper is the investigation of the mechanical properties the Helix Wire, a device that has been employed for subcapital humerus fracture ostheosynthesis in recent years. There are several potential clinical advantages associated with its use, but clinical results reported in literature are controversial. The Helix Wire has been assimilated to a helical spring, and several analytical solutions for displacements and stresses have been compared and experimentally validated, showing the importance of the pitch angle contribution. Based on the results, the main factor for the clinical indication of this fixation device was found to be the patient age. In fact, the use of the Helix Wire should be avoided in case of young patients or of patients with well-developed muscular masses, where the forces may easily lead to critical stresses in the spring and separation of the fracture surfaces. The clinical results obtained on 30 elderly patients confirmed these findings.