Biomechanical performance of an intramedullary Echidna pin for fixation of comminuted mid-shaft clavicle fractures

Abstract

Background: Surgical fixation of comminuted mid-shaft clavicle fractures commonly employs intramedullary devices; however, pins with smooth surfaces are prone to migration, whilst threaded pins can be challenging to remove post-operatively. The aim of this study was to evaluate the biomechanical performance of fractured clavicles repaired using a novel intramedullary Echidna pin device and a non-threaded Knowles pin. The Echidna pin features retractable spines that engage with the bone to minimize migration and facilitate ease of device removal. Methods: A total of 28 cadaveric clavicle specimens were harvested and a mid-shaft wedge-shaped osteotomy was performed to simulate a comminuted butterfly fragment. Specimens were allocated randomly to either the Echidna pin or Knowles pin fracture repair groups. Following surgery, eight specimens in each group underwent 200 cycles of four-point bending, whilst six specimens in each group underwent torsional testing and pull-out. Cyclic construct bending stiffness, torsional stiffness and ultimate strength were recorded. Results: Echidna pin intramedullary repair constructs showed significantly greater bending stiffness (mean difference 0.55 N.m/°, 95% confidence interval −0.96, −0.14, P = 0.01) and pull-out strength (mean difference 146.03 N, 95% confidence interval 29.14, 262.92, P = 0.019) in comparison to Knowles pin constructs. There was no significant difference in torsional stiffness between Echidna pin and Knowles pin repair constructs (P > 0.05). Conclusion: The intramedullary Echidna pin device, which exhibits greater bending strength and pull-out strength than that of the Knowles pin, may produce a more stable clavicle fracture reduction compared to that of commercially available threadless intramedullary pins.