An intramedullary Echidna pin for fixation of comminuted clavicle fractures: a biomechanical study

Abstract

BackgroundIntramedullary fixation of comminuted mid-shaft clavicle fractures has traditionally been employed with satisfactory clinical outcomes; however, pins with smooth surfaces may protrude from the bone and are prone to migration, while some threaded pins are difficult to remove post-operatively. The aim of this proof-of-concept study was to develop and evaluate the biomechanical strength of a novel intramedullary Echidna pin device designed to maintain fracture reduction, resist migration and facilitate ease of post-operative removal.MethodsThirty human clavicle specimens were harvested and fractured in a comminuted mid-shaft butterfly configuration. Each specimen was randomly allocated to three surgical repair groups including intramedullary fixation using the Echidna pin and Herbert Cannulated Bone Screw System, as well as plate fixation using bi-cortical locking screws. Using a biomechanical testing apparatus, construct bending and torsional stiffness were measured, as well as ultimate bending strength.ResultsThere was no significant difference in torsional stiffness and ultimate bending moment between the Echidna pin and Herbert screw repair constructs (p > 0.05); however, the Echidna pin construct demonstrated a significantly greater bending stiffness compared to that of the Herbert screw construct (mean difference 0.55 Nm/deg., p = 0.001). The plate construct demonstrated significantly greater torsional stiffness, bending stiffness and ultimate bending moment compared to those of the Herbert screw and Echidna pin (p < 0.05).ConclusionsAn intramedullary Echidna pin device was designed to stabilize comminuted fractures of the clavicle, maintain fracture compression and provide ease of removal post-operatively. Since the results suggest equivalent or superior torsional and bending stability in the Echidna pin compared to that of the Herbert screw, the Echidna pin concept may represent an alternative fixation device to conventional intramedullary screws, nails and pins; however, superior plating using bi-cortical locking screws provides substantially higher construct structural rigidity than intramedullary devices, and may therefore be useful in cases of osteoporotic bone, or where high fracture stability is required.

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

“…A total of 28 embalmed clavicles (14 matched pairs) were harvested from human cadavers (mean age 82.5 years, range 55–91 years, 14 left, 14 right). A sample size of 28, with 14 specimens per group, was chosen as this has been shown to yield a study power of 0.8 for detecting significant differences in bending stiffness . Soft tissue was removed by sharp dissection and all specimens were radiographically screened for macroscopic osseous degeneration or fracture (Fluoroscan InSight 2; Hologic, Inc., Marlborough, MA, USA).…”

“…Clavicle pairs were randomly allocated to Knowles pin (Syntec Scientific Corporation, Taichung, Taiwan) and Echidna pin fixation groups (Echidna Surgical Solutions Pty Ltd., Ringwood, VIC, Australia). The Echidna pin was deployed into the intramedullary canal using a previously described methodology, without the application of torsion . The intramedullary canal of each specimen was identified and predrilled to allow placement of each intramedullary device from the posterolateral aspect.…”

“…Titanium elastic nails, Rockwood pins and non‐threaded Knowles pins can be easily placed intraoperatively, safely removed after healing and have been employed with good clinical, functional and cosmetic outcomes; however, smooth intramedullary devices are prone to migration, which can ultimately risk injury of adjacent neurovascular structures and viscera . The Herbert cannulated bone screw is reverse threaded, and locks cortical bone fragments during fracture reduction; however, its removal is challenging and may result in bone damage, and thus this implant is typically considered permanent . Biomechanical studies have demonstrated that clavicles repaired with Rockwood pins perform similarly in bending to those fixed with plates .…”

“…The Echidna pin, which was designed as an alternative to currently commercially available intramedullary devices (Fig. ), features retractable spines that anchor the implant within the bone of the intramedullary canal, reducing risk of migration, increasing construct stability and facilitating ease in device removal . It lacks a lateral head, and therefore resides entirely beneath the surface of the bone.…”

“…It lacks a lateral head, and therefore resides entirely beneath the surface of the bone. Preliminary research has demonstrated improved bending stiffness compared with that of the Herbert screw; however, the functional performance of the Echidna pin under cyclic bending–fatigue conditions, as well as axial loading, has not been evaluated, and its fixation strength has not been compared to that of conventional removable intramedullary pins. The aim of the present study was to evaluate the bending fatigue strength, torsional strength and ultimate tensile capacity of the Echidna pin intramedullary fixation device in a human cadaveric model of a comminuted mid‐shaft clavicle fracture, and to compare the results with those of the Knowles pin.…”