Developing a Finite Element Model of the Cervical Collar-Head Interface

BACKGROUND<br/>Cervical collars provide external support to the upper spine, aiding rehabilitation and reducing the risk of damage. The mechanical loading that cervical collars put on the skin causes discomfort, pain, and damage in the form of pressure ulcers [1]. To date, there has been limited design innovation through bioengineering approaches to improve device design and interfaces.<br/><br/>AIM<br/>This study aims to evaluate cervical collar design through observed and predicted contact pressures at the device interface through finite element (FE) modelling and a phantom physical model.<br/><br/>METHOD<br/>A finite element and in vitro physical model were developed to evaluate the application of the rear of a cervical collar onto a phantom head shape. The FE model (fig. 1a) includes a uniform soft tissue with a thickness of 8 mm, and linear elastic modulus E = 200 kPa, v = 0.45. The collar was modelled with linear elastic shell elements for the stiff support material (E = 600 MPa, v = 0.3). A first-order Hyperfoam model was fitted to material test data for the foam padding. A friction coefficient of 0.6 was used at the collar-skin interface. The collar was pulled from either side onto the head. This was replicated in the physical model with pressure recorded at the device-skin interface in key locations while a load cell monitored tension.<br/><br/>RESULTS<br/>Initial contact was made with the edge of the collar foam resulting in the highest interface pressures (fig. 1b). Both the FE and physical models show an increase in the interface pressure with increasing tension. Contact pressure values were in a similar order of magnitude according to strap tension between FE and physical model testing, though the FE model generally underpredicts the interface pressures (fig. 1c). As more tension was applied a greater contact area was observed, while the pressure peak at the occput moved down corresponding to stiffer plastic of the collar impinging on the foam material.<br/><br/>DISCUSSION AND CONCLUSION<br/>This study presents the first step in developing an FE model that can be used as a preclinical in-silico evaluation of cervical collar design. While these specific results have limited generalisability, future developments will evaluate collar fit across a population of head shapes and collar designs. This may enable the evaluation of new collar designs that better suit the needs of all users and help reduce device-related pressure ulcers.<br/><br/>REFERENCES<br/>1. Brannigan; 2022, Global Spine Journal<br/><br/>ACKNOWLEDGEMENTS<br/>Supported by the UK EPSRC grant EP/S02249X/1 for the Centre of Doctoral Training in Prosthetics and Orthotics