Several specimen specific vertebral (VB) models have been proposed in the literature; these replicate the typical set-up of a vertebral body mounted in bone cement and subject to a compressive ramp. VB and cement geometries are obtained from micro-CT images, the cement is typically assigned properties obtained from the literature while VB properties are inferred from the Hounsfield units- where the conversion factor between grayscale data and Young's modulus is optimised using experimental load-displacement data. Typically this calibration is performed on VBs dissected from the same spines as the study group. This, alongside the use of non-specific cement properties, casts some doubts on the predictivity of the models thus obtained. The predictivity of specimen specific FE models was evaluated in this study.

VBs obtained from three porcine cervical segments (C2-C6) were stripped of all soft tissues, potted in bone cement and subject to a compressive loading ramp. A speckle pattern was applied to the anterior part of the specimen for DIC imaging. Specimen specific FE models were constructed from these specimens and a conversion factor between grayscale and material properties was optimised. Cement properties were assigned based on literature data. VBs from a further cervical spine (C2-C7) were subject to the same experimental protocol. In this case, the models generated from microCT images the material properties of bone were assigned based on the average conversion factor obtained previously. The predicted load-displacement behaviour thus obtained was compared to experimental data. Generally, poor agreement was found between overall load-displacement. The use of generic cement properties in the models was found to be partly responsible for this. When the load displacement behaviour of the VB was studied in isolation, good agreement within one standard deviation was found with 4 out of 6 models showing good correlation between simulation and DIC data.

Digital image correlation (DIC) is rapidly increasing in popularity in biomechanical studies of the musculoskeletal system. DIC allows the re-construction of full field displacement and/or strain maps of the surface of an object. DIC systems typically consist of two cameras focussing on the same region of interest. This constrains the angle between the cameras to be relatively narrow when studying specimens characterised by complex geometrical features, giving rise to concerns on the accuracy of the out of plane estimates of movement.

The aim of this research was to compare the movement profiles of bony segments measured by DIC and by an optoelectronic motion capture system.

Five porcine cervical spine segments (C2-C6) were obtained from the local butcher. These were stripped of all anterior soft tissues while the posterior structures were left intact. A speckle pattern was applied to the anterior aspect of the specimens, while custom made infrared clusters were rigidly attached to the 3 middle vertebral bodies (C3-C5). The specimens were mounted in a custom made impact rig which fully constrained C6 but allowed C2 to translate in the axial direction of the segment. Images were acquired at 4kHz, both for the DIC (Photron Europe Ltd, UK) and motion capture cameras (Qualisys Oqus 400, Sweden). The in-plane and out of plane displacements of each of the VBs were plotted as a function of time and the similarity between the curves thus obtained was analysed using the SPM1D technique which allowed a comparison to be made in terms of t-statistics. No statistical differences were found between the two techniques in all axis of movement, however the out of plane movements were characterised by higher variance which is attributed to the uncertainty arising from the near parallel positioning of the cameras in the experimental set-up.

Head collisions in sport can result in catastrophic cervical spine injuries. Musculo-skeletal (MSK) modelling can help analyse the relationship between players' motion, external loading and internal stresses that lead to injury. However, the literature lacks sport specific MSK models. In automotive research the intervertebral disc behaviour has been represented as viscoelastic elements (“bushing”), whose stiffness and damping parameters are often estimated under quasi-static conditions and may lack validity in dynamic impacts. The aim of this study was to develop a validated cervical spine model for axial impacts for future use in the analysis of head-first rugby collisions.

A drop test rig was used to replicate a sub-catastrophic axial head impact. A load of 80 N from 0.5 m was applied to the cranial aspect of a C2-C6 porcine spinal specimen mounted in the neutral position. The 3D motion of C3-C5 vertebras (4 kHz) and the cranial axial load (1 MHz) were measured via motion capture (Qualysis, Sweden) and a uniaxial load cell (RDP Electronics Ltd, UK). Specimen specific models were created in NMSBuilder and OpenSim after the vertebrae geometries were obtained from the segmentation of micro-CT images of the specimens. The compressive viscoelastic properties of four vertebral joints (C2-C3 through to C5-C6) were optimised via a Genetic Algorithm (MATLAB v2016b, The Mathworks Inc) to minimise tracking errors.

The optimisation converged to a solution of 140–49000 kN/m and 2000–8000 Ns/m for stiffness and damping respectively (RMSE=5.1 mm). Simulated joint displacements ranged between 0.09 – 1.75 mm compared to experimental 0.1 – 0.8 mm.

Optimal bushing parameters were higher than previously reported values measured through quasi-static testing. Higher stiffness and damping values could be explained by the higher-dynamics nature of the event analysed related to a different part of the non-linear intervertebral disc load-displacement curve.

Cervical spine fractures are frequent in impact sports, such as rugby union. The consequences of these fractures can be devastating as they can lead to paraplegia, tetraplegia and death. Many studies have been conducted to understand the injury mechanisms but the relationship between player cervical spine posture and fracture pattern is still unclear. The aim of this study was to evaluate the influence of player cervical spine posture on fracture pattern due to an impact load. Nineteen porcine cervical spines (C2 to C6) were dissected, potted in PMMA bone cement and mounted in a custom made rig. They were impacted with a mean load of 6 kN. Eight specimens were tested in an axial position, five in flexion and six in lateral bending. All specimens were micro-CT imaged (Nikon XT225 ST Scanner, Nikon Metrology, UK) before and after the tests, and the images were used to assess the fracture patterns. The injuries were classified according to Allen-Ferguson classification system by three independent observers. The preliminary results showed that the main fracture modalities were consistent with those seen clinically. The main fractures for the axial orientation were observed in C5-C6 level with fractures on the articular process and endplates. These findings support the concept that the fracture patterns are related to the spine position and give an insight for improvements on sports rules in order to reduce the risk of injury.