Material Behaviours of Healthy, Degenerate and Hydrogel Injected Bovine Intervertebral Discs

Dougill, GM, Thorpe, A, Andrews, K, Sammon, C, Reeves, N, LeMaitre, CL and Cooper, G (2015) Material Behaviours of Healthy, Degenerate and Hydrogel Injected Bovine Intervertebral Discs. In: DISCS 10th Henry Crock Lecture, 30th September 2015. (Unpublished)

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Abstract

Objectives Low back pain (LBP) is an increasing drain on developed economies due to direct medical costs and lost working days. The majority of medical costs can be attributed to long-term problems resulting from specific physiological conditions. Acute injury and/or chronic degeneration of the intervertebral disc (IVD) has been linked with long term pain with high levels of nerve in-growth in degenerate IVDs. The fact that disc degeneration is a structural failing and not just a pathogenesis of pain may lead to reduced mobility and quality of life (QOL). Mesenchymal stem cell (MSC) interventions have been proposed as a treatment for degenerate IVDs but little is known about how the injection of a hydrogel matrix required by such interventions affects the material properties of the intervertebral disc and what effects this might have on disc health. This study aims to determine the difference in material behaviours of healthy, degenerate and hydrogel injected IVDs subjected to cyclic loading simulating activities of daily living (ADL). Materials and Methods Bovine coccygeal discs were dissected whole from tail sections and split in to three equal test groups; healthy, degenerate and hydrogel injected. Degenerate and hydrogel injected groups were injected with a 2 mg/ml collagenase solution and incubated at 37°C for 2 hours to simulate moderate degeneration, the hydrogel injected group then received a hydrogel injection. All discs were then subjected to sinusoidal loading at 2Hz at force levels equivalent to those in the human spine during walking and mechanical data analysed to determine respective material behaviours of each group. Results Under axial loading simulating walking in the lumbar spine compression (absolute and relative strain) and stiffness of discs varied across all three test groups. Conclusions Cyclic loading simulating activities of daily living was found to result in different material behaviours in bovine intervertebral discs that were moderately degenerated and/or injected with hydrogel relative to healthy discs.