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BIOMECHANICAL STUDIES OF THE DISCO-VERTEBRAL JOINT IN AN OVINE MODEL OF DISC DEGENERATION

J.J. Costi^*; HearnTC ^*; and FazzalariNL

^* Dept. Orth., Repatriation General Hospital & The Flinders Uni. of South Australia Div. of Tissue Path., IMVS, Adelaide, Daws Road, Daw Park SA 5041, Australia.

Purpose: The aim of this study was to examine the intervertebral disc (IVD) biomechanics in a sheep model with concentric tears.

Methods: Fifty two adult merino wethers were randomly allocated into two groups with circumferential tears introduced by injection with saline (group 1) or needle stick with no saline (group 2). They were then sacrificed at 0, 1, 3, 6, 12 and 18 months for biomechanical testing. An additional ten sheep were used as an unoperated control at time 0 (Group 0). Biomechanical tests on each functional spinal unit (FSU) and IVD were performed.

Results: The effect of procedure overall was significant for torsion (P<0.022), axial compression (P<0.014), extension (P<0.001) and left lateral bending (P<0.004) for both the FSU and IVD. In almost every case, both groups 1 and 2 were significantly stiffer than group 0 but no different to each other. The effect of time overall was significant for flexion (P<0.0028) and right lateral bending (P<0.022) for both the FSU and IVD. In torsion, twisting to the left was significant for the intact FSU (P=0.008) and twisting to the right for the isolated IVD (P=0.009).

Discussion: The results of this study show that any intervention in the disc alters the biomechanics compared to an unoperated control group. To our knowledge this has not been shown before and these findings may have relevance to any intervention into the disc in the patient.

The abstracts were prepared by Professor Jegan Krishnan. Correspondence should be addressed to him at the Flinders Medical Centre, Bedford Park 5047, Australia.