Abstract
Background: The intervertebral disc has a highly organised collagen network (1) which has an important role in regulating the mechanical properties of the tissue. A recent study of bovine discs has also revealed an abundant and organised elastic fibre network (2) indicating that elastic fibres could play an important mechanical role. The aim of this study was to describe changes in organisation of the collagen and elastin fibre networks in scoliotic relative to normal discs.
Methods: Intact wedges of intervertebral disc were obtained from patients undergoing routine spinal surgery where the disc was removed by an anterior approach. Frozen sections were cut and examined as described in detail elsewhere (2). Briefly, they were digested with hyaluronidase to remove glycosaminoglycans. Micrographs of the sections were examined by polarised light to visualise collagen organisation. The elastic fibre network was visualised by histochemical staining with orcein or immunohistochemically. We examined 9 discs from 6 scoliotic patients (12–22y), ranging in level from T1 0/11 to L4/L5; three had adolescent idiopathic scoliosis and three neuromuscular scoliosis. We also examined 4 discs from a 12 year old female patient with a spinal tumour not affecting the discs, and 2 discs from a 17 year female patient who had discs removed as the result of trauma.
Results: The ‘control’ discs showed a highly organised collagen network arranged in regular lamellae as described previously (1). A highly organised elastic fibre network, similar to that described in bovine discs (2) was also revealed in the ‘control’ human discs. Dense elastic fibres were located between adjacent lamellae of the annulus. Elastic fibres appeared to be long (> 100μm) and straight in outer annulus and were at angle of approximately 600 or 1200 to those in adjacent lamellae in the inner annulus. Elastic fibre bridges crossing the lamellae perpendicularly or obliquely were observed. In scoliotic discs however, the organisation of the collagen network was grossly disturbed with marked loss of lamellar structure. Elastic fibres were very sparse and the elastic fibre networks were highly disorganised in all regions. Cell clusters, typical of disc degeneration, were seen in scoliotic but not in age-matched ‘control’ discs.
Conclusion: Our results reveal an abundant and organised network of elastic fibres in the young (12–17yr) human intervertebral disc. The localisation of these fibres in the inter-lamellar space suggests that the elastic fibre network plays a significant biomechanical role. This network is sparse and disrupted in scoliotic discs; loss of network integrity could affect disc biomechanical function adversely and could be involved in the progression of the spinal deformity.
The abstracts were prepared by Mr Colin E. Bruce. Correspondence should be addressed to Colin E. Bruce, Consultant Orthopaedic Surgeon, Alder Hey Children’s Hospital, Eaton Road, Liverpool, L12 2AP.
References:
1 Takeda T. Three-dimensional observations of collagen framework of human lumbar discs. J Japan Orthop Assoc1975; 49:45–57. Google Scholar
2 Yu J, Peter C, Roberts S, Urban JP. Elastic fibre organization in the intervertebral discs of the bovine tail. J Anat2002; 201(6):465–475 Google Scholar
