4.2 Matrix Turnover In The Scoliotic Disc S Roberts, J Menage, EH Evans, VC Duance1, J Crean1 and SM Eisenstein Centre for Spinal Studies, Robert Jones and Agnes Hunt Orthopaedic Hospital, Oswestry, Shropshire. SY10 7AG 1CTBL, University of Wales, Cardiff The mechanical properties of the intervertebral disc are a reflection of the composition of the matrix, the major components being collagen, proteoglycan and water. It is known that the composition differs across the wedged, scoliotic disc, with the thinner disc at the concavity having less proteoglycan, water and collagen than the contralateral tissue. How this difference arises, however, is not known. We have investigated indices of catabolism and anabolism to determine if there is a difference in the balance of these processes at opposite sides of the disc. The enzymes, matrix metalloproteinases (MMPs) are capable of degrading all the known macromolecular constituents of the disc matrix and are therefore taken as an indication of catabolism. Indicators of anabolism are reducible collagen crosslinks, found in newly synthesised collagen, and expression of the proteoglycan neo-epitopes, 3B3(-) and 7D4. These are found at elevated levels in young developing connective tissues and in some repair processes. All these parameters have been measured and compared in two localities in each scoliotic disc, one nearest the convex aspect of the curve and the other nearest the concavity, in patients with idiopathic scoliosis undergoing corrective anterior fusion. Matrix metalloproteinases (MMPs 2 and 9) were measured on tissue extracts using quantitative zymography whilst the presence of these and MMPs 1,3 and 8 together with their inhibitors, TIMPs, were studied immunohistochemically on paraffin embedded tissue sections. The reducible crosslinks (hydroxylysinonorleucine (HLNL) and di hydroxylysinonorleucine (DHLNL)) have been measured per mg collagen, using amino acid analysis with ninhydrin detection. Competitive inhibition ELISA was used to measure 3B3(-) and 7D4 contents as a percentage of the total proteoglycan content. The levels of MMPs 2 and 9 at the concave side of the scoliotic disc were similar to those found in non-scoliotic discs (approximately 1.0 units/mg dry weight). However, towards the convexity higher levels were found (approximately 1.5-2.0 units/mg). The concentration of crosslinks was also lower at the concave side than at the convex side, with the values from non-scoliotic discs falling between the two. Similar trends were seen with the proteoglycan neo-epitopes. Hence there are lower levels of all parameters measured in the thinnest part of the scoliotic disc nearest the concavity, than at the opposite side. These results suggest that there is the greatest matrix turnover, both synthesis and degradation, towards the convexity. However, relative to comparable, non-scoliotic discs the level of MMPs (taken here to indicate catabolism) are of a similar level at the concavity. One mechanism which could explain the relative differences with location would be if the loads differed across the scoliotic disc since applied load is known to influence cell metabolism.