The intervertebral disc is a highly organized matrix laid down by relatively few cells in a specific manner. The central gelatinous nucleus pulposus is contained within the more collagenous anulus fibrosus laterally and the cartilage end plates inferiorly and superiorly. The anulus consists of concentric rings or lamellae, with fibers in the outer lamellae continuing into the longitudinal ligaments and vertebral bodies. This arrangement allows the discs to facilitate movement and flexibility within what would be an otherwise rigid spine. At birth, the human disc has some vascular supply within both the cartilage end plates and the anulus fibrosus, but these vessels soon recede, leaving the disc with little direct blood supply in the healthy adult. With increasing age, water is lost from the matrix, and the proteoglycan content also changes and diminishes. The disc-particularly the nucleus-becomes less gelatinous and more fibrous, and cracks and fissures eventually form. More blood vessels begin to grow into the disc from the outer areas of the anulus. There is an increase in cell proliferation and formation of cell clusters as well as an increase in cell death. The cartilage end plate undergoes thinning, altered cell density, formation of fissures, and sclerosis of the subchondral bone. These changes are similar to those seen in degenerative disc disease, causing discussion as to whether aging and degeneration are separate processes or the same process occurring over a different timescale. Additional disorders involving the intervertebral disc can demonstrate other changes in morphology. Discs from patients with spinal deformities such as scoliosis have ectopic calcification in the cartilage end plate and sometimes in the disc itself. Cells in these discs and cells from patients with spondylolisthesis have been found to have very long cell processes. Cells in herniated discs appear to have a higher degree of cellular senescence than cells in nonherniated discs and produce a greater abundance of matrix metalloproteinases. The role that abnormalities play in the etiopathogenesis of different disorders is not always clear. Disorders may be caused by a genetic predisposition or a tissue response to an insult or altered mechanical environment. Whatever the initial cause, a change in the morphology of the tissue is likely to alter the physiologic and mechanical functioning of the tissue.

The proteoglycans normally found in the endplate regulate movement of solutes into and out of the disc. It has been shown previously that removal of proteoglycans from the endplate accelerates the loss of proteoglycans from the nucleus. Hence, a major function of the cartilage endplate may be to prevent fragments of osmotically active proteoglycans from leaving the disc.

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3D = three-dimensional; ACI = autologous chondrocyte implantation; H&E = haematoxylin and eosin; ICC = intraclass correlation; MOD = modified O'Driscoll; MRI = magnetic resonance imaging; TE = echo time; TR = repetition time. (Print ISSN 1478-6354; Online ISSN 1478-6362). This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any non-commercial purpose, provided this notice is preserved along with the article's original URL. Arthritis Research and Therapy AbstractAutologous chondrocyte implantation is being used increasingly for the treatment of cartilage defects. In spite of this, there has been a paucity of objective, standardised assessment of the outcome and quality of repair tissue formed. We have investigated patients treated with autologous chondrocyte implantation (ACI), some in conjunction with mosaicplasty, and developed objective, semiquantitative scoring schemes to monitor the repair tissue using MRI and histology. Results indicate repair tissue to be on average 2.5 mm thick. It was of varying morphology ranging from predominantly hyaline in 22% of biopsy specimens, mixed in 48%, through to predominantly fibrocartilage in 30%, apparently improving with increasing time postgraft. Repair tissue was well integrated with the host tissue in all aspects viewed. MRI scans provide a useful assessment of properties of the whole graft area and adjacent tissue and is a noninvasive technique for long-term follow-up. It correlated with histology (P = 0.02) in patients treated with ACI alone. Keywords: cartilage repair, collagens, glycosaminoglycans histology, MRI Open AccessAvailable online http://arthritis-research.com/content/5/1/R60 R61Cartilage function reflects its biochemical composition [8]. A small biopsy specimen such as is used for histochemical assessment can provide only limited information, as it is from a discrete location. MRI, in contrast, can provide information on the whole area. In addition, it is noninvasive and successive scans can be carried out, so allowing longitudinal monitoring at different time points. MR images have been shown to correlate with biochemical composition in other tissues, in cartilage in vivo, and even in engineered cartilage generated in a bioreactor [9][10][11]. Thus in this study we have used both forms of assessment of articular cartilage and correlated them where they are available at the same time points post-treatment. We have previously reported on the immunohistochemical appearance of such biopsy specimens, but only on two individuals and at 12 months after implantation [12]. Here we report on a much more extensive sample group, obtained up to 3 years after treatment, and compare histological assessments with those obtained by MRI. Materials and methods Tissue biopsiesPatients receiving ACI in our centre undergo arthroscopic assessment and biopsy of the treated region as part of their routine follow-up at approximately 12 months postgraft. The taking of biopsies from grafted regions was given ethical ap...