Introduction: Intervertebral disc degeneration occurs with ageing and is often associated with back pain. During such degeneration, gross morphological differences between the central nucleus pulposus (NP) and outer annulus fibrosus (AF) are lost and the disc loses hydration and height due to decreased proteoglycan content. The cartilage endplate may also become calcified and this blocks the passage of nutrients into the disc, causing cell death and further degeneration. A potential therapy of degeneration is “re-inflation” of the disc with the use of hydrogels seeded with autologous disc cells. In this study, we have assessed the ability of a variety of hydrogels to support intervertebral disc cell growth.

Method: Intervertebral disc cells were isolated enzymatically from bovine tails and cultured as a monolayer in 10% foetal calf serum in DMEM containing antibiotics and ascorbic acid. This stimulates the cells to proliferate and thereby produces increased cell numbers. The cells were then seeded onto various hydrogels including hyaluronic acid (HA), 2-hydroxyethyl methacrylate (HEMA), N’N’ dimethyl methacrylate (NNDMA) and polyacryloyl morpholine (AMO) before harvesting at set time points of 1, 3, 6 and 9 days for hyaluronic acid and 1, 7, 14, 21, and 28 days for the other hydrogels. Cell number, morphology, viability and adherence to or migration into the hydrogels were assessed. Cell proliferation was also determined by immunostaining for the Ki67 antigen.

Results: Disc cells became incorporated in the HA gel, adopted a spherical morphology and remained viable for up to nine days. However, after a few days, a large proportion of the cells began to migrate through the gel to form a monolayer on the bottom of the tissue culture well. These monolayered cells became fibroblastic and proliferated. NP cells appeared to proliferate to a greater extent than AF cells both in monolayer and in suspension. Ki67 antigen immunostaining confirmed cell proliferation. On the non-porous HEMA, NNDMA and AMO, both cell types adhered and adopted a fibroblast-like morphology. Cell adhesion was greatest to the HEMA. NNDMA and AMO had lower levels of cell adherence. Both cell types became incorporated into the porous materials and adopted a rounded morphology. Cell incorporation appeared to be greatest into porous HEMA.

Conclusion: These initial studies show that intervertebral disc cells will adhere to or migrate into a variety of hydrogels and remain viable. The morphology and proliferative capacity of cells derived from both the AF and NP were responsive to the structure of the hydrogel with which they were cultured. Thus, cells were able to become fibroblastic or chondrocytic. Further analyses will reveal whether matrix synthesis by disc cells is similarly responsive to the hydrogel format. The results of these experiments suggest that the hydrogels tested have potential as support matrices in intervertebral disc repair to provide relief from discogenic low-back pain.

The occurrence of osteonecrosis following renal transplantation is well recognised but its pathogenesis remains unknown. We have quantified the number of empty osteocytic lacunae in the subchondral bone of femoral heads from a control group of patients, and compared these with femoral heads from a group of renal transplant recipients without evidence of overt osteonecrosis. There is a significant increase in empty osteocytic lacunae in renal transplant patients. We conclude that loss of osteocytes precedes other manifestations of osteonecrosis.

The clinical and pathological findings in a case of early avascular necrosis of the femoral head following renal transplantation are described. Regions of subchondral bone distant from the principal lesions showed increased numbers of empty osteocytic lacunae. This has been quantified and it is suggested that a loss of osteocytes is perhaps one of the earliest lesions leading to established avascular necrosis.