ABSTRACT

This PhD dissertation is based on the works carried out in the Orthopedic Research Laboratory and the Clinical Institute of Aarhus University. The aim of the study was to investigate the influence of the intervertebral disc tissue on osteoblast metabolism in vitro and its effect on autograft healing in vivo.

In the in vitro study, the exposure of human nucleus pulposus (NP) and annulus fibrosus (AF) to osteoblast-like cells (SaOS-2) cells resulted in an increase of 3 H-thymidine incorporation and collagen type I production, while alkaline phosphotase production could only be stimulated by addition of NP. The profile of the cytokines released by the intervertebral discs was screened in the conditioned media from cultured human intervertebral discs. High levels of Eotaxin, IP-10 Rantes IL-6 and IL-8 were found in the conditioned media. Seven other cytokines were found to be present in low but detectable levels. When the conditioned media from the discs were applied to human bone marrow stem cells, cellular proliferation was significantly increased but alkaline phosphotase activity remained unchanged. The cellular proliferation was in negative correlation with the IL-6 levels.

In the animal experiment, 2-level (L3/4, L5/6) anterior spinal interbody fusion with carbon fiber cages was performed on each of 10 pigs. NP was mixed into the autograft and then packed into one of the carbon fiber cages. Cages packed only with autograft served as control. The pigs were followed for 12 weeks. The results showed that when autograft was mixed with NP, bone formation inside the cage could be decreased or delayed, which could thus influence final fusion rate in the pig model.

The present studies support the concept of the total removal of intervertebral disc tissue, especially nucleus pulposus, during intercorporal spinal fusion surgery. Otherwise, fusion is likely to be impaired. Cytokines in relation to specific disc diseases and their possible link to the clinical outcomes can be worth of further investigation.