Changes of the Adjacent Mobile Segment After Cat Spine Fixation

Ha, Kee Yong; Sung, Tae Phyo

Abstract

Many believe the reduction in the number of mobile segments causes an increased strain in the unfused segments, predisposing them to early degeneration. This degeneration of the adjacent segment could be a cause of low back pain after spinal fusion. The clinical manifestations supporting the increased stress of the unfused segments are the significant incidence rates of spondylolisthesis, spondylolysis acquisita and spinal stenosis. However, there was a paucity of reports in the literature on the histological observation at the adjacent, unfused sgements. Therefore, the purpose of this study was to observe the histological changes of the unfused, mobile segments following fixation in the cat spine. The cat lumbar spines from L6 to L7 were fixed posteriorly with acrylic cement and wires. Histological and histochemical observation of the upper adjacent segment were performed after H-E, trichrome, reticulin and Safranin-O staining at postoperative 6 and 12 months, respectively. The results were as follows: 1. There were mild degenerative changes in the intervertebral disc, but no evidence of definitive degeneration in the articular cartilage of the facet joints at postoperative 6 months in the spinal fixation group. 2. The marked degenerative changes of the intervertebral disc were shown at postoperative 12 months in the spinal fixation group. Of 5 cats sacrificed at 12 months, 3 cats had irregular configuration of the fiber's arrangement of the annulus fibrosus. 3. At postoperative 12 months in the spinal fixation group, marked degeneration was noted on the articular cartilage of the adjacent facet joints. Through this study, it is clarified that degenerativce changes of the intervetebral disc and facet joint at the adjacent segments will develop after certain period of time following spinal fusion. Especially the facet joints of the adjacent, unfused segment were found to be most vulnerable to the adverse effects. This may be responsible for the back pain in the future after spine fusion.