Metabolic and haemodynamic changes in the pathologic hypermobile spine

The purpose of the study was to evaluate whether pathologic hypermobility of the lumbar spine could produce haemodynamic, metabolic, and histologic changes similar to those found in osteoarthritis. Five adult goats were surgically made hypermobile in the lumbar spine by an extensive laminectomy involving exarticulation of the facet joints of the L4 and L5 levels. Seven months following the operation oxygen partial pressure (pO2), was measured in situ in the nucleus pulposus and in the adjacent lumbar body of the hypermobile segment. A segment three levels more cranially served for control. Mass spectrometry was used for continuous registration of pO2. Intraosseous pressure (IOP) was measured in the lumbar bodies of the same levels. Hypermobility averaged a 60 per cent increase at the operated segment as measured on flexion-extension radiograms preoperatively and 7 months postoperatively. The hypermobile discs had decreased in height as measured by CT scanning and this was confirmed by histologic sections. Significant hypoxia was found in the nucleus pulposus of the hypermobile segment, while increased pO2 and IOP existed in the adjacent lumbar body.