Exogenous cross-linking increases the stability of spinal motion segments

Study Design. The mechanical stability of cross-linked and control spinal motion segments was evaluated using neutral zone, range of motion (ROM), and instability score metrics. Objective. To determine if exogenous cross-linking could increase the stability of spinal motion segments. Summary of Background Data. The microstructure of the anulus fibrosus extracellular matrix can affect the stability of the intervertebral joint. Parallel testing in our laboratory has shown that exogenous cross-linking can improve the fatigue resistance of anulus fibrosus. Methods. There were 3 separate experimental protocols conducted. The first study used calf lumbar intervertebral joints randomly divided into a genipin cross- linked group and phosphate buffered saline-soaked controls. After 2 days of soaking, flexion-extension ramp cycles were applied to the specimens. The second study repeated the test protocol using 22 moderately and severely degenerated human lumbar intervertebral joints. The third experiment compared the effect of cross- linking treatment on human discs with known degrees of preexisting mechanical instability. Each data set was used to assess joint instability by 3 calculations: ROM, neutral zone, and an instability score. Joint instability for each data set was evaluated using 3 calculations: ROM, neutral zone, and a novel instability score. Results. These results show that cross- link augmentation can effectively reduce instability of intervertebral discs. The stabilizing effect was observed to be higher in the more mechanically unstable discs. However, cross-linking did not appear to affect the total range of sagittal motion. Conclusions. By reducing the neutral zone, exogenous cross- linking may help combat the progression of instability in degenerative disc disease.