Influence of surgical treatment for disc degeneration disease at C5-C6 on changes in some biomechanical parameters of the cervical spine.

A detailed three-dimensional solid model of the full cervical spine (C1-C7 levels) and the finite element analysis method were used to investigate the extent of changes in various biomechanical properties brought about when surgical methods are used to treat condition(s) caused by or are a sequela of disc degeneration disease at the C5-C6 level. The surgical methods simulated were anterior cervical discectomy and fusion, with interbody fusion achieved using a notional brick-shaped graft only; anterior cervical discectomy alone; percutaneous nucleotomy; and three variants of nucleus replacement. The control case was a model of an intact, healthy, adult spine. Each of these seven models was subjected to (1) flexion moment, extension moment, left lateral bending moment, right lateral bending moment, clockwise-acting axial rotation moment, and counterclockwise-acting axial rotation moment, with a compression pre-load applied simultaneously with each of these loadings and (2) an axial compression force (applied as a uniform pressure) only. For each combination of model and applied loading, the maximum von Mises stress and the maximum strain energy density were determined for tissues at the treated level, at one level above the treated level, and at one level below the treated level and (2) the total principal rotation angles at each of the intersegmental positions of the entire model. In addition, for each of the study cases, we obtained the longitudinal displacement of each of the models when subjected to the axial compression force only. We found markedly fewer changes (relative to the results when the intact, healthy spine model was used) in each of the above-mentioned biomechanical parameters above a specified threshold in the case of the simulated percutaneous nucleotomy and simulated nucleus replacement models, on one hand, compared to the simulated fusion and simulated discectomy models, on the other. This finding is in consonance with the evolving clinical practice of using minimally invasive surgical methods for treating problem(s) such as soft cervical disc herniations.