Effects of intervertebral disc and articular facet joint on occurrence and development of degenerative scoliosis: a biomechanical analysis on cadaveric spine

English Keywords:Intervertebral discs  Facet joints  Degeneration  Scoliosis  Biomechanics

English Abstract:

  【Abstract】 Objectives: To investigate the role of intervertebral disc and articular facet joint in occurrence and development of degenerative scoliosis by biomechanical analysis on cadaveric lumbar specimens. Methods: A total of 39 fresh cadaveric lumbosacral spines(T12-S1) was evaluated by three-dimensional CT, scoliosis Cobb′s angles, wedging angle of discs and orientation of facet joints were measured. The Osirix Dicom imaging system was used to assess the degeneration of intervertebral disc and facet joints with Mimura and Lane′s standard. Spine mechanical tests were performed in sinusoidal displacement control with a maximum torque equal to 7.5Nm and a frequency of 0.005Hz, and intervertebral disc range of motion(ROM), neutral zone(NZ) of flexion-extension(FE), lateral bending(LB) and axial torsion(AT) were obtained. Each specimen underwent 3 times of test, and the results of the 3rd test were collected for data analysis. The ROM and NZ test data were compared among groups by one-way ANOVA. Pearson correlation analysis was performed on the degenerative degree of intervertebral disc, the shape of disc(intervertebral Cobb angel), the degenerative degree of facet joints, the shape of facet joints(asymmetric angle), with ROM and NZ. Results: All the 39 lumbar spine specimens were degenerated, among them 5 specimens were in degenerative scoliosis(DS) group with Cobb angles ＞10°, 9 specimens were in pre-degenerative scoliosis(PS) group with Cobb angles between 3° and 10°, and 25 specimens were in none scoliosis(NS) group with Cobb angles ＜3°. Among the total 187 functional spinal uints(FSU), 38 pairs of facet joints were asymmetrical. In comparison among the three groups, biomechanical analysis showed that AT in PS group and DS group was significantly greater than that in NS group(P＜0.05), FE and LB had no significant difference among 3 groups(P＞0.05). Correlation analysis showed that the degenerative degree of intervertebral discs and facet joints and the wedging angles of discs were positively correlated to AT(P＜0.05). There was no significant difference between asymmetrical facet joints and spine biomechanical parameters(P＞0.05). Conclusions: Degeneration of intervertebral disc and facet joint can cause greater AT, and asymmetric degeneration of intervertebral discs can cause spinal rotation and DS formation. There is no correlation between asymmetric degeneration of facet joints and DS formation.