Background: Knowledge on the time course of changes in cervical disc height and cervical kinematics at motion segments adjacent to congenital block vertebrae is fragmentary. Compared with this, after surgical fusion of cervical spine segments some find increased degenerative processes in combination with hypermobility or instability while others were unable to confirm these changes. This cross sectional study was undertaken to investigate whether congenital block vertebrae are associated with an increased risk of disc degeneration and hypermobility at adjacent motion segments.
Methods: In 25 subjects (mean age 40 years) disc height, vertebral height and segmental mobility at motion segments adjacent to a congenital block vertebra were assessed quantitatively by distortion-compensated Roentgen analysis. The findings were compared to a normal database.
Findings: Height of the disc cranially adjacent to the block vertebra did not deviate from the norm while height of the caudally adjacent disc was significantly reduced. The height of the vertebrae adjacent to the block did not deviate from normal. The motion segments formed by the block vertebra and the adjacent discs and vertebrae exhibited no deviation from normal with respect to sagittal plane rotational or translational motion.
Interpretation: Congenital block vertebrae do not result in rotational or translational hyper- or hypomobility at motion segments adjacent to the block. Whether the observed, significant height reduction of the caudally adjacent disc is caused by degeneration following the block formation cannot undoubtedly be concluded as the initial state is not known. Further longitudinal studies are needed to investigate this issue.