Thoracic spinal kinematics is affected by the grade of intervertebral disc degeneration, but not by the presence of the ribs: An in vitro study.

Abstract

BACKGROUND CONTEXT\nThoracic spinal three-dimensional kinematics is widely unknown. For the evaluation of surgical treatments and the complete validation of numerical models, however, kinematic data of the thoracic spine are essential.\n\n\nPURPOSE\nTo identify possible effects of rib presence and grade of intervertebral disc degeneration on thoracic spinal kinematics including three-plane helical axes and instantaneous centers of rotation.\n\n\nSTUDY DESIGN/SETTING\nRadiological grading of intervertebral disc degeneration and in vitro tests using n\u202f=\u202f8 human thoracic functional spinal units of the segmental levels T1-T2, T3-T4, T5-T6, T7-T8, T9-T10, and T11-T12, respectively, were performed with as well as without ribs to analyze the specific kinematic properties.\n\n\nMETHODS\nSpecimens were loaded with pure moments of 5\xa0Nm and constant loading rates of 1°/s in flexion/extension, lateral bending, and axial rotation. Optical motion tracking was performed to visualize helical axes and instantaneous centers of rotation on three-plane x-rays and to evaluate primary ranges of motion and coupled motions.\n\n\nRESULTS\nMotion segments with no or mild disc degeneration showed reproducible kinematics in all motion planes, while medium or severely degenerated specimens offered high variations and shifts of the rotational axes to the distal direction as well as lower range of motion. Coupled motions were generally not detected.\n\n\nCONCLUSIONS\nWith progressing disc degeneration, the rotational axes show higher variation and tend to shift in distal direction, especially in flexion/extension with a shift to the anterior direction, while rib resection does not affect thoracic spinal kinematics but its stability.\n\n\nCLINICAL SIGNIFICANCE\nRib resections as part of spinal deformity treatment destabilize the thoracic spine, but do not alter its kinematics. Young and healthy discs, however, could be affected by surgical treatments of the thoracic spine regarding thoracic spinal kinematics.