The rib cage reduces intervertebral disc pressures in cadaveric thoracic spines by sharing loading under applied dynamic moments

Abstract

The effects of the rib cage on thoracic spine loading are not well studied, but the rib cage may provide stability or share loads with the spine. Intervertebral disc pressure provides insight into spinal loading, but such measurements are lacking in the thoracic spine. Thus, our objective was to examine thoracic intradiscal pressures under applied pure moments, and to determine the effect of the rib cage on these pressures. Human cadaveric thoracic spine specimens were positioned upright in a testing machine, and Dynamic pure moments (0 to ±5 N·m) with a compressive follower load of 400 N were applied in axial rotation, flexion - extension, and lateral bending. Disc pressures were measured at T4-T5 and T8-T9 using needle-mounted pressure transducers, first with the rib cage intact, and again after the rib cage was removed. Changes in pressure vs. moment slopes with rib cage removal were examined. Pressure generally increased with applied moments, and pressure-moment slope increased with rib cage removal at T4-T5 for axial rotation, extension, and lateral bending, and at T8-T9 for axial rotation. The results suggest the intact rib cage carried about 62% and 56% of axial rotation moments about T4-T5 and T8-T9, respectively, as well as 42% of extension moment and 36-43% of lateral bending moment about T4-T5 only. The rib cage likely plays a larger role in supporting moments than compressive loads, and may also play a larger role in the upper thorax than the lower thorax.

Rib Presence, Anterior Rib Cage Integrity, and Segmental Length Affect the Stability of the Human Thoracic Spine: An in vitro Study

“…The highest impact of rib cage resection on thoracic spinal stability was generally found in axial rotation movement, especially in the upper rib cage half and after transversally cutting the sternal and cartilaginous rib-to-rib connections. This indicates that the rib cage mainly stabilizes the thoracic spine in the transversal plane, which was also detected in previous in vitro studies investigating the mechanical contribution of the rib cage on thoracic spinal stability (Mannen et al, 2015(Mannen et al, , 2018Liebsch et al, 2017a;Anderson et al, 2018). This effect can be explained by the specific morphology of the rib cage, generally allowing forward and backward bending as well as sideward bending rather than axial rotation movement due to an increased torsional resistance in this motion plane.…”

The influence of the rib cage on the static and dynamic stability responses of the scoliotic spine

“…These results demonstrated that the modal shape of the normal spine was completely symmetrical, but there was a large curvature to the right side of T6 which led to asymmetry of the modal shape in the X-axis. The rib cage's role in spinal stability and stiffness has been proven by cadaver experiments which studied the range of motions (ROMs) of the spine with and without a rib cage under clinical rotation loads instead of dynamic loads 28,31 . In this study, our results also showed that both normal and scoliotic spines with a rib cage were more stable than spines without a rib cage in the vibration load.…”

The rib cage stiffens the thoracic spine in a cadaveric model with body weight load under dynamic moments

“…Eight specimens were included in the study (four male, four female) with an average age of 66.9±4.4 years. Data on the impact of various follower load magnitudes and the changes in disc pressures have been previously reported on these specimens, though our prior manuscripts have not addressed the motion and stiffness impact of the rib cage on the thoracic spine with a follower load (Dennis E Anderson et al, 2016; Anderson et al, 2017; Sis et al, 2016).…”

“…Analyses were conducted on the third cycle of data, and angular displacements of the upper (T1 to T4), middle (T4 to T8), and lower (T8 to T12) segments were calculated from the motion-capture pins (Wilke et al, 1998). The data from the rib cage intact condition has been reported previously as part of a set of parallel studies examining effect of follower-load magnitudes on motion and disc pressures, and all experiments from the set of studies on one specimen were conducted on the same day to avoid effects of multiple freeze-thaw cycles (Anderson et al, 2017; Sis et al, 2016).…”

“…In published work from the same set of experiments reported in the current study, Sis et al introduced a novel follower load technique allowing for the rib cage to remain intact and reported on the thoracic mechanics of 0 N, 200 N, and 400 N follower loads, highlighting the differences in ROM and stiffness when using a follower load with an intact rib cage (Sis et al, 2016). Anderson et al then reported the static disc pressure and curvature changes resulting from various follower load levels and the dynamic disc pressure changes on thoracic cadaveric models, both with and without an intact rib cage (Dennis E Anderson et al, 2016; Anderson et al, 2017). However, no work has directly compared the mechanics of the thoracic spine with a follower load under dynamic loading with and without an intact rib cage.…”