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

Abstract

The thoracic cage plays an important role in maintaining the stability of the thoracolumbar spine. In this study, the influence of a rib cage on static and dynamic responses in normal and scoliotic spines was investigated. Four spinal finite element (FE) models (T1–S), representing a normal spine with rib cage (N1), normal spine without rib cage (N2), a scoliotic spine with rib cage (S1) and a scoliotic spine without rib cage (S2), were established based on computed tomography (CT) images, and static, modal, and steady-state analyses were conducted. In S2, the Von Mises stress (VMS) was clearly decreased compared to S1 for four bending loadings. N2 and N1 showed a similar VMS to each other, and there was a significant increase in axial compression in N2 and S2 compared to N1 and S1, respectively. The U magnitude values of N2 and S2 were higher than in N1 and S1 for five loadings, respectively. The resonant frequencies of N2 and S2 were lower than those in N1 and S1, respectively. In steady-state analysis, maximum amplitudes of vibration for N2 and S2 were significantly larger than N1 and S1, respectively. This study has revealed that the rib cage improves spinal stability in vibrating environments and contributes to stability in scoliotic spines under static and dynamic loadings.

Computational modelling of the scoliotic spine: A literature review

“… 82 Other studies have investigated the scoliotic spine under vibrational loading, expanding the knowledge to include the effect in adult degenerative scoliosis cases, 93 the effect of curve type, 78 and of the rib cage. 79 The findings of these studies have supported those of Li et al, that the scoliotic spine has more resonant frequencies and a larger response than a healthy spine. Thus scoliotic subjects are exposed to greater risk of increasing the deformity, lesions at the resonant frequencies, 78 , 93 and injuries associated with vibrations.…”

“…These differences can probably be attributed to geometric differences because the study used literature data for the material properties which is based on healthy spines 82 . Other studies have investigated the scoliotic spine under vibrational loading, expanding the knowledge to include the effect in adult degenerative scoliosis cases, 93 the effect of curve type, 78 and of the rib cage 79 . The findings of these studies have supported those of Li et al, that the scoliotic spine has more resonant frequencies and a larger response than a healthy spine.…”

“…Ideally, the model should be validated under the same conditions in which it is being used: therefore, validation would be performed using data from scoliotic spines 119 . Unfortunately, a lack of in vivo and in vitro data from scoliotic subjects means scoliotic models have only been validated against normal spine data 79,105 …”

“… 79 The rib cage, ligaments, vertebrae and IVD were examined and the magnitude of the maximum Von Mises stress and displacements reduction ranged between 19.7%–53.4% (in axial compression an increase of 31.5%) and 2.1%–16.9%, respectively, depending on the loading direction. 79 …”

“…In vivo, in vitro, and/or in silico literature data has been used for validation. Model predictions are compared to the reported RoM, 68 , 78 , 79 , 97 , 119 muscle activation 142 or force, 130 IDP, 73 , 105 , 130 screw pull out forces, 73 loads on the vertebrae, 88 shear stresses within the IVD, 105 and IVD stiffness. 67 These parameters have been compared to the values reported in literature, sometimes to a single data set from literature and the standard deviation on that data if it is available.…”