In vitro flexibility of the cervical spine after ventral uncoforaminotomy

Biomechanical in vitro evaluation of the kangaroo spine in comparison with human spinal data

On the basis of the kangaroo's pseudo-biped locomotion and its upright position, it could be assumed that the kangaroo might be an interesting model for spine research and that it may serve as a reasonable surrogate model for biomechanical in vitro tests. The purpose of this in vitro study was to provide biomechanical properties of the kangaroo spine and compare them with human spinal data from the literature. In addition, references to already published kangaroo anatomical spinal parameters will be discussed. Thirteen kangaroo spines from C4 to S4 were sectioned into single-motion segments. The specimens were tested by a spine tester under pure moments. The range of motion and neutral zone of each segment were determined in flexion and extension, right and left lateral bending and left and right axial rotation. Overall, we found greater flexibility in the kangaroo spine compared to the human spine. Similarities were only found in the cervical, lower thoracic and lumbar spinal regions. The range of motion of the kangaroo and human spines displayed comparable trends in the cervical (C4-C7), lower thoracic and lumbar regions independent of the motion plane. In the upper and middle thoracic regions, the flexibility of the kangaroo spine was considerably larger. These results suggested that the kangaroo specimens could be considered to be a surrogate, but only in particular cases, for biomechanical in vitro tests.

BIOMECHANICAL STABILITY OF THE CERVICAL SPINE AFTER UNCINATE PROCESS RESECTION: A FINITE ELEMENT ANALYSIS

When performing anterolateral foraminotomy for the treatment of cervical spondylotic radiculopathy, the extent of uncinate process resection affects the stability of the cervical spine. The aim of this study was to determine the stability of the cervical spine after resection of various amounts of the uncinate process. Based on computed tomography (CT) scans of an adult male volunteer, a three-dimensional geometric model of the cervical spine (C4-C6) was established using Mimics 13.1, SolidWorks 2012, and ANSYS 15.0 software packages. Next, the mechanical parameters of the tissues were assigned according to their different material characteristics. Using the tetrahedral mesh method, a three-dimensional finite element model of the cervical spine was then established. In modeling uncinated process resection, two excision protocols were compared. The first excision protocol, protocol A, mimicked the extent of resection used in current clinical surgical practice. The second excision protocol, protocol B, employed an optimal resection extent as predicted by the finite element model. Protocols A and B were then used to resect the left uncinate process of the C5 vertebra to either 50% or 60% of the total height of the uncinate process. The stability of the cervical spine was assessed by evaluating values of deformation and maximum equivalent stress during extension, flexion, lateral bending, and rotation. After protocol A resection, the total deformation was increased as was the maximum equivalent stress during left and right rotation. After protocol B resection, the total deformation was little changed and the maximum equivalent stress was visibly decreased during left and right rotation. As evidenced by these results, protocol B resection had relatively little effect on the stability of the cervical spine, suggesting that resection utilizing the limits proposed in protocol B appears to better maintain the stability of the cervical spine when compared with current clinical surgical practice as replicated in protocol A.

Analysis of the uncinate processes of the cervical spine: an anatomical study

Object

Although the uncovertebral region is neurosurgically relevant, relatively little is reported in the literature, specifically the neurosurgical literature, regarding its anatomy. Therefore, the present study aimed at further elucidation of this region's morphological features.

Methods

Morphometry was performed on the uncinate processes of 40 adult human skeletons. Additionally, range of motion testing was performed, with special attention given to the uncinate processes. Finally, these excrescences were classified based on their encroachment on the adjacent intervertebral foramen.

Results

The height of these processes was on average 4.8 mm, and there was an inverse relationship between height of the uncinate process and the size of the intervertebral foramen. Degeneration of the vertebral body (VB) did not correlate with whether the uncinate process effaced the intervertebral foramen. The taller uncinate processes tended to be located below C-3 vertebral levels, and their average anteroposterior length was 8 mm. The average thickness was found to be 4.9 mm for the base and 1.8 mm for the apex. There were no significant differences found between vertebral level and thickness of the uncinate process. Arthritic changes of the cervical VBs did not necessarily deform the uncinate processes. With axial rotation, the intervertebral discs were noted to be driven into the ipsilateral uncinate process. With lateral flexion, the ipsilateral uncinate processes aided the ipsilateral facet joints in maintaining the integrity of the ipsilateral intervertebral foramen.

Conclusions

A good appreciation for the anatomy of the uncinate processes is important to the neurosurgeon who operates on the spine. It is hoped that the data presented herein will decrease complications during surgical approaches to the cervical spine.