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Biomechanics of the Spine
Published in Manoj Ramachandran, Tom Nunn, Basic Orthopaedic Sciences, 2018
Amir Ali Narvani, Arun Ranganathan, Brian Hsu, Lester Wilson
The functional spinal unit is the smallest physiological unit of the spine that exhibits biomechanical properties similar to that of the entire spine (White and Panjabi). This includes two adjacent vertebral bodies, the intervertebral disc, facet joints and all adjoining ligaments, but excludes muscles (Figure 21.1). It is also called a spinal motion segment or an articular triad.
The neck
Published in Ashley W. Blom, David Warwick, Michael R. Whitehouse, Apley and Solomon’s System of Orthopaedics and Trauma, 2017
This vague term refers to the cluster of abnormalities arising from the ageing of the functional spinal unit (two adjacent vertebrae and the disc in between), especially the intervertebral (IV) disc. Changes are most common in the C5–C6 and C6–C7 segments, the area that is more prone to intervertebral disc prolapse. As the discs degenerate, they lose their original biochemical and biomechanical properties. The ability of the disc to retain water is impaired, it desiccates, the amount of keratin sulfate increases and chondroitin sulfate decreases, which results in altered viscoelasticity. The disc loses its original height and becomes thinner and less elastic. Facet joints are progressively submitted to increased stresses and instability and the uncovertebral joints become arthritic, giving rise to pain and stiffness in the neck. Bony spurs, ridges or bars appear at the anterior and posterior margins of the vertebral end plates reducing the dimensions of the spinal canal and foramina. The disc collapses and protrudes and posterior bone spurs and infolded ligamentum flavum may encroach upon the spinal canal and foramina, causing pressure on the pain sensitive dura and the neural structures, resulting in a variably complex clinical picture.
Reduction and Fixation of Sacroiliac joint Dislocation by the Combined Use of S1 Pedicle Screws and an Iliac Rod
Published in Kai-Uwe Lewandrowski, Donald L. Wise, Debra J. Trantolo, Michael J. Yaszemski, Augustus A. White, Advances in Spinal Fusion, 2003
Kai-Uwe Lewandrowski, Donald L. Wise, Debra J. Trantolo, Michael J. Yaszemski, Augustus A. White
The spine is flexible tube containing and protecting the cauda equina and at the same time provides a stable base for the locomotor system. Two adjacent vertebrae, the intervening disc, the upper and lower facet joints form a spinal motion segment called a functional spinal unit (FSU). The FSU is surrounded by ligaments, the joint capsule, and muscles. All these structures stabilize the spine. Every FSU provides flexibility but is also a weak point where trauma and degenerative processes can lead to changes impinging on the spinal canal and its neural content.
Changes of adjacent segment biomechanics after anterior cervical interbody fusion with different profile design plate: single- versus double-level
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Lin-Yu Jin, Ke Wei, Da-Ming Feng, Jian-Dong Li, Xiao-Xing Song, Hong-Ling Yin, Xin-Feng Li
To validate the FE model, range of motion (RoM) of each cervical segment was the major indicator. Subaxial RoM and functional spinal unit RoM (movement in sagittal plane, coronal plane and axial plane) were chosen for comparison with the published experimental results (Miura et al. 2002; Wheeldon et al. 2006; Yoganandan et al. 2007, 2008). The subaxial RoM was defined as the measurement of the total motion between the C2 and C7 vertebrae. The functional spinal unit RoM, intersegmental motion, was the motion between two adjacent vertebrae. The same boundary and loading conditions were simulated with the controlled experiments. All degrees of freedom (DoF) were constrained on the lower surface of T1 in our FE model. Pure moments of 2-Nm were applied to the superior surface of C2 in the three main planes to produce flexion, extension, lateral bending and axial rotation respectively. Using the follower load technique, a compressive follower load of 100 N was also applied to the upper surface of C2 to simulate physiologic compressive loads. The validation and following FE analysis were performed in ABAQUS (Simulia, Providence, RI). Subaxial RoM and functional spinal unit RoM were recorded.
Contribution of injured posterior ligamentous complex and intervertebral disc on post-traumatic instability at the cervical spine
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
Marie-Hélène Beauséjour, Yvan Petit, Jeremy Hagen, Pierre-Jean Arnoux, Jean-Marc Mac Thiong, Eric Wagnac
In vitro studies have proposed stability criteria based on the comparison of pre- and post-trauma flexibility (Goel et al. 1984; White and Panjabi 1990). At the cervical spine, the changes in angular and horizontal displacement prior to failure in flexion and extension was evaluated in vitro by reducing the disco-ligamentous elements sequentially from the anterior or posterior (White et al. 1975). However, specimens of only one functional spinal unit (FSU) were used. The impact of sequential removal of NL, ISL and facet capsules (FC) at C5-C6 on rotation at C4-C5 and C5-C6 was evaluated in all three anatomical planes using C2-T2 segments but only up to 0.3 Nm (Goel et al. 1984). One study tested the impact of sequential disco-ligamentous injuries at C5-C6 inflicted from the anterior on the neutral zone and range of motion (ROM) (Richter et al. 2000). Another study evaluated the effect of discectomy, anterior fixation and the subsequent progressive disruption of the PLC on the intervertebral ROM (Pitzen et al. 2003), but little is known about the contribution of the PLC versus the IVD in flexion-distraction type injuries on spinal stability at the cervical spine.
Posterior percutaneous endoscopic cervical discectomy through lamina–hole approach for cervical intervertebral disc herniation
Published in International Journal of Neuroscience, 2019
Chao Liu, Kaixuan Liu, Lei Chu, Liang Chen, Zhongliang Deng
PPECD is performed through the interlaminar approach and causes less damage to the nucleus pulposus compared with the transdiscal APECD. Therefore, PPECD may not cause postoperative degeneration of the intervertebral disc. However, in a conventional PPECD, the medial side of the facet joint is removed [14,15]. The capability for damage repair of articular cartilage in the facet joint is very poor [16–18], so that the damage to the facet joint may lead to its irreversible injury and accelerated degeneration. Moreover, the cervical functional spinal unit (FSU) consists of vertebrae, facet joints, Luschka’s joints and intervertebral disc [19], the damage to each may influence the physical function of the cervical spine. So, the PPECD may cause the higher potential of secondary degeneration of the facet joint and FSU.