Parametric study of anterior percutaneous endoscopic cervical discectomy (APECD).

Anterior percutaneous endoscopic cervical discectomy (APECD) is a common treatment for cervical spondylotic radiculopathy (CSR). In this study, the effects of various channel diameters and approach angles on cervical vertebrae on postoperative outcomes in APECD surgery were explored. A finite element model of intact cervical C3-C7 was constructed and then modified to obtain six surgical models. Range of motion (ROM) and intradiscal pressure (IDP) were calculated under different conditions of flexion (Fle), extension (Ext), lateral bending, and axial rotation. During Fle and bending to the left (LB), the ROM was closer to the intact model when the angle of approach was 90°. During bending to the left (LB) and rotation to the left (LR), the ROM changed considerably (43.2%, 33.7%, respectively) where the angle of approach was 45°. As the surgical channel diameter increased, the extent of the change in ROM compared with the intact model also increased. IDP decreased by 48% and 49%, respectively, compared with the intact model at the C5-C6 segment where the angle of approach was 45° and 60° during Fle, while it changed little at 90°, by less than 10%. The IDP was increased noticeably by 117.6%, 82.1%, and 105.8%, for channel diameters of 2, 3 and 4 mm, respectively. And declined noticeably during LB and LR (LB: 27.1%, 27.1%, 38.5%; LR: 37.4%, 35.5%, 48.7%). The results demonstrated that the shorter the surgical path, the smaller surgical diameter, the less the biomechanical influence on the cervical vertebra.

The effect of cervical intervertebral disc degeneration on the motion path of instantaneous center of rotation at degenerated and adjacent segments: A finite element analysis.

BACKGROUND: The motion path of instantaneous center of rotation (ICR) is a crucial kinematic parameter to dynamically characterize cervical spine intervertebral patterns of motion; however, few studies have evaluated the effect of cervical disc degeneration (CDD) on ICR motion path. The purpose of this study was to investigate the effect of CDD on the ICR motion path of degenerated and adjacent segments. METHOD: A validated nonlinear three-dimensional finite element (FE) model of a healthy adult cervical spine was used. Progressive degeneration was simulated with six FE models by modifying intervertebral disc height and material properties, anterior osteophyte size, and degree of endplate sclerosis at the C5-C6 level. All models were subjected to a pure moment of 1 Nm and a compressive follower load of 73.6 N to simulate physical motion. ICR motion paths were compared among different models. RESULTS: The normal FE model results were consistent with those of previous studies. In degenerative models, average ICR motion paths shifted significantly anterior at the degenerated segment (ß = 0.27 mm; 95% CI: 0.22, 0.32) and posterior at the proximal adjacent segment (ß = -0.09 mm; 95% CI: -0.15, -0.02) than those of the normal model. CONCLUSION: CDD significantly affected ICR motion paths at the degenerated and proximal adjacent segments. The changes at adjacent segments may be a result of compensatory mechanisms to maintain the balance of the cervical spine. Surgical treatment planning should take into account the restoration of ICR motion path to normal. These findings could provide a basis for prosthesis design and clinical practice.

The effect of follower load on the range of motion, facet joint force, and intradiscal pressure of the cervical spine: a finite element study.

Follower loads are used to simulate physiological compressive loads on the human spine. These compressive loads represent the load-carrying capacity of the human cervical spine and play an important role in maintaining its stability. However, under different follower loads the biomechanical response of the cervical spine is unknown. Therefore, the aim of this study was to determine the effect of follower load on the biomechanics of the cervical spine. A three-dimensional nonlinear finite element (FE) model of the cervical spine (C3-C7) was developed and validated. Using this FE model, we evaluated the effect of different follower loads (0 N, 50 N, 100 N, and 150 N) on the range of motion (ROM), facet joint forces (FJFs), and intradiscal pressure (IDP) in the cervical spine. In addition, a moment of 1 Nm was applied in three anatomical planes (sagittal, coronal, and transverse planes) to simulate different postures. The results indicate that as follower load was increased, the ROM of the cervical spine in extension decreased (4.06°-0.95°), but increased in other postures (flexion 4.19°-6.04°, lateral bending 1.74-3.03°, axial rotation 2.64°-4.11°). Follower loads increased the FJF in all postures (0 N-52 N). In lateral bending (LB), FJFs were only generated in the ipsilateral facet joints. In axial rotation (AR), there was large asymmetry in the FJF, which increased as follower load increased. The IDP of each segment increased nonlinearly with increasing follower load in all postures (0.01 MPa-1.23 MPa). In summary, follower loads caused changes in motion and loading patterns in the cervical spine (C3-C7). Therefore, in common daily activities, we should pay attention to the muscle strength of the neck through exercise to adapt to the biomechanical changes in the cervical spine following an increase in follower load. Graphical Abstract Follower load is defined as the compressive load directed approximately along the axis of the spine. The purpose of this investigation was to determine the effect of the follower compressive load on biomechanics of the cervical spine. To do so, a three-dimensional nonlinear FE model of the cervical spine (C3-C7) was built and validated. Using this FE model of the cervical spine, we evaluated the effect of different follower loads (0 N, 50 N, 100 N, 150 N) on range of motion, facet joint force, and IDP in the cervical spine. In this study, the follower load was applied to the finite element model by connector elements. At the same time, a moment of 1 Nm was applied in the three anatomical planes to simulate different postures.

Using finite element analysis to determine effects of the motion loading method on facet joint forces after cervical disc degeneration.

BACKGROUND: Understanding the biomechanical effects of cervical disc degeneration (CDD) on the cervical spine is fundamental for understanding the mechanisms of spinal disorders and improving clinical treatment. While the biomechanical effects of CDD on segmental flexibility and the posterior facets have been reported, a clear understanding of the effect of the motion loading method on facet joint forces after CDD is still lacking. Therefore, the objective of this study was to determine the effect of the motion loading method on facet joint forces after CDD. METHODS: A three-dimensional nonlinear finite element (FE) model of the cervical spine (C3-C7) was developed and validated to represent normal conditions. This normal model was modified to create six degenerative models simulating mild, moderate, and severe grades of disc degeneration at C5-C6. While under a follower compressive preload (73.6 N), a 1-Nm moment was applied to all models to determine range of motion (ROM). A displacement load was applied to all degenerative models under the same follower load, making the C5-C6 degeneration segment motion same to the ROM of C5-C6 in normal model, and facet joint forces were computed. RESULTS: Compared with the normal model, ROM of the C5-C6 degenerative segments dramatically declined in all postures with increasing degenerative pathologies in the disc. The ROM in the adjacent normal segments of the degenerative segments also declined, with the exception of C4-C5 during extension. Under a 1-Nm moment load, there were not obvious changes in facet joint forces in the C5-C6 degenerative segment with increasing grades of degeneration, but facet joint forces in the adjacent normal segments did increase. Under a displacement load, the facet joint forces of the C5-C6 degenerative segment increased with increasing grades of degeneration. CONCLUSIONS: Facet joint forces were positively correlated with the ROM of the degenerative segment, demonstrating that the motion loading method had a significant effect on facet joint forces after CDD. Loading conditions must be strictly controlled in future finite element analysis studies to improve the comparability between models built by different units.

Comparative analysis of the biomechanics of the adjacent segments after minimally invasive cervical surgeries versus anterior cervical discectomy and fusion: A finite element study.

PURPOSE: Percutaneous full-endoscopic anterior cervical discectomy (PEACD) and posterior cervical foraminotomy (PCF) as alternatives to anterior cervical discectomy and fusion (ACDF) are extensively used in the treatment of patients with cervical spondylotic radiculopathy. The possibility of avoiding the risk of accelerated degeneration of the adjacent segments caused by fusion is claimed to be the theoretical advantage of these approaches; however, there is a paucity of supportive evidence from biomechanical data. Therefore, this study investigated and compared the effects of PCF, PEACD, and ACDF on the adjacent segments and operative segments of the cervical spine from a biomechanical standpoint. METHOD: A normal and intact three-dimensional finite element digital model of C4-C7 was constructed and validated, and the finite element models of PEACD, PCF, and ACDF were obtained by modifying the C4-C7 model. All models were exposed to identical conditions of load during flexion, extension, axial rotation, and lateral bending. We calculated the range of motion (ROM), intervertebral disc pressure (IDP), and facet joint contact force (FJCF) of the operative segment and the adjacent segment in different motion conditions. RESULT: The conventional ACDF had a remarkable influence on the ROM and IDP of the operative segment and the adjacent segments. In the PEACD model, the change of ROM was not noticeable; the IDP of the operative segment was significantly smaller, whereas the change of IDP of the adjacent segment was insignificant. In the PCF model, the ROM and IDP of all segments remained unaffected.During extension, the facet joint contact force changed significantly after ACDF, and it changed slightly after PECAD and PCF. CONCLUSION: By comparatively analyzing the biomechanical changes of the cervical spine after PCF, PEACD, and ACDF using the finite element method, we suggested that PCF and PEACD were more suitable for surgical intervention of cervical spondylotic radiculopathy than ACDF from a biomechanical point of view and PCF may outperform PEACD.

Comparison of the Biomechanical Changes After Percutaneous Full-Endoscopic Anterior Cervical Discectomy versus Posterior Cervical Foraminotomy at C5-C6: A Finite Element-Based Study.

OBJECTIVE: Percutaneous full-endoscopic anterior cervical discectomy (PEACD) and posterior cervical foraminotomy (PCF) have been reported as effective treatments for the cervical spondylosis radiculopathy (CSR), but the biomechanical effects on the discs and facet joints of PEACD and PCF remain largely unclear. The purpose of this paper is to investigate and compare the biomechanical changes on cervical spine after PECAD and PCF procedures, thus providing evidences for surgeons to select a more appropriate approach. METHODS: An intact cervical C5-C6 digital model was constructed and then modified to obtain the PCF and PEACD models using finite element method. All the models were subjected to a 73.6N preload accompanied by a 1.8 Nm moment during flexion, extension, axial rotation, lateral bending. The range of motion (ROM), intervertebral disc pressure (IDP), facet joint contact area, and contact pressure were calculated under different loading conditions. RESULTS: The ROM of the PCF model changed slightly (0.28%), whereas that of the PEACD model increased significantly (20.49%) compared with intact model. The trend of IDP changes in these 2 surgical models were similar to ROM in the corresponding motion state. The contact pressure on the facet joint of the PEACD model increased by 20.53%, 33.38%, and 17.46% during extension, lateral bending, and axial bending, respectively, compared with the intact model, and the PCF increased by 33.53% and 16.16% during extension and lateral bending, respectively, whereas it decreased 0.97% in axial rotation. The facet joint contact area of the PCF model increased by 85.71%, 1.54%, and 2.17% during extension, lateral bending, and axial rotation, respectively, and the area of the PEACD model increased by 157.14% and 36.96% during extension and axial rotation, whereas it decreased by 13.85% during lateral bending. CONCLUSIONS: This is the first biomechanical finite element study comparing PEACD with PCF for the treatment of CSR. Our results showed that PEACD led to hypermobility with high IDP within the cervical segment undergone surgery, whereas the ROM and IDP changed slightly after PCF. The variations of the contact stress indicated that both procedures changed the transmission path of the force on the facet joint and may accelerate the degeneration of the facet joint. PCF may be a better choice for the treatment of CSR compared with PEACD.