Effect of Different Types of Ossification of the Posterior Longitudinal Ligament on the Dynamic Biomechanical Response of the Spinal Cord: A Finite Element Analysis.

Ossification of the posterior longitudinal ligament (OPLL) has been identified as an important cause of cervical myelopathy. However, the biomechanical mechanism between the OPLL type and the clinical characteristics of myelopathy remains unclear. The aim of this study was to evaluate the effect of different types of OPLL on the dynamic biomechanical response of the spinal cord. A three-dimensional finite element model of the fluid-structure interaction of the cervical spine with spinal cord was established and validated. The spinal cord stress and strain, cervical range of motion (ROM) in different types of OPLL models were predicted during dynamic flexion and extension activity. Different types of OPLL models showed varying degrees of increase in stress and strain under the process of flexion and extension, and there was a surge toward the end of extension. Larger spinal cord stress was observed in segmental OPLL. For continuous and mixed types of OPLL, the adjacent segments of OPLL showed a dramatic increase in ROM, while the ROM of affected segments was limited. As a dynamic factor, flexion and extension of the cervical spine play an amplifying role in OPLL-related myelopathy, while appropriate spine motion is safe and permitted. Segmental OPLL patients are more concerned about the spinal cord injury induced by large stress, and patients with continuous OPLL should be noted to progressive injuries of adjacent level.

Biomechanical Effects on Cervical Spinal Cord and Nerve Root Following Laminoplasty for Ossification of the Posterior Longitudinal Ligament in the Cervical Spine: A Comparison Between Open-Door and Double-Door Laminoplasty Using Finite Element Analysis.

Many clinical case series have reported the predisposing factors for C5 palsy and have presented comparisons of the two types of laminoplasty. However, there have been no biomechanical studies focusing on cervical spinal cord and nerve root following laminoplasty. The purpose of this study is to investigate biomechanical changes in the spinal cord and nerve roots following the two most common types of laminoplasty, open-door and double-door laminoplasty, for cervical ossification of the posterior longitudinal ligament (OPLL). A finite element (FE) model of the cervical spine and spinal cord with nerve root complex structures was developed. Stress changes in the spinal cord and nerve roots, posterior shift of the spinal cord, and displacement of the cervical nerve roots were analyzed with two types of cervical laminoplasty models for variations in the degree of canal occupying ratio and shape of the OPLL. The shape and degree of spinal cord compression caused by the OPLL had more influence on the changes in stress, posterior shift of the spinal cord, and displacement of the nerve root than the type of laminoplasty. The lateral-type OPLL resulted in imbalanced stress on the nerve roots and the highest nerve root displacement. Type of laminoplasty and shape and degree of spinal cord compression caused by OPLL were found to influence the changes in stress and posterior displacement of the cervical spinal cord and nerve roots. Lateral-type OPLL might contribute to the development of C5 palsy due to the imbalanced stress and tension on the nerve roots after laminoplasty.

Effects of Different Angles of the Traction Table on Lumbar Spine Ligaments: A Finite Element Study.

BACKGROUND: The traction bed is a noninvasive device for treating lower back pain caused by herniated intervertebral discs. In this study, we investigated the impact of the traction bed on the lower back as a means of increasing the disc height and creating a gap between facet joints. METHODS: Computed tomography (CT) images were obtained from a female volunteer and a three-dimensional (3D) model was created using software package MIMICs 17.0. Afterwards, the 3D model was analyzed in an analytical software (Abaqus 6.14). The study was conducted under the following traction loads: 25%, 45%, 55%, and 85% of the whole body weight in different angles. RESULTS: Results indicated that the loading angle in the L3-4 area had 36.8%, 57.4%, 55.32%, 49.8%, and 52.15% effect on the anterior longitudinal ligament, posterior longitudinal ligament, intertransverse ligament, interspinous ligament, and supraspinous ligament, respectively. The respective values for the L4-5 area were 32.3%, 10.6%, 53.4%, 56.58%, and 57.35%. Also, the body weight had 63.2%, 42.6%, 44.68%, 50.2%, and 47.85% effect on the anterior longitudinal ligament, posterior longitudinal ligament, intertransverse ligament, interspinous ligament, and supraspinous ligament, respectively. The respective values for the L4-5 area were 67.7%, 89.4%, 46.6%, 43.42% and 42.65%. The authenticity of results was checked by comparing with the experimental data. CONCLUSIONS: The results show that traction beds are highly effective for disc movement and lower back pain relief. Also, an optimal angle for traction can be obtained in a 3D model analysis using CT or magnetic resonance imaging images. The optimal angle would be different for different patients and thus should be determined based on the decreased height of the intervertebral disc, weight and height of patients.

A Modified Laminoplasty Technique to Treat Cervical Myelopathy Secondary to Ossification of the Posterior Longitudinal Ligament (OPLL).

BACKGROUND This study aimed to evaluate the validity of modified laminoplasty in treating close-base OPLL with an occupying ratio of more than 60%. MATERIAL AND METHODS Forty-seven close-base OPLL patients with an occupying ratio of more than 60% were treated through modified laminoplasty (N=22) and combined anterior-posterior approach (N=25) in the study, including 17 females and 30 males, with a mean age of 60.59±6.76 years (ranging from 46 to 75 years). The patients' characteristics, the recovery rate of neurological function, length of the operation, intraoperative blood loss, hospital costs, and complications were recorded and compared between the 2 groups. RESULTS The recovery rate of neurological function did not demonstrate a significant difference between the 2 groups (P=0.886). However, length of the operation and intraoperative blood loss in the modified laminoplasty group were shorter than those in the combined anterior-posterior approach group (P=0.001 and P=0.023). Moreover, the mean hospital costs in the modified laminoplasty group (5166.61±123.27 USD) decreased by 33.6% compared with the combined anterior-posterior approach group (7780.12±256.73 USD). Additionally, the complications of the modified laminoplasty group were lower than in the combined anterior-posterior approach group. CONCLUSIONS Modified laminoplasty may be considered a safe and effective strategy for patients that have demonstrated close-base OPLL with an occupying ratio of more than 60% and who cannot endure the trauma caused by the combined anterior-posterior approach due to medical disease.

Increased stress and strain on the spinal cord due to ossification of the posterior longitudinal ligament in the cervical spine under flexion after laminectomy.

Myelopathy in the cervical spine due to cervical ossification of the posterior longitudinal ligament could be induced by static compression and/or dynamic factors. It has been suggested that dynamic factors need to be considered when planning and performing the decompression surgery on patients with the ossification of the posterior longitudinal ligament. A finite element model of the C2-C7 cervical spine in the neutral position was developed and used to generate flexion and extension of the cervical spine. The segmental ossification of the posterior longitudinal ligament on the C5 was assumed, and laminectomy was performed on C4-C6 according to a conventional surgical technique. For various occupying ratios of the ossified ligament between 20% and 60%, von-Mises stresses, maximum principal strains in the spinal cord, and cross-sectional area of the cord were investigated in the pre-operative and laminectomy models under flexion, neutral position, and extension. The results were consistent with previous experimental and computational studies in terms of stress, strain, and cross-sectional area. Flexion leads to higher stresses and strains in the cord than the neutral position and extension, even after decompression surgery. These higher stresses and strains might be generated by residual compression occurring at the segment with the ossification of the posterior longitudinal ligament. This study provides fundamental information under different neck positions regarding biomechanical characteristics of the spinal cord in cervical ossification of the posterior longitudinal ligament.

Effect of multilevel lumbar disc arthroplasty on spine kinematics and facet joint loads in flexion and extension: a finite element analysis.

Total disc arthroplasty (TDA) has been successfully used for monosegmental treatment in the last few years. However, multi-level TDA led to controversial clinical results. We hypothesise that: (1) the more artificial discs are implanted, the stronger the increases in spinal mobility and facet joint forces in flexion and extension; (2) deviations from the optimal implant position lead to strong instabilities. A three-dimensional finite element model of the intact L1-L5 human lumbar spine was created. Additionally, models of the L1-L5 region implanted with multiple Charité discs ranging from two to four levels were created. The models took into account the possible misalignments in the antero-posterior direction of the artificial discs. All these models were exposed to an axial compression preload of 500 N and pure moments of 7.5 Nm in flexion and extension. For central implant positions and the loading case extension, a motion increase of 51% for two implants up to 91% for four implants and a facet force increase of 24% for two implants up to 38% for four implants compared to the intact spine were calculated. In flexion, a motion decrease of 5% for two implants up to 8% for four implants was predicted. Posteriorly placed implants led to a better representation of the intact spine motion. However, lift-off phenomena between the core and the implant endplates were observed in some extension simulations in which the artificial discs were anteriorly or posteriorly implanted. The more artificial discs are implanted, the stronger the motion increase in flexion and extension was predicted with respect to the intact condition. Deviations from the optimal implant position lead to unfavourable kinematics, to high facet joint forces and even to lift-off phenomena. Therefore, multilevel TDA should, if at all, only be performed in appropriate patients with good muscular conditions and by surgeons who can ensure optimal implant positions.

High glucose potentiates collagen synthesis and bone morphogenetic protein-2-induced early osteoblast gene expression in rat spinal ligament cells.

Type 2 diabetes mellitus (T2DM) is an independent risk factor for ossification of the posterior longitudinal ligament, but the mechanism is unclear. We isolated cells from rat cervical spine ligaments and studied the effects of high glucose on expression of osteoblast genes to provide insight into molecular mechanism. Using these cells, high glucose stimulated the synthesis of type I collagen and significantly potentiated expression of early osteoblast genes (Runx2; alkaline phosphatase, ALP; and osteopontin, OP) induced by bone morphogenetic protein-2 (BMP-2). Notably, these effects of high glucose were fully mimicked and augmented by H(2)O(2), although blocked by the reactive oxygen species inhibitor N-acetyl cysteine. Furthermore, exposure of these cells to high glucose significantly suppressed the phosphorylation of p38MAPK while enhancing the phosphorylation of protein kinase C (PKC) in the cells. Consistent with these observations, an inhibitor of p38 augmented the potentiation of high glucose on BMP-2-induced early osteogenic gene expression, whereas the PKC inhibitor repressed the effect of high glucose on type I collagen synthesis of the cells. In conclusion, high glucose, via production of reactive oxygen species, subsequent activation of PKC, and inhibition of p38, enhances type I collagen synthesis and expression of early osteogenesis genes induced by BMP-2 in rat spinal ligament cells. Hyperglycemia may play an important role in the onset or progression of ossification of the posterior longitudinal ligament by promoting the responsiveness of ligament cells to osteogenic differentiation.

Regeneration of a spinal ligament after total lumbar disk arthroplasty in primates.

Total disk arthroplasty (TDA) is a new procedure that replaces the intervertebral disk space with an artificial motion segment and necessitates the resection of the anterior longitudinal ligament (ALL). We assessed whether a collagen-based graft made from porcine small-intestine submucosa (SIS) can be used as a regenerative scaffold to restore the function and structure of the ALL in the lumbar spine. A total of 10 mature male baboons underwent TDA at L5-L6 using one of two treatments: (1) TDA only (n = 5) or (2) TDA combined with SIS (n = 5). Six months postoperatively, mock revision surgery was performed to assess tissue adhesions followed by non-destructive multidirectional flexibility testing of the spinal segment. The vertebral segments were then processed for histology. The tissue adhesion score was 2.8 +/- 0.8 in the TDA only group and 1.8 +/- 1.4 in the TDA-SIS group (p = 0.2). Segmental range of motion and the length of the neutral zone were similar in both groups. Histology showed that the SIS scaffold led to an organized ligamentous structure with a significantly (p = 0.027) higher thickness (2.18 +/- 0.25 mm) compared to the connective tissue structure in the TDA-only group (1.66 +/- 0.33 mm). We concluded that using a SIS bioscaffold after TDA did not lead to increased great vessel adhesion while its use facilitated the formation of highly organized ligamentous tissues. However, the SIS- induced and newly formed ligamentous tissue anterior to the spinal segment did not lead to a measurable limitation of spinal extension.

Clinical and radiological results following cervical arthroplasty.

BACKGROUND: This was a retrospective study of clinical and radiological results of cervical arthroplasty using the Bryan cervical disc prosthesis to evaluate the efficacy of arthroplasty in clinical applications. METHODS: A total of 46 patients underwent arthroplasty of a single level using the Bryan disc prosthesis. Clinical outcome was assessed using the visual analogue scale (VAS) and the neck disability index (NDI). All patients were evaluated using preoperative and postoperative static cervical spine radiographs to compare cervical sagittal balance. Dynamic cervical spine radiographs were used to compare movement at the level of the procedure, movement at the adjacent level and movement of the whole cervical spine. FINDINGS: With the exception of four patients with aggravated neck pain, the NDI and VAS scores decreased significantly in late follow-up evaluations. The range of movement of the whole cervical spine, the functional segmental unit, and the adjacent segments were preserved after arthroplasty. The sagittal alignment of the cervical spine showed kyphosis after surgery but restored lordosis at a later time. The postulated cause of kyphotic changes include "over-milling" at the dorsal endplate, inappropriate angle of disc insertion, structural absence of lordosis in the Bryan disc, removal of posterior longitudinal ligament, and pre-existing kyphosis. CONCLUSIONS: Arthroplasty using the Bryan disc appears to be safe and provided a favorable preliminary clinical and radiological outcome. Postoperative kyphosis can be prevented by understanding the biomechanical properties of the Bryan disc. Future studies will need to address the association between postoperative kyphosis, clinical outcome and adjacent segment disease.

A pilot study to evaluate the effectiveness of small intestinal submucosa used to repair spinal ligaments in the goat.

BACKGROUND CONTEXT: Destabilization of the lumbar spine results from sacrifice of the anterior longitudinal ligament and disc when removed for graft or cage placement. In a similar fashion, transection of the interspinous ligament during surgical approaches to the posterior spine may result in segmental instability. Such instability can cause abnormal motion or implant migration resulting in a higher incidence of pseudarthrosis. Small intestinal submucosa (SIS) is a naturally occurring extracellular collagen-based matrix, which is derived from porcine small intestine. SIS contains cytokines and growth factors and has been shown to act as a resorbable scaffold in vivo that promotes host soft tissue regeneration with little scar tissue formation. SIS can be manufactured in laminated sheets of various sizes and thicknesses for different indications. Successful applications of SIS in animals have included dural substitution, rotator cuff repair, vessel repair, abdominal and bladder wall repair, and others. However, SIS has not been investigated to determine its ability to facilitate regeneration of spinal ligaments. PURPOSE: The purpose of this pilot study was to evaluate the efficacy of SIS as a barrier to prevent interbody device migration, and to act as a scaffold for regeneration of the anterior longitudinal ligament (ALL) and posterior interspinous ligament (PISL) in a goat model. STUDY DESIGN/SETTING: The thoracolumbar spine of the goat was exposed surgically. After resection and removal of the ALL or PISL at alternating levels, either SIS was placed or no treatment was administered. New ligament formation and SIS resorption were monitored over a 12-week period. OUTCOME MEASURES: Plain film radiographs and histomorphometry were used to assess the progress of healing over a 12-week time period. METHODS: Four skeletally mature nubian-alpine crossbred goats were used in this study. Under general anesthesia, each T10 to L5 motion segment was exposed surgically. Both anterolateral and posterior approaches were performed simultaneously at each level. Anteriorly, alternating levels received either 1) anterior discectomy, sacrifice of ALL and placement of SIS (SIS group); 2) anterior discectomy, sacrifice of ALL and no SIS (surgical control group) or 3) no surgical intervention (nonoperative group). A solid interbody spacer was placed into the disc space after discectomy to deter spontaneous anterior interbody fusion. Posteriorly, alternating levels were treated with either 1) sacrifice of the PISL with placement of SIS (SIS group); 2) sacrifice of PISL and no SIS (surgical control group) or 3) no surgical intervention (nonoperative group). The SIS was secured to the adjacent superior and inferior spinous processes to create a tension-band effect. Animals were radiographed immediately postoperatively to confirm placement of interbody spacers and anchors and to serve as a baseline for monitoring interbody spacer positioning. After surgery, all animals were allowed unrestricted motion for 12 weeks. At the end of the 12-week period, animals were radiographed and euthanized. The lumbar spine was harvested en bloc and processed for decalcified histologic evaluation. The dorsal and ventral aspects of each motion segment were analyzed for signs of inflammation and scar tissue formation, residual SIS and regenerated ALL or PISL. RESULTS: All animals tolerated the surgical procedure well, and there were no intraoperative or anesthesia-related complications. Twelve-week radiographs showed some evidence of ventral migration of the interbody spacers in several animals. Fifty percent (two of four) of spacers in surgical control group levels had migrated more than 10 mm (resulting in complete migration out of the disc space), whereas no spacers migrated completely out of levels with SIS placed. Gross analysis at necropsy indicated iatrogenic scar formation at operated levels, the degree of which was not different from surgical control group to SIS levels. Histologic evaluation of areas where the ALL had been removed indicated formation of organized fibrilar collagenous tissue that spanned the disc space at some levels where the SIS was placed. In some cases, the newly formed tissue was approximately the thickness of the ALL at the nonoperative group levels. The newly formed collagenous tissue was accompanied by sparse focal areas of inflammation, with small fragments of residual SIS at some levels. At surgical control group levels, there was a varying degree of connective tissue that ranged from moderately organized to randomly oriented with no significant signs of inflammation. Similarly, histologic analysis of some levels where SIS was placed posteriorly showed formation of organized collagenous tissues where the PISL had been removed. CONCLUSIONS: In this model, the SIS patch was sufficient to prevent acute ventral migration of interbody spacers from the disc space. The extent of long-term healing and new tissue formation in the SIS group indicates that it may be efficacious as a reparative intervention for transected ligaments in the spine. Most SIS specimens showed formation of organized collagenous tissue, indicating a long-term potential for ligament formation. However, in this model, 12 weeks of postoperative healing is insufficient to assess the full potential of SIS as a spinal ligament repair. Further research that follows the healing process to a longer time point postoperatively may be necessary to fully understand the potential of SIS as a resorbable scaffold for tissue replacement.

Biomechanical effect of anterior cervical spine fusion on adjacent segments.

The biomechanical effects of superior (C4-C5) and inferior (C5-C6) level fusions with different graft materials on the adjacent unaltered components were quantified using an anatomically accurate and experimentally validated C4-C5-C6 finite element model. Smith-Robinson and Bailey-Badgley fusion procedures were analyzed with five different types of inter-body fusion materials with varying stiffnesses. Intact and surgically altered finite element models were subjected to physiologic compression, flexion, extension and lateral bending. The external axial and angular stiffness, and the internal unaltered intervertebral disc (C5-C6 for the superior and C4-C5 for inferior fusion) and C5 vertebral body stresses were determined. The superior level fusion resulted in the highest increase in external response in lateral bending for all implant materials in both surgical procedures. In contrast, the inferior level fusion produced a higher increase in the C4-C5 disc and C5 vertebral body stresses in compression than the superior level fusion in both surgical procedures. The increased internal stress responses reflecting the changes in the load-sharing following inferior level fusion may explain clinical observations such as enhanced degeneration subsequent to surgery. Because of the inclusion of three levels in the present multi-segment finite element model, it was possible to determine these responses in the unaltered adjacent components of the cervical spine.

Influences of walking speed change on the lumbosacral joint force distribution.

To more understand the influence of the walking speed on the spinal joint force distribution, a three-dimensional biomechanical model was used to estimate the spine loads during human gait with three different walking speeds. This previously developed and validated model included a dynamic external model and an internal model with forces of disc, 8 major muscles, 2 ligaments and 2 facet joints at L5/S1 level. A linear optimization method was used to solve the internal model to estimate the L5/S1 spinal joint force distribution. The results of five young male subjects showed that the mean peak L5/S1 disc compressive forces on the slow, preferred and fast speeds were 2.28, 2.53, 2.95 body weight, respectively. The peak forces happened right after the heel strike and before completely toe off. The facet joint forces were generally increased with the walking speed increase, too. To reduce the loads on the spine, the slow walking is then recommended for the patients with low back pain or after spinal surgery.

[Influence of foods on the posterior longitudinal ligament of the cervical spine and serum sex hormones].

To investigate the involvement of sex hormones as a potential cause of ossification in the posterior longitudinal ligament (OPLL) of the cervical spine, we experimentally examined the influence of ingested foods on the serum levels of sex hormones and changes in the spinal ligament. Castrated rabbits were administered a sex hormone and raised with special feed. Assay of the serum sex hormone levels, analysis of the carbon and nitrogen isotope ratios in body hairs, and histological studies were carried out. In the group administered soybeans and highly concentrated saline solution, the serum estrogen level was high, the serum testosterone level was low and the delta 15N value of the body hairs was also low. Histologically, a group of newly formed chondroblasts was seen in the posterior longitudinal ligament in the angular region of a narrowed intervertebral disc, and many fibroblasts were detected by assay using a microspectrophotometer (MSP) in this group. These findings suggested that a diet high in vegetable protein, consisting mainly of beans, and foods high in salt may lead to an unbalanced state for sex hormones and cause histological changes in the spinal ligament. This, as well as other general ossifying factors of ligament, may play a role in the etiology of ossification.