According to the physiological characteristics of lumbar vertebrae in Chinese, we designed and made a lumbar vertebral fusion cage of titanium and then engaged in its biomechanical test. T12-S1 of lumbar vertebrae from 18 fresh dead bodies were used. We measured the stress relaxation and the creep effects of the normal group (T12-S1 of intact lumbar vertebrae), the control group 1(simulating operation of excising intervertebral disc and planting bone on the back route) and the control group 2(simulating operation of excising intervertebral disc and inserting fusion cage). The data and stress, strain-time curves under the condition of constant stress and strain were obtained. Regression analysis yielded the reduced stress relaxation and creep functions. Finally, we analyzed and discussed the effects of the operation of excising intervertebral disc and planting bone on the back route and the operation of excising intervertebral disc and inserting fusion cage on the stability of spine.
Elasticity ; Humans ; Intervertebral Disc ; physiology ; surgery ; Lumbar Vertebrae ; physiology ; Spinal Fusion ; Spine ; Titanium

To investigate the effects of postoperative fusion implantation on the mesoscopic biomechanical properties of vertebrae and bone tissue osteogenesis in idiopathic scoliosis, a macroscopic finite element model of the postoperative fusion device was developed, and a mesoscopic model of the bone unit was developed using the Saint Venant sub-model approach. To simulate human physiological conditions, the differences in biomechanical properties between macroscopic cortical bone and mesoscopic bone units under the same boundary conditions were studied, and the effects of fusion implantation on bone tissue growth at the mesoscopic scale were analyzed. The results showed that the stresses in the mesoscopic structure of the lumbar spine increased compared to the macroscopic structure, and the mesoscopic stress in this case is 2.606 to 5.958 times of the macroscopic stress; the stresses in the upper bone unit of the fusion device were greater than those in the lower part; the average stresses in the upper vertebral body end surfaces were ranked in the order of right, left, posterior and anterior; the stresses in the lower vertebral body were ranked in the order of left, posterior, right and anterior; and rotation was the condition with the greatest stress value in the bone unit. It is hypothesized that bone tissue osteogenesis is better on the upper face of the fusion than on the lower face, and that bone tissue growth rate on the upper face is in the order of right, left, posterior, and anterior; while on the lower face, it is in the order of left, posterior, right, and anterior; and that patients' constant rotational movements after surgery is conducive to bone growth. The results of the study may provide a theoretical basis for the design of surgical protocols and optimization of fusion devices for idiopathic scoliosis.
Humans ; Scoliosis/surgery* ; Spinal Fusion/methods* ; Lumbar Vertebrae/surgery* ; Osteogenesis ; Biomechanical Phenomena/physiology* ; Finite Element Analysis

We have studied the characteristics of stress relaxation and creep on lumbar vertebrae(T12-T5) of 18 fresh corpses. We measured the stress relaxation and creep of the normal group(intact spine), the control group 1(simulating the operations by the front route) and the control group 2(simulating the operations by the back route). Then we obtained the stress, strain-time curves and data under the conditions of constant stress and strain. By using regression analysis we obtained the reduced stress relaxation and creep functions. Finally, We analyzed and discussed the effects of the operations of excising the disc intervertebrales by the front route and the back route.
Diskectomy ; methods ; Elasticity ; Humans ; Lumbar Vertebrae ; physiology ; surgery ; Male ; Relaxation ; Stress, Mechanical

In order to study the mechanical behavior of degeneration and nucleotomy of lumbar intervertebral disc, compression experiments with porcine lumbar intervertebral discs were carried out. The lumbar intervertebral discs with trypsin-treated and nucleus nucleotomy served as the experimental group and the normal discs as the control group. Considering the effects of load magnitude and loading rate, the relationship between stress and strain, instantaneous elastic modulus and creep property of intervertebral disc were obtained. The creep constitutive model was established. The results show that the strain and creep strain of the experimental group increase significantly with the increase of compression load and loading rate, whereas the instantaneous elastic modulus decreases obviously, compared with the control group. It indicates that the effect of load magnitude and loading rate on load-bearing capacity of intervertebral disc after nucleotomy is larger obviously than that of normal disc. The creep behavior of the experimental group can be still predicted by the Kelvin three-parameter solid model. The results will provide theoretical foundation for clinical treatment and postoperative rehabilitation of intervertebral disc disease.
Animals ; Biomechanical Phenomena ; Intervertebral Disc ; physiology ; surgery ; Lumbar Vertebrae ; Stress, Mechanical ; Swine ; Weight-Bearing

OBJECTIVETo determine the stress distribution on endplate after lumbar prosthetic disc nucleus (PDN) replacement.

METHODSSix fresh lumbar vertebrae with normal Modic classification were harvested. The specimens were used to establish L4-5 intact, nucleotomy, prosthetic nucleus pulposus replacement models. Vertical compression tests were performed with MTS machine at the rate 50 N per second to maximum load of 1300 N. The stress under the endplate were measured directly with accurate pressure sensors.

RESULTSFor intact specimens, the stress on the endplate maintained higher in the central zone of the endplate, and decreased gradually to the periphery, and was well-distributed. After nucleotomy, the stress on the central zone of endplate was significantly decreased, and increased stress occurred in the periphery of endplate. After PDN replacement, the stress on the central zone of endplate was found more 15.1% higher than that in intact disc (P < 0.05), and the neighboring zone also showed higher stress measurements.

CONCLUSIONSAfter lumbar prosthetic disc nucleus replacement, the stress concentration on endplate may occur in the central zone of prosthetic disc nucleus insertion. Therefore, the prosthetic nucleus pulposus with suitable shape, proper biomechanical functions and updated materials need further study.

Adult ; Arthroplasty, Replacement ; Cartilage, Articular ; physiology ; Humans ; Intervertebral Disc ; surgery ; Joint Prosthesis ; Lumbar Vertebrae ; surgery ; Middle Aged ; Stress, Mechanical

OBJECTIVETo test the changes of the stiffness of the intact, released, and instrumented spines in an in vitro porcine model.

METHODSTwelve porcine spines (12 segments each) were harvested for the biomechanical tests with Material Test System. Stiffness during flexion, extension, lateral bending, and axial rotation were recorded; then the specimen was released with intervertebral discs and the facet joints removed, followed by repeating the biomechanical tests for stiffness; and finally, a double-rod titanium construct was applied for internal fixation to each released spine and stiffness tests were repeated again.

RESULTSCompared with the intact porcine spines [stiffness during flexion, extension, lateral bending, and axial rotation was 52.89 +/- 15.98, 105.43 +/- 56.38, 42.09 +/- 14.73, and (16.94 +/- 4.85) N x mm/degrees, respectively], the stiffness of the released porcine spines [stiffness during flexion, extension, lateral bending, and axial rotation was 44.04 +/- 13.73, 41.46 +/- 10.80, 31.75 +/- 7.23, and (9.10 +/- 2.07)N x mm/degrees, respectively] significantly decreased (P < 0.05), while significantly increased stiffness was found in the instrumented porcine spines [stiffness during flexion, extension, lateral bending, and axial rotation was 385.96 +/- 143.25, 138.96 +/- 59.41, 152.56 +/- 87.15, and (55.91 +/- 16.49) N x mm/degrees, respectively] (P < 0.05).

CONCLUSIONHigher instant stiffness was found in instrumented spine than the intact one during flexion, extension, lateral bending and axial rotation.

Animals ; Biomechanical Phenomena ; Diskectomy ; Fracture Fixation, Internal ; Internal Fixators ; Lumbar Vertebrae ; surgery ; Range of Motion, Articular ; physiology ; Spinal Fusion ; methods ; Spine ; surgery ; Stress, Mechanical ; Swine ; Thoracic Vertebrae ; surgery

BACKGROUND: Some porous materials have been developed to enhance biologic fusion of the implants to bone in spine fusion surgeries. However, there are several inherent limitations. In this study, a novel biomedical porous tantalum was applied to in vitro and in vivo experiments to test its biocompatibility and osteocompatibility. METHODS: Bone marrow-derived mesenchymal stem cells (BMSCs) were cultured on porous tantalum implant. Scanning electron microscope (SEM) and Cell Counting Kit-8 assay were used to evaluate the cell toxicity and biocompatibility. Twenty-four rabbits were performed discectomy only (control group), discectomy with autologous bone implanted (autograft group), and discectomy with porous tantalum implanted (tantalum group) at 3 levels: L3-L4, L4-L5, and L5-L6 in random order. All the 24 rabbits were randomly sacrificed at the different post-operative times (2, 4, 6, and 12 months; n = 6 at each time point). Histologic examination and micro-computed tomography scans were done to evaluate the fusion process. Comparison of fusion index scores between groups was analyzed using one-way analysis of variance. Other comparisons of numerical variables between groups were made by Student t test. RESULTS: All rabbits survived and recovered without any symptoms of nerve injury. Radiographic fusion index scores at 12 months post-operatively between autograft and tantalum groups showed no significant difference (2.89 ± 0.32 vs. 2.83 ± 0.38, F = 244.60, P = 0.709). Cell Counting Kit-8 assay showed no significant difference of absorbance values between the leaching liquor group and control group (1.25 ± 0.06 vs. 1.23 ± 0.04, t = -0.644, P = 0.545), which indicated the BMSC proliferation without toxicity. SEM images showed that these cells had irregular shapes with long spindles adhered to the surface of tantalum implant. No implant degradation, wear debris, or osteolysis was observed. Histologic results showed solid fusion in the porous tantalum and autologous bone implanted intervertebral spaces. CONCLUSION This novel porous tantalum implant showed a good biocompatibility and osteocompatibility, which could be a valid biomaterial for interbody fusion cages.
Animals ; Cell Proliferation ; physiology ; Diskectomy ; Lumbar Vertebrae ; surgery ; Microscopy, Electron, Scanning ; Prostheses and Implants ; Rabbits ; Spinal Fusion ; Tantalum ; chemistry

OBJECTIVE: To examine the biomechanical effect of lumbar discectomy and disc replacement on compressive load in proximal adjacent segment, to understand the characteristics of the prosthesis and effects in spine after artificial disc replacement (ADR), and to evaluate long-term clinical effect in adjacent segments. METHODS: Complete human cadaveric ligamentous lumbar spine specimens were used to make 3 models: an intact sample, a discectomy sample, and a sample of ADR after the discectomy. The compressive load in proximal segment above the injury segment was measured separately in various loading cases on the 3 models. RESULTS: The changes of intervertebral loads in the adjacent segments made the compressive load increase in the proximal segment after the discectomy. The compressive load in the proximal segment was lower in the ADR group than that in the injury group. There was no significant difference between the ADR group and intact group. CONCLUSION Discectomy increases the compressive load in the proximal segment, while ADR reduces it, showing the same compressive load level with the intact model in the proximal segment. Changes of compressive loading in adjacent level segments after discectomy and ADR, may be the cause of abnormal stress distribution and movements of adjacent segments, and be of benefit for the disc replacement.
Adult ; Biomechanical Phenomena ; Cadaver ; Diskectomy ; methods ; Humans ; Intervertebral Disc ; surgery ; Lumbar Vertebrae ; physiology ; surgery ; Models, Biological ; Prosthesis Implantation ; Weight-Bearing ; physiology

OBJECTIVETo study vertebral body stress distribution of normal disc, post-Diskectomy and artificial disk respectively by 3-D finite element methods, and to explore artificial intervertebral disk insertion impact on stress distribution of vertebral body.

METHODSModels of normal disk, post-Diskectomy, artificial disk and L(4 - 5) motion segment were established by using finite element software MSC. MARK, then vertebral body stress was analyzed through model of L(4 - 5) motion segment respectively.

RESULTSThe vertebral body's stress was the smallest after insertion of artificial intervertebral disk (AID), and its stress distributed equally. But the stress under post-discectomy was bigger than the normal disc's in all the motion state. On the other hand, the stress distribution state of the post-discectomy changed while the spine were in different motion state, during the spine flexion, the stress in the anterior of vertebral body was the biggest; While extension, in the posterior and in right flexion state, the biggest stress was in the right. While vertical compression and rotation, the stress distributed equally.

CONCLUSIONThe results illustrate that the vertebral body's stress is the smallest after insertion of AID in 3 groups of all motion state, and its stress distributes equally. But the level of vertebral body stress increases after discectomy comparing with the normal group. In generally, it is much more reasonable that the disc is reconstructed with AID because of the biomechanical effect on vertebral body made by AID insertion.

Diskectomy ; Finite Element Analysis ; Humans ; Intervertebral Disc ; physiology ; surgery ; Lumbar Vertebrae ; physiology ; surgery ; Models, Biological ; Prostheses and Implants ; Prosthesis Implantation ; Stress, Mechanical

We performed biomechanical comparison of a xenograft bone plate-screw (XBPS) system for achieving cadaveric lumbar transpedicular stabilization (TS) in dogs. Twenty dogs' cadaveric L2-4 lumbar specimens were harvested and their muscles were removed, but the discs and ligaments were left intact. These specimens were separated to four groups: the L2-4 intact group as control (group I, n = 5), the L3 laminectomy and bilateral facetectomy group (LBF) (group II, n = 5), the LBF plus TS with metal plate-screw group (group III, n = 5) and the LBF plus TS with XBPS group (group IV, n = 5). Five kinds of biomechanical tests were applied to the specimens: flexion, extension, left-right bending and rotation. The averages of the 16 stiffness values were calculated and then these were statistically analyzed. The statistical results show that the XBPS system contributes spinal stability and this system can be a good choice for achieving TS.
Animals ; Biomechanics ; Bone Plates/*veterinary ; Bone Screws/*veterinary ; Cadaver ; Dogs ; Lumbar Vertebrae/physiology/*surgery ; Range of Motion, Articular/physiology ; Spinal Fusion/instrumentation/*methods ; Transplantation, Heterologous/instrumentation/*methods