摘要:

Study DesignThe present study evaluated the anterior sacral foramen using plain radiographs and projected the positions of S1-S3 anterior sacral foramen and corresponding nerve root groove on the posterior aspect of the sacrum.ObjectivesTo evaluate the plain radiographs of anteroposterior, inlet, and outlet views regarding the sacral foramen, and to determine quantitatively the location of the anterior sacral foramens on the posterior aspect of the sacrum.Summary of Background DataInjury to the sacral nerve roots associated with posterior sacral screw placement remains a potential hazard. Few studies regarding the evaluation of the anterior sacral foramen and its projection on the posterior sacral surface are available.MethodsSix bony pelves were harvested from preserved cadavers. The superior aspect of the sacral alae, the openings of the anterior and posterior foramens of S1-S2, were marked by outlining them with K-wires. Anteroposterior, inlet, and outlet plain radiographs were taken. The bony sacra were further disarticulated from the above six pelvic specimens. K-wires were drilled through the sacra to project the dimensions of the anterior foramens and nerve grooves of S1-S3 onto the posterior sacral surface. The dimensions between the perimeter of the projection and the corresponding posterior foramen were measured.ResultsThe plain radiographs show that the shape and relative position between the anterior and posterior foramens vary with different projections. It was believed that outlet projection is the best view of plain radiographs in the evaluation of the sacral foramens and corresponding pedicles. The approximate boundaries of the anterior sacral foramens' projections were 6 mm superior, 10 mm lateral, 3 mm inferior, and 3 mm medial to the corresponding margins of the posterior foramens.ConclusionsThe outlet projection is the most useful view in plain radiographs for the evaluation of sacral foramens and pedicles. Quantitative data of the anterior sacral foramen's anatomic position on the dorsal aspect of the sacrum may be helpful in the sacral pedicle screw placement.

ISSN:0362-2436    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Study DesignUltrastructural changes were analyzed by transmission electron microscopy in nerve roots exposed to autologous nucleus pulposus experimentally.ObjectivesTo assess if ultrastructural changes were present in areas with no light microscopic changes in nerve roots exposed to autologous nucleus pulposus in a pig model.Summary of Background DataPrevious analyses have shown that there is focal nerve fiber damage in nerve roots exposed to autologous nucleus pulposus in the pig. These changes could not fully explain the reduction in nerve conduction velocity seen in the same nerve roots. In the present study, the parts of the nerve roots that did not display breakdown of axons or myelin sheaths at the light microscopic level were analyzed regarding ultrastructural changes.MethodsIn a previous study, nucleus pulposus was harvested from a lumbar disc and placed epidurally onto the cauda equina at the sacrococcygeal level in pigs. Retroperitoneal fat was used as control. After 1, 3, and 7 days, the nerve roots were excised and processed for light microscopy. Parts of the nerve roots that appeared normal at the light microscopic level were further processed for the present electron microscopic examination.ResultsSignificant ultrastructural changes, such as expansion of the Schwann cell cytoplasm and intracellular edema with vesicular swelling of the Schmidt-Lanterman incisures, were observed in nerve fibers with normal axons. Although present after nucleus pulposus and control application, the changes were more pronounced after the application of nucleus pulposus.ConclusionsEpidural application of autologous nucleus pulposus without any pressure may induce not only nerve function impairment but also axonal injury and significant primary Schwann cell damage with vesicular swelling of the Schmidt-Lanterman incisures. However, because axonal and Schwann cell changes affected only part of the nerve fibers, further causes of the impaired nerve conduction need to be determined.

ISSN:0362-2436    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Study DesignThe transport properties of solutes of different sizes and conformations were studied in cartilage endplates.ObjectivesThe results were correlated with the composition of the cartilage matrix to determine if a relationship existed between this and the movement of molecules within it.Summary of Background DataSolute transport through the hyaline cartilage endplate is important not only for the physiologic and metabolic processes of that tissue, but also for those of the adjacent intervertebral disc. Movement of solutes depends on solute size, shape or charges, and the composition of the matrix itself. Changes in composition of the cartilage endplate, such as those that occur in degeneration or scoliosis, may affect transport.MethodsPartition and diffusion coefficients of solutes ranging in molecular weight from 115 to 70,000 d have been measured on cores of cartilage endplate. Transport properties were assessed in relation to core composition.ResultsThe shape and size of the solutes were found to affect their transport through cartilage matrix, with larger molecules being more highly excluded and diffusing more slowly. Long-chain polymers were able to penetrate the matrix less readily than the more globular molecules. The more hydrated the matrix, the higher the degree of penetration and the more easily solutes could move, in contrast to the inverse relationship between the other components of the matrix and solute transport. With increased proteoglycan, collagen, or calcification in the tissue, there was greater restriction of solute movement.ConclusionsThe proteoglycans normally found in the endplate regulate movement of solutes into and out of the disc. It has been shown previously that removal of proteoglycans from the endplate accelerates the loss of proteoglycans from the nucleus. Hence, a major function of the cartilage endplate may be to prevent fragments of osmotically active proteoglycans from leaving the disc.

ISSN:0362-2436    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Study DesignThis study is anin vitroinvestigation of the effects of substance P on intervertebral disc cell metabolism.ObjectivesTo determine whether the neuropeptide, substance P, affects cells isolated from the intervertebral disc.Summary of the Background DataNerve fibers containing substance P are present in the anulus fibrosus and may be released from the nerve terminals as in other tissues. Substance P is mitogenic for a variety of immune and connective tissue cells, and a fragment of the peptide affects the metabolism of articular chondrocytes.MethodsCells were isolated enzymically from the anulus fibrosus of intervertebral disc of 8-week-old rabbits. The effects of substance P and the C-terminal pentapeptide fragment SP7-11 on cell proliferation and proteoglycan deposition were determined by crystal violet and Alcian blue staining, respectively.ResultsSubstance P (10-11-10-7mol/l) had a small stimulatory effect on disc cell proliferation. Proteoglycan deposition in the cell layer increased concomitantly. A greater proliferative effect was observed with substance P fragment 7-11 or with the addition of the neutral endopeptidase inhibitor, phosphoramidon.ConclusionsSubstance P has small mitogenic effects on rabbit intervertebral disc cellsin vitro. Further investigation is required to establish whether this might have biologic relevance in relation to the maintenance or repair of the intervertebral disc.

ISSN:0362-2436    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Study DesignTask-specific and subject-specific lumbar trunk muscle function, muscle geometry, and vertebral density data were collected from 16 men. A biomechanical model was used to determine muscle strength and the compressive forces acting on the lumbar spine.ObjectivesTo develop an anatomic biomechanical model of the low back that could be used to derive task-specific muscle function parameters and to predict compressive forces acting on the low back. Several model-specific constraints were examined, including the notion of bilateral trunk muscle anatomic symmetry, the influence of muscle lines of action, and the use of density-derived vertebral strength for model validation.Summary of Background DataClinical and basic science investigators are currently using a battery of diverse biomechanical techniques to evaluate trunk muscle strength. Noteworthy is the large variability in muscle function parameters reported for different subjects and for different tasks. This information is used to calculate forces and moments acting on the low back, but limited data exist concerning the assessment of subject-specific, multiaxis, isometric trunk muscle functions.MethodsA trunk dynamometer was used to measure maximum upright, isometric trunk moments in the sagittal (extension, flexion) and coronal (lateral flexion) planes. Task- and subject-specific trunk muscle strength or “gain” was determined from the measured trunk moments and magnetic resonance image-based muscle cross-sectional geometry. Model-predicted compressive forces obtained using muscle force and body force equilibrium equations were compared with density-derived estimates of compressive strength.ResultsIndividual task-specific muscle gain values differed significantly between subjects and between each of the tasks they performed (extension > flexion > lateral flexion). Significant differences were found between left side and right side muscle areas, and the lines of action of the muscles deviated significantly from the vertical plane. Model-predicted lumbar compressive forces were 38% (lateral flexion) to 73% (extension) lower than the L3 vertebral compressive strength estimated from vertebral density.ConclusionThe present study suggests that biomechanical models of the low back should be based on task-specific and subject-specific muscle function and precise geometry. Vertebral strength estimates based upon vertebral density appear to be useful for validation of model force predictions.

ISSN:0362-2436    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Study DesignCadaveric motion segment experiment. Measurements on each specimen were compared before and after creep loading.ObjectivesTo show how sustained “creep” loading affects stress distributions inside intervertebral discs.Summary of Background DataThe central region of an intervertebral disc acts like a hydrostatic “cushion” between adjacent vertebrae. However, this property depends on the water content of the tissues and may be lost or diminished after creep.MethodsTwenty-seven lumbar motion segments consisting of two vertebrae and the intervening disc and ligaments were loaded to simulate erect standing postures in life. The distribution of compressive stress in the disc matrix was measured by pulling a miniature pressure transducer through the disc in the midsagittal plane. Profiles of vertical and horizontal compressive stress were repeated after each specimen had been creep loaded in compression for 2-6 hours.ResultsCreep reduced the hydrostatic pressure in the nucleus by 13-36%. Compressive stresses in the anulus were little affected when the profiles were measured at 1 kN, but at 2 kN, localized peaks of compressive stress appeared (or grew in size) in the posterior anulus after creep.ConclusionsIncreased loading of the apophysial joints causes an overall reduction in intradiscal stresses after creep. In addition, water loss from the nucleus causes a transfer of load from nucleus to anulus. Stress concentrations may lead to pain, structural disruption, and alterations in chondrocyte metabolism. Disc mechanics depend on loading history as well as applied load.

ISSN:0362-2436    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Study DesignThe technique of hole preparation and the placement or orientation of anterior transvertebral screws in relation to the endplates were the subjects of two experiments.ObjectivesExperiment 1-to determine if anterior transvertebral body screws have higher pull-out strengths after unicortical predrilling compared with a biocortical predrilling; Experiment 2-to determine the effect of the screw's orientation in the vertebral body on its resistance to loosening.Summary of Background DataThere are a variety of surgical techniques for using anterior transvertebral screws in the vertebral body without any clear guidelines as to which techniques optimize the strength of fixation.MethodsIn Experiment 1, 31 cadaveric vertebral bodies were tested for pull-out strength of transvertebral body screws placed after unicortical predrilling compared with bicortical predrilling. In Experiment 2, 48 cadaveric vertebral bodies were tested with transvertebral screws inserted using four different screw orientations.ResultsThere is no statistically significant difference in pull-out strength of anterior transvertebral body screws inserted after unicortical compared with bicortical predrilling (Experiment 1). The resistance to loosening is greatest when transvertebral screws are oriented in the “superior oblique” position (Experiment 2).ConclusionsExperiment 1-preparation of the far cortex by predrilling is not necessary. Experiment 2-transvertebral screws should be obliquely oriented so that the forces applied to the screws are resisted by both of the endplates.

ISSN:0362-2436    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Study DesignThisin vitrostudy analyzed the effects of a supralaminar hook on pedicle screw fixation in compromised pedicle bone.ObjectivesTo determine the ability of pediculolaminar fixation to restore pedicle screw pull-out strength after stripping of senile pedicle bone.Summary of Background DataDespite improvements in pedicle screw design, the bone-screw interface remains the “weakest link” in pedicle screw fixation. This interface is especially vulnerable in osteoporotic bone, previously instrumented pedicles, and at the ends of long instrumentation constructs.MethodsSide-to-side testing between a pedicle screw and a pedicle screw supplemented with a supralaminar hook (pediculolaminar fixation) was performed in human cadaveric lumbar vertebrae. Comparisons were made for intact and compromised pedicle bone.ResultsPediculolaminar fixation restored 89% of intact pedicle screw pull-out strength, whereas the pedicle screw alone restored only 19% of intact pull-out strength. The role of pediculolaminar fixation was greatest in weaker bone. Significant differences were noted in energy to failure and post-failure energy. In intact bone, the pediculolaminar construct did not increase pull-out strength or energy to failure, although it did have a greater post-failure energy.ConclusionPediculolaminar fixation can augment pedicle screw fixation in pedicle bone compromised by previous stripping or significant osteoporosis or both.

ISSN:0362-2436    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Study DesignThein vitrotensile behavior of multiple-layer samples of anulus fibrosus were investigated from nondegenerate intervertebral discs.ObjectivesTo quantify the intrinsic tensile behavior of nondegenerate anulus fibrosus and the variations with position and age in the intervertebral disc.Summary of Background DataTension is an important loading mode in the anulus fibrosus. The tensile behavior of single- and multiple-layer samples of anulus fibrosus has been shown to vary with specimen orientation, position in the disc, and environmental conditions. Little is known of the changes in these site-specific tensile properties of the anulus with aging or degeneration of the intervertebral disc.MethodsMultiple-layer specimens of anulus fibrosus were harvested with an orientation parallel to the circumference of the disc. Constant strain rate and uniaxial tensile tests were performed in 0.15 mol/l NaCl at slow strain rates to measure the intrinsic properties of the collagen-proteoglycan matrix of the anulus fibrosus. The tensile modulus, failure stress, failure strain, and strain energy density were determined. Statistical analyses were done to evaluate regional and age-related differences in these properties.ResultsSignificant radial and circumferential variations in the intrinsic tensile properties of anular samples were detected. The anterior anulus fibrosus had larger values for tensile moduli and failure stresses than the posterolateral anulus. Also, the outer regions of the anulus had greater moduli and failure stresses and lower failure strains than the inner regions. Strain energy density did not vary significantly with region. Significant, but very weak, correlations were detected between tensile properties and age of the intervertebral disc.ConclusionsThe observed variations in tensile behavior of multiple-layer anulus samples indicate that larger variations in tensile modulus and failure properties occur with radial position in the disc than from anterior to posterolateral regions. This pattern is likely related to site-specific variations in the tensile properties of the single-layer samples of anulus fibrosus lamellae and the organization of successive lamellae and their interactions. The results of the present study suggest that factors other than age, such as compositional and structural variations in the disc, are the most important determinants of tensile behavior of the anulus fibrosus.

ISSN:0362-2436    

出版商:OVID    

年代:1996

数据来源: OVID

摘要:

Study DesignThe strength of posterior cervical lateral mass fixation was evaluated in a cadaver model for two techniques of screw insertion.ObjectiveTo compare the flexion failure strengths of posterior cervical plate fixation for two techniques of screw placement at the superior and inferior screw hole positions, and to evaluate the effect of bone mineral density on fixation strength.Summary of Background DataBiomechanical analyses of various screw insertion techniques for posterior cervical lateral mass fixation have never evaluated the effect of screw position along the plate.MethodsIndividual C3-C6 segments of 24 human cadaveric cervical spines were used. The spinous process and lamina were removed to simulate a postlaminectomy situation. Vertebral body bone mineral density for each specimen was determined by dual-energy radiograph absorption scanning. In each lateral mass, a bicortical 3.5-mm screw was placed using either the Magerl or Roy-Camille insertion technique through an end hole of a titanium bone plate. For “superior” screws, the plate was directed caudally; for “inferior” screws, the plate was directed cranially. Screw violation of the surrounding facet joints was noted. An increasing flexion moment was applied by loading the plate 4 cm from the screw head at a rate of 10 cm/min using a servohydraulic testing machine until screw failure.ResultsFor the superior screw hole position, the Magerl screw sustained a significantly higher average moment to failure (190.2 Ncm) than the Roy-Camille screw (138.7 Ncm;P< 0.05). For the inferior screw hole position, there was no significant difference in flexion failure strength between the two techniques (Magerl screws, 287.7 Ncm; Roy-Camille screws, 308.2 Ncm). For each insertion technique, inferior screws were nearly twice as strong as superior screws (P< 0.01). Violation of the inferior articular process occurred with 53% of Roy-Camille screws and with none of the Magerl screws. Lateral mass fracture on screw insertion occurred with 6% of the Roy-Camille screws and with 7% of the Magerl screws. Significant correlation between screw path length and load to failure was found only at the superior screw hole position. Correlation with vertebral body bone mineral density was significant at both positions.ConclusionsThe Magerl technique has advantages over the Roy-Camille technique for placing the end screws when performing posterior cervical lateral mass plate fixation, providing greater strength superiorly and not violating unfused facet joints inferiorly. Evaluation of bone mineral density by dual-energy radiographic absorption scanning is predictive of failure strength for both test modes.

ISSN:0362-2436    

出版商:OVID    

年代:1996

数据来源: OVID