摘要:

Study DesignThis study evaluated the lower cervical pedicle from C3 to C6 to provide information for accurate transpedicular screw fixation in this region.ObjectivesTo measure the dimensions of the lower cervical pedicle and to determine the correct location of the pedicle axis on the posterior aspect of the lateral mass.Summary of Background DataSeveral anatomic studies and clinical applications of transpedicular screw fixation in the cervical spine have been documented, but little quantitative data concerning the lower cervical pedicle and its projection are available.MethodsForty dry cervical specimens from C3 to C6 (160 cervical vertebrae) were used for this study. Anatomic evaluation included pedicle height, width, effective length, and anguli. The distances from the projection point of the pedicle axis to reference lines related to the lateral edge of the lateral mass (vertical) and the inferior edge of the superior facet (horizontal) also were measured. The means, ranges, and standard deviations were calculated for all of the specimens and separately for male and female spines.ResultsStatistically significant differences in dimensions of males and females were found in one linear and one angular measurement, which included the pedicle height of C6 and the pedicle sagittal angle of C4. The greatest variation for males and females was found in the pedicle sagittal angle, with a range of 4.3-9.8 degrees. The distances from the projection point to the horizontal line did not show any real pattern of change from C3 to C6, whereas the distances from the projection point to the vertical line consistently increased from cephalad to caudad.ConclusionsTaking into consideration some variations between individuals, this information, combined with evaluation of results of preoperative axial computed tomography and conventional radiography, may enhance the safety of transpedicular screw fixation in the lower cervical spine.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignThis report examines the permeability coefficient and aggregate modulus of slices of anulus cut from canine lumbar intervertebral discs.ObjectivesTo examine the influence of radial position on the properties of these materials, including outer samples with intact anulus edge.Summary of Background DataThe outer edge of anulus fibrosus shows radial bulge during axial compression of motion segments. The radial bulge increases monotonically when the axial compression is sustained for several hours, until a plateau is reached. Triphasic modeling of axial compression shows that this time course of radial bulge can not be obtained using a uniform permeability coefficient according to values in the literature.MethodsConfined consolidation experiments (controlled load) were designed to measure the time course of uniaxial deformation of samples of anulus that were 4 mm in diameter and 1 mm tall. The rotation symmetry axis of the samples was defined in the radial direction of the disc. The radial permeability coefficient and the aggregate modulus were determined using the consolidation data and the linear biphasic theory.ResultsThe permeability coefficient was lower at the periphery than in deeper layers of the anulus. Outer samples with outer surfaces that were 0.0-0.5 mm from the anulus edge had an average permeability coefficient of (1.02 ± 0.57) × 10-16m4/Ns (n = 24). Inner samples that were 2.0-2.5 mm from the anulus edge had an average permeability coefficient of (2.81 ± 0.98) × 10-16m4/Ns (n = 13). The aggregate modulusHAof outer samples was significantly higher (HA= 1.56 ± 0.34 MPa) than that of inner samples (HA= 1.31 ± 0.47 MPa).ConclusionsThe fact that the outer anulus is less permeable than the inner anulus may explain why radial bulge of anulus fibrosus increases monotonically in time to an equilibrium value during sustained axial compression of a motion segment.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignThis study traced the location, extent, and pathway of sensory feedback after the mechanical stretching of a lateral spinal ligament in young chickens. The pathway was traced by locating the sites of Fos protein production in neuronal cell bodies at various sites in the nervous system.ObjectivesTo trace the location, extent, and pathway of sensory feedback after the mechanical stretching of a lateral spinal ligament in young chickens.Summary of Background DataThe innervation of ligaments is thought to form part of a protective feedback mechanism to provide stability for joints. The precise pathway and extent of the feedback for spinal ligaments is currently unknown. Such information would provide a clear focus for future studies, especially for diseases such as scoliosis where it has been suggested that there is abnormality in perception of sensory feedback.MethodsThe intertransverse ligament on the right side at T3-T4 in 4-week-old chickens was exposed by blunt dissection. After Fos production resulting from the surgery had been stopped, the ligament was stretched mechanically and repeatedly for 60 minutes using a 300-g weight. Various areas of the nervous system then were sectioned and processed immunohistochemically to identify areas of Fos production in nerve cell bodies. The presence of Fos indicated neurons that had been stimulated by the stretching the ligament, including interneurons along the feedback pathway.ResultsFos protein was identified in nerve cell bodies in the dorsal root ganglia and intermediate gray matter of the spinal cord at the level of stimulation as well as at several spinal cord levels above and below the site of stimulation. Identification was made on the ipsilateral and the contralateral sides, although the extent of Fos production was less on the contralateral side. Fos presence also was identified in sympathetic ganglia at these sites. Nerve cell bodies in the combined nucleus cuneatus and gracilis in the medulla oblongata, the vestibular nuclei, and the thalamus also contained Fos-positive particles.ConclusionsStretching a single lateral ligament of the spine produces a barrage of sensory feedback from several spinal cord levels on both sides of the spinal cord. This sensory information also is transferred to higher levels in the brain, including the nucleus gracilis and cuneatus, the vestibular nuclei, and the thalamus. These sites of Fos production suggest the locations of pathways for this sensory information, which include the dorsal columns and the spinocerebellar tracts. The information obtained from this study provides a clear focus for future studies in this area, particularly for diseases such as scoliosis where it is thought that incorrect perception of sensory information from the ligaments might be a major contributing factor.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignIn vitrobiomechanical testing was performed on eight lumbar calf spines.ObjectivesTo compare the initial stiffness of a standard method of posterior lumbar interbody fusion using structural autograft with the same procedure using additional posterior instrumentation. These constructs also were compared to a new titanium implant.Summary of Background DataPosterior lumbar interbody fusion is gaining wide acceptance for the treatment of segmental spinal instability, spondylolisthesis, and discogenic pain. Many methods have been described, including use of autograft or allograft bone, in either structural or nonstructural form, with or without additional fixation. A new threaded titanium interbody implant has been designed to increase initial stability while allowing bony ingrowth for fusion.MethodsEight lumbar calf spines were subjected to axial compression, sagittal moments (flexion-extension), and axial torque while displacement was measured. Stiffness was calculated from the load displacement curves, for each construct under each load pattern.ResultsThe posterior lumbar interbody fusion by bone graft alone was the least stiff construct of all modes tested. In two of eight specimens the bone graft dislodged posteriorly into the canal during torsional testing. The titanium interbody implant was similar in stiffness to the bone graft posterior lumbar interbody fusion with posterior instrumentation group in all three modes. They were both significantly stiffer than the normal spine, the destabilized spine, and the posterior lumbar interbody fusion by bone graft alone (P< 0.05).ConclusionsIn this model, the posterior lumbar interbody fusion with bone graft alone had less initial stiffness than that of the intact spine. The addition of posterior instrumentation or interbody implants can increase initial stiffness significantly.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study designServohydraulic load displacement testing was used to study the biomechanical properties of sacral fixation in human cadaveric specimens.ObjectivesTo evaluate a modification of standard sacral fixation that uses the first dorsal sacral foramina as an adjunct location for the placement of a sacral hook in addition to S1 pedicle screws.Background DataThe stiffness or rigidity of an instrumentation construct governs the amount of relative movement allowed between motion segments undergoing fusion. This property provides the greatest influence over the mechanical conditions necessary for fusion to occur.MethodsSixteen human cadaveric specimens were divided into two groups with similar bone density assessed by quantitative computed tomography scan. All were instrumented with pedicle screws at L4 and S1. One group also had downgoing offset hooks in the first sacral foramina distracted against the S1 pedicle screw. Instron servohydraulic testing was performed in anterior compressive flexion, and load displacement curves were recorded.ResultsThe bending stiffness of the specimens instrumented with screw and hook was significantly higher than in those instrumented with pedicle screws alone. The ultimate strength and energy absorbed did not differ between the two groups.ConclusionsThe addition of sacral foraminal hooks to standard pedicle screw instrumentation constructs across the lumbosacral junction provides more rigid stabilization of the lumbosacral motion segment in this model.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignThree-hole Roy-Camille posterior plates (Howmedica, Inc., Rutherford, NJ) were used to fix severely destabilized fresh cadaveric cervical spines. Fixed spine constructs were tested mechanically in flexion-extension and torsion, and the results were compared with the same characteristics in the intact spine before destabilization. Stainless steel and titanium plates and screws were evaluated.ObjectivesTo determine if the application of Roy-Camille posterior plates provided suitably strong and rigid fixation of a severe, surgically created three-column instability.Summary of Background DataControversy still remains regarding the exclusive use of posterior cervical plating in the face of three-column instability. Posterior plating has been evaluated biomechanically in severely destabilized calf spines; however, posterior plating of similarly destabilized human cadaveric cervical spines using the Roy-Camille system has not been examined.MethodsThe authors chose to test the main motions of the neck (flexion, extension, and torsion) in the intact and the plated state using a servohydraulic materials testing system. Testing the surgically altered spine before fixation proved to be futile because of drastic instability, which is characteristic of the chosen defect. Once fixed, the spines were tested, and the rigidity of the constructs were compared with that of the intact state. Strength and failure mechanisms were evaluated.ResultsThe rigidity of the plated spine constructs surpassed that of the intact spines; the stainless steel and titanium systems were mechanically equivalent. Thus, application of the Roy-Camille plates of either type dramatically reduced the motion of the unstable spine. Strength of the fixed spine constructs was limited by screw pull-out at theoretically predictable levels of force.ConclusionsPosterior application of Roy-Camille plates can fix cervical spines with severe destabilizing defects rigidly. Screw pull-out of the most proximal or distal screw was always the mechanism of failure.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignA prospective, functional assessment based on physical ability and independence in daily activities was performed of patients who had severe physical handicaps and spinal deformities and were undergoing scoliosis surgery.ObjectivesTo determine whether improving spinal alignment and truncal balance improved the functional abilities of handicapped patients.Summary of Background DataLoss of truncal stability compromises the physical independence of children who are severely handicapped. Physiologic function also may be compromised. It is not clear whether improving truncal balance actually improves their level of independence or merely halts further deterioration.MethodsTwenty patients with significant physical handicaps resulting from neuromuscular disorders or multiple congenital anomalies and significant spinal deformity and truncal imbalance were treated surgically to realign and stabilize their spines. Their level of physical independence was evaluated before surgery, including their ability to sit, ambulate, and complete activities of daily living. Evaluation was done before surgery, 6 months after surgery, and 12 months after surgery. A subjective assessment of cosmesis also was made.ResultsCorrective spinal surgery resulted in a deterioration of physical ability for the first 6 months. Most patients subsequently returned to their preoperative level of function. An improvement of function exceeding their preoperative level was not seen after 12 months. The cosmetic results of surgery were excellent.ConclusionsCorrective spinal surgery in patients with severe physical handicap should be performed early to preserve function and should not be dictated solely by the severity of the curvature. Improvement in the patient's level of independence may not necessarily occur after truncal stabilization. Cosmetic results in these patients with severe disabilities were extremely gratifying to the patients and their caregivers.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignThe authors studied the rotational effect of sublaminar wiring on the spinal pelvic axis on 20 patients who were being treated for adolescent idiopathic scoliosis.ObjectivesTo determine if sublaminar wiring effectively derotates the scoliotic spine.Summary of Background DataThe correction of the rotational deformity in adolescent scoliosis via sublaminar wiring is not well quantified in the literature. The derotation maneuver of Cotrel-Dubousset has been shown to produce variable and unpredictable amounts of axial derotation.MethodsTwenty patients who underwent posterior spine fusion for adolescent idiopathic scoliosis were evaluated using computed tomography scans and plain radiography before and after surgery and at a subsequent follow-up examination (average time of follow-up examination, 35 months after surgery). The degree of angle of vertebral rotation about the sagittal plane and that relative to the pelvis were measured before and after surgery and at a follow-up examination.ResultsThe primary thoracic curves were not derotated significantly relative to the pelvis with sublaminar wiring. Primary thoracolumbar curves instrumented on the convexity with pedicle screws were derotated significantly relative to the pelvis (P=.001). The average initial correction was 57%. On final follow-up examination, the correction was 24% (18 of 20 twenty individuals lost axial correction by an average of 34%). In nine of 20 patients the spine was more rotated, relative to the pelvis, than it had been before surgery. No coronal or sagittal decompensation was seen in any curve type.ConclusionsCoronal and sagittal plane correction of scoliotic curves may be achieved with sublaminar instrumentation. The ability to derotate axially the scoliotic spine appears to be variable, however, and, in most cases, curve-type dependent. Over time, much correction appears to be lost, and in many patients the scoliosis actually becomes worse than it was before surgery. Nonetheless, the apical derotation that takes place appears to be reasonably true: the percent correction of angle of rotation about the sagittal plane and the percent correction of angle of rotation about the sagittal plain relative to the pelvis were closely correlated. Derotation forces applied to the instrumented spine do not appear to be transmitted to more distal segments.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID

摘要:

Study DesignThis retrospective study evaluated the progression of deformity after posterior fusion by reviewing 63 consecutive patients with idiopathic scoliosis who were all in Risser sign 0 at the time of surgery. All patients were observed beyond the time of skeletal maturity. Average follow-up time was 9 years and 8 months (range 5-16 years).ObjectivesTo investigate the risk factors for the crankshaft phenomenon after posterior fusion and to build a model for predicting the probability of curve progression until maturation of growth.Summary of Background DataThere remains considerable controversy concerning the incidence, risk factors, and necessity of combined anterior fusion to prevent the crankshaft phenomenon in patients who are skeletally immature.MethodsSerial radiographs were measured for Cobb angle, apical rotation according to Perdriolle, and apical rib-vertebra angle of Mehta. Multivariate and univariate logistic regression analysis was performed using seven potential predictors as independent variables and Cobb angle progression and rotational progression as dependent variables.ResultsAverage progression of deformity was 3° Cobb angle (range, -8-16°) and 3° Perdriolle rotation (range, -9-17°). Progression of deformity more than 5° of either Cobb angle or rotation was observed in 22 (35%) of 63 curves with 7 (11%) of 63 curves greater than 10 degrees. Chronologic age and skeletal age were found to be significantly associated with progression of deformity in univariate analysis. In multivariate analysis, only skeletal age seemed to be independently prognostic. The authors tried to build the logistic model using the three factors of chronologic age, skeletal age, and apical rib-vertebra angle. This model correctly classified 81% of all patients as progressive or nonprogressive. The positive predictive value was 90%.ConclusionsThe results showed that patients with chronologic age of 11 years of younger, especially those with a skeletal age of 10 years or younger, had a high estimated probability of progression of deformity. The progression was fairly moderate, however, with an average Cobb angle of 9° and average rotation of 7°, which neither the patients nor the surgeon believed was of such magnitude as to warrant routine combined anterior fusion.

ISSN:0362-2436    

出版商:OVID    

年代:1997

数据来源: OVID