摘要:

Study DesignThis study analyzed the anatomic relationships between bony structures and soft tissues of the cervicothoracic junction.ObjectivesTo provide composite reference data for intrasegmental and intersegmental gradlents of anatomic variation within the cervical-thoracic junction.Summary of Background DataBecause of the risk of soft tissue damage during posterior spinal stabilization, an understanding of bony and soft tissue changes in the cervicothoracic junction is necessary.MethodsThree-hundred-twenty-four cross-sectional spinal segments from nine spines were analyzed to characterize cervicothoracic junctional anatomy.ResultsThere were predictable cranial-to-caudal alterations in both bone and soft tissue anatomy of the cervicothoracic junction. Neural and vascular structures directly anterior to the lateral mass or transverse process and lateral to the pedicle tend to decrease in frequecy, whereas measured parameters of the vertebrae increase in size from C5-T3, except for pedicle dimensions that land to increase at the C7-T1 junction.ConclusionThe anatomic changes that occur within the cervicothoracic junction are consistent and predictable, and their recognition should lead to a better appreciation of their clinical implications.

ISSN:0362-2436    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Study DesignMeasured trunk kinematics, applied moments, and trunk muscle activities were employed in a biomechanical model to determine load experiences by the spine during dynamic torsional exertions.ObjectivesThe purpose of this investigation was to examine the influence of dynamic twisting parameters on spinal load.Summary of Background DataAxial twisting of the torso has been identified as a significant risk factor for occupationally related low back disorders. However, previous studies have had difficulty describing how twisting is accomplished biomechanically, or how the spine is loaded during twisting motions.MethodsElectromyograph activity of 10 trunk muscles was monitored while 12 subjects performed twisting exertions under various conditions of force, velocity, position, and direction. An electromyograph-assisted biomechanical model was developed to interpret the effects of those twisting parameters on spine loading.ResultsSignificant flexion-extension and lateral moments were generated during the twisting exertions. Muscle coactivity associated with twisting exertions was significantly greater than that associated with lifting exertions. Employing electromyograph data to represent muscle coactivity, the model accurately predicted trunk moments and hence was assumed to reasonably reflect spine loading.ConclusionsUnder the conditions tested, the results indicated that relative spinal compression during dynamic twisting exertions was twice that of static exertions. Spine loading also varied as a function of whether the trunk was twisted to the left or right and according to the direction of applied torsion—i.e., clockwise or counterclockwise. The results may help explain, biomechanically, why epidemiologic findings have repeatedly identified twisting as a risk factor for low back disorder.

ISSN:0362-2436    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Study DesignThis study analyzed the changes in the load-displacement behavior of lumbar spine segments caused by burst fractures that were experimentally produced in fresh human cadaveric spines. The effect of three transpedicular surgical constructs on stability was investigated in each specimen.ObjectivesTo quantify the loss of mechanical stiffness caused by the injury, and to evaluate the stiffness of three transpedicular surgical constructs.Summary of Background DataAlthough various investigators have studied the biomechanical characteristics of the burst fracture and surgical stabilization techniques, few have reported quantitative data on the three-dimensional biomechanical instability of these fractures.MethodsLoad-displacement data were acquired in flexion, lateral bending, and axial rotation for intact specimens, after the L1 burst fracture was created and after the T12-L2 segments were stabilized using Luque plates, VSP plates, and Isola rods with one transverse connector.ResultsSpines with burst fractures showed a bilinear load-displacement behavior with significant instability (loss of stiffness relative to intact) at low loads (up to 3 N.m) in flexion, lateral bending, and axial rotation. The loss of stiffness was greatest in axial rotation over the entire load range (up to 10 N.m). If posterior element injury also was present, a significantly larger loss of stiffness was obsarved in flexion and axial rotation. The three transpedicular constructs improved the stability of the injured spine beyond that of the intact spine in flexion and lateral bending at low loads. At high loads, they restored the stiffness to intact levels. However, in axial rotation they did not restore the stiffness to pre-injury level, particularly when the posterior column was disrupted.ConclusionsReduction of the burst fracture returns the spine to its position of greatest inherent instability, essentially requiring the transpedicular instrumentation to be loadbearing.To enhance mechanical stability, it may be necessary to augment the transpedicular construct, particularly when the posterior column is disrupted.

ISSN:0362-2436    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Wolff's law describes the mechanical ultrastructure of tissue and indicates a design for minimal stress or minimal energy expenditure. Formation of this theory for the mechanism of the back reveals the critical design of members of this musculoskeletal system, which is comparable with other anthropoids. It also reveals that the pre-adaptations that enable the individual to lift heavy weights are the same adaptations that allow him or her to walk and run.

ISSN:0362-2436    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Study DesignThis study evaluated a lightweight Minerva cervicothoracic orthosis with an occipital flare and forehead strap.ObjectiveThe orthosis was evaluated for its ability to immobilize the cervical spine in normal healthy volunteers.Summary of Background DataPrevious studies have been performed to evaluate cervical orthoses. Exception for the halo brace, none have controlled the upper cervical spine very well. The brace tested in the present report incorporates an occipital flare and forehead strap to better control the upper cervical spine.MethodsSixteen healthy male volunteers were evaluated in and out of the orthosis in three planes of motion. Maximal active cervical flexion, extension, and lateral bending were recorded and measured radiographically. Rotation was measured from overhead photographs.ResultsIn a comparison of the present results with those of similar previous studies, improvement in control of flexion/extension of the upper cervical spine and in control of rotation was found. The occiput to C1 level, however, remained poorly controlled.ConclusionThis orthosis provides good control of the cervical spine below C1.

ISSN:0362-2436    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Study DesignThis study determined the relative efficacy of somatosensory-evoked potentials and motor-evoked potentials in monitoring spinal cord function during surgery for patients with idiopathic versus neuromuscular scoliosis.ObjectivesTo determine whether patients with idiopathic versus neuromuscular scoliosis demonstrate significantly different somatosensory-evoked potentials and motor-evoked potentials recorded during surgery.Summary of Background DataAshkenaze et al (1993) and others have reported that cortical somatosensory-evoked potentials are unreliable when used to monitor spinal cord function in patients with neuromuscular scoliosis. It was recommended that other neurophysiologic tests be used.MethodsSomatosensory-evoked potentials and motor-evoked potentials were recorded from two groups of patients: those with idiopathic scollosis and those with neuromuscular scoliosis. Somatosensory-evoked potentials were obtained before and during surgery. Motor-evoked potentials were obtained during surgery. Normal variability, as indicated from idiopathic scoliotic results, was compared with data obtained from patients with neuromuscular scoliosis. Motor-evoked potentials and somatosensory-evoked potentials were obtained sequentially during the duration of surgery.ResultsSingle-channel cortical somatosensory-evoked potentials demonstrated a 27% positive rate, which was consistent with results (28%) from Ashkenaze et al. The use of multiple recording sites for the somatosensory-evoked potentials and the addition of motor-evoked potential procedures indicated that a reliable response could be obtained in more than 96% of the patients. It also was found that cortical somatosensory-evoked potentials were more affected by anesthetic agents when recorded from patients with neuromuscular scoliosis compared with patients with idiopathic scoliosis.ConclusionsSingle-channel cortical sometosensory-evoked potentials demonstrated a high level of unreliability, which reduced their clinical effectiveness. However, by using multiple recording sites with the somatosensory-evoked potentials and by administering motor-evoked potential procedures, it was possible to monitor spinal cord function in neuromuscular patients and avoid postoperative neurologic deficits.

ISSN:0362-2436    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Study DesignRepeated measurements were made of lumbar sagittal range of motion by 14 examiners using three different measurement instruments.ObjectivesTo determine the reliability of lumbar range of motion measurements among examiners, subjects, and instruments, and to determine whether variance is due to subject inconsistency, examiner inconsistency, differences between examiners, or differences between instruments.Summary of Background DataMeasurements of lumbar spine range of motion are widely used in research and clinical applications as well as in disability rating systems for patients with low back pain.MethodsFourteen examiners measured the sagittal range of motion. Using three instruments, 18 healthy subjects were measured twice in a randomized sequence with blinded readings when performing full flexion, and pertial flexion to a defined midpoint. None of the examiners routinely used the particular instruments in their practices.ResultsThe mean test-retest reliability was 4.90. The intraexaminer reliability did not differ significantly among the examiners. Furthermore, there was no systematic difference resulting from instruments or posture condition. However, there was a statistically significant variance among examiners—i.e., a poor interexaminer reliability.ConclusionThe most likely explanation for these findings is the variability among examiners in locating bony landmarks. The results indicate that range of motion measurements must be interpreted with caution in clinical, research, and disability applications. Test administrator training may improve results, but this could not be determined from this study.

ISSN:0362-2436    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Study DesignPostoperative radiographs and computed tomography scans were used to evaluate 74 pedicle screws in 16 consecutive patients who underwent lumbar spine fusion with pedicle screw fixation.ObjectiveTo evaluate pedicle screw placement using plain radiographs versus computed tomographic scans.Summary of Background DataPlain radiographs are the primary means of assessing pedicle screw placement. Comparison of plain radiographs and computed tomography has not been done.MethodsScrews were graded as IN, OUT, or QUESTIONABLE; the direction of misplacement was noted. All evaluations were performed independently by three observers.ResultsFewer screws were clearly within the pedicle on computed tomography when compared with plain radiographs. Computed tomography showed 10 times as many screws violating the medial cortex as did radiographs. Interobserver differences were not statistically significant. Intraobserver differences approached statistical significance when the two tests were compared. No recognized neurologic complications resulted from pedicle screw placement.ConclusionsPlain radiographs alone may not accurately reveal pedicle screw placement. Plain radiographs and thin section computed tomographic scans should be used to evaluate postoperative neurologic deficits in patients undergoing instrumented lumbar spine fusion with pedicle screws.

ISSN:0362-2436    

出版商:OVID    

年代:1995

数据来源: OVID