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Biomedical subjects

D J Maiman

Publications and source records attributed to D J Maiman.

At least 37 records · Page 2Linked to original sources
PubMed1993

Is chronic spinal cord injury associated with increased risk of venous thromboembolism?

To determine the incidence of symptomatic thromboembolism in patients with chronic spinal cord injury, a retrospective review of patients followed in a Veteran's Affairs Spinal Cord Injury Unit was conducted. Followed for a mean of 13.7 years after injury, 287 patients were reviewed. Forty events were identified, an incidence of 10 percent. Thirty-three (83 percent) occurred in the first 6 months following injury. The remainder occurred at 1, 1.5, 7, 9, 10, 12, and 14 years after injury, an incidence of 0.17 percent per year. The incidence of clinically significant thromboembolism in spinal cord injury decreases dramatically after the first 6 months to a level similar to that in the general population (0.18 percent). Possible explanations for this include: 1) immobilization by itself may not be a risk factor for thromboembolism; 2) physiologic adaptations in the chronic state may protect against thromboembolism; and, 3) thromboembolism occurs, but remains subclinical in most patients.

Adult↗
PubMed1993

Effects of anterior vertebral grafting on the traumatized lumbar spine after pedicle screw-plate fixation.

This study was conducted to determine the effects of corpectomy and anterior strut grafting on the biomechanics of traumatized lumbar spine after pedicle screw-plate fixation. Eight lumbar spines were loaded until fracture (initial cycle) and then reloaded to the same deformation (injury cycle). After transpedicular fixation, spines were again loaded (fixation cycle). Partial corpectomy of the fractured body and anterior strut grafting were accomplished; the spine reloaded (strut cycle). Spine angles were measured and biomechanical strength and kinematic parameters analyzed. Load-deformation relationships were similar for fixation and strut cycles until maximum load; at failure, loads were higher for the former (P < 0.05), however. Alignment was improved by stabilization or stabilization plus anterior grafting (P < 0.05). Vertebral height was best maintained by grafting as an adjunct to pedicle fixation (P < 0.05). Kinematics were largely unaffected by grafting, except for reduced motion at the posterior vertebral targets between the fixated levels (P < 0.05). The strength of the fixated spine is relatively unchanged by corpectomy and anterior grafting; alignment may be improved in the latter group.

Biomechanical Phenomena↗
PubMed1993

Biomechanical effects of laminectomy on thoracic spine stability.

Thoracic columns (T1-L1 levels) from 15 fresh human cadavers were used to quantify alterations in the biomechanical response after laminectomy. Eight specimens were tested intact (Group I); the remaining seven preparations were tested after two-level laminectomy (Group II) at the midheight of the column. All specimens were fixed at the proximal and distal ends and loaded until failure. Force and deformation were collected by use of a data acquisition system. Failure of the Group I specimens included compressive fractures with or without posterior element distractions, generally at the midheight of the column. Group II preparations failed at the superior aspect of laminectomy or at a level above laminectomy, suggesting an increased load sharing. Biomechanical responses of the Group II preparations were significantly different (P < 0.05) from those of the Group I specimens at deformations from the physiological to the failure range. In addition, failure forces for Group II preparations were significantly lower (P < 0.001) than for Group I specimens. The stiffness and energy-absorbing capacities of the laminectomized specimens were also significantly different (P < 0.05) from those of the intact columns. In contrast, the deflections at failure for the two groups were not statistically different, suggesting that the human thoracic spine is deformation sensitive. Our data demonstrate that a two-level laminectomy decreases the strength and stability of the thoracic spine throughout the loading range. Although this is not a practical concern with an otherwise intact vertebral column, laminectomy, when other abnormalities such as vertebral fracture, tumor, or infection exist, may require stabilization by fusion and instrumentation.

Adult↗
PubMed1993

Biomechanical evaluation of Caspar cervical screws: comparative stability under cyclical loading.

Anterior cervical instrumentation is used as an adjunct to bone fusion; however, definitive biomechanical data to support some applications and techniques are lacking. In the absence of supportive experimental data, posterior cortical penetration has been recommended with the Caspar system. Previously, we compared the axial pull-out strength of Caspar screws with and without posterior cortical penetration. This study compares the stability of unicortical versus bicortical screw penetration groups under cyclical loading simulating physiological flexion-extension. Caspar screws were placed in human cadaveric vertebrae with or without posterior cortical purchase. Each screw was separately tested, simulating flexion-extension to 200 cycles. Deformation time data allowed a direct comparison of screw "wobble" with and without posterior cortical purchase. The mean deformation differences between subcortical and bicortical groups were statistically significant and increased over time within both groups. Enhanced stability was noted with bicortical purchase throughout most of the examined range, becoming more pronounced over longer periods of cyclical loading. Significant (P < 0.05) increases in deformation over time were noted for both groups, suggesting potentially significant deterioration at the screw-bone interface, despite bicortical purchase. Such deterioration with repeated flexion-extension loading may be of concern in the use of Caspar plates in the presence of multicolumn instability.

Absorptiometry, Photon↗
PubMed1992

Pull-out strength of Caspar cervical screws.

Anterior cervical instrumentation as an adjunct to bone fusion has an important role in cervical spine surgery. Posterior vertebral body cortex purchase is strongly recommended in the use of the Caspar system, although few biomechanical data exist to validate this requirement. In this study, Caspar screws were placed in 43 human cadaveric cervical vertebral bodies, either putting them into the posterior vertebral cortex as identified radiographically or penetrating it by 2 mm as recommended in the literature. Pull-out tests were conducted with tension applied to a connected plate at 0.25 mm/s, and force-deformation data were obtained. Failure typically occurred with clean pull-out; in most instances, cancellous bone remained attached to screw threads. Mean load without posterior cortical purchase was 375 +/- 53 N; with penetration it was 411 +/- 70 N. These differences were nonsignificant. Average deformation to failure was 1.41 +/- 0.10 mm in the group without posterior cortical penetration. In the posterior penetration group, mean deformation was 1.56 +/- 0.16 mm. Again, differences were not significant. Posterior cortical penetration does not improve the pull-out strength of Caspar screws in an isolated vertebral body model, but other biomechanical studies need to be done before insertion methods are altered.

Biomechanical Phenomena↗
PubMed1991

Traumatic facial injuries with steering wheel loading.

This study was conducted to evaluate the biomechanics of facial fractures caused by steering wheel loading. Twelve intact fresh human cadaver heads were impacted onto standard or energy-absorbing steering wheels with a custom-designed and validated vertical-drop apparatus. Either zygoma was impacted once at a velocity of 2.0-6.9 m/s. The specimens were oriented to permit a direct comparison between pretest and posttest radiography, and two-dimensional and three-dimensional CT images. Bone mineral content was determined, and biomechanical forces, accelerations, and deformations were recorded. More severe fractures were associated with higher forces on the zygoma. With increasing velocities, fractures initiated at the zygomatic region propagated to other unilateral regions such as the mandible and orbit or to the contralateral side. Less facial trauma was observed with energy-absorbing steering wheels compared with standard wheels at similar impact velocities. Bone mineral content did not correlate well with specimen age or with fracture severity. Clinically significant fractures were identifiable on 3-D CT images. The flexibility of 3-D CT in evaluating the spatial extent of facial abnormalities in different orientations may have significant impact in planning surgical procedures.

Accidents, Traffic↗
PubMed1991

Strength and motion analysis of the human head-neck complex.

This study was conducted to correlate the pathology of the experimentally tested human cervical spine with biomechanical strength information and localized temporal movements of the various spinal components. Eight fresh human cadaveric head-neck complexes were subjected to compressive forces at a quasistatic rate of 2.5 mm/s until failure. Biomechanical force and deflection data were collected. Localized kinematic data as a function of time were obtained from retroreflective targets placed in the anterior and posterior regions of the vertebral body, facet column, and spinous process at every level of the cervical spine. The specimens were radiographed prior to, during, and following failure; they were then deep frozen at the level of failure to preserve the localized tissue deformations. Specimens underwent computed tomography scanning and sequential sectioning using a cryomicrotome. The failure forces and compressions ranged from 1.3 to 3.6 kN and 0.9 to 3.7 cm. Stiffness and energy-absorbing characteristics ranged from 96.1 to 220.5 kN/m and 12.2 to 53.6 J, respectively. Varying localized temporal motions among spinal components were found to exist at all levels of the head-neck complex. With increasing compressive loads, the specimen components reorient as demonstrated by kinematic changes in the spinal elements; failure was imminent when the structure no longer resisted any further increase in external load. The study demonstrated that an evaluation of the human head-neck complex in a relaxed state, as in clinical observations on posttraumatic radiographs, is often different from that documented immediately following the traumatic insult; this underscores the importance of conducting controlled in vitro investigations to determine the injury biomechanics of the human cervical spine.

Aged↗
PubMed1990

Biomechanics of lumbar pedicle screw/plate fixation in trauma.

This investigation was conducted to determine alterations in the biomechanical strength and stiffness characteristics of the lumbar spine fixated with Steffee instrumentation. Comparative studies of these parameters were conducted using seven lumbar columns from fresh human cadavers. Three runs were conducted on each T12-L5 column: control, injured, and fixated. The specimens were loaded under the compression-flexion mode until failure (control run) and then reloaded (injury run) to the failure deformation determined in the control run. Screw/plates were then inserted one level proximal and distal to injury, and the specimens were reloaded (fixation run). Radiographs were taken before and after each trial. Data on deformation and force histories were gathered. The load-deflection response of the injured and fixated specimens were bimodal with two representative stiffnesses. Control failure loads and stiffnesses were higher than those for the injured (P less than 0.001) or fixated (P less than 0.01) spine. Initial stiffness was significantly higher for the fixated than for injured columns (P less than 0.001), but the final stiffnesses were similar. The increase in the initial stiffness in the fixated specimen compared to the injured specimen indicates the strength added to the posterior region of the spine. The relatively smaller alteration in the final stiffness between the fixated and the injured columns, corresponding to the load shared by the anterior column, may suggest that, above a critical strain level, the anterior column absorbs a higher portion of the external load and posterior fixation may be inadequate as sole treatment in trauma.

Adult↗
PubMed1990

Injury biomechanics of the human cervical column.

In this study, the authors have developed a technique to replicate clinically relevant traumatic cervical spine injuries and determined the injury biomechanics. Because of the importance of compressive forces in neck injuries, this research was conducted using compression as the primary load vector. Six fresh human cadaveric head-neck complexes were prepared by fixing the distal end in methylmethacrylate. Tests were done with varying loading rates to include quasistatic and dynamic conditions. For quasistatic experiments, the proximal end was fixed to the piston of the testing device. In dynamic tests, the cranium was unconstrained, and to maintain stability, the effects of the spinal musculature were simulated by means of pulleys, deadweights, and springs in the anterior and posterior parts of the head-neck complex. Quasistatic tests conducted at a rate of 2.0 mm/sec produced cervical spine trauma at forces ranging from 1.7 to 2.3 kN, with deformations ranging from 2.2 to 3.7 cm. The specimens were deep-frozen at the level of injury, preserving the local deformation of the tissues to enable a detailed evaluation immediately after the injury. Dynamic tests conducted at velocities of 3.2 to 5.7 m/sec resulted in impact injuries at one level of the head-neck complex. The applied forces at the vertex were considerably higher than those recorded at the distal end. The failure deformations for both the quasistatic (2.2-3.7 cm) and dynamic (1.7-3.2 cm) tests, however, were found to be similar, suggesting that the human head-neck complex is a deformation-sensitive structure.

Aged↗
PubMed1990

Neurologic recovery in quadriplegia following operative treatment.

Records and radiographs of 90 patients suffering complete or motor-complete quadriplegia and treated surgically were reviewed. There were 76 men or boys and 14 women or girls; ages ranged from 15 to 75. Eighty-one were complete quadriplegics and nine had some degree of sensory preservation. After surgery 30 were unchanged, 47 obtained root recovery, and 13 recovered cord function, including two who became ambulatory. Fifty-three of the 74 (71%) patients undergoing decompressive procedures showed neurological improvement while seven of the 16 (49%) patients with fusion and no root decompression had improvement (p less than 0.05). All 26 patients with dislocations underwent closed or open reduction as part of their operative procedures; this did not appear to improve the likelihood of nerve root recovery. Since independence and quality of life may be improved by cord and root recovery, decompression of all neural structures should be considered in cervical spinal cord injury.

Adolescent↗
PubMed1989

Gradient recalled echo MR imaging of superior sagittal sinus occlusion.

With T1-weighted gradient recalled echo (GRE) MR images and flow compensation, we studied the superior sagittal sinus in 3 normal volunteers and 3 patients with sinus occlusion. In these images, sites of patency of the superior sagittal sinus were identified due to the high signal intensity of the normal sinus. Tumor invading the sinus was nearly isointense with cerebral gray matter. T1-weighted GRE imaging proves to be an effective technique to evaluate sinus blood flow.

Cerebrovascular Circulation↗
PubMed1989

Cord/spine motion in experimental spinal cord injury.

We examined cord motion and cord-spine coupling associated with the axial tension and dorsal impact models of spinal cord injury. In 20 cats, distraction forces up to 15 kg were applied. Five microliters of radiopaque agent was injected into the central cord at C4-C7 (14 cats) and T6-L1 (6 cats) at 2-mm intervals. In 20 cats, 300 g/cm impacts were delivered after injection of contrast at 2-mm intervals from the impact point. Trials were conducted under fluoroscopy. At 5-kg distraction, vertebral motion averaged 2.12 mm and cord motion averaged 1.03 mm (coupling ratio = .49). At 10-kg coupling increased to .75. Between 10 and 15-kg distraction, the amount of increase in cord length slowed, as did the ratio (.59). Differences in length between load groups were significant at most levels, and motion corresponded with histologic injury reported previously. In the thoracolumbar region, minimal spine motion and no cord motion occurred. Spine motion was not seen with dorsal impact although cord motion at 2 mm from impact averaged 1.3 mm/300 g/cm, which decreased away from the impact point. The spinal cord has limited elasticity, which may be related to injury. Because spine and cord motion occur in clinical injury, experimental models need to incorporate this element.

Animals↗
PubMed1989

Experimental spinal cord injury produced by axial tension.

Fifty cats underwent spine distraction with forces applied until the evoked potential (EP) amplitude was reduced 50 or 95%. Neurologic status and EPs were monitored for up to 6 weeks. Fifty percent reduction occurred at (x) = 4.2-kg distraction/kg body weight (BW); 95% at 7.4 kg distraction/kg BW: differences were significant (p less than .05). The 50% group showed quadriparesis at 24 hours (Tarlov 1), improving by 4 weeks (x = 3). Ninety-five percent-group animals were quadriplegic initially, progressing to Tarlov 2.2. Residual EP changes occurred, particularly in the 95% group. Early histologic changes included central necrosis and neuronal chromatolysis. Later, axon disruption was observed, with cystic degeneration and gliosis at 4-6 weeks. Tissue damage correlated with ultimate neurologic status. Correlations between latency changes and early neurologic status, and between amplitude and histology were observed. The axial tension model may be of value in the study of spinal cord injury mechanisms.

Animals↗
PubMed1988

Dysphagia associated with cervical spine disorders: pathologic relationship?

Three cases of dysphagia in patients with large anterior cervical osteophytes are discussed. Although all three showed mechanical obstruction thought to be secondary to the bone growth, only one patient reported significant relief of the dysphagia after resection of the growths. The spinal etiologies of dysphagia and the operative results are discussed.

Aged↗
PubMed1988

Microtrauma in the lumbar spine: a cause of low back pain.

Excessive mechanical stress on the intervertebral disc may be one of the causes of low back pain. Most studies testing this thesis, however, have been based on quantification of the mechanical response of functional units at failure. Typically, radiography is used to demonstrate trauma to the vertebral body at the failure load. The description of failure and radiographic demonstration of damage are meaningful in specifying the tolerance limits of the structure. It is important, however, to understand the sequence underlying the initiation of injury, which may occur at subfailure physiological loads. In this study, we identified the initiation of injury to the lumbar spine by subjecting functional units to axial compressive loads using the mechanical response as a basis. Because conventional radiography failed to detect trauma at this level, advanced sectioning techniques were used. The initiation of injury (microtrauma) is defined as the point on the load-deflection curve where the structure exhibits a decreasing level of resistance for the first time before reaching its ultimate load-carrying capacity. The load deflection curve on this basis was classified into the ambient or preload phase, physiological loading phase, traumatic phase, and post-traumatic phase. Structures loaded to the end of the physiological loading phase did not exhibit any yielding or microtrauma. Injury in the form of microfractures of the endplate not detected on radiography, however, was observed under cryomicrotomy for structures loaded into the traumatic loading phase.

Adult↗