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Biomedical subjects

S J Larson

Publications and source records attributed to S J Larson.

At least 19 recordsLinked to original sources
PubMed1992

Increased sacroiliac joint uptake after lumbar fusion and/or laminectomy.

Of 753 adult patients undergoing SPECT and planar bone scintigraphy for the evaluation of low back pain, 43 (6%) showed either unilateral or bilateral increased sacroiliac joint (SIJ) uptake. Five of the 58 abnormal joints were only identified with SPECT (9%), whereas 20 of the 58 abnormal joints were much more convincingly demonstrated by SPECT (34%). Fifteen of the 43 patients with increased SIJ uptake had undergone prior lumbar laminectomy and/or spinal fusion. Such spinal surgery can increase impact loading on the SIJ, leading to mechanical overload and sacroiliitis. Degenerative joint disease, trauma, or other benign pathology accounted for the remaining patients with increased SIJ uptake. The authors conclude that for patients with a history of lumbar spinal fusion and/or laminectomy, increased SIJ uptake usually is caused by altered spinal mechanics rather than malignancy or infection.

Adult↗
PubMed1992

The thermoplastic Minerva body jacket: a clinical comparison with other cervical spine splinting techniques.

A retrospective analysis of the efficacy of a variety of external stabilization techniques used in 155 cases of unstable cervical spine injuries is presented. The movement at each intervertebral level was evaluated during thermoplastic Minerva body jacket stabilization in 18 additional patients. Many currently available approaches to external stabilization of the cervical spine were, thus, assessed. Thermoplastic Minerva body jacket stabilization offered superior segmental immobilization compared with published data for the halo. It is concluded that some unstable injuries to the high cervical spine might best be treated with a halo device, whereas mid to low cervical injuries and the remaining upper cervical spine injuries appear to be optimally treated with a Minerva jacket. Lesser injuries may be treated with a variety of available orthoses. The thermoplastic Minerva body jacket offers a superior limitation of intervertebral movement compared with other commonly used braces, including the halo jacket, for most cervical spine injuries. The technique of application of the thermoplastic Minerva body jacket is reviewed.

Braces↗
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 kinematic response of dynamic cervical spine injuries.

This study was conducted to evaluate the biodynamic strength and localized kinematic response of the human cervical spine under axial loading applied to the head. Intact ligamentous fresh human cadaveric head-neck complexes were subjected to dynamic compressive forces with a custom-designed electrohydraulic testing device at varying rates. The structure included the effects of anterior and posterior cervical spine muscles with a system of pulleys, dead weights, and spring tension. Localized kinematic data were obtained from retroreflective targets placed on the bony landmarks of the specimen at every level of the spinal column. Input forces, accelerations, displacement, and output generalized force histories were recorded as a function of time with a digital data acquisition system at dynamic sampling rates in excess of 8,000 Hz. High-speed photography at 1,000-1,200 frames/sec also was used. Pathologic alterations to the head-neck complex were evaluated with conventional radiography, computed tomography, and cryomicrotomy. In all specimens, cervical spine injuries occurred as a result of impact. Compressive forces recorded at the distal end of the preparation indicated large-duration, short-magnitude pulses in contrast to short-duration, high-amplitude input waveforms at the head, suggesting decoupling characteristics of the head-neck system. Cervical vertebral body accelerations were consistently smaller than the accelerations recorded on the head. Kinematic data demonstrated temporal deformation characteristics as well as a plausible sequence of spinal deformations leading to injury, which were correlated with the pathoanatomic alterations documented with the post-test computed tomographic and sequential cryomicrotome sections.

Acceleration↗
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↗
PubMed1989

Dynamic response of human cervical spine ligaments.

This study was undertaken to investigate the dynamic response of human cervical spine ligaments. Uniaxial tensile failure tests were conducted on anterior longitudinal ligament (AL) and ligamentum flavum (LF) structures. These ligaments were tested under in situ conditions by transecting all the elements except the one (AL or LF) under study. A fixture was designed to properly align the specimen to induce a uniaxial mode of loading. A six-axis load cell was placed at the distal end of the specimen. The proximal end of the specimen was attached to the piston of a specially designed electrohydraulic testing device. The biomechanical properties of the ligaments were determined at four different loading rates of 8.89, 25.0, 250.0 and 2500 mm/sec. The mechanical response indicated nonlinear and sigmoidal characteristics. The ultimate tensile failure load, stiffness, and energy-absorbing capacity at failure were found to increase with increasing loading rates for both the AL and LF. However, the distractions at failure did not indicate this tendency. While the ultimate tensile force and ultimate energy-absorbing capacity varied nonlinearly with the logarithm of the loading rate, the stiffness varied linearly.

Aged↗
PubMed1989

Postoperative stabilization of the posttraumatic thoracic and lumbar spine: a review of concepts and orthotic techniques.

A review of 109 case histories of patients who had undergone a spine fusion and/or posterior instrumentation procedure for thoracic and/or lumbar spine trauma was performed with respect to efficacy of several postoperative external splinting techniques. These data formed the basis for a review of external spinal splinting techniques. The type of orthosis that appears to offer the most efficacious immobilization and maximum patient comfort for fractures in the upper thoracic region in a body shell jacket extending from the submental and suboccipital regions to the lumbar region (modified Minerva jacket). To gain a lower point of fixation in patients with mid-to-low lumbar fractures, it was found that an extended body shell or an extension of a body jacket to one leg (hip spica) was necessary. Thoracic and thoracolumbar injuries may be stabilized with either a Jewett brace or a body jacket. The lack of maintenance of the cylindrical body shell, as well as excessive discomfort, make the Jewett brace and similar orthotic devices a second choice to body shell jackets for fractures in this region. The application of plastic polymer (Thermoplast) to spine splinting techniques offers the patient increased comfort and stability, as well as facilitating easy application and a more snug fit.

Equipment Design↗
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↗
PubMed1988

Magnetic resonance imaging in the diagnosis of lower thoracic disc herniation.

The diagnosis of thoracic disc herniation can be difficult due to the lack of a characteristic clinical presentation. In six recent cases, magnetic resonance imaging (MRI) provided excellent noninvasive definition of the pathology and its level, in spite of atypical clinical presentation, and also provided anatomic information allowing surgical planning. Two examples are presented in which myelography was not helpful, but MRI was diagnostic. MRI scanning is the radiographic procedure of choice when thoracic disc herniation is in the differential diagnosis.

Adult↗
PubMed1979

Spinal cord evaluation by cortical evoked responses.

In ten monkeys, selective segmental lesions of the dorsal columns at the upper thoracic and middle cervical levels resulted in almost total attenuation of the cortical evoked potential responses to peripheral nerve stimulation. Conversely isolated segmental dorsal column preservation showed intact transmission of the evoked responses at rostral spinal cord, nucleus ventralis posterior lateralis, and cortical levels. Responses recorded from the intralaminar thalamic nuclei in the region of nucleus centrum medianum were unaffected by dorsal column ablation, but were markedly attenuated following bilateral ventral column ablation.

Animals↗
PubMed1979

Gas myelography in spinal cord injury.

Using polytomographic techniques, gas myelography was performed in 162 patients with post-traumatic neurologic deficit. The type, extent, and location of lesions were easily demonstrated, allowing adequate preoperative surgical planning. In cases in which expected neurologic improvement did not follow surgery, postoperative myelography provided information so that remedial measures could be taken. No neurologic deterioration was noted in any of the patients and furthermore, arachnoiditis, which may accompany positive contrast myelography, has not been detected in any of the patients in the series reported.

Humans↗
PubMed1978

Early somatosensory evoked potentials.

The early somatosensory evoked potential secondary to median nerve stimulation in the human had an onset latency of 9--12 msec when recorded from scalp electrodes at vertex-to-mastoid, vertex-to-inion or at the base of the skull. Similar latencies were observed from responses recorded over the cervical dorsal columns during neurologic surgery. A latency difference of 1.5 msec was observed between the early response and the responses recorded from the junction of medial lemniscus and nucleus ventralis posterior lateralis of the thalamus during human stereotaxic surgery. Cervical cord transections and transection at the midpontine levels of the monkey showed that the evoked potential was due to generators between these levels. Depth recording of the monkey indicate that the early evoked potential originates in the region of dorsal column nuclei, while the later components are secondary to generators in cerebral cortex.

Animals↗
PubMed1978

Arachnoiditis from experimental myelography with aqueous contrast media.

Myelography was performed on 80 monkeys to study postmyelographic arachnoiditis. Metrizamide myelography caused arachnoiditis when high concentrations were used, but not with the usual clinical concentrations. Arachnoiditis resulted after myelography with meglumine iocarmate; however, the risk of arachnoiditis was reduced by diluting the contrast medium. Prophylactic intrathecal methylprednisolone was not effective in preventing arachnoiditis. Blood in the cerebrospinal fluid did not affect the degree of arachnoiditis.

Animals↗
PubMed1978

Ineffectiveness of prophylactic intrathecal methylprednisolone in myelography with aqueous media.

The effectiveness of prophylactic intrathecal methylprednisone (MP) in preventing arachnoiditis from iocarmate myelography was studied. Monkeys were injected intrathecally with locarmate, MP, or a combination of the two. Twelve weeks later the severity of arachnoiditis was determined in each animal. There was no significant prophylactic effect of intrathecal MP on arachnoiditis from locarmate. Some arachnoiditis was found in control animals treated with MP alone.

Animals↗