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Biomedical subjects

S J Larson

Publications and source records attributed to S J Larson.

At least 37 records · Page 2Linked to original sources
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

Femoral obturator and sciatic neurectomy with iliacus and psoas muscle section for spasticity following spinal cord injury.

The treatment of severe refractory spasticity following spinal cord injury may raise challenging therapeutic problems. Classical approaches involve various types of myelotomies, rhizotomies and intrathecal injections of neurolytic substances. Alternative approaches include percutaneous rhizotomies and, more recently, the possible use of electrical stimulation of the spinal cord. Certain cases, however, may not be amenable to commonly accepted techniques. An operative technique is presented which involves a suprapubic incision for an infraperitoneal approach to a femoral and obturator neurectomy and an incision of the iliacus and psoas muscles bilaterally. This may be followed, when indicated, by a bilateral infragluteal section of the sciatic nerves. This technique offers a viable surgical alternative to the treatment of spasticity following spinal cord injury in cases where other traditional methods are contraindicated or have failed.

Adolescent↗
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↗
PubMed1987

Functional recovery after decompressive spine operation for cervical spine fractures.

Ninety-nine patients with cervical spine fractures from C-4 through C-7 were operated upon from 1975 to 1981. Operation was performed to restore normal relationships between the spinal cord and roots and the spinal canal and foramina and to maintain these relationships by fusion when necessary. Neurological function was recorded pre- and postoperatively using a functional scale. Satisfactory fusion without adverse change in vertebral alignment was achieved in each patient. The average interval between injury and operation was 29 days. When neurological recovery was observed, it began promptly after operation, suggesting a cause and effect relationship.

Cervical Vertebrae↗
PubMed1986

Experimental spinal injuries with vertical impact.

Fifteen fresh, intact, human male cadavers suspended head down were dropped vertically from a height of 0.9-1.5 meters. In eight specimens the heads were restrained to simulate muscle forces. The head-neck complex was oriented for maximal axial loading of the cervical and upper thoracic spine. In several cadavers, load cells were placed in cervical bodies. Head impact forces of 3,000-7,000 N in the unrestrained, and 9,800-14,600 N in the restrained, cadavers were recorded. There were more cervical and upper thoracic fractures in the restrained cadavers than in the nonrestrained subjects. The biomechanic and pathologic findings, including results of cryomicrotomography and computed tomography (CT), are discussed.

Aged↗
PubMed1986

Management of bilateral locked facets of the cervical spine.

A total of 28 cases of cervical spine dislocation with bilateral locking of facets treated between 1976 and 1984 were analyzed to determine whether treatment modality had any effect on outcome based on cord or root function. Motor vehicle accidents were responsible for 19 cases; the most common levels of dislocation were C-5, C-6 and C-6, C-7, with 10 each. Twenty patients were admitted with complete myelopathies. Ten patients whose dislocations were successfully reduced with traction had no neurological changes, but 1 reduced elsewhere deteriorated from a C-5 to C-2 level. Eleven of these patients underwent posterior cervical fusions after delays of 1 to 17 days (mean = 6.3); 2 died, and 1 patient achieved slight root return. Seven underwent anterior decompression and fusion or combined anterior and posterior approaches after delays of 9 to 120 days. One patient died in the postoperative period, 1 had substantial recovery of cord function, and 5 had recovery of root function. There was no operation or improvement in 2 patients. Eight patients had incomplete myelopathies; 4 were initially reduced, with 2 improving slightly as a result. Three patients underwent posterior fusions with foraminotomies with minimal improvement. Five had anterior or combined approaches; these patients improved at least one neurological grade each, including 3 who became newly ambulatory. All 24 surviving patients achieved spinal stability, although it occurred slightly earlier in the anterior fusion groups. Surgical approaches designed to provide spinal stability and restore the normal anatomy of the spinal canal and neural foramina may be of functional benefit in the management of these dislocations.

Adolescent↗
PubMed1986

Operative stabilization of the posttraumatic thoracic and lumbar spine: a comparative analysis of the Harrington distraction rod and the modified Weiss spring.

To assess the efficacy of operative stabilization techniques, a retrospective study of Harrington distraction rod (HDR) and modified Weiss spring instrumentation was performed in 90 patients. An operation was performed for one or both of two indications: persistent spine instability or the presence of a neurological deficit in patients with incomplete neurological injuries and myelographic evidence of spinal cord or cauda equina compression. The lateral extracavitary operative approach to the spine for decompression and anterior interbody fusion was performed with an accompanying HDR (47 patients) or modified Weiss spring placement (43 patients). Eight HDRs failed, resulting in gross instability (17 per cent) that either resulted in further neurological injury (1 patient), further surgery (2 patients), or increased morbidity secondary to prolonged bed rest (5 patients). One Weiss spring failed, requiring further surgery (2.3 per cent). Nonsurgical complications were similar in both groups and appeared to be unrelated to the type of instrumentation utilized. The modified Weiss spring instrumentation technique, which offers a dynamic compression fixation of the spine, was clearly superior to the HDR technique, which offers a rigid distraction fixation. The biomechanics of distraction versus compression and rigid versus nonrigid spine stabilization are discussed.

Bone Wires↗
PubMed1986

Functional recovery after decompressive operation for thoracic and lumbar spine fractures.

A series of 105 operative cases of thoracic and lumbar spine trauma is presented. All patients underwent an anterior decompression and fusion via the lateral extracavity approach with or without an accompanying posterior internal stabilization procedure (modified Weiss springs or Harrington distraction rods). All patients were allowed to plateau neurologically before reconstructive spine surgery was performed. The patient's neurological grade at the time of surgery and after recovery was assessed according to a seven-grade scale presented herein. None of the 34 patients with a motor and sensory complete myelopathy recovered any function below the level in injury. Of the 10 motor-complete patients with some sensory perception, 4 improved neurologically; however, only 1 of these improved to a state of limited ambulation. The rest remained nonambulatory. Of the 33 patients with significantly disabling incomplete motor and sensory myelopathies, 17 improved to a level of minimal neurological deficit; only 3 patients were left nonambulatory. Of the 21 patients whose physical finding demonstrated a minimal neurological deficit preoperatively, 17 recovered to a normal neurological state. Seven patients were neurologically normal preoperatively and were unchanged postoperatively. Reconstruction of the spine with an anterior decompression and an accompanying stabilization procedure, when appropriate, leads to a better neurological outcome than that expected with either a conservative, nonoperative approach or an operative posterior stabilization approach.

Adolescent↗
PubMed1986

Recovery of nerve root function after complete quadriplegia from cervical spine fractures.

Thirty-five patients with complete myelopathies secondary to cervical spine fractures from C-4 to C-7 underwent spinal decompressions and fusions between 1975 and 1981. Twenty-five of these patients underwent simultaneous nerve root decompressions, 23 with an accompanying anterior decompression and fusion and 2 with an accompanying posterior fusion. Substantial recovery of nerve root function occurred in 15 of these patients. A posterior reduction and fusion without nerve root decompression was performed in each of the remaining 10 patients. None of these patients demonstrated a significant improvement neurologically. Operation for nerve root decompression is indicated in selected victims of spinal cord injury.

Cervical Vertebrae↗
PubMed1985

Nonoperative management of traumatic facial nerve palsy.

Forty-five patients with facial nerve palsy resulting from head injury were treated nonoperatively between 1975 and 1981. Of 31 patients who had polytomography, temporal bone fractures were demonstrated in 29. In 44 of 45 injuries, satisfactory clinical improvement in motor function was noted, including 65% (overall) who showed complete recovery. Fracture direction on polytomography, results of electromyography (performed in ten cases), and time of onset of paralysis were not correlated with outcome. The present findings suggest a limited role for early surgery in closed traumatic facial nerve palsy.

Adolescent↗
PubMed1985

Comparison of the failure biomechanics of spinal fixation devices.

The failure biomechanics of Harrington distraction rods, modified Weiss springs, and Luque rods were studied in intact cadavers and isolated spinal columns using flexion-compression loading. Most spines fractured at T-11 or T-12 at applied loads ranging between 556 and 4220 newtons (mean = 1833 N). After Harrington distraction rod placement, the same spines failed at a mean load of 859 N (42% of control), always as a result of hook extrusion and often including lamina fracture (seven cases). When modified Weiss springs were used, the spines failed at a mean load of 1128 N (54% of control) by allowing the spine to bend to the initial failure angle; in most instances, deformities resolved when the load was reduced. Luque rods were tested in four specimens; these provided the most rigid stabilization and failed at 83% of control values. Modified Weiss springs often maintain spinal stability better than Harrington distraction rods.

Aged↗
PubMed1984

Lateral extracavitary approach to the spine for thoracic disc herniation: report of 23 cases.

Twenty-three patients were operated upon for thoracic disc herniation between 1973 and 1982. The lateral approach to the vertebral column was used in each. Most patients had severe local pain; 13 had severe myelopathy or complete motor paralysis, including 4 who had become paraplegic after laminectomy. Eleven patients had calcified discs or osteophytic ridges. Air myelography and computed tomography were diagnostic in all cases. Postoperatively, 17 patients achieved significant relief of pain, 20 improved neurologically, and none became worse. Complications of the operation were minimal. The lateral extracavitary approach to the spine is a valuable technique for the management of thoracic disc herniation.

Adolescent↗
PubMed1984

Neurological improvement associated with late decompression of the thoracolumbar spinal cord.

We reviewed the cases of 20 patients admitted to our institution with thoracolumbar spinal cord injury who had previously undergone laminectomy and/or spinal instrumentation. Thirteen patients had a mass in the spinal canal, and 7 had kyphotic deformities. The lateral extracavitary approach to the spine and posterior stabilization when indicated were done in each. Seventeen patients obtained substantial neurological improvement. All 7 patients with kyphosis regained the ability to walk, as did all but 3 of the nonambulatory patients with a mass in the spinal canal. Morbidity was limited to pneumothorax and 1 case of late kyphosis associated with premature removal of the spinal fixation devices. Elective anterior approaches for reconstruction of the spinal canal with appropriate stabilization afford the best opportunity for neurological improvement in cases of thoracolumbar spinal cord injury.

Fracture Fixation↗