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.

Cerebral release of gastric acid inhibitor.

1. Gastric juice collected during electro-anesthesia and limbic system stimulation in monkeys contains a substance which, when injected into other monkeys, produces reduction in basal gastric acid secretion. 2. Cross-circulation experiments indicate that a factor producing reduction in acid secretion is also present in blood during electroanesthesia.

The biomechanics of spinal injuries.

This manuscript is directed to review the epidemiology of spinal trauma, the anatomy of the vertebral column, spinal ligaments, muscles, motion of the spine and spinal cord. Because little information is available on the material properties of ligaments and the components of the vertebral column, this material is also included. A review of the experimental spinal cord injury models is given because of the concerted interest in this area today. Laboratory studies conducted in animals to develop typical spinal cord injury models and the corresponding alterations in perfusion and metabolic pathways, forces, and changes in the evoked potentials are discussed. Light and electron microscopy evaluations of the spinal cord are also treated. Clinical classifications of spinal injuries, pathology, and typical examples of upper cervical injuries, atlanto-axial disc locations and fractures, lower cervical spine injuries, injuries to thoracolumbar column with mathematical models, and typical force levels are given. The final section, investigation examples, provides a review of typical spinal injuries associated with sports injuries, motorcycle helmets, industrial helmets, and swimming pools investigated in our laboratories and by those of others. With lumped parameter mathematical model which predicts cervical compression, force, the various energies encountered in a one-dimensional impact is given. Typical examples of studies conducted on football helmets, motorcycle helmets, and industrial helmets are also included. Because of the importance of crash dummies used in the analysis of spinal injuries, a separate appendix is included, as well as an appendix reviewing motorcycle standards which are often dispersed throughout the literature. Considerable emphasis is placed upon actual experimental values of force and energy measured in the living animal and the most recent studies conducted in the fresh human cadaver to delineate the biomechanical mechanisms of spinal injury.

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.

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.

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.

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.

Management of odontoid fractures.

Fifty-one adults with odontoid fractures were treated between 1966 and 1979. Approximately 50% had additional trauma; over half of the patients were younger than 40 years old. Three patients presented with myelopathy: 1 was complete at C-2 and the others recovered. Cervical roentgenograms were initially considered normal in 4 patients. The fracture was through the base of the odontoid process (Type 2) in 49 patients and was into the body of C-2 (Type 3) in 2 patients. Thirty-four patients underwent early posterior cervical fusion, whereas the others were treated initially with external immobilization. Only the 2 patients with Type 3 fractures healed in Minerva casts. All 15 Type 2 fractures initially treated conservatively failed to heal and were fused. There were no age, sex, or radiological characteristics (other than fracture location) peculiar to the nonunion group. Two patients died after operation, and there was 1 minor infection in an iliac crest donor site. All patients who were operated upon demonstrated evidence of fusion within 6 weeks after operation; 16 demonstrated healing of the fracture at 6 months. After follow-up ranging from 16 months to 15 years, 7 patients complain of neck pain, of whom 6 do not require regular analgesics. Of 40 patients tested, 7 have evidence of decreased range of motion in the neck, of whom 6 have loss of less than 15% of normal motion. Traction followed by posterior cervical fusion is effective treatment for Type 2 odontoid fractures. The surgical and long term morbidity is low, and satisfactory fusion can be expected.

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.

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.

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.

Electrophysiological effects of lumbar dorsal root stimulation.

Electrical stimulation was applied to the L-5 and L-6 dorsal root ganglia of 14 monkeys with concurrent monitoring of cortical and intralaminar thalamic evoked potentials. Both responses were decreased by root stimulation, although cortical suppression required current levels 50 to 100% higher. The evoked potentials remained suppressed for periods of up to 60 minutes after 10- to 15-minute stimulation of the lumbar root electrodes. There was no increase in the duration of transmission block with longer stimulation periods. These results and available clinical data suggest that a local conduction block may be responsible for the pain relief produced by peripheral electrical stimulation. Further studies to identify more precisely the neural systems affected are required.

Intravertebral pressure changes caused by spinal microtrauma.

Clinical studies indicate variations in intravertebral pressures in patients with and without low back pain. It is known that not all patients with back pain have abnormal lumbar radiographs and, furthermore, microfractures of the endplate may be one of the causes in the origin of low back pain. Consequently, this study was conducted to determine the interrelationship between microtrauma and intraosseous pressures in the lumbar spine. Miniature pressure transducers were inserted into the vertebral bodies and spinous processes of human cadaver spinal units. Radio-opaque medium was injected into the nucleus to fluoroscopically monitor the movement of the fluid from the disc as the preparation was loaded up to the initiation of microtrauma (before reaching the ultimate load-carrying capacity). The onset of injury was evidenced by the microfracture of one of the two endplates and impregnation of the contrast medium into the spongiosa. After relaxation, another cycle of loading was applied by limiting the deflections to the maximum compression sustained under the intact configuration. The load, stiffness, and energy-absorbing capacities were lower (P < 0.05) for the injured specimen compared with the intact configuration. The intraosseous pressures were higher (P < 0.05) in the vertebral body and the spinous process of the vertebra where the endplate exhibited microtrauma in the injured cycle compared with the intact cycle. In contrast, the intraosseous pressures in the vertebral body and the spinous process at the level where the endplate remained intact were not significantly different between the two cycles of loading.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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.

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.

Compression injuries of the cervical spine: a biomechanical analysis.

Three intact cadavers and 10 isolated cervical spinal columns underwent compression, with forces directed vertically, forward, or rearward. Failure modes were often different than force directions. The loads required to produce bony injury or ligamentous disruption ranged from 645 to 7439 N. Flexion and extension injuries were produced at approximately 50% of the loads required for axial compression failures. The direction of force delivery correlated only partially with the resulting pathological condition. Clinical decisions based on retrospective analysis of roentgenograms may not account for the variability of forces and the prominence of ligament injuries seen in spinal trauma. Some of the difficulties encountered in biomechanical analyses of spinal trauma are discussed.

Influence of stimulus location and limb position on motor responses in the comatose patient.

Motor responses to standardized stimuli were evaluated in 18 comatose patients with abnormal motor reactions. Painful stimuli were applied to three areas: the supraorbital, sternal, and medial aspects of the arm. Stimulations were carried out with the upper limbs first flexed and then extended. The initial position of the arm significantly influenced the posturing pattern. With the arm initially flexed there was a significantly higher percentage of abnormal flexor reactions, and the opposite occurred with the arm initially extended. Supraorbital stimulation yielded a significantly higher number of extensor responses. Arm stimulation, instead, caused a higher percentage of abnormal flexor reactions. When painful stimulation was applied to an arm initially flexed, the percentage of extensor responses was extremely low. Conversely, supraorbital stimulation with the arms extended yielded the highest percentage of extensor responses. The study shows that, within the frame of abnormal motor responses, the same patient can exhibit different reactions according to the site of stimulation and initial position of the upper extremities. These patterns are fairly constant and should be borne in mind in the evaluation of comatose patients.

Lateral extracavitary approach to traumatic lesions of the thoracic and lumbar spine.

The lateral extracavitary approach to the spine was used for resection of displaced bpne and disc located anterior to the dura in 62 patients with traumatic lesions of the thoracic and lumbar spine. Fifty-two patients had closed vertebral fractures and 10 had gunshot wounds. The spinal cord was involved in 44 patients, and the cauda equina in 18. A spinal subarachnoid block was demonstrated in 17 of 57 preoperative gas myelograms. Evoked potential recordings, although related to preception of joint rotation, tended to reflect the overall neurological condition and had some prognostic value. Significant improvement followed surgery in 46 patients with incomplete neurological lesions, and one was transiently worse. Before operation 18 patients were able to walk; nine with assistance and nine without. After operation 47 patients were able to walk; 12 with assistance and 35 without. Adequate bladder function was present in 17 patients before surgery, and in 44 after surgery. A laminectomy had been done previously in 16 patients, 11 of whom improved significantly after anterior resection. Spine fusions were required in 26 patients, five of whom had a prior laminectomy. The major factor in the pathogenesis of the incomplete neurological deficit appeared to be distortion of the cord and roots by displaced bone and disc. Consequently, the primary object of treatment was the restoration and maintenance of normal anatomical relationships between the spinal cord or cauda equina and the spinal canal.