Comparison of the biomechanics of hydroxyapatite and polymethylmethacrylate vertebroplasty in a cadaveric spinal compression fracture model.

OBJECT: Polymethylmethacrylate (PMMA) has long been used in the stabilization and reconstruction of traumatic and pathological fractures of the spine. Recently, hydroxyapatite (HA), an osteoconductive, biocompatible cement, has been used as an alternative to PMMA. In this study the authors compare the stabilizing effects of the HA product, BoneSource, with PMMA in an experimental compression fracture of L-1. METHODS: Twenty T9-L3 cadaveric spine specimens were mounted individually on a testing frame. Light-emitting diodes were placed on the neural arches as well as the base. Motion was tracked by two video cameras in response to applied loads of 0 to 6 Nm. The weight-drop technique was used to induce a reproducible compression fracture of T-11 after partially coring out the vertebra. Load testing was performed on the intact spine. postfracture, after unilateral transpedicular vertebroplasty with 7 to 10 ml of PMMA or HA, and after flexion-extension fatiguing to 5000 cycles at +/- 3 Nm. No significant difference between the HA- and PMMA cemented-fixated spines was demonstrated in flexion, extension, left lateral bending, or right and left axial rotation. The only difference between the two cements was encountered before and after fatiguing in right lateral bending (p < or = 0.05). CONCLUSIONS: The results of this study suggest that the same angular rigidity can be achieved using either HA or PMMA. This is of particular interest because HA is osteoconductive, undergoes remodeling, and is not exothermic.

A biomechanical comparison between anterior and transverse interbody fusion cages.

STUDY DESIGN: Human cadaveric lumbar spines underwent placement of threaded fusion cages (TFCs) in either an anterior or transverse orientation. Spines underwent load testing and angular rotation measurement in the intact state, after diskectomy, after cage placement, and after fatiguing. Angular rotations were compared between cage orientations and interventions. OBJECTIVE: To determine which cage orientation resulted in greater immediate stability. SUMMARY OF BACKGROUND DATA: There has been extensive biomechanical study of interbody fusion cages. The lateral orientation has been increasingly used for intervertebral fusion, but a direct biomechanical comparison between cages implanted either anteriorly or transversely in human cadaveric spines has not been performed. METHODS: Fourteen spines were randomized into the anterior group (anterior diskectomy and dual anterior cage placement) and the lateral group (lateral diskectomy and single transverse cage placement). Pure bending moments of 1.5, 3.0, 4.5, and 6.0 Nm were applied in flexion, extension, lateral bending, and axial rotation. Load testing was performed while intact, after diskectomy, after cage placement, and after fatiguing. Angular rotation was compared between anterior and lateral groups and, within each group, among the different interventions. RESULTS: Segmental ranges of motion were similar between spines undergoing either anterior or lateral cage implantation. CONCLUSIONS: These results demonstrate few differences between angular rotation after either anterior or lateral TFC implantation. These findings add to data that find few differences between orientation of implanted TFCs. Combined with a decreased risk of adjacent structure injury through a lateral approach, these data support a lateral approach for lumbar interbody fusion.

In vitro biomechanical analysis of three anterior thoracolumbar implants.

OBJECT: The goal of this study was to evaluate the comparative efficacy of three commonly used anterior thoracolumbar implants: the anterior thoracolumbar locking plate (ATLP), the smooth-rod Kaneda (SRK), and the Z-plate. METHODS: In vitro testing was performed using the T9-L3 segments of human cadaver spines. An L-1 corpectomy was performed, and stabilization was achieved using one of three anterior devices: the ATLP in nine spines, the SRK in 10, and the Z-plate in 10. Specimens were load tested with 1.5-, 3-, 4.5-, and 6-Nm in flexion and extension, right and left lateral bending, and right and left axial rotation. Angular motion was monitored using two video cameras that tracked light-emitting diodes attached to the vertebral bodies. Testing was performed in the intact state in spines stabilized with one of the three aforementioned devices after the devices had been fatigued to 5000 cycles at +/- 3 Nm and after bilateral facetectomy. There was no difference in the stability of the intact spines with use of the three devices. There were no differences between the SRK- and Z-plate-instrumented spines in any state. In extension testing, the mean angular rotation (+/- standard deviation) of spines instrumented with the SRK (4.7 +/- 3.2 degrees) and Z-plate devices (3.3 +/- 2.3 degrees) was more rigid than that observed in the ATLP-stabilized spines (9 +/- 4.8 degrees). In flexion testing after induction of fatigue, however, only the SRK (4.2 +/- 3.2 degrees) was stiffer than the ATLP (8.9 +/- 4.9 degrees). Also, in extension postfatigue, only the SRK (2.4 +/- 3.4 degrees) provided more rigid fixation than the ATLP (6.4 +/- 2.9 degrees). All three devices were equally unstable after bilateral facetectomy. The SRK and Z-plate anterior thoracolumbar implants were both more rigid than the ATLP, and of the former two the SRK was stiffer. CONCLUSIONS: The authors' results suggest that in cases in which profile and ease of application are not of paramount importance, the SRK has an advantage over the other two tested implants in achieving rigid fixation immediately postoperatively.

Spinal stability with anterior or posterior ray threaded fusion cages.

OBJECT: The authors conducted a study to determine if the rigidity supplied to the spine by posterior placement of the Ray threaded fusion cage (TFC) is further enhanced by the placement of pedicle screws and, additionally, if bilateral anteriorly placed TFCs render the spine more rigid than a single anteriorly placed TFC. METHODS: Ten human cadaveric spinal specimens (L2-S1) were affixed within a testing frame. Loads of 1.5, 3, 4.5, and 6 Nm were applied to the spine in six degrees of freedom: flexion-extension, right and left lateral bending, and right and left axial rotation. Motion in an x, y, and z cartesian axis system was tracked using dual video cameras following light-emitting diodes attached to the spine and base plate. Load testing of the spines was performed in the intact mode, following which the spinal segments were randomized to receive anterior or posterior instrumentation. In five spine specimens we performed posterior discectomy, posterior lumbar interbody fusion (PLIF) with placement of femoral rings and pedicle screws, PLIF with bilateral TFCs, and bilateral TFCs with pedicle screws. Five other spines underwent anterior-approach discectomy, followed by implantation of a unilateral cage and bilateral cages. Load testing was performed after each step. CONCLUSION: Spines in which PLIF with pedicle screws and TFCs with pedicle screws were placed were more rigid than after discectomy in all directions of motion except flexion. Anterior discectomy provided significantly (p < or = 0.05) less stability in left and right axial rotation than the intact spines and following posterior discectomy. Following anterior implantation of bilateral TFCs, spines were significantly more rigid than after discectomy in all directions except extension.

Clinical measurement, statistical analysis, and risk-benefit: controversies from trials of spinal injury.

BACKGROUND: The National Acute Spinal Cord Injury Studies have been a series of trials assessing the role of pharmacologic agents in the prevention of secondary neuronal damage after acute spinal cord injury. METHODS: The trials were multicenter randomized, controlled studies. RESULTS: Two trials have demonstrated the efficacy of high-dose methylprednisolone in improving neurologic and functional recovery and have shown a reassuring safety profile. CONCLUSION: This study responds to a recent commentary on these trials and examines in particular the roles of clinical measurement, statistical analysis, and risk benefit in assembling evidence for or against innovative therapies.

Biomechanical studies of a dynamized anterior thoracolumbar implant.

STUDY DESIGN: An in vitro investigation into the biomechanical properties of a dynamized anterolateral compression implant that allows controlled subsidence. OBJECTIVES: To determine the extent to which both modes of the anterolateral compression implant (controlled collapsing and rigid) are able to reestablish the stability of the lumbar spine after L4 corpectomy. SUMMARY OF BACKGROUND DATA: Over time, anterior and posterior spinal implants have been associated with progressive angulation, and occasionally implant failure and breakage. To circumvent this occurrence and provide better graft loading, dynamized or collapsing devices for clinical use have been developed. METHODS: Eight fresh calf spines (L1-L6) were placed in a biomechanical testing frame. Pure moments of 6 Nm were loaded onto the intact spine in six directions: flexion, extension, right and left lateral bending, and right and left axial rotation. A total L4 corpectomy then was performed, and the defect grafted with a wooden dowel. Loading was repeated after the specimens were stabilized using the two modes of the anterolateral compression implant in succession. RESULTS: The results showed that both modes of the implant (the rigid mode in particular) restore the stiffness of the unstable spine to normal levels of flexion, extension, and right and left lateral bending, even to levels exceeding normal. These devices, however, fall short of achieving normal stability in right and left axial rotation. CONCLUSION: In the cadaveric calf spine after L4 corpectomy, restoration of stability with a dynamized anterior spinal implant is possible in flexion, extension, and right and left lateral bending, but not in axial rotation.

Biomechanical studies on two anterior thoracolumbar implants in cadaveric spines.

STUDY DESIGN: A biomechanical comparison of two commonly used anterior spinal devices: the Smooth Rod Kaneda and the Synthes Anterior Thoracolumbar Spinal Plate. OBJECTIVES: To compare the stability imparted to the human cadaveric spine by the Smooth Rod Kaneda and Synthes Anterior Spinal Plate, and to assess how well these devices withstand fatigue and uni- and bilateral facetectomy. SUMMARY OF BACKGROUND DATA: Biomechanical studies on the aforementioned and similar devices have been performed using synthetic, porcine, calf, or dog spines. As of the time of this writing, studies comparing anterior spinal implants using human cadaveric spines are scarce. METHODS: An L1 corpectomy was performed on 19 spines. Stabilization was accomplished by an interbody wooden graft and the application of the Smooth Rod Kaneda in 10 spines and the Synthes Anterior Spinal Plate in the remaining 9. Biomechanical testing of the spines was performed in six degrees of freedom before and after stabilization, and after fatiguing to 5000 cycles of +/- 3 Nm of flexion and extension. Testing was repeated after uni- and bilateral facetectomy. RESULTS: After stabilization, the Smooth Rod Kaneda was significantly more rigid than the anterior thoracolumbar bar spinal plate in extension. After fatigue, the Smooth Rod Kaneda was significantly stiffer than the anterior thoracolumbar spinal plate in flexion, extension, right lateral bending, left lateral bending, and right axial rotation. A significant decrease in stiffness was noted with the Synthes device in flexion after bilateral facetectomy compared with the stabilized spine. CONCLUSIONS: The smooth Rod Kaneda device tends to be stiffer than the anterior thoracolumbar spinal plate, particularly in extension, exceeding the anterior thoracolumbar spinal plate in fatigue tolerance. The spine stabilized with the anterior thoracolumbar spinal plate is more susceptible to the destabilizing effect of bilateral facetectomy than than that stabilized with the Smooth Rod Kaneda. The additional rigidity encountered with the Smooth Rod Kaneda must be weighed against the simplicity of anterior thoracolumbar spinal plate application.

Methylprednisolone or tirilazad mesylate administration after acute spinal cord injury: 1-year follow up. Results of the third National Acute Spinal Cord Injury randomized controlled trial.

OBJECT: A randomized double-blind clinical trial was conducted to compare neurological and functional recovery and morbidity and mortality rates 1 year after acute spinal cord injury in patients who had received a standard 24-hour methylprednisolone regimen (24MP) with those in whom an identical MP regimen had been delivered for 48 hours (48MP) or those who had received a 48-hour tirilazad mesylate (48TM) regimen. METHODS: Patients for whom treatment was initiated within 3 hours of injury showed equal neurological and functional recovery in all three treatment groups. Patients for whom treatment was delayed more than 3 hours experienced diminished motor function recovery in the 24MP group, but those in the 48MP group showed greater 1-year motor recovery (recovery scores of 13.7 and 19, respectively, p=0.053). A greater percentage of patients improving three or more neurological grades was also observed in the 48MP group (p=0.073). In general, patients treated with 48TM recovered equally when compared with those who received 24MP treatments. A corresponding recovery in self care and sphincter control was seen but was not statistically significant. Mortality and morbidity rates at 1 year were similar in all groups. CONCLUSIONS: For patients in whom MP therapy is initiated within 3 hours of injury, 24-hour maintenance is appropriate. Patients starting therapy 3 to 8 hours after injury should be maintained on the regimen for 48 hours unless there are complicating medical factors.

Posterior ventricular catheter burr-hole localizer. Technical note.

Proper ventricular catheter placements are associated with improved shunt performance. When placing ventricular catheters via the posterior approach, the surgeon must determine an optimum trajectory and then pass a catheter along that trajectory. The incidence of optimal posterior catheter placements is increased by using a posterior catheter guide (PCG); however, errors may still occur because of poor selection of a posterior burr-hole site. In this report an easy-to-use posterior burr-hole localizer (Localizer) is described that defines the optimum burr-hole location based on geometric relationships involving the ear and supraorbital rims. The basic design principle of the Localizer was formulated and tested by using neuronavigational imaging tools to examine normal adult ventricular anatomy in relation to surface landmarks and by reviewing imaging studies obtained in 50 adult patients with hydrocephalus. Subsequently, the Localizer was used in 28 consecutive patients scheduled to undergo shunt surgery performed by using the PCG. In all cases the catheter entered the ventricle on the first pass and postoperative imaging studies demonstrated successful placement in the ipsilateral anterior horn. There were no catheter-related complications. These early results indicate that the Localizer and PCG devices may be safe and effective when used in combination for placement of posterior ventricular catheters.

Management options in thoracolumbar burst fractures.

BACKGROUND: Both surgery and recumbency have been adopted in the treatment of spinal fractures. Herein we present the indications for each, and our experience with thoracolumbar junction (T12, L1 and L2) burst fractures. METHODS: Sixty-eight patients with thoracolumbar burst fractures were treated operatively in 36 cases, and nonoperatively in 32 with recumbency for 1-6 weeks. Treatment was based on clinical and radiological criteria. Eighty-one percent of the recumbency patients, but only 14% of the surgical patients were intact on admission. Patients were followed for a mean+/-SD of 9+/-10 months in the recumbency group, and 21+/-21 months in the surgical group. RESULTS: Neurological improvement and progressive angular deformity occurred in both groups. The cost of recumbency in our patients was nearly half that of those who required surgery, though the length of hospitalization between the two groups was similar at 1 month +/-2 weeks. CONCLUSION: The above study emphasizes that the selection of operative versus nonoperative treatment in burst fractures should not be random but based on clinical as well as radiological criteria. Recumbency is favored in patients who are intact, with angular deformity less than 20 degrees , a residual spinal canal greater than 50% of normal, and an anterior body height exceeding 50% of the posterior height. Surgical intervention is generally indicated in patients with partial neurological deficit, and those with severe instability.

Computed imaging-assisted stereotactic brain biopsy: a risk analysis of 225 consecutive cases.

BACKGROUND: Treatment strategies for intracranial mass lesions are most effective when based upon histopathological diagnoses. Image-guided stereotaxy has provided the means to sample tissue from small or deeply seated intraparenchymal lesions with a relatively high degree of safety and accuracy. Although procedural complications are infrequent, devastating neurological sequelae may result from hemorrhage or direct trauma. This study was undertaken to identify factors that may confer an increased risk of morbidity from stereotactic brain biopsy. METHODS: Two hundred twenty-five consecutive computer-assisted stereotactic brain biopsy procedures were reviewed. Patient age averaged 47.4 years (range, 3-84 years); gender ratio was approximately 2:1 (male:female). Pre-existing medical conditions were identified in nearly half of the cohort. 61.3% of biopsied lesions were lobar; the remainder (38.7%) were "deep-seated" (thalamus, basal ganglia, pineal, hypothalamus, cerebellum, brainstem). Glial tumors accounted for the majority (44.4%) of biopsied lesions; metastases (12.9%) and lymphoma (11.6%) were also relatively common. Demographical, anatomical, surgical, and histological data were compiled and putative risk factors for morbidity identified. These variables were then subjected to univariate and logistic regression analyses to determine their significance as independent predictors of operative risk. RESULTS: Twelve patients suffered complications as a consequence of the biopsy procedure (eight from hemorrhage, four from direct trauma). Major morbidity (hemiparesis, aphasia, obtundation) occurred in eight patients (3.6%). Three patients (1.3%) suffered minor morbidity (transient, mild neurological deficits). One operative fatality occurred (0.4%). An increased risk of morbidity was associated with the preoperative use of antiplatelet agents, chronic corticosteroids, deep-seated lesions, malignant gliomas, and a greater number of biopsy attempts (p < 0.05). Factors not conferring increased morbidity included gender, age, pre-existing illness, extracranial malignancy, cardiac disease, hypertension, diabetes, HIV status, and instrument used to procure the specimen. CONCLUSIONS: Complications arising from stereotactic brain biopsy are infrequent but can be disastrous. Operative risk is a function of several independent variables, including lesion properties (location, histology), preoperative pharmacological therapy (corticosteroids, antiplatelet agents), and operative technique. This analysis suggests that the morbidity of stereotactic brain biopsy may be minimized by risk factor modification.

Recumbency in thoracolumbar fractures.

Fractures of the thoracic and lumbar spine are often treated successfully without surgery. Patients best suited for recumbency are those without deficit and minimal angular deformity and canal compromise. Angulation less than 20 dg, residual spinal canal of 50% or greater, and an anterior body height greater than 50% of the posterior height were additional criteria used in selecting recumbency. Patients were kept at bed rest for 1 to 4 weeks or until their pain resolved. They were then mobilized gradually in molded thoracolumbar orthoses for 3 to 5 months with sequential radiographs.

Administration of methylprednisolone for 24 or 48 hours or tirilazad mesylate for 48 hours in the treatment of acute spinal cord injury. Results of the Third National Acute Spinal Cord Injury Randomized Controlled Trial. National Acute Spinal Cord Injury Study.

OBJECTIVE: To compare the efficacy of methylprednisolone administered for 24 hours with methyprednisolone administered for 48 hours or tirilazad mesylate administered for 48 hours in patients with acute spinal cord injury. DESIGN: Double-blind, randomized clinical trial. SETTING: Sixteen acute spinal cord injury centers in North America. PATIENTS: A total of 499 patients with acute spinal cord injury diagnosed in National Acute Spinal Cord Injury Study (NASCIS) centers within 8 hours of injury. INTERVENTION: All patients received an intravenous bolus of methylprednisolone (30 mg/kg) before randomization. Patients in the 24-hour regimen group (n=166) received a methylprednisolone infusion of 5.4 mg/kg per hour for 24 hours, those in the 48-hour regimen group (n=167) received a methylprednisolone infusion of 5.4 mg/kg per hour for 48 hours, and those in the tirilazad group (n=166) received a 2.5 mg/kg bolus infusion of tirilazad mesylate every 6 hours for 48 hours. MAIN OUTCOME MEASURES: Motor function change between initial presentation and at 6 weeks and 6 months after injury, and change in Functional Independence Measure (FIM) assessed at 6 weeks and 6 months. RESULTS: Compared with patients treated with methylprednisolone for 24 hours, those treated with methylprednisolone for 48 hours showed improved motor recovery at 6 weeks (P=.09) and 6 months (P=.07) after injury. The effect of the 48-hour methylprednisolone regimen was significant at 6 weeks (P=.04) and 6 months (P=.01) among patients whose therapy was initiated 3 to 8 hours after injury. Patients who received the 48-hour regimen and who started treatment at 3 to 8 hours were more likely to improve 1 full neurologic grade (P=.03) at 6 months, to show more improvement in 6-month FIM (P=.08), and to have more severe sepsis and severe pneumonia than patients in the 24-hour methylprednisolone group and the tirilazad group, but other complications and mortality (P=.97) were similar. Patients treated with tirilazad for 48 hours showed motor recovery rates equivalent to patients who received methylprednisolone for 24 hours. CONCLUSIONS: Patients with acute spinal cord injury who receive methylprednisolone within 3 hours of injury should be maintained on the treatment regimen for 24 hours. When methylprednisolone is initiated 3 to 8 hours after injury, patients should be maintained on steroid therapy for 48 hours.

Response of spinal cord blood flow to the nitric oxide inhibitor nitroarginine.

OBJECTIVE: The extent to which nitric oxide (NO) is involved in the modulation of spinal cord blood flow (SCBF) in the uninjured and injured cord is unknown. To elucidate these questions, the following experiments in anesthetized rats were conducted. METHODS: Because NO is an unstable free radical with a half-life of seconds, its role can be understood through the study of the NO synthase inhibitor L-NG-nitroarginine (L-NOARG). L-NOARG was administered intravenously for 30 minutes at a dose of 100 or 500 micrograms/kg/min in 12 and 10 uninjured animals, respectively. SCBF fluctuations at C7-T1 were measured using laser doppler flowmetry. In a second set of 12 rats, L-NOARG (500 micrograms/kg/min) was administered 10 minutes before spinal cord injury using a modified aneurysm clip at C7-T1 and continued for 30 minutes thereafter. RESULTS: In the uninjured animals, L-NOARG was associated with a dose-dependent increase in mean arterial pressure of 20 to 80% above baseline (P = 0.0001), together with a dose-related decrease in SCBF (P = 0.0373). In the injured animals, L-NOARG was associated with a 48% increase in mean arterial pressure. With L-NOARG, the changes in SCBF from baseline after injury were similar to those of noninjured controls (n = 25) and significantly less than injury controls (n = 18) or those receiving phenylephrine (n = 8). CONCLUSION: NO synthase inhibitors, by reducing available NO, cause systemic vasoconstriction and a decrease in SCBF in the uninjured spinal cord. In the injured spinal cord, the administration of L-NOARG results in a redistribution of blood flow with an augmentation in posttraumatic SCBF at the injury site.

Computed tomography versus magnetic resonance imaging in stereotactic localization.

Neurosurgeons are often faced with a lesion that is obvious on magnetic resonance imaging (MRI), but not well-defined on computerized tomography (CT). However, questions remain regarding the distortion inherent in MRI images. Therefore the following comparative study was conducted. Five patients with intracranial lesions (1 lymphoma, 1 multiple sclerosis, 2 glioblastomas, and 1 AVM), underwent both CT and MRI for purpose of stereotactic biopsy or radiosurgery. The Brown-Roberts-Wells CT and MRI compatible localizing rings were used. Coordinates of the left optic nerve-globe junction, the aqueduct, pineal and optic chiasm were recorded from both CT and MRI. With MRI, all three imaging planes, axial, coronal and sagittal, were used. Coordinates were calculated in millimeters and submitted to statistical analysis using Pierson correlation coefficients. In all, there were 17 CT, 17 MRI axial, 13 MRI coronal, and 13 MRI sagittal coordinates. The analysis revealed that of the MRI coordinates, the axial coordinates were more available and retrievable. Lateral targets, such as the left optic nerve-globe junction, were more difficult to identify on coronal and sagittal images and often lacked a full compliment of fiducial points for calculation. The correlation with CT was best for axial, followed by coronal and then sagittal MRI planes. Geometric image distortion occurs owing to nonlinearity of the magnetic field as well as magnet susceptibility to different tissues at an interface. We feel that MRI stereotaxy can be utilized in conjunction with CT for verification of lesion coordinates in relatively large lesions, and particularly in those not well delineated on CT.

Interstitial brachytherapy versus cytoreductive surgery in recurrent malignant glioma.

In selected patients with recurrent malignant glioma, interstitial brachytherapy has been advocated as an effective method for tumor control and prolonged survival. We are presenting our results with brachytherapy in patients with recurrent glioma, and comparing this technique with cytoreductive surgery. Twenty patients (9 male, 11 female) underwent stereotactic 125I implantation for recurrent malignant glioma (9 grade III, 11 grade IV). The average age was 43 years and the average Karnofsky score was 76. All patients had received radiation therapy following their initial surgical procedure and 17 received chemotherapy. The median interval from initial procedure to implantation was 70.5 weeks. The median survival following implantation was 24 weeks and total median survival for the group was 94.5 weeks. This group was compared to a contemporary series of 22 patients (16 male, 6 female) who underwent cytoreductive surgery for malignant glioma (10 grade III, 12 grade IV). The average age was 44 years and the average Karnofsky score was 76. All patients received radiation therapy following their initial procedure and 20 patients also received chemotherapy. The median interval from initial procedure to second procedure was 35.5 weeks, and from the second procedure to death was 28 weeks. The median survival for the group was 63.5 weeks. The interval from the first procedure to the second procedure was statistically significant comparing the implant group (median 70.5 weeks) versus the cytoreductive surgery group (median 35.5 weeks; p = 0.04). No significant difference could be demonstrated between the interval from second procedure to death in the implant group (median 24 weeks) versus cytoreductive surgery group (median 28 weeks; p = 0.45).(ABSTRACT TRUNCATED AT 250 WORDS)

Herniated thoracic disks: treatment and outcome.

The optimal surgical approach for thoracic disk herniation is controversial, and long-term follow-up is poorly documented. We retrospectively reviewed the records of 31 patients who underwent surgery for herniated thoracic disks at our institution during a 17-year period (1975-1992). Two patients had multiple disk herniations; 16 of 33 herniated disks occurred at or below the T10-11 level. There were three surgical approaches to diskectomy: laminectomy in four patients, transpedicular surgery in 12, and costotransversectomy in 15. Weakness resolved postsurgery in nine of 18 patients. One patient transiently deteriorated neurologically after a laminectomy, three had wound infections, and two required second operations for their herniated disks. Postsurgery half the patients with symptoms continued to have pain or weakness.

Effects of spinal cord ischemia on evoked potential recovery and postischemic regional spinal cord blood flow.

The effects of spinal cord ischemia on spinal cord blood flow (SCBF) and somatosensory (SSEP) and motor (MEP) evoked potentials were investigated in a rabbit model of reversible spinal cord ischemia. Spinal cord ischemia was produced by balloon occlusion of the infrarenal aorta for 30, 60, and 90 min. SCBF, SSEPs, and MEPs were measured before, during, and 1 h after aortic occlusion. Aortic occlusion produced absolute ischemia of the caudal cord followed by hyperemia upon reperfusion. SSEP's and MEP's were obliterated during ischemia but demonstrated gradual albeit incomplete recovery following reperfusion with amplitude recovery inversely proportional to the duration of ischemia. Later peaks were more severely affected by a given period of ischemia than were early waves. In general, SSEP's were more resistant to ischemia than were MEP's although the differences were not significant.

Treatment options in primary Ewing's sarcoma of the spine: report of seven cases and review of the literature.

Primary Ewing's sarcoma of the spine is reviewed, and seven cases are presented. Ewing's sarcoma of the spine is a rare condition that appears with a clinical triad of local pain, neurological deficit, and a palpable mass. The clinical picture, imaging characteristics, and management are discussed. The definitive management of Ewing's sarcoma of the spine, as in other locations, could include three main modalities: surgery, radiotherapy, and combination chemotherapy. In the presence of acute neurological decompensation, decompressive surgery via an appropriate approach should be performed. Because Ewing's sarcoma is usually sensitive to chemotherapy, initial chemotherapy, in neurologically stable patients, could be attempted first without surgical resection. Further management could then be gauged according to the response.