Postoperative deep wound infections in adults after spinal fusion: management with vacuum-assisted wound closure.

OBJECTIVE: Vacuum-assisted wound closure (VAC) exposes the wound bed to negative pressure, resulting in removal of edema fluid, improvement of blood supply, and stimulation of cellular proliferation of reparative granulation tissue. It has been used to treat open wounds in the extremities, open sternal wounds, pressure ulcers, and abdominal wall wounds. This study retrospectively reviewed instrumented spine fusions complicated by surgical wound infection and managed by a protocol including the use of VAC in order to evaluate the efficacy of applying vacuum therapy on patients with deep spine infections and exposed instrumentation. METHODS: Twenty consecutive patients with deep wound infections after undergoing spinal fusion procedures were studied. There were 12 men and 8 women with an average age of 55 years (31-81 years). Eight patients had undergone concomitant anterior and posterior arthrodesis, nine patients had a posterior spinal fusion, and three patients had a transforaminal lumbar interbody fusion. Seven patients had a decompression with exposed dura. Sixteen patients presented with a draining wound within the first 6 weeks postoperatively (average 24 days). There were four patients who presented with back pain and temperature after 1 year postoperatively (average 3 years). All patients were taken to the operating room for irrigation and debridement followed by placement of the VAC with subsequent delayed closure of the wound. RESULTS: There was an average of 1.8 (1-8) irrigation and debridement procedures prior to placement of the VAC. Once the VAC was initiated, there was an average of 2.2 (2-3) procedures until and including closure of the wound. The wound was closed an average of 7 days (5-14 days) after the placement of the initial VAC in the wound. All patients tolerated the VAC without adverse effects. All patients were kept on a 6-week course of intravenous antibiotic therapy. The average follow-up was 10 months (6-24 months). There were no cases of uncontrolled sepsis once the VAC was initiated. All patients achieved a clean closed wound without removal of instrumentation at a minimum follow-up of 6 months. CONCLUSION: VAC therapy is an effective adjunct in closing complex deep spinal wounds with exposed instrumentation.

Extension of fusions to the pelvis in idiopathic scoliosis.

STUDY DESIGN: Retrospective study of patients after extension of previous scoliosis fusions to the pelvis. OBJECTIVE: To determine whether modern instrumentation and surgical techniques provide for increased fusion rates with fewer complications. SUMMARY OF BACKGROUND DATA: Traditionally, long fusions to the pelvis in adults with idiopathic scoliosis have resulted in high complication rates, including pseudarthrosis. METHODS: The hospital and clinic charts of 41 patients (40 female, 1 male) were reviewed 41 months (range: 24-116) after surgery for extension to the pelvis of previous scoliosis fusions. Thirty-nine of 41 had a combined anteroposterior fusion extension; two had posterior extension only. In 37 of 41 patients, Cotrel-Dubousset (CD) instrumentation was used; in two, Isola (Acromed Corp., Cleveland, OH), in one, TSRH; (Sofamor-Danek, Memphis, TN), and in one, Synergy (Cross Medical Products, Columbus, OH). Parameters analyzed were fusion rate, sagittal and coronal balance, lumbar lordosis, length of fusion extension, and distal fixation method. RESULTS: Complications were seen in 30 of 41 patients. The pseudarthrosis rate was 37% (15/41) and was significantly related to the method of distal posterior fixation. With sacral fixation only, the rate was 53% (8/15), with iliac fixation only 42% (3/7), and with both iliac and sacral fixation 21% (4/19; P < 0.05). This was not correlated with fusion rate, and the length of fusion extension did not affect the pseudarthrosis rate or sagittal balance. CONCLUSION: When fixed to the ilium and sacrum, modern instrumentation appears capable of maintaining sagittal balance with lower rates of pseudarthrosis when previous scoliosis fusions are extended to the pelvis. The complication rate remains significant.

Lumbosacral chordoma. Prognostic factors and treatment.

STUDY DESIGN: Retrospective analysis. OBJECTIVES: To analyze the prognostic factors in patients with chordomas, the success of various treatments, the diagnostic value of open versus needle biopsy, the neurologic impairment after sacral nerve resection, and the clinical presentation and site of origin. SUMMARY OF BACKGROUND DATA: Staging of chordomas has not been of much value, compared with other bone tumors, because for chordomas, grade is similar, metastasis is infrequent at presentation, and the prognostic significance of size is uncertain. METHODS: A review of patients with chordoma from 1965 through 1996 found 23 cases (mean age of patients, 55 years). The mean follow-up was 84 months. Mean tumor size was 81 mm (range, 35-135 mm), location was lumbar (n = 6), S1 (n = 4), S2 (n = 3), S3 (n = 7), S4 (n = 2), and S5 (n = 1). RESULTS: No tumors were found in the higher sacrum (S1-S2) alone, without involvement of the lower sacrum. Survival analysis at 5 years showed overall survival (OS) 86%, continuous disease-free survival (CDFS) 58%, and local recurrence-free survival (LRFS) 60%. The location of tumor, defined by highest level of involvement (lumbar vs. sacrum) was of prognostic significance for OS (P = 0.01; log-rank test), CDFS (P = 0.036), but not for LRFS (P = 0.189). Results of multivariate regression showed that location was significant for OS (P = 0.007), CDFS (P = 0.008), and LRFS (P = 0.001). For patients with positive margins (n = 16), initial radiation correlated with longer CDFS (P = 0.002; Mantel-Cox) and LRFS (P = 0.005, Mantel-Cox), but was not significant for OS (P = 0.41). For patients who received no radiation, a positive margin correlated with a shorter CDFS (P = 0.04), a trend to shorter LRFS (P = 0.08), but no difference in OS. Therefore, both a tumor-free margin and initial radiation correlated with a longer survival. No patients had urinary or bowel dysfunction when both S3 nerves were preserved. If one S3 nerve was preserved, 1 of 3 patients had partial urinary incontinence and 2 of 3 patients required bowel medications. If both S3 nerves were resected, all patients required intermittent urinary catheterization and bowel medications. If both S2 nerves were resected, there was complete urinary and bowel incontinence. CONCLUSIONS: The highest level of tumor involvement was prognostically significant for OS, CDFS, and LRFS. Radiation was of value when complete excision was not achieved. Bilateral S3 nerve preservation is necessary to ensure retention of normal urinary and bowel function.

The effect of spinal instrumentation on lumbar intradiscal pressure.

The purpose of this study was to investigate the effect of spinal instrumentation on the intradiscal pressure (IDP) within the fixed motion segment. In vitro biomechanical testing was performed in six single functional spinal units of fresh calf lumbar spines using a pressure needle transducer. Various loads were applied by a materials testing system device. In addition to intact spine (control), anterior spinal instrumentation (ASI) and pedicle screw fixation (PS) constructs, as well as destabilized spine were tested. Relative to the control, the destabilized spine tended to have an increased IDP; by 15% in axial compression and by 9-36% in flexion-extension. Compared to the control, PS decreased the IDP by 23% in axial loading and 51% in extension loading and increased it by 60% in flexion for each loading. ASI decreased the IDP by 32% in flexion and 1% in extension. Lateral bending produced symmetrical changes of IDP in the control and destabilized spine, but no change in the PS construct. The IDP of the ASI construct was decreased by 77% in ipsilateral bending and increased by 22% in contralateral bending. These results demonstrated that eccentric loading from the spinal instruments increased IDP and significant disc pressure may still exist despite an increase in motion segment stiffness after lumbar stabilization.

Lumbar fusion results related to diagnosis.

STUDY DESIGN: Pain outcome and functional outcome after primary lumbar fusion surgery were determined by a self-assessment questionnaire. The responses were correlated with various clinical parameters. OBJECTIVES: To determine the result of fusion surgery among patients in various diagnostic groups using semiquantitative outcome scales. SUMMARY OF BACKGROUND DATA: Most previous studies on the results of primary lumbar fusion have reported the presence of pain, but few have addressed function outcomes. Results of a literature review were inconclusive as to whether a patient's diagnosis is a predictor of improved results. METHODS: During the 3-year period from 1988 to 1990, 165 patients underwent a primary lumbar fusion procedure. They had a chart and radiograph review and were categorized into five major diagnostic groups: 1) pediatric, 2) grade I-II spondylolisthesis (low-slip), 3) grade III-IV spondylolisthesis (high-slip), 4) degenerative disc disease, and 5) postdiscectomy. At a follow-up period of 5 years (mean) after the fusion, patients were mailed a questionnaire in which they described their pain and functional status before and after their lumbar fusion surgery. Questionnaires were returned by 92% of the patients. The questionnaire scores, complications, and revision procedures were grouped by patient diagnosis and analyzed. RESULTS: Patient satisfaction with the results of primary lumbar fusion ranged from 69% (for the postdiscectomy group) to 100% (for the pediatric and high-slip groups). For all diagnostic groups, lumbar fusion resulted in a significant decrease in back pain and leg pain (visual analog scale), which was maintained throughout the follow-up period. For back pain, the pediatric and high-slip groups showed significantly more improvement than the degenerative disc disease or postdiscectomy groups. Leg pain among patients in the pediatric and high-slip groups was significantly more improved than leg pain among patients in the low-slip, degenerative disc disease, or postdiscectomy groups. There was no deterioration of pain scores during the follow-up period. After fusion, all groups had a significant decrease in Oswestry disability scores; patients in the pediatric and high-slip group had significantly more improvement than patients in the degenerative disc disease or postdiscectomy groups. High- and low-slip groups had a significant improvement in their pain drawing score. Medication use was substantially reduced in all groups. After fusion, a lack of improvement in back pain score or disability score was significantly correlated with pseudarthrosis. CONCLUSIONS: The outcome of primary lumbar fusion surgery was decreased pain and increased function for the majority of patients in all five diagnostic categories. The amount of improvement varied by diagnostic group. Patients with developmental conditions showed greater improvement than patients with degenerative conditions.

Lumbar intradiscal pressure after posterolateral fusion and pedicle screw fixation.

In vitro biomechanical testing was performed in single-functional spinal units of fresh calf lumbar spines, using pressure needle transducers to investigate the effect of posterolateral fusion (PLF) and pedicle screw constructs (PS) on intradiscal pressure (IDP), in order to elucidate the mechanical factors concerned with residual low back pain after PLF. IDP of 6 calf lumbar spines consisting of L4 and L5 vertebrae and an intervening disc was measured under axial compression, flexion-extension and lateral bending in the intact spine, PS, PLF and the destabilized spine. Relative to the intact spines, the destabilized spines showed increased IDP in all of lordings and moments. IDP under PS and PLF were significantly decreased in axial compression, extension and lateral bending loads (p<0.05). In flexion, IDP under PS and PLF increased linearly proportional to the magnitude of flexion moment and reached as high as IDP of the intact spines. These results demonstrated that despite an increase in the stiffness of motion segments after PLF and PS, significant high disc pressure is still generated in flexion. Flexibility of PS and PLF may cause increased axial load sharing of the disc in flexion and increased IDP. This high IDP may explain patients' persisting pain following PS and PLF.

Does scoliosis have a psychological impact and does gender make a difference?

STUDY DESIGN: A population-based case-control study, we identified adolescents with and without scoliosis in Minnesota who were 12 through 18 years of age. Matched control subjects were randomly selected from school children who did not have scoliosis or any other condition. Information on scoliosis was obtained by a self-administered questionnaire, the Adolescent Health Survey. Collected on more than 75,000 school age adolescents, with established validity and reliability, a secondary analysis of adolescents with scoliosis was performed as compared with a normative peer group. OBJECTIVE: To describe and characterize the psychosocial impact of scoliosis on the areas of peer relations, body image, and health-compromising behavior, such as suicidal thought and alcohol consumption. SUMMARY OF BACKGROUND DATA: The impact of adolescent idiopathic scoliosis has not been assessed using generic health status measures appropriate for adolescents. Previous studies have concentrated on the health status of adults by measuring work status, marriage status, and other adult measures. The purpose of this study was to study the health status of patients with adolescent idiopathic scoliosis, using the Adolescent Health Survey, a generic health status measure with established validity and reliability. METHODS: Body image, peer relations, social and high-risk behavior, and comparative health were assessed to determine if scoliosis was an independent risk factor and to determine if scoliosis was associated with these psychosocial issues. RESULTS: Six hundred eighty-five cases of scoliosis were identified from the 34,706 adolescents. The prevalence was 1.97%. Of the 685 adolescents with scoliosis and their control subjects, the adjusted odds ratio for having suicidal thought among adolescent with scoliosis, compared to adolescents without scoliosis, was 1.40 (P value of 0.04) after adjustment for race, gender, socioeconomic status, and age. The adjusted odds ratio for having feelings about poor body development among adolescents with scoliosis was 1.82 (P value 0.001) compared with adolescents without scoliosis after adjustment for race, gender, socioeconomic status, and age. Scoliosis was an independent risk factor for suicidal thought, worry and concern over body development, and peer interactions after adjustment. CONCLUSION: Scoliosis is a significant risk factor for psychosocial issues and health-compromising behavior. Gender differences exist in male and female adolescents with scoliosis.

Vertebral body MRI related to lumbar fusion results.

The evaluation of continued pain after a technically successful posterolateral lumbar spine fusion is often challenging. Although the intervertebral disc is often a source of low back pain, abnormal endplates may also be a focus of pain, and possibly a source of continued pain after a posterolateral fusion. MRI allows noninvasive evaluation for disc degeneration, as well as for abnormal endplates and adjacent vertebral body marrow. Previous studies have found inflammatory marrow changes, adjacent to abnormal endplates, associated with disc degeneration in low back pain patients. In this study, preoperative MRI scans in 89 posterolateral lumbar fusion patients were reviewed, by an independent radiologist, to determine whether vertebral body marrow changes adjacent to the endplates were related to continued pain. Independent chart review and follow-up telephone interview of all patients at a 4-year follow-up (mean) formed the basis for the clinical results. Vertebral body MRI signals consistent with inflammatory or fatty changes were found in 38% of patients, and always occurred adjacent to a degenerated disc. Inflammatory MRI vertebral body changes were significantly related to continued low back pain at P = 0.03. We conclude that posterolateral lumber fusion has a less predictable result for the subset of degenerative disc patients with abnormal endplates and associated marrow inflammation. More research is needed to determine the biological and biomechanical effects of posterolateral fusion upon the endplate within the fused segments. If indeed further study supports the hypothesis that abnormal endplates associated with inflammation are a source of pain, then treating the endplates directly by anterior fusion may be a preferred treatment for this subset of degenerative patients.

Differences in sensitivity between magnetic motor-evoked potentials and somatosensory-evoked potentials in experimental spinal cord lesions.

STUDY DESIGN: Graded posterior spinal cord compression and partial sectioning of the spinal cord were performed, and magnetically induced descending spinal cord potentials were recorded. OBJECTIVES: To compare the sensitivity of transcranial magnetic motor-evoked potentials in the spinal cord and other spinal cord evoked potentials to spinal cord lesions. SUMMARY OF BACKGROUND DATA: Somatosensory-evoked potentials have been the standard technique for monitoring spinal cord function during spinal surgery. These potentials, however, do not necessarily reflect descending motor tract function. Transcranial electric or magnetic stimulation for motor-evoked potentials is a more direct measure of motor tract function. However, more research on magnetic motor-evoked potentials is needed. METHODS: Fifteen adult cats were used. Graded posterior spinal cord compression was performed at L2 in 10 cats, and partial sectioning of the spinal cord was performed at L2 in five cats. The location sequence of lesioning was dorsal column section, dorsal 1/2 section, dorsal 2/3 section, and total spinal cord section. Magnetic motor-evoked potentials were recorded by epidural catheter electrodes placed above at, and below the lesion. Electric motor evoked potentials and spinal and cortical somatosensory-evoked potentials were recorded serially for a comparison of their sensitivity to spinal cord dysfunction. RESULTS: In posterior spinal cord compression, N1 amplitude of magnetic motor-evoked potentials at and below the lesion decreased after 1 minute of compression with a 70 g weight, and N1 and N2 amplitude disappeared after 1 minute of compression with a 100 to 120-g weight. Electric motor-evoked potentials changed at amplitudes comparable with those shown by magnetic motor-evoked potentials. Spinal somatosensory-evoked potentials showed the most sensitive changes to spinal cord posterior compression and disappeared after 1 minute of compression with 80 g Cortical somatosensory-evoked potentials in five cats were not sensitive enough for spinal cord posterior compression injury and did not disappear even after 1 minute of compression with 120 g. In magnetic motor-evoked potentials, after dorsal hemisectioning of the spinal cord only N3 disappeared; N1 and N2 disappeared after ventral spinal cord sectioning in spinal somatosensory-evoked potentials, amplitudes decreased after dorsal column sectioning, and all negative peaks disappeared after dorsal hemisectioning of the spinal cord. CONCLUSIONS: Posterior compression injuries are diagnosed more easily with spinal somatosensory-evoked potentials. Motor-evoked potentials were slightly less sensitive, but they were significantly more useful in diagnosing posterior compression injuries than were cortical somatosensory-evoked potentials.

The effect of the platelet derived wound healing formula and the nerve growth factor on the experimentally injured spinal cord.

The main purpose of this study is to investigate the effect of platelet derived wound healing formula (PDWHF) and nerve growth factor (NGF) in the treatment of experimental spinal cord injury. PDWHF is a conglomerate of growth factors which include platelet derived growth factor (PDGF), platelet derived angiogenesis factor (PDAF), transforming growth factor-beta (TGF beta) and platelet factor IV (PF4). Complete spinal cord transection was performed at T12 in rats and the treatment of the spinal cord injury was achieved by filling the dead space with type 1 collagen gel impregnated with PDWHF, or with 2.5S-NGF. Controls were treated with only type 1 collagen gel. Animals were sacrificed at 1, 2 or 3 months. Histopathologically, tissue autolysis and cavity formation by phagocytosis expanded 1-3 mm into the cord stumps and the volume of cavitation was less in the two treated groups. In the NGF group, a greater number of surviving nerve cells were observed in this region. Most of the control animals formed only thin, short axonal bundles, however, increased axonal regrowth was noted in animals treated with trophic factors, especially in the NGF group. The NGF group formed thick axonal bundles and abundant neuroma. Increased angiogenesis was observed in the collagen gel matrix and the injured spinal cord parenchyma, in the PDWHF group. Recent studies have shown that mammalian adult CNS possesses the ability for structural and/or functional plasticity following injury under appropriate circumstances. In this in vivo study, exogenous NGF appeared to induce axomal outgrowth and nerve cell survival. PDWHF produced notable angiogenesis which seemed to improve the extracellular microenvironment. This may be important for the delivery of exogenous trophic factors, nutrients and for the changes of extracellular matrices to support nerve cells and axons.

Reduction of high-grade spondylolisthesis using Edwards instrumentation.

STUDY DESIGN: Sixteen patients with high-grade spondylolisthesis (Grade III or higher) who underwent posterior decompression and reduction using the Edwards Modular Spine System (Spinal System Ltd., Baltimore, MD) were reviewed clinically and radiographically. OBJECTIVES: This study was undertaken to determine the efficacy of one specific reduction technique to treat patients with high-grade spondylolisthesis where there has been a loss of sagittal balance, intractable pain, and/or neurologic deficit. SUMMARY OF BACKGROUND DATA: The average age of our patients was 20 years. Preoperative slippage averaged 89%; preoperative slip angle averaged 50 degrees. Indications for surgery were back and leg pain, progression of slippage (in 9 patients), and/or the inability to stand upright with the knees straight. METHODS: Pre- and postoperative radiographic films were reviewed. The percent slip and the slip angle were measured pre- and postoperatively. Clinical data were obtained via chart review, telephone interview, and/or office visit. RESULTS: The average preoperative slip was 89%; postoperatively, the average slip was 29%. Slip angle averaged 50 degrees preoperatively and improved to a postoperative average of 24 degrees. Three patients had neurologic impairment postoperatively; one did not resolve. Four patients had hardware failure; all were revised. Ten patients had an excellent result, 5 patients had a good result, and 1 patient had a fair result. The average follow-up was 3.8 years. CONCLUSION: This procedure is technically demanding and is subject to the known risks of surgical treatment for high-grade spondylolisthesis. For select patients, it may be effective for reducing severe deformity and can be expected to afford good to excellent results. Improved sacral fixation may reduce the rate of hardware-related complications.

The segmental effect of Cotrel-Dubousset instrumentation on vertebral rotation, rib hump and the thoracic cage in idiopathic scoliosis.

The segmental effect of Cotrel-Dubousset instrumentation (CDI) on the spine and thoracic cage was investigated in 38 patients with adolescent idiopathic scoliosis by preoperative and postoperative postero-anterior and lateral radiographs and computed tomography from T1 to S1. Mean Cobb angle decreased by 67%. The T5-T12 kyphosis in the hypokyphotic patients increased on average by 8.4 degrees (P < 0.001). Average preoperative as well as postoperative maximal vertebral rotation was located at the apex level, and was reduced from 19.0 degrees to 14.3 degrees (P < 0.001). All vertebrae between the upper and lower instrumented vertebrae were significantly derotated. Average derotation for the apical zone was 4.8 degrees (P < 0.001), for the upper instrumented zone it was 2.5 degrees (P < 0.01), and for the lower instrumented zone it was 2.6 degrees (P < 0.01). Vertebral derotation was significantly higher in the apical zone than in the upper and lower instrumented zones. The apical rib hump index (RHi) decreased by 38% (P < 0.001) and the cumulative RHi for the five apical levels decreased by 34% (P < 0.001). The RHi for the two levels above and below the instrumentation each decreased by 20% (n.s.). No significant increase in sagittal or transverse rib cage diameter at any level was observed. The translation in the coronal plane of the apical vertebra of major right thoracic curves improved significantly (P < 0.001). The preoperative flexibility index of the major curve correlated positively (r = 0.47) with derotation at the apex level (P < 0.01). However, no correlation was found between flexibility index and reduction of RHi at the apex level. Vertebral derotation did not correlate with reduction in RHi at any level. The study shows that CDI results in a postoperative three-dimensional improvement of the spine and a limited improvement of the thoracic cage, with no tendency towards a worsened deformity at any level within or outside the instrumentation.

Application of polyvinyl alcohol hydrogel membrane as anti-adhesive interposition after spinal surgery.

STUDY DESIGN: Three inflammatory and adhesive changes inside the spinal canal were analyzed histopathologically in cats. OBJECTIVE: To investigate the usefulness of a polyvinyl alcohol hydrogel sheet as an interposition over the dura to prevent inflammatory and adhesive reaction after laminectomy. SUMMARY OF BACKGROUND DATA: A major concern after laminectomy is scar tissue formation that may result in extradural compression or make subsequent surgery to the same area difficult and hazardous. METHODS: Wide laminectomy was performed at L5 in 30 adult cats. The dura was covered with a polyvinyl alcohol hydrogel sheet, free fat graft, or without interposition as a control. Animals were killed at 3 or 12 weeks. RESULTS: In the control group, adhesion of the exposed dura was apparent. Thick, fibrous connective tissue was observed between the dura and the paravertebral muscles. In the fat graft group, the dura was separated from the scar tissue by living grafted fat. However, the dura was adherent to the grafted fat and fibroblasts migrated into the interstitial space. In the polyvinyl alcohol hydrogel group, only a thin synovium-like layer was formed around the polyvinyl alcohol hydrogel sheet. CONCLUSIONS: Polyvinyl alcohol hydrogel is made of water and alcohol, and has been shown to be nontoxic to tissues. This is permeable to low molecular weight, but impermeable to large cells such as fibroblasts. Thus, the polyvinyl alcohol hydrogel sheet prevents migration of inflammatory cells and subsequently reduces intraspinal canal scar tissue formation and adhesive reaction. Other beneficial properties are extreme elasticity and low friction, which eliminate mechanical reaction to the spinal cord. The polyvinyl alcohol hydrogel sheet is believed to be useful in eliminating scar tissue formation and does not interfere with the dynamic gliding movement of the spinal cord and nerve roots.

General anesthetic effects on compound muscle action potentials elicited by single or dual spinal cord stimulation.

The aim of this study was to determine the optimal conditions, during general anesthesia, to obtain reproducible monitoring of compound muscle action potentials (CMAPs) as a means to evaluate motor tract integrity. The CMAPs were recorded in the soleus muscle of cats and were elicited by either single or double pulse stimulations (with various amplitudes and interpulse durations) of the spinal cord via an epidural electrode. The effects of various depths of general anesthesia with halothane, enflurane, isoflurane, or propofol on such recordings were also determined. For each agent, the CMAP amplitudes were significantly greater following double pulse stimulations (2-ms optimal interpulse duration) relative to single pulses. The CMAP amplitudes elicited by double pulse stimulations were the same at propofol concentrations of 50, 100, 150, and 200 micrograms/kg/min, whereas those for each volatile anesthetic, at all concentrations studied (0.5%, 1.0%, 1.5%, or 2.0%), were significantly lower. It was concluded that to obtain reliable CMAP amplitudes, general anesthesia with propofol should be employed and the potentials should be evoked by double pulse stimulations.

Effect of transcranial magnetic stimulation on cerebral function in a monkey model.

The effect of transcranial magnetic stimulation on higher cerebral function was studied using 3 monkeys. They were trained in a delayed response task which required spatial short-term memory. The task was presented by a computer on a cathode-ray tube and results of the delayed response task, which consisted of the percentage of correct choices, reaction time and trial number, were analyzed. For stimulation, small and large round coils were used as well as a figure 8 configuration. Their maximal B-fields were 3.3 T, 1.9 T and 2.4 T, respectively. A total of more than 7000 stimuli were given to each monkey in various patterns. There was no deficit in the delayed response. Further complications such as epileptic seizures were not observed either. In conclusion, transcranial magnetic stimulation does not appear to have any effect on higher cerebral functions in monkeys.

Radiographic evaluation of instability in spondylolisthesis.

STUDY DESIGN: The amount of intervertebral motion seen during dynamic radiography when imaged with the patient in the standing position was compared with that obtained with the patient in the lateral decubitus position. SUMMARY OF BACKGROUND DATA: Regarding analysis of spondylolisthesis, whether flexion/extension radiographs should be obtained with the patient in the lateral decubitus or standing position has been anecdotal. METHODS: Fifty consecutive adult patients with spondylolisthesis underwent flexion/extension lumbar spine radiographs in both positions. Abnormal motion was considered above 12 degrees dynamic angulation or 8% translation. RESULTS: Thirty-one of 50 patients displayed abnormal translation. Of these, 18 had abnormal motion only when they were examined in the lateral decubitus position and not when standing. Nine displayed excessive motion in both positions. Only four displayed more translation while standing. There was no statistical difference in the evaluation of dynamic angulation based on patient position. Neither age, degree of slip, listhetic level, nor type of spondylolisthesis correlated with abnormal motion. CONCLUSIONS: When spondylolisthesis is being analyzed, to maximize motion, flexion/extension radiographs should be obtained in the lateral decubitus position.

The effects of volatile anesthetics on the relative amplitudes and latencies of spinal and muscle potentials evoked by transcranial magnetic stimulation.

STUDY DESIGN: The effects of halothane, enflurane, or isoflurane on motor-evoked potentials via transcranial magnetic stimulation were investigated in cats. Time and dose effects on muscle potentials and spinal potentials were determined by measuring relative changes in amplitudes and latencies. METHODS: In 16 cats, muscle potentials and spinal potentials were evoked transcranially using magnetic stimulation. Potentials were recorded every 2 minutes for 10 minutes at end-tidal anesthetic concentrations of 0.25%, 0.5%, 0.75%, or 1.0%, and for 10 minutes after agents were removed. RESULTS: These anesthetics significantly attenuated the amplitude, but not the latency of muscle potentials. Effects were reversible and time and dose dependent. In contrast, these agents had little or no effect on amplitudes or latencies of spinal potentials. CONCLUSIONS: Monitoring intraoperative changes in spinal potentials may provide useful information regarding motor pathway assessment, because anesthetics have minimal effects on spinal potentials, whereas this is not so for muscle potentials.

Ligaments of the lumbosacral spine and their role in possible extraforaminal spinal nerve entrapment and tethering.

The extraforaminal ligaments of the lumbosacral spine were studied in 34 cadavers. The corporotransverse ligament attached to the body and transverse process of the same vertebra. The ligament may entrap the exiting nerve root below it in rotary subluxation or in complete disk space loss. The lumbosacral ligament extends from the transverse process of L5 and the L5-S1 disk to the sacral ala, forming the roof of the lumbosacral tunnel through which the L5 spinal nerve passes. This may be the site of extraforaminal entrapment if lateral disk herniations, osteophytes, or tumor metastasis are also present. The nerve suspensory ligament attaches to the nerve sheath and to the disk and is felt to be significant as a vehicle for mechanoreception.

The effects of immobilization of long segments of the spine on the adjacent and distal facet force and lumbosacral motion.

Long levels of spinal instrumentation and fusion are common in surgery for spinal deformity. The effect on the remaining mobile segments is not well understood. The changes in lumbar facet loading and lumbosacral motion were evaluated as the number of immobilized levels increased. Four fresh canine cadaveric spines from T6 to sacrum were used. Lumbosacral motion was measured with an instrumented spatial linkage device, and facet loads were measured at L1, L4, and L7 using a strain gauge technique. Lumbosacral motion and facet loading were significantly increased (P < 0.05) after immobilization of proximal segments, and the amount of the increase was dependent on the number of immobilized segments (P < 0.05). This indicates that immobilization of long segments of the spine influences the remaining mobile segments by increasing the load and motion not only at the immediately adjacent segment but also at the distal segments.

Electrophysiologic evaluation of intermittent sacral nerve dysfunction in lumbar spinal canal stenosis.

Intermittent sacral nerve dysfunction, induced by walking in lumbar spinal canal stenosis, may cause symptoms including hyperesthesia and pain in perineum, urinary bladder incontinence, and penile erection. However, it is difficult to objectively document these symptoms. Evoked external urethral sphincter potentials by conus medullaris stimulation were measured both before walking and after walking in five patients who complained of sexual organ or urinary dysfunction during walking, and were compared with simultaneously induced sacral nerve symptoms. These potentials were also measured during surgery. Sacral nerve symptoms were reproduced by walking 80-350 meters (average 177.5 m). These potentials disappeared in one patient and were decreased in four patients at the time when the claudicant symptoms disabled the patient during walking. The amplitude subsequently recovered in keeping with relief of those symptoms during rest. Monitoring of these potentials during surgery showed an increase of amplitude shortly after the decompression procedure of the cauda equina. In conclusion, this measuring method was valuable as an objective evaluation of intermittent sacral nerve dysfunction in lumbar spinal canal stenosis.