Risk Of Spinal Cord Damage Research Articles

Photodynamic therapy outcome modelling for patients with spinal metastases: a simulation-based study

Spinal metastases often occur in the advanced stages of breast, lung or prostate cancer, resulting in a significant impact on the patient’s quality of life. Current treatment modalities for spinal metastases include both systemic and localized treatments that aim to decrease pain, improve mobility and structural stability, and control tumour growth. With the development of non-toxic photosensitizer drugs, photodynamic therapy (PDT) has shown promise as a minimally invasive non-thermal alternative in oncology, including for spinal metastases. To apply PDT to spinal metastases, predictive algorithms that optimize tumour treatment and minimize the risk of spinal cord damage are needed to assess the feasibility of the treatment and encourage a broad acceptance of PDT in clinical trials. This work presents a framework for PDT modelling and planning, and simulates the feasibility of using a BPD-MA mediated PDT to treat bone metastases at two different wavelengths (690 nm and 565 nm). An open-source software for PDT planning, PDT-SPACE, is used to evaluate different configurations of light diffusers (cut-end and cylindrical) fibres with optimized power allocation in order to minimize the damage to spinal cord or maximize tumour destruction. The work is simulated on three CT images of metastatically involved vertebrae acquired from three patients with spinal metastases secondary to colorectal or lung cancer. Simulation results show that PDT at a 565 nm wavelength has the ability to treat 90% of the metastatic lesion with less than 17% damage to the spinal cord. However, the energy required, and hence treatment time, to achieve this outcome with the 565 nm is infeasible. The energy required and treatment time for the longer wavelength of 690 nm is feasible ({sim },40 min), but treatment aimed at 90% of the metastatic lesion would severely damage the proximal spinal cord. PDT-SPACE provides a simulation platform that can be used to optimize PDT delivery in the metastatic spine. While this work serves as a prospective methodology to analyze the feasibility of PDT for tumour ablation in the spine, preclinical studies in an animal model are ongoing to elucidate the spinal cord damage extent as a function of PDT dose, and the resulting short and long term functional impairments. These will be required before there can be any consideration of clinical trials.

Factors resulting in underutilization of pediatric spinal anesthesia in South Punjab (Pakistan)

Background & objectives: Spinal anesthesia in children a useful alternative to general anesthesia, is not usually practiced in most of the hospitals of South Punjab. We aimed to evaluate the utilization of spinal anesthesia in children in South Punjab (Pakistan) and to discover the elements preventing its use in children.
 Methodology: A questionnaire was delivered to all 47 FCPS qualified anesthesiologists working in South Punjab vide e-mail and whatsapp messages to them. Out of 47 anesthesiologists, 38 (80.85%) responded. Questionnaire consisted of 3 components. All participants were asked to fill the first component regarding demographic data, but only those who did not administer spinal in children, needed to fill second and third components. In the second component, structured questions with scale 1 to 5 (strongly disagree to strongly agree). In the third component, the participant had open choice to write three most important factors (most important, second most and third most) prohibiting the practice of spinal anesthesia in children.
 Results: All of the 47 senior anesthesiologists working in South Punjab were included in this survey. The response rate was 80.85%. Demographic data showed 33/38 (87%) males and 05/38 (13%) females, mean age 44.34 ± 11.06 yrs, mean of total experience in anesthesia 17.03 ± 9.12 yrs and mean experience after postgraduation 8.01 ± 6.85 yrs. The number of respondents administering spinal anesthesia in children was just 3 (7.88%) and 35 (92%) never used spinal in children.
 Lack of expertise/training/guidance (4.69 ± 0.83) is the most common cause prohibiting the use of pediatric spinal anesthesia followed by risk of high/total spinal (4.14 ± 1.31), lack of cooperation of child (3.83 ± 1.34), risk of spinal cord injury (3.71 ± 1.51), difficulty in assessment of block (3.34 ± 1.64). Less common factors avoiding pediatric spinal include objection by family, objection by surgeon and lack of proper recommendations.
 The number of participants considering lack of expertise/training/guidance most important factors for avoiding spinal anesthesia in children was 9 (25.71%), followed by uncooperative children 8 (22.86%), risk of spinal cord damage 5 (14.28%), risk of high/total spinal 3 (8.57%) and objection by family 3 (8.57%). Other factors quoted were objection by the surgeon, risk of postdural puncture headache, risk of neurological complications, being short duration, not recommended and not acceptable by society.
 Conclusion: Pediatric spinal anesthesia is practiced by only three consultants (7.88%) in South Punjab out of a total of 47. There is a need to enhance the expertise level of the anesthesiologists during postgraduate training and to remove the fears / phobias attached with this particular practice.
 Key words: Pediatric; Anesthesia, Spinal; Barriers; South Punjab
 Citation: Durrani HD, Sadaf S, Naqvi SAA, Siddique A, Bajwa MH. Factors resulting in underutilization of pediatric spinal anesthesia in South Punjab (Pakistan). Anaesth. pain intensive care 2020;24(6):---
 Received: 20 August 2020, Reviewed: 17 October 2020, Revised: 25 October 2020, Accepted: 6 October 2020

Re-irradiation of vertebral bodies

Improvements in clinical care and therapy mean that more patients are diagnosed and living longer with vertebral metastases. Thus, they are at risk of the development of recurrence that requires re-irradiation. Normal tissues often recover some of the damage caused by the primary radiotherapy with time and specific normal tissues can tolerate a considerable retreatment radiation dose. However, the risk of normal tissue damage and the impact on the quality of life must be considered and should be done with maximum care and accuracy especially in the vertebral area.For many years conventional external beam radiation therapy was the standard treatment modality. Fortunately, with crucial technological progress in the field of radiation oncology we are able to integrate body imaging with accurate treatment delivery methods as stereotactic body radiotherapy to improve the efficacy, shorten the overall treatment time and potentially reduce treatment-related toxicities.A short description of re-irradiation strategy covering diagnostic procedures, volume delineation, dose reconstructions, treatment planning, and guidelines are outlined. Moreover, publications on vertebral bodies re-irradiation summarizing available knowledge about toxicity, dose-volume constraints, local control, and pain response are followed.Although the knowledge is limited to a series of a single institution, it shows that re-irradiation is an effective treatment for local control and pain response. Furthermore, treatment was also shown to be safe with low risk of spinal cord damage which is one of the most worrisome toxicity.

Dura to spinal cord distance at different vertebral levels in children and its implications on epidural analgesia: A retrospective MRI-based study.

The distance from the dura to spinal cord is not uniform at different vertebral levels. The dura to spinal cord distance may be a critical factor in avoiding the potential for neurological injury caused by needle trauma after a dural puncture. Typically, the greater the dura to spinal cord distance, the larger the potential safety margin. The objective of our study is to measure dura to spinal cord distance at two thoracic levels T6 -7 , T9 -10 , and one lumbar level L1 -2 using MRI images. Eighty-eight children under the age of 8years old qualified for the study. The distance from dural side of ligamentum flavum to the posterior margin of the spinal cord was defined as dura to spinal cord distance. Sagittal T2 -weighted images of the thoracic and lumbar spine were used to measure the dura to spinal cord distance at the T6-7 , T9-10 , and L1-2 interspaces. Measurements were taken perpendicular to long axis of the vertebral body at each level. The dura to spinal cord distance was 5.9 ± 1.6mm at T6-7 (range: 1.4-9.9mm), 5.0 ± 1.6mm at T9-10 (1.2-8.1mm), and 3.6 ± 1.2mm at L1-2 (1.2-6.8mm). There were no evident differences in dura to spinal cord distance by gender, age, height, or weight. The present study reports that the largest dura to spinal cord distance is found at the T5-6 level, and the shortest dura to spinal cord distance at the L1-2 level. There appears to be substantially more room in the dorsal subarachnoid space at the thoracic level. The risk of spinal cord damage resulting from accidental epidural needle advancement may be greater in the lumbar region due to a more dorsal location of the spinal cord in the vertebral canal compared to the thoracic region.

A cervical flexion-extension MRI study in Down syndrome.

To assess what kind of information MR examination in flexed and extended positions provides in Down syndrome subjects with suspected cranio-cervical instability. Between 2005 and 2008, 35 subjects with DS were recruited in the study. Ethics committee approval was granted and a signed informed consent was obtained from the parents. All the subjects were affected by hypotonic status and ligament laxity established by clinical evaluation, but were asymptomatic about focal neurological symptoms due to medullar damage caused by cranio-cervical instability. Each patient underwent lateral supine radiographs and MR imaging in the neutral, active flexed and extended positions. For evaluating the atlanto-axial and atlanto-occipital joint stability, multiple measurements were calculated. A significant reduction of anterior subarachnoid space in flexed position was evident in DS subjects compared to healthy controls in neutral and flexed positions. Both, space available for cord and ligamentous thickness showed significant differences between DS subjects and healthy controls. In DS subjects with occipito-cervical instability, the anterior subarachnoidal space reduction was significantly reduced in flexed position. In DS subjects with asymptomatic cranio-cervical instability, anterior subarachnoidal evaluation and ligamentous status could add new information about the risk of spinal cord damage.

Is Simpson grade I removal necessary in all cases of spinal meningioma? Assessment of postoperative recurrence during long-term follow-up.

It is generally accepted that the first choice of treatment for spinal meningiomas is “radical” surgical removal. However, Simpson grade I removal is sometimes difficult, especially in cases with ventral dural attachment, because of the risk of spinal cord damage or the difficulty of dural repair after radical resection. In addition, there is no consensus on a surgical strategy for radicality, whether or not Simpson grade I resection should be performed in all cases of spinal meningioma. In this study, we retrospectively analyzed clinical and radiological data of surgically treated 14 patients with spinal meningioma, to assess the influence of the Simpson grade to tumor recurrences during long-term follow-up (median 8.2 years, 1.3–27.9). The number of patients in Simpson grades I, II, III, and IV were 2, 8, 0, and 3, respectively; Simpson grading was not applicable to one patient with non-dura-based meningioma. No postoperative permanent neurological worsening was encountered. The recurrence rate was 21.4% (3 out of 14 cases). Of these 3 recurrent cases, 1 was a case of non-dura-based meningioma and another was a case of neurofibromatosis type 2 (NF2); both of them are known as risk factors for recurrence after surgical removal of spinal meningiomas. Considering this background of these two recurrences, the clinical results of the present study are consistent with previous results. Therefore, we propose that surgeons do not always have to achieve Simpson grade I removal if dural repair is complicated and postoperative cerebrospinal fluid (CSF) leakage or neurological worsening are estimated after resection of dural attachment and repair of dural defect.

Expectations of Benefit and Tolerance to Risk of Individuals with Spinal Cord Injury Regarding Potential Participation in Clinical Trials

We conducted a survey of individuals living with spinal cord injury (SCI) to determine their receptivity to participating in clinical trials of drug therapies or stem cell therapies, their anticipation of therapeutic benefits, and their tolerance to risk. A 46-item questionnaire was administered to individuals with cervical or thoracic SCI identified through a provincial database. The average age was 42 years and the individuals were, on average, 5.5 years post-injury. Receptivity to neuroprotective drug trials in the acute setting was very high, but somewhat less so for stem cell trials in the subacute or chronic (current) setting. With respect to expectation of functional benefit, approximately one third of the respondents indicated that they would want a 5-25% chance of achieving some functional recovery if enrolling in a stem cell therapy clinical trial in the current, chronic injury state. Whereas the majority typically would require the risk of spinal cord damage, cancer, infection, and nerve pain from invasive cell transplantation trials to be ≤1%, 15-30% would participate regardless of the risk of these complications. The factors associated with this high risk tolerance were gender (males>females), age (elderly>young), and self-reported knowledge of SCI research (greater knowledge>less knowledge). Injury severity or chronicity did not have a significant correlation with risk tolerance. Whereas previous studies have shown that the understanding of stem cell science is limited among individuals with SCI, here we show that many still have high hopes for the possibility of neurological benefit, are anxious to participate in invasive stem cell trials, and, in many cases, have high tolerance for risk in such trials. Taken together, the data underscore the need for careful communication with individuals with SCI to avoid unrealistic expectations and therapeutic misconception in experimental trials.

Ultrasound-Guided Neuraxial Blocks: Recent Developments

Peripheral nerve blocks and neuraxial blocks are one of the most common procedures performed by anaesthetists. There has been enormous development in the use of ultrasound (US) for regional anaesthesia during last decade. In our previous article, 1 we reviewed such use of US in regional anaesthesia. Many studies have been published on this subject but most of the studies are on the use of ultrasound for peripheral nerve blocks and only few look into its use for neuraxial blocks. This article is a review of recently published papers on the subject of ultrasound for neuraxial blocks. IDENTIFICATION OF INTERVERTEBRAL LEVEL Spinal anaesthesia is commonly performed at L3-4 level. Performing a subarachnoid injection above this level has potential for spinal damage in a proportion of normal adult population. 2 Position of conus medullaris varies from middle third of T 12 to upper third of L 3 in adult population and mean position of conus is lower third of L 1 . 3 The importance of correctly identifying the intervertebral level during regional anaesthesia has been highlighted in the past. 4 Tuffier’s line is commonly used to identify the lumbar interspaces but this does not bear constant relationship to these spaces. Reliance on this landmark might lead to more cranial placement of epidural or spinal needles than intended and this subsequently will increase the risk of spinal cord damage. 5-8 Broadbent C R and colleagues 5 in their study of 100 patients undergoing spinal MRI scans demonstrated that identification of lumbar space by anaesthetists by palpatory method is not reliable. The study included total 200 observations from 100 patients by different observers. All observers had more than five years anaesthetic experience and had performed several hundred spinal anaesthetics. Correct space was identified in 58 (29%) observations. In six (3%) observations, anaesthetist identified a lower space than intended. In remaining 136 (68%) observations, anaesthetist marked higher spaces than intended. This was one, two and three spaces higher in 102 (51%), 31 (15.5%) and two (1%) occasions respectively. The marker was four spaces higher in one (0.5%) observation. Study by Furness G and colleagues 6 showed that US can identify correct intervertebral level in upto 71% of case as compared to 30% by palpatory method. The same study showed that ultrasound was inaccurate by one level only in all inaccurate cases, while palpatory method was inaccurate by more than one level in 27% of inaccurate cases. This study considered identification of intervertebral space by lateral lumbar spine X-ray as a benchmark. Watson and colleagues 9 in their study-correctly identified the L3-4 space with ultrasound in nearly 76% (13/17) of cases when confirmed with MRI scan. In four cases, the anaesthetist identified one space lower than intended. It is small but otherwise simple and relevant study, where investigator used the gold standard (MRI) to confirm the level of intervertebral space. Study by Whitty R and colleagues 10 demonstrated that there was poor agreement between palpation and ultrasound estimation of the specific lumbar interspace. When there was disagreement between the two methods, the ultrasound estimate was more often higher than the palpatation estimate. This study compares the two methods but does not use any gold standard to conclude superiority of one method over the other. Based on the fact from previous studies that by palapatory method clinicians select interspaces that are one or two spaces higher than intended, this study indirectly supports that US is more accurate in identifying the lumbar inetrspaces. In their study, Schlotterbeck H and colleagues 11 reviewed

Saline-Infused Bipolar Radiofrequency Ablation of High-Risk Spinal and Paraspinal Neoplasms

We present three cases of symptomatic high-risk metastases involving the vertebral body treated using infused bipolar radiofrequency ablation either alone or in combination with vertebroplasty. In our experience, the bipolar technique can reduce the risk of spinal cord damage in radiofrequency ablation of lesions within 1 cm of neural structures and involving paravertebral soft tissue.

Effect of Segmental Artery Ligation on the Blood Supply of the Thoracic Spinal Cord During Anterior Spinal Surgery: A Quantitative Histomorphological Fresh Cadaver Study

Human cadaver quantitative morphometric analysis of the blood vessels in the spinal cord after ligation of segmental arteries. To investigate the effect of ligation of segmental arteries on the quantity and density of the blood vessels in the spinal cord. Ligation of segmental arteries is often used in the anterior approach for correction scoliosis. However, whether or not segmental artery ligation is liable to deny the spinal cord an adequate blood supply, thus leading to paraplegia, still remains controversial. Eleven fresh cadavers were divided into control, unilateral, and bilateral groups. For the unilateral and bilateral groups, 5 segmental vertebral arteries (T7-T11) were ligated unilaterally and bilaterally, respectively. Then, the number and density of blood vessels at different levels in the 3 groups were measured. Compared to that of the corresponding level in the control group, the number of blood vessels at T5 to L1 all decreased in the ligation groups. And significant differences were found at T8 (82.80 +/- 16.36), T10 (77.80 +/- 19.80), and T11 (99.20 +/- 14.85) levels, compared to those of the corresponding levels in the control group: T8 (175.80 +/- 8. 31), T9 (176.40 +/- 32. 33), T10 (171.40 +/- 9. 73), and T11 (189.20 +/- 15. 92). Further decrease was found at each corresponding level in the bilateral group, and significant differences were found at T8 (65.80 +/- 15.55), T9 (24.80 +/- 13.43), T10 (0), T11 (0), and T12 (0) levels. Similar results were obtained with regard to the density of blood vessels. Significant differences were found at T11 (1.246 +/- 0.112) and L1 (1.349 +/- 0.109) in the unilateral group, and T9 (0.260 +/- 0.088), T10 (0), T11 (0), T12 (0), and L1 (0.147 +/- 0.117) in the bilateral group compared to those of the corresponding levels in the control group: T9 (1.810 +/- 0.202), T10 (1.833 +/- 0.175), T11 (2.308 +/- 0.335), T12 (2.510 +/- 0.617), and L1 (2.193 +/- 0.033). This study suggests that the more levels the ligation encompasses, the higher the risk of spinal cord damage. Therefore, caution should be taken when several segmental arteries are to be ligated in the clinical setting. What is more, bilateral ligation, which is worse than unilateral ligation, can lead to a significant decrease in the number and density of blood vessels of the spinal.

Syringomyelia, neuropathic pain and Caesarean section

Syringomyelia, neuropathic pain and Caesarean section

Anaesthesia for Correction of Scoliosis in Children

Surgical correction of spinal deformities in children presents a challenge to the anaesthetist because of the extensive nature of the surgery, the co-morbidities of the patients and the constraints on anaesthetic techniques of intraoperative neurophysiological monitoring of the spinal cord. Adolescent idiopathic scoliosis is the most common deformity. Patients with scoliosis secondary to neuromuscular conditions are at greatest risk of perioperative problems, particularly excessive blood loss and respiratory failure. The risk of spinal cord damage can be decreased by the use of intraoperative spinal cord monitoring, particularly monitoring of the lower limb compound muscle action potential evoked by transcranial electrical stimulation. Specific anaesthetic techniques are required for this monitoring to be reliable. Because of concerns about spinal cord perfusion there is now less reliance on induced hypotension and haemodilution to reduce blood loss, with emphasis on proper patient positioning, controlled haemodynamics and antifibrinolytic therapy. Effective postoperative pain management requires a multimodal approach.

THIS MONTH IN ANESTHESIOLOGY

THIS MONTH IN ANESTHESIOLOGY

CT-guided internal fixation of a hangman's fracture.

Most hangman's fractures are treated conservatively. If surgery is indicated, an anterior approach using a C2/C3 graft and plate fusion is usually preferred. Another surgical method according to Judet is direct transpedicular osteosynthesis by the dorsal approach. This surgery is frequently rejected because of the high risk of spinal cord damage or vertebral artery tear. Direct transpedicular osteosynthesis of hangman's fracture according to Judet is a "physiological operation" that does not cause fusion and creates anatomical conditions. This procedure enables appropriate reduction, compression of fragments and immediate stabilization of the C2 segment. A new aspect of Judet's method of internal fixation of a hangman's fracture is now proposed. Computed tomographic (CT) guidance is used to ensure safe and exact introduction of two screws from the posterior approach. This method of CT-guided internal fixation of hangman's fracture allows, preoperatively, for an accurate assessment of the pattern and course of fracture line, selection of the anatomically safest screw path and determination of an appropriate screw length. The procedure also allows for accurate intraoperative control of instrument and implant placement, screw tightening, fracture reduction and anchoring of the screw tip in the contralateral cortex, using repeated CT scans. The procedure is performed in a CT unit under sterile conditions. This method was used in the treatment of eight male and two female patients aged 21-71 years. All treated patients were without neurological deficit. Follow-up ranged from 12 to 57 months (mean 33.3 months). No intraoperative or early or late postoperative complications were apparent. This new aspect of the surgical procedure ensures highly accurate screw placement and minimal risks, and fully achieves the "physiological" internal fixation.

The reproducibility of the iliac crest as a marker of lumbar spine level.

The postero-anterior lumbar spine X rays of 163 patients undergoing investigation for back pain were reviewed and the spinal level marking the intersection of a line joining the iliac crests was determined. This point coincided with the L4 spinous process or the L4-5 interspace in 78.6% of patients but was as high as the L3-4 interspace in 3.7% of cases. Reliance on this landmark might lead to more cranial placement of epidural or spinal needles than was intended and this may increase the risk of spinal cord damage.

Risk of replacement of descending aorta with a standardized left heart bypass technique

Replacement of the descending aorta for aneurysms (51%) and dissection (49%) was performed in 132 patients with a highly standardized left heart vortex-pump bypass. No adjuncts other than staged aortic clamping and intercostal artery reconnection were used to reduce spinal cord injury in extensive involvement. Four patients (3%) died early, two of cardiac cause, and nine (7%) died late. Complications of vital organ function occurred in eight patients, two having reversible renal failure and six spinal cord injury that was permanent in three (2.3%). Cord injury occurred only in replacement beyond thoracic segment 8 and could not be completely avoided despite distal intercostal artery reconnection in two cases; in the other four cases such vessels either did not appear worth reconnecting or were sacrificed in emergency operations. We conclude that left heart bypass effectively unloads the proximal circulation during aortic occlusion while maintaining adequate perfusion of distal vital organs as evidenced by low rates of early mortality and renal failure. The remaining risk of spinal cord damage may be lowered by more aggressive reconnection of all distal intercostal arteries and by extending the permissible cord ischemic period by means of hypothermia. (J THORAC CARDIOVASC SURG 1994;107:126-33)

Hypoplastic posterior arch of C-1 in children with Down syndrome: a double jeopardy.

Radiographs of 38 children with Down syndrome (aged 2-3 years) were retrospectively evaluated for hypoplasia of the posterior arch of the C-1 vertebra. The anteroposterior dimensions of the posterior arch of C-1 were measured and compared with those of an age- and sex-matched control group. The posterior arches of C-2 to C-5 were similarly evaluated. Radiographs demonstrated hypoplasia of the posterior arch of C-1 in 26%. This anomaly of C-1 was an isolated event; sagittal diameters of C-2 to C-5 were within normal limits compared with those of the control group and published standards. Because of the known, potentially devastating atlantoaxial dislocation in Down syndrome, the increased prevalence of a second C-1 anomaly causing preexistent narrowing of the vertebral canal is of clinical concern. A hypoplastic posterior arch of C-1 may amplify the risk of spinal cord damage following atlantoaxial subluxation, as the subsequently smaller vertebral canal has less room for dorsal movement of the odontoid process. This potential "double jeopardy" of C-1 vertebral abnormalities should be recognized and assessed on cervical spine screening radiographs in children with Down syndrome.

The Cervical Spine in Maxillofacial Trauma: Assessment and Airway Management

Although the presence of a real or potential cervical spine injury limits the options for emergency airway management, many choices still remain. The otolaryngologist-head and neck surgeon frequently is called on to treat patients with airway emergencies; therefore, familiarity with the risk of spinal cord damage and methods to avoid it when establishing a safe airway constitute important knowledge. Experience with the variety of airway techniques available increases the number of options and decreases the risks of morbidity and mortality for the patient with cervical spine injury.

Myelopathy following hyperfractionated accelerated radiotherapy for anaplastic thyroid carcinoma

From 1975 to 1982, 32 patients with a diagnosis of anaplastic carcinoma of the thyroid were entered into a protocol of hyperfractionated accelerated radiotherapy. The tumor dose was 30–45 Gy at 1 Gy per fraction given 4 times a day at 3-h intervals. The results were disappointing with a median survival of less than 6 months. Two patients developed radiation myelopathy at 8 and 13 months, total spinal cord dose being 39.9 and 48.3 Gy, respectively. The risk of spinal cord damage was much higher than expected. The possible radiobiological causes and clinical implications are discussed.

Monitoring spinal cord function during scoliosis surgery with Cotrel‐Dubousset instrumentation

Cotrel-Dubousset instrumentation has been a major advance in spinal surgery but, at least theoretically, it carries a higher risk of spinal cord damage. This paper describes our experience in monitoring the function of either ascending sensory pathways or both ascending sensory and descending motor pathways in the spinal cord during such procedures. Seventy-nine juvenile and adult patients are presented in whom either somatosensory recording (n = 39) or simultaneous corticospinal and somatosensory monitoring (n = 40) was attempted by means of epidural electrodes during corrective surgery with Cotrel-Dubousset instrumentation. Abnormal evoked responses were seen in two cases but these resolved in both before the operation was completed. No new neurological deficits occurred nor were any pre-existing deficits increased.