Response to local corticosteroid injections in carpal tunnel syndrome with normal conduction studies.

INTRODUCTION: Nerve conduction studies (NCS) have been considered as the gold standard in carpal tunnel syndrome (CTS) diagnosis, despite correlation between clinical symptomatology and NCS severity has shown to be poor. In fact, clinical symptoms precede NCS changes in months or years. Few papers have been published about the clinical response to treatment of clinically typical CTS, but with normal NCS (NNCS). OBJECTIVE: To compare the clinical response to local corticosteroid injections (LCI) in clinically typical CTS, with NNCS and abnormal NCS (ANCS). METHOD: We included patients older than 18, with typical CTS symptoms (ongoing daily nocturnal pain/paresthesias in hand, at least during 3 months). Follow-up was done at 3, 6 and 12 months. Primary outcome was the visual analog scale for pain (p-VAS), comparing NNCS CTS wrists with ANCS CTS wrists. Statistic signification was established by the Student's t test, Mann-Whitney's "U", χ2 test and Yates' correction. RESULTS: We included 44 wrists in the NNCS group, and 83 in the ANCS group. There was no statistical significance between data in both groups, except in the 12-month follow-up, where the NNCS group achieved better results than the ANCS group in the 20% response (p=0.006). There was a trend toward a better 50% response in the 12-month follow-up. CONCLUSIONS: Our data suggest that LCI are similarly effective in both CTS with NNCS and ANCS. Nonetheless, there is a mild better effect in NNCS than in ANCS at 12-month follow-up.

Pulse-train versus single-pulse t-EMG stimulation for intraoperative neurophysiologic monitoring of thoracic pedicle screws in adolescent idiopathic scoliosis.

OBJECTIVE: To assess the PTS method in neuromonitoring of thoracic pedicle screws in a young cohort of AIS patients. The accuracy of both PTS (Pulse-train stimulation) and SPS (Single-pulse stimulation) techniques in the detection of misplaced thoracic screws was compared with special reference to the screws placed at the concavity and the convexity of the curve. PATIENTS AND METHODS: A single-center prospective clinical cohort study. LEVEL OF EVIDENCE II: Twelve AIS patients who underwent elective surgery were included in this study. Screw stimulation using repetitive constant-current stimulus train of variable intensities was first performed after screw insertion. SPS was performed immediately after PTS. Postoperatively, CT scan was used to check the final position of the screws. A total of 246 thoracic pedicle screws were placed. Thresholds of screws placed in the convexity and the concavity were compared. RESULTS: Invasion of the spinal canal was postoperatively confirmed in 29 of the pedicle screws. The SPS technique detected three (10.3%) of these screws using a threshold limit of 12 mA. The PTS technique detected 25 (86.2%) of the 29 misplaced screws using threshold of 30 mA (negative predictive value, 93.1%). When using a PTS threshold of < 20 mA, the positive predictive value was 70%. SPS did not detect any of the misplaced screws at the apex level of the scoliotic curves, and PTS detected 10 out of 17 of these screws. Overall, area under the ROC curve was 0.82 for PTS and 0.61 for SPS. CONCLUSIONS: PTS is a reliable method for detecting medially misplaced screws among young AIS patients undergoing scoliosis surgery. PTS provides more accurate predictions than SPS and improves the identification of screws invading the spinal canal at the apex or near the apex levels.

Long-term Outcome of Local Steroid Injections Versus Surgery in Carpal Tunnel Syndrome: Observational Extension of a Randomized Clinical Trial.

Background: In a previous paper, we have demonstrated that: (1) local injection of corticosteroids for carpal tunnel syndrome (CTS) is as effective as decompressive surgery, at 1-year follow-up; and (2) surgery has an additional benefit in the 2-year follow-up. In this study, we assess the long-term outcomes of both therapies in an observational extension of the patients originally enrolled in our randomized clinical trial. Methods: Patients were included in an open, randomized clinical trial, comparing injections versus surgery in CTS. After the end of the clinical trial, patients received the treatment prescribed by their general practitioner or specialist. Therapeutic failure was defined as the need of any new therapeutic intervention on the involved wrist. Comparison between groups was made using Cox multiple regression analysis. Estimation of the accumulated incidence of new therapeutic failure was made considering the withdrawal as a competitive risk (Gooley's test). Results: Of 163 randomized wrists at the beginning of the study, only 148 were available at the final follow-up. The mean follow-up was 6.3 and the median was 5.9 years. In the long-term follow-up, the accumulated incidence of therapeutic failure in the surgery group was 11.6% versus 41.8% in the injection group. The Cox multiple regression analysis showed a risk of failure associated with injection group of 4.5 (95% confidence interval [CI], 2.1-9.8; P < .0001). Conclusions: In long-term follow-up, surgery seems more effective than local corticosteroid injections in primary CTS. Nonetheless, about 58% of the patients in the injection group will not need further therapeutic interventions during the follow-up.

Response to Local Corticosteroid Injections in Carpal Tunnel Syndrome With Normal Conduction Studies.

INTRODUCTION: Nerve conduction studies (NCS) have been considered as the gold standard in carpal tunnel syndrome (CTS) diagnosis, despite correlation between clinical symptomatology and NCS severity has shown to be poor. In fact, clinical symptoms precede NCS changes in months or years. Few papers have been published about the clinical response to treatment of clinically typical CTS, but with normal NCS (NNCS). OBJECTIVE: To compare the clinical response to local corticosteroid injections (LCI) in clinically typical CTS, with NNCS and abnormal NCS (ANCS). METHOD: We included patients older than 18, with typical CTS symptoms (ongoing daily nocturnal pain/paresthesias in hand, at least during 3 months). Follow-up was done at 3, 6 and 12 months. Primary outcome was the visual analog scale for pain (p-VAS), comparing NNCS CTS wrists with ANCS CTS wrists. Statistic signification was established by the Student's t test, Mann-Whitney's "U", χ2 test and Yates' correction. RESULTS: We included 44 wrists in the NNCS group, and 83 in the ANCS group. There was no statistical significance between data in both groups, except in the 12-month follow-up, where the NNCS group achieved better results than the ANCS group in the 20% response (p=0.006). There was a trend toward a better 50% response in the 12-month follow-up. CONCLUSIONS: Our data suggest that LCI are similarly effective in both CTS with NNCS and ANCS. Nonetheless, there is a mild better effect in NNCS than in ANCS at 12-month follow-up.

Neurophysiological monitoring during acute and progressive experimentally induced compression injury of the spinal cord in pigs.

PURPOSE: To evaluate the degree of acute or progressive lateral compression needed to cause neurologic injury to the spinal cord assessed by electrophysiological monitoring. METHODS: In five domestic pigs, the spinal cord was exposed and compressed between T8-T9 roots using a precise compression device. Two sticks placed on both sides of the spinal cord were sequentially brought together (0.5 mm every 2 min), causing progressive spinal cord compression. Acute compression was reproduced by a 2.5-mm displacement of the sticks. Cord-to-cord evoked potentials were obtained with two epidural catheters. RESULTS: Increasing latency and decreasing amplitude of the evoked potentials were observed after a mean progressive displacement of the sticks of 3.2 ± 0.9 mm, disappearing after a mean displacement of 4.6 ± 1.2 mm. The potential returned after compression removal (16.8 ± 3.2 min). The potentials disappeared immediately after an acute compression of 2.5 ± 0.3 mm, without any sign of recovering after 30 min. CONCLUSIONS: The experimental model replicates the mechanism of a spinal cord injury caused by medially displaced screws into the spinal canal. The spinal cord had more ability for adaptation to progressive and slow compression than to acute mechanisms.

Local injection versus surgery in carpal tunnel syndrome: neurophysiologic outcomes of a randomized clinical trial.

OBJECTIVE: The aim of our study was to characterize the neurophysiologic outcomes in a randomized clinical trial comparing local corticosteroid injection and decompressive surgery in idiopathic carpal tunnel syndrome. METHODS: Clinical and neurophysiologic assessments were done at baseline and 12 months after treatment. Four parameters were evaluated in the nerve conduction study (NCS): distal motor latency, motor amplitude, sensory conduction velocity and sensory amplitude. Statistic signification was established by the Student's t test, independent and paired samples, and Mann-Whitney test. Repeated measures analysis of variance was used by the three domains of symptoms. Correlations between the changes showed in clinical parameters and those evidenced by electromyography were calculated by the Pearson's test. RESULTS: Both groups of therapy were comparable at baseline. In 95 wrists, a second NCS was done 12 months post-treatment. Although clinical outcome improved in a similar way in both groups, we found statistically significant improvement in three (distal motor latency, sensory conduction velocity and sensory amplitude) of four neurophysiologic parameters only in the surgery group, when compared to baseline values. CONCLUSIONS: Although local corticosteroid injection and decompressive surgery are clinically effective in reducing symptoms of carpal tunnel syndrome, only surgery results in an improvement of the neurophysiologic parameters, at 12-months follow-up. SIGNIFICANCE: Only decompressive surgery allows resolution of neurophysiologic changes. The symptoms of the syndrome are resolved with corticosteroid injections.

Intraoperative Neurophysiological Changes Induced by Thoracic Pedicle Screws Intentionally Placed Within the Spinal Canal: An Experimental Study in Pigs.

STUDY DESIGN: Experimental study, OBJECTIVES: To document and analyze the neurophysiological changes during spinal cord monitoring when thoracic pedicle screws are intentionally placed within the spinal canal. SUMMARY OF BACKGROUND DATA: Although the rate of misplaced screws is relatively high, few patients have neurological impairment. This suggests that a significant degree of medullary displacement and/or compression is necessary to produce neurophysiological changes. METHODS: The spinal cord of 3 experimental pigs was surgically exposed at 3 different levels (T11, T9, and T6). Two pedicle screws were placed within the spinal canal at each vertebral level under direct vision. One was placed on the lateral edge of the dural sac, causing only a slight cord displacement; a second screw was placed in the middle of the spinal canal, producing marked displacement of the neural structures. During the procedure, neurophysiological monitoring of the spinal cord was performed. RESULTS: No neurophysiological changes were observed in any screws placed at the lateral edge of the dural sac for 20 minutes after screw placement. When the screws were placed in the center of the spinal canal, neurophysiological changes occurred with a mean latency of 10.1 ± 2.1 minutes, and at 11.6 ± 1.9 minutes there was complete loss of the spinal cord evoked potentials in all cases. After these centered screws were removed, evoked potentials began to recover, with a latency of 9.7 ± 3.0 minutes in 7 of 9 cases. CONCLUSIONS: Neurophysiological monitoring of the spinal cord does not detect moderate compression even 20 minutes after neural compression. Only thoracic pedicle screws provoking marked displacement of the spinal cord were able to cause delayed neurophysiological changes leading to loss of spinal cord evoked potentials, which in 22% of cases did not recover after the pedicle screw was removed.

Influence of hypotension and nerve root section on the ability to mobilize the spinal cord during spine surgery. An experimental study in a pig model.

BACKGROUND CONTEXT: The correction of severe spinal deformities by an isolated posterior approach often involves cord manipulation together with hypotensive anesthesia. To date, the efficiency of methods to increase the tolerance of the cord to displacement and the influence of hypotension on this tolerance is yet to be assessed. PURPOSE: The objective of this study was to determine the limits of cord displacement before the disappearance of neurophysiologic signals. The influence of the type of force applied, the section of the roots, and the induced hypotension on the cord's tolerance to displacement was also assessed. STUDY DESIGN: Experimental study using a domestic pig model. OUTCOME MEASURES: Successive records of cord-to-cord motor evoked potentials were obtained during displacement maneuvers. Displacing forces were released immediately after the absence of neurophysiologic signals. METHODS: Surgical procedures were performed under conventional general anesthesia. The spinal cord and nerve roots from T6 to T10 levels were exposed by excision of the posterior elements, allowing for free cord movement. Three groups were established according to the method of spinal cord displacement: the separation (Group 1, n=5), the root stump pull (Group 2, n=5), and the torsion groups (Group 3, n=5). An electromechanical external device was used to apply the displacing forces. The three displacement tests were repeated after sectioning the adjacent nerve roots. The experiments were first carried out under normotension and afterward under induced hypotension. RESULTS: In Group 1, evoked potential disappeared with a displacement of 10.1±1.6 mm with unharmed roots and 15.3±4.7 mm after the sectioning of four adjacent roots (p<.01). After induced hypotension, potentials were lost at 4.0±1.2 mm (p<.01). In Group 2, the absence of potentials occurred at 20.0±4.3 mm and increased to 23.5±2.1 mm (p<.05) after cutting the two contralateral roots. Under hypotensive conditions, the loss of neurophysiologic signals was detected at 5.3±1.2 mm (p<.01). In Group 3, the cord allowed torsion of 95.3±.2° that increased to 112.4±7.1° if the contralateral roots were cut. Under hypotension, the loss of potentials was found at 20±6.2° (p<.01). CONCLUSIONS: In this experimental model, it was possible to displace the thoracic spinal cord by a distance superior to the spinal cord width without suffering neurophysiologic changes. The limits of cord displacement increase when the adjacent nerve roots are sacrificed. Induced hypotension had a dramatic effect on the tolerance of the spinal cord for displacement. This work has an important clinical significance because induced hypotension during specific spine surgery procedures requiring spinal cord manipulation in humans may increase the risk of neurologic spinal cord injury.

Comparison of surgical decompression and local steroid injection in the treatment of carpal tunnel syndrome: 2-year clinical results from a randomized trial.

OBJECTIVE: To compare the efficacy of surgical decompression vs local steroid injection in the treatment of idiopathic CTS. METHODS: This is an open, prospective, randomized clinical trial. We studied the effects of surgical decompression vs local steroid injection in 163 wrists with a clinical diagnosis and neurophysiological confirmation of CTS, with an extended follow-up of 2 years. The primary end point was the percentage of wrists that reached a ≥ 20% improvement in the visual analogue scale score for nocturnal paraesthesias. Statistical analysis was done by Student's t-test for continuous variables and by chi-square test for categorical variables. Analyses were performed on an intent-to-treat basis. P < 0.05 were considered statistically significant. RESULTS: Both treatment groups had comparable severity of CTS at baseline. Eighty wrists were randomly assigned to surgical decompression and 83 wrists to local steroid injection. Fifty-five wrists in the surgery group and 48 wrists in the injection group completed the 2-year follow-up. In the intent-to-treat analysis, at 2-year follow-up, 60% of the wrists in the injection group vs 69% in the surgery group reached a 20% response for nocturnal paraesthesias (P < 0.001). CONCLUSION: Our findings suggest that both local steroid injection and surgical decompression are effective treatments in alleviating symptoms in primary CTS at 2-year follow-up. Surgery has an additional benefit in the 2-year follow-up, although clinical relevance of those differences remains to be defined. TRIAL REGISTRATION: Current Controlled Trials, www.controlled-trials.com, ISRCTN26264638.

Electromyographic thresholds after thoracic screw stimulation depend on the distance of the screw from the spinal cord and not on pedicle cortex integrity.

BACKGROUND CONTEXT: Present studies concerning the safety and reliability of neurophysiological monitoring during thoracic pedicle screw placement remain inconclusive, and therefore, universally validated threshold levels that confirm osseous breakage of the instrumented pedicles have not been properly established. PURPOSE: The objective of this work was to analyze whether electromyographic (EMG) thresholds, after stimulation of the thoracic pedicle screw, depend on the distance between the neural structures and the screws. The modifier effect of different interposed tissues between a breached pedicle and neural structures was also investigated. STUDY DESIGN: This experimental study uses a domestic pig model. METHODS: Electromyographic thresholds were recorded after the stimulation of 18 thoracic pedicle screws that had been inserted into five experimental animals using varying distances between each screw and the spinal cord (8 and 2 mm). Electromyographic thresholds were also registered after the medial pedicle cortex was broken and after different biological tissues were interposed (blood, muscle, fat, and bone) between the screw and the spinal cord. RESULTS: Mean EMG thresholds increased to 14.1±5.5 mA for screws with pedicle cortex integrity that were placed 8 mm away from the dural sac. After the medial pedicle cortex was broken and without varying the distance of the screw to the dural sac, the mean EMG thresholds were not appreciably changed (13.6±6.3 mA). After repositioning the screw at a distance of 2 mm from the spinal cord and after medial cortical breach of the pedicle, the mean threshold significantly slowed to 7.4±3.4 mA (p<.001). When the screw was placed in contact with the spinal dural sac, even lower EMG thresholds were registered (4.9±1.9, p<.001). Medial pedicle cortex rupture and the interposition of different biological tissues in experimental animals did not alter the stimulation thresholds of the thoracic pedicle screws. CONCLUSIONS: In the experimental animals, the observed electrical impedance depended on the distance of screws from the neural structures and not on the integrity of the pedicle cortex. The screw-triggered EMG technique did not reliably discriminate the presence or absence of bone integrity after pedicle screw placement. The response intensity was not related to the type of interposed tissue.

Safe pedicle screw placement in thoracic scoliotic curves using t-EMG: stimulation threshold variability at concavity and convexity in apex segments.

STUDY DESIGN: A cross-sectional study of nonconsecutive cases (level III evidence). OBJECTIVE: In a series of young patients with thoracic scoliosis who were treated with pedicle screw constructs, data obtained from triggered electromyography (t-EMG) screw stimulation and postoperative computed tomographic scans were matched to find different threshold limits for the safe placement of pedicle screws at the concavity (CC) and convexity (CV) of the scoliotic curves. The influence of the distance from the medial pedicle cortex to the spinal cord on t-EMG threshold intensity was also investigated at the apex segment. SUMMARY OF BACKGROUND DATA: Whether the t-EMG stimulation threshold depends on pedicle bony integrity or on the distance to neural tissue remains elusive. Studying pedicle screws at the CC and CV at the apex segments of scoliotic curves is a good model to address this issue because the spinal cord is displaced to the CC in these patients. METHODS: A total of 23 patients who underwent posterior fusions using 358 pedicle thoracic screws were reviewed. All patients presented main thoracic scoliosis, with a mean Cobb angle of 58.3 degrees (range, 46-87 degrees). Accuracy of the screw placement was tested at surgery by the t-EMG technique. During surgery, 8 screws placed at the CC showed t-EMG threshold values below 7 mA and were carefully removed. Another 25 screws disclosed stimulation thresholds within the range of 7 to 12 mA. After checking the screw positions by intraoperative fluoroscopy, 15 screws were removed because of clear signs of malpositioning. Every patient underwent a preoperative magnetic resonance imaging examination, in which the distances from the spinal cord to the pedicles of the concave and convex sides at 3 apex vertebrae were measured. Postoperative computed tomographic scans were used in all patients to detect screw malpositioning of the final 335 screws. RESULTS: According to postoperative computed tomographic scans, 44 screws (13.1%) showed different malpositions: 40 screws (11.9%) perforated the medial pedicle wall, but only 11 screws (3.2%) were completely inside the spinal canal. If we considered the 23 screws removed during surgery, the true rate of misplaced screws increased to 18.7%. In those screws that preserved the pedicle cortex (well-positioned screws), EMG thresholds from the CC showed statistically significantly lower values than those registered at the CV of the deformity (21.1 ± 8.2 vs 23.9 ± 7.7 mA, P < 0.01). In the concave side, t-EMG threshold values under 8 mA should be unacceptable because they correspond to screw malpositioning. Threshold values above 14 mA indicate an accurate intrapedicular position with certainty. At the convex side, threshold values below 11 mA always indicate screw malpositioning, and values above 19 mA imply accurate screw placement. At the 3 apex vertebrae, the average pedicle-spinal cord distance was 2.2 ± 0.7 mm at the concave side and 9.8 ± 4.3 mm at the convex side (P < 0.001). In well-positioned screws, a correlation between pedicle-dural sac distance and t-EMG threshold values was found at the concave side only (Pearson r = 0.467, P < 0.05). None of the patients with misplaced screws showed postoperative neurological impairment. CONCLUSION: Independent of the screw position, average t-EMG thresholds were always higher at the CV in the apex and above the apex regions, presuming that the distance from the pedicle to the spinal cord plays an important role in electrical transmission. The t-EMG technique has low sensitivity to predict screw malpositioning and cannot discriminate between medial cortex breakages and complete invasion of the spinal canal.

Recording triggered EMG thresholds from axillary chest wall electrodes: a new refined technique for accurate upper thoracic (T2-T6) pedicle screw placement.

This study was aimed at evaluating the sensitivity and safety of a new technique to record triggered EMG thresholds from axillary chest wall electrodes when inserting pedicle screws in the upper thoracic spine (T2-T6). A total of 248 (36.6%) of a total of 677 thoracic screws were placed at the T2-T6 levels in 92 patients with adolescent idiopathic scoliosis. A single electrode placed at the axillary midline was able to record potentials during surgery from all T2-T6 myotomes at each side. Eleven screws were removed during surgery because of malposition according to intraoperative fluoroscopic views. Screw position was evaluated after surgery in the remaining 237 screws using a CT scan. Malposition was detected in 35 pedicle screws (14.7%). Pedicle medial cortex was breached in 24 (10.1%). Six screws (2.5%) were located inside the spinal canal. Mean EMG threshold was 24.44 ± 11.30 mA in well-positioned screws, 17.98 ± 8.24 mA (p < 0.01) in screws violating the pedicle medial cortex, and 10.38 ± 3.33 mA (p < 0.005) in screws located inside the spinal canal. Below a threshold of 12 mA, 33.4% of the screws (10/30) were malpositioned. Furthermore, 36% of the pedicle screws with t-EMG stimulation thresholds within the range 6-12 mA were malpositioned. In conclusion, assessment of upper thoracic pedicle screw placement by recording tEMG at a single axillary electrode was highly reliable. Thresholds below 12 mA should alert surgeons to suspect screw malposition. This technique simplifies tEMG potential recording to facilitate safe placement of pedicle screws at upper thoracic levels.

Neurophysiological study in cerebrotendinous xanthomatosis.

INTRODUCTION: Cerebrotendinous xanthomatosis (CTX) is a rare autosomal-recessive disease due to mutations of the 27α-hydroxylase. It is characterized by cataracts, xanthomas, and neurological manifestations. Polyneuropathy has been reported, although it is unclear whether it is axonal or demyelinating. METHODS: We report clinical and neurophysiological results of 13 patients with CTX diagnosed in Spain. RESULTS: In 8 patients (62%), peripheral neuropathy was demonstrated (4 demyelinating, 3 axonal, and 1 mixed; 3 predominantly motor and 5 sensorimotor). All patients had clinical signs/symptoms of peripheral neuropathy. Upper limb somatosensory evoked potentials (SSEPs) were affected in 38% of patients, and lower limb SSEPs in 67%. Fifty percent of patients had delayed brainstem auditory evoked potentials, and 43% had affected visual evoked potentials. DISCUSSION: In this series, polyneuropathy was predominantly sensorimotor and demyelinating. Neurophysiological studies correlated only partially with clinical follow-up. Therefore, we recommend neurophysiological follow-up studies only if clinical symptoms are present.

Recording diffusion responses from contralateral intercostal muscles after stimulus-triggered electromyography: refining a tool for the assessment of thoracic pedicle screw placement in an experimental porcine model.

STUDY DESIGN: A new stimulus-triggered electromyography (EMG) test for detecting stimulus diffusion to contralateral intercostal muscles during thoracic pedicle screw placement was assessed in a porcine model. OBJECTIVE: To determine if electromyographic thresholds in the intercostal muscles of both sides of the thorax could discriminate thoracic pedicle screw malpositions with and without neural contact at different aspects of the spinal cord and nerve roots. SUMMARY OF BACKGROUND DATA: There is controversy about the value of triggered EMG stimulation for aiding precise insertion of thoracic pedicle screws. A universally validated threshold that confirms screw malposition has not been established. Diffusion of EMG responses to the contralateral intercostal muscles has not previously been investigated. METHODS: Nine domestic pigs weighing 60 to 75 kg had 108 pedicle screws placed bilaterally in the thoracic spine from T8-T13. Before spine instrumentation, neural structures were stimulated in 4 animals under direct vision at different anatomic locations from T9-T12. Recording electrodes were placed over the right and left intercostal muscles. Increasing stimulus intensity was applied until muscle response was detected at the contralateral side (EMG diffusion phenomenon). After this first experiment, the thoracic spine was instrumented in all 9 animals. Screws were placed in the pedicle in different positions, the anatomic intrapedicular location and within the spinal canal, with and without contact with the neural elements. RESULTS: Response thresholds to direct nerve root stimulation were significantly lower than those obtained by stimulation of the dorsal aspect of the spinal cord (0.44 +/- 0.22 mA vs. 1.38 +/- 0.71 mA, P < 0.01). However, a 14-fold stimulation intensity (6.50 +/- 0.29 mA) was necessary to obtain diffusion of the EMG response to the opposite (left) side if the right nerve root was stimulated. A 2-fold increment (3.17 +/- 0.93 mA) elicited diffusion of the EMG responses to the contralateral side when stimulation was applied to the dorsal aspect of the spinal cord. EMG recordings of the 108 stimulated screws showed a significant decrease in the EMG response when the screw was in contact with the spinal cord (2.72 +/- 1.48 mA; P < 0.01) compared with that found when the pedicle track was intact (mean: 5.01 +/- 1.89 mA). Screws violating the medial wall of the pedicle, but not touching neural tissues, responded to slightly lower intensities than well-positioned screws, but this was not statistically significant (3.91 +/- 1.39 mA vs. 4.89 +/- 1.30 mA, P > 0.05). CONCLUSION: Stimulus-triggered EMG can identify screws that violate the medial pedicle wall if they are in contact with neural tissues. EMG thresholds could not discriminate screws that violated the medial pedicle wall without neural contact from screws with accurate intraosseous placement. However, recording EMG potentials at the contralateral intercostal muscles (stimulus diffusion phenomenon) proved to be a reliable method for identifying the neural structures at risk.

Using triggered electromyographic threshold in the intercostal muscles to evaluate the accuracy of upper thoracic pedicle screw placement (T3-T6).

STUDY DESIGN: A prospective clinical study of high thoracic pedicle screws monitored with triggered electromyographic (EMG) testing. OBJECTIVE: To evaluate the sensitivity of recording intercostal muscle potentials to assess upper thoracic screw placement. SUMMARY OF BACKGROUND DATA: Triggered EMG testing from rectus muscle recordings, which are innervated from T6 to T12, has identified medially placed thoracic pedicle screws. No clinical study has correlated an identical technique with the intercostal muscle for upper pedicle screws placed in the upper thoracic spine (T3-T6). METHODS: A total of 311 high thoracic screws were placed in 50 consecutive patients. Screws were placed from T3 to T6 and were evaluated using an ascending method of stimulation until a compound muscle action potential was obtained from the intercostal muscles. Screw position was then evaluated using computed tomography and results were compared with evoked EMG threshold values. RESULTS: Fifteen screws (5%) showed penetration on postoperative computed tomography scans. Eleven screws showed medial cortical breakthrough (3.6%), 6 had stimulation thresholds 20 mA. Of the 296 screws with thresholds between 6 and 20 mA, 285 (91%) were within the vertebra. No postoperative neurologic complications were noted in any of the 50 patients. CONCLUSION: In this series, cortical violation is highly unlikely in patients whose stimulation threshold lies between 6 and 20 mA with values 60% to 65% decreased from the mean (98% negative predictive value). Although verification of screw placement should not depend solely on stimulation thresholds, pedicle screw stimulation provides rapid and useful intraoperative information on screw placement during procedures involving the use of thoracic pedicle screws.

Surgical decompression versus local steroid injection in carpal tunnel syndrome: a one-year, prospective, randomized, open, controlled clinical trial.

OBJECTIVE: Optimal treatment of carpal tunnel syndrome (CTS) has not been established. This study compared the effects of local steroid injection versus surgical decompression in new-onset CTS of at least 3 months' duration. METHODS: In a 1-year, prospective, randomized, open, controlled clinical trial, we studied the effects of surgical decompression versus local steroid injection in 163 wrists with a clinical and neurophysiologic diagnosis of CTS. Clinical assessments were done at baseline and at 3, 6, and 12 months after treatment. The primary end point was the percentage of wrists that reached a >or=20% improvement in the visual analog scale score for nocturnal paresthesias at 3 months of followup. Statistical analysis was done by Student's t-test for continuous variables and by chi-square test for categorical variables. Analyses were performed on an intent-to-treat basis. P values less than 0.05 were considered statistically significant. RESULTS: Both treatment groups had comparable severity of CTS at baseline. Eighty wrists were randomly assigned to the surgery group and 83 wrists to the local steroid injection group. In the intent-to-treat analysis, at 3 months of followup, 94.0% of the wrists in the steroid injection group versus 75.0% in the surgery group reached a 20% response for nocturnal paresthesias (P = 0.001). At 6 and 12 months, the percentages of responders were 85.5% versus 76.3% (P = 0.163) and 69.9% versus 75.0% (P = 0.488), for local steroid injection and surgical decompression, respectively. CONCLUSION: Over the short term, local steroid injection is better than surgical decompression for the symptomatic relief of CTS. At 1 year, local steroid injection is as effective as surgical decompression for the symptomatic relief of CTS.