Biomechanical response in the ankle to stimulation of lumbosacral nerve roots with spiral cuff multielectrode--preliminary study

Biomechanical response in the ankle to tetanic stimulation of the lumbosacral root was investigated to assess the potential for lower limb functional neurostimulation. Myotomal response in the leg was measured as the three-dimensional isometric torque in the ankle after extradural tetanic stimulation of the L3-S1 roots exposed surgically for herniated disc removal in five patients. The cuff multielectrode was employed to investigate functional topography of the roots by monopolar, bipolar, and tripolar electrode configurations. Four response patterns in the direction of three-dimensional torque vectors were observed. The L-5 and S-1 roots had the same response pattern, but S-1 roots produced stronger torques. Dorsiflexion torque was not obtained by stimulation of L-5 roots despite coactivation of the tibial anterior and peroneal muscles. Dorsiflexion torques were produced only by stimulating the L-4 roots. More selective bipolar and tripolar stimulations recruited force at higher thresholds and less gain. Additionally, some muscles were not activated by tripolar stimulation of the same root. In one L-4 root, the torque at lower electrical threshold was replaced by inverse torque at higher threshold, providing indirect evidence that different muscles may have motoneuron populations that differ in diameter or location within the root. Although dorsiflexion and plantarflexion torques are functional per se, they are accompanied by foot inversion and leg rotation torques (as well as proximal muscle contractions). Further experimental investigations on direct extradural stimulation of lumbosacral roots, either single or in combination, are recommended to explore the potential of lumbosacral nerve root stimulation for restoration of leg function.     

Continuous EMG recordings and intraoperative electrical stimulation for identification and protection of cervical nerve roots during foraminal tumor surgery

OBJECTIVE: Spinal cord function is now routinely monitored with somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) during surgery for intraspinal cervical dumbbell and foraminal tumors. However, upper extremity nerve roots are also at risk during these procedures. Anatomic relations are frequently difficult to interpret because the nerve roots may be displaced by the tumor. We used electrical stimulation with compound muscle action potential (CMAP) recordings at multiple sites to identify the location and course of the involved nerve root and to provide real-time information regarding the functional status of the roots to predict postoperative outcome. METHODS: Ten patients were monitored during surgery for cervical dumbbell or foraminal tumors. SEPs and MEPs were monitored as a routine procedure. CMAPs were recorded from needle electrodes placed in the deltoid, biceps, triceps, and flexor carpi ulnaris muscles. Spontaneous electromyography (EMG) muscle activity was also continuously monitored. A handheld monopolar stimulation electrode was used to elicit evoked EMG responses to identify and trace the course of nerves in relation to the tumor. In four patients, the stimulation threshold was tested before and after tumor resection to predict postoperative nerve root function. RESULTS: Electrical stimulation with CMAP recording was successful in localizing nerve roots during tumor resection in all 10 patients. Monitoring predicted postoperative nerve root preservation after tumor removal in each case. It was possible to identify either by using low-level stimulation (<2.0 V) or by observing changes in spontaneous EMG amplitude if activation was present during surgical dissection. The monitoring of spontaneous muscle activity in response to direct or indirect surgical manipulation during tumor resection also provided continuous assessment of nerve root function and identified any physiologic disturbance induced by surgical manipulation. CONCLUSIONS: Electrical stimulation in the operating field and recording of CMAPs facilitated nerve root identification and predicted postoperative function during dissection and separation from ligamentous or neoplastic tissue in 10 patients. Electrical stimulation might also be useful to predict postoperative preservation of function when nerve root sacrifice is necessary and no motor response is detected intraoperatively.     

Electrophysiological monitoring and identification of neural roots during somatic-autonomic reflex pathway procedure for neurogenic bladder

Artificialsomatic centralnervoussystem autonomicreflexpathwayprocedurehasbeenprovedtobeaneffectiveandsafetreatmentforneurogenicbladderandbowelcausedbyspinalcordinjuryordiseaseslikespinabifida.1 3 Duringnearly10yearsoclinicalexperiences, wehaverealizedthat…     

Evaluation of traumatic cervical nerve root injuries by intraoperative evoked potentials

OBJECTIVE: To evaluate intraoperative evoked potentials as a diagnostic tool in traumatic brachial plexus injuries. METHODS: Thirteen patients with traumatic brachial plexus injuries were investigated by intradural nerve root inspection (n = 28 roots) via cervical hemilaminectomy to assess or rule out nerve root avulsion from the spinal cord. Two to 8 weeks later, evoked potentials from neck and scalp were recorded after direct electrical nerve root stimulation close to the vertebral foramen during operative brachial plexus repair via an anterior (supraclavicular and infraclavicular) approach. Recordings were performed without and after full muscle relaxation. RESULTS: There was a clear relationship between the state of the root as documented by intradural root inspection and the result of intraoperative recording of evoked potentials: the absence of evoked muscle action potentials from neck muscles demonstrated a 100% sensitivity for anterior root lesions, whereas sensory evoked potentials from the scalp demonstrated a 100% sensitivity for posterior root lesions. Moreover, roots could be identified with preserved continuity that did not conduct, suggesting a nerve lesion in continuity. CONCLUSION: Intraoperative evoked muscle action potentials and sensory evoked potentials after electrical nerve root stimulation allow selective functional evaluation of anterior and posterior nerve roots in patients with traumatic brachial plexus injuries. The high sensitivity and reliability of this test obviate the need for additional diagnostic surgery.     

Lumbar Root Stimulation for Restoring Leg Function: Results in Paraplegia

Abstract: We have implanted an intradural array of 12 tripolar electrodes on the anterior roots L2-S2, left and right, at cauda equina level, in a 33-year-old woman with a complete T9 cord lesion of 3 years' duration. They are driven by an implanted multiplexed stimulator system using radio frequency (RF) power and control signals. All channels generate movements, in patterns that might be predicted from the known anatomy of the cauda equina. In particular, stimulation of L2 and L3 gives hip adduction; L3, L4, and L5 gives quadriceps femoris movements; L5, S1, and S2 gives hamstrings movement; and S1 and S2 give plantar flexion. Stimulation of L5 gives mixed movements at the ankle. Surprisingly, stimulation of the L2 roots has not given strong hip flexion. Responses have been stable. Some thresholds have varied, probably as a result of tissue encapsulation. The moment generated within each degree of freedom of the legs has been measured for each root, using a specially designed multimoment measurement apparatus. For several roots, a movement of lower threshold may be accompanied by a second movement of higher electrical threshold, suggesting that different muscles may have fiber populations that differ in their diameter or their location in the root. The use of stimulus forms that enable selective anodal block may, in the future, enable separation of two distinct movements from a single motor root.     

Spinal cord mapping as an adjunct for resection of intramedullary tumors: surgical technique with case illustrations

OBJECTIVE: Resection of intramedullary spinal cord tumors may result in transient or permanent neurological deficits. Intraoperative somatosensory evoked potentials (SSEPs) and motor evoked potentials are commonly used to limit complications. We used both antidromically elicited SSEPs for planning the myelotomy site and direct mapping of spinal cord tracts during tumor resection to reduce the risk of neurological deficits and increase the extent of tumor resection. METHODS: In two patients, 3 and 12 years of age, with tumors of the thoracic and cervical spinal cord, respectively, antidromically elicited SSEPs were evoked by stimulation of the dorsal columns and were recorded with subdermal electrodes placed at the medial malleoli bilaterally. Intramedullary spinal cord mapping was performed by stimulating the resection cavity with a handheld Ojemann stimulator (Radionics, Burlington, MA). In addition to visual observation, subdermal needle electrodes inserted into the abductor pollicis brevis-flexor digiti minimi manus, tibialis anterior-gastrocnemius, and abductor halluces-abductor digiti minimi pedis muscles bilaterally recorded responses that identified motor pathways. RESULTS: The midline of the spinal cord was anatomically identified by visualizing branches of the dorsal medullary vein penetrating the median sulcus. Antidromic responses were obtained by stimulation at 1-mm intervals on either side of the midline, and the region where no response was elicited was selected for the myelotomy. The anatomic and electrical midlines did not precisely overlap. Stimulation of abnormal tissue within the tumor did not elicit electromyographic activity. Approaching the periphery of the tumor, stimulation at 1 mA elicited an electromyographic response before normal spinal cord was visualized. Restimulation at lower currents by use of 0.25-mA increments identified the descending motor tracts adjacent to the tumor. After tumor resection, the tracts were restimulated to confirm functional integrity. Both patients were discharged within 2 weeks of surgery with minimal neurological deficits. CONCLUSION: Antidromically elicited SSEPs were important in determining the midline of a distorted cord for placement of the myelotomy incision. Mapping spinal cord motor tracts with direct spinal cord stimulation and electromyographic recording facilitated the extent of surgical resection.     

Influence of halothane, enflurane, and isoflurane on motor evoked potentials.

The influence of the inhalational anesthetics halothane, enflurane, and isoflurane on motor evoked potentials was studied in a total of 10 rabbits. Motor evoked potentials were recorded from the extremity muscles as well as from the epidural space of the spinal cord and cauda equina in response to electrical stimulation of the motor cortex at baseline conditions and equianesthetic concentrations (0.25 to 1.5 minimal alveolar concentration). Our results show a dose-dependent suppression of the electromyographic responses, which was similar with all anesthetics. Beyond 0.5 minimal alveolar concentration of any of the agents, electromyographic responses were absent. In contrast, spinal evoked responses representing neural activity were only slightly affected by the anesthetics. We hypothesize that the descending impulse elicited by the electrical stimulation of the motor cortex is mainly inhibited at the level of the spinal interneuronal or motoneuronal systems, because 1) electromyographic responses evoked by the stimulation of the cervical and lumbar nerve roots were only minimally affected by 1.5 minimal alveolar concentration halothane; and 2) spinal evoked responses were stable several minutes after cardiac arrest, indicating a subcortical action site of the electrical impulse. In conclusion, intraoperative monitoring of descending pathways by means of motor evoked potentials during anesthesia with the inhalational agents halothane, enflurane and isoflurane is only feasible when neural activity is evaluated.     

Electrophysiologic evaluation of lumbosacral single nerve roots using compound muscle action potentials

Transcutaneous electrical stimulation applied to the vertebral column produces compound muscle action potentials (CMAPs) from the leg muscles. Using this method, we evaluated the efferent pathways of the lumbosacral nerve roots. The subjects were 26 healthy volunteers and 31 patients with lumbar disc herniation (LDH). CMAP recordings were obtained from the bilateral vastus medialis, tibialis anterior, extensor digitorum brevis, and abductor hallucis muscles using low-output-impedance stimulation. In normal subjects, the CMAP latency increased linearly with the distance between the stimulating electrode and the recording electrode, with little difference in latency between the left and the right sides in each subject. The CMAP amplitude was significantly lower in the patients with LDH, and the latency was also prolonged when the stimulating electrode was placed above the lesion. This technique may thus be a useful noninvasive method for assessing lumbosacral nerve root function in patients with LDH.     

Triggered electromyographic threshold for accuracy of thoracic pedicle screw placement in a porcine model.

STUDY DESIGN: A porcine model of thoracic pedicle screw insertion was used to determine the effect of screw position on triggered electromyographic response. OBJECTIVE: To develop a model of intraoperative detection of misplaced thoracic pedicle screws. SUMMARY OF BACKGROUND DATA: Triggered electromyographic stimulation has been a valuable aid in determining appropriate placement of lumbar pedicle screws. The use of pedicle screws is increasing in the thoracic spine. Misplaced thoracic pedicle screws may have significant implications if the spinal cord is injured. This study was an attempt to determine whether the established lumbar model can be used for thoracic pedicle screws. METHODS: Five 120- to 150-lb domestic pigs had 85 pedicle screws placed bilaterally in the thoracic spine at each level from T6 to T15. Screws were inserted entirely in the pedicle (Group A). After removal of the medial pedicle wall, the screws were reinserted in the pedicle with no neural contact (Group B). The screws were then placed with purposeful contact with the neural elements (Group C). The screws were stimulated, eliciting an electromyographic response in the intercostal muscles for each instrumented level. The type of response noted was classified as either primary (response from appropriate nerve root), secondary (response at different root) or no response (response at different root, no response at appropriate root). RESULTS: Two hundred fifty responses were recorded. A primary response was noted in 72% of recordings. There was a relatively consistent decrease in the triggered electromyographic response from Group A (mean 4.15 +/- 1.80 mA) to Group C (mean 3.02 +/- 2.53 mA) screws (P = 0.0003). There was little difference in the response obtained from Group A to Group B (mean 4.37 +/- 2.48 mA) screws (P > 0.05). When a primary response was recorded, the mean threshold electromyographic response recorded was significantly lower than recordings with secondary and no response recordings (P < 0.05). CONCLUSION: Even though there was a consistent decrease between the A and C screws that was more definitively separated when a primary response was elicited, it was not possible to determine a cutoff trigger electromyographic level that would consistently differentiate intraosseous from epidural pedicle screw placement. Furthermore, this method could not differentiate screws clearly in the pedicle from screws with medial pedicle wall breakthrough. A more direct method of spinal cord monitoring must be established to provide the surgeon with early warning of the potential of neural injury in the placement of thoracic pedicle screws.     

Compound Muscle Action Potentials and Spontaneous Electromyography Can be Used to Identify and Protect the Femoral Nerve During Resection of Large Retroperitoneal Tumors

Background Resection of large retroperitoneal neoplasms may injure the femoral nerve, thereby causing a permanent neurological deficit. We used electrical neurophysiological monitoring to identify, map, and preserve the femoral nerve during surgical resection to reduce the risk of neurological deficit. Methods Seven patients with retroperitoneal neoplasms underwent eight resections. Compound muscle action potentials (CMAPs) were recorded from needle electrodes placed in the iliacus, quadriceps, and sartorius muscles. Spontaneous electromyography (EMG) was contnuously monitored from the same muscle groups. A handheld monopolar stimulator was used to elicit evoked EMG responses to identify and map the course of the femoral nerve. A stimulating strength of 10 mA was used to map the nerve. The stimulation threshold was tested after neoplasm resection to predict postoperative femoral nerve function. Results Electrical stimulation with CMAP recording and a stimulating strength of 10 mA successfully localized the femoral nerve in six cases. Monitoring with a stimulating threshold between 0.6 and 1.6 mA predicted postoperative femoral nerve preservation after tumor resection in four of the six cases. Conclusion Neurophysiological monitoring using CMAP and spontaneous EMG can protect the femoral nerve during resection of large retroperitoneal neoplasms.     

Influence of fentanyl, alfentanil, and sufentanil on motor evoked potentials

The effects of the opioids fentanyl, alfentanil, and sufentanil on motor pathways were studied in a total of 30 rabbits. Compound muscle action potentials (CMAP) were recorded from the extensor muscles of the upper extremity as well as evoked spinal cord potentials (ESCP) from the thoracic epidural space in response to electrical stimulation of the motor cortex. After establishing stable baseline values, an equipotent intravenous bolus of one of the three opioids was applied that abolished reflex motor response to noxious stimulation. Motor evoked potentials (MEP) were recorded from the time of bolus administration until recovery of MEP amplitudes and latencies. Afterwards, the opioids were administered continuously with cumulative dosage up to total absence of motor evoked response. Our results show a dose-dependent suppression of the CMAP: When reflex movement to noxious stimulation was extinguished, we found a significant (P < .001) reduction of the amplitudes to 34+/-18% (mean +/- SD) in the fentanyl group, to 43+/-24% in the alfentanil group, and to 53+/-20% of baseline values in the sufentanil group. Increasing opioid plasma levels were associated with complete extinction of the CMAP. We hypothesize that the descending volleys within motor pathways are mainly inhibited at a spinal level, because ESCP, particularly the number of spinal I-waves, are not severely affected even when CMAP are completely suppressed. In conclusion, intraoperative monitoring of descending pathways by means of MEP during anesthesia with opioids is feasible at anesthetic plasma concentrations maintaining a surgical level of analgesia. Even with high opioid plasma levels, a valid MEP monitoring could be performed evaluating neural activity of spinal MEP.     

Intraoperative electromyographic techniques for the decision-making of tumor-involved nerve root resection for treating spinal schwannomas

BACKGROUND CONTEXTTotal removal of spinal schwannomas is ideal but it sometimes requires tumor-involved root resection, which increases the risk of postoperative motor deterioration (PMD). Therefore, it is important for clinicians to predict the impact of tumor-involved root resection on motor function in spinal schwannomas.PURPOSETo investigate the role of intraoperative electromyographic (EMG) techniques in decision-making of tumor-involved root resection for treating spinal schwannomas.STUDY DESIGNA retrospective analysisPATIENT SAMPLESixty-eight patients with spinal schwannomas arising from C5-T1 or L3-S1 roots underwent total resection of schwannoma, including tumoral root.OUTCOME MEASURESNerve root activation threshold, free-running EMG signals, visual analogue scale, and American Spinal Injury Association scale.METHODSDuring evoked EMG, nerve root activation threshold for tumoral root stimulation was recorded from muscles anatomically corresponding to tumoral root. During free-running EMG, abnormal EMG signals were identified as irregularly recurrent, monomorphic signals, low frequency (<5 Hz) or absent discharges recorded from muscles innervated by tumoral root. Clinical assessments were performed before, 3 to 5 day's and six months’ after operation.RESULTSSixteen (16 of 68, 23.5%) patients showed PMD, and muscle strength improved or was not affected in the other 52 patients. Absent myogenic responses were observed in 19 patients with non–PMD, and nerve root activation threshold in non–PMD group was higher than that in PMD group (p<.05). Receiver operating characteristic curve revealed that cut-off value of nerve root activation threshold for distinguishing functional and nonfunctional roots was 11.8 mA. A larger number of patients without PMD than with PMD showed abnormal free-running EMG signals (p<.05). At postoperative 6-months’ follow-up, ten patients with muscle weakness after tumor-involved root resection showed functional recovery (full vs. partial recovery: 5 vs. 5), and intraoperative nerve root activation threshold in these patients was higher than that in the other patients without functional recovery (p<.05). Furthermore, there is negative relationship between the duration for full recovery and nerve root activation threshold (p<.05).CONCLUSIONSBoth evoked and free-running EMG can be used as supplementary tests for differentiating functional and nonfunctional tumoral roots in spinal schwannomas, and nerve root activation threshold may be also related to prognosis of patients with muscle weakness caused by tumor-involved root resection. Therefore, intraoperative EMG techniques may provide additional references in decision-making of tumor-involved root resection.     

Recordings of evoked electromyographic responses from the extraocular muscles to monitor the oculomotor, trochlear, and abducens nerve function during skull base and orbital surgery

The methods to record evoked electromyographic responses by micro malleable clip electrodes applied directly to the extraocular muscles are described. This electrophysiological monitoring enables surgeons to localize the ocular motor nerves accurately in the skull base of the middle, posterior fossa, and orbit. In cavernous sinus surgery, electrical stimulation over the dura elicited vigorous responses from the extraocular muscles and subsequently it was possible for the surgeon to avoid severing the ocular motor nerves. In orbital surgery, distended and thinned extraocular muscles were precisely localized and preserved anatomically and functionally. These monitoring methods may play the same role as electrical stimulation to the facial nerves in acoustic neuroma surgery.     

Optimal stimulus duration for extracranial cortical stimulation

Motor cortex stimulation is a new testing area in which either electrical or magnetic fields are used to produce transcranial stimulation of the underlying brain. The resulting signals, recorded from the spinal cord, peripheral nerves, or muscles, are monitored by electromyographic and evoked potential techniques. This report considers the issues in effective stimulation with minimal noxious sensation. Short duration pulses are optimal for electrical fields, and electrodeless stimulation with magnetic fields also makes use of short duration pulses.     

Intraoperative electrophysiological monitoring for functional preservation of the cauda equina during lumbosacral surgery]

Adequate electrophysiological techniques to monitor function of the cauda equina have been proposed for surgery in patients with lumbosacral lipoma or myeloschisis. Motor fibers were identified by electrical stimulation in the operating field with bipolar rectangular impulses of 200 mu sec duration at 2 Hz under 5 mA and compound muscle action potentials (CMAPs) recorded from the leg and anal muscles. By recording CMAPs from the tibialis anterior, the biceps femoris, the gastrocnemius, and the external anal sphincter muscles, all of the roots from the fourth lumbar to the fourth sacral segment were continuously monitored. To spare recording channels, recordings were obtained from the right versus the left side. In our institute, 5 patients have undergone lumbosacral surgery while using this monitoring system, and the results indicated that there was no postoperative neurological exacerbation in any of the cases. According to a combination of the CMAPs produced by stimulation, the segment of the stimulated motor root could be identified electrophysiologically. Monitoring of somatosensory evoked potentials was not performed because this would have required too much time and would have prolonged surgery. However, some sensory fibers, which appeared to be posterior roots of the cauda equina on intraoperative inspection, could be identified indirectly with CMAPs recording because of current spreading from the stimulation to motor fibers.     

Neurophysiologic studies of the penilo-cavernosus reflex: normative data

AIMS: To determine normative values for the penilo-cavernosus reflex on single and double pulse electrical, and mechanical stimulation. METHODS: All men without neurologic disorder, with normal neurologic examination, and with bilaterally normal quantitative electromyography of the external anal sphincter muscles referred for sacral neurophysiologic studies in the years 2003-2005 were included. The penilo-cavernosus reflex was studied on single and double electrical, and mechanical stimulation. Responses were detected by a needle electrode inserted consecutively into the left and right bulbocavernosus muscle. In each subject, latency of the response, and using electrical stimulation, the sensory threshold, reflex threshold and stimulation strength, were determined. Normative values were calculated using parametric statistics and optimal data transformations. RESULTS: In all 26 men with minor non-neurogenic sacral dysfunction reflex responses were recorded using each stimulation technique. Minimal latencies of reflex responses (in msec) were 29.88 +/- 5.65 (upper limit: 39.4), 30.00 +/- 4.11 (36.0), 28.16 +/- 5.80 (35.5) on single electrical, double electrical and mechanical stimulation, respectively. Sensory thresholds (in mA) were 7.80 +/- 2.73 (upper limit: 14.5) and 6.08 +/- 2.30 (10.5), and reflex thresholds (in mA) 25.36 +/- 11.04 (upper limit: 49.6) and 12.78 +/- 6.06 (26.9) on single and double electrical stimulation, respectively. CONCLUSIONS: The obtained normative values for latency on single electrical and mechanical stimulation were similar to those previously published. Additional data on latency on double electrical stimulation, and on the sensory and reflex thresholds on single and double electrical stimulation are expected to increase the diagnostic utility of the penilo-cavernosus reflex.     

Spinal cord and nerve root monitoring during surgical treatment of lumbar stenosis

The author describes application of intraoperative neurophysiologic monitoring to surgical treatment of lumbar stenosis. Benefits of somatosensory and motor evoked potential studies during surgical correction of spinal deformity are well known and documented. Free-running and evoked electromyographic studies during pedicle screw implantation is an accepted practice at many institutions. However, the functional integrity of spinal cord, cauda equina, and nerve roots should be monitored throughout every stage of surgery including exposure and decompression. Somatosensory evoked potentials monitor overall spinal cord function. Intraoperative electromyography provides continuous assessment of motor root function in response to direct and indirect surgical manipulation. Electromyographic activities observed during exposure and decompression of the lumbosacral spine included complex patterns of bursting and neurotonic discharge. In addition, electromyographic activities at distal musculature were elicited by impacting a surgical instrument or graft plug against bony elements of the spine. All electromyographic events provided direct feedback to the surgical team and were regarded as a cause for concern. Simultaneously monitored evoked potential and electromyographic studies protect spinal cord and nerve roots during seemingly low-risk phases of a surgical procedure when neurologic injury may occur and the patient is placed at risk for postoperative myelopathy or radiculopathy.     

A Guidance Channel Seeded With Autologous Schwann Cells for Repair of Cauda Equina Injury in a Primate Model

Background/Objective:

To evaluate an implantable guidance channel (GC) seeded with autologous Schwann cells to promote regeneration of transected spinal nerve root axons in a primate model.

Methods:

Schwann cells were obtained from sural nerve segments of monkeys (Macaca fascicularis; cynomolgus). Cells were cultured, purified, and seeded into a PAN/PVC GC. Approximately 3 weeks later, monkeys underwent laminectomy and dural opening. Nerve roots of the L4 through L7 segments were identified visually. The threshold voltage needed to elicit hindlimb muscle electromyography (EMG) after stimulation of intact nerve roots was determined. Segments of 2 or 3 nerve roots (each ∼8–15 mm in length) were excised. The GC containing Schwann cells was implanted between the proximal and distal stumps of these nerve roots and attached to the stumps with suture. Follow-up evaluation was conducted on 3 animals, with survival times of 9 to 14 months.

Results:

Upon reexposure of the implant site, subdural nerve root adhesions were noted in all 3 animals. Several of the implanted GC had collapsed and were characterized by thin strands of connective tissue attached to either end. In contrast, 3 of the 8 implanted GC were intact and had white, glossy cables entering and exiting the conduits. Electrical stimulation of the tissue cable in each of these 3 cases led to low-threshold evoked EMG responses, suggesting that muscles had been reinnervated by axons regenerating through the repair site and into the distal nerve stump. During harvesting of the GC implant, sharp transection led to spontaneous EMG in the same 3 roots showing a low threshold to electrical stimulation, whereas no EMG was seen when harvesting nerve roots with high thresholds to elicit EMG. Histology confirmed large numbers of myelinated axons at the midpoint of 2 GC judged to have reinnervated target muscles.

Conclusions:

We found a modest rate of successful regeneration and muscle reinnervation after treatment of nerve root transection with a Schwann cell–seeded, implanted synthetic GC. Newer treatments, which include the use of absorbable polymers, neurotrophins, and antiscar agents, may further improve spinal nerve regeneration for repair of cauda equina injury.     

The effect of neuromuscular blockade on pedicle screw stimulation thresholds

STUDY DESIGN: Nerve root stimulation thresholds were studied relative to the level of neuromuscular blockade in patients undergoing lumbar decompression surgery. OBJECTIVES: To determine what levels of intraoperative neuromuscular blockade can be used during pedicle screw stimulation. BACKGROUND DATA: Previous studies of intraoperative pedicle screw stimulation thresholds have failed to determine the effect of neuromuscular blockade on the stimulation threshold. METHODS: Twenty-one roots in 10 patients undergoing lumbar decompression surgery were studied at different levels of neuromuscular blockade. Ninety-five nerve root thresholds were determined relative to level of blockade. RESULTS: Neuromuscular blockade below 80% provides nerve root thresholds similar to thresholds without blockade. CONCLUSIONS: Neuromuscular blockade should be less than 80% when using pedicle screw electrical stimulation testing.     

Stepping-like movements in humans with complete spinal cord injury induced by epidural stimulation of the lumbar cord: electromyographic study of compound muscle action potentials

STUDY DESIGN: It has been previously demonstrated that sustained nonpatterned electric stimulation of the posterior lumbar spinal cord from the epidural space can induce stepping-like movements in subjects with chronic, complete spinal cord injury. In the present paper, we explore physiologically related components of electromyographic (EMG) recordings during the induced stepping-like activity. OBJECTIVES: To examine mechanisms underlying the stepping-like movements activated by electrical epidural stimulation of posterior lumbar cord structures. MATERIALS AND METHODS: The study is based on the assessment of epidural stimulation to control spasticity by simultaneous recordings of the electromyographic activity of quadriceps, hamstrings, tibialis anterior, and triceps surae. We examined induced muscle responses to stimulation frequencies of 2.2-50 Hz in 10 subjects classified as having a motor complete spinal cord injury (ASIA A and B). We evaluated stimulus-triggered time windows 50 ms in length from the original EMG traces. Stimulus-evoked compound muscle action potentials (CMAPs) were analyzed with reference to latency, amplitude, and shape. RESULTS: Epidural stimulation of the posterior lumbosacral cord recruited lower limb muscles in a segmental-selective way, which was characteristic for posterior root stimulation. A 2.2 Hz stimulation elicited stimulus-coupled CMAPs of short latency which were approximately half that of phasic stretch reflex latencies for the respective muscle groups. EMG amplitudes were stimulus-strength dependent. Stimulation at 5-15 and 25-50 Hz elicited sustained tonic and rhythmic activity, respectively, and initiated lower limb extension or stepping-like movements representing different levels of muscle synergies. All EMG responses, even during burst-style phases were composed of separate stimulus-triggered CMAPs with characteristic amplitude modulations. During burst-style phases, a significant increase of CMAP latencies by about 10 ms was observed. CONCLUSION: The muscle activity evoked by epidural lumbar cord stimulation as described in the present study was initiated within the posterior roots. These posterior roots muscle reflex responses (PRMRRs) to 2.2 Hz stimulation were routed through monosynaptic pathways. Sustained stimulation at 5-50 Hz engaged central spinal PRMRR components. We propose that repeated volleys delivered to the lumbar cord via the posterior roots can effectively modify the central state of spinal circuits by temporarily combining them into functional units generating integrated motor behavior of sustained extension and rhythmic flexion/extension movements. This study opens the possibility for developing neuroprostheses for activation of inherent spinal networks involved in generating functional synergistic movements using a single electrode implanted in a localized and stable region.