Somatosensory evoked potential monitoring during closed humeral nailing: a preliminary report.

OBJECTIVES: To assess the role of intraoperative somatosensory evoked potential (SSEP) monitoring of the radial and median nerves in preventing iatrogenic nerve injury during closed, locked intramedullary (IM) nailing of the humerus. DESIGN: Prospective clinical study. SETTING: Pacific Northwest Level One trauma center and Southern California military medical center. PATIENTS: Thirteen patients with indications for surgical stabilization of fractures of the humeral diaphysis and either unknown neurologic status of the affected limb or anticipated difficult reduction maneuvers due to fracture complexity or displacement. INTERVENTION: Closed, antegrade or retrograde locked IM nailing of the humerus was attempted while intraoperative monitoring of the radial and median nerves with SSEP was performed. MAIN OUTCOME MEASUREMENTS: Intraoperative radial and median nerve SSEP changes during closed fracture manipulation, guide rod insertion, reaming, and humeral nail placement. RESULTS: Baseline recordings were obtained in twelve of thirteen patients for both the radial and median nerves. An absence of radial nerve signal in one patient with a closed head injury prompted an open procedure, revealing entrapment of the radial nerve in the fracture. Intraoperative SSEP changes were observed in two of the twelve remaining patients during fracture manipulation and distal interlocking. The signal amplitude returned after discontinuation of manipulation and traction, and alteration of the interlocking maneuver. No neurologic deficits were noted in these two patients. CONCLUSIONS: Intraoperative radial nerve SSEP monitoring appears to reliably reflect the status of the radial nerve in those patients with a humerus fracture. In three of eleven patients, intraoperative signal changes prompted a change in surgical plan. In no patient did there appear to be evidence of iatrogenic nerve injury.

Intraoperative monitoring of nerve repairs.

These examples illustrate the interplay of the electrophysiologic techniques of SEP, EMG, NCAPs, and nerve conduction studies to achieve the goals of monitoring, guiding, identifying and localizing, and assessing nerve function. Through their successful application, intraoperative neurophysiology moves from solely monitoring to serving as an electrophysiologic aid to the surgeon. Using all of these techniques provides a comprehensive analysis of nerve function. The overall goal is both to prevent intraoperative neural compromise and to optimize postoperative outcome by providing the surgeon with the best possible information regarding the functional condition of the nerves under investigation.

Cerebral N-acetylaspartate is low in patients with multiple sclerosis and abnormal visual evoked potentials.

PURPOSE: Our purpose was to compare cerebral proton MR metabolite changes in patients with multiple sclerosis (MS) and abnormal visual evoked potentials (VEPs) with those in MS patients with normal VEPs. METHODS: Seventeen subjects with clinically definite MS were studied with VEPs and MR spectroscopic imaging. Proton MR metabolites were measured using a fast spectroscopic imaging technique called proton echo-planar spectroscopic imaging (PEPSI). Kurtzke's Expanded Disability Status Scale (EDSS) score was also ascertained for each subject to obtain a clinical rating. Twelve regions of interest within the visual pathway of the cerebrum were evaluated for levels of N-acetylaspartate (NAA), choline, creatine, and the presence or absence of MR-detectable lesions. RESULTS: PEPSI NAA values (water-normalized, CSF-corrected) were significantly lower in MS subjects with abnormal VEPs than in subjects with normal VEPs. MR-detectable lesion fractions and EDSS scores were also significantly different between the two VEP groups, but NAA comparison had a P value 100 times less than either of these measures. CONCLUSION: In patients with MS, NAA measurements in the optic pathways of the brain were sensitive to VEP abnormalities. NAA was more sensitive to VEP changes than were choline, creatine, MR-detectable lesions, and EDSS score.

Spine and scalp recordings as a function of intensity. A model for changes during spinal cord monitoring.

STUDY DESIGN: Spinal cord monitoring has used both spine and scalp recordings as indicators of spinal cord integrity. The relative merits of spine or scalp recordings to predict the quality of the afferent volley in the somatosensory pathway were addressed in this study by using various stimulus intensities as a way to model alterations of the size of the afferent volley. OBJECTIVES: The results were analyzed to determine the correlation of central recordings taken at the spine or scalp with peripheral recordings. SUMMARY OF BACKGROUND DATA: Spinal cord monitoring with somatosensory evoked potentials has been achieved with recordings of signals generated by either the spinal cord or the somatosensory cortex. Spine recordings are thought to be more stable, yet little evidence exists to document this statement. METHODS: Seven patients were studied in the course of standard intraoperative spinal cord monitoring. Responses were recorded at the popliteal fossa, thoracic epidural, cervical spine, and scalp to tibial nerve stimulation at intensities varying from 0.5 to 2.0 times muscle twitch threshold. RESULTS: Normalized amplitudes of the response at the popliteal fossa were used to reflect the magnitude of the afferent volley. The amplitudes of the popliteal fossa response showed a high correlation (r = 0.90) with normalized amplitudes of epidural and cervical spine responses and moderate correlation (r = 0.49) with normalized amplitudes of scalp responses. The width of the 95% confidence limits for the inverse prediction of the afferent volley from epidural and cervical responses was nearly a third narrower than that from scalp responses. At low stimulus intensities, scalp responses were consistently observed when spine responses were absent, and scalp responses had lower response thresholds than did spine responses. The latencies of the popliteal fossa responses were not well correlated with latencies of either the epidural or cervical responses. CONCLUSIONS: These correlation and inverse prediction data suggest that the size of an afferent volley may be predicted more accurately by spine responses than by scalp responses. The presence of scalp responses at intensities too low to elicit detectable spinal-level responses suggests that scalp responses may be considered a sensitive indicator of a minimal afferent volley.

Inhibition of neutrophil adhesion does not prevent ischemic spinal cord injury.

Paraplegia may occur after transient aortic occlusion as a consequence of primary ischemia to the spinal cord or injury during the reperfusion period. In animal models of ischemia/reperfusion there is evidence that reperfusion injury may be modulated partially by neutrophils. The efficacy of the neutrophil adherence blocking murine monoclonal antibody (MAb 60.3) was assessed in spinal cord ischemia/reperfusion in rabbits. Spinal cord ischemia was accomplished by balloon catheter occlusion of the infrarenal aorta. Neurologic assessment was graded as normal, partial neurologic deficit, or complete paralysis. Electrophysiologic monitoring with somatosensory evoked potentials was used to determine the optimal length of time of occlusion. Animals were treated randomly with 2 mg/kg of intravenous Mab 60.3 (n = 8) or saline solution (n = 9) with the investigator unaware of treatment. Mean occlusion times were no different between groups (control, 32.7 +/- 3.6 minutes versus MAb, 32.4 +/- 6.0 minutes). Five (55%) saline-treated and four (50%) MAb 60.3-treated animals became paraplegic. Animals with initial paraparesis all progressed to flaccid paraplegia within 24 hours. We conclude that spinal cord injury after transient aortic occlusion is independent of the CD11/CD18 glycoprotein complex of the neutrophil. Injury in this setting may occur during ischemia and thus may not be dependent on neutrophils or reperfusion.

The efficacy of femoral nerve intraoperative somatosensory evoked potentials during surgical treatment of thoracolumbar fractures.

Somatosensory evoked potential (SEP) monitoring of thoracolumbar procedures typically includes posterior tibial and peroneal nerve recordings. The addition of femoral nerve SEP monitoring, however, should better predict the evolution of postoperative neurologic deficits affecting the midlumbar roots. To assess the value of intraoperative femoral SEPs, 26 cases of traumatic injury to the thoracolumbar spine between T12 and L4 were prospectively assessed. Twenty-four had clear femoral nerve responses bilaterally recorded from an epidural electrode. Five had significant intraoperative SEP changes: one had isolated femoral nerve changes, two had only peroneal or tibial nerve changes, and two had concomitant changes in both femoral and peroneal or tibial nerves. Loss of the femoral nerve response in one patient was correlated with marked postoperative knee extensor weakness, in spite of immediate action taken by the surgeon. The authors conclude that femoral nerve SEPs provide an effective tool to monitor the midlumbar roots intraoperatively.

Dermatomal somatosensory evoked potentials in the diagnosis of lumbosacral spinal stenosis: comparison with imaging studies.

Dermatomal somatosensory evoked potentials (DSEPs) and computerized tomography/magnetic resonance (CT and/or MR) images were retrospectively analyzed to evaluate their relationship in the diagnosis of lumbosacral spinal stenosis (SS). Of 155 patients referred for DSEPs with a clinical suspicion of lumbosacral SS, 58 met the inclusion criteria. DSEP abnormality was defined as: (1) N1 latency absent or greater than 2.5 SD; (2) side-to-side latency difference greater than 2 SD; (3) amplitudes greater than 2 SD below the mean; or (4) amplitude ratio greater than 2 SD. Involvement of two or more DSEP levels by any of the above criteria was labeled multiple root disease (MRD). Involvement of one level was labeled single root disease (SRD). Images were reviewed independently by a neuroradiologist. Results revealed 54 subjects with SS by imaging; 42 had MRD and 8 had SRD by DSEPs. Sensitivity for MRD and SS was 78%, and for MRD plus SRD and SS was 93%.

Dermatomal somatosensory evoked potentials: cervical, thoracic, and lumbosacral levels.

Somatosensory evoked potentials were recorded at the scalp to stimulation of the skin at C4, C5, C6, C7, C8, T2, T4, T6, T8, T10, T12, L2, L3, L4, L5, and S1 dermatomes and of the tibial nerve. Stimulation and recording techniques are described. Data were obtained from 41 normal subjects, 25 of which had all 16 dermatomes studied. Wave form descriptions include both typical and atypical presentations. Descriptive statistics for latency, amplitude, left to right comparisons, and level to level comparisons are given. Scalp response latencies for distal extremity dermatomes were well correlated with height but not with vertebral column length, whereas latencies for thoracic dermatomes were not well correlated with either height or vertebral column length. Since scalp response amplitude data were not normally distributed, they were logarithmically transformed and minimum and maximum limits for 1 S.D., 2 S.D., and 3 S.D. derived. Left/right amplitude ratios were similarly treated. Level to level comparisons were achieved with a Z score concordance analysis, which showed that the response values at one level can be used to predict the response values at another level.

Comparison of median and posterior tibial nerve somatosensory evoked potentials in ambulatory patients with definite multiple sclerosis.

Somatosensory evoked potentials (SEPs) were recorded for stimulation of both median nerves and both posterior tibial nerves in control subjects and in subjects with multiple sclerosis (MS) of several years' duration, who were ambulatory and not experiencing exacerbation. Documentation of peripheral nerve conduction revealed no abnormalities in any of the subjects. Centrally, abnormal responses to median and posterior tibial nerve stimulation were found at the spinal level and/or the scalp in nearly all MS patients. Using the latency of the initial negativity of scalp SEPs, posterior tibial SEPs were abnormal significantly more often than median SEPs. Calculations suggested a significant increase in spinal conduction time. The high incidence of abnormal SEPs does not support any substantial physiological recovery in this group of MS patients.

Spatial distribution of modalities and receptive fields in sensorimotor cortex of awake cats.

A sample of 504 single neurons isolated in three curvilinear arrays of 10 closely spaced tracks in primary somatosensory and in pericruciate sensorimotor cortex was studied in two awake, restrained domestic cats. Modality sensitivity and receptive field size and location were assessed for each neuron, along with response adaptation rate and state of arousal at the time of recording. Reconstruction of the spatial distribution of these response properties failed to show any simple organization, beyond general somatotopy. The spatial distribution of modality sensitivities was quantitatively tested in relation to a strict columnar model and to a random model; the data could not be clearly distinguished from the random model, in any of the three recording arrays. Observations made on two or more neurons isolated simultaneously at the same recording site revealed that few shared both modality and receptive field (RF) in common. Among the simultaneously recorded neurons, five-ninths showed disparate modality sensitivities and two-thirds showed limited or no RF overlap. Many pairs of neurons showing the same modality sensitivity showed limited or no RF overlap, and many pairs showing partial or complete RF overlap showed disparate modality sensitivities. Hence, the data failed to support any model of cerebral organization that features local, bounded regions within which all neuron response properties are the same and, in particular, the model of columnar organization. On the other hand, models that feature intermingled local clusters of neurons (a cluster consists of neurons that share the same response properties) are not excluded by the data.

Physical medicine and rehabilitation: somatosensory evoked potentials in monitoring spinal operations.

The Scientific Board of the California Medical Association presents the following inventory of items of progress in physical medicine and rehabilitation. Each item, in the judgment of a panel of knowledgeable physicians, has recently become reasonably firmly established, both as to scientific fact and important clinical significance. The items are presented in simple epitome and an authoritative reference, both to the item itself and to the subject as a whole, is generally given for those who may be unfamiliar with a particular item. The purpose is to assist busy practitioners, students, research workers, or scholars to stay abreast of these items of progress in physical medicine and rehabilitation that have recently achieved a substantial degree of authoritative acceptance, whether in their own field of special interest or another.The items of progress listed below were selected by the Advisory Panel to the Section on Physical Medicine and Rehabilitation of the California Medical Association and the summaries were prepared under its direction.

Somatosensory evoked potentials after removal of somatosensory cortex in man.

Somatosensory evoked potentials (SEPs) to median nerve, ulnar nerve, thumb, middle finger, and posterior tibial nerve stimulation were recorded in a patient with a discrete resection of part of the postcentral somatosensory cortex as a treatment for focal epilepsy. Comparison of the different stimulation sites confirmed electrophysiologically the restricted locus of the lesion. The results strongly suggest that the early negative component (N20) and subsequent components recorded postcentrally are of cortical origin and depend upon postcentral gyrus cytoarchitectonic areas 3, 2, and 1. Moreover, these postcentral SEPs are distinct from precentrally recorded activity.

Heterosexual, autosexual and social behavior of adult male rhesus monkeys with medial preoptic-anterior hypothalamic lesions.

Bilateral radiofrequency lesions were made in the medial preoptic-anterior hypothalamic (MP-AH) area of 6 adult male rhesus monkeys; 5 sham-lesioned subjects served as controls. Behavioral analysis consisted of observations on copulatory behavior, yawning, masturbation and some aspects of social behavior. MP-AH lesions reduced or completely eliminated the display of manual contacts of the partner, mounts, intromissions and ejaculations without interfering with masturbation. Yawning, a sexually dimorphic behavior, was not affected either, Measure of several social behaviors indicated no evidence of social withdrawal or other aberrance of social interactions, which might have led to the decline in heterosexual behavior. The results with regard to copulatory behavior were consistent with the effects of MP-AH lesions in rats, cats and dogs. In rhesus monkeys it appears as though the MP-AH region is specifically involved in the mediation of heterosexual copulation and is not vital to the performance of other forms of male sexual activity such as masturbation. Also the MP-AH is not critical for the display of all sexually dimorphic behaviors. The types of behavioral change in MP-AH lesioned subjects differed to some extent from those following castration, indicating that the effects of the lesions cannot be explained as basically that of functional castration.