Hooked-wire Electrodes Research Articles

Methodology for intraoperatively eliciting motor evoked potentials in the vocal muscles by electrical stimulation of the corticobulbar tract

To establish a methodology for recording corticobulbar motor evoked potentials (CoMEPs) from vocal muscles after transcranial electrical stimulation (TES) and direct cortical stimulation (DCS). Twenty-four patients were included in this study (22 for TES, 2 for DCS, 3 for TES plus DCS) that underwent different surgical procedures. We used two methods to elicit CoMEPs: (a) TES by stimulation over C3/Cz or C4/Cz and (b) DCS with a strip electrode placed over the primary motor area (M1) for laryngeal muscles. To record CoMEPs from vocal muscles we used two hook wire electrodes 76 microm of diameter passing through 27 gauge needle endotracheally placed in the vocal muscles after intubation. Recording of CoMEPs in the vocal muscles after TES was successfully performed in 22 patients. TES over the right or left hemisphere elicit responses bilaterally. The onset latencies for the right vocal muscle was 12.4+/-3.1 ms (ipsilateral stimulation) and 12.7+/-2.2 ms (contralateral stimulation) while for the left vocal muscle, onset latency was 12.9+/-2.3 ms (ipsilateral stimulation) and 14.1+/-3.4 ms (contralateral stimulation). In five patients DCS elicited CoMEPs in right and left vocal muscle with latency of 16.6+/-4.7 and 15.6+/-3.7 ms, respectively. The method to elicit and record CoMEPs in vocal muscles shows reliable results and adds one more tool in the armamentarium of intraoperative neurophysiology. This method shows the ability to continuously monitor the functional integrity of corticobulbar pathways, vagal nucleus and laryngeal nerves.

Model of Evoked Rabbit Phonation

We describe a method for eliciting phonation in an in vivo rabbit preparation using low-frequency, bipolar pulsed stimulation of the cricothyroid muscles with airflow delivered to the glottis. Ten New Zealand White breeder rabbits weighing 3 to 5 kg were used in this study. The cricothyroid muscles were isolated bilaterally, and separate pairs of anode-cathode hooked-wire electrodes were inserted into each muscle. A Grass S-88 stimulator and 2 constant-current PSIU6 isolation units were used to deliver bipolar square wave pulses to each cricothyroid muscle, with airflow delivered to the glottis through a cuffed endotracheal tube. Phonation was evoked with a 50-Hz, 4-mA stimulus train of 1-ms pulses delivered to each cricothyroid muscle. The pulse trains were on for 2 seconds and were repeated every 5 seconds over a period of 180 minutes. Airflow was delivered at 143 cm3/s, producing phonation measuring 71 to 85 dB sound pressure level. Evoked phonation is feasible in rabbits by use of bipolar stimulation of the cricothyroid muscles with airflow delivered to the glottis. The in vivo rabbit preparation described may provide a useful small animal option for studies of evoked phonation. From the level and consistency of the adduction observed, we hypothesize that current spreading to the underlying adductor muscles and nerves resulted in neural pathway involvement beyond discrete activation of the cricothyroid muscle, providing sufficient approximation of the vocal folds for phonation.

Genioglossus and Intrinsic Electromyographic Activities in Impeded and Unimpeded Protrusion Tasks

Eight muscles invest the human tongue: four extrinsic muscles have external origins and insert into the tongue body and four intrinsic muscles originate and terminate within the tongue. Previously, we noted minimal activation of the genioglossus tongue muscle during impeded protrusion tasks (i.e., having subjects push the tongue against a force transducer), suggesting that other muscles play a role in the production of tongue force. Accordingly, we sought to characterize genioglossus tongue muscle activities during impeded and unimpeded protrusion tasks (i.e., having subjects slowly and smoothly move the tongue out of their mouth). Electromyographic (EMG) and single motor-unit potentials of the extrinsic genioglossus muscle were recorded with tungsten microelectrodes and EMG activities of intrinsic tongue muscles were recorded with hook-wire electrodes inserted into the anterior tongue body. Tongue position was detected by an isotonic transducer coupled to the tongue tip. Protrusive force was detected by a force transducer attached to a rigid bar. Genioglossus and intrinsic tongue muscles were simultaneously active in both impeded and unimpeded protrusion tasks. Genioglossus whole muscle EMG and single motor-unit activities changed faithfully as a function of tongue position, with increased discharge associated with protrusion and decreased discharge associated with retraction back to the rest position. In contrast, during the impeded protrusion task drive the genioglossus muscle remained constant as protrusion force increased. Conversely, intrinsic tongue muscle activities appropriately followed changes in both tongue position and force. Importantly, we observed significantly higher levels of intrinsic muscle activity in the impeded protrusion task. These observations suggest that protrusion of the human tongue requires activation of the genioglossus and intrinsic protrudor muscles, with the former more important for establishing anterior-posterior tongue location and the latter playing a greater role in the generation of protrusive force. A biomechanical model of these actions is provided and discussed.

Self-Triggered Functional Electrical Stimulation During Swallowing

Hyolaryngeal elevation is essential for airway protection during swallowing and is mainly a reflexive response to oropharyngeal sensory stimulation. Targeted intramuscular electrical stimulation can elevate the resting larynx and, if applied during swallowing, may improve airway protection in dysphagic patients with inadequate hyolaryngeal motion. To be beneficial, patients must synchronize functional electrical stimulation (FES) with their reflexive swallowing and not adapt to FES by reducing the amplitude or duration of their own muscle activity. We evaluated the ability of nine healthy adults to manually synchronize FES with hyolaryngeal muscle activity during discrete swallows, and tested for motor adaptation. Hooked-wire electrodes were placed into the mylo- and thyrohyoid muscles to record electromyographic activity from one side of the neck and deliver monopolar FES for hyolaryngeal elevation to the other side. After performing baseline swallows, volunteers were instructed to trigger FES with a thumb switch in synchrony with their swallows for a series of trials. An experimenter surreptitiously disabled the thumb switch during the final attempt, creating a foil. From the outset, volunteers synchronized FES with the onset of swallow-related thyrohyoid activity (approximately 225 ms after mylohyoid activity onset), preserving the normal sequence of muscle activation. A comparison between average baseline and foil swallows failed to show significant adaptive changes in the amplitude, duration, or relative timing of activity for either muscle, indicating that the central pattern generator for hyolaryngeal elevation is immutable with short term stimulation that augments laryngeal elevation during the reflexive, pharyngeal phase of swallowing.

Laryngeal muscle responses to mechanical displacement of the thyroid cartilage in humans

Speakers may use laryngeal sensory feedback to adjust vocal fold tension and length before initiating voice. The mechanism for accurately initiating voice at an intended pitch is unknown, given the absence of laryngeal muscle spindles in animals and conflicting findings regarding their existence in humans. Previous reports of rapid changes in voice fundamental frequency following thyroid cartilage displacement suggest that changes in vocal fold length modulate laryngeal muscle contraction in humans. We tested the hypothesis that voice changes resulting from mechanical perturbation are due to rapid responses in the intrinsic laryngeal muscles. Hooked wire electrodes were used to record from the thyroarytenoid, cricothyroid, and sternothyroid muscles along with surface electrodes on the skin overlying the thyroid cartilage in 10 normal adults. Servomotor displacements produced consistent changes in the subjects' vocal fundamental frequency at 70-80 ms, demonstrating changes in vocal fold length and tension. No simultaneous electromyographic responses occurred in the thyroarytenoid or cricothyroid muscles in any subjects. Instead, short-latency responses at 25-40 ms following stimulus onset occurred in the sternothyroid muscles, simultaneous with responses in the surface recordings. The sternothyroid responses may modulate long-latency changes in voice fundamental frequency (approximately 150 ms). The absence of intrinsic laryngeal muscle responses is consistent with a lack of spindles in these muscles. Our results suggest that other sensory receptors, such as mucosal mechanoreceptors, provide feedback for voice control.

Timing of Glottic Closure during Swallowing: A Combined Electromyographic and Endoscopic Analysis

We performed a case series to enhance our understanding of the coupling between neuromuscular events and glottic closure. We performed combined flexible video laryngoscopy and electromyography in 4 healthy human subjects. Hooked-wire electrodes were placed in the superior pharyngeal constrictor, longitudinal pharyngeal, cricopharyngeus, thyroarytenoid, genioglossus, suprahyoid, and posterior cricoarytenoid muscles. A flexible endoscope tip was positioned in the oropharyngeal-hypopharyngeal region. The subjects performed multiple trials each of 10-mL normal and super-supraglottic liquid swallows. Arytenoid movement consistently preceded full glottic closure and was associated with cessation of activity of the posterior cricoarytenoid muscle. In 89% of normal swallows, the glottis was partially open in the video frame before bolus passage. The maximum amount of thyroarytenoid electromyographic activity occurred during endoscopic whiteout. When subjects executed a super-supraglottic swallow, early thyroarytenoid activity coincided with arytenoid contact. The initial medialization of the arytenoids is due to a decrease in motor tone of the posterior cricoarytenoid muscle. Full glottic closure typically occurs late in the process of swallowing, with activation of the thyroarytenoid muscle. Shifting of arytenoid medialization and glottic closure earlier in the super-supraglottic swallow indicates that glottic closure is under significant voluntary control.

Laryngeal Electromyography for Adult Unilateral Vocal Fold Immobility: A Survey of the American Broncho-Esophagological Association

Diagnostic and management strategies for adult unilateral vocal fold immobility (UVFI) vary among otolaryngologists. The aim of this study was to determine the current attitudes and practices regarding laryngeal electromyography (LEMG) for the management of adult UVFI within a cohort of subspecialty laryngologists. A 19-item instrument focused on diagnosis and management of adult UVFI was mailed to active members (n = 249) of the American Broncho-Esophagological Association (ABEA). The subset of questions related to LEMG is reviewed in this report. Statistical analysis using a chi2 test was performed. The survey response rate was 34% (n = 84), with 8 surveys returned incomplete because of pediatric-limited practices. Of the respondents, 75% (n = 57) rely on LEMG for evaluation of UVFI, whereas 25% (n = 19) do not use LEMG. Of those who use LEMG, 54% place their own electrodes and 44% interpret the LEMG results themselves. Monopolar electrodes are used by 57% (n = 25), bipolar electrodes by 27% (n = 12), and hooked-wire electrodes by 17% (n = 7). Muscles evaluated by LEMG include the thyroarytenoid (100%), cricothyroid (94%), posterior cricoarytenoid (70%), lateral cricoarytenoid (43%), cricopharyngeus (27%), and interarytenoid (17%). The LEMG is performed in an unblinded fashion by most respondents (85%), and many (66%) feel a more accurate result is obtained when clinical information is known. There was no statistically significant difference in use of LEMG, placement of electrodes, and interpretation of LEMG according to percentage of laryngology practice. The survey results demonstrate congruence among ABEA members in the utility of LEMG in the management of adult UVFI. Some variability was noted in the methods by which LEMG is performed and interpreted.

Suppression of Thyroarytenoid Muscle Responses during Repeated Air Pressure Stimulation of the Laryngeal Mucosa in Awake Humans

Repeated stimulation of the laryngeal mucosa occurs during speech. Single stimuli, however, can elicit the laryngeal adductor response (LAR). Our hypothesis was that the LAR to repeated rapid air pressure stimuli is centrally suppressed in humans. Hooked-wire electrodes were inserted into the thyroarytenoid and cricothyroid muscles on both sides and into the posterior cricoarytenoid muscle on one side. Pairs of air puff stimuli were presented to the mucosa over the arytenoids at pressure levels three times threshold with interstimulus intervals from 250 to 5,000 ms. Bilateral thyroarytenoid responses occurred at around 150 ms to more than 70% of the initial stimuli. With repeated presentation at intervals of 2 seconds or less, the percent occurrence decreased to less than 40% and response amplitudes were reduced by 50%. Central suppression of adductor responses to repeated air puff stimuli may allow speakers to produce voice without eliciting reflexive spasms that could disrupt speech.

Intraoperative electromyographic monitoring of the recurrent laryngeal nerve in reoperative thyroid and parathyroid surgery

Injury to the recurrent laryngeal nerve (RLN) is a rare complication of initial thyroid and parathyroid surgery, but the prevalence is much higher in the reoperative setting. The use of continuous, intraoperative electromyographic monitoring of the RLN has been suggested to improve the safety of cervical explorations. Outcomes of a group of reoperative thyroid and parathyroid cases that used EMG monitoring with endoscopically applied hook-wire electrodes were compared with a group of cervical reoperations without monitoring. Office laryngoscopy (indirect or fiberoptic) was used to evaluate and follow suspected RLN complications. Electromyography was used in 52 cervical reexploration procedures. Patients averaged 1.8 previous explorations (range, 1-7 explorations) and underwent procedures for parathyroid (31%) and/or thyroid (77%) disease (overall, 72% malignant). The non-monitored group had 59 patients with similar characteristics. Only 1 permanent nerve complication in each group was unintended (electromyography, 1.9%; non-electromyography, 1.7%). Seven false-negative and 2 false-positive electromyographic findings occurred. No complications resulted from placement of the electromyography electrodes. Intraoperative electromyographic monitoring of the RLN in reoperative neck surgery can be performed safely but did not decrease RLN complications in this study. Experience and routine nerve exposure remain crucial to the minimization of RLN complications.

Morbidity Following Central Compartment Reoperation for Recurrent or Persistent Thyroid Cancer

To determine the incidence of recurrent laryngeal nerve injury and hypoparathyroidism, we reviewed our experience with central compartment reoperation. Patients underwent preoperative ultrasonography and magnetic resonance imaging of the neck. Ultrasound-guided fine-needle aspiration biopsy was performed and demonstrated evidence of tumor in 15 patients. At the time of surgery, hook wire electrodes were placed endoscopically into 1 or both vocal cords to monitor the integrity of the recurrent laryngeal nerve. The study population comprised 20 patients who had undergone reoperative central compartment dissections between the years 1997 and 2001. There were 15 women and 5 men whose mean age was 49.4 years. All of the patients had prior total or subtotal thyroidectomy, and 4 patients had prior neck dissections. A primary thyroid cancer recurrence in the thyroid bed was present in 7 patients, and the remainder of the patients had cytological evidence of paratracheal or mediastinal metastases. A single patient had evidence of distant metastases involving the lung. Short- and long-term postoperative morbidity. Of the 20 patients, 18 had histologic evidence of metastases to the paratracheal lymph nodes, whereas 8 patients had metastases involving the anterior mediastinal lymph nodes. The mean number of lymph nodes removed was 6.5, and the mean number of positive lymph nodes was 4.7. None of the patients with normal preoperative laryngeal function had postoperative recurrent laryngeal nerve paresis or paralysis. There were 18 patients with normal preoperative parathyroid function. Four patients developed transient postoperative hypocalcemia. All 4 patients with transient postoperative hypocalcemia are currently eucalcemic. A single patient continues to receive calcium and calcitriol supplementation 1 month following her third central compartment dissection for recurrent thyroid cancer. Reoperation for recurrent or persistent thyroid cancer presents a significant challenge. However, intraoperative recurrent laryngeal nerve monitoring and preservation of the vascular pedicle of the parathyroid glands has reduced the morbidity of reoperative central compartment dissections to acceptable levels. Revision surgery in the central compartment of the neck is compatible with successful eradication of recurrent thyroid cancers and acceptable morbidity.

Identification of swallowing cortex by means of magnetoencephalography in the normal human

Problem: Swallowing is a complex motor sequence; it is initiated voluntarily by the act of assumed cerebral cortex, and is subsequently evoked by peripheral inputs to the brainstem essentially in the pharyngeal stage. Little is known about the mechanism of transition from cortical initiation to pharyngeal reflexogenic stage of swallowing, and about the swallowing representation of the cerebral cortex and its functional role in pharyngeal swallowing. Methods: Studies were performed in 6 healthy adult volunteers. Electromyographic (EMG) activity of the thyrohyoid (TH) muscle was recorded with platinum bipolar hooked wire electrodes as an indicator for pharyngeal swallowing. Magnetoencephalographic (MEG) were measured by means of 37 channel SQUID and averaged 32 to 128 times that of swallowing in each subject with the reference of the TH EMG onset. The origin of the current dipole related to the pharyngeal swallowing was calculated and localized in the cerebral surface. Results: Calculated equivalent current dipoles related to the oropharyngeal swallowing were observed 50 to 100 msec prior to the TH EMG onset, which lasted until the pharyngeal stage of swallowing. These dipoles were located around the opercum adjacent to the insula on the superimposed MR images. After the surface application of 1 to 2 mL of 4% lidocaine to pharyngo-laryngeal mucosa, those current dipoles could not be identified anymore. Conclusion: Swallowing-related cortex located in and around the opercum not only initiates oral stage of swallowing, but significantly affects the triggering of pharyngeal swallowing. Significance: The results of this study give us a unique understanding of oropharyngeal dysphagia caused by lesion of the swallowing-related cortex and its descending pathway to the brainstem. Applying MEG study to clinical cases may provide a new aspect of pathophysiology in dysphagia. Support: None reported.

Influences of laryngeal afferent blockade on laryngeal muscle activity during speech

Problem: A previous study determined that sensory blockade reduced symptoms in spasmodic dysphonia. The purpose of this study was to determine how laryngeal afferent feedback blockade alters laryngeal muscle activity during speech, to explain this benefit in patients with spasmodic dysphonia. Methods: We used hooked wire electrodes to record from intrinsic laryngeal muscles (thyroarytenoid, cricothyroid, and posterior cricoarytenoid) during sentence production in subjects with either adductor and abductor spasmodic dysphonia before and after bilateral superior laryngeal nerve blockade with lidocaine. Prior to the block, sensory thresholds were determined for air puff stimuli presented to the mucosa overlying the arytenoid cartilages. Following the block, laryngeal muscle activity during production of the same sentences was recorded again and sensory testing confirmed blockade on both sides. Measures included the mean muscle activity during the first syllable of each sentence, syllable duration, and the pre-phonatory interval between muscle activity onset and voice onset for the first syllable of each sentence. Results: No changes occurred in mean muscle activity level following afferent blockade in all 3 muscles. Significant within-subject reductions were found in the duration of the first syllable of the sentence and in the pre-phonatory interval between thyroarytenoid muscle activity onset and vocalization onset for speech. The pre-phonatory interval decreased in 7 of the 8 subjects. No significant changes in pre-phonatory interval were found in the posterior cricoarytenoid or cricothyroid muscles. Conclusion: Symptom benefits following a reduction in afferent feedback are not a result of reduced muscle activity level but may reflect changes in central patterning of muscle activity in patients with spasmodic dysphonia. Significance: These results provide further understanding of the pathophysiology of symptom generation in spasmodic dysphonia. Support: The research was supported by the National Institute of Neurological Disorders and Stroke, 1 Z01 NS002980-05.

The Role of the Pars Recta and Pars Oblique of Cricothyroid Muscle in Speech Production

To evaluate the functional difference of the pars recta and pars oblique during speech production, the electromyographic activities of these muscles were measured in thyroidectomized patients. The hooked wire electrodes were inserted into the normal side of the bellies of the pars recta and pars oblique bundles. Two kinds of sentences were used to obtain pitch changes, a simple interrogative sentence and a complex sentence with stress contrasts. The pars recta and pars oblique were simultaneously activated for initial lengthening and tensing of vocal folds to produce speech. The pars oblique might be initially more active than the pars recta at the initial task of speech and the pars recta might be more active at the pitch elevation in the interrogative sentence and the stress contrast of the complex sentence. The maximum electromyographic activity range of the pars recta and pars oblique seemed to be nearly equal. These results demonstrated that the patterns of electrical activities of the two bellies are different during speech and the combined activities of the pars recta and pars oblique are important in the adjustment of the vocal fold length during speech.

Laryngospasm and diaphragmatic arrest in immature dogs after laryngeal acid exposure: a possible model for sudden infant death syndrome.

Laryngopharyngeal reflux has been proposed as a possible cause of sudden infant death syndrome (SIDS). We investigated the efferent laryngeal and diaphragmatic responses to acid exposure on the laryngeal mucosa using a neonatal canine model. Electromyographic (EMG) recordings from the thyroarytenoid muscle and the diaphragm were measured with hooked-wire electrodes. Reproducible laryngospasm responses occurred in all animals after laryngeal exposure to hydrochloric acid at pH 2.0 or less. Laryngospasm occurred in combination with tachypnea and increased diaphragmatic activity in most of the animals. Laryngospasm was associated with prolonged apnea and total cessation of diaphragmatic EMG activity in 1 animal, and in another, initial tachypnea was followed by erratic diaphragmatic activity and brief apnea. Laryngeal acid exposure (below pH 2.0) causes laryngospasm and may result in paradoxical apneic events in neonatal dogs. Acid-induced, laryngospasm-associated apnea may represent a potential cause of SIDS, and the immature dog appears to be an excellent model for further investigations.

Laryngeal reflexomyographic responses in rabbits: a neurolaryngological study of glottal movement.

The role of the laryngeal reflex in glottal movement has been reported, but its mechanism remains unclear. To further investigate the neurophysiological characteristics of glottal movement, we recorded the laryngeal reflexomyographic responses (LRMRs) to electrical stimulation of the superior laryngeal nerve (SLN) in rabbits. The procedure involved simultaneous recording of the LRMRs from the thyroarytenoid muscles by means of bipolar hooked wire electrodes after electrical stimulation to the SLN. The results demonstrated characteristic patterns of the responses, consisting of R1 and R2, similar to those found in humans. The R1 response was obtained with a latency of 10.7 +/- 0.78 ms. The ipsilateral R2 response was obtained with a latency of 43.76 +/- 4.67 ms in all rabbits, and the contralateral R2 response with a latency from 42.6 to 50.2 ms in 4 rabbits. It was concluded that LRMRs may serve as a potential central laryngeal function test in the investigation of glottal movement control.

Muscles alive!

As the Haskins work on speech perception revealed the importance of the contribution to speech perception of time-varying aspects of the acoustic signal, Frank Cooper began a search for techniques to make detailed studies of the dynamic aspects of articulation. While some important work using cinefluorography, by Moll and his associates, had appeared in the 1960s, increasing concern about the hazards of radiation exposure severely limited the collection of substantial bodies of data by such a means. Frank suggested that recording the muscle signals underlying articulator movement, using the techniques suggested by Basmajian for various nonarticulatory systems, might have important advantages. To solve the problem of recording from tongue surfaces, he developed a suction electrode system. However, a later collaboration with researchers from the University of Tokyo using hooked wire electrodes provided better isolation of muscle fiber groups with complex relations to articulator surfaces. This work has led to present day modeling of the relationship of muscles to movement, although substantial problems remain for the work of future generations.

A New Method of Monitoring the Effect of Muscle Relaxants on Laryngeal Muscles Using Surface Laryngeal Electromyography

A New Method of Monitoring the Effect of Muscle Relaxants on Laryngeal Muscles Using Surface Laryngeal Electromyography

Electrode Impedance in Neurophysiologic Recordings: 3. Effects on Recorded Signals

ABSTRACT.EEG and evoked potential (EP) recordings depend on the properties of the electrodes used. The current set of experiments explores the effects of electrode properties on signal recordings in the absence of intrinsic noise or electromagnetic interference (EMI). The entire electrode-amplifier unit can be considered as a single electronic device with its own characteristic frequency response, which is more complex than that expected simply on the basis of setting the high- and low-frequency filters on the amplifier itself. These experiments demonstrate that the response of platinum-iridium pin electrodes and gold cup electrodes is decreased by roughly 50% for 1 Hz signals when compared to their responses at 100 Hz. Sensitivity increases again for a narrow band of frequencies below 1 Hz. This effect is most dramatic for stainless steel hookwire electrodes, which demonstrate much higher sensitivity to signals in the .1–1 Hz waveband than in the 1–1000 Hz waveband, although their sensitivity increases above 1000 Hz. Although similar responses are seen with electrodes placed in physiologic saline and embedded in a potato, dramatically different responses are recorded when the same electrodes are placed in a saturated saline solution. Changing electrode impedances can have complex and substantial effects on the frequency-dependent gain of the electrode-amplifier unit as well.

甲状腺手術時における反回神経の術中モニター

One of the major complications of thyroid surgery is damage to the recurrent laryngeal nerve (RLN). This injury can be avoided by intraoperative nerve identification. A technique is described for electromyographic monitoring of the RLN during thyroidectomy. The RLN was electrically stimulated with a hand-held bipolar stimulator, delivering a voltage of 1 to 7 V. Hooked-wire electrodes were placed in the thyroarytenoid muscles through the cricothyroid membrane. Laryngeal evoked responses were readily recognized by a EMG waveform. No responses were evoked by stimulation of tissue 1 or 2 mm adjacent to the RLN. This procedure can be used to confirm the presence of the RLN during the course of the operation.

Comparison of concentric needle versus hooked-wire electrodes in the canine larynx

BACKGROUND: The use of a specific electrode type in laryngeal electromyography has not been standardized. Laryngeal electromyography is usually performed with hooked-wire electrodes or concentric needle electrodes. Hooked-wire electrodes have the advantage of allowing laryngeal movement with ease and comfort, whereas the concentric needle electrodes have benefits from a technical aspect and may be advanced, withdrawn, or redirected during attempts to appropriately place the electrode. OBJECTIVES: This study examines whether hooked-wire electrodes permit more stable recordings than standard concentric needle electrodes at rest and after large-scale movements of the larynx and surrounding structures. A histologic comparison of tissue injury resulting from placement and removal of the two electrode types is also made by evaluation of the vocal folds. METHODS: Electrodes were percutaneously placed into the thyroarytenoid muscles of 10 adult canines. Amplitude of electromyographic activity was measured and compared during vagal stimulation before and after large-scale laryngeal movements. Signal consistency over time was examined. Animals were killed and vocal fold injury was graded and compared histologically. RESULTS: Waveform morphology did not consistently differ between electrode types. The variability of electromyographic amplitude was greater for the hooked-wire electrode ( p < 0.05), whereas the mean amplitude measures before and after large-scale laryngeal movements did not differ ( p > 0.05). Inflammatory responses and hematoma formation were also similar. CONCLUSIONS: Waveform morphology of electromyographic signals registered from both electrode types show similar complex action potentials. There is no difference between the hooked-wire electrode and the concentric needle electrode in terms of electrode stability or vocal fold injury in the thyroarytenoid muscle after large-scale laryngeal movements. (Otolaryngol Head Neck Surg 1998;118:655-62.)