The Laryngoscope C 2014 The American Laryngological, V

Rhinological and Otological Society, Inc.

Comparison of Microsuspension Laryngoscopy Positions: A Randomized, Prospective Study Libby J. Smith, DO; Jenna M. Trout, BS; Shaum S. Sridharan, MD; Joan R. Guyer, BS; Grace E. Owens; April J. Chambers, PhD; Clark A. Rosen, MD Objectives/Hypothesis: To evaluate muscle fatigue and participant pain in the upper back, cervical, and arm muscles associated with microlaryngeal surgery (MLS) in standardized favorable and unfavorable ergonomic positions. Study Design: Individual randomized counterbalanced design. Methods: Electromyographic sensors were placed on targeted muscles involved with performing MLS on 18 otolaryngology residents/fellows. Subjects were randomly counterbalanced in both favorable and unfavorable positions while completing simulated laryngeal microsurgical tasks. Participants reported their extent of muscle discomfort in targeted muscle regions on a standardized survey. Results: Muscle fatigue and self-reported pain were reduced, and productivity was improved in the favorable position. In the lower trapezius, significantly less muscle activation (P 5 0.025) and less pain (P < 0.05) were found while in the favorable position compared to the unfavorable position. Conclusion: This is the first study to demonstrate electromyographic evidence of decreased muscle activation and fatigue, in addition to self-reported pain with a more favorable microsurgical ergonomic position, which may help surgeons avoid musculoskeletal injuries. Key Words: Surface electromyography, EMG, ergonomics, microlaryngeal surgery, laryngeal surgery, laryngeal surgical ergonomics, surgical ergonomics. Level of Evidence: 1b. Laryngoscope, 00:000–000, 2014

INTRODUCTION Musculoskeletal symptoms associated with performing microsuspension laryngeal surgery (MLS) are common. Wong et al. found that 83% of otolaryngology survey respondents reported the presence of musculoskeletal symptoms while performing MLS, with some symptoms even persisting 48 hours after performing surgery.1 Accommodations to avoid pain associated with MLS need evaluation. Based on the National Institute of Occupational Safety and Health review, microsuspension laryngoscopy is an inherently at-risk maneuver.2 A compelling relationship exists between musculoskeletal disorders and certain work-related factors such as static contraction, fixed work postures, neck flexion greater than 15 , and

Additional Supporting Information may be found in the online version of this article. From the University of Pittsburgh Voice Center, Department of Otolaryngology, University of Pittsburgh School of Medicine (L.J.S., S.S.S., C.A.R.); and the Department of Bioengineering, University of Pittsburgh (J.M.T., J.R.G., G.E.O., A.J.C.), Pittsburgh, Pennsylvania, U.S.A. Editor’s Note: This Manuscript was accepted for publication August 25, 2014. Presented in the American Laryngological Association (ALA) poster session at the Combined Otolaryngological Spring Meeting, Las Vegas, Nevada, U.S.A., May 14–15, 2014. The authors have no funding, financial relationships, or conflicts of interest to disclose. Send correspondence to Libby J. Smith, DO, 1400 Locust St., Bldg B, Suite 11500, Pittsburgh, PA 15219. E-mail: [email protected] DOI: 10.1002/lary.24932

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holding a limb in a flexed or extended position. Many of these at-risk behaviors are inherent to MLS. Statham et al. was the first to look at the ergonomics specifically related to MLS.3 In that study, three fellowship-trained laryngologists reached a consensus for the most comfortable (favorable) surgeon positioning. Regardless of variable surgeon heights, two measurements remained constant: neck flexion 0 to 10 and laryngoscope angle 40 from the horizon. The patient bed and microscope were manipulated to achieve this favorable position. This consensus-based favorable position with chair-based arm support was then compared against two other arm positions, Mayo stand arm support, and no arm support. Chair, microscope, laryngoscope, and bed positioning remained constant throughout the different surgeon positions with variable arm support. Arm support was more ergonomically favorable than not having arm support, as determined by using the Rapid Upper Limb Assessment (RULA) tool. RULA is a validated survey method developed to assess ergonomic postures in the occupational setting and estimate risk of injury.4 Despite this compelling data, 38% of otolaryngologists continue to report not using arm support during MLS.1 This highlights the lack of insight regarding the ergonomics of performing MLS. Surgeons are unknowingly placing themselves at higher risk of musculoskeletal injury. In general terms, fatigue is present once there is an inability to sustain an effort related to mechanical performance.5 Fatiguing effects in muscles are due to Smith et al.: Comparison of Microlaryngoscopy Positions

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Fig. 1. Subjects were asked to palpate each point in order, using the instrument in the opposite hand. They were instructed to be precise. The number of repetitions was counted.

inadequate perfusion, depletion of energy, and buildup of metabolites such as lactic acid and excessive hydrogen atoms.6 Several physiological manifestations of fatigue can be quantitatively measured using surface electromyography (EMG) sensors that record myoelectric signals. The goal for our study is to compare the ergonomics of one favorable and one unfavorable MLS position during a standardized simulated MLS task with regard to muscle activity and fatigue, surgeon-perceived musculoskeletal discomfort, and the number of repetitions of the MLS task. We hypothesize that muscle fatigue and musculoskeletal symptoms will decrease, whereas repetitions will increase when subjects are in the favorable ergonomic position.

MATERIALS AND METHODS Residents and fellows from the training program at the University of Pittsburgh School of Medicine, Department of Otolaryngology, were recruited. Informed consent, approved by the University of Pittsburgh Institutional Review Board, was obtained for all participants. Pilot studies were conducted to determine

appropriate targeted muscles, study time duration, rest time duration, and the most appropriate simulated surgical task. Wireless surface EMG sensors (Delsys, Inc.; Boston, MA) were placed on targeted muscles of the participants’ dominant side involved with performing MLS: the lower, middle, upper, and cervical trapezii; triceps; anterior deltoid; and extensor carpi radialis. Reflective markers were also placed on bony landmarks of the participants’ body for analysis using RULA (Appendix 1). For normalization purposes, participants executed isometric maximum voluntary contractions (MVC) for each muscle for 5 seconds prior to testing. Two microsuspension laryngoscopy simulators, each with an artificial larynx, and two synthetic vocal folds were used to facilitate performance of the simulated MLS task7 (Appendix 2). Subjects were trained to perform a simulated surgical task consisting of bimanual, ambidextrous, sequential, and repetitive vocal-fold palpation with blunt laryngeal dissectors (curved microlaryngeal elevators, Instrumentarium, Montreal, Canada). Five marked locations on each vocal fold, totaling 10 contact points, were palpated during each surgical task cycle. The participants palpated each marked point in numerical order, using the instrument in the contralateral hand (i.e., left vocal-fold marker touched with instrument in right hand) (Fig. 1). Ergonomically favorable and unfavorable positions were determined by previous microlaryngeal ergonomic work, using RULA scores to quantify injury risk in different ergonomic positions.3 Favorable positioning was defined as the laryngoscope angle 40 from the horizon and 0 to 10 neck flexion, with the addition of forearm support at a comfortable height for each surgeon. Unfavorable positioning resulted from the laryngoscope angle being increased to 60 and the neck flexion increased to 20 to 30 . Forearm support was not provided in the unfavorable position because 38% of otolaryngologists report not using arm support during MLS,1 and it is a higher-risk ergonomic position (Fig. 2).3 The bed height; chair height; and microscope placement, including eye pieces (Leica Wild Microscope, Model 655) were manipulated for each subject to achieve the predetermined favorable and unfavorable surgeon conditions. Equipment manipulations were unique for each subject to accommodate variable subject anthropometrics and habitus. Foot support was provided in both positions, such that the surgeons’ hip angle and knee angle were 90 . Back support was offered in both ergonomic positions. The role of back support has not been evaluated as a solitary ergonomic factor.

Fig. 2. Subject in a favorable (a) and unfavorable (b) ergonomic position for microlaryngeal surgery. Note the increased angle of laryngoscope as evidenced by trajectory of laryngeal instument and the increased neck flexion in the unfavorable position. [Color figure can be viewed in the online issue, which is available at www.laryngoscope.com.]

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Smith et al.: Comparison of Microlaryngoscopy Positions

relaxed, with their hands in their lap for the remainder of the break period between testing sessions.

TABLE I. Demographics of Subjects. Age (years)

31.6 6 3.8 (27–40)

Height (inches) Weight (pounds)

67.1 6 3.5 (62–73) 161.8 6 34.8 (109–239)

Sitting height ratio (dimensionless) Postgraduate

0.51 6 0.02 (0.43–0.53) Second

4

Third Fourth

2 4

Fifth

3

Sixth Seventh

4 1

Gender

Male

11

Dominant hand

Female Right

7 16

Left

2

Weekend Weekday

12 6

year levels

Testing session

RESULTS Eighteen healthy otolaryngology residents and fellows (11 male; mean age 31.6 6 3.8 years) participated in the study. All participants were between their second and seventh years of postgraduate training (residency/ fellowship). No participants reported any musculoskeletal problems prior to testing. Demographics are shown in Table I. The average angle of the laryngoscope, participant neck flexion angle, and participant shoulder angle are listed in Table II.

RULA The RULA scores were significantly different (P 5 0.0002) between the favorable (3.1 6 0.3) and unfavorable (3.8 6 0.5) positions.

Microbreaks Participants were randomly counterbalanced into both favorable and unfavorable ergonomic positions. Then, they performed the simulated surgical task for 15 minutes without stopping (Fig. 1). A 15-minute break was provided before repeating the same 15-minute task in the other ergonomic position to allow for complete muscle relaxation to baseline levels prior to starting another task. All participants were instructed to avoid microbreaks during task performance. They were defined as a momentary halting of the procedure, usually accompanied by musculoskeletal movement (i.e., head shake, shoulder roll, deep breath). The number and timing of microbreaks were recorded by dedicated observers. Subjects were instructed to be precise while performing the surgical task and were continuously monitored by a laryngologist watching on a video monitor connected to the microscope. The number of repetitions of the task was recorded for each participant in both positions. Flash photographs of the participants were taken at the end of each testing session for RULA analysis. EMG signals were collected at 2000 Hz during the simulated surgical tasks. The EMG data were band-pass filtered with cutoff frequencies of 10 to 400 Hz and down-sampled to 1200 Hz. Joint analysis of EMG spectrum and amplitude (JASA) was used to quantify fatigue.8–10 Fatigue over time was defined as an increase in EMG amplitude and a decrease in median frequency (MF) over time. Within subject repeated measure analysis of variances were performed for number of fatigued muscles, normalized mean EMG amplitude for each muscle, number of microbreaks, RULA scores, number of task repetitions, and responses to pain and usability questionnaires with position as the independent fixed factor. Statistical significance was set at 0.05. After each testing session in both favorable and unfavorable positions, participants completed pain and usability questionnaires. Participants reported the extent of their muscle discomfort in targeted muscle regions on a diagram of the human body, using the Pain Visual Analog Scale, for which 1 was no pain and 10 was the worst pain possible (Appendix 3). The usability questionnaire was designed based on our national survey results regarding MLS.1 Participants answered questions on a scale from 1 to 5, whereas 1 was strongly disagree and 5 was strongly agree. The participants were asked to sit,

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The number of microbreaks was statistically different (P 5 0.0011) between the favorable (0.7 6 0.8) and unfavorable (3.2 6 3.0) positions.

Task Repetitions Participants in the ergonomically favorable position completed significantly more task repetitions (P < 0.05). Participants performed 73.5 6 13.8 repetitions in the favorable position and only 67.0 6 15.4 repetitions in the unfavorable position.

Mean EMG Amplitude The greatest average EMG amplitude differences between the favorable and unfavorable positions were noted for the lower trapezius (5.6 % MVC) and cervical trapezius (7.0% MVC), with increased amplitude while in the unfavorable position. On average, most muscles exhibited between 16.4 and 35.2% MVC, except for the triceps (4% for both positions) and anterior deltoid (10.5% for favorable and 12.2% for unfavorable) (Appendix 4).

Muscle Fatigue When in the favorable position, an average of 3.8 and 5.7 muscles per participant demonstrated an increase in EMG amplitude and a decrease in MF, TABLE II. Average and Standard Deviations of Parameters for Favorable and Unfavorable Ergonomic Positioning of Participants. Parameter

Favorable

Unfavorable

Scope angle (o)

39.7 (0.5)

59.9 (1.5)

Neck angle (o) Shoulder angle (o)

11.7 (2.2) 49.0 (6.7)

29.7 (4.7) 44.4 (3.2)

Yes

No

Arm rests

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TABLE III. Number of Participants (out of 18 total) Showing Fatigue in Each Muscle According to Joint Analysis of EMG Spectrum and Amplitude for the Favorable and Unfavorable Positions. Muscle

Favorable

Unfavorable

Lower trapezius

5

7

Middle trapezius Upper trapezius

3 6

6 10

Cervical trapezius

8

10

Triceps Anterior deltoid

5 8

12 8

Extensor carpi radialis

4

4

respectively. While in the unfavorable position, an average of 5.3 and 5.1 muscles per participant demonstrated an increase in EMG amplitude and decrease in MF, respectively. The JASA fatigue quadrant (defined as increased EMG amplitude and decreased MF) contained the majority of participants for the cervical trapezius (8 for favorable, 10 for unfavorable) and anterior deltoid (8 for both favorable and unfavorable) (Table III). According to JASA requirements, the number of participants with fatigued muscles in the unfavorable position was equal to or greater than the number of participants with fatigued muscles in the favorable position (Appendix 5), although the differences were not statistically significant.

Pain Survey On average, participants reported greater pain in the unfavorable position (Fig. 3). Pain was significantly greater in the unfavorable position for the anterior shoulder (P 5 0.005) and posterior shoulder (P 5 0.0321).

Usability Questionnaire According to the usability survey, participants found the favorable position significantly easier to use (P < 0.0001) and were significantly more likely to respond positively to future use of the favorable than unfavorable surgical position (P < 0.0001). Participants were significantly less confident in the unfavorable posi-

Fig. 3. Average pain score (1 5 no pain, 10 5 worst pain possible) for dominant side in favorable (䊏) and unfavorable ( ) positions. Statistical significance (*) for anterior shoulder (P 5 0.005) and posterior shoulder (P 5 0.0321).

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tion (P < 0.0001) and also reported that the unfavorable position was more cumbersome to use than the favorable position (P 5 0.0006) (Fig. 4).

DISCUSSION Surgical ergonomics in otolaryngology, although not specifically for MLS, have been only recently described.11–13 Microlaryngeal surgery is a keystone of otolaryngology. It requires manual dexterity with precise fine motor movements. Unfortunately, this is often undertaken without consideration for optimal ergonomic surgical positioning. With increased knowledge of the accommodations, surgeons can and should improve on their surgical ergonomic positions; otolaryngologists may be able to avoid musculoskeletal injuries and prolong their surgical careers.

RULA RULA scores indicate risk level associated with occupational ergonomic positioning. Both the favorable and unfavorable ergonomic positions support the concept that MLS inherently places the surgeon at possible risk of musculoskeletal injury. The RULA recommendation associated with MLS in this study is: “A potential risk of injury from the posture, which should be investigated further and corrected if possible.” This risk may accumulate over years of MLS experience, manifesting as musculoskeletal pain. The significant increase in RULA score with the unfavorable position places the surgeon at a greater risk of musculoskeletal injury. However, it also highlights that the risk decreases significantly with simple accommodations to improve ergonomic positioning. Nonsurgical studies have evaluated the desired neck angle during stationary tasks.14 Neck extension is ergonomically unfavorable and places surgeons at a higher risk for musculoskeletal injury.2,14 Therefore, neck extension should be avoided at all times during MLS. Pronounced neck flexion is also to be avoided; it worsens the RULA scores and likely contributed to the increased muscle pain seen in our participants. Optimal

Fig. 4. Average responses to the usability questionnaire or favorable (䊏) and unfavorable ( ) positions. 1 5 strongly disagree, 5 5 strongly agree. Questions. 1. I think that I would like to use this surgical positioning frequently. 2. I found the surgical positioning unnecessarily complex. 3. I thought the surgical positioning was easy to use. 4. I think that I would need the support of a technical person to be able to use this surgical positioning. 5. I would imagine that most people would learn to use this surgical positioning very frequently. 6. I found the surgical positioning very cumbersome to use. 7. I felt very confident using the surgical positioning. 8. I needed to learn a lot of things before I could get going with this surgical positioning.

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neck placement (0 –10 flexion) can be achieved by manipulating the following: 1) the angulation of the laryngoscope by placing the patient in variable amounts of Trendelenburg positioning (which is facilitated by attaching the laryngoscope suspension system directly to the patient’s bed), 2) patient bed height, 3) microscope eyepiece angulation, and 4) surgeon chair height. Arm support is also important. A study on the effect of arm rest height on neck and shoulder muscle activity in keyboard typing showed that optimal/resting elbow position results in the lowest mean normalized EMG amplitude.15 This correlates with the use of arm rests for forearm stabilization in the favorable position compared to the lack of arm rests in the unfavorable position. The impact of neck position and arm support were not evaluated separately. The ergonomic literature states that proper neck position and arm support are critical to improved ergonomic positioning, thus decreasing the potential musculoskeletal effects of remaining in a static posture for lengths of time.

Microbreaks The number of microbreaks was statistically greater while in the unfavorable position. Whereas all subjects were instructed to not take breaks during the task period, subjects performed more shoulder shrugging and deep breathing while in the unfavorable position. This finding corroborates with previously reported data from our national MLS survey, with respondents taking breaks due to musculoskeletal symptoms when MLS surgery lasted longer than 30 minutes.1 Interestingly, even with our 15minute testing period, more microbreaks were taken when not in a favorable position. Microbreaks are likely subconscious reactions to increased muscle contraction and fatigue, which is increased while in an unfavorable ergonomic position. These breaks are restorative and should be encouraged in a proactive approach to diminish musculoskeletal injury. The timing of microbreaks has not been studied.

Task Repetitions The number of task repetitions was significantly different between the two ergonomic positions. There was, however, no significance in the number of repetitions completed in each ergonomic position related to years of training. The number of task repetitions was used to correlate with surgical productivity. The simulated surgical task was simple, but required dexterity and precision, both being qualities utilized in MLS. The number of repetitions may have been influenced by the presence of an observer who was monitoring when the subject took a microbreak. One hypothesis is that with decreased pain, extremity stability, and proper neck positioning, the subject was more comfortable, which optimized completion of the task.

Mean EMG Amplitude EMG amplitude is related to muscle activity level: As more muscle units are recruited, increases in the myoelectric signal are evident. Ergonomic positions with Laryngoscope 00: Month 2014

higher signal amplitudes indicate a greater perceived workload, leading to a greater risk for musculoskeletal disorders.15,16 Our study found that the average normalized muscle amplitude, averaged across all subjects, was higher in the unfavorable position compared to the favorable position. The lower trapezius and cervical trapezius showed the greatest differences, with higher amplitude while in the unfavorable position. We hypothesize that this is in part due to the lack of arm support in the unfavorable position. The higher amplitudes in the unfavorable position could present a higher risk for development of musculoskeletal symptoms.

Fatigue Quantified With JASA When using EMG to indicate fatigue, it is important to remember that myoelectric manifestations are not directly translatable to mechanical fatigue. Changes in the frequency distribution of an EMG signal are dependent on fatigue, but also on the level of muscular force.17 In workplace situations with variable loading conditions for which ergonomics are being evaluated, the cause of the observed change can be unclear. De Looze et al. reviewed studies evaluating shoulder fatigue in prolonged activities involving low-force contractions.18 Six of the studies evaluating fatigue used the JASA criteria of increased amplitude and decreased frequency over time, which is a generally accepted fatigue criteria for prolonged static efforts. The studies that positively demonstrated fatigue had an intensity level of at least 15% MVC.18 The intensity levels ranged from 16.4% to 35.2% MVC for most of the muscles in our study, except for the triceps (4% MVC) and anterior deltoid (10.5%–12.2% MVC). Because our % MVC is in the same intensity range as other static ergonomic studies with positive demonstrations of fatigue, this validates the use of JASA to evaluate fatigue. Previous studies have shown that prolonged activity in a static posture increases stress on the body for instrument nurses and laparoscopic surgeons.17,19,20 In the Luttmann study of muscle fatigue of four urological surgeons, surface EMGs were recorded for the trapezius, deltoid, and erector spinae muscles.10 Just over one-half of the muscles fell into the fatigue quadrant during JASA analysis. Comparatively, in our study, 31% and 45% of muscles were fatigued in the favorable and unfavorable positions, respectively, according to JASA. For most participants, our study showed that the number of fatigued muscles in the unfavorable position was equal to or greater than the number of fatigued muscles in the favorable position on average.

Pain Survey The significant increase in perceived pain in the anterior and posterior shoulder is likely due to the lack of arm support in the unfavorable position. This is more evidence highlighting the importance of arm support while performing MLS. Despite this, 38% of otolaryngologists report not using arm support during MLS, while 83% of those same respondents reported musculoskeletal symptoms during MLS. Ten percent reported that they stop operating while performing MLS due to pain. Smith et al.: Comparison of Microlaryngoscopy Positions

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Impressively, 53% of respondents reported continued musculoskeletal symptoms 48 hours after performing MLS.1 This suggests the possible cumulative sequel of a poor ergonomic operating position. Nonoptimal ergonomic positioning leads to increased pain, which is counterproductive to what is required to perform the delicate tasks of MLS. The addition of proper arm support and proper neck and laryngoscope positions should reduce the number of otolaryngologists who report musculoskeletal symptoms during and after performing microlaryngeal surgery.

favorable MLS ergonomic position compared to a less favorable position. This provides quantifiable evidence that improved surgeon ergonomics can positively impact the extent of muscle activation and pain associated with MLS. With this knowledge, ergonomic alterations should be made in the operating room, thus helping surgeons avoid musculoskeletal injuries. This should result in less musculoskeletal symptoms during and after surgery, in addition to the potential cumulative long-term effects of repeated unfavorable MLS positioning.

Usability Questionnaire

Acknowledgments

The preference to use the favorable position suggests that otolaryngologists are able to discern a difference in the two ergonomic positions. Their reported desire to utilize the favorable ergonomic position suggests that it was physically intuitive, but highlights the need to cognitively think about the ergonomics of MLS.

We would like to thank Drs. Adam Klein and Michael Johns III for use of the microlaryngeal surgical simulators and synthetic vocal folds. We also thank Tina Harrison, who was invaluable for coordinating the study sessions.

Validated Positions These data corroborate previous results regarding favorable ergonomics of MLS.1,3 This study proves the importance of proper ergonomic positioning (neck position 0 –10 flexion and laryngoscope angle 40 ) and the use of arm rests from both electrophysiological and perceived pain standpoints. The implication of increased task repetition while in the favorable position is unknown and may or may not be clinically relative to precision when performing MLS.

Limitations Although this was a prospective cohort study with random counterbalance, it did not evaluate surgical precision during surface EMG monitoring because surgical experience would likely influence surgical precision. Instead, a simple, repetitive surgical task was used, which would potentially equalize the different levels of otolaryngology training. This was achieved because there were no differences in any parameters tested based upon the level of participant experience. This allowed for testing of the desired parameters (i.e., surface EMG results), irrespective of years of training. Testing was only performed on otolaryngology residents and fellows, precluding the study of surgeons with advanced MLS experience. However, we hypothesize that the surface EMG changes seen during the simulated surgical task in both favorable and unfavorable positions would still exist, despite years of experience, because muscle activity and fatigue are related to ergonomic positioning and not to the extent of experience. Further testing is needed to confirm this hypothesis. The effects of individual ergonomic components were not studied (neck angle, arm support), thus necessitating further study.

CONCLUSION This is the first study to demonstrate electromyographic evidence of decreased muscle activation and fatigue, in addition to self-reported pain, with a more

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BIBLIOGRAPHY 1. Wong A, Baker N, Smith L, Rosen CA. Prevalence and risk factors for musculoskeletal problems associated with microlaryngeal surgery: a national survey. Laryngoscope 2014;124:1854–1861. Doi: 10.1002/ lary.24367. Epub 2014. 2. Bernard BP. Neck musculoskeletal disorders: evidence of work-relatedness. In: Musculoskeletal Disorders and Workplace Factors: A Critical Review of Epidemiologic Evidence for Work-Related Musculoskeletal Disorders of the Neck, Upper Extremity, and Low Back. Publication No. 97–141. Cincinnati, OH: National Institute for Occupational Safety and Health; 1997. 3. Statham MM, Sukits AL, Redfern MS, Smith LJ, Sok JC, Rosen CA. Ergonomic analysis of microlaryngoscopy. Laryngoscope 2010;120:297–305. 4. McAtamney L, Nigel Corlett, E. RULA: a survey method for the investigation of work-related upper limb disorders. Appl Ergon 1993;24:91–99. 5. Merletti R, Rainoldi A, Farina D. Myoelectric manifestations of muscle fatigue. In: Merletti R, Parker P, eds. Electromyography: Physiology, Engineering, and Non-Invasive Applications. Hoboken, NJ: Wiley-IEEE Press; 2004:233–258. 6. Criswell E. Cram’s Introduction to Surface Electromyography 2nd ed. Sudbury, MA: Jones and Bartlett Publishers; 2011. 7. Contag SP, Klein AM, Blount AC, Johns MM 3rd. Validation of a laryngeal dissection module for phonomicrosurgical training. Laryngoscope 2009; 119:211–215. doi: 10.1002/lary.20018. 8. Luttmann A, Schmidt KH, Jager M. Working conditions, muscular activity and complaints of office workers. Int J Ind Ergonom 2010;40:549–559. doi: 10.1016/j.ergon.2010.04.006. 9. Stulen FB, DeLuca C J. Frequency parameters of the myoelectric signal as a measure of muscle conduction velocity. IEEE Trans Rehabil Eng 1981; 28:515–523. 10. Luttmann A, Jager M, Sokeland J, Laurig W. Electromyographical study on surgeons in urology. II. Determination of muscular fatigue. Ergonomics 1996;39:298–313. doi: 10.1080/00140139608964460. 11. Cavanagh J, Brake M, Kearns D, Hong P. Work environment discomfort and injury: an ergonomic survey study of the American Society of Pediatric Otolaryngology members. Am J Otolaryngol 2012;33:441–446. 12. Little RM, Deal AM, Zanation AM, McKinney K, Senior BA, Ebert CS Jr. Occupational hazards of endoscopic surgery. Int Forum Allergy Rhinol 2012;2:212–216. 13. Wunderlich M, Jacob R, Stelzig Y, Ruther T, Leyk D. Analysis of spinal stress during surgery in otolaryngology. HNO 2010;58:791–798. 14. Szeto GP, Straker L, Raine S. A field comparison of neck and shoulder postures in symptomatic and asymptomatic office workers. Appl Ergon 2002;33:75–84. 15. Zhu X, Shin G. Effects of armrest height on the neck and shoulder muscle activity in keyboard typing. In: Proceedings of the Human Factors and Ergonomics Society Annual Meeting. SAGE Publications. 2011;55:958– 962. 16. Rolander B, Jonker D, Karsznia A, Oberg T. Evaluation of muscular activity, local muscular fatigue, and muscular rest patterns among dentists. Acta Odontol Scand 2005;63:189–195. doi: 10.1080/00016350510019964. 17. Hagg GM, Luttmann A, Jager M. Methodologies for evaluating electromyographic field data in ergonomics. J Electromyogr Kinesiol 2000;10:301– 312. 18. de Looze M, Bosch T, van Dieen J. Manifestations of shoulder fatigue in prolonged activities involving low-force contractions. Ergonomics 2009; 52:428–437. 19. Berguer R, Rab GT, Abu-Ghaida H, Alarcon A, Chung J. A comparison of surgeons’ posture during laparoscopic and open surgical procedures. Surg Endosc 1997;11:139–142. 20. Kant IJ, de Jong LC, van Rijssen-Moll M, Borm PJ. A survey of static and dynamic work postures of operating room staff. Int Arch Occup Environ Health 1992;63:423–428.

Smith et al.: Comparison of Microlaryngoscopy Positions

Comparison of microsuspension laryngoscopy positions: a randomized, prospective study.

To evaluate muscle fatigue and participant pain in the upper back, cervical, and arm muscles associated with microlaryngeal surgery (MLS) in standardi...
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