Early Identification of Median Nerve Pathology
Nearly 70% of dental hygienists report experiencing discomfort in their forearms/wrists/hands, primarily due to the use of dental scaling instruments. Dental scaling requires sustained pinching and repetitive movements that place high load on the forearm and hand muscles. This high muscle load, combined with pinching and non-neutral wrist positions, approximately doubles the risk of developing hand and median nerve pathology due to strain on the tendons and compression of the median nerve. Scaling of more than four hours per day has been directly associated with pathology.
Dental hygiene students have an elevated risk of musculoskeletal injury due to intensive exposure to scaling during their educational training. We have documented a significant increase in subjective reports of discomfort in the hand, wrist, and fingers of these students, with the prevalence of students with discomfort doubling to tripling across their two-year training program. Up to 60% of individuals report having discomfort at the end of their training. To enhance education, develop preventive training, and address work-related musculoskeletal disorders in dental hygienists, it is necessary to better understand the link between exposure and pathology development.
Our interdisciplinary team is attempting to advance this goal with funding from the National Institute for Occupational Safety and Health (NIOSH). We are specifically interested in the use of sonographic imaging to identify factors that may predispose individuals to injury and to monitor changes in tissues in response to exposure to scaling activities, as well as evaluating the relative contribution of body postures and strain related to dental scaling tasks themselves. Using these data we aim to develop and validate a novel method for early detection of median nerve pathology and determine the effects of task components on changes in morphology.
This study is following dental hygiene students throughout their two-year educational training, obtaining measures each semester. First, we are using sonographic imaging to monitor changes in tissue morphology of the distal upper extremity. Sonographic imaging has been used in an animal model to observe early progressive increases in median nerve size due to task exposure. By understanding this progression in humans, it would be possible to develop an early detection technique to stop, slow, or reverse pathology before it becomes costly and debilitating.
These sonographic measures are being compared to neurophysiological changes using nerve conduction testing, subjective reports of symptoms and functional limitations using questionnaires, and task exposures during scaling using video analyses. This work will establish predictive validity of a novel method for early detection of work-related pathology using sonographic imaging, while also identifying task components of intensive functional hand activity (e.g., scaling) associated with morphologic changes.
Intermediate outcomes of this research will establish sonographic imaging as an early detection tool for workplace-screening and inform methods for combining measures of nerve morphology, neurophysiology, and subjective symptoms for predicting the development of work-related injuries. This work will also inform the development of targeted preventive interventions for task components of intensive hand activities that are related to changes in tissue morphology. Identifying morphologic changes in early-stages of pathology and the specific task components linked to these changes are the first steps toward early detection and prevention of work-related musculoskeletal injuries in dental hygienists.
Sonographic tissue morphology in early stage work-related pathology
National Institute for Occupational Safety and Health / Centers for Disease Control
R01-OH010665 (PI: Roll)
Total Funding: $2,324,186
Funding Period: 9/30/15 – 9/29/20
Median nerve mobility: Changes across time and associations with personal and work factors
USC Office of Undergraduate Programs – Undergraduate Research Associates Program
Total Funding: $6,000
Funding Period: 8/15/20 – 5/15/21
Association of nerve movement during functional hand use to pathology development in dental hygienists
USC Office of Undergraduate Programs – Undergraduate Research Associates Program
Total Funding: $6,000
Funding Period: 8/15/18 – 5/15/19
Yao, B., & Roll, S. C. (2022). An ultrasound study of the mobility of the median nerve during composite finger movement in the healthy young wrist. Muscle and Nerve, 65(1), 82-88. https://doi.org/10.1002/mus.27437 Show abstract
Introduction/Aims. There is a lack of consensus regarding median nerve movement in the carpal tunnel during composite finger flexion in healthy individuals. This study aimed to examine the amount and direction of median nerve movement and differentiate nerve mobility between dominant and non-dominant sides in a large healthy young adult cohort.
Methods. Sonographic videos of the median nerve during composite finger motion from extension to full flexion were analyzed in 197 participants without median nerve pathology. Displacement of the nerve’s centroid was calculated based on a change in the relative location of the nerve. Longitudinal nerve sliding was categorized as none, independently from the tendons, or with the tendons.
Results. In short axis, median nerves moved within 1 mm vertically and 3 mm horizontally; no direction was predominant. About half of the nerves (52.5%) slid independently while 26.9% slid with the tendons; 21.3% did not slide at all. On the non-dominant side, median nerves that slid with the tendons had a larger absolute vertical displacement than nerves that slid independently or did not slide at all (p<0.01). Nerves on the dominant side moved in a radial direction more frequently than on the non-dominant side (p=0.02).
Discussion. Transverse nerve movement during composite finger flexion in healthy individuals varies widely with no clear pattern in the direction of transverse movement or amount of longitudinal sliding. These data provide a foundation for future research to better understand the biomechanical contribution of nerve movement to median nerve pathologies.
Yao, B., & Roll, S. C. (2021). Effect of functional hand use on compression and displacement of the median nerve. American Journal of Occupational Therapy, 75(Supplement_2), 7512505196. https://doi.org/10.5014/ajot.2021.75S2-RP196 Show abstract
Accepted for AOTA INSPIRE 2021 but unable to be presented due to online event limitations.
Repetitive wrist and hand movement is a risk factor for carpal tunnel syndrome. During daily functional hand use, some people develop carpal tunnel syndrome. However, the exact mechanism of injury remains unknown. We evaluated the effect of functional hand use on the median nerve and assessed the compression and displacement of the median nerve using state-of-the-art sonography.
Yao, B., Gan, K., Lee, A., & Roll, S. C. (2020). Comparing shape categorization to circularity measurement in the evaluation of median nerve compression using sonography. Journal of Diagnostic Medical Sonography, 36(3), 224-232. https://doi.org/10.1177/8756479319898471 Show abstract
Purpose. This study aimed to develop a subjective categorization of nerve shape and to examine the relationship of shape categorizations to measurement of nerve circularity.
Methods. Wrists were evaluated with sonography in healthy participants. Images of the median nerve were obtained in the transverse plane at the level of pisiform with the fingers resting, gripping, and pinching. Nerves were categorized as ovoid, angular, or irregular, and the cross-sectional area and perimeter were measured to calculate nerve circularity.
Results. Across 167 participants, the median nerve shifted from being primarily ovoid at rest to angular shaped when the fingers were in a full fist or pinching. Approximately three-quarters of subjects exhibited a shape change during dynamic movement. Irregular nerves had the lowest circularity values; however, the majority of nerves had similar circularity measures despite having different shapes.
Conclusions. Subjective categorization of shape has the potential to be a valid technique for evaluation of the median nerve using sonography, and this evaluation may provide additional information regarding nerve compression that is not fully captured by a circularity measure. Further investigation is needed to determine how these two techniques may be best used individually or together to advance clinical diagnosis, prevention, and rehabilitative interventions.
Keywords. sonography, carpal tunnel syndrome, median nerve, circularity
Takata, S. C., Kysh, L., Mack, W. J., & Roll, S. C. (2019). Sonographic reference values of median nerve cross-sectional area: A protocol for a systematic review and meta-analysis. Systematic Reviews, 8(1), 2. https://doi.org/10.1186/s13643-018-0929-9 Show abstract
Background. Median nerve cross-sectional area (CSA) is the primary sonographic parameter for assessing and diagnosing median nerve pathology, such as carpal tunnel syndrome. However, variability in the sensitivity of diagnostic thresholds exists, which may be due to a lack of standardized normative reference values. Current estimates of normal median nerve CSA stem largely from small studies using a local pool of healthy controls. A systematic review and meta-analysis will be conducted to identify all available data for median nerve CSA in healthy, asymptomatic individuals to create a comprehensive set of normative reference values.
Methods. Articles that include sonographic measures of median nerve CSA will be identified through a rigorous search of published evidence, a hand search through tables of contents of key journals, and the gray literature, including ClinicalTrials.gov and conference abstracts. Each abstract and full text will be reviewed by multiple raters to identify studies from 2000 to present that include original data. Any study that provides median nerve CSA values from healthy individuals will be included (e.g., reference value study, control participants in a diagnostic study). Studies will be assessed for quality using a modified version of the National Institute of Health Study Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies, with primary focus on the use of a detailed and acceptable image acquisition and analysis protocol. Using data from included studies, reference values will be calculated for median nerve CSA by anatomical regions, including the distal forearm, wrist, and carpal tunnel at the level of the pisiform. Reference values will be stratified by gender, ethnicity, and age based upon the specificity of the data provided by the included articles.
Discussion. A comprehensive set of normative reference values of median nerve CSA will reduce variability across studies, allowing future research to more accurately evaluate and establish diagnostic thresholds. Additionally, normative values can serve as a reference for evaluating treatment outcomes and provide a means to investigate and understand minor nuances in CSA changes that may be indicative of preclinical stages of median nerve pathology.
Systematic review registration. PROSPERO 2016 CRD42016037286
Keywords. Meta-analysis, Systematic review, Musculoskeletal sonography, Median nerve, Reference values
Takata, S. C., & Roll, S. C. (2019). Identification of aberrant muscle bellies in the carpal tunnel using sonography. Journal of Diagnostic Medical Sonography, 35(1), 62–68. https://doi.org/10.1177/8756479318807469 Show abstract
Musculoskeletal sonography is being widely used for evaluation of structures within the carpal tunnel. While some anatomical variants, such as bifurcated median nerves and persistent median arteries, have been well documented, limited literature describes the sonographic appearance of aberrant muscle bellies within the carpal tunnel. Multiple examples of the sonographic appearance of flexor digitorum superficialis and lumbrical muscle bellies extending into the carpal tunnel are provided. Techniques for static image acquisition and analysis are discussed, and the use of dynamic imaging to confirm which specific muscle belly is involved is described. Knowledge of the potential presence of muscle bellies in these images and ability to identify these structures is vital to avoid misclassification or misdiagnosis as abnormal pathology. The case examples are situated among current published evidence regarding how such anomalies may be related to the development of pathologies, such as carpal tunnel syndrome.
Keywords. carpal tunnel, aberrant muscle, musculoskeletal sonography
Roll, S. C., Evans, K. D., Volz, K. R., & Sommerich, C. M. (2013). Longitudinal design for sonographic measurement of median nerve swelling with controlled exposure to physical work using an animal model. Ultrasound in Medicine & Biology, 39(12), 2492-2497. https://doi.org/10.1016/j.ultrasmedbio.2013.08.008 Show abstract
In the study described here, we examined the feasibility of a longitudinal design to measure sonographically swelling of the median nerve caused by controlled exposure to a work task and to evaluate the relationship of changes in morphology to diagnostic standards. Fifteen macaques, Macaca fascicularis, pinched a lever in various wrist positions at a self-regulated pace (8 h/d, 5 d/wk, 18–20 wk). Nerve conduction velocity (NCV) and cross sectional area (CSA) were measured every 2 wk from baseline through working and a 6-wk recovery. Trending across all subjects revealed that NCV slowed and CSA at the carpal tunnel increased in the working arm, whereas no changes were observed in CSA either at the forearm or for any measure in the non-working arm. There was a small negative correlation between NCV and CSA in the working arm. This study provides validation that swelling can be observed using a longitudinal design. Longitudinal human studies are needed to describe the trajectory of nerve swelling for early identification of median nerve pathology.
Complete Presentation List
Yao, B., Gan, H., Lee, A., & Roll, S. C. (2019). Dynamic evaluation of median nerve shape in the carpal tunnel. Poster presentation at USC Ostrow School of Dentistry Research Day, Los Angeles, CA.
Takata, S. C., & Roll, S. C. (2019). Sonographic prevalence of space-occupying long flexor muscle bellies in the carpal tunnel of healthy individuals. Paper presentation at American Institute of Ultrasound in Medicine Annual Conference, Orlando, FL.
Roll, S. C., Forrest, J. L., & Mack, W. J. (2019). Differential effects of work-related task training on upper extremity health in occupational therapy and dental hygiene students. Poster presentation at 97th Annual Conference of the American Occupational Therapy Association, New Orleans, LA.
Roll, S.C., & Takata, S. C. (2018). Illuminating the nuances of carpal tunnel syndrome: Advanced concepts in prevention and rehabilitation for the experienced therapist. Short course presentation at American Society of Hand Therapists Annual Conference, Dallas, TX.
Takata, S. C., & Roll, S. C. (2017). Relationship of internal carpal tunnel measurements to external wrist-ratio: Implications for prevention of carpal tunnel syndrome. Paper presentation at 6th Annual Occupational Therapy Summit of Scholars, Boston, MA.
Melrose, M. D., Wilkins, K., Forrest, J. L., & Roll, S. C. (2017). Identifying risk of hand injuries in dental hygienists: A longitudinal cohort study. Poster presentation at American Dental Educators Association Allied Program Directors’ Conference, Baltimore, MD.
Roll, S. C., & Mitchell, J. (2017). Relationship of internal carpal tunnel measurements to external wrist-ratio: Implications for prevention and diagnosis. Paper presentation at Annual Convention of the American Institute of Ultrasound in Medicine, Orlando, FL.
Roll, S. C., Mack, W. J., & Forrest, J. L. (2017). Identification of early-stage median nerve pathology: Longitudinal multiple cohort study protocol. Electronic poster at Annual Convention of the American Institute of Ultrasound in Medicine, Orlando, FL.
Roll, S. C., Mack, W. J., Forrest, J. L., Baker, L. L., & Baker, N. A. (2016). Identification of early-stage median nerve pathology: Protocol for a longitudinal, multiple cohort study. Paper presentation at 5th Annual Occupational Therapy Summit of Scholars, Pittsburgh, PA.