Association between wrist ratio and carpal tunnel syndrome: Effect modification by body mass index.

INTRODUCTION: Previous studies have reported higher wrist ratios (WR) related to carpal tunnel syndrome (CTS) but have not assessed effect modification by obesity and may have inadequately controlled for confounders. METHODS: Baseline data of a multicenter prospective cohort study were analyzed. CTS was defined by nerve conduction study (NCS) criteria and symptoms. RESULTS: Among the 1,206 participants, a square-shaped wrist was associated with CTS after controlling for confounders (prevalence ratio = 2.27; 95% confidence interval [95% CI], 1.33-3.86). Body mass index (BMI) was a strong effect modifier on the relationship between WR and both CTS and abnormal NCS results, with normal weight strata of rectangular versus square wrists = 8.18 (95% CI, 1.63-49.96) and 7.12 (95% CI, 2.19-23.16), respectively. DISCUSSION: A square wrist is significantly associated with CTS after controlling for confounders. Effect modification by high BMI masked the eightfold magnitude adjusted relationship seen between WR and CTS among normal weight participants. Muscle Nerve 56: 1047-1053, 2017.

The WISTAH hand study: a prospective cohort study of distal upper extremity musculoskeletal disorders.

BACKGROUND: Few prospective cohort studies of distal upper extremity musculoskeletal disorders have been performed. Past studies have provided somewhat conflicting evidence for occupational risk factors and have largely reported data without adjustments for many personal and psychosocial factors. METHODS/DESIGN: A multi-center prospective cohort study was incepted to quantify risk factors for distal upper extremity musculoskeletal disorders and potentially develop improved methods for analyzing jobs. Disorders to analyze included carpal tunnel syndrome, lateral epicondylalgia, medial epicondylalgia, trigger digit, deQuervain's stenosing tenosynovitis and other tendinoses. Workers have thus far been enrolled from 17 different employment settings in 3 diverse US states and performed widely varying work. At baseline, workers undergo laptop administered questionnaires, structured interviews, two standardized physical examinations and nerve conduction studies to ascertain demographic, medical history, psychosocial factors and current musculoskeletal disorders. All workers' jobs are individually measured for physical factors and are videotaped. Workers are followed monthly for the development of musculoskeletal disorders. Repeat nerve conduction studies are performed for those with symptoms of tingling and numbness in the prior six months. Changes in jobs necessitate re-measure and re-videotaping of job physical factors. Case definitions have been established. Point prevalence of carpal tunnel syndrome is a combination of paraesthesias in at least two median nerve-served digits plus an abnormal nerve conduction study at baseline. The lifetime cumulative incidence of carpal tunnel syndrome will also include those with a past history of carpal tunnel syndrome. Incident cases will exclude those with either a past history or prevalent cases at baseline. Statistical methods planned include survival analyses and logistic regression. DISCUSSION: A prospective cohort study of distal upper extremity musculoskeletal disorders is underway and has successfully enrolled over 1,000 workers to date.

Measuring sensory nerve action potential electrical power.

Sensory nerve action potential (SNAP) amplitudes are frequently examined for evidence of axonal loss. Because digital nerves have parallel fibers, and parallel voltages do not add, SNAP amplitude may not accurately reflect axonal loss. In contrast, electrical power can be measured for digital nerves, and is additive. In this study we explore the ability of SNAP electrical power (SELP) to discriminate the increased number of axons in fingers with two median digital nerves versus fingers with only one median digital nerve. Antidromic SNAP amplitudes and SELPs were obtained for 15 fingers. Seventeen external resistors, R(ext), were sequentially connected from electrode to ground for SELP determination. The resulting bell-shaped power vs. R(ext) plot was regressed to the power transfer equation, which has a peak that defines SELP. SELPs of two-digital-nerve (median) fingers were 360-670 femtowatts (mean 525 fW). For one-digital-nerve fingers, SELP was 90-230 fW (mean 190 fW). Evaluation of one- vs. two-median-digital-nerve statistics showed the SNAP amplitude difference-of-means to be insignificant, whereas the SELP difference-of-means was 3.3 SD (P < 0.01). Using a criterion of 2 SDs, SNAP amplitude did not discriminate any one-median-digital-nerve fingers, whereas SELP discriminated all with no false positives. Because parallel voltages do not add, SNAP amplitudes may not reflect axonal loss. In contrast, electrical power is additive. We describe the SELP technique and demonstrate its ability to discriminate different numbers of axons as reflected by one digital nerve vs. two digital nerves.

Biomechanics of the double rocker sole shoe: gait kinematics and kinetics.

The use of footwear with contoured soles is common in treatment and care of patients with diabetes; these rocker sole shoes are designed to alleviate loading in key areas on the plantar surface of the foot, reducing pressure in key areas and alleviating pain, and potential soft tissue damage. While investigations of pressure changes have been conducted, no quantitative study to date has addressed the three-dimensional (3D) kinematic and kinetic changes that result from using these shoes. Forty subjects were tested wearing both unmodified and double rocker sole shoes, and the resulting motion patterns were compared to assess change caused by the rocker sole. Overall walking speed remained unchanged throughout testing; slightly increased flexion (<5 degrees ) was apparent at the hip, knee, and ankle during early and mid-stance. These results demonstrate the maintenance of gait function with minimal kinematic changes when using the rocker sole shoe. Investigations of multisegmental foot motion may reveal additional information about the contour effects; analysis of contour variations may also be warranted to investigate the possibility of controlling motion based on rocker sole parameters.

Association Between Cardiovascular Risk Factors and Carpal Tunnel Syndrome in Pooled Occupational Cohorts.

OBJECTIVE: The aim of the study was to ascertain if cardiovascular (CVD) risk factors are carpal tunnel syndrome (CTS) risk factors. METHODS: Analysis of pooled baseline data from two large prospective cohort studies (n = 1824) assessed the relationships between a modified Framingham Heart Study CVD risk score both CTS and abnormal nerve conduction study prevalence. Quantified job exposures, personal and psychosocial confounders were statistically controlled. Odds ratio and 95% confidence intervals were calculated for individual risk scores. RESULTS: There was a strong relationship between CVD risk score and both CTS and abnormal nerve conduction study after adjustment for confounders, with odds ratios as high as 4.16 and 7.35, respectively. Dose responses were also observed. CONCLUSIONS: In this workplace population, there is a strong association between CVD risk scores and both CTS and abnormal nerve conduction study that persisted after controlling for confounders. These data suggest a potentially modifiable disease mechanism.

Effects of the toe-only rocker on gait kinematics and kinetics in able-bodied persons.

Rocker sole shoes are commonly prescribed to diabetic patients with insensate feet. Recent passage of the therapeutic shoe bill has drawn an increased focus on prescription of rehabilitative footwear. The purpose of this work is to investigate the dynamics of lower extremity joints (hip, knee, and ankle) with the application of a toe-only rocker sole shoe under controlled laboratory conditions. Forty (40) normal adults volunteered for gait analysis using controlled baseline and prescription toe-only rocker sole shoes. Three-dimensional motion analysis techniques were used to acquire kinematic and kinetic data using a six camera Vicon 370 motion system and two AMTI force plates. While significant changes from baseline to toe-only rocker were noted in cadence (increased) and stride length (decreased), no significant change in walking speed was observed. The most significant kinematic changes with the application of the toe-only shoe occurred at the ankle and knee in the sagittal plane during stance. The most significant kinetic effects were observed in the hip and knee during swing phase. Changes in power were noted at all joints, mostly in terminal stance. These kinematic and kinetic changes, along with previously studied effects of pressure relief at the metatarsal heads, should aid medical professionals in prescribing prophylactic footwear.

Development of a quantitative reflex hammer for measurement of tendon stretch reflex.

Quantification of tendon stretch reflex requires precise measurement of the tapping force of a reflex hammer. A quantitative reflex (QR) hammer consisting of two cut rubber pieces from a generic rubber reflex hammer and a uniaxial force transducer was constructed. Finite element stress analyses were conducted to estimate the natural frequency characteristics of the hammer and to find the stress distributions during the impact. Pendulum impact testing was conducted at four different heights to assess the calibration linearity and repeatability of the measurement. The QR hammer had a fundamental natural frequency of 515 Hz and showed minimal displacement and stress at the tip from the finite element simulation of the impact. The QR hammer also provided reliable and repeatable measurements as demonstrated with high coefficients of determination, exceeding 0.994 and small coefficients of variations, less than 4%. The calibration linearity was 0.64% compared with the reference force platform measurement. The QR hammer demonstrated sufficient accuracy and reliability for precise clinical assessment of tendon stretch reflexes.

Analysis of postural control synergies during quiet standing in healthy children and children with cerebral palsy.

OBJECTIVE: To estimate the contribution of body transverse rotation using weighted differential center of pressure signals during quiet standing in healthy children and in children with cerebral palsy. DESIGN: Body sway was indirectly measured through center of pressure data, which was calculated using dual force platforms. BACKGROUND: Assessment of postural control synergies using center of pressure data provides a unique method for center of mass data analysis in characterizing complex balance sway. METHODS: Using dual force platforms, linear expressions for the coordinates of right and left center of pressure signals were developed to identify and characterize balance control synergies during quiet standing. Subjects were also tested during eyes open and eyes closed trials to determine the significance of visual input on these control synergies. RESULTS: The limb protraction/retraction control was found to be dominant during medial-lateral sway, whereas the estimated body transverse rotation contribution was found to be more significant than the previously reported measures of anterior-posterior balance. These findings were consistent in healthy children and in children with cerebral palsy during both eyes open and eyes closed trials. CONCLUSION: The weighted differential center of pressure signals show that the estimated body transverse rotation contribution is significant in healthy children and critical for postural stability in children with cerebral palsy. RELEVANCE: This study identifies the significance of body transverse rotation control contribution in upright posture. Children with cerebral palsy with relatively poor ankle control demonstrate the importance of body transverse rotation for postural stability.

Quantitative electromyography.

Quantitative EMG is an MUAP analysis technique providing objective information on the NEE. The concept and techniques are not new; however, with the advancement of computer technology, quantitative EMG is now more easily performed. The study requires solid knowledge of basic neurophysiology and access to the appropriate instrument to provide smooth technique and accurate interpretation. Despite recent technical advances, the original MUAP parameters defined by Buchthal are still widely used today as reference values. It is increasingly recognized that many factors can influence the obtained parameters. The ability to measure something does not mean that it is fully understood. The future of quantitative EMG will depend on increased understanding of the physiologic and pathophysiologic significance of the detailed numeric parameters that are generated.

Impacts of differences in epidemiological case definitions on prevalence for upper-extremity musculoskeletal disorders.

OBJECTIVE: The aim of this study was to systematically evaluate prevalence based on variations in case definitions used for epidemiological studies of musculoskeletal disorders (MSDs). BACKGROUND: Prior studies of MSDs have mostly relied on a single case definition based on questionnaires. METHOD: In a multicenter prospective cohort study, we systematically collected data to evaluate impacts of differences in case definitions of MSDs on prevalence of three common musculoskeletal disorders: (a) shoulder tendinosis, (b) lateral epicondylalgia, and (c) carpal tunnel syndrome. Production workers were from 21 employment settings in three diverse U.S. states and performed widely varying work. All workers completed laptop-administered structured interviews, two standardized physical examinations, and nerve conduction studies (NCS). Case definitions included symptoms only, and symptoms plus physical examinations and/or NCS. RESULTS: A total of 1,227 subjects had complete health data at baseline. The prevalence for shoulder tendinosis is 23.0% if only glenohumeral pain is used for a case definition, compared with 8.0% if a combination of pain plus a positive supraspinatus test is used. The prevalence for lateral epicondylalgia varied on the basis of lateral elbow pain (12.0%), pain plus tenderness on palpation (9.9%), or pain plus tenderness on palpation plus resisted wrist or middle finger extension (3.5%). Carpal tunnel syndrome prevalence varied on the basis of tingling or numbness in a median nerve-served digit (29.9%) or tingling or numbness plus NCS abnormalities consistent with carpal tunnel syndrome (9.0%). CONCLUSION: Variations in epidemiological case definitions have major impacts on prevalence of common MSDs. Wide-ranging differences in prevalence may have impacts on purported risk factors that need to be determined.

Fatigue analysis before and after shaker exercise: physiologic tool for exercise design.

Recent studies suggest that the Shaker exercise induces fatigue in the upper esophageal sphincter (UES) opening muscles and sternocleidomastoid (SCM), with the SCMs fatiguing earliest. The aim of this study was to measure fatigue induced by the isometric portion of the Shaker exercise by measuring the rate of change in the median frequency (MF rate) of the power spectral density (PSD) function, which is interpreted as proportional to the rate of fatigue, from surface electromyography (EMG) of suprahyoid (SHM), infrahyoid (IHM), and SCM. EMG data compared fatigue-related changes from 20-, 40-, and 60-s isometric hold durations of the Shaker exercise. We found that fatigue-related changes were manifested during the 20-s hold. The findings confirm that the SCM fatigues initially and as fast as or faster than the SHM and IHM. In addition, upon completion of the exercise protocol, the SCM had a decreased MF rate, implying improved fatigue resistance, while the SHM and IHM showed increased MF rates, implying that these muscles increased their fatiguing effort. We conclude that the Shaker exercise initially leads to increased fatigue resistance of the SCM, after which the exercise loads the less fatigue-resistant SHM and IHM, potentiating the therapeutic effect of the Shaker exercise regimen with continued exercise performance.

Nerve conduction topography in geriatric hand assessment.

Motor nerve conduction is a noninvasive clinical test used to diagnose nerve problems such as carpal tunnel syndrome or peripheral neuropathy. Current techniques use a single-site recording over a superficial muscle. This traditional approach does not account for the electrical contributions from the other muscles innervated by the nerve being stimulated, which need to be considered with thumb carpometacarpal (CMC) degenerative joint disease (DJD) because these electrical contributions may change the anatomic relationship of the thenar muscles. This study recorded from 15 sites over the thenar eminence during motor nerve conduction studies of the median nerve of 12 young subjects with normal thenar anatomy and 25 elderly subjects with thumb CMC DJD. The maximum compound muscle action potential (CMAP) values did not occur in the same electrode position for the two groups, and traditional single-site recording would have resulted in smaller amplitudes and longer latencies for the elderly than the values noted with the multiple-site recordings. This pilot study of nerve conduction topography mapping with multiple-site recording illustrates that single-site studies may be misleading and supports further exploration of multichannel grid electrodes for topographic display and analysis of the CMAP.

Effect of rocker soles on plantar pressures.

OBJECTIVE: To examine the effect of different types of rocker soles on plantar pressures. DESIGN: In-shoe plantar pressures were measured in subjects without deformity with baseline shoes and 3 types of rockers: toe-only, negative heel, and double. SETTING: Medical college. PARTICIPANTS: Forty healthy patients (20 men, 20 women) without foot deformity. INTERVENTIONS: Plantar pressures were recorded over a 2 1/2-hour test period with over 400 steps analyzed for each type of rocker sole. Peak pressures, pressure-time integral (PTI), and sensor contact duration were computed for each step. MAIN OUTCOME MEASURES: Peak plantar pressure PTI, and contact duration were compared for each rocker with a baseline shoe. RESULTS: Significant reduction (P<.01) in peak pressure and PTI were recorded across the forefoot for all 3 rockers. The reduction of pressure at the forefoot was balanced by shifting pressure to the midfoot with the negative heel and toe-only rockers. CONCLUSION: This study lends scientific credence to the prescription of rocker soles for patients who need forefoot pressure reduction, such as in diabetic neuropathy and possible ulceration.

Effect of reference electrode position on the compound muscle action potential (CMAP) onset latency.

Compound muscle action potential (CMAP) onset latency is interpreted to reflect the arrival time at the muscle of impulses in the fastest-conducting motor nerve fiber. However, we have observed that the position of the reference or indifferent electrode (E2) affects CMAP onset latency. Motor nerve conduction studies (NCS) of the median, ulnar, and deep ulnar motor (DUM) nerves on 20 normal hands were performed using both traditional bipolar and experimental monopolar (referenced to the contralateral hand) montages. As the position of E2 was altered, the CMAP onset latency varied 0.1-0.5 ms for the median NCS, 0.1-0.3 ms for the ulnar NCS, and 0.1-1.5 ms for the DUM NCS. This study demonstrates that E2 recorded potentials are significant and vary with positioning, affecting motor onset latency. This has implications both for reference values and the physiologic interpretation of the CMAP waveform.