Wrist Postures While Typing on a Standard and Split Keyboard

Fifty experienced typists participated in a laboratory based repeated measures study with two factors: keyboard height (three) and keyboard configuration (three). The work surface heights tested were 63, 67 and 71 cm. The three keyboard configurations tested were: standard (Apple Extended™), alternative keyboard A (Microsoft Natural Keyboard) and alternative keyboard B (equivalent to Natural Keyboard with Leveler™ extended). Wrist and forearm posture data was acquired using electronic goniometers during 10 minutes of typing at each keyboard/height level. Across all heights tested, wrist extension, wrist ulnar deviation, and forearm pronation were statistically significantly closer to neutral when using alternative keyboard B than when using the standard keyboard.

Changes in wrist postures during a prolonged typing task

Twenty experienced typists participated in a laboratory based study to determine whether wrist and forearm postures changed over a 4 hour period of intensive keyboard use. Subjects were randomly assigned to use a conventional keyboard or a fixed split keyboard. Posture data was acquired using electrogoniometers after a 10 warm-up period and at the end of each hour. Wrist and forearm postures did not change significantly over the four hour period among subjects using the split geometry keyboard. On the conventional keyboard, all joint postures were stable except right wrist extension and left forearm pronation. The right wrist extension increased by 5° over the four hour period (p=.002) and left pronation decreased by approximately 9° (p=.001). Wrist postures among typists exposed for the first time to a split keyboard remained constant throughout a four hour period of intensive typing. On the conventional keyboard, some postures drifted over the four hour period.

Abstract P4-03-05: Wide-field optical coherence tomography (WF-OCT) for near real-time, point-of-care assessment of margin status in breast-conserving surgery specimens: Results of a feasibility study at a high-volume single-centre

Wide-Field Optical Coherence Tomography (WF-OCT) is a non-destructive, non-contact light imaging modality capable of label-free visualization of the internal microscopic architecture of breast tissue specimens. Its unique combination of high-resolution imaging in near real-time with tissue penetration depths approaching 2-mm makes it a promising imaging modality for obtaining detailed surgical margin status in breast-conserving surgery (BCS) specimens. A prototype WF-OCT imaging platform developed by Perimeter Medical Imaging, Inc. (Toronto, Canada) has permitted fully-automated, dynamically-focused visualization of margin widths around the intact surfaces of freshly excised BCS specimens. Herein are reported the results of a feasibility study at a high-volume single-centre evaluating the routine use of WF-OCT for sampling of surgical margin status in BCS specimens at the point-of-care.

Methods: Women with biopsy confirmed breast cancer and scheduled for primary BCS were recruited at Princess Margaret Cancer Centre (Toronto, Canada). Standard medical care was not altered. Freshly excised BCS specimens including all lumpectomy samples were imaged by WF-OCT immediately prior to standard histological processing. The system acquired dynamically-focused, hemispherical coverage over two contra-lateral surfaces of the intact BCS specimen within the time constraints of the cold ischemic time window. High-resolution (10 μm) images of the tissue surface down to a 1 to 2-mm depth were obtained. Blinded assessments were performed on image data sets by two clinical readers (surgeon and radiologist) trained on a validated and unrelated data set correlating OCT images with histology slides. The readers were first asked to independently assess margin status using only blinded pre- and intra-operative knowledge (without OCT). Upon completion, the readers were provided OCT images of all scanned surface and similarly asked to assess the margin status with the additional OCT information. These assessments were subsequently evaluated by a breast pathologist comparing the OCT images and corresponding histopathology sections. The added utility of WF-OCT imaging information for margin prediction was studied.

Results: [Pending study completion in August 2015]. Through accurate correlation with the histopathologic gold standard, OCT demonstrated capability to differentiate tissue microstructures, including: distinctive patterns for adipose tissue, fibrous stroma, breast lobules and ducts, cysts and microcysts, as well as in-situ and invasive carcinomas.

Implications: The fully-automated WF-OCT imaging platform can integrate conveniently into standard pathological processing workflows to provide comprehensive sampling of surgical margin status in BCS specimens at the point-of-care. Clinical readers from surgical and radiological backgrounds can be trained to competently interpret WF-OCT images of BCS specimens for accurate prediction margin status. The implementation of WF-OCT at the point-of-care for routine surgical margin assessments will be further explored in future clinical trials.

Citation Format: Valic MS, Leong WL, Done SJ, Wilson BC, Kulkarni S, McCready DR, Niu CJ, Atachia Y, Munro EA, Rempel D. Wide-field optical coherence tomography (WF-OCT) for near real-time, point-of-care assessment of margin status in breast-conserving surgery specimens: Results of a feasibility study at a high-volume single-centre. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P4-03-05.

Effectiveness of workplace interventions in the prevention of upper extremity musculoskeletal disorders and symptoms: an update of the evidence

The burden of disabling musculoskeletal pain and injuries (musculoskeletal disorders, MSDs) arising from work-related causes in many workplaces remains substantial. There is little consensus on the most appropriate interventions for MSDs. Our objective was to update a systematic review of workplace-based interventions for preventing and managing upper extremity MSD (UEMSD). We followed a systematic review process developed by the Institute for Work & Health and an adapted best evidence synthesis. 6 electronic databases were searched (January 2008 until April 2013 inclusive) yielding 9909 non-duplicate references. 26 high-quality and medium-quality studies relevant to our research question were combined with 35 from the original review to synthesise the evidence on 30 different intervention categories. There was strong evidence for one intervention category, resistance training, leading to the recommendation: Implementing a workplace-based resistance training exercise programme can help prevent and manage UEMSD and symptoms. The synthesis also revealed moderate evidence for stretching programmes, mouse use feedback and forearm supports in preventing UEMSD or symptoms. There was also moderate evidence for no benefit for EMG biofeedback, job stress management training, and office workstation adjustment for UEMSD and symptoms. Messages are proposed for both these and other intervention categories.

In vivo flexor tendon forces generated during different rehabilitation exercises

We measured in vivo forces in the flexor digitorum profundus and the flexor digitorum superficialis tendons during commonly used rehabilitation manoeuvres after flexor tendon repair by placing a buckle force transducer on the tendons of the index finger in the carpal canal during open carpal tunnel release of 12 patients. We compared peak forces for each manoeuvre with the reported strength of a flexor tendon repair. Median flexor digitorum profundus force (24 N) during isolated flexor digitorum profundus flexion and median flexor digitorum superficialis force (13 N) during isolated flexor digitorum superficialis flexion were significantly higher than during the other manoeuvres. Significantly higher median forces were observed in the flexor digitorum superficialis with the wrist at 30° flexion (6 N) compared with the neutral wrist position (5 N). Median flexor digitorum profundus forces were significantly higher during active finger flexion (6 N) compared with place and hold (3 N). Place and hold and active finger flexion with the wrist in the neutral position or tenodesis generated the lowest forces; isolated flexion of these tendons generated higher forces along the flexor tendons.

LEVEL OF EVIDENCE

III (controlled trial without randomization).

Ergonomic Aspects of Clinical and Surgical Procedures

This discussion panel aims to identify ergonomic concerns, solutions and research needs, physical stresses, and outcomes related to clinical and surgical procedures. This session will begin with formal presentations to demonstrate current ergonomic concerns and research initiatives associated with clinical and surgical procedures to frame the panel discussion for the second part of the session. Discussion of different procedures will help to identify solutions and research needs that relate to a broad range of ergonomic problems. Questions will be collected from the attendees and speakers and organized so as to guide the panel discussion and to engage all of the speakers in the discussion to achieve the symposium aims.

Influence of time pressure and verbal provocation on physiological and psychological reactions during work with a computer mouse

The overall aim of this study was to investigate whether time pressure and verbal provocation has any effect on physiological and psychological reactions during work with a computer mouse. It was hypothesised that physiological reactions other than muscle activity (i.e. wrist movements, forces applied to the computer mouse) would not be affected when working under stressful conditions. Fifteen subjects (8 men and 7 women) participated, performing a standardised text-editing task under stress and control conditions. Blood pressure, heart rate, heart rate variability, electromyography, a force-sensing computer mouse and electrogoniometry were used to assess the physiological reactions of the subjects. Mood ratings and ratings of perceived exertion were used to assess their psychological reactions. The time pressure and verbal provocation (stress situation) resulted in increased physiological and psychological reactions compared with the two control situations. Heart rate, blood pressure and muscle activity in the first dorsal interosseus, right extensor digitorum and right trapezius muscles were greater in the stress situation. The peak forces applied to the button of the computer mouse and wrist movements were also affected by condition. Whether the increases in the physiological reactions were due to stress or increased speed/productivity during the stress situation is discussed. In conclusion, work with a computer mouse under time pressure and verbal provocation (stress conditions) led to increased physiological and psychological reactions compared to control conditions.

Determination of photomodified oligodeoxynucleotides by exonuclease digestion, matrix-assisted laser desorption/ionization and post-source decay mass spectrometry

A fast method to detect and sequence photomodified oligodeoxynucleotides (ODNs) by exonuclease digestion and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is reported. Upon treatment of modified ODNs with both phosphodiesterase I and phosphodiesterase II, the digestion stops at the sites of photomodification. Post-source decay (PSD) of MALDI-produced ions from two enzymatic digestion end products distinguishes isomers such as 5'-d(T[cis-syn]TAAGC) and 5'-d(CGAAT[cis-syn]T), which have symmetrical or identical compositions at the 3' and 5' ends, respectively. Studies have also been done to follow the kinetics for enzyme degradation of photomodified ODNs. The calculated rate constants from a mathematical treatment of the time-dependent MALDI data clearly show that the enzymatic digestion rate slows as the enzyme approaches the modified site.

Matrix-assisted laser desorption/ionization mass spectrometry for locating abasic sites and determining the rates of enzymatic hydrolysis of model oligodeoxynucleotides

A method using a combination of exonuclease enzymatic digestion and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry was developed to locate model abasic sites in a series of model 21-base oligodeoxynucleotides in which a nucleobase was replaced by a hydrogen atom. The exonuclease digestion rate, with either snake venom phosphodiesterase (SVP) or bovine spleen phosphodiesterase (BSP), clearly slows as the digestion approaches the abasic sites and stops as it reaches it. An oligodeoxynucleotide containing an abasic site in which OH replaces the nucleobase shows similar results. MALDI mass spectra taken at appropriate times during the course of hydrolysis are the basis for rate measurements, and the kinetics also reveal the location of the abasic site. A mathematical treatment of the time-dependent MALDI data was implemented to obtain rate curves and rate constants for the enzymatic digestion of both modified and unmodified oligodeoxynucleotides.

The effects of reduced oxygen tension on cell proliferation and matrix synthesis in synovium and tendon explants from the rabbit carpal tunnel: an experimental study in vitro

Local ischemia may play an important role in the development of tendon degeneration as well as entrapment neuropathies. In order to investigate the cellular effects of hypoxia on tendon and synovial tissue from the carpal canal, dose response effects of oxygen on cell proliferation and synthesis of matrix components were examined in segments of synovial and flexor digitorum profundus tendon from the carpal tunnel of rabbits during short term culture. Explants were incubated in airtight containers flushed with either 0%, 1%, 3%, 20% O2 plus 2% CO2 and N2 to balance and labeled with either 3H-thymidine or 3H-proline and 35S-sulfate. Cell proliferation was significantly inhibited by hypoxia in synovium but not in tendon (P = 0.03). In parallel, the synthesis of non-collagenous proteins was significantly reduced in synovium but not in tendon (P = 0.006). In both tissues hypoxia significantly inhibited collagen synthesis. On the other hand, hypoxia had no significant effect on the synthesis of new proteoglycans as determined by 35S-sulfate incorporation. Hypoxia can inhibit cell proliferation and alter synthesis of matrix components in synovial tissue, but may only have minor effects on non-collagen protein synthesis in tendon explants from the carpal canal of rabbit forepaws.

Measuring and characterizing force exposures during computer mouse use

OBJECTIVES

The purpose of this study was to develop and validate a sampling strategy for characterizing the finger force exposures associated with computer mouse use.

METHODS

Mouse forces were measured from 16 subjects (8 men, 8 women), on 3 separate days, at their actual workstations while they performed (i) their regular work, (ii) a battery of standardized tasks, and (iii) simulated mouse use.

RESULTS

The forces applied to the mouse did not vary between hours or days. During regular work, the mouse was used 78.0 (SD 40.7) times per hour, accounting for 23.7 (SD 9.5)% of the worktime. The mean forces applied to the sides and button of the mouse were low, averaging 0.6 % (0.35 N) and 0.8 % (0.43 N) of the maximal voluntary contraction, respectively. The forces applied to the mouse during the standardized tasks differed from the regular work forces; however, there were moderate-to-strong correlations between the 2 measures.

CONCLUSIONS

With respect to performing exposure assessment studies, the 3 major findings were (i) mouse force measurements should be made while subjects perform their actual work in order to characterize the absolute applied force accurately, (ii) the forces applied to the mouse during the performance of a short battery of standardized tasks can be used to characterize relative exposure and identify computer operators or work situations for which higher forces are applied to the mouse, and (iii) subjects cannot accurately simulate mouse forces.

Classification criteria and severity assessment in work-associated upper extremity disorders: methods matter

Work-associated musculoskeletal disorders of the upper extremity are common and disabling. Research on these disorders is needed and requires valid methods of classification of the disorders for epidemiologic studies and measurement of their impact on functional status. This commentary discusses the methodologic aspects of classification and functional status assessment in upper extremity musculoskeletal disorders.

Sensitivity of trapezius electromyography to differences between work tasks - influence of gap definition and normalisation methods

Surface electromyography (EMG) has been used extensively to estimate muscular load in studies of work related musculoskeletal disorders, especially for the trapezius muscle. The occurrences of periods of EMG silence (gaps), the time below a predetermined threshold level (muscular rest) and various percentiles of the amplitude distribution (APDF) are commonly used summary measures. However, the effects of the criteria used to calculate these measures (e.g., gap duration, threshold level, normalisation method) on the sensitivity of these measures to accurately differentiate work loads is not well known. Bilateral trapezius EMG was recorded, for a full workday, for 58 subjects following both maximal (MVE) and submaximal (RVE) reference contractions. Gap frequency, muscular rest, and percentiles were derived for eight fundamental work tasks. The calculations were performed using different gap duration criteria, threshold levels and normalisation methods.A gap duration of less than 1/2 s, and threshold level approximately 0.3% MVE for gap frequency, and approximately 0.5% MVE for muscular rest, were the criteria that optimised sensitivity to task differences. Minimal sensitivity to tasks and a high sensitivity to individuals was obtained using gap frequency with a threshold level of approximately 1% MVE. Normalisation to RVE, rather than MVE, improved sensitivity to differences between tasks, and reduced undesirable variability. Muscular rest was more sensitive to task differences than APDF percentiles.

Effects of computer mouse design and task on carpal tunnel pressure

Computer mouse use has become an integral part of office work in the past decade. Intensive mouse use has been associated with increased risk of upper extremity musculoskeletal disorders, including carpal tunnel syndrome. Sustained, elevated fluid pressure in the carpal tunnel may play a role in the pathophysiology of carpal tunnel syndrome. Carpal tunnel pressure was measured in 14 healthy individuals while they performed tasks using three different computer mice. Participants performed a multidirectional dragging ('drag and drop') task starting with the hand resting (static posture) on the mouse. With one mouse, an additional pointing ('point-and-click') task was performed. All mice were associated with similar wrist extension postures (p = 0.41) and carpal tunnel pressures (p = 0.48). Pressures were significantly greater during dragging and pointing tasks than when resting the hand (static posture) on the mouse (p = 0.003). The mean pressures during the dragging tasks were 28.8-33.1 mmHg, approximately 12 mmHg greater than the static postures. Pressures during the dragging task were higher than the pointing task (33.1 versus 28.0 mmHg), although the difference was borderline non-significant (p = 0.06). In many participants the carpal tunnel pressures measured during mouse use were greater than pressures known to alter nerve function and structure, indicating that jobs with long periods of intensive mouse use may be at an increased risk of median mononeuropathy. A recommendation is made to minimize wrist extension, minimize prolonged dragging tasks and frequently perform other tasks with the mousing hand.

Wrist and forearm postures and motions during typing

Awkward upper extremity postures and repetitive wrist motions have been identified by some studies as risk factors for upper extremity musculoskeletal disorders during keyboard work. However, accurate body postures and joint motions of typists typing on standardized workstations are not known. A laboratory study was conducted to continuously measure wrist and forearm postures and motions of 25 subjects while they typed for 10-15 min at a standard computer workstation adjusted to the subjects' anthropometry. Electrogoniometers continuously recorded wrist and forearm angles. Joint angular velocities and accelerations were calculated from the postural data. The results indicate that wrist and forearm postures during typing were sustained at non-neutral angles; mean wrist extension angle was 23.4 +/- 10.9 degrees on the left and 19.9 +/- 8.6 degrees on the right. Mean ulnar deviation was 14.7 +/- 10.1 degrees on the left and 18.6 +/- 5.8 degrees on the right. More than 73% of subjects typed with the left or right wrist in greater than 15 degrees extension and more than 20% typed with the left or right wrist in greater than 20 degrees ulnar deviation. Joint angles and motions while typing on an adjusted computer workstation were not predictable based on anthropometry or typing speed and varied widely between subjects. Wrist motions are rapid and are similar in magnitude to wrist motions of industrial workers performing jobs having a high risk for developing cumulative trauma disorders. The magnitude of the dynamic components suggests that wrist joint motions may need to be evaluated as a risk factor for musculoskeletal disorders during typing.

Effect of four computer keyboards in computer users with upper extremity musculoskeletal disorders

Eighty computer users with musculoskeletal disorders participated in a 6-month, randomized, placebo-controlled trial evaluating the effects of four computer keyboards on clinical findings, pain severity, functional hand status, and comfort. The alternative geometry keyboards tested were: the Apple Adjustable Keyboard [kb1], Comfort Keyboard System [kb2], Microsoft Natural Keyboard [kb3], and placebo. Compared to placebo, kb3 and to a lesser extent kb1 groups demonstrated an improving trend in pain severity and hand function following 6 months of keyboard use. However, there was no corresponding consistent improvement in clinical findings in the alternative geometry keyboard groups compared to the placebo group. Overall, there was a significant correlation between improvement of pain severity and greater satisfaction with the keyboards. These results provide evidence that keyboard users may experience a reduction in hand pain after several months of use of some alternative geometry keyboards.

Effect of four computer keyboards in computer users with upper extremity musculoskeletal disorders

Eighty computer users with musculoskeletal disorders participated in a 6-month, randomized, placebo-controlled trial evaluating the effects of four computer keyboards on clinical findings, pain severity, functional hand status, and comfort. The alternative geometry keyboards tested were: the Apple Adjustable Keyboard [kb1], Comfort Keyboard System [kb2], Microsoft Natural Keyboard [kb3], and placebo. Compared to placebo, kb3 and to a lesser extent kb1 groups demonstrated an improving trend in pain severity and hand function following 6 months of keyboard use. However, there was no corresponding consistent improvement in clinical findings in the alternative geometry keyboard groups compared to the placebo group. Overall, there was a significant correlation between improvement of pain severity and greater satisfaction with the keyboards. These results provide evidence that keyboard users may experience a reduction in hand pain after several months of use of some alternative geometry keyboards.

Workplace use of an adjustable keyboard: adjustment preferences and effect on wrist posture

This study presents an evaluation of an adjustable keyboard based on subjective preference and wrist joint motion during typing. Thirty-five computer users used the adjustable split design keyboard for 7-14 days during their usual work and were instructed to adjust the keyboard to the opening angle they preferred. At the end of this period, three-dimensional motion analysis was performed to compare the distribution of wrist joint angles while subjects typed on a conventional keyboard and the adjustable keyboard adjusted to the subject's preferred angle. The mean preferred opening angle was 14 degrees +/- 10. The mean ulnar deviation of the subjects who selected the opening angles between 21 and 28 degrees (n = 12) decreased from 18 degrees +/- 5 on the flat to 14 degrees +/- 5 on the adjustable (p < 0.05), while those who selected 0 to 10 degrees (n = 6) and 11 to 20 degrees (n = 17) split angles showed no significant differences in ulnar deviation. Mean wrist extension on the adjustable keyboard was 17 degrees +/- 5 and was significantly less than the 24 degrees +/- 5 observed on the conventional keyboard and most likely due to the presence of palm support. On average, subjects reported that the adjustable keyboard was more comfortable (0.5 +/- 0.5) (worse = -1, same = 0, better, = 1) in comparison with the conventional keyboard.

Effect of keyboard keyswitch design on hand pain

This randomized clinical trial evaluated the effects of keyboard keyswitch design on computer users with hand paresthesias. Twenty computer users were matched and randomly assigned to keyboard A (n = 10) or B (n = 10). The keyboards were of conventional layout and differed in keyswitch design. Various outcome measures were assessed during the 12 weeks of use. Subjects assigned keyboard A experienced a decrease in hand pain between weeks 6 and 12 when compared with keyboard B subjects (P = 0.05) and demonstrated an improvement in the Phalen test time (right hand, P = 0.006; left hand, P = 0.06). Keyboard assignment had no significant effect on change in hand function or median nerve latency. We conclude that use of keyboard A for 12 weeks led to a reduction in hand pain and an improved physical examination finding when compared with keyboard B. There was no corresponding improvement in hand function or median nerve latency.

Risk factors for musculoskeletal disorders among computer users

This investigation of current epidemiologic and ergonomic research demonstrates consistent relationships between certain computer-related factors and musculoskeletal disorders.

Consensus criteria for the classification of carpal tunnel syndrome in epidemiologic studies

Criteria for the classification of carpal tunnel syndrome for use in epidemiologic studies were developed by means of a consensus process. Twelve medical researchers with experience in conducting epidemiologic studies of carpal tunnel syndrome participated in the process. The group reached agreement on several conceptual issues. First, there is no perfect gold standard for carpal tunnel syndrome. The combination of electrodiagnostic study findings and symptom characteristics will provide the most accurate information for classification of carpal tunnel syndrome. Second, use of only electrodiagnostic study findings is not recommended. Finally, in the absence of electrodiagnostic studies, specific combinations of symptom characteristics and physical examination findings may be useful in some settings but are likely to result in greater misclassification of disease status.

A structural model of the forced compression of the fingertip pulp

The fingertip pulp modulates the force transmitted to the underlying musculoskeletal system during finger contact on external bodies. A model of the fingertip pulp is needed to represent the transmission of forces to the tendons, muscles, and bone during these contacts. In this study, a structural model of the in vivo human fingertip was developed that incorporates both the material inhomogeneity and geometry. Study objectives were to determine (1) if this fingertip model can predict the force-displacement and force contact area responses of the in vivo human fingertip during contact with a flat, rigid surface, and (2) if the stresses and strains predicted by this model are consistent with the tactile sensing functionality of the in vivo human fingertip. The in vivo fingertip pulp was modeled as an inflated, ellipsoidal membrane, containing an incompressible fluid, that is quasi-statically compressed against a flat, frictionless surface. The membrane was assigned properties of skin (Veronda and Westmann, 1970) and when inflated, possessed dimensions approximating those of a human fingertip. Finite deformation was allowed. The model was validated by the pulp force-displacement relationship obtained by Serina et al. (1997) and by measurements of the contact area when the fingertip was pressed against a rigid surface with contact forces between 0.25 and 7.0 N. Model predictions represent the experimental data sufficiently well, suggesting that geometry, inhomogeneous material structure, and initial skin tension appear to represent the nonlinear response of the in vivo human fingertip pulp under compression. The predicted response of the fingertip pulp is consistent with its functionality as a tactile sensor.

Effects of forearm pronation/supination on carpal tunnel pressure

The effects of forearm rotation and metacarpophalangeal (MP) flexion on carpal tunnel pressure were investigated in 17 healthy adults who had no evidence of carpal tunnel syndrome (CTS). Pressure was continuously recorded with a saline-filled catheter inserted into the carpal tunnel and connected to a pressure transducer while test subjects slowly rotated the forearm from full pronation to full supination. Forearm rotation was repeated with MP flexion of 0 degrees, 45 degrees, and 90 degrees. Both forearm rotation and MP flexion, and their interaction term, significantly affected carpal tunnel pressure and accounted for most of the variability in the data. Highest mean pressures (55 mmHg) were recorded in full supination and 90 degrees MP flexion and lowest pressures (12 mmHg) were recorded at 45 degrees pronation and 45 degrees MP flexion. These data may be useful in the design of tasks and hand tools in the management and prevention of CTS.

Force response of the fingertip pulp to repeated compression--effects of loading rate, loading angle and anthropometry

Repeated loading of the fingertips has been postulated to contribute to tendon and nerve disorders at the wrist during activities associated with prolonged fingertip loading such as typing. To fully understand the pathomechanics of these soft tissue disorders, the role of the fingertip pulp in attenuating the applied dynamic forces must be known. An experiment was conducted to characterize the response of the in vivo fingertip pulp under repeated, dynamic, compressive loadings, to identify factors that influence pulp dynamics, and to better understand the force modulation by the pulp. Twenty subjects tapped repeatedly on a flat plate with their left index finger, while the contact force and pulp displacement were measured simultaneously. Tapping trials were conducted at three fingertip contact angles from the horizontal plane (0 degree, 45 degrees, and 90 degrees) and five tapping rates (0.25, 0.5, 1, 2, and 3 Hz). The fingertip pulp responds as a viscoelastic material, exhibiting rate-dependence, hysteresis, and a nonlinear force-displacement relationship. The pulp was relatively compliant at forces less than 1 N, but stiffened rapidly with displacement at higher forces for all loading conditions. This suggests that high-frequency forces of a small magnitude (< 1 N) are attenuated by the nonlinearly stiffening pulp while these forces of larger magnitude are transmitted to the bone. Pulp response was significantly influenced by the angle of loading. Fingertip dimensions, gender, and subject age had little to no influence on pulp parameters.

The effect of keyboard keyswitch make force on applied force and finger flexor muscle activity

The design of the force-displacement characteristics or 'feel' of keyboard keyswitches has been guided by preference and performance data; there has been very little information on how switch 'feel' alters muscle activity or applied force. This is a laboratory-based repeated measures design experiment to evaluate the effect of computer keyboard keyswitch design on applied finger force and muscle activity during a typing task. Ten experienced typists typed on three keyboards which differed in keyswitch make force (0.34, 0.47 and 1.02 N) while applied fingertip force and finger flexor electromyograms were recorded. The keyboard testing order was randomized and subjects typed on each keyboard for three trials, while data was collected for a minimum of 80 keystrokes per trial. No differences in applied fingertip force or finger flexor EMG were observed during typing on keyboards with switch make force of 0.34 or 0.47 N. However, applied fingertip force increased by approximately 40% (p < 0.05) and EMG activity increased by approximately 20% (p < 0.05) when the keyswitch make force was increased from 0.47 to 1.02 N. These results suggest that, in order to minimize the biomechanical loads to forearm tendons and muscles of keyboard users, keyswitches with a make force of 0.47 N or less should be considered over switches with a make force of 1.02 N.

Effects of static fingertip loading on carpal tunnel pressure

The purpose of this study was to explore the relationship between carpal tunnel pressure and fingertip force during a simple pressing task. Carpal tunnel pressure was measured in 15 healthy volunteers by means of a saline-filled catheter inserted percutaneously into the carpal tunnel of the nondominant hand. The subjects pressed on a load cell with the tip of the index finger and with 0, 6, 9, and 12 N of force. The task was repeated in 10 wrist postures: neutral; 10 and 20 degrees of ulnar deviation; 10 degrees of radial deviation; and 15, 30, and 45 degrees of both flexion and extension. Fingertip loading significantly increased carpal tunnel pressure for all wrist angles (p = 0.0001). Post hoc analyses identified significant increase (p < 0.05) in carpal tunnel pressure between unloaded (0 N) and all loaded conditions, as well as between the 6 and 12 N load conditions. This study demonstrates that the process whereby fingertip loading elevates carpal tunnel pressure is independent of wrist posture and that relatively small fingertip loads have a large effect on carpal tunnel pressure. It also reveals the response characteristics of carpal tunnel pressure to fingertip loading, which is one step in understanding the relationship between sustained grip and pinch activities and the aggravation or development of median neuropathy at the wrist.

Keyboard reaction force and finger flexor electromyograms during computer keyboard work

This study examines the relationship between forearm EMGs and keyboard reaction forces in 10 people during keyboard tasks performed at a comfortable speed. A linear fit of EMG force data for each person and finger was calculated during static fingertip loading. An average r2 of .71 was observed for forces below 50% of the maximal voluntary contraction (MVC). These regressions were used to characterize EMG data in force units during the typing task. Averaged peak reaction forces measured during typing ranged from 3.33 N (thumb) to 1.84 N (little finger), with an overall average of 2.54 N, which represents about 10% MVC and 5.4 times the key switch make force (0.47 N). Individual peak or mean finger forces obtained from EMG were greater (1.2 to 3.2 times) than force measurements; hence the range of r2 for EMG force was .10 to .46. A closer correspondence between EMG and peak force was obtained using EMG averaged across all fingers. For 5 of the participants the force computed from EMG was within +/-20% of the reaction force. For the other 5 participants forces were overestimated. For 9 participants the difference between EMG estimated force and the reaction force was less than 13% MVC. It is suggested that the difference between EMG and finger force partly results from the amount of muscle load not captured by the measured applied force.

Upper-limb Postures and Movements during Diamond Polishing

Previous occupational health studies of diamond polishers have identified high rates of musculoskeletal disorders of the hands and arms in this population, specifically, ulnar neuropathy in the right elbow. These disorders may be due to the repetitive and forceful motions of the upper extremity required to manipulate the hand-held polishing tools. A video-based, biomechanical analysis of the upper extremities of polishers at several diamond-processing factories in Israel was conducted. Detailed motion measurements of the wrists, elbows, and shoulders of polishers were made while the subjects performed their usual work. During a typical workday, the basic polishing cycle, which involves a series of stereotyped hand and arm movements, is repeated more than 5,000 times. Sustained, extreme flexion of the right elbow, which is the arm holding the eyepiece, may account for the higher rates of ulnar neuropathy in this extremity.

Musculoskeletal symptoms related to video display terminal use: an analysis of objective and subjective exposure estimates

The occupational use of video display terminals (VDTs) has been associated with the increasing incidence of upper extremity musculoskeletal disorders, often called cumulative trauma disorders. To guide clinical and policy decisions about the prevention and treatment of these VDT related disorders, valid and economic measures of total daily VDT use and VDT related job tasks such as data entry or editing will be important. In this study of newspaper reporters and copy editors (n = 83), VDT use was measured with employee self reports and by sampling the work behaviors of a subsample of employees. Behavioral sampling estimated VDT use as a characteristic of the job as opposed to a characteristic of individual employee performance. Overall, the two techniques of measuring occupational VDT use compared favorably, with the exception that self reported hours of VDT use tended to exceed the hours of use estimated by behavioral observation for employees who were younger and those who reported greater job demands. The findings suggest that behavioral sampling is a valid technique for estimating VDT use as a job characteristic.

Temperature effects on vibrotactile sensitivity threshold measurements: implications for carpal tunnel screening tests

This study examines the effect of skin temperature on fingertip vibrotactile sensitivity measurements and the resulting implications for carpal tunnel syndrome screening tests. Twenty subjects (11 men, 9 women) were tested for fingertip vibrotactile thresholds using the method of limits at four different frequencies (31.5, 125, 250, and 500 Hz) and six temperature categories (17 degrees-20 degrees C, 20 degrees-23 degrees C, 23 degrees-26 degrees C, 26 degrees-29 degrees C, 29 degrees-32 degrees C, 32 degrees-35 degrees C). Vibrotactile sensitivity thresholds increased with decreasing fingertip skin temperature. Furthermore, the relationship was a function of vibration frequency. Higher frequencies were more affected by temperature than lower frequencies, with significant effects beginning at 29 degrees C. These temperature-related effects may lead to possible false positive results in screening for carpal tunnel syndrome or other neuropathies. To minimize potential temperature-induced misclassification errors during these screening tests, fingertip skin temperature should be recorded before measurement and probably maintained above 29 degrees C during the measurement.

VDT-related musculoskeletal symptoms: interactions between work posture and psychosocial work factors

Video display terminal (VDT) operators (n = 150) in the editorial department of a large metropolitan newspaper participated in a study of day-to-day musculoskeletal symptoms. Work posture related to the VDT workstation and psychosocial work factors were also investigated for their contributions to the severity of upper body pain, numbness, and stiffness using a representative subsample (n = 70). Self-report measures included Karasek's Job Content Instrument and the author-designed Work Interpersonal Relationships Inventory. Independent observations of work posture were performed using techniques similar to those reported by Sauter et al. [1991]. Pain during the last week was reported by 59% (n = 88) of the respondents, and 28% (n = 42) were categorized by symptom criteria potentially to have musculoskeletal disorders. More hours per day of VDT use and less decision latitude on the job were significant risk factors for potential musculoskeletal CTDs. Head rotation and relative keyboard height were significantly related to more severe pain and stiffness in the shoulders, neck, and upper back. Lower levels of co-worker support were associated with more severe hand and arm numbness. For both the region of the shoulders, neck, and upper back and the hand and arm region, however, the contributions of relative keyboard and seat back heights to symptom severity were modified by psychological workload, decision latitude, and employee relationship with the supervisor. Alternative explanations for these findings are discussed.

A method of measuring fingertip loading during keyboard use

A single keycap on a standard alphanumeric computer keyboard was instrumented with a piezoelectric load cell and the fingertip motion was recorded with a high-speed video motion analysis system. Contact force histories between the fingertip and the keycap were recorded while four subjects typed a standard text for five minutes. Each keystroke force history is characterized by three distinct phases: (I) keyswitch compression, (II) finger impact and (III) fingertip pulp compression and release. Each keystroke force history contained two relative maxima, one in phase II and one in phase III. The subject mean peak forces ranged from 1.6 to 5.3 N and the subject mean peak fingertip velocities ranged from 0.3 to 0.7 m/s. Motion analyses and force measurements suggest a ballistic model of finger motion during typing.

Carpal tunnel syndrome among grocery store workers

The California Department of Health Services evaluated carpal tunnel syndrome (CTS), a median nerve entrapment condition associated with forceful and repetitive wrist motion, among grocery store workers at a large California supermarket where a CTS cluster had been reported. Forceful and repetitive wrist motion was measured, in three exposure levels, through a job classification scheme based upon type of work tasks and average time per week spent performing these tasks. A medical questionnaire and measurements of median sensory nerve conduction were used to measure CTS. CTS prevalence was 23% based upon a sample of 56 participants drawn from a workforce of 69 employees. A relative risk of 8.3 (95% confidence interval 2.6-26.4) for a history of CTS-like symptoms between the high and low exposure level groups held up after adjustment for the potential confounders of age, sex, alcohol consumption, and high-risk medical history. It was concluded that the basic principles of good ergonomic design should be used to prevent or diminish the risk of musculoskeletal injury in the workplace.

The effect of wearing a flexible wrist splint on carpal tunnel pressure during repetitive hand activity

We investigated how repetitive hand activity normally affects carpal tunnel pressure and whether a flexible wrist splint can influence this effect. Nineteen healthy subjects were evaluated under four test conditions: at rest with and without a wrist splint (baseline) and while performing a repetitive task with and without a wrist splint. The task involved loading and unloading 1 lb. cans from a box at a rate of 20 cans per minute for period of 5 minutes. Carpal tunnel pressure and wrist angles were continuously monitored by means of a fluid-filled catheter inserted into the carpal canal and a two-channel electrogoniometer mounted on the dorsum of the hand and forearm. Without the splint, carpal tunnel pressure rose from a median baseline level of 8 +/- 6 mmHg to 18 +/- 13 mmHg during activity. With the splint, carpal tunnel pressure rose from a baseline of 13 +/- 5 mmHg to 21 +/- 12 mmHg during activity. Median carpal tunnel pressure during activity with the splint was no different from that without the splint. Our data indicate that the median nerve is subjected to increased pressure within the carpal tunnel during repetitive hand activity. Wearing a flexible wrist splint during activity limits the range of wrist motion but has no significant effect on carpal tunnel pressure.

Hospital records as a data source for occupational disease surveillance: a feasibility study

To assess the feasibility of using hospital records for occupational disease surveillance and to evaluate the quality of the industry/occupation (I/O) information available in these records, the computer file of all discharge diagnoses from a large health maintenance organization during 1985 was reviewed. The frequencies of discharge diagnoses previously listed as Sentinel Health Events (Occupational), or SHE (O), were calculated and three possible SHE(O) diagnoses--lung cancer, bladder cancer, and toxic hepatitis--were selected for further review. Outpatient charts of patients discharged for each diagnosis were abstracted with regard to I/O information and the discharged patients were interviewed by telephone to obtain a lifetime occupational history. The accuracy of the I/O information obtained from the hospital chart was compared to that obtained by patient interview by number of digits matched on standard classification codes. The frequencies of matches for occupation and industry were greater for "usual" than for "last" categories with both cancer diagnoses, but were similar for "usual" and "last" categories with toxic hepatitis. To assess the proportion of each possible SHE(O) diagnosis that was related to workplace exposures, the I/O information obtained by interview was rated in a blinded fashion by an experienced occupational medicine physician. The highest probability ratings for work-relatedness were noted for lung cancer, primarily due to asbestos exposure. The results of this study suggest that hospital records can be used to identify possible SHE(O); if adequate I/O information is available, then work-relatedness can be assessed. However, the accuracy of I/O obtained from hospital charts is relatively low. The efficient and accurate collection of I/O information from hospital records will require the use of a simple, easily coded instrument to be routinely administered on admission.

Respiratory effects of exposure of shipyard workers to epoxy paints

Epoxy resin systems have been associated with occupational asthma in several case reports, but medical publications contain little on the potential adverse respiratory effects of these chemicals in exposed worker populations. To further evaluate the association of workplace exposure to epoxy paints and respiratory dysfunction, the cross workshift changes in pulmonary function and symptoms of 32 shipyard painters exposed to epoxy paints were compared with 28 shipyard painters not exposed to epoxy paints. The prevalence of lower respiratory tract symptoms was significantly higher among painters exposed to epoxy paints compared with controls. Among exposed painters the mean cross workshift change in forced expiratory volume in one second (FEV1) (-3.4%) was greater than the decrement in the non-exposed group (-1.4%). A significant linear relation was seen between % decrement in FEV1 and hours of exposure to epoxy paints. This study suggests that epoxy resin coatings as used by shipyard painters are associated with increased lower respiratory tract symptoms and acute decrements in FEV1. Adequate respiratory protection and medical surveillance programmes should be established in workplaces where exposure to epoxy resin systems occurs.

Medical surveillance in the workplace: overview

Medical surveillance in the workplace is the systematic collection and evaluation of employees' health data to identify specific instances of illness or health trends suggesting an adverse effect of workplace exposures on employees' health. This process is coupled with actions to reduce hazardous workplace exposures, as reviewed in this issue.

Biological monitoring

It is important to distinguish biological from medical or health monitoring because the submission of a biological specimen often leads to the assumption of the part of workers and also health professionals that health effects are being measured, and that measurement exceeding a reference value indicates disease rather than exposure or health risk. This chapter briefly reviews the basic principles of biological monitoring, focusing primarily on its role within medical surveillance.

Occupational illness and poison control centers. Referral patterns and service needs

In a study of occupational illness reported to a regional poison control center and to gauge the center's outreach and services, we did follow-up interviews of 301 case contacts over a 6-month period. We ascertained referral routes, reasons for contacting the poison control center, and awareness of the center's function. For 122 cases a nonphysician was the initial poison control center contact. Of the nonphysician contacts, 41 had already consulted a health care provider and been referred to the poison control center for assistance. Of the 70 persons with exposure, only 21 had been aware before their exposures that poison control center services might include occupational chemical illness consultation. Physicians and nonphysicians expressed similar reasons for contacting the poison control center, with 118 of 301 identifying the need for an exposure hazard risk assessment. These data suggest that although those contacting a poison control center because of occupational illness include a variety of cases, they have many similar service needs.

Occupational illness: case detection by poison control surveillance

STUDY OBJECTIVE

To evaluate the usefulness of poison control center detection in occupational illness surveillance.

DESIGN

Case series of all occupationally related exposures referred for poison control center consultation over 6 months. Follow-up structured interviews were done of exposed persons and health care providers. Cases were traced under established occupational illness reporting programs.

SETTING

A regional poison control center.

PATIENTS

Consecutive sample of 461 symptomatic occupational exposure cases. After exclusions and losses to follow-up, interview of 301 patients and the treating physician, physician's assistant, or nurse practitioner for the 223 of the patients under direct medical care.

MEASUREMENTS AND MAIN RESULTS

One hundred and fifty-five persons (61%; CI, 55% to 67%) had systemic or respiratory illness; 109 (36%; CI, 31% to 41%) had eye or skin conditions. Work practices were associated with exposures more often than technical failure; 118 persons (39%; CI, 33% to 45%) reported lack of respirators or other appropriate personal protective equipment. For 223 persons who received direct medical care, only five treating health care providers (2%; CI, 0.2% to 4%) reported occupational specialization, although occupational care was a regular practice activity for 128 of the health care providers (57%; CI, 51% to 63%). Sixty-seven cases (22%; CI, 17% to 27%) were detected by the Doctor's First Report surveillance program; 97 cases (32%; CI, 27% to 37%) comprised the maximal detection estimated for Occupational Safety and Health Administration surveillance.

CONCLUSIONS

Poison control center detection provides a useful surveillance measure for occupational illness. The proportion of case detection failures by established surveillance programs suggests that the incidence of occupational illness in the United States, which is calculated from these incomplete programs, may be three to five times greater than previously estimated.