Neutral Wrist Research Articles

An MRI evaluation of carpal tunnel dimensions in healthy wrists: Implications for carpal tunnel syndrome

Deviated wrist postures and pinch grip use have been linked to the development of carpal tunnel syndrome and are likely related to the size and shape of the carpal tunnel. The purpose of this study was to quantify carpal tunnel dimensions with changes in wrist posture and pinch grip. Eight healthy volunteers (4 male, 4 female) underwent magnetic resonance imaging of their dominant wrists under seven conditions which included: 30 degrees wrist extension, neutral and 30 degrees flexion (with and without a 10 N pinch force) and a fist with a neutral wrist. Cross-sectional area of the carpal tunnel and its contents were calculated at 3mm increments along the length of the tunnel and integrated to calculate volumes. Ratios were calculated between the contents of the tunnel to the tunnel itself for area and volume. The use of a correction factor significantly reduced volume and distal carpal tunnel area in flexed and extended wrists. Carpal tunnel areas were largest in neutral and smallest at the distal end with wrist flexion. An extended wrist resulted in the smallest carpal tunnel and content volumes as well as the smallest carpal tunnel content volume to carpal tunnel volume ratios. While men had significantly larger areas and volumes than women for both the carpal tunnel and it contents, there were no differences in ratios between the contents and tunnel size. A simple correction factor for non-perpendicular magnetic resonance images proved useful in relating volume changes to known pressure changes within the carpal tunnel. More inclusive and detailed evaluation of the carpal tunnel and its contents is required to fully understand mechanisms for median nerve compression in the carpal tunnel.

Symptoms and Radiographic Findings in the Proximal and Distal Ulnar Stumps After the Sauvé-Kapandji Procedure for Treatment of Chronic Derangement of the Distal Radioulnar Joint

We analyzed correlations between symptoms and radiographic findings with respect to the proximal and distal ulnar stumps after the Sauvé-Kapandji procedure for treating chronic derangement of the distal radioulnar joint. A total of 26 patients were studied (13 men, 13 women) with a mean age of 46 years at examination. Clinical assessment included elicitation of postoperative symptoms related to the proximal and distal ulnar stumps. In the radiographic study the radioulnar distance in the neutral wrist position and the presence or absence of scalloping at the radius were determined from posteroanterior (PA) views. The total mobility distance of the proximal ulnar stump was measured on the PA and lateral views while the wrist moved from radial to ulnar deviation or from extension to flexion. Eleven patients complained of tenderness over the distal ulnar stump and 5 patients felt discomfort around the proximal ulnar stump during forearm rotation. The postoperative radioulnar distance in patients with tenderness was significantly smaller than in the group without tenderness. Scalloping at the radius was shown in 9 patients but it was not related to the radioulnar distance. The total mobility distance of the proximal ulnar stump on the PA view was significantly greater in patients with tenderness than in those without, and it also was significantly greater in patients with scalloping than in those without. The total mobility distance on the lateral view was significantly greater in the group with discomfort than in the group without discomfort. The radioulnar distance was related to tenderness over the distal ulnar stump but not to the scalloping. Tenderness and scalloping each were related to radioulnar instability of the proximal ulnar stump. Discomfort around the proximal ulnar stump was related to dorsovolar instability of the stump. Prognostic, Level IV.

Coordinate systems for the carpal bones of the wrist

The eight small and complexly shaped carpal bones of the wrist articulate in six degrees of freedom with each other and to some extent with the radius and the metacarpals. With the increasing number and sophistication of studies of the carpus, a standardized definition for a coordinate system for each the carpal bones would aid in the reporting and comparison of findings. This paper presents a method for defining and constructing a coordinate system specific to each of the eight carpal bones based upon the inertial properties of the bone, derived from surface models constructed from three-dimensional (3-D) medical image volumes. Surface models from both wrists of 5 male and 5 female subjects were generated from CT image volumes in two neutral wrist positions (functional and clinical). An automated algorithm found the principal inertial axes and oriented them according to preset conditions in 85% of the bones, the remaining bones were corrected manually. Six of the eight carpal bones were significantly more extended in the functional neutral position than in the clinical neutral position. Gender had no significant effect on carpal bone posture in either wrist position. Correlations between the 3-D carpal posture and the commonly used 2-D clinical radiographic carpal angles are established. 3-D coordinate systems defined by the anatomy of the carpal bone, such as the ones presented here, are necessary to completely describe 3-D changes in the posture of the carpal bones.

Different computer tasks affect the exposure of the upper extremity to biomechanical risk factors

In order to determine differences in biomechanical risk factors across computer tasks, a repeated measures laboratory experiment was completed with 30 touch-typing adults (15 females and 15 males). The participants completed five different computer tasks: typing text, completing an html-based form with text fields, editing text within a document, sorting and resizing objects in a graphics task and browsing and navigating a series of intranet web pages. Electrogoniometers and inclinometers measured wrist and upper arm postures, surface electromyography measured muscle activity of four forearm muscles and three shoulder muscles and a force platform under the keyboard and force-sensing computer mouse measured applied forces. Keyboard-intensive tasks were associated with less neutral wrist postures, larger wrist velocities and accelerations and larger dynamic forearm muscle activity. Mouse-intensive tasks (graphics and intranet web page browsing) were associated with less neutral shoulder postures and less variability in forearm muscle activity. Tasks containing a mixture of mouse and keyboard use (form completion and text editing) were associated with higher shoulder muscle activity, larger range of motion and larger velocities and accelerations of the upper arm. Comparing different types of computer work demonstrates that mouse use is prevalent in most computer tasks and is associated with more constrained and non-neutral postures of the wrist and shoulder compared to keyboarding.

Ergonomics Evaluation of the Use of a Handled Shower-Cleaning Tool

Cleaning a bathroom presents several risk factors for acute and cumulative musculoskeletal injury. This study attempted to determine if using a handled tool while cleaning a typical North American bathtub/shower combination reduces the stress placed on the musculoskeletal system when compared to the use of a spray cleaner and sponge. Nineteen right-handed female subjects cleaned a systematically dirtied shower/bathtub combination using a sponge and a handled tool 21 inches long. The subjects' rated their perceived strain and effort both during and after cleaning. Videotape was obtained simultaneously from three cameras at different locations in the test bathroom and subsequently analyzed for postural data. Subjective responses indicated that subjects felt more comfortable while using the handled tool, and the majority of respondents said they preferred it to a typical sponge and spray cleaner. Postural analysis clearly indicated that the handled tool allowed users to remain in more neutral wrist, shoulder, and trunk postures a greater percentage of the time, and enabled them to remain in less awkward, more stable foot and lower extremity positions. The handled tool significantly reduced the percentage of time that subjects spent cleaning the bathtub, but not the entire shower enclosure.

Predictors of Persistent Elbow Tendonitis Among Auto Assembly Workers

Lateral and medial epicondylitis associated with work activity is a common upper extremity musculoskeletal disorder with a prevalence of 4-30% depending upon the work setting and diagnostic criteria. The influence of treatment, ergonomic factors, medical history, psychosocial variables, and aging on the improvement of symptoms has not been well defined. This was a prospective cohort study of a cohort of 45 workers with active elbow tendonitis for an average of 13 months. Complete resolution of symptoms was the defined outcome measure. The predictive factors for persistent elbow tendonitis included older age (OR = 1.1, 95% CI: 0.99, 1.33), higher hand repetition level for their job(s) (OR = 2.5, 95% CI: 1.00, 6.25), more deviation from a neutral wrist position during the work activity (OR = 2.0, 95% CI: 0.80, 5.56), and lower perceived decision authority on the job (OR = 0.9, 95% CI: 0.79, 0.98). Other ergonomic, psychosocial, and electrophysiologic measures were not predictive. The models had relatively high sensitivity and specificity. Treatment effects could not be evaluated due to incomplete data available. Older workers with jobs requiring more repetition and awkward wrist postures, and less decision authority were less likely to have resolution of their elbow tendonitis. Workers at highest risk for persistent elbow tendonitis should be placed at jobs with lower repetition levels and that use more neutral wrist postures. Effective interventions must address both the ergonomic and psychosocial risk factors in a multifaceted approach to this problem.

Training Keyboarding Skills on a Simulator: Student Trainees in Grades Three to Six

A training program was designed and developed for students in an elementary school. Accepted design criteria were used and organizational, task, trainee, document and device analysis, system specifications, design concept development and prototyping and user testing were addressed. The program is three-fold: training students to operate a keyboarding simulator, educating students about the importance of neutral wrist and finger placement and transfer of this keyboarding ability to a standard computer system with a Qwerty keyboard configuration. Four job aids were developed to illustrate examples and nonexamples of correct seated posture, correct finger placement on the home row keys, an enlargement of the trainee scorecard, and an instructor checklist. The trainees performed the tasks specified in the original system specifications. The final training and evaluation took place at the beginning of the subsequent academic year

Postoperative changes of carpal canal pressure in carpal tunnel syndrome: a prospective study with follow-up of 1 year

Carpal canal pressures were measured in 103 patients with idiopathic carpal tunnel syndrome, before and after open release, with a postoperative follow-up of 1 year. Twenty-five normal subjects were used as controls. Pressures were measured with the wrists in three positions: neutral, full passive flexion and full passive extension. At each wrist position, the mean pre-operative pressures in the study group were significantly higher than in the control group. In both groups, the pressures were maximal with full passive extension and minimal in the neutral wrist position. Immediately after surgical release, there was a marked decrease of the carpal canal pressures. However, during the second postoperative month, there was a significant increase of the pressures at each wrist position, although these were still within the normal control range. This rise in pressures persisted to 12 months. These findings suggest that the carpal ligament reconstitutes by normal scar formation, but with lengthening such that the volume of the carpal canal is enlarged, so preventing a rise in pressure with return of the pre-operative problem.

Influence of hand forces and handle size on power absorption of the human hand–arm exposed to zh-axis vibration

The effect of handle size and hand forces, on the power absorbed by the hand–arm system, was investigated in a laboratory study using seven healthy male subjects exposed to two levels of broadband random vibration in the 8–1000 Hz frequency range along the z h-axis. The measurements were performed with three instrumented cylindrical handles of different diameter (30, 40 and 50 mm). The influence of hand forces applied by the subjects holding the vibrating handles was investigated under nine different grip/push force combinations. The posture adopted by the subjects consisted of the bent forearm with elbow angle of 90° and neutral wrist position, as described in the ISO 10819 standard. The pressure distribution at the hand–handle interface was also measured to quantify the static contact force corresponding to each combination of grip force, push force and handle size. The hand–handle coupling force, as defined in ISO/WD 15230, was further evaluated by summing the grip and push forces. The measured total absorbed power revealed relatively low inter-subject variability (generally less than 12%). Total absorbed power was found to be better correlated with coupling force than the contact force, while most of the absorbed power occurred in the low-frequency range, below 200 Hz. The magnitude of power absorbed within the hand and arm was observed to be strongly dependent upon the handle size; larger handles cause higher absorption of energy. The results also suggested that the power absorption is influenced by the grip as well as push force. The results attained from ANOVA confirmed the significance of all studied factors, i.e. vibration magnitude, handle diameter, and the grip and push forces on the power absorbed into the human hand and arm exposed to vibration.

Wrist discomfort levels for combined movements at constant force and repetition rate

Sixteen male subjects each performed a repetitive, downwards, non-prehensile wrist exertion task with the arm pronated, at a rate of 15 times per minute and with a force of 10N ± 1N in 49 combinations of flexion/extension and radial/ulnar deviation to 0%, 18%, 38% and 55% of the Range of Motion (ROM) for 5 min each. The dependent measure was discomfort measured on a 100 mm visual analogue scale and for most of the analyses these were standardized by using the min - max procedure of <citeref rid="b20">Gescheider (1988)</citeref>. These Standardised Discomfort Levels (SDLs) were fitted to mathematical equations from which iso-discomfort contours were derived relative to the percentages of flexion/extension and radial/ulnar-deviation ROM used. The lowest standardized discomfort was found for the neutral wrist posture, followed by 18% extension with neutral radial/ulmar deviation. The results reveal interesting features of the processes involved and provide useful avenues for further research.

Effect of Graphic Input Device and Repetition on Wrist Posture

This study investigated the Wacom Intuos2 pen and tablet and/or standard Microsoft mouse on wrist posture of 20 experienced users. Wrist posture, measured by extension, flexion, ulnar, and radial deviation, was compared across three independent variables: repetition (repetitive or alternative), input device (mouse and/or pen), and session (session 1 and session 2). Devices were used during a graphical computer task, which was repeated or alternated for two 30 minute test sessions. Neutral wrist range was defined within 15 degrees of 0 in any direction. Input device group interacted with session to significantly impact wrist extension, F (3, 16) = 9.42, p&lt;.001 and ulnar deviation, F (3, 16) = 3.23, p&lt;.05. When analyzing repetition while using the mouse, less extension was found than the pen. Both devices required movement outside the defined neutral range for extension. A significant repetition by session interaction effect for wrist flexion was revealed: F (1, 16) = 6.83, p&lt;.05. The repetitive group revealed little to no flexion during the first session which was statistically different than the alternative group; both groups were inside the neutral range.

Measurement of angular wrist neutral zone and forearm muscle activity

Objectives. To determine the forearm muscles activity in different wrist deviated positions and wrist neutral zone, and to assess the self-selected resting position without visual feedback. Background. Wrist deviation occurs in almost all industrial and office jobs. This has been deemed hazardous for carpal tunnel syndrome. Proper resting wrist position is likely to decrease the hazard for carpal tunnel pressure. Methods. Twenty blindfolded subjects without history of hand/forearm musculoskeletal disorders participated in the study. The EMG of the forearm muscles (flexor carpi radialis, flexor carpi ulnaris, extensor carpi radialis and, extensor carpi ulnaris) in deviated and neutral wrist postures was recorded at a sampling rate of 1 kHz. Also, wrist neutral zone at rest was measured using a custom-made calibrated uniaxial electrogoniometer. One-way anova with repeated measures was used in order to find the impact of wrist deviation on muscles activity. Results. The participants positioned their wrist in rest at 7°–9° extension and 5°–7° ulnar deviation. Significantly higher EMG activity was recorded for each muscle in the wrist deviated postures when compared to neutral position ( P<0.001). Conclusions. Self selected wrist neutral posture decreased the muscle activity significantly. Placement of wrists in neutral zone is expected to reduce risk of injuries. Relevance A knowledge of wrist neutral zone and associated muscle activity is likely to be of assistance in treating patients that require wrist reconstruction. Also, these results would assist job and workstation design/redesign for control and prevention of carpal tunnel problems

MRI of the Carpal Tunnel

2003 Carpal tunnel syndrome (CTS) has been associated with repetitive and forceful use of the hand. While CTS is cited as the most common peripheral neuropathy, its pathomechanics are not well understood. Pressures in the carpal tunnel are known to increase with wrist deviation as is impingement of the median nerve. Detailed imaging is needed to determine the anatomical changes that could account for these pressure increases. PURPOSE: To quantify the dimensions of the carpal tunnel as a function of wrist posture and finger loading. METHODS: Using magnetic resonance imaging (MRI), 8 healthy wrists (4 male, 4 female) were examined in 7 conditions: 3 wrist postures (neutral, 30o flexion and 30o extension), each with and without exerting a 10 N pinch force, and a fist (neutral wrist). Cross-sectional area(CSA) for the carpal tunnel and its contents were calculated at 3 mm increments along the length of the tunnel and used to calculate respective tunnel volumes. Additionally, ratios between the contents and carpal tunnel itself (CTC/CT) were determined for CSA and volume. RESULTS: Gender and use of a pinch grip had no effect on area or volume measures per se, but a reduction in the CTC/CT volume ratio was found with the pinch grip (p = 0.014). A significant interaction was found between posture and level of the wrist. At the distal end of the tunnel, CSA was larger in extension (196.4 ± 34.8 mm2) than neutral (183.8 ± 31.7 mm2) and flexion (176.4 ± 37.0 mm2); the opposite was true in the proximal tunnel. Also, the smallest contents CSA was found in distal tunnel with the wrist extended (69.7 ± 9.5 mm2), with the largest in neutral (77.9 ± 14.6 mm2). Tunnel volume with extended (5564 ± 727 mm3) and neutral wrist postures (5439 ± 715 mm3) were larger than when fiexed (4928 ± 597 mm3). DISCUSSION: This is the first study to analyze carpal tunnel area and volume under a variety of conditions in vivo. Contrary to what would be expected based on carpal tunnel pressure studies, we found that both tunnel area and volume were largest, and the area of the contents was smallest, with the wrist extended. This indicates our current understanding of the relationship between pressure and volume in the carpal tunnel may be too simplistic and needs refining. Our finding that the CTC/CT volume ratio was reduced by tendon loading may relate mechanical compression of the median nerve. However, space occupied by muscle tissue was not included in the current analysis and, as a proposed mechanism in elevating carpal tunnel pressure, needs further evaluation.

MRI of the Carpal Tunnel

2003 Carpal tunnel syndrome (CTS) has been associated with repetitive and forceful use of the hand. While CTS is cited as the most common peripheral neuropathy, its pathomechanics are not well understood. Pressures in the carpal tunnel are known to increase with wrist deviation as is impingement of the median nerve. Detailed imaging is needed to determine the anatomical changes that could account for these pressure increases. PURPOSE: To quantify the dimensions of the carpal tunnel as a function of wrist posture and finger loading. METHODS: Using magnetic resonance imaging (MRI), 8 healthy wrists (4 male, 4 female) were examined in 7 conditions: 3 wrist postures (neutral, 30o flexion and 30o extension), each with and without exerting a 10 N pinch force, and a fist (neutral wrist). Cross-sectional area(CSA) for the carpal tunnel and its contents were calculated at 3 mm increments along the length of the tunnel and used to calculate respective tunnel volumes. Additionally, ratios between the contents and carpal tunnel itself (CTC/CT) were determined for CSA and volume. RESULTS: Gender and use of a pinch grip had no effect on area or volume measures per se, but a reduction in the CTC/CT volume ratio was found with the pinch grip (p = 0.014). A significant interaction was found between posture and level of the wrist. At the distal end of the tunnel, CSA was larger in extension (196.4 ± 34.8 mm2) than neutral (183.8 ± 31.7 mm2) and flexion (176.4 ± 37.0 mm2); the opposite was true in the proximal tunnel. Also, the smallest contents CSA was found in distal tunnel with the wrist extended (69.7 ± 9.5 mm2), with the largest in neutral (77.9 ± 14.6 mm2). Tunnel volume with extended (5564 ± 727 mm3) and neutral wrist postures (5439 ± 715 mm3) were larger than when fiexed (4928 ± 597 mm3). DISCUSSION: This is the first study to analyze carpal tunnel area and volume under a variety of conditions in vivo. Contrary to what would be expected based on carpal tunnel pressure studies, we found that both tunnel area and volume were largest, and the area of the contents was smallest, with the wrist extended. This indicates our current understanding of the relationship between pressure and volume in the carpal tunnel may be too simplistic and needs refining. Our finding that the CTC/CT volume ratio was reduced by tendon loading may relate mechanical compression of the median nerve. However, space occupied by muscle tissue was not included in the current analysis and, as a proposed mechanism in elevating carpal tunnel pressure, needs further evaluation.

Load-sharing at the wrist following radial head replacement with a metal implant. A cadaveric study.

Surgical excision of the radial head is frequently required after a comminuted fracture of the radial head. The outcome of this procedure is often unpredictable, with some patients experiencing ulna-sided pain in the wrist secondary to proximal migration of the radius. Insertion of a radial head prosthesis could prevent proximal radial migration and restore normal load-sharing at the wrist. The thickness of the radial head implant is an important variable in restoring anatomical radial length; however, the effects of varying the length of implants that were used to reconstruct the radius on load-sharing at the wrist have not been studied biomechanically, to our knowledge. A miniature load cell was attached to fifteen fresh-frozen cadaveric forearms to record force in the distal part of the ulna as the wrist was axially loaded to 134 N of compression force. Proximal displacement of the radius relative to the capitellum was also recorded. Loading tests on intact forearms were performed with the elbow in valgus and varus alignment and with three positions of wrist rotation (neutral, 45 degrees of pronation, and 45 degrees of supination). Loading tests were then repeated, with the same positions of varus and valgus elbow alignment and wrist rotation as had been used in the tests of the intact forearm, after radial head excision and subsequent insertion of metal radial head implants that restored anatomical length, implants that produced a radial length that was longer than the anatomical length, and implants that produced a radial length that was shorter than the anatomical length. Testing of these different implant thicknesses was repeated after sectioning of the interosseous membrane. The mean distal ulnar forces and mean proximal radial displacements following insertion of an implant that restored anatomical length were not significantly different from the corresponding values for the intact forearm. At neutral wrist rotation, replacing that implant with an implant that increased the radial length by 4 mm (after sectioning of the interosseous membrane) decreased the mean distal ulnar force from 13.4% to 3.3% of the applied wrist force with the elbow in valgus alignment and from 29.1% to 8.6% with the elbow in varus alignment. Replacing the implant that restored anatomical length with one that decreased the length by 4 mm (after sectioning of the interosseous membrane) significantly increased the mean distal ulnar force from 13.4% of the applied wrist load to 33.3% with the elbow in valgus alignment and from 29.1% to 51.6% with it in varus alignment. The mean distal ulnar forces were not significantly affected by the position of wrist rotation when the elbow was in valgus alignment. However, when the elbow was in varus alignment, the mean distal ulnar forces associated with all reconstructed radial lengths were significantly higher when the wrist was placed in 45 degrees of supination. In this cadaveric model, insertion of a metal implant maintained distal ulnar forces at normal levels, at all three positions of wrist rotation, when the radius had been restored to its original anatomical length. Distal ulnar forces and proximal radial displacements were significantly affected by the reconstructed length of the radius. Radial head implants are utilized to prevent proximal migration of the radius as the wrist is loaded; this is especially important when the interosseous membrane has been ruptured and thus cannot help to limit radial displacement. At the time of surgery, comminution and displacement of a radial head fracture may make estimation of the original radial length difficult. Our results demonstrate that, in terms of distal ulnar loading, it is preferable to insert an implant that is too thick rather than too thin.

Evaluation and Treatment of Carpal Tunnel Syndrome Reviewed

These authors review the evidence for and provide clinical recommendations regarding diagnostic strategies and treatments for carpal tunnel syndrome (CTS). History- and examination-based diagnostic methods have limited sensitivity and specificity. Nonetheless, to identify probable CTS, the authors favor using history, facilitated by a hand-pain diagram, and examination, including sensory and motor testing and provocative maneuvers. They recommend treating probable CTS conservatively, with neutral wrist splinting, which alleviates symptoms in …

Improved usability of a new handle design for laparoscopic dissection forceps

Recent studies have shown that the shape of most instrument handles causes user discomfort and that none of the handles currently available on the market satisfies all ergonomic criteria. Therefore, we designed a handle with improved usability; i.e., it is easier to manipulate and its use entails less risk of injury for the operator. The aim of this study was to demonstrate that the intended improvements of the new design were successful. Six handles representative of the types that are currently available were compared with the new version. Eight surgeons used the seven handles during a precision task and a rough task in a pelvi-trainer. A questionnaire and video analyses were used to assess the usability of the handles. Based on the responses to the questionnaire, we determined that there were significant differences between the new handle and the Aesculap handle (means of rotation and angle between handle and shaft). No significant differences were found between the new handle and the five other handles. The video analyses (documenting extreme vs neutral wrist excursions) showed significant differences between the new handle and the six other handles. Compared to the six existing handles, the new handle has significantly improved usability; in particular, its hinged design obviates the need to make extreme wrist excursions.

Do Handle Design and Hand Posture Affect Pointing Accuracy?

The design of ergonomic tools has focused on reducing the awkward wrist angles during tasks. However, anecdotal evidence shows that the adoption of ergonomic tools has been slow. This may be due, in part, to the ergonomic handles reducing accuracy of the task performed. A pilot study employing 20 subjects (9 men, 11 women) was undertaken to evaluate 4 handles, with two handles being used both in a pistol-grip and an inline-grip. All handles were evaluated while either seeing the target or blindfolded and either using the index finger extended as a guide or not. Each subject performed 24 total trials, which consisted of aiming at a sheet of vertically mounted A3 paper. The center point was marked and positioned such that the subject, when holding a pistol grip tool, had an adducted shoulder, a right angle at the elbow and a neutral wrist position. Each subject was asked to aim and puncture 10 holes in each target paper at a fixed pace. The results of the pilot study show that the dependent variables of the vector distance from the origin and the vector distance from the centroid of the points is affected primarily by the sight condition, but that the handle orientation with the inline condition was significantly better than the pistol grip for accuracy. In addition, the main effects of gender and tool type were significant for the dependent variable of the vector distance from the centroid. The overall implication is that the most ‘ergonomic’ handle may not yield the most accurate cluster or grouping when pointing and that handles held in an ergonomically awkward wrist posture (average 23° ulnar deviation).

Effect of Setup Configurations of Split Computer Keyboards on Wrist Angle

Alternative computer keyboards whose halves can be slanted toward each other can reduce a risk factor (ulnar deviation) for work-related musculoskeletal disorders (WMSDs) affecting the upper limbs. Two questions that computer keyboard operators face when using keyboards that can be separated into halves (split keyboards) are: (1) At what angle should the keyboard halves be opened? and (2) At what distance apart should the keyboard halves be placed? The objective of this study was to investigate the effects of the opening angle and separation distance between halves of a split keyboard on wrist ulnar deviation and typing efficiency. Eleven experienced computer keyboard operators participated in this study and used a split keyboard that was set up in a conventional (nonsplit) format and also in 3 alternative configurations: (1) centers of keyboard halves were separated at 20-cm distance, (2) keyboard halves were separated half of the distance of shoulder width, and (3) keyboard halves were separated at shoulder width distance. The 3 alternative configurations resulted in ulnar deviation of both wrists that were less than ulnar deviation from typing on a conventional setup. There were no differences in ulnar deviations among the 3 alternative configurations. The results of this research provide physical therapists and ergonomists with a set of configurations of a split keyboard that they can recommend to their patients or clients. All of the alternative configurations of the split keyboard are beneficial in promoting a neutral wrist position, which theoretically would decrease exposure to WMSDs such as tenosynovitis in the wrist and carpal tunnel syndrome.

New Ergonomic Design Criteria for Handles of Laparoscopic Dissection Forceps

The shape of laparoscopic instrument handles can cause physical discomfort. This problem may be ascribed to a lack of standards for instrument design. In this study, new ergonomic requirements for the design of laparoscopic dissection forceps were created. Three representative handles (a Karl Storz [click-line] scissors handle, an Access Plus scissors handle, and an Aesculap cylindrical handle) currently available on the market were evaluated according to the new list of ergonomic criteria. The handles were subjectively (questionnaire) and objectively (video analyses) tested in order to find out whether the new requirements are valid for the evaluation and design of instrument handles. The outcome of the subjective and objective tests matched the predictions by the new criteria list. New criteria were introduced (neutral wrist excursions), and existing general criteria were specified (e.g., a minimal contact area of 10 mm). Significant differences were found among the three handles. The Storz handle met 8 of the 10 requirements, the Access handle met 5, and the Aesculap handle met only 4. The new list of ergonomic requirements is a valid tool to determine the ergonomic value of a handle for laparoscopic dissecting tasks. It gains its strength from its specialized character. Significant differences were found among the three tested handles. Cylindrical handles were inferior to scissors handles.