Effect of wrist posture on carpal tunnel pressure while typing

Department of Medicine, University of California, San Francisco, California, USA.
Journal of Orthopaedic Research (Impact Factor: 2.97). 09/2008; 26(9):1269-73. DOI: 10.1002/jor.20599
Source: PubMed

ABSTRACT Long weekly hours of keyboard use may lead to or aggravate carpal tunnel syndrome. The effects of typing on fluid pressure in the carpal tunnel, a possible mediator of carpal tunnel syndrome, are unknown. Twenty healthy subjects participated in a laboratory study to investigate the effects of typing at different wrist postures on carpal tunnel pressure of the right hand. Changes in wrist flexion/extension angle (p = 0.01) and radial/ulnar deviation angle (p = 0.03) independently altered carpal tunnel pressure; wrist deviations in extension or radial deviation were associated with an increase in pressure. The activity of typing independently elevated carpal tunnel pressure (p = 0.001) relative to the static hand held in the same posture. This information can guide the design and use of keyboards and workstations in order to minimize carpal tunnel pressure while typing. The findings may also be useful to clinicians and ergonomists in the management of patients with carpal tunnel syndrome who use a keyboard.

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Available from: David Rempel, Aug 14, 2015
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    • "Biomechanically these non-neutral postures can increase internal loading on the muscles and joints. Rempel et al. (2008) reported that changes in wrist posture altered carpal tunnel pressure, which may contribute to the development or aggravation of carpal tunnel syndrome (Rempel et al., 1999, 2008). Specifically, wrist deviations in extension or radial deviation while typing are associated with an increase in pressure. "
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    ABSTRACT: Non-neutral wrist posture is a risk factor of the musculoskeletal disorders among computer users. This study aimed to assess internal loads on hand and forearm musculature while tapping in different wrist postures. Ten healthy subjects tapped on a key switch using their index finger in four wrist postures: straight, ulnar deviated, flexed and extended. Torque at the finger and wrist joints were calculated from measured joint postures and fingertip force. Muscle stresses of the six finger muscles and four wrist muscles that balanced the calculated joint torques were estimated using a musculoskeletal model and optimization algorithm minimizing the squared sum of muscle stress. Non-neutral wrist postures resulted in greater muscle stresses than the neutral (straight) wrist posture, and the stress in the extensor muscles were greater than the flexors in all conditions. Wrist extensors stress remained higher than 4.5 N/cm² and wrist flexor stress remained below 0.5 N/cm² during tapping. The sustained high motor unit recruitment of extensors suggests a greater risk than other muscles especially in flexed wrist posture. This study demonstrated from the perspective of internal tissue loading the importance of maintaining neutral wrist posture during keying activities.
    Applied ergonomics 04/2013; 44(6). DOI:10.1016/j.apergo.2013.03.013 · 1.33 Impact Factor
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    • "The impact of wrist, forearm and finger position on carpal tunnel pressure and the impact of fingertip loading (e.g., pinch grip) have been well-documented for both healthy participants and patients with CTS (Seradge et al., 1995; Keir et al., 1998b). However, the impact of many functional tasks, such as typing (Rempel et al., 2008) and computer mouse operation (Keir et al., 1999), has only been investigated for healthy people. With respect to the effect of non-invasive treatment, only the effect of wearing a splint has been investigated. "
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    ABSTRACT: Elevated carpal tunnel pressure is an important pathomechanism in carpal tunnel syndrome (CTS). Several invasive methods have been described for direct measurement of carpal tunnel pressure, but all have two important limitations. The pressure gauge requires sterilisation between uses, which makes time-efficient data collection logistically cumbersome, and more importantly, the reliability of carpal tunnel pressure measurements has not been evaluated for any of the methods in use. This technical note describes a new method to measure carpal tunnel pressure using inexpensive, disposable pressure sensors and reports the within and between session reliability of the pressure recordings in five different wrist positions and during typing and computer mouse operation. Intraclass correlation coefficients (ICC[3,1]) were calculated for recordings within one session for healthy participants (n = 7) and patients with CTS (n = 5), and for recordings between two sessions for patients with CTS (n = 5). Overall, the reliability was high. With the exception of two coefficients, the reliability of the recordings at different wrist angles varied from 0.63 to 0.99. Reliability for typing and mouse operation ranged from 0.86 to 0.99. The new method described in this report is inexpensive and reliable, and data collection can be applied more efficiently as off-site sterilisation of equipment is not required. These advances are likely to promote future research into carpal tunnel pressure, such as investigation of the therapeutic mechanisms of various conservative treatment modalities that are believed to reduce elevated carpal tunnel pressure.
    Manual therapy 03/2012; 17(6):589-92. DOI:10.1016/j.math.2012.03.005 · 1.76 Impact Factor
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    • "These keyboards are split into two halves, one for each hand, and include an opening angle to reduce ulnar deviation, a raised centre (gable angle) to reduce pronation and a near flat front-to-back surface angle (slope) to reduce wrist extension (Marklin et al. 1999). The underlying health basis for the split design may be from the neutral wrist and forearm postures, which reduce forearm muscle loads and pressures in the carpal tunnel (Marek et al. 1992, Marklin and Simoneau 2004, Rempel et al. 2008). While a number of studies have compared wrist and forearm postures during typing on a split geometry keyboard to a conventional keyboard (Smith et al. 1998, Marklin et al. 1999, Tittiranonda et al. 1999, Zecevic et al. 2000, Rempel et al. 2007), few studies have evaluated the effects of changes in geometry within a split keyboard design (Nakaseko et al. 1985, Honan et al. 1995). "
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    ABSTRACT: Split, gabled keyboard designs can prevent or improve upper extremity pain among computer users; the mechanism appears to involve the reduction of awkward wrist and forearm postures. This study evaluated the effects of changes in opening angle, slope and height (independent variables) of a gabled (14 degrees) keyboard on typing performance and upper extremity postures. Twenty-four experienced touch typists typed on seven keyboard conditions while typing speed and right and left wrist extension, ulnar deviation, forearm pronation and elbow position were measured using a motion tracking system. The lower keyboard height led to a lower elbow height (i.e. less shoulder elevation) and less wrist ulnar deviation and forearm pronation. Keyboard slope and opening angle had mixed effects on wrist extension and ulnar deviation, forearm pronation and elbow height and separation. The findings suggest that in order to optimise wrist, forearm and upper arm postures on a split, gabled keyboard, the keyboard should be set to the lowest height of the two heights tested. Keyboard slopes in the mid-range of those tested, 0 degrees to -4 degrees, provided the least wrist extension, forearm pronation and the lowest elbow height. A keyboard opening angle in the mid-range of those tested, 15 degrees, may provide the best balance between reducing ulnar deviation while not increasing forearm pronation or elbow separation. These findings may be useful in the design of computer workstations and split keyboards. The geometry of a split keyboard can influence wrist and forearm postures. The findings of this study are relevant to the positioning and adjustment of split keyboards. The findings will also be useful for engineers who design split keyboards.
    Ergonomics 02/2009; 52(1):104-11. DOI:10.1080/00140130802481040 · 1.61 Impact Factor
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