In vivo finger flexor tendon force while tapping on a keyswitch

Abstract

SummaryForce may be a risk factor for musculoskeletal disorders of the upper extremity associated with typing and keying. However, the internal finger flexor tendon forces and their relationship to fingertip forces during rapid tapping on a keyswitch have not yet been measured in vivo. During the open carpal tunnel release surgery of five human subjects, a tendon-force transducer was inserted on the flexor digitorum super-ficialis of the long finger. During surgery, subjects tapped with the long finger on a computer keyswitch, instrumented with a keycap load cell. The average tendon maximum forces during a keystroke ranged from 8.3 to 16.6 N (mean = 12.9 N, SD = 3.3 N) for the subjects, four to seven times larger than the maximum forces observed at the fingertip. Tendon forces estimated from an isometric tendon-force model were only one to two times larger than tip force, significantly less than the observed tendon forces (p = 0.001). The force histories of the tendon during a keystroke were not proportional to fingertip force. First, the tendon-force histories did not contain the highfrequency fingertip force components observed as the tip impacts with the end of key travel. Instead, tendon tension during a keystroke continued to increase throughout the impact. Second, following the maximum keycap force, tendon tension during a keystroke decreased more slowly than fingertip force, remaining elevated approximately twice as long as the fingertip force. The prolonged elevation of tendon forces may be the result of residual eccentric muscle contraction or passive muscle forces, or both, which are additive to increasing extensor activity during the release phase of the keystroke.Although the rate of injury to the tendons at the wrist and adjacent tissues associated with repetitive work is reported to be high (55% of all work-related repetitive motion disorders [6]), the injury mechanisms are not well understood. Along with motion, posture, and vibration, the force exerted during a repetitive task is a risk factor for tendon-related disorders (4,19,23). Understanding how force is transmitted from the site of external application (fingertip) to the internal tissue (finger flexor tendons) is critical to understanding the mechanics of repetitive motion disorders. This understanding determines how the internal biological tissues support an externally applied force, and such knowledge identifies tendons that are exposed to higher forces. The knowledge of in vivo tendon tension also guides techniques of tendon repair, procedures for rehabilitation (15,22), and design of joint replacements (25). Rempel et al. (21) and Martin et al. (18) have measured exposure to force during keyboard work. The fingertip force history during a keystroke contains three distinct phases: (I) the keyswitch compression, (II) the high frequency component during finger impact at the end of keycap motion, and (III) the compression and release of the fingertip (21). Currently, applied fingertip loads and finger postures are used as the input or ind...

Biodynamic modeling, system identification, and variability of multi-finger movements

“…A model with the musculotendon details to ascertain the muscle and tendon forces that produce the required torques is underway (Zhang et al, 2007). Preliminary results indicate the estimated peak forces are within the same order of magnitude (o10 N) as previously modelpredicted (Brook et al, 1995;Buchner et al, 1988;SanchoBru et al, 2001) or measured in vivo (Dennerlein et al, 1999;Kursa et al, 2006), thus lending some credence to the torque profiles resulting from the current study. Second, while the modeling scheme is believed to be general, the estimated model parameters and associated interpretations are specific to the movements studied here.…”

Model-based estimation of muscle forces exerted during movements

“…Otherwise, ill vivo measuremen ts can be con ducted in the operation room where a force transducer can be placed on a tendon, following data collection and the removal of the device before the completion of the sur gery, e.g. fl exor tendons of fingers d uring su rgeries of carpal tunnel (Dennerlein et al, 1998;Dennerlein et al ., 1999;Den nerlein, 2005;Schuind et aI., 1992). Such approaches may not necessarily be feasi ble in a clinical sett ing; therefore such tendon force measurement techniques have been uti lized mostly in research laboratories (R avary et al .. 2004;Fleming and Beynlloll.…”

“…Validation data for pathological conditions however do not currently exist and unfortu nately, direct validation in humans using current in vivo tendon force transducers is limited. The devices are inva sive (Ravary et al, 2004;Fleming and Beynnon, 2004), can only be placed on extrinsic tendons (e.g., the Achilles tendon by Komi et al (1992)) or used in the operation room during surgery (Dennerlein et al, 1998;Dennerlein et al, 1999;Dennerlein, 2005;Schuind et al, 1992), possess measurement errors inherent to transducer design (Ravary et al, 2004), and transducer calibration remains a largely unsolved problem. In large-scale musculoskeletal models, validity of muscle force estimates has been assessed indi rectly by comparing measured joint reaction forces against those predicted by modeling.…”

National occupational research agenda (NORA) future directions in occupational musculoskeletal disorder health research

“…Currently, the low back and the upper extremities are the parts of the body most subject to risk associated with work (Andersson, 1997;Bongers, 2001;Dennerlein et al, 1999;Ferguson and Marras, 1997;Katz et al, 2000;Marras et al, 2000aMarras et al, , 2001Oleske et al, 2000;Rempel et al, 1992Rempel et al, , 1998Viikari-Juntura and Silverstein, 1999;Roquelaure et al, 2006). There is consensus that nonspecific upper-limb symptoms and specific upper-limb MSDs are common in the working population (Roquelaure et al, 2006) as well as low back symptoms (Morken et al, 2003).…”