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Article Excerpt
INTRODUCTION
The thumb has unique kinematic and anatomical characteristics as compared with the other four digits of the hand, and it plays an irreplaceable role in many manipulative tasks. Thumb function is often regarded as accounting for 40% to 50% of the hand's usefulness (Ateshian et al., 1995; Emerson, Krizek, & Greenwald, 1996; Swanson, Goran-Hagert, & Swanson, 1987). Therefore quantitative knowledge of thumb functional and biomechanical capacities is of fundamental value in the field of ergonomics, serving as the basis for a variety of applications. For instance, functional thumb range of motion (ROM) information is needed in developing design criteria for the location of push buttons on multifunctional hand-operated controls (Gilbert, Hahn, Gilmore, & Schurman, 1988). In addition, a normative ROM database with robust population representations can aid in evaluating functional losses or impairments, many of which result from occupational injuries and disorders. Crushing injury, spinal cord injury, damage to the ulnar and/or median nerves, and secondary osteoarthritis are just a few examples of the occupational traumas that are prevalent in industry and likely to cause compromised functional capacity of the thumb (Absoud & Harpo, 1984; Acheson, Chan, & Clemett, 1970; Putz-Anderson, 1988; U.S. Department of Labor, 1999a, 1999b). However, although some basic hand anthropometric databases exist (Buchholz, Armstrong, & Goldstein, 1992; Garrett, 1971), data on thumb kinematic characteristics in vivo, including the functional ROM, are sparse.
One dilemma in quantifying the thumb functional ROM is that whereas joint ranges of motion have traditionally been presented in a plane or two dimensions (2-D), the thumb motions are hardly planar. The carpometacarpal joint (CM[C.sub.1]), which provides the largest motion among the thumb joints, is commonly considered as a universal joint permitting two degrees of freedom (Cooney & Chao, 1977; Cooney, Lucca, Chao, & Linscheid, 1981 ; Kapandji, 1981; Rijpkema & Girard, 1991; Toft & Berme, 1980) with negligible axial rotation (Cooney et al., 1981, Haines, 1944; Napier, 1955). Thus the functional thumb ROM should ideally be measured and modeled in three dimensions (3-D). Nevertheless, in many earlier studies, the measurement or modeling was limited to 2-D (Cooney et al., 1981; Eaton, Glickel, & Littler, 1985; Gilbert et al., 1988; Jacobs & Thompson, 1960; Kuo, Su, Chiu, & Yu, 2002). In fact, the current guidelines of the American Academy of Orthopaedic Surgeons and the International Federation of Societies for Surgery of the Hand still utilize planar data to quantify thumb ROM (Balfour, 1995; Swanson et al., 1987).
A few cadaveric studies in the past have simulated 3-D thumb circumduction in vitro and attempted to characterize the functional ROM. Ou (1980) used six cadaver forearms with fixated metacarpophalangeal (MC[P.sub.1]) and interphalangeal (I[P.sub.1]) joints of the thumb and estimated the tendon moment arms at a few discrete positions along a circumduction. The simulated circumduction, as a conical rotation of a fixated rigid segment following a presumed circular base, was an oversimplified and inaccurate representation of the maximum-range thumb motion. Imaeda, Niebur, Cooney, Linscheid, and An (1994) were the first to realistically quantify the nonsymmetric elliptical base of the cone formed by cadaveric thumb circumduction in vitro. However, only the thumb metacarpal movement was quantified in terms of distance within a plane and flexion-extension and abduction-adduction angles. Continuous angular data for the thumb circumduction motion at the I[P.sub.1] joint and tip of the distal phalanx (D[P.sub.1]) were not obtained. Imaeda et al. (1994) acknowledged that the primary limitation of their study was the failure to simulate a smooth, coordinated thumb motion. These prior studies illustrated that there could be a significant discrepancy between simulated maximum thumb circumductions in vitro and ones in vivo with tissues and structures intact and free from artificial constraints. Data of the latter kind are most germane to the various aforementioned applications but are currently lacking.
This study was motivated by the need for a normative database of the 3-D thumb ROM in vivo that can be readily utilized in ergonomic design and functional assessment applications. It was also encouraged by the recognition that with the advent of much advanced motion capture technology, it is feasible to measure finger movement in vivo with details at the individual segmental level (Kuo et al., 2002; Rash, Belliappa, Wachowiak, Somia, & Gupta, 1999; Somia, Rash, Wachowiak, & Gupta, 1998). Therefore, the specific aims of this study were (a) to measure in vivo maximum thumb circumductions performed by a group of anthropometrically diverse participants and (b), through biomechanical modeling and statistical analysis, to establish a normative database of thumb circumduction ROM and related kinematic characteristics while examining the effects of anthropometry, gender, and circumduction direction.
METHODS
Participants
Participants were selected according to stature through a rigorous screening process, using the following within-gender stratification scheme: 1st, 5th, 25th, 50th, 75th, 95th, and 99th percentile, with reference to a normative database (Eastman Kodak Company, 1986). Four individuals (2 men and 2 women) fitting the appropriate statures, with a tolerance of [+ or -] 1 cm, were designated to each of the seven strata (Table 1). The 28 participants were all right-handed. The mean ([+ or -] SD) weight and age were 72.3 ([+ or -] 9.25) kg and 23.6 ([+ or -] 3.3) years for the 14 men and 57.8 ([+ or -] 8.53) kg and 24.4 ([+ or -] 6.3) years for the 14 women. A set...
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