A normative database of thumb circumduction in vivo: center of rotation and range of motion.

This article reports a systematic research effort aimed at establishing a normative database of thumb circumduction range of motion (ROM) and related kinematic characteristics in vivo while examining the effects of anthropometry, gender, and direction of rotation. Twenty-eight (14 men, 14 women) anthropometrically diverse participants performed maximum voluntary thumb circumductions as the trajectories of the surface markers placed on their thumb landmarks were recorded by an optoelectronic motion capture system. A globographic representation method was employed to model the measured marker trajectories, determining the center of rotation and central reference axes for thumb circumduction. Thumb ROM was quantified using (a) the joint sinuses expressing the thumb orientation change with respect to the reference axes and (b) cone volumes circumscribed by the thumb at the distal phalangeal, interphalangeal, and metacarpophalangeal levels. Data analyses resulted in statistical summaries of the derived kinematic and ROM measures with significant effects identified and regression equations predicting the cone volumes. Potential applications of this research include ergonomic design of hand-operated controls or devices and evaluation of thumb impairments or disorders.

Quantitative analysis of finger motion coordination in hand manipulative and gestic acts.

This article reports an experimental study that aimed to quantitatively analyze motion coordination patterns across digits 2-5 (index to little finger), and examine the kinematic synergies during manipulative and gestic acts. Twenty-eight subjects (14 males and 14 females) performed two types of tasks, both right-handed: (1) cylinder-grasping that involved concurrent voluntary flexion of digits 2-5, and (2) voluntary flexion of individual fingers from digit 2 to 5 (i.e., one at a time). A five-camera opto-electronic motion capture system measured trajectories of 21 miniature reflective markers strategically placed on the dorsal surface landmarks of the hand. Joint angular profiles for 12 involved flexion-extension degrees of freedom (DOF's) were derived from the measured coordinates of surface markers. Principal components analysis (PCA) was used to examine the temporal covariation between joint angles. A mathematical modeling procedure, based on hyperbolic tangent functions, characterized the sigmoidal shaped angular profiles with four kinematically meaningful parameters. The PCA results showed that for all the movement trials (n = 280), two principal components accounted for at least 98% of the variance. The angular profiles (n = 2464) were accurately characterized, with the mean (+/-SD) coefficient of determination (R2) and root-mean-square-error (RMSE) being 0.95 (+/-0.12) and 1.03 degrees (+/-0.82 degrees ), respectively. The resulting parameters which quantified both the spatial and temporal aspects of angular profiles revealed stereotypical patterns including a predominant (87% of all trials) proximal-to-distal flexion sequence and characteristic interdependence--involuntary joint flexion induced by the voluntarily flexed joint. The principal components' weights and the kinematic parameters also exhibited qualitatively similar variation patterns. Motor control interpretations and new insights regarding the underlying synergistic mechanisms, particularly in relation to previous findings on force synergies, are discussed.

Determining finger segmental centers of rotation in flexion-extension based on surface marker measurement.

This paper describes the development of a novel algorithm for deriving finger segmental center of rotation (COR) locations during flexion-extension from measured surface marker motions in vivo. The algorithm employs an optimization routine minimizing the time-variance of the internal link lengths, and incorporates an empirically quantifiable relationship between the local movement of a surface marker around a joint (termed "surface marker excursion") and the joint flexion-extension. The latter relationship constrains and simplifies the optimization routine to make it computationally tractable. To empirically investigate this relationship and test the proposed algorithm, an experiment was conducted, in which hand cylinder-grasping movements were performed by 24 subjects (12 males and 12 females). Spherical retro-reflective markers were placed at various surface landmarks on the dorsal aspect of each subject's right (grasping) hand, and were measured during the movements by an opto-electronic system. Analysis of experimental data revealed a highly linear relationship between the "surface marker excursion" and the marker-defined flexion-extension angle: the average R(2) in linear regression ranged from 0.89 to 0.97. The algorithm successfully determined the CORs of the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints of digits 2-5 during measured motions. The derived CORs appeared plausible as examined in terms of the physical locations relative to surface marker trajectories and the congruency across different joints and individuals.