Abstract
BackgroundThe concept of reachable workspace is closely tied to upper limb joint range of motion and functional capability. Currently, no practical and cost-effective methods are available in clinical and research settings to provide arm-function evaluation using an individual’s three-dimensional (3D) reachable workspace. A method to intuitively display and effectively analyze reachable workspace would not only complement traditional upper limb functional assessments, but also provide an innovative approach to quantify and monitor upper limb function.Methodology/Principal FindingsA simple stereo camera-based reachable workspace acquisition system combined with customized 3D workspace analysis algorithm was developed and compared against a sub-millimeter motion capture system. The stereo camera-based system was robust, with minimal loss of data points, and with the average hand trajectory error of about 40 mm, which resulted to ∼5% error of the total arm distance. As a proof-of-concept, a pilot study was undertaken with healthy individuals (n = 20) and a select group of patients with various neuromuscular diseases and varying degrees of shoulder girdle weakness (n = 9). The workspace envelope surface areas generated from the 3D hand trajectory captured by the stereo camera were compared. Normalization of acquired reachable workspace surface areas to the surface area of the unit hemi-sphere allowed comparison between subjects. The healthy group’s relative surface areas were 0.618±0.09 and 0.552±0.092 (right and left), while the surface areas for the individuals with neuromuscular diseases ranged from 0.03 and 0.09 (the most severely affected individual) to 0.62 and 0.50 (very mildly affected individual). Neuromuscular patients with severe arm weakness demonstrated movement largely limited to the ipsilateral lower quadrant of their reachable workspace.Conclusions/SignificanceThe findings indicate that the proposed stereo camera-based reachable workspace analysis system is capable of distinguishing individuals with varying degrees of proximal upper limb functional impairments.
Highlights
A wide range of daily activities require unrestricted movement of the upper limb, primarily in the shoulder, to extend the reachability of the hand which is used to grasp, position or otherwise interact with various objects and environment
Individual joint angles from such measures are helpful in evaluation of segmental function of the upper limb, it is often difficult to appreciate and readily visualize the overall functional capability of the upper limb based on a long list of joint angular range of motion (ROM) values, typically representing only the primary joint movements that are tested for each individual joint
The difference in 3D reachable workspace and abstracted upper limb functional status can be readily visualized between a healthy individual and individuals with varying degrees of shoulder girdle muscle weakness due to neuromuscular disorders
Summary
A wide range of daily activities require unrestricted movement of the upper limb, primarily in the shoulder, to extend the reachability of the hand which is used to grasp, position or otherwise interact with various objects and environment. The concept of reachable/functional workspace is closely tied to range of motion (ROM) of the upper limb joints [1,2]. Active range of motion assessment represents a quantitative method to evaluate movement and functional status of an impaired upper extremity [3]. Individual joint angles from such measures are helpful in evaluation of segmental function of the upper limb, it is often difficult to appreciate and readily visualize the overall functional capability of the upper limb based on a long list of joint angular ROM values, typically representing only the primary joint movements that are tested for each individual joint. The concept of reachable workspace is closely tied to upper limb joint range of motion and functional capability. A method to intuitively display and effectively analyze reachable workspace would complement traditional upper limb functional assessments, and provide an innovative approach to quantify and monitor upper limb function
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