Heuristics for locating upper extremity joint centres from a reduced set of surface markers

This article presents a set of heuristic algorithms (computational procedures) for determining upper extremity joint centers from a reduced set of surface markers (as compared to the conventional scenario of three markers per segment) during three-dimensional (3-D) motions. Two experiments were conducted to empirically derive and evaluate the algorithms. The first experiment characterized the geometric relations between the instantaneous helical axes and corresponding surface markers at the shoulder and elbow. These relations, along with anatomic data available in the literature, were employed to derive the geometric heuristics. The heuristics were then enhanced through a solidification optimization procedure with the objective function of minimizing segment length variability over time. This latter variability was also used as the error measure in evaluation of the algorithms. The second experiment, incorporating a wide range of upper extremity motions in 3-D, showed the following: (1) the geometric heuristics alone yielded an average error of approximately 7.5 mm; (2) with optimization-based enhancement, the average error was reduced to 3.7 mm; (3) further improvement of the algorithm performance is achievable by modifying the parameter setting of the optimization procedure. While more extensive evaluation is needed before the proposed approach can be generalized, the current work demonstrates the viability of heuristic algorithms for estimating upper extremity joint centers based on a reduced set of surface markers and in an efficient manner. (C) 2000 Elsevier Science B.V. All rights reserved.