Abstract
The wrist is arguably the most complex joint in the body and is essential for optimal hand function. The joint may be represented as two roughly orthogonal hinge axes, providing flexion-extension and radial-ulnar deviation. The location and orientation of these axes with respect to the underlying anatomy is essential for the design of successful joint prostheses. A population study was performed in order to obtain the parameters of this two-hinge joint.
Data for 108 normal right wrists was gathered using a Fastrak electrogoniometer with sensors fixed to the distal medial radial styloid and the distal third metacarpal head. Data was recorded as a series of three-dimensional coordinates covering the entire locus of movement.
The two-hinge geometry of the joint was represented mathematically with nine parameters describing the configuration of the axes and two angles controlling rotation about these axes. The configuration giving the closest kinematic match to the experimental data was determined using two nested optimisation processes. During the inner optimisation process, the third metacarpal head was brought as close as possible to each of the experimental points in turn by adjusting the two positioning angles. The sum of distances from each experimental point to the point of closest approach gave the “cost” of the current configuration. The outer optimisation process repeated the inner process iteratively, minimising the cost by adjusting the nine configuration parameters.
The double optimisation method was found to offer an innovative solution to the problem of analysing kinematic data from a population study. The mean joint configuration showed the axis of radial-ulnar deviation to be 1.9 mm (sd = 12.5 mm), distal to the flexion-extension axis, with axes almost orthogonal to one another. This data together with the radii of the rotations is invaluable in determining the optimal articulation geometries for wrist joint replacement prostheses.
The abstracts were prepared by Nico Verdoschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, Universitair Medisch Centrum, Orthopaedie / CSS1, Huispost 800, Postbus 9101, 6500 HB Nijmegen, Th. Craanenlaan 7, 6525 GH Nijmegen, The Netherlands.
