Differences in the Rotation Axes of the Scapholunate Joint During Flexion-Extension and Radial-Ulnar Deviation Motions.

Purpose To determine the location of the rotation axis between the scaphoid and the lunate (SL-axis) during wrist flexion-extension (FE) and radial-ulnar deviation (RUD). Methods An established and publicly available digital database of wrist bone anatomy and carpal kinematics of 30 healthy volunteers (15 males and 15 females) in up to 8 different positions was used to study the SL-axis. Using the combinations of positions from wrist FE and RUD, the helical axis of motion of the scaphoid relative to the lunate was calculated for each trial in an anatomical coordinate system embedded in the lunate. The differences in location and orientation between each individual axis and the average axis were used to quantify variation in axis orientation. Variation in the axis location was computed as the distance from the closest point on the rotation axis to the centroid of the lunate. Results The variation in axis orientation of the rotation axis for wrist FE and RUD were 84.3 degrees and 83.5 degrees, respectively. The mean distances of each rotation axis from the centroid of the lunate for FE and RUD were 5.7 +/- 3.2 mm, and 5.0 +/- 3.6 mm, respectively. Conclusions Based on the evaluation of this dataset, we demonstrated that the rotation axis of the scaphoid relative to the lunate is highly variable across subjects and positions during both FE and RUD motions. The range of locations and variation in axis orientations in this data set of 30 wrists shows that there is very likely no single location for the SL-axis. Copyright (C) 2019 by the American Society for Surgery of the Hand. All rights reserved.