Traditionally our understanding of carpal kinematics relates to the orthogonal sagital (flexion/extension) and coronal (radial/ulnar deviation) planes of wrist motion. Nevertheless, most activities involving tool use are performed in an oblique plane from radial deviation-extension to ulnar deviation-?exion. This movement has been called the dart-throwing motion (DTM).

The DTM occurs predominantly through the midcarpal joint with only little scaphoid and lunate motion. Almost full range of DTM can be achieved after radiolunate or radioscapholunate fusion. Therefore, for partial wrist arthrodesis, radiocarpal fusions might result in a more functional result than the widely performed midcarpal fusions.

The DTM also involves rotation of the forearm. In wrist radial deviation/extension, there is slight pronation of the forearm. In wrist ulnar deviation/?exion, there is slight supination of the forearm. This is a facilitatory motion of the forearm that maintains the grasped object in the vertical plane and aligned with the visual axis. Our hypothesis is that the default functional position of the forearm with regard to rotation is between 30° and 45° of pronation, in order to maintain alignment between the function axis and the visual axis during utilisation of the DTM.

In previous studies of DTM, the rotation of the forearm as well as motion at the elbow and the shoulder have not been taken into consideration. We started to investigate DTM globally as a multiple-joint 3D motion in relation to the visual axis. Therefore we used an optical motion capture system (Optotrak® Certus™) with infrared emitting surface markers placed on definded landmarks.

We further hypothesize on the influence that capacity to accurately throw projectiles has had on human evolution and present some new theories in regard to the evolution of bipedal primates.