Wrist arthroplasty

The radiocarpal and midcarpal motion comprises flexion (volar flexion), extension (dorsal flexion), radial- and ulnar deviation, and slight rotation (Palmer et al. 1985). The dorso-volar movement primarily occurs in the radiocarpal joint during which the scaphoid flexes/extends and rotates, while the lunate mainly flexes/extends. The remaining flexion and extension occurs in the midcarpal joint. Radio-ulnar deviation is mainly accomplished by a minor radiocarpal translation and angulation (with flexion of the scaphoid/extension of the capitate in RD and the opposite in UD) and a larger midcarpal angulation mainly by the capitate, making the midcarpal joint the major contributor to this particular motion (Craigen and Stanley 1995, Kaufmann et al. 2005). The mechanical center of rotation of the wrist was described by Youm and associates (1978), as being located in the proximal part of the capitate in the anterior and lateral planes. More recently, much attention has been focused on the so-called dart throwers motion (DTM), the movement of the hand from dorsoradially to ulnavolarly, a mobility exclusive for humans (Rohde et al. 2010). So-called dart-throwing is the maximum unrestricted motion the wrist can perform, and it is possible due to the lack of constraining ligaments between the lunate and the capitate. The DTM utilizes the midcarpal joint to the largest extent, which has its greatest freedom of motion in this oblique plane, and not in the coronal plane (Moritomo et al. 2007). Crucial to a wide range of wrist motions, it is important to preserve some radiodorsal and ulnovolar movement (Kijima and Viegas 2009). A recent report found the mechanical axis of the wrist to be oriented in the same plane as the DTM, obliquely to the direction of the flexion-extension (Crisco et al. 2011).