To design a new type of external-fixed wrist prosthesis and to evaluate the function of it.

According to the radial and ulnar inclinations of distal radius articular surface measured in 50 cases of adult wrist radiographs, and combining the data from literatures and abroad artificial wrist joint design experience, a new type of external-fixed artificial wrist joint system was designed, of which the radial and ulnar inclinations were designed as 10° and 7°. Six wrists from fresh frozen adult cadavers were fixed in 3D motion experiment table. Markers which can be identified by the infrared camera were set in the wrist joint; 4 Nm was loaded to the upper limb at four directions including flexion, extension, ulnar deviation and radial deviation. The corresponding images were captured when the zero load and maximum load applied to the wrist joint by Cotex 3.0 software, and the ranges of motion of wrist joint in four directions were calculated. Total wrist arthroplasty using new type of external-fixed wrist prosthesis was performed in the six specimens, and the experimental procedures were repeated to measure the range of motions of the wrist joint prostheses. Paired t test was applied to compare the pre- and postoperative data.

Total wrist arthroplasty was successfully performed on all the samples, and the postoperative joint activities were good. Under the same load, the postoperative ranges of motion of the wrist in dorsal flexion, ulnar deviation, and radial deviation showed no statistical difference comparing with the preoperative ones (P>0.05). The preoperative flexion was (72.3±4.8) °, the postoperative maximum activity of flexion was (54.9±6.1) °, there were significant differences between the two(t=8.34, P<0.01).

The new design of external-fixed wrist prosthesis can meet the basic requirements of wrist biomechanics, which is worthy of further research.