Wrist kinematics after limited intercarpal arthrodesis Two limited intercarpal fusions, scapho-trapezlal-trapezoldal and scapho-capitate, were simu- lated in six fresh human cadaver wrists by means of two Herbert screws. By use of a biplanar radiographic 'measurement system, the relative kinematic behavior of selected carpal bones, before and after the simulated limited fusions could be analyzed, Both scapho-trapezlal- trapezoidal and scapha-capitate fusions produced a similar reduction in global range of motion and comparable effects on the relative intracarpal motion. In both fusions, a significant reduction in relative motion at the lunocapitate joint was recorded. The scaphoid, being fused to the distal carpal row, was shown to lose its role in the adaptative mechanism that allows preservation of articular congruency to the always changing space between the distal carpal row and the radius. After both types of fusion, increased sliding motion of the lunate on the radius was found. These kinematic changes are likely to enhance shear stresses on the lunate and tension on the sur- rounding ligaments, potentially diminishing long.term functional results. (J HAND SURG 1989;14A:791-9.) M. Garcia-Elias, MD, W. P. Cooney, MD, K. N. An, PhD, R. L. Linscheid, MD, and E. Y. S. Chao, PhD, Rochester, Minn . Global kinematics of the wrist is an in- teraction and accumulation of partial motions occurring at different levels within this joint. Surgical fusions affecting one of these levels will of necessity change the kinematics according to the biomechanical impor- tance of the joint fused. Several limited wrist fusions have been reported for treatment of problems around the wrist. One of the most frequently performed limited intercarpal fusions is the one involving trapezium, trapezoid, and scaphoid. This procedure, also known as SIT or triscaphe fusion, has recently received considerable attention not only for the treatment of localized degenerative disease!" but also From the Orthopedic Biomechanics Laboratory, Department of Or- thopedics, Mayo Clinic/Mayo Foundation, Rochester, Funded by a grant from the Orthopedic Research and Education Foundation, Received for publication July 13, 1988; accepted in revised form Nov. 25, 1988. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Reprint requests: Kai-Nan An, PhD, Orthopedic Biomechanics Lab- oratory, Department of Orthopedics, Mayo Clinic/Mayo Foun- dation, Rochester, MN 55905 . 3/1113484 for Kienbock's disease," and scapho-lunate - dissoci- ations." :" Another type of limited intercarpal arthrodesis is the scapho-capitate (SC) fusion . Initially described for treatment of nonunions of the scaphoid.P: 14 the SC fusion has been also suggested for the treatment of scaphoid instabilities IS. 16 and Kienbock's disease. IS The theory as stated is that both SIT and SC fusions provide a load-bearing column that, transmits forces from the hand across the wrist to the radius, bypassing the weak- ened lunate." Several laboratory studies":" have investigated lim- ited intercarpal fusions from a kinematic point of view. All of these studies have primarily looked at the re- striction in overall range of wrist motion. Kleinmanrr" looked at the changes in relative motion between the carpal bones after SIT fusion as a qualitative kinematic analysis of the procedure for scapho-lunate dissocia- tions. With this background in mind, the purpose of this study is to document and compare the effects of simulating both the SIT and SC fusions on individual carpal bone motion and to better define intercarpal ki- nematics. Materials and methods Six freshly frozen human cadaveric wrists were used in this experiment. X-ray films were obtained on each TIlE JOURNAL OF HAND SURGERY 791