IN VITRO ANALYSIS OF CARPAL KINEMATICS DURING VALIDATION OF A STABILIZED SCAPHOID HEMIARTHROPLASTY.

Objective: Pseudoarthrosis and necrosis of the proximal pole of the scaphoid require complex treatment. If primary treatments fail, there are only techniques that sacrifice part of the mobility. We present the design and in vitro results of an anatomical partial prosthesis of the scaphoid bone.

Material And Method: The kinematics of the carpus are tested in vitro on 6 cadaveric forearms before and after prosthetic replacement, applying active loads on the main muscles. Pre- and post-intervention movements are recorded by Kinescan/IBV®, translating an angular value.

Results: After prostheticization, a decrease in the movement of the capitate (-19.36º) and scaphoid (-15.46º) is recorded during flexion-extension, while that of the lunate increases (11.67º). With the radial-ulnar deviation, only the movement of the great muscle decreases (-11.78º), but that of the scaphoid (4.03º) and lunate (5.9º) increases. We find significant differences whenever there is a decrease in movement. In the "throwing darts" movement (DTM), the average movement decreases in flexion-extension (-18.44º) and in radial-ulnar deviation (-3.66º), without significant differences. While the descent of the scaphoid in flexion-extension and radio-ulnar deviation of the DTM will affect the kinematics (p<0.05). There is no involvement of the lunate in the DTM.Regarding the relative interosseous movement, significant differences are observed in the main axis of the F-E.

Conclusions: The implantation of a stabilized partial scaphoid prosthesis does not significantly modify the movement pattern of a healthy wrist. Therefore, in the future it could be a viable alternative for the treatment of recalcitrant pathology of the carpal scaphoid.