[Comparison of screw implantation parameters between two approaches in capitolunate arthrodesis: an imaging analysis based on CT of the normal wrist].

Objective: To compare the parameters of screw implantation in capitolunate arthrodesis between the 2nd and 3rd metacarpal bones and via the distal dorsal capitate bone approach based on CT images of the normal wrist, and provide reference for the selection of surgical approaches and planning of screw insertion trajectory.

Methods: CT data of 50 patients who met the criteria between February 2022 and April 2022 were selected as the study objects. There were 30 males and 20 females, and the age ranged from 18 to 69 years (mean, 37 years). The normal wrist alignment was conformed in all CT images. All CT data from the unilateral wrist of the patients was imported into Mimics Medical 20.0 software to construct a three-dimensional plane model, in which a virtual 3.5 mm screw was implanted between the 2nd and 3rd metacarpal bones and via the distal dorsal capitate bone approach. The angle between screw and coronal, sagittal, and transverse planes, the total length of the screw, the length of the screw in the lunate bone and the capitate bone were measured. The ratios of the length of the screw in capitate bone to the length of the long axis of the capitate bone, the length of the screw in lunate bone to the length of the long axis of the lunate bone, and the length of screw in lunate bone to the length of the screw in capitate bone were calculated. Assuming that the result of screw implantation between the 2nd and 3rd metacarpal bones was better than that via the distal dorsal capitate bone approach, the difference in length of the screw in the lunate bone between the two approaches was calculated, and the superiority test was performed.

Results: Compared with the distal dorsal capitate bone approach, the total length of the screw increased, the length of the screw in the capitate bone decreased, and the length of the screw in the lunate bone increased, the angle between the screw and coronal plane decreased, the angles between screw and sagittal, transverse planes increased after the screw was implanted between the 2nd and 3rd metacarpal bones. And the ratio of the length of the screw in capitate bone to the length of the long axis of capitate bone decreased, the ratio of the length of the screw in lunate bone to the length of the long axis of lunate bone increased, and the ratio of the length of the screw in lunate bone to the length of the screw in capitate bone also increased. All the differences were significant ( <0.05). The difference in the length of the screw in the lunate bone between the two approaches was 1.86 mm [95% (1.54, 2.18) mm], which was greater than the superiority margin (1.35 mm). The superiority hypothesis was supported.

Conclusion: Compared with the distal dorsal capitate bone approach, the screws implanted between the the 2nd and 3rd metacarpal bones in the capitolunate arthrodesis are longer in lunate bone and more vertical to the articular surface of the capitolunate joint. Theoretically, the capitolunate joint are more firmly fixed.