gms | German Medical Science

Objectives/Interrogation: Although osteoarthritis of the thumb carpometacarpal (CMC) joint is common, the effect of thumb movement at the joint surface remains unclear. The purpose of this study was to examine the changes in joint distance during flexion and abduction of the thumb by computed tomography (CT) at multiple positions.

Methods: The subjects were 5 healthy men (mean age 44.4±14.9 years). CT images of one hand of each subject were obtained during motion of the thumb from maximum extension to maximum flexion, taken at 4 equally divided positions using a supportive device made of Styrofoam. Similarly, images were obtained in 4 positions during movement from maximum adduction to maximum abduction. A three-dimensional model was constructed from the images, and the joint distance at each position was measured. Solidworks was used as the analytical software, and a measurement perpendicular to the metacarpal joint surface was used as the joint distance.

Results and Conclusions: The minimum joint distance became smaller as the joint flexed from the extended position. The mean minimum joint distance was decreased from 0.66 mm in the extended position to 0.51 mm in the flexed position, but this change was not statistically significant. In the flexed position, the joint distance became smaller on the volar and ulnar sides of the metacarpal joint surface. The minimum joint distance also became smaller as the joint abducted from the adducted position. The mean minimum joint distances was significantly decreased from 0.71 mm in the adducted position to 0.34 mm in the abducted position (p<0.05). In the abducted position, the joint distance became smaller on the volar side of the metacarpal joint surface.

Movement of the thumb CMC joint consists of a complex balance of a saddle joint, ligaments, muscles, and tendons. However, its specific movement has been under-investigated. Some studies report that wear of the thumb CMC joint occurred on the volar side of the metacarpal joint surface. However, in our study, as the thumb joint flexed or abducted, the joint distance decreased. Moreover, in the flexed and abducted positions, the joint distance on the volar side was smaller. Importantly, this movement is involved in the occurrence and progression of osteoarthritis of the thumb CMC joint.