The morphology of the thumb carpometacarpal joint does not differ between men and women, but changes with aging and early osteoarthritis

Abstract

The high prevalence of thumb carpometacarpal (CMC) joint osteoarthritis (OA) in women has been previously linked to the articular morphology of the trapezium. Studies report conflicting results on how the articular shapes of male and female trapezia compare to one another, however, mainly because their findings are based on data from older cadaveric specimens. The purpose of this in vivo study was to dissociate the effect of sex from that of aging and early OA by using cohorts of healthy young and healthy older subjects, as well as patients with early stage OA. Computed tomography scans from 68 healthy subjects and 87 arthritic subjects were used to obtain 3-D bone models. The trapezial and metacarpal articular surfaces were manually delineated on scaled bone models and compared between sex, age, and health groups by using polar histograms of curvature and average curvatures. We found no sex-related differences, but significant age-group and health-group differences, in the articular surfaces of both bones. Older healthy subjects had higher curvature in the concave and lower curvature in the convex directions of both the trapezial and metacarpal saddles than healthy young subjects. Subjects with early OA had significantly different metacarpal and trapezial articular shapes from healthy subjects of the same age group. These findings suggest that aging and OA affect the articular shape of the CMC joint, but that, in contrast to previously held beliefs, inherent sex differences are not responsible for the higher incidence of CMC OA in women.

Keywords: Articular joint shape; Computed tomography; Osteoarthritis; Thumb CMC joint; in vivo.

Figure 1

a) The wrists and thumbs of our participants were CT-scanned at a resolution of 0.4 mm × 0.4 mm × 0.625 mm or higher, and the CMC joints were segmented in Mimics; b) the trapezia and the first metacarpals were exported as meshed surfaces; c) the articular surfaces of the CMC joint were manually selected; d & e) fifth order polynomials were fit to the articular surfaces and principal curvatures were computed at 400pts/mm²—shown here at a lower resolution—and then averaged across the whole surface: k_min of the trapezial surface and k_max of the metacarpal surface correspond to curvature in the ulnar-radial direction, whereas k_max of the trapezial surface and k_min of the metacarpal surface correspond to curvature in the volar-dorsal direction; f) polar histograms of curvature, which preserve spatial information on local curvature were also used computed for the articular surfaces

Figure 2

For both the trapezium (TPM) and metacarpal (MC1), bone volumes (Vol.), whole bone surface areas (SA), and articular surface areas (ASA) were significantly different between sex groups, but not between age and health groups, whereas the ratios of the articular surface areas to whole bone surface areas (ASA/SA) were not different between sex, age, or health groups

Figure 3

Mean (±SD) average curvatures: a & b) differed between age groups in the metacarpal (MC1) and c & d) differed between age and health groups in the trapezium (TPM) (* p < 0.05 considered statistically significant)