Articular Shape of the Thumb Carpometacarpal Joint Differs with Age but Not Sex

Introduction Thumb carpometacarpal joint osteoarthritis (CMC OA) is often considered a mechanically mediated disease. Joint incongruity increases contact stress and cartilage degradation. The higher prevalence of CMC OA in women and increasing incidence with aging implicates potential sex and age differences. Conflicting reports on CMC joint curvature and its relationship to OA exist^1–3; small sample sizes and investigation with older cadaveric specimen limit current literature.

We evaluated CMC joint shape in vivo related to sex and age using a large, cross-sectional experimental design. We hypothesized that articular shape varies with sex and age.

Materials and Methods We enrolled 65 healthy subjects without pathology, grouped by sex and age (“young”: 14 males/16 females, aged 18 to 25 years; “old”: 16 males/19 females, aged 45 to 75 years). High-resolution (0.625 × 0.4 × 0.4 mm3 voxel size), 3-D volume images of the trapezia and first metacarpals obtained with a 16-slice CT scanner (GE LightSpeed 16). Bone segmentation, mesh surfaces, and articular delineation from CT scans were performed and computed (Mimics v12 and Geomagic Studio). A fifth-order polynomial fit to articular surface points and the average principal curvatures (kmin and kmax) were computed. Group comparisons of curvature and scaling were performed, with statistical modeling of size and curvature parameters as a function of sex and age.

Results Our findings show that the trapezium becomes more curved in the radio-ulnar (kmin) direction and less curved in the dorso-volar (kmax) direction, whereas the metacarpal becomes less curved in the radio-ulnar (kmax) and more curved in the dorso-volar (kmin) direction with aging. Whole bone surface areas and articular facet surface areas were significantly greater in young males than in young females for both bones; however, the surface area ratio of articular to whole bone was not different between sexes. The average kmax for the trapezium was significantly higher in females, a difference that disappeared after scaling.

Discussion No difference between the articular shape of male and female joints, after accounting for size, is consistent with the finding of Marzke,³ but refutes Ateshian,¹ who found female trapezia more curved than male, even after normalization, and North and Rutledge,² who conversely found female joints to be flatter. No previous studies have reported a quantitative analysis of joint shape differences with aging. These findings, along with geometric differences of the trapezium as more curved in the dorso-volar direction and the metacarpal in the radio-ulnar, suggest that the articular surfaces conform with age. Joint congruence requires geometric conformity as well as positioning, which requires further investigation. We postulate that trapezial flattening in the dorsal-volar direction with aging may accompany the oft-reported laxity in this direction.

Conclusion Aging, not sex, affects the articular surface shape of the CMC joint. If articular shape plays a role on the pathogenesis of CMC OA, it is a mediating, rather than a leading one.

Table 1 Mean (± SD) average principal curvature values

	TPM				MC1
	YM (n = 14)	YF (n = 16)	Y (n = 30)	O (n = 35)	YM (n = 14)	YF (n = 16)	Y (n = 30)	O (n = 35)
*Significant group difference.
kmin (m-1)	−53 ± 14	−56 ± 18	−55 ± 16 *	−75 ± 19 *	20 ± 16	15 ± 13	17 ± 15	32 ± 22
kmax (m-1)	143 ± 19 *	165 ± 21 *	155 ± 23 *	125 ± 24 *	141 ± 15	154 ± 23	148 ± 21 *	133 ± 26 *
skmin (m-1)	−52 ± 14	−50 ± 15	51 ± 14 *	73 ± 17 *	−19 ± 16	−13 ± 11	16 ± 14	31 ± 21
skmax (m-1)	140 ± 16	149 ± 15	145 ± 16 *	120 ± 20 *	142 ± 13	143 ± 25	142 ± 20	129 ± 22

References

References

1 Ateshian, et al. J Biomech 1992

2 North. Hand 1955

3 Marzke, et al. J Hand Surg [Br] 2012