1. Proceedings of the 9
th
Triennial
Hand and Wrist Biomechanics International (HWBI) Symposium
Milan, Italy, June 16-17, 2015
INTRODUCTION. It is believed that the morphology of the CMC joint may play a role in the mechanical onset of CMC OA
(Ateshian et al., 1992), providing an explanation for the discrepancy in the prevalence of disease between men and women
(North and Rutledge, 1983; Felson et al., 2000). However, previous studies have reported inconsistent articular shape
differences (North and Rutledge, 1983; Ateshian et al., 1992). Recent evidence suggests that the morphology of the CMC joint
does not differ between men and women (Halilaj et al. 2014). Statistical shape models have the potential to realistically
describe anatomy and its variation in a population by decomposing shapes into a set of mathematical descriptors (Cootes et
al., 1992). Here we present a statistical shape model of the articular surfaces of the first metacarpal and trapezium bones to
characterize the size and shape of the CMC joint and investigate any differences in morphology with respect to sex and age.
METHODS. A training set of 50 healthy CMC joints were manually segmented from CT images of the hand with a resolution
of 0.4x0.4x0.625mm (age range: 18 yrs to 67 yrs; 24 females and 26 males). A custom piecewise parametric template mesh
was created for the articulating surface, and fitted to manual segmentations of the articulating surface to create a set of
correspondent meshes of the CMC joint surface. Principal component analysis was performed on this training set resulting in
a SSM of the articular surface. We then performed linear regression and one-way ANOVA on the mode scores against age
and sex.
RESULTS. As expected, the first mode (size) of the articular surface correlated with sex (p< 0.001) (Figure 1). None of the
other modes (of morphological variation) were correlated to sex. After size-normalization, none of the modes were correlated
with sex. Furthermore, none of the modes showed significant correlation with age.
Figure 1 – Statistical shape model of CMC joint showing variation along the first principal component (size) from 2 std (men),
to 0 std, to +2 std (women).
DISCUSSION. The purpose of this research was to characterize the size and shape of the articular surfaces of the trapezium
and first metacarpal bones with the novel use of a statistical shape model. Contrary to our expectations, we discovered that
the only difference in the morphology between men and women was size. In terms of CMC OA, these data in conjunction with
previous data from our study on entire CMC joint morphology suggest that size, not shape, may be the main morphological
contributor towards increased prevalence of OA in women. Size is important when considering activities of daily living that
involve the wrist and hand, and a smaller trapezia and metacarpal will affect the mechanics and function of the CMC joint. For
example, if we consider that the moment arms of muscles crossing the joint would scale with bone size, the forces required to
generate the same torques for a given task would be higher. If we consider this together with the smaller articular surfaces,
this points towards potentially higher stresses in a smaller hand.
Acknowledgements. We would like to thank the Auckland Bioengineering Institute, Stanford Orthopaedics, and the NIH for
funding.
COI. We declare no conflict of interest
Abstract XX
WOMEN HAVE SIMILAR CARPOMETACARPAL JOINT MORPHOLOGY TO MEN
M.T.Y.Schneider1
, J. Crisco2
, A. C. Weiss2
, A. L. Ladd3
, P. Nielsen1,4
, T. Besier1,4
, J. Zhang1
1) Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
2) Department of Orthopaedics, Brown University, RI, USA
3) Department of Orthopaedic Surgery, Stanford, Stanford University, CA, USA
4) Department of Engineering Science, The University of Auckland, Auckland, New Zealand