ARTICULAR SIZE AND CURVATURE AS DETERMINANTS OF CARPAL JOINT MOBILITYAND STABILITY IN STREPSIRHINE PRIMATES

Theoretical and empirical evidence suggest that limb joint surface mor phology is mechanically related to joint mobility, stability, and stre ngth. This study tests hypotheses relating aspects of joint surface sh ape to joint function by comparing carpal joint size and curvature amo ng strepsirhine primates that differ significantly in their positional behaviors and hand postures: vertical clingers, active arboreal quadr upeds, and slow cautious climbers. Joints that are very mobile are exp ected to have increased size and curvature of male joint mating surfac es, whereas those that function primarily in weightbearing are expecte d to have relatively expanded female joint mating surfaces. Results sh ow that 1) high male joint mating surface curvature is related to incr eased joint mobility and 2) increased female joint mating surface curv ature is related to increased joint stability under loads of different orientation. Are lengths of both male and female joint mating surface s do not differ significantly between locomotor groups. Moreover, carp al joint curvature is not significantly correlated with either joint s ize (are length) or body size, but carpal joint size and body size are highly correlated with one another. Relative to body size, articular are lengths scale close to isometry (geometric similarity) both within and among groups. These results suggest that structural changes leadi ng to increased joint mobility involve modifying joint surface curvatu re, and in the case of the carpal joints do not include altering joint size. Curvature of female joint mating surfaces appears related to va riation in load orientation, but not necessarily load magnitude and fr equency. (C) 1996 Wiley-Liss, Inc.