Novel 3D analysis of the proximal femur and hip joint function in arhropoids: implications for the human hip joint functional analyses [abstract]

Abstract

Fossil catarrhines are hypothesized to display a range of locomotor adaptations, creating specialized joint morphology. Many of these primate taxa are known from the proximal femur, which directly reflects hip function. Although some work has been done, certain aspects of femoral and hip morphology (functional axes and curved surfaces) have proved difficult to quantify. This study employs novel 3D methods to quantify shape variation of the proximal femur and acetabulum in a large sample of extant anthropoids, allowing us to test hypotheses of locomotor adaptation. Continuous laser scan data were analyzed using PolyWorks (Innovmetric, Inc.). This software enabled us to establish and compare functional axes, joint centers, and articular size, shape and distribution. Our results demonstrate that abduction capacity of the femur is affected by trochanteric height, neck shaft angle and bone segment lengths, as well as head and fovea position. Furthermore, although femoral head and lunate surface areas as a whole scale allometrically, species vary in size, shape and position of the femoral head, with terrestrial monkeys having less articular surface area posteroinferiorly relative to the fovea, and significantly more femoral articular area extending laterally from the spherical head surface onto the neck, reflecting an emphasis on flexed and adducted hip postures. Fossil primates exhibit a suite of morphologies that reflect differential patterns of hip joint function, providing important insights into catarrhine evolution. Implications for 3D analyses of human joint function are considered.