An analysis of the articular surface distribution of the femoral head and acetabulum in anthropoids, with implications for hip function in Miocene hominoids

Abstract

Abstract Use of linear techniques to represent complex shapes has constrained morphological studies of the hip joint, with the result that functionally significant features have remained unquantified. This study uses a linear least squares sphere fit to the femoral head and acetabular subchondral bone as a framework for mapping the distribution of articular surface on the joint components of several extant anthropoids. The distribution of acetabular articular surface is believed to be related to mobility and the loading environment of the joint. Low dorsal and caudal lunate surfaces inPongopermit a wide range of abduction, while an extensive cranial lunate surface implies substantial cranial loading. The acetabula of pronograde monkeys has a uniform distribution of articular surface, presumably because the hip socket is loaded from cranial, dorsal and caudal directions.Panhas neither as much cranial lunate surface asPongo, nor as much dorsal lunate surface as the monkeys, suggesting a heterogeneous loading environment that may be a consequence of frequently using both orthograde and pronograde postures. The monkeys have a preponderance of articular surface on the anterior aspect of the femoral head, reflecting a greater emphasis on adducted, medially oriented postures and excursions than inPan.Evidence from the femur, and in the case ofProconsul, the acetabulum, was integrated with other data to reconstruct hip mobility and relate it to suspensory behavior in Miocene hominoids. Femoral articular configurations suggest that most Miocene hominoids had mobile hip joints, which would have facilitated climbing and hindlimb suspension, however, available humeral material does not support a similar mobility in the shoulder. The exception to this pattern are the fossil remains from Moroto, which combine a monkey-like hip, compatible with quadrupedal hip use, with a back that suggests orthograde adaptations.