The 88th Annual Meeting of the American Association of Physical Anthropologists (2019)


A natural history of the femoral neck

ALEXANDER G. CLAXTON.

Anthropology, Boston University

March 29, 2019 , CC Ballroom BC Add to calendar

The modern human femoral neck differs from that of our closest living relatives both externally and internally. These differences are in part thought to be indicative of the relatively stereotyped character of hip arthrokinematics in normal human locomotion, whether through evolutionary or bone functional adaptation. It will be helpful to put the human proximal femur into a larger evolutionary and developmental context to better understand how the human condition conforms to larger patterns in proximal femoral morphology and locomotion. A femoral neck evolved independently in at least two tetrapod lineages (archosaurs and mammals), roughly corresponding with a shift to a more parasagittal hind limb posture. However, the extremely prominent femoral neck present in multituberculates, who are often reconstructed as semi-sprawling, demonstrates that it is not inherently connected to hip parasagittalism. The two primary proximal femoral morphotypes in modern mammals, coxa recta and rotunda, roughly correspond to the range of motion at the hip. These morphotypes are congruent with the patterns of epiphyseal ossification (“coalesced” and “separate”). It has been assumed that those mammals with the “coalesced/recta” condition possess the primitive mammalian state and that those with “separate/rotunda” are derived. Observations from the mammalian fossil record and ontogeny call this assumption into question. In addition, there are cases within modern taxa that indicate an apparent reversal to “coalesced/recta” from the “separate/rotunda” condition and vice versa. Modern humans, though "separate/rotunda," have some features in common with "coalesced/recta," including thin superior femoral neck cortex. Care should be taken when interpreting femoral neck traits.