“Evaluating the Effects of the Obturator Externus Tendon on the Posterior Femoral Neck”

Abstract

The anatomical literature describes the insertion tendon of obturator externus (OE) as leaving a distinct groove on the posterior aspect of the femoral neck as it travels distally to insert in the intertrochanteric fossa, a trait proposed to be directly associated with the hyper‐extended position of the human hip. The absence of this osteological correlate from the femoral neck of chimpanzees, a sister taxon to humans and a brachiating quadruped, has resulted in the use of this trait as an indicator for the evolution of bipedalism in extinct hominins. The aim of this study was to dissect and record the path of the OE tendon and adjacent ischiofemoral ligament as well as reassess the reliability of the osteological correlate in order to determine if the groove created by the OE tendon is an acceptable indicator of the origin of bipedalism in extinct hominins. The posterior hip region of embalmed (n=27) and fresh (n=3) cadavers were dissected, and the posterior aspect of the femoral neck was cleared of periosteum to evaluate the presence or absence of the OE groove. We found that 2 cadavers had a groove consistent with the OE, and 24 did not have a groove consistent with the OE. The osteological findings varied, ranging from no bony defects, a small, medially‐placed divot near the lesser trochanter, to a variety of both horizontally and vertically positioned groves on the posterior aspect of the femoral neck. The morphology of the OE as it traveled across the posterior femoral neck also varied, ranged from predominantly muscular, a thin, mostly inferiorly‐placed tendon, to a very thick, rigid, tendinous insertion. In the specimens that demonstrated a clear indication or groove on the posterior surface of the femoral neck that could be aligned with the OE, there was no consistency in the overall morphology of that groove, the OE muscle, or its insertion tendon. Additionally, a groove parallel to the OE tendon often appeared to correlate with a thickened area in the ischiofemoral ligament. As a result, we conclude that this anatomical characteristic of the posterior femoral neck is highly variable and should not be used as an osteological correlate to indicate bipedalism in extinct hominins.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.