The Anthropoid Crista Trochanterica and the Hip Joint Capsule

The tubercle on the posterior aspect of the femoral neck (the crista trochanterica) has been repeatedly remarked upon because of its presence in early fossil apes, yet the function of this tubercle has eluded researchers. The prevailing explanation for the tubercle is that it relates to a strong ischiofemoral ligament, although none of the hypotheses for this bony projection have been systematically evaluated. This study surveyed 41 extant anthropoid species (n = 267 individuals) for the presence of a crista trochanterica. The soft tissue structures of the hip joint were then dissected and described for a sample of anthropoid cadavers (n = 14) in order to evaluate different hypotheses related to function of this tubercle. This study confirmed that the crista trochanterica is found in most cercopithecoids and platyrrhines, and is not present in great apes. The tubercle is rarely present in hylobatids, contrary to prior reports. The ischiofemoral ligament is not usually well-developed in anthropoids and does not fully explain the crista trochanterica morphology, although all cadavers displayed a well-developed zona orbicularis running along the posterior aspect of the joint capsule. The hip joint capsule itself inserted along the crista trochanterica in some individuals, typically those with an elongate crista trochanterica, but was highly variable in regards to the position of the tubercle. The hypotheses for the crista trochanterica are considered within the context of these findings, although the exact function of the tubercle remains unresolved.