Textbook typologies: Challenging the myth of the perfect obstetric pelvis.

Medical education's treatment of obstetric-related anatomy exemplifies historical sex bias in medical curricula. Foundational obstetric and midwifery textbooks teach that clinical pelvimetry and the Caldwell-Moloy classification system are used to assess the pelvic capacity of a pregnant patient. We describe the history of these techniques-ostensibly developed to manage arrested labors-and offer the following criticisms. The sample on which these techniques were developed betrays the bias of the authors and does not represent the sample needed to address their interest in obstetric outcomes. Caldwell and Moloy wrote as though the size and shape of the bony pelvis are the primary causes of "difficult birth"; today we know differently, yet books still present their work as relevant. The human obstetric pelvis varies in complex ways that are healthy and normal such that neither individual clinical pelvimetric dimensions nor the artificial typologies developed from these measurements can be clearly correlated with obstetric outcomes. We critique the continued inclusion of clinical pelvimetry and the Caldwell-Moloy classification system in biomedical curricula for the racism that was inherent in the development of these techniques and that has clinical consequences today. We call for textbooks, curricula, and clinical practices to abandon these outdated, racist techniques. In their place, we call for a truly evidence-based practice of obstetrics and midwifery, one based on an understanding of the complexity and variability of the physiology of pregnancy and birth. Instead of using false typologies that lack evidence, this change would empower both pregnant people and practitioners.

Variations of the Cystohepatic Blood Supply in American Midwestern Donor Cadavers.

Knowledge of right hepatic artery (RHA) and cystic artery (CA) variations is crucial for surgeons performing procedures on the hepatobiliary system, pancreas, and duodenum. Commonly, the RHA originates from the superior mesenteric artery (SMA), while the CA originates from the RHA and is found within the cystic triangle during laparoscopic cholecystectomies. Here we investigated variations in the origin and path of the RHA and CA in a sample of American midwestern cadavers (n = 18) from the Gift of Body Program at A.T. Still University's Kirksville College of Osteopathic Medicine. Portal triads and associated vessels were dissected to reveal the artery pathways. The origin, branching pattern, and course of the RHA and CA were documented, and descriptive measurements were taken. We describe four cases where the RHA originated from the anterolateral proximal SMA, traveled deep to the pancreatic neck, and had a slightly variable but close relationship with the portal triad structures. The CA was present in the cystic triangle in all 18 donors, typically originating from the RHA except for one case where it originated from the left hepatic artery. In six cases, the CA originated outside of the cystic triangle, crossing either superficially or deeply to the common hepatic duct to enter the cystic triangle. Knowledge of these variations will enhance preoperative planning and the overall safety of surgical procedures in this area.

Sexual dimorphism of the relationship between the gut and pelvis in humans.

OBJECTIVES: Obstetric demands have long been considered in the evolution of the pelvis, yet consideration of the interaction of pregnancy, the pelvis, and the gastrointestinal tract (gut) is lacking. Here, we explore sex differences in the relationship of gut volume with body size and pelvic dimensions. MATERIALS AND METHODS: Computed tomography (CT) scans of living adult Homo sapiens (46 females and 42 males) were obtained to measure in vivo gut volume (GV) and to extract 3D models of the pelvis. We collected 19 3D landmarks from each pelvis model to acquire pelvic measurements. We used ordinary least squares regression to explore relationships between GV and body weight, stature, and linear pelvic dimensions. RESULTS: The gut-pelvis relationship differs between males and females. Females do not exhibit significant statistical correlations between GV and any variable tested. GV correlates with body size and pelvic outlet size in males. GV scales with negative allometry relative to body weight, stature, maximum bi-iliac breadth, inferior transverse outlet breadth, and bispinous distance in males. DISCUSSION: The lack of association between GV and body size in females may be due to limits imposed by the anticipation of accommodating a gravid uterus and/or the increased plasticity of the pelvis. The pattern of relationship between GV and the pelvic outlet suggests the role of the bony pelvis in supporting the adominal viscera in females may be small relative to its role in childbirth. We conclude that gut size inference in fossil hominins from skeletal proxies is limited and confounded by sexual dimorphism.

Did Neandertals have large brains? Factors affecting endocranial volume comparisons.

OBJECTIVES: Common wisdom in paleoanthropology is that Neandertals had bigger brains than recent humans. Here we tested the hypothesis that there is no difference in brain size between Neandertals and recent humans while accounting for methodological variation and the makeup of both the Neandertal and recent human samples. MATERIALS AND METHODS: We examined endocranial volume (ECV) derived from virtually reconstructed endocasts of 11 Neandertals, six of which had associated femoral head diameters (FHD). Our recent human comparative dataset consisted of virtually measured ECV and associated FHD from 94 recent humans from the Robert J. Terry Anatomical Collection (63 male, 31 female). ECV of Neandertals and recent humans was compared using bootstrap resampling, repeating the analysis for two groupings of Neandertals (all and classic) and for three groupings of recent humans (all, males, and females). To examine brain size scaling, we completed an ordinary least squares regression of log (ECV) against log (FHD) for Neandertals and recent humans. RESULTS: The results of the bootstrap resampling analyses indicated that Neandertals only had significantly larger ECV when compared with recent human females. The regression between ECV and FHD suggested that Neandertals fall within the range of variation for larger humans. DISCUSSION: Our results demonstrate that Neandertals do not have uniquely large brains when compared with recent humans. Their brain size falls in the large end of the recent human range of variation, but does not exceed it. These results have implications for future research on Neandertal encephalization.

Homo naledi pelvic remains from the Dinaledi Chamber, South Africa.

In the hominin fossil record, pelvic remains are sparse and are difficult to attribute taxonomically when they are not directly associated with craniodental material. Here we describe the pelvic remains from the Dinaledi Chamber in the Rising Star cave system, Cradle of Humankind, South Africa, which has produced hominin fossils of a new species, Homo naledi. Though this species has been attributed to Homo based on cranial and lower limb morphology, the morphology of some of the fragmentary pelvic remains recovered align more closely with specimens attributed to the species Australopithecus afarensis and Australopithecus africanus than they do with those of most (but not all) known species of the genus Homo. As with A. afarensis and A. africanus, H. naledi appears to have had marked lateral iliac flare and either a weakly developed or non-existent acetabulocristal buttress or a distinct, albeit weakly developed, acetabulospinous buttress. At the same time, H. naledi has robust superior pubic and ischiopubic rami and a short ischium with a narrow tuberoacetabular sulcus, similar to those found in modern humans. The fragmentary nature of the Dinaledi pelvic assemblage makes the attribution of sex and developmental age to individual specimens difficult, which in turn diminishes our ability to identify the number of individuals represented in the assemblage. At present, we can only confidently say that the pelvic fossils from Rising Star represent at least four individuals based on the presence of four overlapping right ischial fossils (whereas a minimum of 15 individuals can be identified from the Dinaledi dental assemblage). A primitive, early Australopithecus-like false pelvis combined with a derived Homo-like true pelvis is morphologically consistent with evidence from the lower ribcage and proximal femur of H. naledi. The overall similarity of H. naledi ilia to those of australopiths supports the inference, drawn from the observation of primitive pelvic morphology in the extinct species Homo floresiensis, that there is substantial variation in pelvic form within the genus Homo. In the light of these findings, we urge caution in making taxonomic attributions-even at the genus level-of isolated fossil ossa coxae.

New fossil remains of Homo naledi from the Lesedi Chamber, South Africa.

The Rising Star cave system has produced abundant fossil hominin remains within the Dinaledi Chamber, representing a minimum of 15 individuals attributed to Homo naledi. Further exploration led to the discovery of hominin material, now comprising 131 hominin specimens, within a second chamber, the Lesedi Chamber. The Lesedi Chamber is far separated from the Dinaledi Chamber within the Rising Star cave system, and represents a second depositional context for hominin remains. In each of three collection areas within the Lesedi Chamber, diagnostic skeletal material allows a clear attribution to H. naledi. Both adult and immature material is present. The hominin remains represent at least three individuals based upon duplication of elements, but more individuals are likely present based upon the spatial context. The most significant specimen is the near-complete cranium of a large individual, designated LES1, with an endocranial volume of approximately 610 ml and associated postcranial remains. The Lesedi Chamber skeletal sample extends our knowledge of the morphology and variation of H. naledi, and evidence of H. naledi from both recovery localities shows a consistent pattern of differentiation from other hominin species.

Measuring Lateral Iliac Flare by Different Methods Risks Obscuring Evolutionary Changes in the Pelvis.

The orientation and morphology of the hominin ilium is functionally important for locomotion, yet no standard method exists for quantifying its lateral flare. This lack of standardization stems from fossil preservation issues and morphological differences between hominin species. Many techniques have been developed to measure flare based on what is preserved on a single fossil, but this makes comparisons between fossil species challenging. In some cases, methods developed based on australopith morphology are not appropriate for measuring the morphology in genus Homo. Lateral iliac flare is the angle between the iliac blade and the sagittal plane, and it affects the function and efficiency of the lesser gluteal muscles. Four different methods of quantifying lateral iliac flare are reviewed here, and assessed based on how well they reflect lateral iliac flare. The data show that these metrics measure different parts of the pelvis, none measures lateral iliac flare relative to the sagittal plane, and they yield different results for which fossil hominin is the most (or least) flared. This inconsistency puts paleoanthropologists at risk of misinterpreting the functional importance of lateral iliac flare in hominin evolution. I propose two paths forward to improve our assessment of flare: first, a geometric morphometric comparison of iliac blade variation would properly assess the full three-dimensions of the ilium; second, in hominin fossils that are not complete or numerous enough to include in a geometric morphometric analysis, two-dimensional measurements may still be used to assess functional differences in the ilium provided the researcher does not claim that they measure lateral iliac flare. Anat Rec, 300:956-963, 2017. © 2017 Wiley Periodicals, Inc.

Pelvic Morphology in Homo erectus and Early Homo.

The evolution of the hominin pelvis is generally seen as involving two broad stages: the establishment of bipedal pelvic morphology by the mid-Pliocene (or earlier), followed by architectural changes necessary to enlarge the birth canal in response to increased encephalization in Pleistocene members of the genus Homo. Pelvic and proximal femoral morphology in early Homo (namely H. erectus) has been seen as transitional between these stages, reflecting structural changes necessitated by greater body size (and perhaps moderate increases in brain size) overlain upon a basically primitive pelvic architecture. Here we review the history of thought on the evolution of the pelvis in early Homo, as well as recent fossil discoveries that have improved our understanding of diversity in pelvic morphology in early Homo and late australopiths. These discoveries (1) suggest that the "femoropelvic complex" characteristic of H. erectus emerged after the divergence of various lineages of early Homo (that is, it is not plesiomorphic for the genus) and (2) raise questions about the role that evolutionary change in brain size in the genus Homo played in the emergence of derived features seen in the pelvis of modern humans. Anat Rec, 300:964-977, 2017. © 2017 Wiley Periodicals, Inc.

Homo naledi, a new species of the genus Homo from the Dinaledi Chamber, South Africa.

Homo naledi is a previously-unknown species of extinct hominin discovered within the Dinaledi Chamber of the Rising Star cave system, Cradle of Humankind, South Africa. This species is characterized by body mass and stature similar to small-bodied human populations but a small endocranial volume similar to australopiths. Cranial morphology of H. naledi is unique, but most similar to early Homo species including Homo erectus, Homo habilis or Homo rudolfensis. While primitive, the dentition is generally small and simple in occlusal morphology. H. naledi has humanlike manipulatory adaptations of the hand and wrist. It also exhibits a humanlike foot and lower limb. These humanlike aspects are contrasted in the postcrania with a more primitive or australopith-like trunk, shoulder, pelvis and proximal femur. Representing at least 15 individuals with most skeletal elements repeated multiple times, this is the largest assemblage of a single species of hominins yet discovered in Africa.