Exploring the Significance of the Obturator Externus Groove as a Marker for Bipedalism: A Cadaveric Study

Background Bipedalism, defined as locomotion using only two feet, is a distinctive trait that sets humans apart from most other creatures. This study explores the significance of the obturator externus groove (OEG) as a marker for bipedalism. This topic is important due to its implications in evolutionary history. Previous studies have identified various anatomical features indicative of bipedalism, including an S-shaped spine, a centrally positioned foramen magnum, and unique pelvic and femoral structures. Among these, the morphology of the femur, particularly the presence of the OEG, has been proposed as a potential marker of habitual bipedalism. Material and methods This study examined the presence and dimensions of the OEG in both dry bone and cadaveric specimens. The dry bone study included 18 femur specimens from 14 individuals, analyzed by trained anatomists for the presence, visibility, and dimensions of the OEG. A cadaveric study was conducted on 28 formalin-fixed embalmed cadavers, utilizing precise dissection techniques to examine the relationship between the obturator externus tendon (OET) and the neck of the femur, and to identify and describe the OEG. Results In the dry bone study, 36% of individuals exhibited the OEG, while the cadaveric study found grooves in 21% of individuals. The OEG in this study was seen in 11 out of all 42 study subjects (dry bones and cadaveric), resulting in an incidence of about 26%. The groove's depth varied, with shallow grooves measuring less than 1 mm and deeper grooves measuring more than 1 mm. Additionally, the study identified the obturator externus notch and a soft tissue bed cushioning the OET, providing new anatomical insights. Conclusions The findings revealed that the OEG is uncommon and typically observed unilaterally. The presence of the groove may result from biomechanical factors, such as activities requiring strong hip extension, rather than bipedal locomotion alone. The cadaveric dissection approach allowed for direct observation and measurement of the groove to minimize user interpretation bias, providing more accurate findings. The OEG was an infrequent finding, indicating that it should not be used as a criterion for determining bipedalism in fossils.