Lumbar vertebral body and disc variation in modern humans with implications for reconstructing lumbar lordosis in fossil hominins

Lumbar lordosis plays a significant role in the vertebral column because it supports the weight of the torso during bipedal locomotion (Aeillo and Dean, 2002). In previous studies, vertebral body wedging (VBW) patterns (Williams et al. 2013; García-Martínez et al. 2020) and multiple linear regression formulas have been used to study lordosis in hominins (Been et al. 2010a; Been, Gómez-Olivencia and Kramer, 2012). This project evaluates the accuracy of current methods used for reconstructing lumbar lordosis in hominins through an analysis of how age, sexual dimorphism, VBW and intervertebral disc wedging (IVDW) influences lordosis. This study was the first to investigate the correlation between individual IVDW and VBW in detail and introduces the idea of reconstructing lordosis using the lumbolumbar angle. This study used a sample of modern humans, comprised of individuals between 25 and 50 years of age from the University of New Mexico Decedent Image Database (UNMDID) (n=112) and living South African adults (n=27), to study lordosis (Edgar et al. 2020). Reconstructions of lordosis were reported for fossil specimens Oberkassel 1, Oberkassel 2, Kebara 2, and StS 14. VBW, IVDW, the Cobb and lumbolumbar angle were measured digitally from CT scans. The results revealed that within the sample lordosis did not vary significantly based on age but did show signs of sexual dimorphism. Comparisons between IVDW and VBW demonstrated that IVDW contributed the most to lordotic curvature, but VBW had a stronger correlation with the Cobb and lumbolumbar angles. The relationship between VBW and IVDW was consistently negative. The reconstructed lordosis of fossil specimens was within the range of modern humans. Lordosis reconstructions varied based on methods but suggest that reconstructing the lumbolumbar angle, as opposed to the Cobb angle, could increase the accuracy of future reconstructions.