How to Build a 3D Model of a Fossil Hominin Vertebral Spine Based on Osseous Material

Reconstruction of the spinal curvatures of extinct hominins is essential in order to understand their posture and function. Despite its importance, researchers face many difficulties in reconstructing spinal posture based solely on osseous material due to the absence of soft tissues. In this chapter, we explain how to align two consecutive vertebrae in the absence of the intervertebral discs. Then we summarize and demonstrate the use of the current methods for estimating sacral orientation and spinal curvatures from osseous material. We also discuss the advantages and disadvantages of each method. As an example, we demonstrate the application of these methods to the vertebral column of the Kebara 2 adult male Neandertal and present the 3D reconstruction of its spinal curvatures from the sacrum to the cervical spine. Two methods-pelvic incidence (PI) and sacral anatomical angle (SAA)-are used to describe sacral orientation. Both methods are applicable when the pelvis is relatively complete. Three methods-lumbar vertebral body wedging (LVBW), inferior articular process angle (IAPA), and lumbar lordosis based on PI (LLPI)-are used to define lumbar lordosis. Two methods-thoracic vertebral body wedging (TVBW) and thoracic vertebral body height difference (TVBHD)-are used to estimate thoracic kyphosis. Finally, foramen magnum orientation (FMO) is used to reconstruct the cervical lordosis. The calculated values for Kebara 2 are PI: 34°, SAA: 19°, IAPA: 25°, LLPI: 29°-36°, TVBHD: 44°, TVBW: 37°, FMO: 26°. Based on these calculations, we present here a complete reconstruction of the spine of Kebara 2 from the atlas to the sacrum. This is the first reconstruction of a complete vertebral spine that has been performed for a fossil hominin. Given anatomical variation, utilizing a combination of the methods is advised. The different methods are consistent with each other in each anatomical region and their combined use provides a more robust estimate.