The Neandertal vertebral column 2: The lumbar spine

Abstract

Here we provide the most extensive metric and morphological analysis performed to date on the Neandertal lumbar spine. Neandertal lumbar vertebrae show differences from modern humans in both the vertebral body and in the neural arch, although not all Neandertal lumbar vertebrae differ from modern humans in the same way. Differences in the vertebral foramen are restricted to the lowermost lumbar vertebrae (L4 and L5), differences in the orientation of the upper articular facets appear in the uppermost lumbar vertebrae (probably in L1 and L2-L3), and differences in the horizontal angle of the transverse process appear in L2-L4. Neandertals, when compared to modern humans, show a smaller degree of lumbar lordosis. Based on a still limited fossil sample, early hominins (australopiths and Homo erectus) had a lumbar lordosis that was similar to but below the mean of modern humans. Here, we hypothesize that from this ancestral degree of lumbar lordosis, the Neandertal lineage decreased their lumbar lordosis and Homo sapiens slightly increased theirs. From a postural point of view, the lower degree of lordosis is related to a more vertical position of the sacrum, which is also positioned more ventrally with respect to the dorsal end of the pelvis. This results in a spino-pelvic alignment that, though different from modern humans, maintained an economic postural equilibrium. Some features, such as a lower degree of lumbar lordosis, were already present in the middle Pleistocene populations ancestral to Neandertals. However, these middle Pleistocene populations do not show the full suite of Neandertal lumbar morphologies, which probably means that the characteristic features of the Neandertal lumbar spine did not arise all at once.

Morphology, pathology, and the vertebral posture of the La Chapelle-aux-Saints Neandertal

“…Our assessment corroborates the presence of well-developed cervical and lumbar lordosis in this individual, as suggested previously (3,5,8,9). It challenges recent reconstructions inferring limited Neandertal spinal curvature (10)(11)(12)(13)(14)(15)(16). We base our finding on two lines of evidence, (i) a pelvic incidence, associated with a normal human pelvic posture, close to the mean of modern humans, and (ii) the articulation of the cervical and the lower lumbar vertebrae.…”

“…A typical consequence of the asymmetric subluxations with nearthroses on the right side of L4, L5, and S1 is a right-convex degenerative scoliotic misalignment of these vertebrae (28,29), which is to a lesser degree also present in the cervical spine. (11)(12)(13). Note that the reconstructed sacral promontory projects the S1 body more superiorly than the preserved portion; the reconstruction is therefore conservative, because the preserved portion alone would provide a higher PI.…”

“…Together, these and later analyses (6-9) provided Neandertals with a fully erect (human) posture with normal spinal curvatures. However, a series of recent papers (10)(11)(12)(13)(14)(15)(16) have argued that the Neandertals, including La Chapelle-aux-Saints 1, possessed lumbar vertebrae and pelvic incidence angles indicating reduced lumbar lordosis, flatter cervical lordosis and thoracic kyphosis than modern humans, and little of the pelvic tilt associated with bipedal posture (and lumbar lordosis) in recent humans. Such a flat spinal curve in recent humans is associated with an anterior shift of the line of gravity and instability leading to chronic back pain (17), raising questions about its appropriateness for the Neandertals.…”

3D virtual reconstruction of the Kebara 2 Neandertal thorax

“…Sawyer and Maley 27 also indicated the presence of flaring lower thorax which resulted in what they called a “bell-shaped thoracic region”. More recent studies have provided important morphological information regarding the spinal morphology of Neandertals which has resulted in an interpretative shift regarding Neandertal posture 6 , 7 , 28 – 31 . Additionally, errors in the reconstruction of the K2 ribs have been documented 9 , 10 , which could have affected the previous reconstruction of this thorax.…”

A case of marked bilateral asymmetry in the sacral alae of the Neandertal specimen Regourdou 1 (Périgord, France)

“…The majority of those variables relate to the asymmetry of the alae length or the articular facets orientation. The other measurement is the anteroposterior diameter of the canal which is greater than in the modern sample, and which could also be related to the significantly larger anteroposterior dimension of the canal present in the fifth lumbar vertebra (L5) (Gómez‐Olivencia, Arlegi, Barash, Stock, & Been, ). Right ala length is significantly smaller than our modern human sample.…”