Comparative and functional anatomy of the mammalian lumbar spine

Abstract

As an essential organ of both weight bearing and locomotion, the spine is subject to the conflict of providing maximal stability while maintaining crucial mobility, in addition to maintaining the integrity of the neural structures. Comparative morphological adaptation of the lumbar spine of mammals, especially in respect to locomotion, has however received only limited scientific attention. Specialised features of the human lumbar spine, have therefore not been adequately highlighted through comparative anatomy. Mathematical averages were determined of 14 measurements taken on each lumbar vertebrae of ten mammalian species (human, chimpanzee, orang-utan, kangaroo, dolphin, seal, Przewalski's horse, cheetah, lama, ibex). The revealed traits are analysed with respect to the differing spinal loading patterns. All examined mammalian lumbar spines suggest an exact accommodation to specific biomechanical demands. The lumbar spine has reacted to flexion in a predominant plane with narrowing of the vertebral bodies in quadrupeds. Torsion of the lumbar spine is withstood by an increase in the transverse distance between the inferior articular processes in the upper lumbar spine in primates, but lower lumbar spine in humans, quadrupeds and the seal. Sagittal zygapophyseal joint areas resist torsion in the seal and humans. Ventral shear is resisted by frontal zygapophyseal joint areas in humans and primates, and dorsal shear by encompassing joints in the ibex. The human fifth lumbar vertebra is remarkable in possessing the largest endplate surface area and the widest distance between the inferior articular processes, as an indicator of the high degree of axial load and torsion in bipedalism. Anat Key words: lumbar spine; zygapophyseal joints; comparative anatomy; mammalian; human; locomotion; bipedalism; gaitDue to the high incidence of spinal disorders, the human lumbar spine has maintained the stigma of being inadequately adapted to upright posture and locomotion. The converse point of view (Putz and Mü ller-Gerbl, 1996), however, suggests an exact accommodation of the spine of each mammalian species, including humans, to the specific biomechanical demands of the course of evolution, maintaining maximal stability while granting ideal mobility and securing the protection of neural structures. To date, the published literature on comparative lumbar vertebral anatomy has focused either on singular morphological aspects or selectively upon a mammalian subgroup

Sagittal endplate morphology of the lower lumbar spine

“…The vertebral endplates of the lower human lumbar spine are remarkable in possessing the largest known endplate surface area in relation to body size amongst terrestrial mammals [1]. While surgical procedures replacing the intervertebral disc (total disc replacement-TDR) and fusing the intervertebral space (anterior lumbar interbody fusion-ALIF) have become routine techniques, the endplate designs of these devices are significantly simplified in contrast to the morphological variability and biomechanical demand in vivo.…”

Fast running restricts evolutionary change of the vertebral column in mammals

“…The spine of these species is flexible dorsoventrally and laterally, the rigid ribcase is rather short and narrow, and the lumbar spine is relatively long and slender (11)(12)(13). The mobility of the trunk is largest at the lumbosacral transition (10)(11)(12)14). The laterally projecting transverse processes are slender and point forward, clearly separated from the sacrum and ilium (Fig.…”

“…1B), which hamper the flexibility of the lumbosacral joint and may decrease strength of this portion of the vertebral column. Flexibility of this joint is crucial for speed and agility in running, swerving, and jumping (10)(11)(12). Hence, transitional lumbosacral vertebrae are expected to impair the performance and survival of fast and agile mammals (10)(11)(12).…”

“…Flexibility of this joint is crucial for speed and agility in running, swerving, and jumping (10)(11)(12). Hence, transitional lumbosacral vertebrae are expected to impair the performance and survival of fast and agile mammals (10)(11)(12). Conversely, we expect the abnormal fusions to affect performance in slow and sturdy species only marginally.…”

Important macroscopic and microscopic differences in the bony and cartilaginous regions adjacent to the lumbar intervertebral disc between animal and man: a caveat to overinterpretation of animal experiments

“…Only adult primates, including Vervet [6] and Rhesus monkeys, overcome these limitations by showing a similar ossification pattern, and only larger primates such as baboons [7] additionally have comparable sizes of the FSUs like humans. At least simultaneously choosing further animals for experiments concerning the FSU, already including sheep [10,11], dog, or, for their more bipedal characteristics even more exotic like kangaroo [1,2], detailed information about these possible differences needs to be gathered and made public. …”