What a stranded whale with scoliosis can teach us about human idiopathic scoliosis

Abstract

Scoliosis is a deformation of the spine that may have several known causes, but humans are the only mammal known to develop scoliosis without any obvious underlying cause. This is called ‘idiopathic’ scoliosis and is the most common type. Recent observations showed that human scoliosis, regardless of its cause, has a relatively uniform three-dimensional anatomy. We hypothesize that scoliosis is a universal compensatory mechanism of the spine, independent of cause and/or species. We had the opportunity to study the rare occurrence of scoliosis in a whale (Balaenoptera acutorostrata) that stranded in July 2019 in the Netherlands. A multidisciplinary team of biologists, pathologists, veterinarians, taxidermists, radiologists and orthopaedic surgeons conducted necropsy and imaging analysis. Blunt traumatic injury to two vertebrae caused an acute lateral deviation of the spine, which had initiated the development of compensatory curves in regions of the spine without anatomical abnormalities. Three-dimensional analysis of these compensatory curves showed strong resemblance with different types of human scoliosis, amongst which idiopathic. This suggests that any decompensation of spinal equilibrium can lead to a rather uniform response. The unique biomechanics of the upright human spine, with significantly decreased rotational stability, may explain why only in humans this mechanism can be induced relatively easily, without an obvious cause, and is therefore still called ‘idiopathic’.

Ship Strike Risk for Fin Whales (Balaenoptera physalus) Off the Garraf coast, Northwest Mediterranean Sea

“…Injuries resulting from ship strikes vary in severity depending on the speed and size of the vessel involved in the incident (Laist et al, 2001;Panigada et al, 2006). They typically occur along the lateral and dorsal sides of whales and vary from lacerations caused by propellor movements, blunt force trauma causing broken bones and scarring to deformations and amputations of body parts (Laist et al, 2001;Panigada et al, 2006;de Reuver et al, 2021). Collisions occur most often over continental shelf waters (Laist et al, 2001).…”

Disc and Vertebral Body Morphology From Birth to Adulthood

“…This study's absolute measurements of spinal elements during growth, including the observations that spinal growth is present mostly in vertebral bodies and is more pronounced in males, and that there is a decrease of disc slenderness throughout growth, with overall more slender discs in females, is essential knowledge in understanding the importance of intervertebral disc morphology in the etiology and treatment of pediatric spinal deformity. For example, to interpret the earlier observations that the scoliotic deformity in adolescent idiopathic scoliosis is present mostly in the disc and is associated with more slender spines 9–15 . The present observation of more slender discs in females, especially visible during early adolescence, could play a role in the overrepresentation of females in adolescent idiopathic scoliosis 26 .…”

“…For example, to interpret the earlier observations that the scoliotic deformity in adolescent idiopathic scoliosis is present mostly in the disc and is associated with more slender spines. [9][10][11][12][13][14][15] The present observation of more slender discs in females, especially visible during early adolescence, could play a role in the overrepresentation of females in adolescent idiopathic scoliosis. 26 This is supported by earlier observations of a more slender spine in adolescent idiopathic scoliosis patients compared to asymptomatic controls.…”

“…8 Especially for adolescent idiopathic scoliosis, where most of the deformity was observed in the disc with the vertebral bodies largely retaining their original shape. [9][10][11][12] Stokes et al observed a difference in height growth of discs and bodies between adolescent idiopathic scoliosis patients and controls. 13 Moreover, a recent biplanar radiography study by Vergari et al and a CT-analysis by Chen et al showed the spine in adolescent idiopathic scoliosis patients to be more slender than the asymptomatic population.…”

“…Recent studies suggest the importance of intervertebral disc morphology, including height, width and slenderness (usually defined by a height-to-width ratio), as well as its attachment into the vertebral body, in the etiology of spinal deformity during pediatric growth 8 . Especially for adolescent idiopathic scoliosis, where most of the deformity was observed in the disc with the vertebral bodies largely retaining their original shape 9–12 . Stokes et al observed a difference in height growth of discs and bodies between adolescent idiopathic scoliosis patients and controls 13 .…”