Functional morphology and three-dimensional kinematics of the thoraco-lumbar region of the spine of the two-toed sloth

J Exp Biol. 2010 Dec 15;213(Pt 24):4278-90. doi: 10.1242/jeb.047647.

Abstract

Given the importance of thoraco-lumbar spine movements in the locomotion of mammals, it is surprising that in vivo three-dimensional (3-D) data on the intervertebral movement of the mammalian thoraco-lumbar vertebral column during symmetrical gaits is limited to horses and dogs. To test whether kinematic patterns similar to those published for these cursorial species are also present during a contrasting mode of quadrupedalism, we quantified thoraco-lumbar intervertebral movements, the resulting pelvic displacements and relative femoral movements during the trot-like steady-state suspensory quadrupedal locomotion of the two-toed sloth (Xenarthra, Choloepus didactylus). Scientific rotoscoping, a new, non-invasive approach that combines synchronous biplanar high speed X-ray videos and the reconstruction of skeletal elements from computed tomography bone scans, was used to quantify 3-D kinematics. An analysis of vertebral anatomy and epaxial muscle topography suggests that the thoraco-lumbar spine of sloths is well suited to producing lateral bending and long-axis rotation, but limits powerful sagittal extension. Sloths exhibit complex 3-D movements in the thoraco-lumbar spine that are comparable to those observed in other arboreal quadrupedal mammals. Monophasic lateral bending and long-axis rotation, biphasic sagittal bending and maximal amplitude of sagittal bending at the lumbo-sacral joint were also found in other quadruped mammals and may represent general aspects of mammalian symmetric gaits. Maximal amplitude of lateral bending and long-axis rotation vary in regard to the vertebral level. It is suggested that a cranio-caudal pattern of angular deflections of the spine results from the out-of-phase movement of diagonal forelimbs and hindlimbs in other walking gaits, because it is not evident in the trot-like locomotion analyzed here. The analysis also illustrates the difficulties that arise when lumbar movement is deduced from intervertebral joint morphology alone.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biomechanical Phenomena
  • Femur / anatomy & histology
  • Femur / diagnostic imaging
  • Femur / physiology
  • Hindlimb / anatomy & histology
  • Hindlimb / diagnostic imaging
  • Hindlimb / physiology
  • Imaging, Three-Dimensional
  • Locomotion / physiology*
  • Lumbar Vertebrae / anatomy & histology
  • Lumbar Vertebrae / diagnostic imaging
  • Lumbar Vertebrae / physiology*
  • Pelvis / anatomy & histology
  • Pelvis / diagnostic imaging
  • Pelvis / physiology
  • Radiography
  • Sloths / anatomy & histology
  • Sloths / physiology*
  • Thoracic Vertebrae / anatomy & histology
  • Thoracic Vertebrae / diagnostic imaging
  • Thoracic Vertebrae / physiology*