Loads On Spine

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loads on spine


  • The forces acting on the spine include body weight, the tension in the spinal ligaments, the tension in the surrounding muscles, intraabdominal pressure, and any applied external loads. That is called loads on the spine.
  • When the body is in an upright position than the major form of loading on the spine is axial.
  • In this position, body weight, the weight of any load held in the hands, and tension in the surrounding ligaments and muscles all contribute to spinal compression.
  • During erect standing, the total-body center of gravity is anterior to the spinal column, placing the spine under a constant forward-bending moment.
  • To maintain body position, this torque must be counteracted by tension in the back extensor muscles.
  • As the trunk or the arms are flexed, the increasing moment arms of these body segments contribute to increasing flexor torque and increasing compensatory tension in the back-extensor muscles.
  • Because the spinal muscles have extremely small moment arms with respect to the vertebral joints, they must generate large forces to counteract the torques produced about the spine by the weights of body segments and external loads.
  • the major force acting on the spine is usually from muscle activity.
  • During sitting, the pelvis rotates backward and the normal lumbar lordosis tends to flatten, resulting in increased loading on the intervertebral discs.
  • A slumped sitting posture increases disc loading even more.
  • Ergonomically designed chairs that provide lumbar support and enable slight forward tilting of the seat such that more weight is supported by the thighs have been shown to reduce the load on the spine.
  • Pressure within the intervertebral discs changes significantly with body position and loading but is relatively consistent through the different regions of the spine.
  • During static loading, the discs deform over time, transferring more of the load to the facet joints.
  • After 30 minutes of dynamic repetitive spinal flexion, such as might occur with a lifting task, the general stiffness of the spine is decreased.
  • and deformation of the discs in combination with elongation of the spinal ligaments results in altered loading patterns that may predispose the individual to low back pain
  • During erect standing, body weight also loads the spine in shear.
  • This is particularly true in the lumbar spine, where shear creates a tendency for vertebrae to displace anteriorly with respect to adjacent inferior vertebrae.
  • Tension in the trunk extensors increases with spinal flexion until the spine approaches full flexion when it abruptly disappears.
  • This has been shown to occur at 57% of maximum hip flexion and at 84% of maximum vertebral flexion.
  • At this point, the posterior spinal ligaments completely support the flexion torque.
  • The quiescence of the spinal extensors at full flexion is known as the flexion relaxation phenomenon.
  • Unfortunately, when the spine is in full flexion, the tension in the interspinous ligament contributes significantly to anterior shear force and increases facet joint loading.
  • During repeated trunk flexion and extension movements over time, the flexion relaxation period is lengthened, which reduces lumbar stability and may predispose the individual to low back pain.
  • Intraabdominal pressure is the pressure inside the abdominal cavity.it is believed that this pressure helps to stiffen the lumbar spine against buckling.
  • Researchers hypothesized that intraabdominal pressure works like a balloon inside the abdominal cavity to support the adjacent lumbar spine by creating a tensile force that partially offsets the compressive load.
  • the observation that intraabdominal pressure increases just prior to the lifting of a heavy load.
  • scientists discovered that pressure in the lumbar discs actually increases when intraabdominal pressure increases.
  • For More Update Visit Our Site YourTherapia.com
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