Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Biomechanics of the Human Spine
Transcript
The Biomechanics of the Human Spine Biomechanics and ergonomics-Chapter 9 Structure of the Spine 33 vertebrae structurally divided into five regions: cervical region - 7 vertebrae thoracic region -12 lumbar region - 5 sacrum - 5 fused coccyx - 4 fused Structure of the Spine The motion segment, consisting of two adjacent vertebrae and the associated tissues, is considered to be the functional unit of the spine. Structure of the Spine Verterbral bodies act as primary weight bearing components of spine The spinous and transverse processes improve the mechanical advantage of attached muscles. Atlantooccipital joint is extremely stable (14-15ᵒ flexion/extension) Atlantoaxial joint permits 75ᵒ rotation,14ᵒ extension and 24ᵒ lateral flexion Orientation of facets Structure of the Spine Progressive increase in vertebral size from cervical through lumbar region. Increased surface area of lumbar spine reduces the stress Contact forces are largest at L5-S1 Structure of the Spine What types of joints connect adjacent vertebrae? Intervertebral symphysis joints on the anterior side Two gliding diarthrodial facet joints on the posterior side Structure of the Spine What is the function of the facet joints? • To channel and limit the range of motion in the different regions of the spine • To assist in load bearing, particularly when the spine is in hyperextension and disc degeneration has occurred Structure of the Spine Facet joints and discs provide about 80% of spine’s ability to resist rotational torsion and shear with half contribution from facet joints. Intervertebral disc Intervertebral discs consists of: Nucleus pulposus a colloidal gel Annulus fibrosus, a thick, fibrocartilaginous ring that forms the disk exterior. Annulus is more sensitive to rotational stresses. Nucleus is 90% water High fluid content makes nucleus resistant to compression Intervertebral disc Intervertebral disc Mechanically, annulus behaves as a coiled spring , holding vertebral bodies together, whereas nucleus puposus acts as incompressible ball bearing that the vertebra roll over during flexion/extension and lateral flexion Intervertebral disc IVD contributes to 1/4th of spinal height When disc is loaded in compression it loses water and absorbs ions. Over the coarse of a day spine loses its height up to 2cm. 54% of this loss occurs in first 30 minutes after getting up in the morning. Disc height and volume are greatest when a person wakes up in the morning Point to ponder Astronauts experience a temporary increase in height of 5cm.why? Because of no compression on disc due to earth’s gravity. Intervertebral disc Spinal flexion, extension and lateral flexion cause compression on one side and tension on the other side of disc. Rotations create shear stress Intervertebral disc Disc has blood supply up to the age of 8 years. Relies on mechanically based means for maintaining a healthy nutritional status. Changes in posture alter disc pressure causing a pumping action. Think Why is it important not to maintain anyone body position for too long? Ligaments of the Spine Anterior longitudinal ligament Posterior longitudinal ligament Supraspinous ligament (ligamentum nuchae in neck) Interspinous Intertransverse Ligamntum flavum Ligaments of spine Enlarged cervical portion of supraspinous ligament is called ligamentum nuchae or ligament of neck. Importance of ligamentum flavum Contains high proportion of elastic fibers which lengthen during spinal flexion and shorten during extension. Ligamentum flavum is in tension even when spine is in anatomical position, enhancing stability. This creates constant compression in the discs called prestress Structure of the Spine What are the primary spinal curves? Thoracic and sacral curves Concave anteriorly Are present at birth Structure of the Spine What are the secondary spinal curves? The lumbar and cervical curves Concave posteriorly Develop from supporting the body in an upright position after young children begin to sit and stand Structure of the Spine Summary Vertebras Facet joints Intervertebral disc biomechanics Ligaments of spine Curves of spine
