The Biomechanics of the Human Spine Chapter 9 The Biomechanics of the Human Spine Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D. © 2014 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill/Irwin

Basic Biomechanics, 7th edition Structure of the Spine The spine is a curved stack of 33 vertebrae structurally divided into five regions: Cervical region - 7 vertebrae Thoracic region - 12 vertebrae Lumbar region - 5 vertebrae Sacrum - 5 fused vertebrae Coccyx - 4 fused vertebrae Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Interspinous ligament Posterior longitudinal ligament Structure of the Spine Supraspinous ligament Intervertebral joint and facet Spinous process Ligamentum flavum Interspinous ligament Transverse process Anterior longitudinal ligament Cartilaginous end-plate Intervertebral disc Intervertebral foramen with nerve root Posterior Anterior Vertebral canal Posterior longitudinal ligament Vertebral body The motion segment, consisting of two adjacent vertebrae and the associated tissues, is considered to be the functional unit of the spine. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Structure of the Spine Superior views of typical vertebrae in the three regions of the spine. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition 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 Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Structure of the Spine Facet joints Posterior view of the spine Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition 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, sustaining up to 30% of the compressive load on the spine, particularly when the spine is in hyperextension Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Structure of the Spine Orientations of the facet joints with respect to the transverse plane (left) and frontal plane (right). Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Structure of the Spine The intervertebral discs are fibrocartilaginous structures that cushion the anterior spinal symphysis joints. The center region is the nucleus pulposus, a colloidal gel with a high fluid content. This is surrounded by the annulus fibrosus, a thick, fibrocartilaginous ring that forms the disk exterior. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Structure of the Spine Mechanically, the anulus fibrosus behaves as a coiled spring, holding the vertebral bodies together. The nucleus pulposus acts like a ball bearing that the vertebrae roll over during flexion/extension and lateral bending. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Structure of the Spine What are the primary spinal curves? The thoracic and sacral curves (concave anteriorly) are present at birth Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition 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 Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Structure of the Spine Vertical alignment Lordosis Kyphosis Scoliosis Lordosis - exaggerated lumbar curve Kyphosis - exaggerated thoracic curve Scoliosis - lateral spinal curvature Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Movements of the Spine What movements of the spine are allowed? The movement capabilities of the spine are those of a ball and socket joint, including movement in all three planes, and circumduction. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Movements of the Spine Extreme hyperextension of the lumbar spine. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Movements of the Spine The cervical spinal flexor muscles include rectus capitus anterior, rectus capitis lateralis, longus capitis, longus colli, and eight pairs of hyoid muscles. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Movements of the Spine The abdominal spinal flexor muscles include rectus abdominis, the internal obliques, and the external obliques. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Movements of the Spine The cervical spinal extensor muscles include splenius capitis and splenius cervicis, assisted by rectus capitis posterior major and minor, and obliquus capitis superior and inferior. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Movements of the Spine The thoracic and lumbar spinal extensors are erector spinae - (spinalis, longissimus, and iliocostalis), semispinalis - (capitis, cervicis, and thoracis), and the deep spinal muscles - (mulitifidi, rotatores, interspinales, intertransversarii, and levatores costarum). Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Movements of the Spine The cervical lateral flexor muscles include sternocleidomastoid, levator scapulae, and scalenus anterior, posterior, and medius. When developing tension unilaterally, the cervical flexors and extensors also contribute. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Movements of the Spine The lumbar lateral flexor muscles are the quadratus lumborum and psoas major. The lumbar flexors and extensors also contribute when developing tension unilaterally. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Loads on the Spine What forces commonly act on the spine? Body weight Tension in the spinal ligaments Tension in the spinal muscles Any external loads carried in the hands Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Loads on the Spine In normal standing position, body weight acts anterior to the spine, creating a forward bending load (moment) on the spine. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Loads on the Spine Fc Fs wt Because the spine is curved, body weight, acting vertically, has components of both compression (Fc) and shear (Fs) at most motion segments. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Compression reaction force Loads on the Spine Muscle tension Shear reaction force Compression reaction force Joint center During lifting, both compression and anterior shear act on the spine. Tension in the spinal ligaments and muscles contributes to compression. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Loads on the Spine Compression Tension Lumbar hyperextension can create a bending load (moment) in the posterior direction. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Loads on the Spine Hyperextension Lumbar hyperextension produces compressive loads at the facet joints. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Loads on the Spine Superior view Lateral view Spinal rotation generates shear stress in the intervertebral discs. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Loads on the Spine The load on the third lumbar disc during upright standing (100%) is markedly reduced in a supine position, but increases for each of the other positions shown. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Loads on the Spine It is advisable to maintain normal lumbar curvature rather than allowing the lumbar spine to flex when lifting. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.

Basic Biomechanics, 7th edition Loads on the Spine Annulus fibrosus Nucleus pulposus Spinal cord Spinal nerve Superior view of a herniated disc showing nuclear material pressing against the spinal cord. Basic Biomechanics, 7th edition By Susan J. Hall, Ph.D.