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Download Chapter 9 Vertebral Column Motion Segment Vertebral Joints Facet
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Vertebral Column Chapter 9 Biomechanics of the Human Spine • Curved stack of 33 vertebrate divided into 5 regions • • • • • Cerivcal Region – 7 Thoracic Region – 12 Lumbar Region – 5 Sacrum – 5 fused Coccyx – 4 fused Vertebral Joints Motion Segment • 2 adjacent vertebrae and the associated soft tissues • Functional unit of the spine • Anterior – intervertebral symphysis joints • Posterior – Gliding diarthrodial facet joints Facet Joint Functions Intervertebral Discs • Channel and limit ROM in the different regions of the spine • Assist in lad bearing, sustaining up to 30% of the compressive load on the spine • Fibrocartilaginous discs that cushion the anterior spinal symphysis joints • Composed of a nucleus pulposus surrounded by the annulus fibrosus – Especially in hyperextension 1 Spinal Curves Spinal Movements • All three planes • circumduction • Lordosis – Exaggerated lumbar curve • Kyphosis – Exaggerated thoracic curve • Scoliosis – Lateral spinal curvature Abdominal Flexors Cervical Flexors • Rectus capitus anterior • Rectus capitis lateralis • Rectus abdominis • Internal obliques • Longus capitis • Longus colli • External obliques • 8 pairs of hyoid muscles Thoracic/Lumbar Extensors Cervical Extension • Splenius capitis • Splenius cervicis • – Iliocostalis – Longissimus – Spinalis • Semispinalis – Capitis – Cervicis – Thoracis • Assisted by: – Rectus capitis posterior major/minor – Obliques capitis superior/inferior Erector Spinae • Deep Spinal Muscles – – – – – Multifidi Rotatores Interspinales Intertransversarii Levatores cotarum 2 Lateral Cervical Flexors • Sternocleidomastoid • Levator scapulae Lateral Lumbar Flexors • Quadratus Lumborum • Psoas Major • Scalenus – Anterior – Posterior – Medius • Lumbar Flexors/Extensors – unilaterally • Cervical flexors/extensors – Unilaterally Forces Acting on the Spine Anatomical Load • Body Weight • Ligament Tension • Muscle Tension • Body weight acts anterior to the spine – Causing forward bending (moment) • External loads Spinal Loading • Because the spine is curved, body weight, acting vertically, has components of both compression (FC) and shear (FS) at most motion segments. Lifting Loads • Compression • Anterior Shear 3 Lumbar Hyperextension Lumbar Hyperextension • Produces compressive forces on facet joints • Supporting up to 30% of force • Bending load (moment) in posterior direction • Anterior Tension • Posterior Compression Spinal Rotation • Generates shear stress in the intervertebral discs 4
