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PHED 386

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  1. PHED 386 Biomechanics of the Spine

  2. Today’s objectives… • Analyze structure vs. function of the spine • Identify factors influencing mobility & stability of regions of the spine • Identify the relationship between muscle location & its effectiveness on the trunk • List mechanical contributions to common injury

  3. Structure of the spine • Vertebral column • Curved stack of 33 vertebrae • Movements: motion segments • Joints of the movement segment • Symphysis: bodies & discs • Gliding (diarthroses): facet joints

  4. Structure of the Spine • Vertebrae • Body, neural ring, processes • Processes provide MA for mms • Body size-function relationship • Spines & facet joint relationship • Facet joints assist in loading • Facet joint compression

  5. Structure of the spine • Intervertebral discs • Composition • Annulus fibrosus: collagen bands cross vertically at 30° to each other • Nucleus pulposus: 90% water + collagen & proteoglycans • Function • Bind vertebrae together • Allow for movement • Bear & distribute loads

  6. Structure of the spine • Mechanics of discs • Flexion, extension & lateral flexion forces • Rotation forces

  7. Structure of the spine • Compression forces • Water loss & sodium /potassium gain • Results in loss of ~2cm of height • Within first 30 minutes • Increased volume  stiffness • Theory: risk of disc injury early in day

  8. Disc nutrition • Blood supply to age 8 • Pumping action from position change • Negative aspect of fixed position • Affect of injury & aging

  9. Discs and aging • Reduced water absorption • Decreased shock absorbing • Abnormal movements between vertebrae • Loads assumed by other structures • Reduced spinal column height • Postural alterations

  10. Ligaments of the spine • Anterior longitudinal ligament • Posterior longitudinal ligament • Supraspinous ligament (ligamentum nuchae) • Short ligaments • Interspinous • Intertransverse • Ligamentum flavum**

  11. Spinal curves • Primary • Thoracic & sacral • Secondary • Cervical & lumbar • Life changes

  12. Postural & mechanical changes • ?? Wolff’s law • Lordosis • Associated w/weak abdominal mm’s & anterior tilt • Causes • Kyphosis • Cause (Scheuermann’s disease) • Population/s • Scoliosis • Lateral/rotational deformity • Causes

  13. Neck Normal Hypolordotic Military Kyphotic S-Shaped Lower Back

  14. Movements of the spine • Flexion, extension, hyperextension • Greatest in cervical & lumbar regions • Lateral flexion & rotation • Greatest in cervical • Least in lumbar

  15. Muscles of the spine • Complex arrangement • Naming • Pairs • Unilaterally or bilaterally

  16. Muscles of the spine • Anterior (cervical region) • Pre-vertebral muscles • Rectus capitus anterior & lateralis • Longus capitus • Longus colli • Hyoid muscles – 8 pairs • Bilateral tension: flexion of the head • Unilateral: lateral flexion or rotation

  17. Muscles of the spine • Anterior • Abdominals • Rectus abdominus • External obliques • Internal obliques • Bilateral tension: flex spine, reduce anterior tilt • Unilateral tension: lateral flexion, rotaion • Abdominal wall function

  18. Muscles of the spine • Posterior • Cervical • Spenius capitus • Splenius cervicis • Assisted by smaller/deeper mms • Thoracic & lumbar • Errector spinae • Sacrospinalis, semispinalis, • Spinalis, longissimus, iliocostalis • Deep spinal mms Primary extensors

  19. Muscles of the spine • Lateral • Sternocleidomastoid (antagonistic) • Scalenes • Lumbar region • Quadratus lumborum • Psoas major

  20. Loads on the spine • Forces acting on • Body weight • Tension in ligaments • Muscles tension • Intra-abdominal pressure • External loads • Axial loading • Spinal compression

  21. Loads on the spine • Effect of center of gravity • Role of spinal extensor mms • Effect of actual forward bending or arm position • Spinal mms have very small moment arms  must generate large forces • Increased compression forces on lumbar spine

  22. Loads on the spine • Shear forces on spine • On lumbar spine in standing position • Increases during flexion & hyperextension • Contributor to disc herniation

  23. Loads on the spine • Flexion relaxation phenomenon • Tension in extensors increases w/flexion • At full flexion – extensor tension disappears • Flexion torque supported by posterior spinal ligaments • But increased shear from tension in interspinous ligaments • Also increased facet loading

  24. Loads on the spine • Lateral flexion and rotation • Role of movement speed

  25. Common injuries • Low back pain • 75-80% of population • Second only to common cold • Most frequent/expensive of workman’s comp claims • More prevalent in males • Causes: • Children – strains & sprains • Adults – • Sitting for prolonged periods/unable to sit at all • Unnatural postures • Sudden unexpected motions • Weak abdominal muscles

  26. Common injuries • Soft tissue • Contact or overload • Spasm response • Acute fractures: • forceful contraction of mms • Contact: direct or indirect • Large compressive loads

  27. Common injuries • Stress fractures • Spondylolysis • Spondylolisthesis • From repeated axial loading while hyperextended

  28. Common injuries • Disc herniations • Bulging, slipped, ruptured • Protrusion of pulposus from annulus • Common locations cervical & lumbar