PHED 386 Biomechanics of the Spine

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

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

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

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

Structure of the spine Mechanics of discs  Flexion, extension & lateral flexion forces  Rotation forces

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

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

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

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

Spinal curves Primary  Thoracic & sacral Secondary  Cervical & lumbar Life changes

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

Normal Hypolordotic Military Kyphotic S-Shaped Neck Lower Back

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

Muscles of the spine Complex arrangement Naming  Pairs  Unilaterally or bilaterally

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

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

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

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

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

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

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

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

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

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

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

Common injuries Stress fractures  Spondylolysis  Spondylolisthesis  From repeated axial loading while hyperextended

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