Transcript document

PHED 386
Biomechanics of the Spine
Today’s objectives…
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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
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Vertebral column
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Curved stack of 33 vertebrae
Movements: motion segments
Joints of the movement segment
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Symphysis: bodies & discs
Gliding (diarthroses): facet joints
Structure of the Spine
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Vertebrae
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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
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Intervertebral discs
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Composition
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Annulus fibrosus: collagen bands cross vertically at
30° to each other
Nucleus pulposus: 90% water + collagen &
proteoglycans
Function
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Bind vertebrae together
Allow for movement
Bear & distribute loads
Structure of the spine
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Mechanics of discs
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Flexion, extension & lateral flexion forces
Rotation forces
Structure of the spine
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Compression forces
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Water loss & sodium /potassium gain
Results in loss of ~2cm of height
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Within first 30 minutes
Increased volume  stiffness
Theory: risk of disc injury early in day
Disc nutrition
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Blood supply to age 8
Pumping action from
position change
Negative aspect of fixed
position
Affect of injury & aging
Discs and aging
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Reduced water absorption
Decreased shock absorbing
Abnormal movements between vertebrae
Loads assumed by other structures
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Reduced spinal column height
Postural alterations
Ligaments of the spine
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Anterior longitudinal ligament
Posterior longitudinal ligament
Supraspinous ligament (ligamentum nuchae)
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Short ligaments
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Interspinous
Intertransverse
Ligamentum flavum**
Spinal curves
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Primary
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Secondary
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Thoracic & sacral
Cervical & lumbar
Life changes
Postural & mechanical changes
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?? 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
Neck
Normal
Lower Back
Hypolordotic
Military
Kyphotic
S-Shaped
Movements of the spine
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Flexion, extension, hyperextension
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Greatest in cervical & lumbar regions
Lateral flexion & rotation
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Greatest in cervical
Least in lumbar
Muscles of the spine
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Complex arrangement
Naming
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Pairs
Unilaterally or bilaterally
Muscles of the spine
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Anterior (cervical region)
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Pre-vertebral muscles
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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
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Anterior
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Abdominals
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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
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Posterior
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Cervical
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Spenius capitus
Primary extensors
Splenius cervicis
Assisted by smaller/deeper mms
Thoracic & lumbar
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Errector spinae
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Sacrospinalis, semispinalis,
Spinalis, longissimus, iliocostalis
Deep spinal mms
Muscles of the spine
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Lateral
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Sternocleidomastoid (antagonistic)
Scalenes
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Lumbar region
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Quadratus lumborum
Psoas major
Loads on the spine
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Forces acting on
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Body weight
Tension in ligaments
Muscles tension
Intra-abdominal pressure
External loads
Axial loading
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Spinal compression
Loads on the spine
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Effect of center of gravity
Role of spinal extensor mms
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Effect of actual forward bending or arm position
Spinal mms have very small moment arms 
must generate large forces
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Increased compression forces on lumbar spine
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Loads on the spine
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Shear forces on spine
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On lumbar spine in standing position
Increases during flexion & hyperextension
Contributor to disc herniation
Loads on the spine
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Flexion relaxation phenomenon
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Tension in extensors increases w/flexion
At full flexion – extensor tension disappears
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Flexion torque supported by posterior spinal ligaments
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But increased shear from tension in interspinous ligaments
Also increased facet loading
Loads on the spine
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Lateral flexion and rotation
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Role of movement speed
Common injuries
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Low back pain
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75-80% of population
Second only to common cold
Most frequent/expensive of workman’s comp claims
More prevalent in males
Causes:
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Children – strains & sprains
Adults –
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Sitting for prolonged periods/unable to sit at all
Unnatural postures
Sudden unexpected motions
Weak abdominal muscles
Common injuries
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Soft tissue
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Contact or overload
Spasm response
Acute fractures:
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forceful contraction of mms
Contact: direct or indirect
Large compressive loads
Common injuries
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Stress fractures
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Spondylolysis
Spondylolisthesis
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From repeated axial loading while hyperextended
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Common injuries
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Disc herniations
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Bulging, slipped, ruptured
Protrusion of pulposus from
annulus
Common locations cervical &
lumbar