Download document

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


Secondary


Thoracic & sacral
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
Neck
Normal
Lower Back
Hypolordotic
Military
Kyphotic
S-Shaped
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
Primary extensors
Splenius cervicis
Assisted by smaller/deeper mms
Thoracic & lumbar

Errector spinae



Sacrospinalis, semispinalis,
Spinalis, longissimus, iliocostalis
Deep spinal mms
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