Cervical Vertebrae Anatomy Quiz

Spine Biomechanics

• Subject: Spine Biomechanics
• Instructor: Dr. Öğr. Üyesi Berrak Varhan
• Email: [email protected]
• Department: Physiotherapy and Rehabilitation

Contents

• Features of the spine
• Biomechanics and pathomechanics of the cervical spine
• Biomechanics and pathomechanics of the thoracic spine
• Biomechanics and pathomechanics of the lumbar spine

Structures of the Spine

• Support base: Connects lower and upper extremities
• Protection of the spinal cord
• Stability
• Mobility

Regions of the Vertebra

• Cervical
• Thoracic
• Lumbar
• Sacral
• Coccygeal
• 33 bones, 23 discs

Curvatures Visible from Lateral

• C-shaped curvatures at birth
• 4 different curves in adulthood
• Lordotic curves: Cervical, lumbar
• Kyphotic curves: Thoracic, sacral
• Semi kyphotic curves: Pelvic

Spinal Curvatures

• 4 curves in the sagittal plane
• Cervical curve: Extends from C1 to T2, lordotic
• Thoracic curve: Extends from T2 to T12, kyphotic
• Lumbar curve: Extends from T12 to lumbosacral joint, lordotic
• Pelvic curve (lumbosacral joint to coccyx), semi kyphotic

Spinal Movement

• Combination of intervertebral discs and facet joints

Intrinsic Balance

• Separating back column from front reduces height by 14%
• Due to tension in ligaments (supraspinous, interspinous, Lig. Flavum)
• Tension decreases when posterior column is separated from anterior
• Ligaments ensure tight connection of vertebrae and maintain spinal continuity
• All intersegmental and intrasegmental ligaments under tension in normal spine

Intervertebral Discs

• 20-30% of interarticular height
• Cervical region: 3 mm thick
• Thoracic region: 5 mm thick
• Lumbar region: 9 mm thick

Structure of the Disk

• Nucleus pulposus (NP): Located in center (posteriorly in lumbar)
• Gelatinous mass: Rich in proteoglycan (PG) and glycoaminoglucose (GAG) molecules
• Hydration decreases with load increase
• 80-90% of structure is water; decreases with age

Annulus Fibrosus

• Thick in anterior
• Innervated from synovertebral nerve (1/3 outer section)
• Connected to Sharpey fibers of vertebra (1/3 outer section)
• Connected to endplate (2/3 outer section)

Disc Pathologies—Herniation

• C5–6, C6–7,L4–5,L5–S1 most common locations
• Disc herniation
• Disc protrusion/bulging
• Annulus
• Laterally localized
• Diffusion in posterior
• Extrusion-migration (imaging shown)

Longitudinal Ligaments

• Supraspinous
• Anterior longitudinal
• Posterior longitudinal
• Ligamentum flavum (elastic)

Facet Joint

• Between superior (concave) and inferior (convex) faces
• Transfers and movement in frontal plane

Facet Joint Capsule

• Limited movements; strong in thoracolumbar and cervicothoracic regions (especially at spinal changes)

Intervertebral Foramina

• Nerve outlet width depends on disc height, pedicle shape, osteophytes, ligament hypertrophy, disc height decrease with age; leads to lateral stenosis
• Decreases by 20% in extension, increases by 24% in flexion

Spinal Stability

• Vertebral column reacts to forces from different directions simultaneously
• Instability increases with degeneration
• Restructuring via fibrous tissue and/or osteophyte changes

Segmental Loads

• Axial compression
• Bending
• Torsion
• Shear

Axial Compression

• Result of reactions of ligaments to gravity, ground reaction forces, muscle contraction tensile forces
• Interdisk loads range from 294 N to 3332 N (1kg = 9.81 N)
• Anterior segment lifts more load, overflows more frequent posteriorly

Axial Compression (cont.)

• Compression in disc causes annulus tension, angular fiber changes, increased stability
• Disc wear increases with increased strength and aging

Bending

• Combination of compression, shear, and tension forces during movement
• During bending flexion, posterior annulus resists
• Anterior compressive forces on posterior longitudinal ligament, capsule, and anterior segments cause disc displacement (protrusion)
• Extension: Tension load on joint and anterior ligament by posterior compressive forces to anterior segment

Torsion

• Axial rotation and several movements
• Stiffness may occur due to joint compression; flexion increases torsional hardness in L3-4

Shear

• Force exerted by opposing forces on same point
• Complex movements increase disc load; injury if wear present

Flexion

• Superior vertebrae tilt anteriorly, move forward (anterior gliding)
• Intervertebral foramina expand
• Nucleus pulposus shifts posteriorly
• Compression force formed in anterior; tension force on posterior annulus, flavum, capsule, and posterior longitudinal ligament

Extension

• Superior vertebrae tilt and shift posteriorly
• Intervertebral foramina narrows
• Nucleus pulposus moves anteriorly

Lateral Flexion-Rotation

• Superior vertebrae displaced inferiorly
• Concavity in movement direction becomes convexity in opposite direction
• Tension force on convex side, compression force on concave side

Cervical Spine

• Stable column of 7 vertebrae between head and thorax; allows flexion, extension, and rotation
• C1 and C2 have unique structural differences from others
• C7 is a transitional vertebra between cervical and thoracic region

Cervical Spine (cont.)

• Cervical vertebrae distinguished by foramen transversarium in transverse processes; vertebral artery, venous plexus, and sympathetic plexus pass through
• Spinous process is short except for C7

Cervical Spine: Atlas

• First cervical vertebra ("Atlas")
• No vertebral corpus, spinous process
• Lateral masses carry weight
• Upper articular facets with occipital condyles; lower facets with axis

Cervical Spine: Axis

• Second cervical vertebra ("Axis")
• Dens (odontoid process) protrusion; shows other cervical vertebra features

Cervical Spine: C7

• Vertebral prominens (C7)
• Longest spinous process; thick, horizontally extends
• Ligamentum nuchae and deep/superficial back muscles attached

Cervical Spine: Joints

• Atlantooccipital joint: Between atlas mass lateralis and occipital bone condyles
• Atlantoaxial joint: Lateral (planar) and medial (pivot) types:
  • Lateral: Atlas and axis objects
  • Medial: Atlas archus anterior and axis dens

Muscles of the Cervical Region

• Hypersensive; react to motor system
• Important roles in controlling and stabilizing spine
• Biomechanical abnormalities in any region can cause secondary dysfunction anywhere in the spine

Cervical Spine: Functions

• Create or accelerate movement (concentric contractions)
• Slow down or stabilize movement (isometric/eccentric contractions)
• Apply force to structures absorbing/transferring force (intervertebral discs, articular cartilage)
• Provide shock-absorbing properties
• Provide afferent proprioceptive feedback for muscle coordination & regulation

Posterior Neck Muscles

• Superficial group: Trapezius, levator scapulae muscles
• Middle group: Splenius capitis, splenius cervicis muscles
• Deep group: Erector spinae muscles

Anterolateral Region Muscles

• Platysma
• Sternocleidomastoid
• Hyoid muscles
• Scalene muscles
• Longus colli and longus capitis muscles

Cervical Region Muscles (cont.)

• Majority of posterior muscles provide head/neck extension
• Anterolateral cervical neck muscles provide head/neck flexion, lateral flexion, and rotation
• Posterior cervical muscle contractions increase normal cervical lordosis; anterior deep cervical muscles (esp. middle cervical segment) provide postural and segmental control via hardening/stabilizing
• Deep cervical muscles show lower, continuous tonic activity beside posture support; superficial neck muscles (e.g., SCM) have torque formation function
• Neck muscles contain higher proportion of afferent fibrils; makes them more sensitive
• Emotional system disorders can affect neck muscles (e.g., anxiety causes muscle spasms)

Vertebral Biomechanics

• Spine is flexible but stable column
• 4 natural curvatures in sagittal plane (lordosis and kyphosis)
• Axial loads are affected differently due to curvatures
• Burst fractures and compression fractures (due to anatomy/geometry)

Cervical Spine Summary

• 3 principal functions: Support and stability of the head, facilitates head mobility in facet joints, provides sheltered/protected passage for the vertebral artery and spinal cord
• Passive components: Facet joints, discs, ligaments, and bones; active: Muscles
• Rotational abnormalities at multiple levels affect range of motion, neutral zone, patterns of connectedness, and axis of sudden rotation

Spine Movements

• Vertebrae perform flexion, extension, lateral flexion, and rotation
• Intervertebral ligaments compress in front during flexion; joint surfaces slide apart; upper vertebrae slide forward and upward
• Flexion: anterior longitudinal ligament relaxes, posterior components (longitudinal ligament, flavum, interspinous/supraspinous ligaments) stretch

Spine Movements (cont.)

• Limited extension: disc compression in back, articular processes slide back and down, limiting lamina and spinous protrusions
• Lateral flexion usually accompanied by rotation; facet joint slides on convex side, overlaps on concave side
• Anterior longitudinal ligament is stretched during lateral flexion

Cervical Stability

• Anterior longitudinal ligament, annulus fibrosus, posterior longitudinal ligament, apophyseal anular ligament, ligamentum flavum, inter and intra supraspinous ligaments, transverse ligament are key
• Anterior vertebral column is static, carrying weight
• Intervertebral discs alleviate shocks; posterior column structures are dynamic, directing & maintaining movement
• Cervical stability achieved through combination of front group and rear group elements

Thoracic Region Kinesiology

• Costa connection place, minimal movement, load carrying
• T1 is similar to C7 in vertebral body but discs are largest
• Low flexibility due to costa articulations, disc size, and spinous processes
• Facet joints are more sagittal (T9-12)

Thoracic Ligaments

• Ligamentum flavum
• Facet capsulary ligament
• Interspinous ligament

Thoracic Movements

• Flexion (30-40°): posterior components limited by tension
• Extension (20-25°): limited by bone structures/anterior longitudinal ligament tension with abdominals
• Rotation (30°): restricted by costae
• Lateral flexion (25°): facet joint and ribs limit movement

Lumbar Region Kinesiology

• Most load-bearing part of skeletal system
• Movements in sagittal plane
• Largest corpus, disc, and laminates
• Pedicles are short and thin; load bearing

Weight Transfer

• L3 disc in 70 kg person is loaded with ~70 kg while standing upright
• Body part above L3 is half body's size; weight is twice this amount
• Bending forward increases load by 2x, ground lifting increases this 2x

Sitting and Standing

• Unsupported sitting causes most strain on waist (pelvis tilted backward, body somewhat forward)
• Gravity line passes ahead of movement center; distance increases axial moment and load
• Upright sitting posture: slightly increased lumbar curve, decreased waist load

Sitting and Standing (cont.)

• Loose standing position: Normal lumbar lordosis—less distance between gravity line and movement center; less load on waist

Supported Sitting Posture

• Least waist load
• Upper body weight supported by backrest
• Backward angle of backrest reduces load further

Supine Position

• Increased waist load in straight leg position
• Flexion with hip/knee support: decreased waist load

Prone Position

• High stress on lumbar region
• Pillow under abdomen reduces waist stress

Pathomechanics of the Cervical Region

• Ligament injury and bone damage after trauma—major cervical instability causes
• Ligament effectiveness depends on strength and moment arm length

Cervical Instability

• Ligament injury is serious; mild damages heal, but tears don't; healing/fusion process in bone damage determined by extreme arrival and immobility of fragments

Cervical Flattening

• Paravertebral muscle spasm—main contributing factor
• Likely result of disc herniation, emotional tension, trauma, infection, incorrect positioning (e.g., computer use)

Scheuermann's Juvenile Kyphosis

• Growth age disease (↑ dorsal kyphosis, ↑ lumbar lordosis)
• ↑ age 11-12, X-ray findings apparent
• Clinical signs ages 13-17

Scheuermann's Juvenile Kyphosis (cont.)

• Postural defect initially correctable, but kyphosis often fixes after 6–9 months
• Anterior wedging of vertebrae, and posterior disproportionate growth occurs
• Wedged areas ↑ static stress, inhibits growth plate

Scheuermann's Juvenile Kyphosis (cont.)

• Posterior intermittent stress leads to faster back growth; rapidly developing cases with cord lesions, often accompanied by scoliosis
• Kyphoscoliosis in 30-40% of cases

Transverse Process Syndrome

• More common in men
• Unilateral vs. bilateral transverse protrusions of L5
• Unilateral: Lateral flexion increases towards protruding side, iliolumbar ligament stretched—pain appears
• Bilateral: Lateral flexion in both directions restricted; compression by iliolumbar ligament

Tropism

• Sagittal plane change of L5-S1
• L5-S1 articular facets in frontal plane; lumbar facets are in sagittal plane
• Unilateral or bilateral facet redirection called tropism; 1 side directed to normal plane, other to right

Sacralization

• Lumbar vertebra fuses with sacral vertebrae
• Complete block with L5 crista, fusion; single or double sided
• L5-S1 movement eliminated; movement shifts to L4-L5—early degeneration

Sacralization (cont.)

• If not complete block, structure present, lateral movements not completely restricted; compression stress on flexed side; tension on opposite side; degeneration in joints

Lumbarization

• S1 has L5 characteristics (long waist back)
• Symptoms limited to facet and disc degeneration from increased mobility

Spondylolysis

• Separation of intervertebral joint elements
• ↓ intradiscal pressure; disc narrows
• Reduced pressure leads to ↓ intervertebral foramina Size
• Annulus elastic fibers transform into fibrous tissue

Lomber Spondylosis

• Degenerative changes in intervertebral discs, corpus, intervertebral foramen, facet joints, lamina, and ligaments

Spondylolisthesis

• Vertebrae slide forward or backward over each other
• Shift 5% back, 95% forward
• Three main causes:
  • Facet defects (congenital or later)
  • Peduncle/neural arch defects (congenital or later)
  • Structural insufficiency of bone (lumbal vertebrae most affected)

Spondylolisthesis (cont.)

• 4th lumbar vertebra and 3rd lumbar most affected, but multiple vertebrae often affected; L4-L5 segments
• Also observed in cervical region, but defects are in pedicle

Congenital Muscular Torticollis

• Unilateral contracture of SCM muscle
• Asymmetrical head/neck deformity
• Head tilted toward shortened muscle; jaw rotates opposite side

Oxipitalization

• Congenital absence of atlantooccipital joint
• Limited head movement

Clipper-Feil Syndrome

• Fusion of anterior and posterior elements of two or more cervical vertebrae
• Called block vertebrae
• Intervertebral discs disappear
• Spinous protrusions merge into single block

Clipper—Feil Syndrome (cont.)

• 3 main symptoms:
  • Short neck
  • Scalp below its normal location
  • Restricted neck movements

Mechanical Low Back Pain

• Change in lumbosacral angle (long axis lumbar vertebrae to sacral vertebra, 135°)
• Elevation above 135°: ↓ lumbar lordosis, ↑ compression, pain
• Dropping below 135°: ↑ lordosis, ↑ stress on disc, fragmentation, degeneration/arthritis

Sacral Angle

• 30° angle between S1 upper surface & horizontal plane
• ↓ angle: ↓lordosis, ↑ angle: ↑lordosis

Cause of Pain

• Mechanical straining of ligaments, muscles, facet joint capsules, periosteum of vertebral bodies, spinal cord membranes, pain-sensitive parts (e.g., stretching, pressure) in blood vessels

Lumbal Disc Lesions

• Clinical picture when one or more disc components in intervertebral space are displaced posteriorly/anteriorly, compressing nerve points; called disc hernia
• Pain severity depends on location, amount, and pressure effect
• Lateral/posterolateral herniations = unilateral sciatica
• Bilateral sciatica is rarer, from central or bilateral herniation

Lumbal Disc Lesions (cont.)

• Pain appearance depends on disc tear type
• Annulus fibrosis fiber tears typically first occur—↑ with rotational movements
• Tears start from disc center; radial tears occur—no innervation/blood vessels, slow repair
• Nucleus mobile = herniation, degenerative changes; instability phase; nucleus enters multiple annular tears

Lumbal Disc Lesions (cont.)

• Annular tears (protrusion, extrusion, sequestrated disc)
• Protrusion: Localized bulging; no problems with posterior longitudinal ligament
• Extrusion: Complete rupture, exit into canal, posterior longitudinal ligament ruptured
• Sequestration: Herniated material breaks off, remains free in epidural area (posterior longitudinal ligament is ruptured)