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Questions and Answers
What distinguishes cervical vertebrae from thoracic and lumbar vertebrae?
What distinguishes cervical vertebrae from thoracic and lumbar vertebrae?
What is the function of the dens on the second cervical vertebra?
What is the function of the dens on the second cervical vertebra?
Which cervical vertebra is referred to as the vertebral prominens?
Which cervical vertebra is referred to as the vertebral prominens?
What is the primary role of the ligaments in the spinal column?
What is the primary role of the ligaments in the spinal column?
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What is the characteristic feature of the first cervical vertebra, or Atlas?
What is the characteristic feature of the first cervical vertebra, or Atlas?
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What is the average range of motion for flexion and extension in the atlanto-occipital joint?
What is the average range of motion for flexion and extension in the atlanto-occipital joint?
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Which cervical segment exhibits the largest flexion-extension movement?
Which cervical segment exhibits the largest flexion-extension movement?
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Which ligaments are affected during flexion of the cervical spine?
Which ligaments are affected during flexion of the cervical spine?
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What percentage of the cervical spine's axial rotation occurs between C1-C2?
What percentage of the cervical spine's axial rotation occurs between C1-C2?
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What happens to the disc during limited extension of the cervical spine?
What happens to the disc during limited extension of the cervical spine?
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What primary movement occurs at the atlantoaxial complex?
What primary movement occurs at the atlantoaxial complex?
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Which statement is true regarding lateral flexion of the cervical spine?
Which statement is true regarding lateral flexion of the cervical spine?
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Which ligament is considered the most basic element for cervical stability?
Which ligament is considered the most basic element for cervical stability?
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What is the primary function of the anterior vertebral column?
What is the primary function of the anterior vertebral column?
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Which statement best describes the thoracic spine in relation to movement?
Which statement best describes the thoracic spine in relation to movement?
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What limits thoracic spine extension?
What limits thoracic spine extension?
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Which region of the spine is known to carry the most load?
Which region of the spine is known to carry the most load?
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What is the range of motion for lateral flexion in the thoracic spine?
What is the range of motion for lateral flexion in the thoracic spine?
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Which structure is associated with providing continuity of movement in the spinal column?
Which structure is associated with providing continuity of movement in the spinal column?
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How much weight is the L3 disc of a person weighing 70 kg loaded with when standing upright?
How much weight is the L3 disc of a person weighing 70 kg loaded with when standing upright?
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What is the primary factor that restricts rotation in the thoracic spine?
What is the primary factor that restricts rotation in the thoracic spine?
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Which sitting position exerts the most strain on the waist?
Which sitting position exerts the most strain on the waist?
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What effect does lumbar support have on the supported sitting posture?
What effect does lumbar support have on the supported sitting posture?
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What happens to the load on the waist when the legs are straightened in the supine position?
What happens to the load on the waist when the legs are straightened in the supine position?
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In which position is the lumbar lordosis considered to be normal?
In which position is the lumbar lordosis considered to be normal?
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Which factor contributes to cervical instability?
Which factor contributes to cervical instability?
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What occurs to ligaments after experiencing trauma?
What occurs to ligaments after experiencing trauma?
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What is the rationale for placing a pillow under the abdomen in the prone position?
What is the rationale for placing a pillow under the abdomen in the prone position?
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Which of the following statements regarding the gravitational line in different positions is true?
Which of the following statements regarding the gravitational line in different positions is true?
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What is the effect of increasing the distance between the center of motion and the gravity line?
What is the effect of increasing the distance between the center of motion and the gravity line?
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Study Notes
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)
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Description
Test your knowledge on the unique features of cervical vertebrae, including their functions and characteristics compared to thoracic and lumbar vertebrae. Explore the role of specific ligaments and movements in the cervical spine, along with key anatomical landmarks.
