Spinal Column: Curvature and Flexibility

Spinal Column Curvatures

• Ventral columns are reciprocal curves forming the neutral spine
• Cervical and lumbar regions have lordotic (extended) curves
• Thoracic and sacral regions have kyphotic (flexed) curves, providing space for vital organs

Spinal Flexibility

• The spine isn't fixed; it's flexible and dynamic
• Extension increases lordosis in cervical and lumbar regions and flattens kyphosis in the thoracic region
• Flexion increases kyphosis in the thoracic region and flattens lordosis in cervical and lumbar regions

Importance of Normal Spinal Curvatures

• Normal curvatures allow greater compressive forces to be supported
• Compressive forces can be shared by tension from stretched connective tissues and muscles on the convex side
• Normal curvatures allow for give under a load

Optimal Posture

• The line of gravity should pass through the mastoid process
• The line of gravity should course anterior to the second sacral vertebrae
• The line of gravity should be slightly posterior to the hip and slightly anterior to the knee and lateral malleoli
• The line of gravity passes to the concave side of each region's curvature, producing torque
• Proper alignment allows standing at ease with minimal muscular activation and stress on connective tissue

Intervertebral Discs

• Intervertebral discs absorb and transmit compression and shear forces in the spinal column
• Each disc consists of the nucleus pulposus, annulus fibrosus, and vertebral end plate
• The nucleus pulposus is a gelatinous center composed of 70-90% water

Nucleus Pulposus Function

• The nucleus pulposus functions as a hydraulic shock absorber
• It transfers forces between vertebrae

Annulus Fibrosis Properties

• Annulus fibrosis is composed of fibrocartilage rings that encase the nucleus pulposus
• With vertebral compression, the nucleus pulposus is squeezed outward
• This creates tension within the annulus fibrosis, which is a stable, weight-bearing structure

Vertebral End Plate

• The vertebral end plate connects the intervertebral disc to the vertebra above and below
• The vertebral end plate provides the disc with nutrition

Vertebral Numbering and Disc Location

• Each vertebra is numbered per region from cephalic to caudal
• Each intervertebral disc is named by its location between two vertebrae
• For example, T11-T12 is the disc between the T11 and T12 vertebrae

Spinal Nerve Location

• In the thoracic and lumbar vertebrae, spinal nerves exit below their respective vertebrae
• In cervical regions, spinal nerves enter above the vertebrae
• The spinal nerve between C7 and T1 is the C8 nerve root

Herniated Nucleus Pulposus

• With time and pressure, the nucleus pulposus can ooze through cracks in the annulus fibrosus
• This causes a herniated nucleus pulposus, which can cause local or radiating pain down the butt and leg

Cervical Vertebrae Characteristics

• Cervical vertebrae are the smallest and most mobile
• C1 (atlas) and C2 (axis) are unique, while C3-C7 are typical
• Transverse foramina are passageways in the transverse process for the vertebral artery
• Uncinate processes are two-pronged and provide muscle attachments
• Facet joints are oriented at 45 degrees between the horizontal and frontal planes, maximizing mobility

Atlas (C1)

• The atlas supports the weight of the cranium (head)
• It has two large lateral masses connected by anterior and posterior arches
• Two concave superior facets attach to the convex occipital condyles, forming the atlanto-occipital joint
• It has the largest transverse processes in the cervical region
• The atlas allows the head to shake "yes"

Axis (C2)

• The axis features the dens, which functions as the axis of rotation for rotary movement
• The superior facets are relatively flat, matching the flattened inferior facets of the atlas
• The bifid spinous process of C2 is broad and palpable, allowing the head to shake "no"

Thoracic Vertebrae

• Spinous processes are sharp and project inferiorly
• Transverse processes are large, posterior, and project laterally
• Costal facets allow articulation with the ribs posteriorly
• Apophyseal joints are aligned nearly in the frontal plane

Lumbar Region

• Vertebral bodies are massive and wide
• Spinous processes are broad and rectangular, with stout and thick laminae and pedicles
• Apophyseal joints in the upper lumbar region (L1-L3) are oriented close to the sagittal plane
• Lower lumbar apophyseal joints (L4-L5) are oriented towards the frontal plane

Sacrum

• The sacrum is a triangle bone that transmits the weight of the vertebral column to the pelvis
• It features the sacral promontory, which articulates with L5 to form the lumbosacral junction
• The posterior and dorsal surface is convex and rough for muscle and ligament attachments
• The sacral canal houses and protects the cauda equina
• Four dorsal sacral foramina transmit the dorsal rami
• Four ventral sacral foramina on the anterior aspect transmit ventral rami of spinal nerves

Coccyx

• The coccyx is the tail bone, consisting of four fused vertebrae
• The base of the coccyx articulates with the inferior sacrum, forming the sacrococcygeal joint

Ligamentum Flavum

• Attaches between the anterior surface of one lamina and the posterior surface of the lamina below
• Limits flexion

Supraspinatus and Interspinous Ligaments

• Attach between adjacent spinous processes from C7 to the sacrum
• Limit flexion

Intertransverse Ligaments

• Attach between adjacent transverse processes
• Limit contralateral lateral flexion

Anterior Longitudinal Ligament

• Attaches between the basilar part of the occipital bone and the entire length of the anterior surfaces of all vertebral bodies
• Provides stability to the vertebral column to limit extension or excessive lordosis

Posterior Longitudinal Ligament

• Attaches along the entire length of the posterior surfaces of vertebral bodies, between the axis and sacrum
• Stabilizes the vertebral column, limits flexion, and reinforces the posterior annulus fibrosus

Capsule of the Apophyseal Joint

• Attaches to the margin of each apophyseal joint
• Strengthens and supports the apophyseal joint

Spinal Movement Definition

• Spinal movement indicates the direction of movement of a point on the anterior side of the vertebrae
• For example, Movement to the right means the vertebrae body is rotating to the right

Spine Regions

• Spinal motion occurs in the craniocervical and thoracolumbar regions
• Each region permits flexion/extension, lateral flexion, and axial rotation in the horizontal plane

Craniocervical Region

• The craniocervical region is made up of the atlanto-occipital, atlanto-axial, and intercevical joints

Craniocervical Flexion and Extension

• The occipital condyles roll back into extension and forward during flexion, opposite for extension
• The atlanto-axial joint allows about 5 degrees of flexion and 10 degrees of extension
• An arc of motion results that is determined by the cervical facet joints oblique plane
• During extension, the inferior facets of the superior vertebrae slide posteriorly and inferiorly related to the vertebrae below

Craniocervical Axial Rotation

• Rotation of the head and neck in the horizontal plane is important for vision and hearing
• Extensive neck rotation allows the visual field to approach 360 degrees without moving the trunk
• The atlanto-axial joint is responsible for half of the rotation
• Head rotation results from C1 and cranium rotating as a unit relative to the axis
• Rotation of C2-C7 is guided by oblique orientation of facet joints
• The combined motion of these joints allows 45 degrees of rotation both ways

Craniocervical Lateral Flexion

• The cranocervical region allows 40 degrees of lateral flexion to each side
• Most motion occurs between C2 and C7
• Motion is guided by the incline of facet joints; some horizontal plane rotation is mechanically coupled with lateral flexion

Thoracolumbar Motion

• The combined motion of the thoracic and lumbar vertebrae allows 85 degrees of flexion
• 50 degrees of flexion occurs in the lumbar region, linked to facet joint orientation
• 35 degrees of horizontal plane rotation occurs mostly in the thoracic region
• Lateral flexion equals 45 degrees in either direction

Anterior Pelvic Tilt

• The anterior rotation occurs in a short arc about the hip, as the trunk is stationary
• Naturally extends the lumbar spine, increasing lumbar lordosis

Posterior Pelvic Tilt

• Short arc posterior rotation of the pelvis and hip joints
• Flexes the lumbar spine and decreases lumbar lordosis

Lumbar Flexion Consequences

• Nucleus pulposus migrates posteriorly, toward neural tissue
• Increases the size of the opening of the intervertebral foramina
• Load transfer from the apophyseal joints to the intervertebral discs
• Tension increases in posterior connective tissues and the posterior margin of the annulus fibrosus
• Compression of the anterior side of the annulus fibrosus

Lumbar Extension Consequences

• Nucleus pulposus migrates anteriorly, away from neural tissue
• Decreases the size of the opening of the intervertebral foramina
• Load transfer from the intervertebral disc to the apophyseal joints
• Tension decreases in posterior connective tissues and the posterior margin of the annulus fibrosus
• Stretches the anterior side of the annulus fibrosus

Ventral Nerve Root

• Contains primarily outgoing (efferent) axons
• Provides motor signals to muscles

Dorsal Nerve Root

• Contains mostly incoming (afferent) dendrites
• Carries sensory information to the spinal cord from the periphery

Spinal Nerve

• Composed of dorsal and ventral nerve roots

Dorsal Ramus

• Posterior branches from the spinal nerve
• Innervates the deeper posterior musculature of the trunk and craniocervical regions

Ventral Ramus

• Anterior branches from the spinal nerve
• Innervates the anterior-lateral musculature of the trunk and craniocervical regions
• Forms the cervical, brachial, and lumbosacral plexus

Sit-up Analysis

• Abdominal flatten the lumbar spine
• This concludes when the scapula clears supporting surface
• Hip flexors then rotate the trunk anteriorly

Key Muscle Contractions

• Strong bilateral contraction of iliopsoas and quadratus lumborum leads to excellet verticle stability throughout the L5-S1 junction

Erector Spinae Muscles

• A large, disoriented group of muscles on either side of the spine, oriented essentially vertically
• They extend and stabilize the entire vertebral column and craniocervical region
• They consist of three thin columns: spinalis, longissimus, and iliocostalis

Transversospinal Muscles

• Semispinalis, multifidus, and rotators
• Lie deep to the erector spinae and run obliquely from one vertebra. transverse prosses to spinous process to another
• Provide stability to the lumbar with contralateral rotation
• Extend the vertebral column
• The oblique fiber direction of these muscles produces contralateral rotation
• The horizontal (shorter) the muscle, the greater its potential to produce horizontal plane rotation

Intertransversus and Interspinalis Muscles

• Attach between consecutive transverse processes, each interspinalis muscle attaches between consecutive spinous processes
• They assist with lateral flexion and are effective at furnishing fine control over vertical stability in sagittal and frontal planes
• They provide sensory feedback for postural alignment