The Spine

The Spine: Comprehensive Study Notes

Overview of the Spine

• The spine consists of $33$ total vertebrae.

  • $24$ of these are individual vertebrae.

  • The remaining vertebrae are fused.

• Vertebrae Breakdown:

  • Cervical: $7$ vertebrae

  • Thoracic: $12$ vertebrae

  • Lumbar: $5$ vertebrae

  • Sacrum: $5$ fused vertebrae

  • Coccyx: $4$ fused vertebrae

• There are $23$ intervertebral discs, located between individual vertebrae.

Spinal Curves

• Primary Spinal Curve:

  • The spine initially develops as one large C-shape (kyphotic curvature) in utero.

• Secondary Spinal Curves:

  • These curves develop as the body adapts to its environment after birth.

  • Cervical Lordosis: Develops as a baby lifts its head.

  • Lumbar Lordosis: Develops as a child learns to sit and stand.

Main Functions of the Spine

• Structural Support: Provides support for the weight of the head, arms, neck, and trunk (KINETICS).

• Movement: Allows for movement of the body (in multiple planes).

• Stable Base: Offers a stable base for the attachment of ligaments and tendons.

• Connecting Link: Serves as the connecting link between the arms and legs (KINETIC CHAIN).

• Protection: Protects the delicate spinal cord.

• Shock Absorption: Absorbs shock for the entire body.

Cervical Spine Anatomy

• The cervical spine comprises $7$ vertebrae, often abbreviated C$1$ to C$7$ .

C$1$ - Atlas

• Articulates with the occiput (base of the skull) to form the atlantooccipital joint – known as the "nodding joint."

• It is wider than other cervical vertebrae.

• Lacks a spinous process, meaning it is not palpable.

• Allows for significant extension of the craniovertebral junction.

• The vertebral artery passes through its transverse foramen.

C$2$ - Axis

• The first palpable vertebra located just below the skull.

• Features the odontoid process (dens), which extends superiorly and acts as a pivot.

  • The dens is the center for rotation of the atlantoaxial joint (C$1$ and C$2$).

• The vertebral artery also passes through its transverse foramen.

• The occiput, C$1$ (Atlas), and C$2$ (Axis) together form the craniovertebral junction.

C$3$ - C$7$ Vertebrae

• These vertebrae are similar in shape, each possessing:

  • A vertebral body.

  • A spinous process.

  • Transverse processes.

  • A vertebral foramen (for the spinal cord).

  • Transverse foramen (for the vertebral artery).

• C$6$ is humorously noted for its role in daily support.

Suboccipital Muscles (Deep Neck Extensors)

• These muscles are primarily stabilizers and postural muscles, contributing to some extension and rotation of the head.

• Muscles and their Attachments:

  • Rectus Capitis Posterior Minor (RCP Minor): Originates from the posterior tubercle of C$1$; inserts on the occiput (with a connection to the dura).

  • Rectus Capitis Posterior Major (RCP Major): Originates from the spinous process of C$2$; inserts on the occiput.

  • Obliquus Capitis Superior (OCS): Originates from the transverse process of C$1$; inserts on the occiput.

  • Obliquus Capitis Inferior (OCI): Originates from the spinous process of C$2$; inserts on the transverse process of C$1$.

• Clinical Significance:

  • Pain often arises from weakness and overuse (especially extension), poor posture, and the weight of the head (lever system and force).

  • The dura connection of RCP Minor suggests a link to cervicogenic headaches.

  • Suboccipital release is a technique used to address cervicogenic headaches.

  • Recommendations: Try protracting the head then extending, or retracting the head then extending.

Craniovertebral Junction Ligaments

Transverse Ligament

• Runs between the transverse processes of C$1$.

• This is a very strong ligament, possessing almost $2 imes$ the tensile strength of other cervical ligaments.

• Its primary function is to resist the dens (odontoid process) from entering the vertebral foramen.

• Also limits flexion of the atlantoaxial (AA) joint.

• Clinical Fun Fact: The dens is more likely to fracture before this ligament tears, though both are quite rare events.

• Conditions of concern for instability: Rheumatoid Arthritis (RA) and Down Syndrome (DS).

Alar Ligaments

• Located on each side of the dens.

• Connect to the sides of C$1$ and the occipital condyles.

• Limit rotation, lateral flexion, and distraction of the skull from the spine.

• Key Movement: The first $45^ extrm{o}$ of cervical rotation primarily occur at the atlantoaxial (AA) joint.

Key Cervical Muscles

Sternocleidomastoid (SCM)

• Origins (Two Heads): Sternum and medial $1/3$ of the clavicle.

• Insertions: Mastoid process of the temporal bone.

• Actions:

  • Contralateral rotation of the neck.

  • Ipsilateral (same side) lateral flexion of the neck.

  • Bilateral contraction causes neck flexion.

• Clinical Condition: Torticollis

  • May affect up to $90$% of the population.

  • Congenital Torticollis: Noted at birth by a head tilt or limited neck range of motion/flexibility.

  • Adult Torticollis: Pain and tightness are usually benign but can sometimes indicate malignancy.

  • A tight SCM would present as a head tilted to one side with the chin rotated to the opposite side.

Scalenes (Anterior, Middle, Posterior)

• Origins: Transverse processes of C$2$ to C$7$.

• Insertions: First and second ribs.

• Actions:

  • Neck flexion.

  • Lateral flexion of the neck.

• Reverse Actions: Elevate the first and second ribs (important for forceful inspiration).

Trapezius (Superficial)

• Origins: Occiput (medial $1/3$ of the superior nuchal line), nuchal ligament, spinous processes of C$7$ to T$12$.

• Insertions: Lateral $1/3$ of the clavicle, acromion process, and spine of the scapula.

• Actions:

  • Upper fibers: Elevate the scapula.

  • Upper and Middle fibers: Retract the scapula.

  • Lower fibers: Depress the scapula.

• Reverse Actions (Upper Trapezius): Cervical extension, contralateral rotation, and lateral flexion.

Longissimus Capitis (Part of Erector Spinae - Deep)

• Origins: Transverse processes of C$4$ to T$7$.

• Insertions: Mastoid process of the temporal bone.

• Actions: Neck lateral flexion, ipsilateral rotation, and extension.

Splenius Capitis (Superficial but considered Deep)

• Origins: Spinous processes of C$7$ to T$3$/T$4$, and nuchal ligament (C$3$ to C$6$).

• Insertions: Occiput (superior nuchal line) and mastoid process of the temporal bone.

• Actions: Neck extension, lateral flexion, and ipsilateral rotation.

Cervical Ligaments

• Anterior Longitudinal Ligament (ALL):

  • Limits hyperextension of the spine.

  • Resists anterior herniation of intervertebral discs.

  • Runs the entire length of the spine (anterior aspect of vertebral bodies).

• Posterior Longitudinal Ligament (PLL):

  • Limits hyperflexion of the spine.

  • Resists posterior herniation of intervertebral discs.

  • Runs the entire length of the spine (posterior aspect of vertebral bodies, within the vertebral canal).

• Nuchal Ligament:

  • Limits flexion of the cervical spine.

  • Runs from the occiput to C$7$.

• Ligamentum Flavum:

  • Limits flexion of the spine.

  • Runs anterior to the spinous processes (connecting laminae).

• Interspinous Ligaments:

  • Limit flexion of the spine.

  • Run between adjacent spinous processes.

• Supraspinous Ligament:

  • Limits flexion of the spine.

  • Connects the tips of the spinous processes (continuous with the nuchal ligament in the cervical region).

Cervical Spine Range of Motion (ROM)

• Flexion: $50^ extrm{o}$

• Extension: $60^ extrm{o}$

• Lateral Flexion: $45^ extrm{o}$

• Rotation: $80^ extrm{o}$

Blood Supply

• The Vertebral Artery is crucial for cervical circulation, traveling through the transverse foramen of C$6$ to C$1$.

Nerves and Spinal Cord Injury (SCI) Levels

• Cervical Division (C$1$ - C$8$):

  • C$1$-C$4$ Nerves: Control breathing and head/neck movement.

  • C$4$-C$6$ Nerves: Influence heart rate and shoulder movement (C$5$).

  • C$6$-C$7$ Nerves: Control wrist and elbow movement.

  • C$7$-T$1$ Nerves: Control hand and finger movement (including C$8$).

• Spinal Cord Injury (SCI) Examples:

  • C$4$ Injury: Results in Quadriplegia/Tetraplegia, causing complete paralysis below the neck.

  • C$6$ Injury: Leads to partial paralysis of hands and arms, as well as the lower body.

• Thoracic Division (T$1$ - T$12$):

  • T$1$-T$12$ Nerves: Regulate sympathetic tone (including temperature) and trunk stability (T$2$-T$12$).

  • T$6$ Injury: Results in Paraplegia, causing paralysis below the chest.

• Lumbar Division (L$1$ - L$5$):

  • T$11$-L$2$ Nerves: Involved in ejaculation and hip motion (L$2$).

  • L$3$ Nerve: Controls knee extension.

  • L$4$-S$1$ Nerves: Control foot motion and knee flexion (L$5$).

  • L$6$ Injury (Typo for L1-L5 region): Results in Paraplegia, causing paralysis below the waist.

• Sacral Division (S$1$ - S$5$):

  • S$2$-S$4$ Nerves: Involved in penile erection.

  • S$2$-S$3$ Nerves: Control bowel and bladder activity.