Cervical Region Anatomy and Kinesiology Review

Cervical Region Anatomy and Spinal Framework

• Conceptual Overview: The cervical region is characterized as the most mobile area of the human spine. This high level of mobility inherently necessitates a sacrifice in structural stability, rendering the region particularly vulnerable to both direct and indirect trauma.

• Anatomic Zones: The cervical spine is categorized into three distinct clinical and functional zones:

  • Craniovertebral / Upper Cervical: Comprised of the $C0$-$C3$ segments.

  • Mid-Cervical: Comprised of the $C3$-$C6$ segments.

  • Cervicothoracic: Comprised of the $C6$-$T1$ segments.

• Thoracic Contribution: Movement of the cervical spine is not isolated; the thoracic spine acts as a prime contributor to cervical range of motion (Tsang 2013).

• Regional Movement Distribution: Movement is distributed across the cervical and thoracic regions as follows:

  • Flexion: Cervical $67\%$, Upper Thoracic $25\%$, Lower Thoracic $8\%$.

  • Extension: Cervical $68\%$, Upper Thoracic $24\%$, Lower Thoracic $8\%$

  • Rotation: Cervical $84\%$, Upper Thoracic $11\%$, Lower Thoracic $5\%$.

  • Lateral Flexion: Cervical $74\%$, Upper Thoracic $14\%$, Lower Thoracic $12\%$.

Articulations and Joint Mechanics

• Zygapophyseal (Facet) Joints:

  • These joints are generally angled at approximately $45^\circ$ between the frontal and transverse planes.

  • Regional Variations: In the upper cervical segments, the angle is more horizontal (approximately $35^\circ$). In the lower cervical segments, the angle becomes more frontal (approximately $65^\circ$).

• Uncovertebral Joints: These joints serve several critical mechanical functions:

  • Guide the primary movements of flexion ($FLEX$) and extension ($EXT$).

  • Serve as a physical limit to lateral flexion.

  • Prevent posterior translation of the vertebral bodies.

  • Provide structural reinforcement to the posterolateral aspect of the intervertebral discs ($IVDs$).

Intervertebral Discs (IVD)

• Quantity and Naming: There are $5$ cervical discs. The disc sequence begins at the $C2$-$C3$ level. Discs are named based on the vertebra immediately superior to them.

• Cervical vs. Lumbar Differences:

  • Nucleus Pulposus (NP) Size: The cervical NP is significantly smaller than the lumbar NP. At birth, the cervical NP constitutes $25\%$ of the disc, compared to $50\%$ in the lumbar spine.

  • Fibrosis Timeline: In the cervical spine, fibrosis of the NP occurs much earlier than in other regions, typically manifesting by the mid-teens.

• Clinical Implications: The structural differences in cervical discs (small NP and early fibrosis) influence the specific pain patterns observed in patients and dictate the appropriate course of physical therapy treatment.

Neurovascular Tunnels and Passageways

• Intervertebral Foramina: These passageways contain the spinal nerve roots exiting the spinal column.

• Vertebral Canal: This central passageway contains the spinal cord.

• Transverse Foramina: These openings house the vertebral artery, which typically enters the transverse foramen at the level of the $C6$ vertebra.

Ligamentous Support Structures

• Continuous Ligaments:

  • Anterior Longitudinal Ligament (ALL): Runs along the anterior aspect of the vertebral bodies.

  • Posterior Longitudinal Ligament (PLL): Runs along the posterior aspect of the vertebral bodies, within the spinal canal.

  • Nuchal Ligament: Extends from the external occipital protuberance to the spinous processes of the cervical vertebrae.

  • Supporting Membranes: Includes the posterior atlanto-occipital membrane.

• Segmental Ligaments:

  • Ligamenta Flava (LF): Connects the laminae of adjacent vertebrae.

  • Interspinous Ligaments: Located between the spinous processes.

  • Intertransverse Ligaments: Located between the transverse processes.

  • Supraspinous Ligament: Connects the tips of the spinous processes.

  • Articular Capsules: Surround the zygapophyseal (facet) joints.

Cervical Musculature and Dynamic Stability

• Deep vs. Superficial Hierarchy:

  • Deep Musculature: Specifically suited to control segmental movement and provide dynamic stability to the spine.

  • Superficial Musculature: Responsible for larger global movements and power.

• Dysfunction Patterns: In instances of ongoing pain, there is typically a decrease in the function of the deep musculature and a compensatory increase in the activity of the superficial musculature, reminiscent of a "fight or flight" response.

• Anterior Muscles:

  • Deep: Longus Coli, Longus Capitis.

  • Superficial: Scalenes, Sternocleidomastoid ($SCM$).

• Posterior Muscles:

  • Deep: Semispinalis Capitis, Semispinalis Cervicis, Multifidus.

  • Superficial: Upper Trapezius, Splenius Capitis.

Kinesiology Principles and Spinal Coupling

• Facet Geometry: Facet planes lie at a $45^\circ$ angle relative to the frontal and transverse planes.

• Coupling Definitions:

  • Type 1 Coupling: Lateral flexion ($LF$) and rotation occur to opposite sides.

  • Type 2 Coupling: Lateral flexion ($LF$) and rotation occur to the same side.

• Mid-to-Lower Cervical Coupling ($C2$-$C7$): Follows a consistent Type 2 coupling pattern (confirmed by $100\%$ of studies in the Cook et al. 2006 systematic review).

• Upper Cervical Coupling (OA and AA): Patterns are less consistent but generally follow these Cook (2006) findings:

  • Rotation Initiation: Typically results in Type 2 coupling (same side).

  • Lateral Flexion Initiation: Typically results in Type 1 coupling (opposite side).

• Joint Kinematics:

  • Flexion ($FLEX$): Characterized by bilateral ($B$) upglide of facets.

  • Extension ($EXT$): Characterized by bilateral ($B$) downglide of facets.

  • Right ($R$) Lateral Flexion/Rotation: Involves a ($R$) downglide and a Left ($L$) upglide.

• Foraminal Dynamics:

  • Narrowing: Occurs with $EXT$, Ipsilateral ($Ipsi$) $LF$, or Ipsilateral ($Ipsi$) Rotation.

  • Opening: Occurs with $FLEX$, Contralateral ($Contra$) $LF$, or Contralateral ($Contra$) Rotation.

Specific Movement Mechanics

• Kinesiology of Flexion:

  • $C2$-$C7$: Facets perform bilateral upglide; intervertebral foramina open bilaterally. Discs experience anterior compression and reduced posterior pressure.

  • OA ($C0$-$C1$): Bilateral anterior roll with simultaneous bilateral posterior glide.

  • AA ($C1$-$C2$): Slight anterior pivot. Tension is placed on the tectorial membrane. The atlanto-odontoid interval ($ADI$) increases.

• Kinesiology of Extension:

  • $C2$-$C7$: Facets perform bilateral downglide; intervertebral foramina narrow bilaterally. Discs experience posterior compression and reduced anterior pressure.

  • OA ($C0$-$C1$): Bilateral posterior roll with simultaneous bilateral anterior glide.

  • AA ($C1$-$C2$): Slight posterior pivot. The $ADI$ is reduced, leading to dens compression.

• Kinesiology of Right (R) Lateral Flexion:

  • $C2$-$C7$: ($R$) Downglide and ($L$) Upglide of facets. Foramina narrow on the ($R$) and open on the ($L$). The disc is compressed on the ($R$) with reduced pressure on the ($L$).

  • OA ($C0$-$C1$): Bilateral roll to the ($R$) and bilateral glide to the ($L$) (Note: The image in the Olson text is identified as incorrect regarding this).

  • AA ($C1$-$C2$): Minimal ($R$) lateral flexion occurs here.

• Kinesiology of Right (R) Rotation:

  • $C2$-$C7$: ($R$) Downglide and ($L$) Upglide of facets. Foramina narrow on the ($R$) and open on the ($L$). Minimal forces are exerted on the disc.

  • OA ($C0$-$C1$): Movement is negligible.

  • AA ($C1$-$C2$): This is the primary site of rotation; the atlas spins into ($R$) rotation around the dens/atlas articulation. Approximately $50\%$ of all cervical rotation originates from the $C1$-$C2$ segment.