1b: Superficial Back Muscles and Vertebral Column

Osteology of the Superficial Back

  • The superficial back involves muscles like trapezius, latissimus dorsi, levator scapulae, rhomboid major, and rhomboid minor.

  • These muscles attach to the scapula and influence movements both in and outside the back (upper limbs).

  • These muscles connect the axial and appendicular skeleton.

Vertebral Column

  • Composed of approximately 33 bones.

  • Regional divisions:

    • 7 cervical vertebrae (neck).

    • 12 thoracic vertebrae.

    • 5 lumbar vertebrae.

    • 5 sacral vertebrae.

    • 4 coccygeal vertebrae.

  • Sacral and coccygeal levels fuse to form the sacrum and coccyx.

  • The vertebral column protects the spinal cord.

Spinal Curvatures

  • Anterior and lateral views of the spinal column provide different perspectives.

  • Lateral view shows the normal curvatures of the vertebral column.

  • Primary and secondary curvatures are normal and important for weight distribution.

  • Curvatures facilitate weight distribution down to the lower limbs.

Types of Curvatures

  • Lordosis: Secondary curvatures in the lumbar and cervical spine.

    • Normal but can be excessive (pathological).

  • Kyphosis: Primary curvatures in the thoracic and sacral regions.

    • Excessive kyphosis = hunchback.

    • May involve forward head posture as compensation.

  • Excessive lumbar lordosis = sway back.

    • Can cause pain.

Typical Vertebrae

  • Anterior: vertebral body (bulk of vertebrae).

  • Posterior: spinous processes (palpable).

  • Lamina: Extends around to a pedicle in the front forming the vertebral foramen.

  • The spinal cord runs through the vertebral foramen.

  • Structures:

    • Spinous process.

    • Body.

    • Transverse process.

    • Pedicle.

    • Lamina.

    • Vertebral foramen.

    • Inferior and superior articular processes.

Laminectomy

  • Surgical removal of lamina to decompress structures.

  • In the class, a portion of the spine will be used to visualize the spinal cord.

Cervical vs. Thoracic vs. Lumbar Vertebrae

  • Lumbar vertebrae have larger bodies (for weight distribution).

  • Thoracic vertebrae have angled spinous processes that point downward, making them harder to palpate.

  • Cervical vertebrae have bifid (split) spinous processes.

  • Cervical vertebrae contain transverse foramen (foramen transversarium) for vertebral arteries.

  • Thoracic vertebrae have facets for rib articulation (rib head and rib tubercle).

Rib Articulation

  • Ribs articulate posteriorly with thoracic vertebrae and anteriorly with the sternum, forming the thoracic cage.

  • Each rib articulates at three areas on the thoracic vertebrae.

  • Facets are flat articulation points.

Cervical Vertebrae Specifics

  • Uncinate process creates an uncovertebral joint.

  • Facet joints or zygopaphyseal joints are found throughout the rest of the spine.

C1 (Atlas)

  • First cervical vertebra.

  • Has facets for occipital condyles (occipital condyles form a joint allowing nodding).

  • Facets for articulation with C2 (axis) allowing rotation.

  • Has transverse foramen.

  • Lateral masses instead of pedicles/laminae.

  • Anterior arch and posterior tubercle instead of a spinous process.

C2 (Axis)

  • Second cervical vertebra.

  • Has a dens (odontoid process) that articulates with C1, allowing rotation.

  • Has superior articular facets that join with C1.

  • Has a bifid spinous process.

Bone Boxes

  • Bone boxes will contain a full set of vertebrae.

  • Identify C1 and C2.

Sacrum

  • The sacrum is the inferior most part of the vertebral column.

  • More details on the sacrum will be provided when discussing the pelvis.

Linking Vertebrae

  • Lateral view shows spinous processes in the back, bodies in the front, and discs in between.

  • Superior articular facet of one vertebra articulates with the inferior articular facet from the vertebra above.

  • Facet joint = zygapophyseal joint.

  • Orientation of facet joints dictates flexion, extension, side bending, and rotation.

Intervertebral Foramen

  • Formed by notches of adjacent vertebrae.

  • Spinal nerves and neurovascular structures pass through these foramen.

Pars Interarticularis

  • The region between superior and inferior facets.

  • Clinically relevant for injuries and fractures.

Stability of the Spine

  • Ligaments provide stability.

Ligaments

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

  • Posterior Longitudinal Ligament (PLL): Runs along the posterior aspect of vertebral bodies (anterior wall of the vertebral canal).

  • Ligamentum Flavum: Located around the lamina.

  • Interspinous Ligaments: Between spinous processes.

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

Intervertebral Discs

  • Annulus Fibrosis: Outer, fibrous layer of the intervertebral disc.

  • Nucleus Pulposus: Inner, gelatinous layer of the intervertebral disc (cushioning).

Superficial Back Muscles

  • Lectures will review osteology, then attach muscles and discuss neurovascular structures.

Trapezius

  • Trapezoid-shaped muscle.

  • Parts: upper, middle, lower.

  • Attachments: head, spinous processes, spine of scapula, acromion, clavicle.

  • Neurovascular structures are underneath it.

  • Reflection will allow identification of nerve, artery, and vein.

  • Innervation: Spinal accessory nerve (cranial nerve).

  • Spinal Accessory Nerve innervates trapezius and sternocleidomastoid.

Latissimus Dorsi

  • Origin: spinous processes, sacrum, iliac crest, thoracolumbar fascia.

  • Insertion: humerus.

  • Action: Pull insertion towards origin.

  • Actions of latissimus dorsi:

    • Extension.

    • Adduction.

    • Internal rotation (hand in pocket).

  • Innervation: Thoracodorsal nerve (middle subscapular nerve).

  • Thoracolumbar fascia is a thick fascia that is part of the origin of the latissimus dorsi.

Rhomboids

  • Rhomboid minor (top) and rhomboid major (below).

  • Shape: rhomboid.

  • Insertion: vertebral border of the scapula (above and below the scapular spine).

  • Origin: spinous processes.

  • Action: retraction (move scapula toward midline and rotate down).

  • Innervation: Dorsal scapular nerve.

Levator Scapulae

  • Underneath the upper trapezius.

  • Attachments: cervical vertebrae, superior angle of the scapula.

  • Action: elevates the scapula.

Serratus Posterior Muscles

  • Serratus posterior superior: Underneath rhomboids on the thoracic cage (accessory respiratory muscle).

  • Serratus posterior inferior: Underneath latissimus dorsi on the lower ribs (accessory respiratory muscle).