Trunk Part #2

CLINICAL TRAINING: THE THORAX, PART II

AUTHOR

  • John Petrizzo, PT, DPT, CSCS

MUSCLES OF THORACIC WALL

Upper Limb Muscles Attaching to the Thoracic Cage

  • Pectoralis Major: A major muscle involved in movements of the shoulder joint.

  • Pectoralis Minor: A smaller muscle located beneath the pectoralis major, aiding in shoulder movements.

  • Serratus Anterior: Muscle that helps to rotate the scapula and is important for raising the arm.

  • Latissimus Dorsi: Large back muscle that extends, adducts, and rotates the shoulder.

Neck Muscles Attaching to the Thoracic Cage

  • Scalenes: Group of three muscles (anterior, middle, posterior) that flex and rotate the neck and elevate the first two ribs.

INTERCOSTAL SPACES AND MUSCLE LAYERS

  • Each typical intercostal space contains three layers of intercostal muscles:

    • Superficial Layer: Formed by the external intercostal muscles whose fibers are oriented infero-anteriorly.

    • Middle Layer: Composed of internal intercostal muscles with fibers oriented infero-posteriorly.

    • Deepest Layer: Formed by the innermost intercostal muscles, similar to internal intercostals but situated internal to the intercostal neurovasculature.

ANATOMY OF INTERCOSTAL SPACE

  • Transverse Section Observations:

    • Intercostal Muscles: Innermost, Internal, and External intercostals.

    • Sympathetic Trunk: Part of the sympathetic nervous system.

    • Ventral and Dorsal Rami: Branches of spinal nerves.

    • Transversus Thoracis Muscle: Thin muscle lying posterior to the sternum.

    • Vascular Structures: Aorta, Azygos vein, spinal root structures.

    • Erector Spinae Muscles: Muscles responsible for movement and support of the spine.

NERVES OF THE THORACIC WALL

  • Thoracic segments of the spinal cord supply 12 pairs of thoracic spinal nerves to the wall:

    • Upon leaving the intervertebral foramina, they divide into anterior and posterior rami.

    • Anterior rami of T1-T11 form intercostal nerves that run along the intercostal spaces.

    • Anterior rami of T12 nerves become subcostal nerves, below the 12th ribs.

    • Posterior rami supply skin and deep back muscles in the thoracic region.

Typical Intercostal Nerves (3rd – 6th)

  • Run along the posterior aspects of intercostal spaces between the parietal pleura and the internal intercostal membrane.

  • Initially run across the internal surface of the internal intercostal membrane before passing between the internal and innermost intercostal muscles near the rib angle.

Lateral Branches and Vessels

  • Consist of lateral branches and collateral branches connected to the intercostal nerves and vessels. Includes:

    • Anterior Branches: Supply the costal groves, arteries, and cutaneous branches.

    • Collateral Branches: Supply adjacent muscles and skin, mainly at mid-axillary line.

ATYPICAL INTERCOSTAL NERVES

  • Intercostal Nerves 1 and 2: Pass along the internal surfaces of the 1st and 2nd ribs rather than their inferior margins.

  • 7th – 11th Intercostal Nerves: Project to supply abdominal skin and muscles.

DERMATOMES AND MYOTOMES

  • Dermatomes: Skin regions supplied by sensory fibers of a single posterior root. Each dermatome contributes to a band-like area of skin.

    • Overlapping occurs typically from adjacent nerves, leading to the necessity of multiple intercostal nerves for complete sensation.

  • Myotomes: Groups of muscles supplied by motor fibers of spinal nerves. In the thoracic region, myotomes include the muscles of intercostal spaces and adjacent deep back muscles.

COMMUNICATING BRANCHES AND SYMPATHETIC SUPPLY

  • Communicating Branches: Connect intercostal and subcostal nerves to the ipsilateral sympathetic trunk.

  • Sympathetic Fibers: Distributed through the branches of spinal nerves to blood vessels, sweat glands, and smooth muscles of the body wall and limbs.

VASCULATURE OF THORACIC WALL

Arterial Supply

  • Arteries from the :

    • Thoracic Aorta

    • Subclavian artery

    • Axillary artery

  • Each intercostal space is supplied by three arteries:

    • Posterior intercostal artery (or its collateral branch)

    • Anterior intercostal arteries (smaller paired arteries)

Venous Supply

  • The venous system accompanies intercostal arteries and nerves, lying superiorly in costal grooves:

    • Consists of 11 posterior intercostal veins and one subcostal vein on each side.

Major Veins

  • Include:

    • Azygos vein

    • Hemiazygos vein

    • Accessory hemi azygos vein

CLINICAL BOXES

Herpes Zoster Infection (Shingles)

  • Viral disease affecting spinal ganglia, results in a skin lesion.

  • Symptoms include sharp burning pain in the dermatome supplied by the involved nerve, followed by red and vesicular eruptions in that area.

  • Vaccination is recommended for adults starting from age 50.

Dyspnea

  • Respiratory muscle engagement during difficulty in breathing due to conditions like asthma, emphysema, or heart failure.

  • Accessory muscles such as Sternocleidomastoid (SCM), upper traps, and scalene are utilized to assist thoracic cavity expansion, sometimes requiring physical fixation of clavicles/scapula for efficiency.

Intercostal Nerve Block

  • Used for rib fractures and thoracic surgeries involving anesthetic infiltration around intercostal nerves and collateral branches.

  • Anesthesia often requires injection of not just one, but adjacent intercostal nerves for effective pain management.

SURFACE ANATOMY

  • Jugular notch: Between the clavicles at the top of the sternum, indicated as suprasternal notch.

  • Sternal angle: The junction between the manubrium and the body of the sternum.

  • Axillary Lines and Spinous Processes: Various anatomical landmarks critical for thoracic assessment.

  • Midclavicular line and other anatomical reference lines are used for clinical assessments.