Spinal Anatomy, Landmarks, and Core Muscles

Spinal Curvatures

• Lordosis: Anterior (forward) curvature of the spine (cervical and lumbar regions). Often associated with hyper-extension, e.g., in pregnancy or poor posture, leading to an exaggerated arch.

• Kyphosis: Posterior (backward) curvature of the spine (thoracic region and sacrum). Can result from osteoporosis, poor posture (e.g., "round back"), or developmental issues such as Scheuermann's disease.

Vertebral Landmarks (Palpation)

• Cervical Vertebra $C_7$: Most pronounced spinous process at the base of the neck when chin is tucked.

• Thoracic Vertebra $T_2$: Lines up with the superior angle of the scapula, useful for identifying upper thoracic segments.

• Thoracic Vertebra $T_7$: Lines up with the inferior angle of the scapula, a key landmark for mid-thoracic assessment.

• Thoracic Vertebra $T_{12}$: Lines up with the twelfth rib (most inferior), marking the thoracolumbar junction.

• Lumbar Vertebra $L_4$: Lines up with the top of the iliac crest (pelvis), an important landmark for lumbar punctures.

Spinal Movements & Muscles

• Spinal Movement Range: Cervical (>, Most) $<br>\rightarrow$ Lumbar $<br>\rightarrow$ Thoracic (<, Least).

• Extension: Straightening the spine; primarily involves the erector spinae group bilaterally.

• Rotation: Twisting the torso; left/right side rotation, involving intersegmental obliques. For example, right rotation involves the left external oblique and right internal oblique.

• Lateral Flexion: Bending the spine to the side (taking hands down of leg); involves same-side musculature primarily, such as the quadratus lumborum, erector spinae, and internal/external obliques on the side of flexion.

Trunk Musculature

• Breathing Muscles:

  • Inhalation: Rib cage expands/elevates (external intercostals, diaphragm, and accessory muscles like scalenes and sternocleidomastoid during forced inspiration).

  • Exhalation: Rib cage depresses/collapses. Quiet exhalation is passive; forced exhalation involves internal intercostals and abdominal muscles.

• Erector Spinae Group: Keeps the spine upright, aids in extension. Always active unless lying down. More superficial. Function to extend the vertebral column, maintain erect posture, and unilaterally perform ipsilateral lateral flexion and slight rotation.

  • Components (from lateral to medial): Iliocostalis, Longissimus, Spinalis.

• Transversospinalis Group: Deep core muscles, foundational for stability. Located segmentally between vertebrae. Play a crucial role in fine-tuning movements between individual vertebrae and providing proprioceptive feedback due to high density of muscle spindles.

  • Components: Multifidi, Rotatores, Semispinalis (e.g., Capitis, Cervicis).

• Quadratus Lumborum (QL):

  • Location: Between pelvis (ilium/iliac crest) and last rib ($12^{th}$ rib) and lumbar transverse processes.

  • Unilateral function: Hip hiking (if insertion fixed), lateral flexion (if origin fixed). Also assists in maintaining pelvic level during gait.

  • Bilateral function: Extension (collectively), anchors rib cage for breathing (especially during forced exhalation by depressing the $12^{th}$ rib), and provides stability to the lumbar spine and pelvis.

• Abdominal Muscles (The "House"):

  • Rectus Abdominis: Runs up and down; flexes trunk forward, posteriorly tilts pelvis, and compresses abdominal contents.

  • External Oblique: Fibers run like hands in front pockets. Bilateral: trunk flexion, compression. Unilateral: contralateral rotation, ipsilateral lateral flexion.

  • Internal Oblique: Fibers run opposite to external oblique (like hands in back pockets). Bilateral: trunk flexion, compression. Unilateral: ipsilateral rotation, ipsilateral lateral flexion.

  • Transverse Abdominis: Fibers run across/horizontally; deepest abdominal muscle, important for core stability. Compresses abdominal contents, stabilizes the lumbar spine, and increases intra-abdominal pressure (essential for coughing, sneezing, forced exhalation, and lifting).

Other Landmarks

• Jugular Notch: Top of the manubrium (sternum).

• Manubrium: Top part of the sternum.

• Xiphoid Process: Bottom of the sternum (Caution during CPR due to risk of damage to underlying organs).

• **Lamina Groove