Applied Anatomy of the Back

Applied Anatomy of the Back - Spinal Curves & Column Chaos

• Normal Spinal Curves:
  • Primary (Kyphotic): Thoracic, Sacral (present at birth, fetal).
  • Secondary (Lordotic): Cervical (lifts head), Lumbar (walking).
• Abnormal Curvatures:
  • Kyphosis: ↑ Thoracic curve (Dowager's hump (osteoporosis); Scheuermann's disease).
  • Lordosis: ↑ Lumbar curve (Pregnancy; obesity; spondylolisthesis).
  • Scoliosis: Lateral curvature + vertebral rotation. Cobb angle (severity). Idiopathic common.
• Common Vertebral Pathologies:
  • Spina Bifida: NTD. Occulta (hair tuft), Meningocele, Myelomeningocele.
  • Spondylolysis: Pars fracture ("Scottie dog" X-ray).
  • Spondylolisthesis: Anterior slip (L5/S1). Meyerding grades.
  • PIVD: Posterolateral herniation (L4-L5, L5-S1). Affects nerve root below.

⭐ L4-L5 disc herniation typically compresses the L5 nerve root; L5-S1 disc herniation usually compresses the S1 nerve root.

Applied Anatomy of the Back - Back's Movers & Groaners

• Extrinsic Muscles (Upper Limb/Respiration):
  • Superficial: Trapezius, Latissimus Dorsi, Levator Scapulae, Rhomboids.
  • Intermediate: Serratus Posterior Superior & Inferior (respiratory).
• Intrinsic Muscles (True Back Muscles - Posture & Spine Movement):
  • Erector Spinae (ILS): 📌 "I Love Spine" - Iliocostalis, Longissimus, Spinalis (Lateral to Medial). Innervated by posterior rami of spinal nerves.
  • Transversospinalis: Semispinalis, Multifidus, Rotatores.
• Clinical Correlations:
  • Back Sprains/Strains: Commonest cause of low back pain (LBP), affecting muscles/ligaments.
  • Triangle of Auscultation: Borders - Trapezius, Latissimus Dorsi, Medial Scapula.
  • Lumbar Triangle (Petit): Borders - Latissimus Dorsi, External Oblique, Iliac Crest. Potential lumbar hernia site.

⭐ The Triangle of Auscultation allows clearer auscultation of posterior lung segments due to relative thinning of overlying musculature here (Rhomboid major forms floor).

Applied Anatomy of the Back - Wiry Woes & Nerve Niggles

• IVDP (Herniated Disc):
  • Lumbar: L4-L5, L5-S1 common. Sciatica, +SLR.

  ⭐ L4-L5 disc herniation → L5 root; L5-S1 → S1 root.

  • Cervical: C5-C6, C6-C7 common (C6, C7 roots).
• Spinal Stenosis:
  • Neurogenic claudication from canal narrowing; pain ↑ walking, ↓ flexion.
• Spondylolisthesis:
  • Anterior vertebral slip (L5-S1 common). Pars defect (spondylolysis) precedes.
• Cauda Equina Syndrome: ⚠️ Surgical emergency!
  • Bilateral leg weakness, saddle anesthesia (S2-S4), bowel/bladder dysfunction.
• Lumbar Puncture (LP):
  • Level: L3-L4/L4-L5 (adult cord ends L1-L2). Ligamentum flavum pierced before epidural space.
• Key Nerve Injuries:
  • Long thoracic (C5-7): Serratus ant. → Winged scapula.
  • Accessory (CN XI): Trapezius → Shoulder droop.
  • Thoracodorsal (C6-8): Lat. dorsi → Weak arm adduction/ext.

Applied Anatomy of the Back - Punctures, Blocks & Bloody Backs

• Lumbar Puncture (LP):
  • Site: L3-L4 or L4-L5 (adults); L4-L5 (children). Supracristal plane (iliac crests) at L4.
  • Layers pierced: Skin → Superficial fascia → Supraspinous lig. → Interspinous lig. → Ligamentum flavum → Epidural space → Dura mater → Arachnoid mater → Subarachnoid space (CSF).
  • Contraindications: ↑ICP, local infection, coagulopathy.
• Epidural Anesthesia:
  • Needle into epidural space (external to dura mater).
  • Lumbar or caudal routes common.
• Caudal Epidural Block:
  • Via sacral hiatus (palpate sacral cornua).
  • For perineal procedures, pediatrics.
• Batson's Venous Plexus:
  • Valveless vertebral venous network.

  ⭐ Facilitates metastasis (e.g., prostate cancer to vertebrae/brain).

• Triangle of Auscultation:
  • Borders: Latissimus dorsi, Trapezius, medial Scapula.
  • Better lung sound auscultation.
• Lumbar Triangle (of Petit):
  • Borders: Latissimus dorsi, External oblique, Iliac crest.
  • Site of potential lumbar hernia.

High‑Yield Points - ⚡ Biggest Takeaways

• Lumbar puncture: L3-L4/L4-L5, needle pierces ligamentum flavum to enter subarachnoid space.
• IVDP: Common at L4-L5/L5-S1 (posterolateral), affects nerve root below (e.g., L5 for L4-L5 disc).
• Spondylolysis (pars defect) can cause spondylolisthesis (vertebral slip), often L5-S1.
• Spina bifida occulta: Neural tube defect, often tuft of hair over L5/S1.
• Triangle of auscultation: For lung sounds, bordered by latissimus dorsi, trapezius, scapula.