Anatomy Msk · Year 1 · from Anatomy Msk
Case 1: Lumbar Puncture Using Surface Landmarks
Clinical Image
Source: Wikimedia Commons - Surface Anatomy of the Back - CC BY-SA 3.0
Case Presentation
A 35-year-old woman presents to the emergency department with the worst headache of her life, neck stiffness, and photophobia. She describes sudden onset of severe headache 4 hours ago while at work. She has no history of migraines or similar headaches. Physical examination reveals temperature 38.2C, neck stiffness, and positive Kernig sign. There is no focal neurological deficit. CT head without contrast is obtained and is negative for hemorrhage. Given concern for meningitis or subarachnoid hemorrhage with negative CT, lumbar puncture is indicated. The patient is positioned in the left lateral decubitus position with knees drawn to chest to open the interspinous spaces. Using surface landmarks, the iliac crests are palpated and a line drawn between them (Tuffier's line) identifies the L4 spinous process or L4-L5 interspace. The L3-L4 interspace is palpated one level above. After sterile preparation, local anesthetic is infiltrated, and a 22-gauge spinal needle is inserted at the L3-L4 interspace, angled slightly cephalad toward the umbilicus. The needle passes through skin, subcutaneous tissue, supraspinous ligament, interspinous ligament, ligamentum flavum, and dura to reach the subarachnoid space. A "pop" is felt as the needle penetrates the dura. Clear CSF is obtained with an opening pressure of 24 cm H2O. Analysis reveals elevated WBC (450 cells/microL, 90% neutrophils), low glucose, and elevated protein consistent with bacterial meningitis. She is started on empiric antibiotics.
Key Learning Points
- Tuffier's line (intercristal line between iliac crests) corresponds to the L4 spinous process or L4-L5 interspace
- LP is performed at L3-L4 or L4-L5 to avoid the conus medullaris (ends at L1-L2 in adults)
- The needle traverses: skin, subcutaneous fat, supraspinous ligament, interspinous ligament, ligamentum flavum, epidural space, dura, arachnoid
- In lateral decubitus position, the subarachnoid space is approximately 4-5 cm deep in average adults
- Surface anatomy landmarks guide safe needle placement and prevent spinal cord injury