Bony Anatomy of Lumbar Spine and Pelvis

Bony Anatomy of the Lumbar Spine and Pelvis

• PSIS/S2: Palpate the iliac crest laterally and a bit cranially, moving inferiorly to identify the iliac crest. Palpate bilaterally along the superior aspect of the iliac crest, moving from the lateral to the posterior medial side. Feel the bone widening and switch from using your fingertips to your thumb. The iliac crest curves downward ending in a bony step, the Posterior Superior Iliac Spine (PSIS). Use your thumb perpendicular to the underside of the PSIS; draw a dashed helper line connecting the PSIS to the S2, which helps locate the level of the S2.The size and location of the S2 spinous process is variable.

• L5 SP: Measure two thumb widths cranially from the S2 spinous process to locate the L5 spinous process. Confirm this by standing to the side of the patient; use one hand (cranial side) to palpate and block the L5 spinous process. Your caudal hand reaches across, and grabs the opposite anterior and lateral portion of the ilium. Stabilize L5, moving the ilium towards the center; if L5 does not move, you are on S1, not S2. Apply a mobilizing rotational force to the pelvis (lifting it towards you while stabilizing L5). If the pelvis moves against the stabilizing hand, you confirm you are on L5's spinous process. Repeat this to confirm or rule out locations of previous processes.

• SP of L1-L4: Palpate the remaining lumbar spinous processes cranially. Also, palpate the sides and interspinous spaces.

Muscles of the Lumbar Spine and Abdomen

• Erector Spinae: The patient lies prone. Palpate the large muscle group, the erector spinae (Spinalis, Longissimus, Iliocostalis) located on the lateral side of the lumbar vertebrae. These muscles run from the sacrum to the occiput, along the posterior vertebral column and are difficult to individually palpate. The patient can perform alternate extensions of the lower limbs to help feel these muscles under the palpating fingers, moving from the sacrum cranially towards the thoracic spine. The patient can raise their head and chest off the table for greater palpation.

• Ischial Tuberosity: To locate the ischial tuberosity, use the palm of your hand, progressing upward from the proximal hamstring into the glutes.

Other Structures

• ASIS: Palpate the Anterior Superior Iliac Spine (ASIS). Starting from the iliac crest, move from the posterior lateral side to the anterior medial portion to the ASIS, which forms a prominent bony edge.

• Pubic Crest: Walk the heel of the hand from the umbilicus towards the pubis. Your fingers will contact the firm ridge of the pubic crest.

• Pubic Tubercles: Palpate the prominent forward-projecting tubercle on the superior border of the medial portion of the superior ramus of the pubis. The inguinal ligament attaches to the pubic tubercle.

• Rectus Abdominis: Ask the patient to raise their head and chest off the table, activating the rectus abdominis, which runs from the xiphoid to the pubic crest.

• External Obliques: The patient raises their head and chest, bringing the shoulder toward the opposite ASIS. Palpate for the oblique fibers.

• Transverse Abdominis: Locate the anterior superior iliac spines (ASIS). Palpate an inch caudal (lower) and medial (toward the midline) to the ASIS. Ask the patient to take a deep breath, then hold their breath, drawing their umbilicus toward their spine; tension should be palpable.

• Piriformis: Locate the PSIS (lower part). Find the lateral edge of the sacrum, then move laterally towards the coccyx. The piriformis, creating a "T" shape, attaches to the anterior aspect of the sacrum and inserts at the greater trochanter. Rotate the patient's leg to find and palpate the piriformis for external rotation.

This quiz focuses on the bony anatomy of the lumbar spine and pelvis, specifically the identification and palpation of key landmarks such as the iliac crest, PSIS, and L5 spinous process. Test your understanding of the anatomical relationships and palpation techniques used in assessing lumbar spine structures.