Iliac Crest

The iliac crest is the thick, curved superior border of the ilium and one of the most important palpable landmarks of the pelvis. It forms the upper contour of the lateral pelvis and can usually be followed through the skin from the anterior part of the hip toward the posterior pelvis.

Anteriorly, the crest terminates at the anterior superior iliac spine (ASIS). Posteriorly, it terminates at the posterior superior iliac spine (PSIS). Between these points, the crest provides extensive attachment for muscles and fascia of the abdominal wall, back, and hip.

Because the highest points of the iliac crests lie approximately at the level of the L4 vertebra or L4-L5 intervertebral space, the crest is also an important landmark for estimating lumbar vertebral levels.

Location

The iliac crest forms the superior border of the ilium, the largest component of the hip bone.

It extends along the upper margin of the pelvis from the ASIS anteriorly to the PSIS posteriorly.

Surface Position

The crest is palpable along the superior lateral aspect of the pelvis.

Its prominence varies with body habitus, muscular development, subcutaneous tissue, age, and pelvic morphology.

Shape

The iliac crest is curved rather than straight.

Viewed from above, it follows the contour of the iliac wing and contributes to the characteristic shape of the upper pelvis.

Anterior Superior Iliac Spine

The ASIS forms the anterior termination of the iliac crest and is a prominent palpable point at the anterior pelvis.

It is an important attachment site and surface landmark for the inguinal region, lower abdominal wall, and proximal thigh.

Posterior Superior Iliac Spine

The PSIS forms the posterior termination of the iliac crest.

It lies near the posterior sacroiliac region and may correspond to a visible skin depression or dimple in some individuals.

Palpation

The iliac crest can be palpated by placing the hands on the lateral waist and moving inferiorly until the firm superior border of the pelvis is encountered.

The examiner can then follow the crest anteriorly toward the ASIS and posteriorly toward the PSIS.

Highest Point of the Iliac Crest

The superior-most point of each iliac crest provides a useful reference for the lower lumbar vertebral column.

An imaginary line connecting these points is called the intercristal line or supracristal line.

Intercristal Line

The intercristal line is traditionally described as crossing the L4 spinous process or the nearby L4-L5 intervertebral space.

This relationship is approximate and varies among individuals.

Tuffier's Line

The intercristal line is also commonly known as Tuffier's line.

It is widely used as a surface guide when estimating lower lumbar vertebral levels for examination and neuraxial procedures.

L4 Relationship

Landmark	Approximate Relationship
Highest points of iliac crests	Define intercristal line
Intercristal line	Approximately L4 or L4-L5 level
ASIS	Anterior end of iliac crest
PSIS	Posterior end of iliac crest

External Lip

The iliac crest has an external lip that provides attachment for muscles and fascia on the external aspect of the pelvis.

This margin can be especially prominent along portions of the lateral crest.

Internal Lip

The internal lip forms the medial margin of the iliac crest.

It provides attachment for structures related to the abdominal wall and posterior abdominal region.

Intermediate Zone

Between the external and internal lips is an intermediate zone.

Together, these features create a broad attachment surface for multiple muscles and fascial structures.

Iliac Tubercle

The iliac tubercle is a prominence on the external lip of the iliac crest, typically located posterior to the ASIS.

It provides an additional palpable and attachment landmark on the lateral pelvis.

Muscle Attachments

The iliac crest provides attachment for numerous muscles of the trunk and hip.

These attachments help transfer forces between the axial skeleton, pelvis, and lower limb.

Abdominal Muscle Attachments

Major abdominal wall muscles attached to the iliac crest include:

• External oblique
• Internal oblique
• Transversus abdominis

External Oblique

The external oblique inserts partly onto the anterior portion of the iliac crest.

Its attachment contributes to the continuity between the lateral abdominal wall and pelvis.

Internal Oblique

The internal oblique arises partly from the iliac crest.

Its fibers contribute to the muscular layers of the anterolateral abdominal wall.

Transversus Abdominis

The transversus abdominis also takes origin in part from the iliac crest.

This attachment helps anchor the deepest broad muscle of the anterolateral abdominal wall.

Tensor Fasciae Latae

The tensor fasciae latae arises from the ASIS and adjacent anterior iliac crest.

It contributes to tension within the iliotibial tract and assists with movements and stabilization of the hip.

Gluteus Maximus

The gluteus maximus has an origin from the posterior ilium, including the region posterior to the posterior gluteal line and adjacent iliac crest.

Its superior fibers contribute to the contour of the posterolateral pelvis.

Gluteus Medius

The gluteus medius arises from the external surface of the ilium inferior to the iliac crest.

The superior pelvic contour therefore provides an important surface reference for the location of this major hip abductor.

Quadratus Lumborum

The quadratus lumborum attaches to the iliac crest posteriorly.

It extends superiorly toward the twelfth rib and lumbar transverse processes and contributes to stabilization and movement of the trunk.

Erector Spinae

The erector spinae muscle group has broad inferior attachments involving the posterior iliac crest, sacrum, and associated ligaments.

These attachments contribute to the powerful posterior musculature of the vertebral column.

Latissimus Dorsi Relationship

The latissimus dorsi has attachments associated with the posterior iliac crest through its broad origin and thoracolumbar fascial connections.

This contributes to the continuity between the pelvis and superficial musculature of the lower back.

Thoracolumbar Fascia

The thoracolumbar fascia attaches to the iliac crest and forms an important fascial framework of the lumbar region.

It provides attachment for several muscles and contributes to force transmission between the trunk and pelvis.

Inguinal Ligament Relationship

The inguinal ligament extends from the ASIS to the pubic tubercle.

Although it does not follow the iliac crest itself, its origin from the ASIS makes the anterior end of the crest an important landmark for the inguinal region.

Pelvic Orientation

The right and left iliac crests help define the superior lateral boundaries of the bony pelvis.

Their relative height and symmetry can be assessed during examination of pelvic alignment.

Pelvic Tilt

Differences in the apparent height of the iliac crests may occur with pelvic tilt, lower limb length differences, scoliosis, posture, muscular imbalance, or structural variation.

Comparison should be made with the patient positioned as symmetrically as possible.

Relationship to the Sacroiliac Joint

The posterior iliac crest approaches the sacroiliac region near the PSIS.

The PSIS is commonly used as a surface landmark when examining the posterior pelvis and sacroiliac area.

Relationship to the Greater Trochanter

The greater trochanter of the femur lies inferior and lateral to the iliac crest.

Palpation of both landmarks helps define the surface orientation of the hip and lateral pelvic region.

Relationship to the Flank

The soft tissue region between the lower ribs and iliac crest forms part of the flank.

The crest therefore provides the inferior bony boundary for portions of the lateral abdominal and lumbar regions.

Inferior Lumbar Triangle

The iliac crest forms the inferior boundary of the inferior lumbar triangle, also known as Petit's triangle.

This small posterolateral abdominal wall region is also bounded by latissimus dorsi and external oblique.

Boundaries of the Inferior Lumbar Triangle

Boundary	Structure
Inferior	Iliac crest
Medial	Latissimus dorsi
Lateral	External oblique
Floor	Internal oblique

Clinical Significance

Lumbar Vertebral Localization

The iliac crests are widely used to estimate the level of L4 and L4-L5.

This makes them important surface landmarks during examination of the lumbar spine.

Lumbar Puncture

The intercristal line can help identify lower lumbar interspaces used during lumbar puncture.

Spaces such as L3-L4 or L4-L5 are commonly selected because they are below the usual termination of the adult spinal cord.

Spinal and Epidural Anesthesia

The iliac crest is also used as an external reference during neuraxial anesthesia.

Because the relationship between the intercristal line and vertebral levels varies, ultrasound or other methods may be used when more precise localization is needed.

Bone Graft Harvesting

The iliac crest is an important source of autologous bone graft.

Both anterior and posterior portions of the crest may provide cancellous and corticocancellous bone for reconstructive procedures.

Bone Marrow Procedures

Parts of the ilium are accessible for bone marrow aspiration or biopsy.

The posterior iliac region is commonly used because of its accessibility and substantial marrow-containing bone.

Trauma

Direct trauma to the iliac crest can cause pain, bruising, soft tissue injury, or fracture.

Because several muscles attach to the crest, forceful impact can also produce painful muscular and periosteal injury.

Iliac Crest Contusion

A direct blow to the exposed lateral crest can produce a painful contusion sometimes referred to in sports settings as a hip pointer.

The injury involves tissues overlying or attached to the iliac crest rather than the hip joint itself.

Lumbar Hernia

The iliac crest forms one boundary of the inferior lumbar triangle, a potential site of lumbar hernia.

Knowledge of the crest and neighboring muscular borders helps localize this posterolateral abdominal wall region.

Pelvic Examination

Comparison of iliac crest heights is commonly incorporated into musculoskeletal examination.

Apparent asymmetry may provide clues about pelvic position, spinal alignment, or lower limb mechanics but requires interpretation with other findings.

Surface Landmark Variability

The iliac crest is generally easy to palpate, but the relationship of its highest point to the lumbar spine is variable.

Body habitus, sex, posture, pelvic shape, spinal curvature, and developmental anatomy can influence the apparent level.

Iliac Crest Compared with ASIS and PSIS

Feature	Iliac Crest	ASIS	PSIS
Position	Superior border of ilium	Anterior end of crest	Posterior end of crest
Palpability	Palpable curved ridge	Prominent anterior point	Posterior point, sometimes associated with skin dimple
Major use	Pelvic contour and L4 estimation	Inguinal and anterior hip landmark	Posterior pelvic and sacroiliac landmark

Key Surface Anatomy Features

Feature	Key Point
Bone	Ilium
Structure	Superior border of ilium
Anterior endpoint	Anterior superior iliac spine
Posterior endpoint	Posterior superior iliac spine
Surface characteristic	Broad palpable curved ridge
Lumbar landmark	Intercristal line approximates L4 or L4-L5
Major muscle relationships	Abdominal, back, and hip muscles
Important fascia	Thoracolumbar fascia
Procedural relevance	Neuraxial level estimation and bone graft harvest
Posterolateral landmark	Inferior boundary of inferior lumbar triangle

Anatomical Importance

The iliac crest is one of the most useful palpable landmarks of the pelvis and lower trunk. Its curved superior border can be followed from the ASIS anteriorly toward the PSIS posteriorly, providing a clear external representation of the upper margin of the ilium.

Its importance extends beyond the pelvis because the highest points of the two crests define the intercristal line, which provides an approximate reference for the L4 or L4-L5 vertebral level. The crest also serves as an extensive attachment site for muscles and fascia linking the abdomen, back, pelvis, and lower limb.

Clinically, the iliac crest is used in musculoskeletal examination, lumbar level estimation, neuraxial procedures, bone graft harvesting, and assessment of pelvic alignment. Its broad accessibility makes it a fundamental landmark in both regional and surface anatomy.