What is the iliac crest?

From the Guidelines

The iliac crest is a crucial anatomical landmark that serves as an attachment site for various muscles and a reference point for medical procedures, with its location and characteristics being essential for accurate assessments and interventions. The iliac crest is the curved upper border of the ilium, extending from the anterior superior iliac spine to the posterior superior iliac spine, and can be felt just below the waist 1. This prominent ridge provides attachment sites for numerous muscles, including the external oblique, internal oblique, transversus abdominis, latissimus dorsi, and quadratus lumborum.

Key Functions and Characteristics

• The iliac crest is an important site for bone marrow aspiration and biopsy procedures, particularly at the posterior superior iliac spine, due to its accessibility and relatively low risk of complications.
• It serves as a reference point for various medical procedures and examinations, such as determining the level of the L4 vertebra, which typically aligns with the top of the iliac crest.
• Pain in this region may indicate various conditions, including muscle strain, inflammation, or referred pain from other structures.

Measurement and Assessment

The suprailiac skinfold is measured in the midaxillary line immediately superior to the iliac crest, involving palpation for the iliac crest, grasping the skin at an oblique angle, and applying the caliper jaws about 1 cm from the fingers holding the skinfold 1. The skinfold is recorded to the nearest 0.1 cm, with the mean of two or four measurements taken if necessary.

Clinical Significance

Understanding the iliac crest's anatomy and functions is vital for accurate diagnoses and effective treatments, particularly in cases involving muscle strain, inflammation, or referred pain from other structures. The iliac crest's role as a reference point for medical procedures and examinations highlights its importance in clinical practice 1.

From the Research

Iliac Crest Morphometry

• The iliac crest is a common site for harvesting bone grafts, and its morphometry is of vital importance in orthopedic surgery 2.
• Measurements of the iliac crest, including length and thickness, have been conducted in various studies to provide a useful guide for harvesting bone grafts 2.
• The thickness of the iliac crest was found to be greatest at 6 cm from the anterior superior iliac spine (ASIS) in both males and females, while the minimum thickness was observed at 12 cm and 10 cm from ASIS in male and female bones, respectively 2.

Anatomical Consistency of the Iliac Crest

• The anatomical consistency of the posterior superior iliac spine (PSIS) has been compared to the iliac crest as landmarks used for spinal palpation 3.
• The study found that the PSIS corresponded to the S2 spinous process in 81% of subjects, while the iliac crest corresponded to the L4 spinous process in 59% of subjects 3.
• The distance between the PSIS and the S2 spinous process was found to be closer than the distance between the iliac crest and the L4 spinous process 3.

Spinal Level of the Iliac Crest

• A systematic review and meta-analyses have been conducted to determine the spinal level of the iliac crests as measured through manual palpation and radiographic imaging procedures 4.
• The study found that the imaged crests were most consistent with and closest to the L4-5 interspace in females and L4 spinous process in males, while the palpated crests were nearest to the L3-4 interspace in both males and females 4.
• The palpated crest line was found to be 0.7 levels cephalad to the imaged crest line in males and 1.0 levels cephalad to the imaged line in females 4.

Anatomical Considerations for Surgical Procedures

• The iliac crest has been found to be an anatomical consideration for percutaneous endoscopic discectomy using a transforaminal approach 5.
• The study found that the trajectory of the transforaminal approach can be limited by the surrounding anatomical structures, including the iliac crest 5.
• The maximum inclination angle of the trajectory was found to be greater at the L4-L5 disc level than at the L5-S1 disc level, indicating that treatment for central type lumbar disc herniation at the L5-S1 disc level may be more difficult due to the iliac crest 5.

Limitations of Anatomical Landmarks for Lumbar Puncture

• The use of anatomical landmarks, including the iliac crest, for identifying the correct level for lumbar puncture has been found to be misleading in more than 30% of cases 6.
• The study found that the concordance rate between clinical examination and ultrasound assessment of intervertebral space identification for lumbar puncture was 64% among patients undergoing lower limb surgery 6.
• The use of spinal ultrasound can reduce the incidence of inappropriate lumbar puncture level in orthopaedic patients 6.