new intro

The iliac crest in Radiography

The iliac crest is an bony structure of the human body that can be externally palpated. It is felt at both sides of the lower abdomen, and extends towards the back of the body. Anatomically, it is the upper border of the hip bone. The iliac crests are major surface landmarks that allow us to achieve accurate positioning for many common radiographic examinations such as: 

- Abdomen/ Kidney-ureter-bladder examinations

- Pelvic examinations

- Lumbosacral spine examinations

However, the iliac crests are not always easily palpable. Patients who are obese, or have congenital or acquired deformities of the hip bone, usually present difficulties during palpation. But such conditions are not at all exclusive; different ethnic body types and different responses to physical touch can also create difficulties in palpating for the iliac crests. We have observed that there were patients who had been incredibly ticklish, and have seen many who were in pain or uncomfortable at the idea of being touched at their sides. 

Thus, it is not uncommon to see radiographers using the level of umbilicus ("belly button") as an alternative way to determine the level of the iliac crests, in actual practice. 

Vertebral location of iliac crest and the umbilicus

Transverse planes of the torso ("level") can be measured according to the 24 vertebrae levels. According to literature, the iliac crests are relatively fixed at the level of the fourth to fifth lumbar vertebrae (L4-L5)¹. The level of the umbilicus, on the other hand, is not as precisely stated as that of the iliac crests, but is given to be between the L3 and L4 vertebral bodies², with a normal variation ranging between L3 to L53. Based on a 2016 study³, of which 72.5% of the sample size were of Caucasian ethnicity, the level of the umbilicus was shown to be at a range of distances in relation to level of the iliac crests. 

Figure 1

This raises the question of whether the level of the umbilicus is an accurate measure of the level of the iliac crests. Our study aims to investigate its statistical reliability and correlation to patient size. 

¹Bogduk, Nikolai; Endres, Stephen M. (2005). Clinical anatomy of the lumbar spine and sacrum (4th ed.). Elsevier Health Sciences. p. 106.

Chakraverty, R., Pynsent, P., & Isaacs, K. (2007). Which spinal levels are identified by palpation of the iliac crests and the posterior superior iliac spines? Retrieved July 28, 2016, from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2100271/

²Ellis, Harold (2006). Clinical Anatomy: Applied Anatomy for Students and Junior Doctors. New York: Wiley.

O'Rahilly, Ronan; Müller, Fabiola; Carpenter, Stanley; Swenson, Rand (2004). "Abdominal walls". Basic Human Anatomy: A Regional Study of Human Structure. Dartmouth Medical School.

³Evidence-Based Regulations : Annals of Plastic Surgery. (n.d.). Retrieved July 28, 2016, from http://journals.lww.com/annalsplasticsurgery/pages/articleviewer.aspx?year=2016

Figure 1: http://www.sbadandrmc.com/our-services-patient-education/digital-x-rays-70ea/abdominal-x-ray-kub/ (image)