Iliac Crest: How to Locate, Measure, and Utilize this Key Landmark

How to Measure Iliac Crest?

Measuring the iliac crest involves precise anatomical palpation to locate this prominent bony landmark of the pelvis, which is essential for accurate body composition assessments, postural analyses, and other biomechanical evaluations.

Understanding the Iliac Crest

The iliac crest is the thick, superior curved border of the il ilium, the largest of the three bones that form the hip bone (pelvis). It extends from the anterior superior iliac spine (ASIS) at the front to the posterior superior iliac spine (PSIS) at the back. This significant anatomical landmark serves as a crucial attachment site for numerous muscles of the trunk, hip, and thigh, including the oblique abdominal muscles, latissimus dorsi, and gluteal muscles. Its prominence makes it a readily palpable and vital reference point in exercise science and clinical practice.

Why Measure the Iliac Crest?

Accurate identification and measurement related to the iliac crest are fundamental for several applications:

• Body Composition Assessment: The iliac crest is a key landmark for:
  • Waist Circumference: Often measured at the narrowest point between the lower rib margin and the iliac crest, or sometimes at the level of the iliac crest itself, providing an indicator of abdominal adiposity and associated health risks.
  • Suprailiac Skinfold: A common site for skinfold caliper measurements, used in conjunction with other sites to estimate body fat percentage.
  • Hip Circumference: While not directly on the iliac crest, the crest's orientation helps define the pelvic region for accurate hip measurements.
• Postural Analysis: The relative height and symmetry of the iliac crests can indicate pelvic tilt (anterior, posterior, or lateral) and potential leg length discrepancies, which can impact gait, spinal alignment, and injury risk.
• Biomechanical Analysis: Understanding the position of the iliac crest is crucial for analyzing movement patterns, assessing muscle imbalances, and designing effective exercise programs.
• Clinical Assessment: In physical therapy and rehabilitation, it helps in diagnosing and monitoring conditions related to the pelvis and lower back.

Preparing for Measurement

Before attempting to locate or measure the iliac crest, ensure proper preparation for accuracy and comfort:

• Environment: Choose a private, well-lit space that allows for comfortable movement.
• Tools:
  • A non-elastic measuring tape (for circumference measurements).
  • Skinfold calipers (if performing body fat assessment).
  • A washable marker (optional, for marking the site).
• Subject Position: The individual should stand relaxed with feet hip-width apart, arms gently resting at their sides. Light clothing or direct skin exposure in the area is necessary for accurate palpation.
• Communication: Clearly explain the procedure to the individual, ensuring their comfort and consent.

Step-by-Step Guide to Locating the Iliac Crest

Locating the iliac crest requires careful palpation. Follow these steps:

• Step 1: Initial Palpation: Begin by placing your hands on the sides of the individual's waist, just above their hips.
• Step 2: Move Downwards and Inwards: Gently slide your fingers downwards from the lower ribs until you feel a firm, bony resistance. This is the top edge of the pelvis.
• Step 3: Trace Anteriorly: Once you've found the general area, follow the bony ridge forward towards the front of the body. You will feel it curve anteriorly and terminate in a distinct bony prominence known as the Anterior Superior Iliac Spine (ASIS). This is the most anterior point of the iliac crest.
• Step 4: Trace Posteriorly: From the initial bony resistance, trace the ridge backwards towards the spine. It will curve posteriorly and terminate in the Posterior Superior Iliac Spine (PSIS), which is generally less prominent and harder to palpate, often marked by "dimples of Venus" in some individuals.
• Step 5: Identify the Most Superior Point: For measurements like waist circumference, you often need to identify the highest point of the iliac crest. This is typically found laterally, around the mid-axillary line (an imaginary line extending downwards from the armpit).
• Step 6: Confirm Bilaterally: Repeat the process on the opposite side to ensure you have accurately located both iliac crests and to assess for symmetry.

Using the Iliac Crest as a Measurement Landmark

Once the iliac crest is accurately located, it serves as a reference for various measurements:

• Waist Circumference: While some protocols use the narrowest point of the torso, another common method involves measuring at the level of the most superior aspect of the iliac crest. The tape should be horizontal, snug but not compressing the skin, and measured at the end of a normal exhalation.
• Suprailiac Skinfold: This measurement is taken by pinching a diagonal fold of skin and subcutaneous fat approximately 2 cm superior (above) and 2 cm medial (towards the midline) to the ASIS. The fold should be oriented along the natural Langer's lines of the skin.
• Pelvic Tilt Assessment: Visual or goniometric assessment of the relative heights of the ASIS and PSIS (and their relationship to the greater trochanter) can help determine if the pelvis is tilted anteriorly, posteriorly, or laterally.

Tips for Accuracy and Reliability

• Consistency: Always use the same palpation technique, measuring tools, and take measurements at the same time of day (e.g., morning before meals).
• Practice: Palpation is a skill that improves with consistent practice.
• Subject Relaxation: Ensure the individual is relaxed and not tensing their abdominal or gluteal muscles, as this can alter the position of the landmarks.
• Normal Respiration: For circumference measurements, take the reading at the end of a normal exhalation.
• Multiple Readings: Take 2-3 measurements and average them to minimize error. If readings vary significantly, take additional measurements.
• Privacy and Professionalism: Always maintain the individual's privacy and communicate clearly and respectfully throughout the process.

When to Seek Professional Guidance

While self-measurement can be useful for tracking personal progress, for highly accurate assessments or clinical interpretations, it is advisable to consult a qualified professional:

• Certified Personal Trainers: Can accurately perform body composition assessments and provide exercise programming based on findings.
• Registered Dietitians: Can interpret body composition data in the context of nutritional health.
• Physical Therapists/Chiropractors: Experts in musculoskeletal assessment, including postural analysis and identifying structural asymmetries.
• Healthcare Providers: For any health concerns related to abdominal adiposity or chronic pain.

Conclusion

The iliac crest is a foundational anatomical landmark in exercise science and health assessment. Mastering its precise location is paramount for obtaining accurate and reliable measurements, whether for tracking body composition changes, analyzing posture, or understanding biomechanical function. By applying systematic palpation techniques and adhering to best practices, you can confidently utilize the iliac crest as a powerful reference point in your health and fitness journey.