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Tuesday, June 6, 2023


Brent Brookbush

Brent Brookbush


Human Movement Science & Functional Anatomy of the:


by Brent Brookbush MS, PES, CES, CSCS, ACSM H/FS

Attachments of the Iliacus – https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcTa9J3hHF4rb5nt0IGzKurcS3OKywXe63WnnmT-S7yjAE_iPDGN

What's in a name?

  • Iliacus - Derivation of the latin root "Ilia" referencing flanks or entrails. The medical or anatomical reference is a more modern derivation of this root, specifically referring to structures related to, or in proximity of the "Ilium" or "Iliac" - in the case of the Iliacus, the bone of origin.
  • The "iliacus" and "psoas " are often referred to as a singular structure known as the "iliopsoas" - likely due to their common tendon and insertion. However, this article will address some stark differences, suggesting that these muscles should be considered separately.


  • * Origin: Superior 2/3 or the iliac fossa, internal lip of the iliac crest, iliolumbar and ventral sacroiliac ligaments and ala of the sacrum (11).
    • Insertion: Lateral side of the psoas tendon investing with fibers inserting just lateral and distal to those of the psoas on the lesser trochanter of the femur (11).
      • The iliacus is bordered posteriorly by the ilium, as the "iliac fossa" referenced above is a mild depression that encompasses nearly the entirety of the internal face of the ilium. Anteriorly, the psoas borders the medial portion of the iliacus, the lateral fibers abut the perotineum. As the muscle courses inferiorly it passes just anterior the pubic ramus at the iliopectineal eminence, posterior to the inguinal ligament and lateral to the fascial structure known as the iliopectineal arch.
        • Palpating the iliacus is a skilled palpation. With your partner lying supine, flex their hip and knee into hook-lying (crunch) position. Place your leg under their leg so they can completely relax. With finger pads over finger pads palpate an inch or so medial to the ASIS (between naval and ilium) - this will allow enough tissue slack for you to palpate this deep structure. Allow your fingers to slowly depress in the direction of the anterior iliac surface (slight lateral inclination) as they exhale. Be gentle and move slowly, this palpation can be slightly uncomfortable as you palpate through the thick abdominal wall. You can be assured you are on the iliacus by having the individual flex their hip and feeling for a contraction. If you do not feel a contraction start the palpation over. Most importantly be careful. Although you are less likely to impinge on delicate tissues palpating the iliacus then you are when palpating the psoas, you must be aware of and sensitive to other structures in the region - feeling a pulse (the abdominal aorta or common iliac artery), causing tingling (femoral nerve), causing a sensation of needing to urinate (pressure on the bladder), or causing GI symptoms (nausea, hunger, bowel motility) are all signs that you are likely compressing and or impinging upon sensitive tissues (14). See image and warning about Self-administered release techniques toward the end of this article.
    • Nerve: Femoral nerve via the lumbar plexus, arising commonly from nerve roots L2 & L3, and possibly L1 and/or L4.

Sacral Landmarks - http://classconnection.s3.amazonaws.com/971/flashcards/2439971/jpg/labeled_anterior__posterior_view_of_sacrum1359036067595.jpg



  • * * Primary hip flexor to 90°. Above 90° the psoas and iliacus become the sole hip flexors as the rectus femoris , TFL , and adductors become actively insufficient. The Psoas may become the sole hip flexor during the last 20 -30° of hip flexion, as even the iliacus is likely actively insufficient.

* External rotation of the hip


  • * * By acting on the pelvis and ilium concurrently the ilium is likely a sacral extensor (counter nutation). However, when the line of pull of the iliacus on the sacrum alone is considered, the result would be nutation. Practically, assessment of iliacus activity in each individual will play a larger role in how the iliacus is treated. For more on sacral motion and dysfunction check out this article - Sacroiliac Joint Motion and Predictive Model of Dysfunction

Ventral (Anterior) Sacral Ligaments and Iliolumbar Ligament

Note the Anterior Iliosacroal, Iliolumbar and inguinal ligaments - http://anatomytopics.wordpress.com/files/2009/01/pelvic-ligaments-ant.jpg

Integrated Function:

  • * Stabilization: Hip and sacroiliac joint.

* While the psoas likely plays a larger role in trunk stability and motion of the hip relative to the pelvis, the iliacus plays a larger role in hip motion relative to the femur (13).

  • Eccentrically Decelerates:
    • Hip extension and internal rotation (possibly adduction)
    • Sacral nutation
    • Posterior pelvic tilt
  • Synergists:
    • Hip Flexion: The iliacus has several synergists for hip flexion including the psoas , TFL , rectus femoris , gluteus minimus , and adductors (primarily the pectineus) Interestingly, the psoas and iliacus are the only hip flexors that may contribute to external rotation, where as the TFL, anterior adductors and gluteus minimus are strong internal rotators.
    • Anterior Rotation of the Innominate (Anterior Pelvic Tilt): The iliacus may be a primary contributor to anterior tilting of the pelvis, acting synergistically with the hip flexors mentioned above and the lumbar extensors (erector spinae , multifidus and latissimus dorsi ).
    • Synergistic Dominance: The iliacus may become synergistically dominant as a compensation for core dysfunction including an inhibition of the intrinsic stabilization subsystem . Inhibition of the glute complex (glute medius and glute maximus ) may also contribute to over-activity of the iliacus, as the iliacus becomes a means of compensation for the reduction in sacrum and hip stability.
      • The real cause of "tight" hamstrings (Biceps Femoris , Semitendinosus and Semimembranosus ): The hamstrings are often implicated as short and tight; however, taking a look at the "Overhead Squat Assessment Solutions Table, " "Lumbo Pelvic Hip Complex Dysfunction, " "Sacroiliac Joint Dysfunction ," and common activity of the "Deep Longitudinal Subsystem, " would indicate that these muscles are actually long, but over-active. Although it is tempting to stretch "tight" hamstrings, it is counter productive to increase the length of a muscle that is in a lengthened position during static and dynamic postures. Releasing the hamstrings may prove beneficial, but to improve length of these structures we must optimize pelvic position. With this goal in mind, stretch the short and over-active hip flexors (Hip Flexor Flexibility ) to return the pelvis to a neutral position and reduce the amount of strain created by the dysfunctional position. In essence, you can think of the hip flexors, as winding the hamstrings around the pelvis; just as the tuners of a guitar act to "wind-up" guitar strings. Most often, release and stretch of the the hip flexors will improve hamstring extensibility - Try it.

Psoas passing inferiorly in-front-of the pubic ramus, behind the inguinal ligament and lateral to the iliopectineal arch - http://nadiyogi.com/wp-content/uploads/2012/05/psoas.jpg


  • Hip: May contribute to superior glide of the femoral head, and anterior translation via the line of pull created from iliopectineal eminence to lesser trochanter.

Fascial Integration:

  • * * Origin on the iliolumbar ligaments and fascial continuity -

* [Quadratus Lumborum](https://brentbrookbush.com/online-courses/online-courses//quadratus-lumborum/ "Quadratus Lumborum") to Iliacus:  There  seems to be fascial continuity between the QL and iliacus, as the anterior thoracolumbar fascia blends with the anterior fascia of the iliacus.  Note, both these muscles also originate on the iliolumbar ligaments.  This may be part of a fascial synergy that results in pelvic elevation and hip flexion during the swing phase of gait.  Both muscles have a propensity toward over activity, and although not easily reached using self-administered techniques, manual therapist may consider assessing the iliacus as well as the QL in patients who exhibit [LPHCD](https://brentbrookbush.com/online-courses/online-courses//lumbo-pelvic-hip-complex-dysfunction-lphcd/ "LPHCD") and/or [SIJD](https://brentbrookbush.com/online-courses/online-courses//sacroiliac-joint-motion-and-predictive-model-of-dysfunction/ "Sacroiliac Joint Dysfunction").  You may visit the [Quadratus Lumborum](https://brentbrookbush.com/online-courses/online-courses//quadratus-lumborum/ "Quadratus Lumborum") article for further consideration of the fascial continuity between iliacus, QL and the diaphragm.

* **Origin on the Lesser Trochanter** -* The most obvious fascial connection exists between the psoas and iliacus which share a common tendon.

* The nearly continuous line of insertion from psoas and iliacus to pectineus, does strengthen the argument made for the [pectineus](https://brentbrookbush.com/online-courses/online-courses//adductors/ "Adductors") as a hip flexor.  An argument that already had some validity due to portions of the muscle being innervated by the femoral nerve.

Insertions on Femur: Note the continuity between psoas, iliacus, and pectineus - Gray's Anatomy via wikipedia.com

May Contribute to the Following Impairments:

  • Knee Pain
    • Patellar tendonitis (Jumper’s Knee)
    • Lateral knee pain (Runner’s Knee)
    • Hamstring tendonitis
    • Generalized knee pain
  • Sacroiliac Joint Pain and Dysfunction
  • Hip Pain
    • Impingement Syndrome (FAI)
    • Lesser trochanteric bursitis
    • Ischial tuberosity bursitis
    • Generalized hip pain
    • Groin pain
    • Groin strain
  • Lumbar spine pain
    • Low back pain
    • Excessive lordosis
    • Functional scoliosis
    • Lateral shift of lumbar spine
  • Trigger points may be felt as lower abdominal, pubic, or groin pain.

The Evolution of Man

Behavior in Postural Dysfunction:

This muscle has a tendency toward adaptive shortening and over-activity. We find altered activity in lumbo pelvic hip complex dysfunction and sacroiliac joint dysfunction. Note this is different than the activity noted in the psoas which may adopt either short/over-active or long/under-active motor behavior. It has been hypothesized that an over-active iliacus may relatively inhibit the psoas during flexion, similar to the way an over-active tensor fasciae latae may inhibit the gluteus medius in abduction. The cause of this is likely a sequencing issue propagated by changes in excitation threshold, rather than altered reciprocal inhibition which is often cited as the cause of dysfunction. For more information on these predictive models of dysfunction click on the link below:

* [Sacroiliac Joint Dysfunction](https://brentbrookbush.com/online-courses/online-courses//sacroiliac-joint-motion-and-predictive-model-of-dysfunction/ "Sacroiliac Joint Motion and Predictive Model of Dysfunction") (SIJD)

In the models above the iliacus is short and overactive when an individual adopts an anterior pelvic tilt. Based on the function of the psoas in lumbar stabilization, the seemingly contradictory research on psoas muscle activity, and practice (assessment of patients with lumbo pelvic hip dysfunction) it is my opinion that the iliacus is actually the larger contributor to LPHCD and SIJD. This has significant implications for manual therapists who practice release techniques on these structures, and may imply that psoas activation exercises are in need of further development. Unfortunately, this does create a gap in our repertoire of exercise as the Iliacus cannot be easily (or safely) released using self-administered techniques. If the iliacus is determined to be the cause of dysfunction than referral to a skilled manual therapist is essential for a return to optimal performance.

In the predictive model of Sacroiliac Joint Dysfunction (SIJD) the iliacus is short and over-active on the side opposite the dysfunction (the side exhibiting relative anterior innominate rotation). However, increased tone would also result in increased rigidity of the sacroiliac joint implicating an overactive iliacus on the dysfunctional side of SIJD as well. To me, this scenario resembles the over-activity that is often noted in both piriformis  in SIJD. In practice, I believe it is more advantageous to initially treat only the side that is both short and overactive, in essence, only release and lengthen the iliacus on the side exhibiting relative anterior innominate rotation.

Signs of Altered Length/Tension and Tone:

  • * * Overhead Squat Assessment:

* Asymmetrical Weight Shift - Short/Overactive on side opposite SIJD* Excessive Forward Lean - Short/Overactive

* Knees Bow Out - Short/Overactive

* Anterior Pelvic Tilt (Excessive Lordosis) - Short/Overactive
* **Single Leg Squat:*** Excessive Forward Lean - Short/Overactive

* Turn Out - Short/Overactive (potential Long/Under-active on opposite side)
* **Goniometry** (Indication of restriction and over-activity):* Hip Internal Rotation < 45° w/ muscular end feel (capsular end feel may still imply psoas tightness, but in conjunction with other structures (TFL, posterior capsule, etc.)

* Hip Extension < 15°
* **Special Tests for Psoas Tightness:*** Thomas Test
* **Palpation of Psoas:*** Tenderness (indication of over-activity)

* Trigger points (indication of over-activity and chronic postural dysfunction)

Trigger Point Map for Psoas:

  • Note: Manual techniques are the only safe and effective way to address this muscular dysfunction

Trigger Point Map of Psoas - www.triggerpoints.net

Specific Test For Psoas/Iliacus Extensibility

Modified Thomas Test

Specific Techniques for the Psoas and Iliacus:

Manual Release of the Iliacus and Psoas

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Static Hip Flexor Stretch:

Active Hip Flexor Stretch:

Dynamic Hip Flexor Stretch:

Releasing the Iliacus

Unfortunately the iliacus is buried underneath the lower portion of the rectus abdominis , on the internal surface of the ilium, and is in close proximity to some very sensitive structures (Namely, the common iliac artery and branches of the lumbar plexus and femoral nerve.). Although, I have seen individuals use a softball to release their own iliacus (lying on belly), I believe this is best left to the skilled hands of a manual therapist. It is hard to justify the risk that may be associated with regular (2-3 minutes per side/most days of the week) pressure and tension placed on arteries, nerves, and internal organs. Besides how are you going to apply pressure toward the iliac fossa (medial to lateral) when lying face down on a ball creates anterior to posterior force?

Signs of impinging on sensitive structures during manual or device assisted release:

  • * feeling a pulse (pressure on the abdominal aorta or common iliac artery)
    • causing tingling (pressure or stretch of the femoral nerve),
    • causing a sensation of needing to urinate (pressure on the bladder)
    • causing GI symptoms such as nausea, hunger, bowel motility (impingement or stretching of the intestine)

Picture of a manual practitioner palpating the iliacus for manual release:

Image of Manual Therapist Releasing Iliacus and Psoas - http://brucebutlertherapy.blogspot.com/2010/11/iliacus-psoas-active-release-technique.html


  • * 3. Phillip Page, Clare Frank Robert Lardner Assessment and Treatment of Muscle Imbalance: The Janda Approach © 2010 Benchmark Physical Therapy, Inc., Clare C. Frank, and Robert Lardner

6. Dr. Mike Clark & Scott Lucette, “_NASM Essentials of Corrective Exercise Training_” © 2011 Lippincott Williams & Wilkins

9. Donald A. Neumann, “Kinesiology of the Musculoskeletal System: Foundations of Rehabilitation – 2nd Edition” © 2012 Mosby, Inc.

12. Michael A. Clark, Scott C. Lucett, _NASM Essentials of Personal Training: 4th Edition_, © 2011 Lippincott Williams and Wilkins

15. Leon Chaitow, _Muscle Energy Techniques: Third Edition_, © Elsevier 2007

18. Tom Myers, _Anatomy Trains: Second Edition_. © Elsevier Limited 2009

21. Shirley A Sahrmann, _Diagnoses and Treatment of Movement Impairment Syndromes,_ © 2002 Mosby Inc.

24. David G. Simons, Janet Travell, Lois S. Simons, _Travell & Simmons’ Myofascial Pain and Dysfunction, The Trigger Point Manual, Volume 1. Upper Half of Body: Second Edition_,© 1999 Williams and Wilkens

27. Cynthia C. Norkin, D. Joyce White, Measurement of Joint Motion: A Guide to Goniometry – Third Edition. © 2003 by F.A. Davis Company

30. Cynthia C. Norkin, Pamela K. Levangie, _Joint Structure and Function: A Comprehensive Analysis: Fifth Edition_ © 2011 F.A. Davis Company

33. Florence Peterson Kendall, Elizabeth Kendall McCreary, Patricia Geise Provance, Mary McIntyre Rodgers, William Anthony Romani__,_ Muscles: Testing and Function with Posture and Pain: Fifth Edition © 2005 Lippincott Williams & Wilkins_

36. Andrew Biel, Trail Guide to the Human Body: 4th Edition, © 2010

39. Carolyn Richardson, Paul Hodges, Julie Hides.  Therapeutic Exercise for Lumbo Pelvic Stabilization – A Motor Control Approach for the Treatment and Prevention of Low Back Pain: 2nd Edition (c) Elsevier Limited, 2004

42. Craig Liebenson, Rehabilitation of the Spine: A Practitioner’s Manual, (c) 2007 Lippincott Williams & Wilkins

45. Stuart McGill, Low Back Disorders: Second Ediction © 2007 Stuart M. McGill

48. Robert Schleip, Thomas W. Findley, Leon Chaitow and Peter A. Huijing.  Fascia: The Tensional Network of the Human Body.  (c) 2012 Elsevier Ltd.

51. Bogduk N., Pearcy M, Hadfield G. Anatomy and biomechanics of the psoas major.  Clinical Biomechanics 7:109-119

54. Andrew Vleeming, Vert Mooney, Rob Stoeckart.  Movement, Stability & Lumbopelivic Pain: Integration of Research and Therapy (c) 2007, Elsevier Limited

© 2014 Brent Brookbush

Questions, comments, and criticisms are welcome and encouraged.