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Tuesday, June 6, 2023

Sacroiliac Joint Motion and Predictive Model of Dysfunction

Brent Brookbush

Brent Brookbush


Sacroiliac Joint Motion and Predictive Model of Dysfunction

Further Issues with our Current Model of LPHCD

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


In this article we will discuss a new model of sacroiliac joint (SIJ) motion, and a predictive model of postural dysfunction originating from this joint complex.

This article could be viewed as "Part 2" of the "Lumbo Pelvic Hip Complex Dysfunction (LPHCD)" article. Sacroiliac Joint Dysfunction (SIJD) seems to be a dysfunction within a dysfunction. That is SIJD exists inside the global postural dysfunction that is LPHCD . My guess is that global postural dysfunction (LPHCD ) will lead to SIJD, or Lower Leg Dysfunction will lead to SIJD, and progress to include the changes associated with the LPHCD .

It is my recommendation that individuals new to corrective exercise start with the LPHCD article, and learn the exercises and sample routine in the article "Lumbo Pelvic Hip Complex Corrective Exercise and Sample Routine," , before continuing with this article and the corrective exercise strategy in "Sacroiliac Joint Dysfunction Corrective Exercise and Sample Routine". For the most part, the exercises used for both dysfunctions are the same; however, assessing which side each technique should be performed on is a bit tricky. I can personally attest to the effectiveness of using the LPHCD Sample Routine, even in the presence of SIJD. It may even be that the analysis of SI joint motion exists as a “dysfunction within a dysfunction,” and that treating SI joint dysfunction will inevitably lead back to this strategy for correction of the “global impairment” in LPHCD .

Why the model of "Lumbo Pelvic Hip Complex Dysfunction" is not enough:

Here is the list of long and short structures from the LPHCD Model:



For starters, several of the muscles listed on the “long” side of the graph are also commonly overactive. Generally, over-activity is an indication that a muscle is in a shortened position (it is hypothesized that muscle length affects excitation threshold). Although, it may be hypothesized that a typically overactive muscle may be pulled into a lengthened position by a group of over-active antagonists; it is only logical that a group of over-active muscles in a lengthened position would overpower their antagonist and pull the joint into a position where a shorter resting length may be maintained. If our graph suggests a single muscle that is “long/overactive” in opposition to a group of “short/overactive” antagonists we may consider it an acceptable solution (remember the “posterior deltoid ” in UBD ), but in the case of the graph above, it is the large and powerful biceps femoris and adductor magnus  muscles that exhibit this strange pairing of attributes. Simply labeling these muscle long/overactive seems questionable and can only lead to crude practice - this logic may be a rationale to use both flexibility and activation techniques on the same muscle. A refinement of this model needs to be developed to explain this occurrence.

What can “trigger points” tell us:

The most puzzling occurrence of trigger points, based on the graph above, may be the piriformis . Trigger points are often noted in association with fairly common pathologies including SI joint dysfunction, sciatica and low back pain. It seems unlikely that a muscle that is listed “long and under-active” in our graphs would develop painful trigger points, over-activity, and would be the primary culprit in several common pathologies.

Practice has highlighted a propensity toward the development of trigger points in the biceps femoris and adductor magnus . Their propensity toward overactive is mentioned above, and is reinforced by this phenomenon.

The psoas is often considered “public enemy #1” in relation to low back pain and LPHCD , as it contributes to both hip flexion and lumbar extension. However, practice would suggest that the psoas is often free of trigger points, even in the most obvious cases of LPHCD . It is far more common that the psoas is trigger point laden on one side only, or that tenderness is found in the iliacus only. The TFL , iliacus , vastus lateralis , and rectus femoris are far more likely to exhibit over-activity and trigger points than the psoas ; creating another incongruency in our model.

Rarely Symmetrical:

The description of LPHCD as an “anterior pelvic tilt” or “lower cross syndrome,” implies a bilateral change in muscle activity, relative length, and joint dyskinesis; however, this is rarely the case in practice. The majority of LPHCD cases present in asymmetrical fashion. This may be exhibited as a “hip hike” or “weight shift” in dynamic assessment, considerable differences in flexibility and strength from right to left, and/or pain originating on one side of the body. If an anterior pelvic tilt or lower cross syndrome alone explained LPHCD , than these assessments would result in nearly symmetrical findings (both sides tight, weak, etc…). This may be a clue that the dysfunction is centrally located, or originating from a central structure that has adopted an uneven position around a central axis. Similar to twisting, bending, or moving the legs, analogous to the two sides of a tetter-totter moving around a central fulcrum. The structure in the lumbo-pelvic-hip complex that best fits this analogy is the sacrum.

Summary of Incongruencies with the Current LPHCD Model:

Motion of the Sacrum:

The sacrum has a complicated set of joint actions that has been explained using a variety of terms. This has lead to much confusion around sacral and iliosacral motion. For this reason I have tried to clarify motion with the simplest set of definitions I am aware of, and ask that you review them before reading on. I have also presented sacral motion in layers. Starting first with isolated sacral motion, then paired actions, then relative sacral motions, and finally introducing the global effects of sacral motion

Layer 1: Relatively Isolated Motion

This terminology I have chosen relates to sacral motion away from a neutral sacral position.

  • Flexion – anterior motion of the sacral base (relative posterior motion of the coccyx) in the sagittal plane
  • Extension – posterior motion of the sacral base (relative anterior motion of the coccyx) in the sagittal plane.
  • Elevation – superior motion of one articular surface in relation to the other articular surface in the frontal plane
  • Depression inferior motion of one articular surface in relation to the other articular surface in the frontal plane.
  • Rotation – one articulating surface acts as the axis of rotation (y axis a.k.a. superior/inferior axis) for the sacrum which pivots around this point to move the opposite articulating surface forward.

A New Model of Sacral Motion

I must first thank my close friend (and human movement science savant), Tony Ambler-Wright, for introducing me to some key concepts that lead to this model, and for being a constant sounding board as I put the model to paper. Hurry up with the blog, homey… You have so much to share!!! I also must thank Dr. Mike Clark, CEO of NASM for his constant mentorship of both Tony and myself. I know that many of the ideas in this model were inspired by the trail of bread crumbs left in conversations, e-mails and articles. Last, this is new information that I have been working on… I was so excited about its development that I had to share, but it still has some kinks. Feel free to leave your ideas and criticisms, but please be kind.

Layer 2: Functional Anatomy and Paired Actions

Flexion and Extension:

Sacral flexion and extension are always paired with lumbar motion in the opposite direction.

Muscles can cause motion in conjunction with a pelvic tilt in the same direction, or independent (opposite) of a pelvic motion.

  • Same Direction
  • Sacral extension with a posterior pelvic tilt
  • Opposite Direction
    • Sacral flexion with posterior pelvic tilt
  • Sacral extension with a anterior pelvic tilt
    • Piriformis
    • Iliacus
      • The iliacus is not a mover of the sacrum itself but will anteriorly tilt the innominate without concurrent sacral flexion; the result is relative sacral extension.


We will consider rotation unilaterally for ease of analysis – For example, if we are discussing the left SI joint; anterior rotation of the sacrum refers to the right articulating surface moving anteriorly (the sacral base acting as a lever), around an axis of rotation at the center of the left SI joint.


Sacral elevation occurs in conjunction with elevation of the ilium and lateral flexion of the spine to the same side.

Level 3: Relative Motion and Functional Anatomy

Before we can create our graphs we have take a step beyond paired actions and consider relative motion. Those of you who have read my other articles on postural dysfunction will be familiar with this concept (ex. tibial external rotation = femoral internal rotation). Sacral motion must be considered in relation to pelvic motion (as above), and in relation to the contralateral side.

  • Flexion of the sacrum is relative to a posterior tilt of the innominate (commonly known as nutation)
  • Extension of the sacrum is relative to anterior tilt of the innominate (commonly known as counternutation)

If activation of the erector spinae , adductor magnus , or biceps femoris cause a change in sacral position (relative to the ilium), it must be unilateral muscle activation resulting in contralateral SI joint motion.

  • The adductor magnus  and biceps femoris cause both sacral extension and a posterior pelvic tilt. If the muscles were to fire bilaterally it would result in both sacral extension and a posterior tilt of the pelvis. This pairing causes little or no actual motion of the SI joint; in essence, the sacrum and ilium move as a solid unit. However, if the biceps femoris and adductor magnus activate on the left side causing sacral extension and a posterior tilt of the left innominate; it would be relative extension and anterior tilting of the right innominate.
  • The erector spinae will cause flexion of both the sacrum and ipsilateral innominate. So, if activation of the erector spinae results in SI joint flexion it must be unilateral activation of the erector spinae resulting in flexion and a relative posterior tilt of the contralateral innominate.
  • The iliacus (extensor) and psoas (flexor) are the only two muscles that can act to flex or extend the sacrum independently, relative to the ilium.

Elevation of the ilium is a “down-slip” of the sacral articulating surface.

  • Elevation of the sacral articulating surface is accompanied by elevation of the ipsilateral ilium. This may be accompanied by an “up-slip” of the ilium on the same side. That is, although the sacral articulating surface has moved superiorly in relation to the contralateral sacral articulating surface, is has moved inferiorly relative to the ipsilateral ilium. You could think of both the ilium and the sacral articulating surfaces elevating, but the ilium elevating more. This may be due to the majority of muscle fibers from the erector spinae and quadratus lumborum  inserting into the posterior iliac crest. However, the “downslip” of the sacral articulating surface is often accompanied by ipsilateral biceps femoris and adductor magnus over-activity resulting in a force via the sacrotuberous ligament that would depress the sacrum.
  • Note: If you are an experienced manual therapist the relative frontal plane position of the ilium and sacrum may have important implications in your application of SI joint mobilizations. The relative lengths of the muscles involved may also be important to guide you in manual release techniques preceding mobilization. However, because these muscles are also represented in the graph below by other compensatory joint actions – sacral elevation and depression has been removed from the graph to help simplify an otherwise complex model.

Elevation of the sacrum and ilium results in relative adduction of the ipsilateral hip.

  • This is the return of the “Positive Trendelenburg Sign” and will result in a long/underactive gluteus medius .

Rotation of the sacrum is relative rotation of the lumbar spine in the opposite direction. You could think of this phenomenon as your body “squaring” your spine and shoulder girdle to maintain eyes forward. If the left SI joint is functional fixed resulting in an anterior sacral rotation, the spine will be in relative right rotation.

  • Practically speaking, rotation of the sacrum and spine seem to be better indicators of relative length than frontal plane motion (elevation, lateral flexion, adduction). Sacral rotators were discussed above. Rotation of the spine is predominately controlled by the global core musculature. This includes the latissimus dorsi , external obliques , and psoas .

Dysfunction of the Left SI Joint:

The set of joint actions below may place the ilium and sacral articulating surfaces in a position that is maximally congruent decreasing joint space and resulting in functional fixedness (“stuck in close pack”). It is my hypothesis that common postural dysfunction at the SI joint results from functional fixedness on one side; a position that may be adopted to passively increase pelvic stability. It should be noted that the set of joint actions below do not match the traditional definition of close pack position for the SI joint.

In this model Close Pack (Maximal Joint Surface Congruence) = Extension + Lateral Flexion (down slip) + Anterior Rotation (contralateral SI joint moves anterior).

Left SI Joint Dysfunction:

Observed Joint Action Short/Overactive Muscle Opposing Joint Action Long Muscles
Rotation (Right side moves anterior) Left Piriformis Posterior Rotation

Right Gluteus Maximus

Right Piriformis

Extension (Relative to R Ilium)

Left Biceps Femoris

Left Adductor Magnus

Left Piriformis

Right Iliacus

Flexion(Relative to Right Ilium)

Right Psoas

Left Erector Spinae

Lateral Flexion Left Left Quadratus Lumborum Lateral Flexion Right Right Obliques
Rotation Right

Left Obliques

Right Latissimus Dorsi

Rotation Left

Right Obliques

Right Psoas

Adduction Left Anterior Adductors Abduction Right Gluteus Medius

Note: Muscular synergies that are synonymous with a particular integrated core subsystem have been replaced with the implied subsystem, although the muscles were left in brackets. This will have a significant effect on our exercise selection in the follow up to this article LPHCD Corrective Exercises and Sample Routine .

Overactive (Release and Stretch):

Underactive (Activate and Integrate):

Level 4: Global Considerations

Anterior rotation of the sacrum results in the contralateral articular surface translating forward around an axis of rotation at the center of the dysfunctional SI joint; “pushing” the contralateral ilium into an anterior pelvic tilt (APT). This results in a relative posterior pelvic tilt (PPT) of the ipsilateral side and anterior pelvic tilt of the contralateral side. Contralateral trunk rotation creates asymmetry in abdominal musculature that may be exacerbated by a functional scoliosis. Lateral flexion of the spine would be to the side of the restricted SI joint; the convexity would be to the opposite side. Further muscle activity often results in changes in gait synonymous with Lower Leg Dysfunction on the side of the restricted SI joint.

  • Posterior Pelvic Tilt on side with SI joint dysfunction
  • Anterior Pelvic Tilt on contralateral side.
  • Ipsilateral flexion and contralateral rotation of the trunk
  • Ipsilateral Lower Leg Dysfunction

Although this does not change the corrective strategy implied by the graph above, it does have implication for core training, resistance training, and the selection of cardiovascular activity. Further, these “global” trends have implications for the perpetuation of dysfunction over time.

Arthrokinematic Dysfunction (SI Joint, Hip & Lumbar Facet Dysfunction):

This model implies that LPHCD will result in hip joint, SI joint, and lumbar facet joint dyskinesis. Joint manipulation is often necessary to optimize movement, especially when dyskinesis results in “fixedness”. The number of effective self-administered mobilization techniques is limited, but a couple of techniques are easily administered and often effective. If joint dyskinesis is expected, an attempt should be made to improve arthrokinematics; assuming that the techniques themselves do not result-in, or exacerbate pain. Luckily, a corrective strategy that addresses all musculature involved will often result in spontaneous manipulation and improved joint motion. Note: be careful not to breach laws dictating scope of practice in your state. When necessary, refer out to a licensed manual therapist (DPT, ATC, DC, DO). This dysfunction can be tricky, as known self-administered mobilization techniques are not consistently effective and are probably more effective in mild cases of dysfunction.

  • The hip has a propensity to internally rotate, and glide anterior and superior in the joint capsule.
  • The arthrokinematics of the SI joint were described above - rotation, extension, and an up-slip of the ilium.
  • The lumbar facets may become fixed as a result of contralateral rotation, extension, and lateral flexion.

Fascial Connections:

The fascial system needs more consideration in our corrective exercise strategies. The work of Tom Myers has brought this system to the forefront of human movement4, however, self-administered techniques for addressing fascial restriction are still fairly crude. There are many brilliant practitioners developing exercise strategies specific to fascia; we can expect to see rapid development in this area in the years to come. This model does reinforce some of Tom Myers work, and illustrate some important fascial connections.

  • Adaptive shortening of the biceps femoris , sacrotuberous ligament, and potentially the erector spinae
  • Adaptive shortening of the tensor fascia latae , the iliotibial band, and the investing fibers of the vastus lateralis
  • Asymmetrical adaptive length changes in the abdominal fascia
  • Adaptive shortening in the fascial connections that are integral to core subsystems (thoracolumbar fascia in POS , fascial network between abdomen, pubis, and medial thigh in the AOS )

Variations Between Individuals - Time Course of Dysfunction Hypothesis:

I hypothesize that much of the variations between individuals with LPHCD can be explained by a time-course of dysfunction. That is, LPHCD is a progressive syndrome that slowly modifies structures over time. This may be due to the rate of adaptability in various tissues, mechanical restriction having a larger impact on movement than soft tissue, muscle fiber type and resistance to fatigue, or motor patterns that are “hard-wired” alternatives mentioned earlier.


SI joint dysfunction seems to be a dysfunction within a dysfunction. That is SI joint dysfunction exists inside the global postural dysfunction that is LPHCD . My guess is that global postural dysfunction (an anterior pelvic tilt) will lead to SI joint Dysfunction, or Lower Leg Dysfunction will lead to SI joint dysfunction, and progress to include the changes associated with the original model.

At this point, I seem to note the following trend (generally, it would appear that dysfunction moves proximal to distal).

  1. Adaptive Shortening of Hip Flexors
  2. Intrinsic Stabilization Subsystem Inhibition
  3. Synergistic Dominance of Lumbar Erectors
  4. Glute Complex Inhibition
  5. Synergistic Dominance of Biceps Femoris
  6. SI joint Dyskinesis
  7. Etc.

Note: This dysfunction may progress in either direction

For a Repertoire of Corrective Exercise and a Sample Routine please check out - Sacroiliac Joint Dysfunction Corrective Exercise and Sample Routine - complete with videos of each movement


  • 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
    1. Dr. Mike Clark & Scott Lucette, “NASM Essentials of Corrective Exercise Training” © 2011 Lippincott Williams & Wilkins
    2. Donald A. Neumann, “Kinesiology of the Musculoskeletal System: Foundations of Rehabilitation – 2nd Edition” © 2012 Mosby, Inc.
    3. Michael A. Clark, Scott C. Lucett, NASM Essentials of Personal Training: 4th Edition, © 2011 Lippincott Williams and Wilkins
    4. Leon Chaitow, Muscle Energy Techniques: Third Edition, © Pearson Professional Limited 2007
    5. Tom Myers, Anatomy Trains. © Elsevier Limited 2001
    6. Shirley A Sahrmann, Diagnoses and Treatment of Movement Impairment Syndromes, © 2002 Mosby Inc.
    7. 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
    8. Cynthia C. Norkin, D. Joyce White, Measurement of Joint Motion: A Guide to Goniometry – Third Edition. © 2003 by F.A. Davis Company

(C) 2012 Brent Brookbush

Comments, questions, and critiques are welcome and encouraged.