Note: This is the ninth blog post article in a series of 11 articles on Psoas Major Function. See below for the other articles in this series on psoas major function.
It is customary to consider the psoas major as a muscle of the hip joint and spinal joints because it attaches across these joints. However, it is often overlooked that the psoas major also crosses the sacroiliac joint. Indeed, only a few sources discuss this (2, 17, 27). Gibbons states that the “… PM (psoas major) crosses the pelvis and therefore must exert a force on the SIJ (sacroiliac joint)” (2). Myers describes the roles of the psoas major and piriformis across the sacroiliac joint (see Figure 13) as integral to maintaining a balancing “stabilization…leaving other muscles free and ready to move us in any direction.” (17).
Interestingly, the psoas major can also potentially affect the sacroiliac joints in another way. When it contracts, the psoas major creates a pulling force toward both the proximal spinal attachments and the distal femoral attachment. If both attachments are stabilized, and therefore do not move, the psoas major would create a “bowstringing” force upon the pelvis that “pushes” it in the posterior direction as seen in Figure 17 (17). This force would certainly translate into and have an effect upon pelvis posture generally as well as specifically upon the sacroiliac joints.
Figure 17. If spinal and femoral attachments of the psoas major are stabilized, its contraction would cause a “bowstringing” force that “pushes” posteriorly against the pelvis. Reproduced with kind permission from Joseph E. Muscolino. Art work by Giovanni Rimasti.
Note: This is the ninth blog post article in a series of 11 articles on Psoas Major Function.
The 11 articles in the series are:
- Introduction & Muscle Biomechanics
- Biomechanics of the Psoas Major (Overview)
- Psoas Major Hip Joint Actions – Sagittal Plane
- Psoas Major Hip Joint Actions – Frontal Plane
- Psoas Major Hip Joint Actions – Transverse Plane
- Psoas Major Spinal Joint Actions – Frontal and Transverse Planes
- Psoas Major Spinal Joint Actions – Sagittal Plane
- Stabilization of the Spine by the Psoas Major
- Psoas Major and the Sacroiliac Joint
- Psoas Major and Fascial Pulls
- Summary of Psoas Major Function & Further Research
Note: This article is modified from an article originally published in the massage therapy journal (mtj): Psoas Major Function: A Biomechanical Examination of the Psoas Major. Spring 2013 issue.