The sacroiliac joint plays a central role in low back and pelvic mobility, in addition to core musculature and hamstring function.1 Human biomechanics and anatomy accomplish SIJ stability in multiple ways including Vleeming's "form closure" and "force closure," as well as Janda's lower crossed model.
Form Closure vs. Force Closure
Form closure is essentially a feature of the anatomy of the SIJ in which articular surfaces are in close contact with each other. Reciprocal contour features (ridges and grooves) of the articular surfaces of the ilium and sacrum provide not only resistance to sheer stresses, but also increased surface areas of the osseous articulation.
Form closure might be regarded as an intrinsic feature of the joint. Keep in mind, however, that form closure is not a complete or tight fit at the sacroiliac joint, since some movement within the joint space, especially the synovial portion, is required for normal mobility.
Force closure, on the other hand, is a functional property of the joint in motion, whereby lateral compressive forces are applied by the action and response of soft tissue.2 Ligaments, muscles, tendons, and the fascial network maintain the joint in a gravitational field and during motion.
Force closure may be regarded as soft-tissue responses to θx rotation on nutation-counternutation of the sacral base. The goal of clinical interventions with SIJ complaints should be to promote better functionality of the force-closure role of soft tissue.
Force closure also includes functional anatomy superior to the pelvis, particularly the abdominal core, with integration of the internal oblique and transverse abdominus muscles, as well as the thoracolumbar fascia. This makes use of the feed-forward mechanism to maintain balance and stability during mobility.
Lower Crossed Syndrome
As Janda describes, lower crossed syndrome involves both deep local and global components for neuromuscular coordination.3 The deep local system includes the transverse abdominus, rotators, multifidi, iliacus, and psoas. These muscles provide the postural and spinal segmental controls for movement and balance of the body.3
The global muscle system, which includes the erector spinae, superficial abdominal, quadratus lumborum, hamstrings, piriformis, and hip adductors, provide support for larger motions of the torso and gait. They need stability and adaptability from the local system to provide overall neuromuscular integration.3
SIJ Dysfunction and Gait
To illustrate the neuromuscular coordination, let us consider the functional anatomy of normal gait with regard to the pelvic articulations. The two main events are heel strike and toe-off, but there are several intermediate events that contribute to the normal fluidity and symmetry of human locomotion.
As the leg swings forward, there is posterior rotation of the ilium relative to the sacrum. This is a consequence of engagement tension arising in the soft-tissue matrix, notably the sacrotuberous and interosseus ligaments. Simultaneously or sequentially, tension builds in the hamstrings prior to heel strike, which tightens the sacrotuberous ligament, whose function is to stabilize the SIJ.4
It is usually during stages of gait that SIJ instability manifests with pain and/or asymmetries such as a limp, torsion of the pelvis, or unilateral restricted range of motion. The net effect is that the kinematic chain of walking is disrupted with altered tension in muscle groups such as the hamstrings, rectus femoris, gluteal muscles, and hip rotators. Flexion deformity in the sagittal plane is a consequence of hypertonic hip flexors, primarily the psoas.
The neurological response to psoas facilitation is inhibition of the gluteal muscles responsible for lateral SIJ stability. To compensate, the hamstrings can become short and tight.5
Looking Deeper: When Your Standard Adjusting Doesn't Work
When a low back or SIJ complaint is recurrent, despite standard osseous adjusting procedures, evaluate the patient for additional causes of SIJ instability. A common non-osseous contributing factor is tight hamstrings applying continuous load to the sacrotuberous ligament. The net result is that the sacroiliac joint is predisposed to posterior inferior misalignment of the ilium relative to the sacrum.
Tight hamstrings may be indicated with a finding of trigger points along the sacrotuberous ligament, palpable muscle rigidity in the belly of the muscle, and tender nodules at the tendinous insertions on the posterior proximal tibia. The most effective test for global hamstring tightness is the supine passive straight-leg-raising test. Decreased flexion at the hip and posterior thigh pain on the maneuver suggests hamstring involvement.
The goal of treatment is to create a balance in multiple planes of motion at the SIJ. Exercising the gluteal muscles increases muscular facilitation, particularly in the sagittal and horizontal planes. As a result, reciprocal inhibition of the psoas occurs, thereby increasing stability in the horizontal plane. Successful management includes retraining of the muscles and associated soft-tissue structures instrumental in form and force closure of the SIJ. The net result will substantially reduce the recurrence and severity of the most common pelvic misalignments, namely the PI and AS ilium.
Clinical interventions that enhance the stability of the SIJ include exercise and osseous adjusting. That combination contributes to the force component of pelvic stabilization and must be factored into patient management. Understanding the mechanisms of force closure and how to increase neuromuscular control will enhance stability, proprioception and balance. The immediate therapeutic goal is to enhance the body's ability to overcome injury and continue to heal, while a successful long-term outcome results in enhanced, pain-free mobility for the patient.
References
- Arumugam A, et al. Effects of external pelvic compression on form closure, force closure, and neuromotor control of the lumbopelvic spine – s systematic review. Manual Ther, 2012;17:275-284.
- Vleeming A, Schuenke M. Form and force closure of the sacroiliac joints. Phys Med & Rehabil, 2019 Aug;11 Suppl 1:S24-S31.
- Key J, et al. A model of movement dysfunction provides a classification system guiding diagnosis and therapeutic care in spinal pain and related musculoskeletal syndromes: a paradigm shift - part 1. J Bodywork Movement Ther, 2008;12:7-21.
- Panayi S. The need for lumbar-pelvic assessment in the resolution of chronic hamstring strain. J Bodywork Movement Ther, 2010;14:294-298.
- Hossain M, Nokes LDM. A model of dynamic sacro-iliac joint instability from malrecruitment of gluteus maximus and biceps femoris muscles resulting in low back pain. Med Hypoth, 2005;65:278-281.
Dr. Howard Pettersson, a 1976 graduate of Logan College of Chiropractic, is an associate professor of technique at Palmer College of Chiropractic. He was the senior editor of Activator Methods Chiropractic Technique – College Edition, published in 1989, and published Pelvic Drop Table Adjusting Technique in 1999. His most recent publication, written with Dr. Green, is How to Find a Subluxation, published in 2003.
Dr. J.R. Green is a 1988 Graduate of Palmer College of Chiropractic. He retired from the Palmer faculty after many years of teaching basic sciences and chiropractic technique. He is currently in private practice in Galva, Ill., and is also an adjunct professor of chemistry with the Eastern Iowa Community College District. Dr. Green was one of the writers of Activator Methods Chiropractic Technique (1997) and also worked as a technical writing consultant on Activator Methods Chiropractic Technique – College Edition and Pelvic Drop Table Adjusting Technique.
Dr. D. Ranier Pavilek graduated as a certified athletic trainer from BYU in 1991, and from Palmer College in 2001. He is currently a faculty clinician in the Chiropractic Rehabilitation and Sports Injury Department, Palmer Chiropractic Clinics. He also teaches Care and Prevention of Athletic Injuries and Kinesiology courses in Palmer's undergraduate program and developed the Advanced Soft Tissue course in Palmer's elective program.