Massage Today
May, 2012, Vol. 12, Issue 05

Exploring the SI Joint

By Whitney Lowe, LMT

Lumbopelvic pain is a common complaint that affects close to three quarters of this country's population. As massage therapists, we have a tendency to look for muscular causes of these pain complaints.

However, a narrowed focus of attention on muscular tissues might cause one to miss key components of the client's complaint. The sacroiliac joint can be a frequent source of lumbopelvic pain. This joint is unlike many others in the body and requires a comprehensive understanding of anatomy, biomechanics and related tissues in order to best help people with the numerous disorders that may stem from dysfunctional joint mechanics.

Anatomical Structure

The first place to begin in a detailed exploration of the sacroiliac joint is its anatomical structure. Most joints in the body consist of two smooth articular surfaces that are designed to glide against each other throughout a full range of motion. This is not the case at the sacroiliac joint. The articulating surfaces between the sacrum and the Ilium are more of a rough, irregular surface (Figure 1). They are designed to fit together like puzzle pieces with the irregular surface of each side matching up so it can provide greater stability. Unfortunately, when these irregular surfaces don't align correctly, which is the case with sacroiliac joint dysfunction, it can be very painful and produce serious dysfunctional mechanics.

sacroiliac joint Figure 1: Rough and irregular contact surface of the sacroiliac joint 3D anatomy images. Copyright of Primal Pictures Ltd. www.primalpictures.com The next prominent aspect of sacroiliac joint anatomy is the extensive webbing of ligamentous structures that surrounds the joint (Figures 2 and 3). This extensive ligamentous complex clues us in to key biomechanical aspects of the joint. Because this joint is so tightly bound by ligaments, very little motion can occur at the joint. The ligamentous mesh is primarily designed to help transfer weight from the upper torso to the pelvis, and yet allow a slight degree of mobility at that juncture. The key stabilizing ligaments in this region include: the anterior sacroiliac ligament complex, the posterior sacroiliac ligaments, and the sacrotuberous, sacrospinous and iliolumbar ligaments.

One of the more interesting facets of anatomical structure at the sacroiliac joint relates to the muscles which span the joint. In most regions of the body, motion at a joint is governed by muscles which attach to each of the bones of that joint. That is not the case in the sacroiliac joint. There are no muscles that span directly from the sacrum to the ilium. There are numerous muscles which cross the sacroiliac joint, but they cross other joints as well. Consequently, addressing sacroiliac dysfunction by treating muscles in this region requires a much greater understanding of the role muscles play immediately around this joint, as well as in distant areas. The role of related tissues and fascial connections will become increasingly apparent after looking at some aspects of this joint's biomechanics.

Biomechanical Considerations

At first glance it would appear as if the sacrum is tightly wedged between the left and right innominate bones. The innominate is the combined ilium, ischium and pubis on each side. However, if the sacrum were tightly wedged between these two bones it would be difficult, as well as painful, for motion to occur due to the very high levels of friction. Instead, the extensive webbing of ligament structures around the joint acts more like a sling to hold the sacrum suspended in this joint and allows a very slight degree of motion while maintaining extensive stability.

Anterior sacroiliac ligaments Figure 2: Anterior sacroiliac ligaments 3D anatomy images. Copyright of Primal Pictures Ltd. www.primalpictures.com The slight degree of motion capable at the sacroiliac joint is a forward and backward tipping of the sacrum in relation to the innominate bones. Forward tipping of the sacrum is called nutation, where backward tipping of the sacrum is called counternutation. Nutation and counternutation are necessary for minor movement between each innominate and the sacrum. During a walking or running stride one hip is in flexion while the other is in extension. The opposing motions of each side of the pelvis require some degree of slight movement with the sacroiliac joint articulation on each side. If these small degrees of movement are not available, significant alterations in joint mechanics occur and can produce serious pain.

Various postural distortions can cause alignment problems at the sacroiliac joint on each side. Lateral pelvic tilts, as well as anterior and posterior pelvic rotations can each produce numerous detrimental biomechanical problems at the sacroiliac joint. These composite movement problems can produce low back pain, as well as radiating pain down the lower extremity. It might be tempting to suspect that low back pain that also extends down the lower extremity is resulting from a neurological disorder at the nerve root level, when in fact it could be a sacroiliac joint disorder instead. Treatment aimed at lumbar nerve roots or intervertebral discs would likely be ineffective in this scenario.

Role of Massage in Treating SI Joint Dysfunction

Sacroiliac joint disorders routinely cause pain and disability. Massage practitioners don't always think about joint dysfunction as a primary need for massage because the emphasis in most massage treatments is so closely aligned to working on muscles. However, practitioners should remember that numerous soft tissues spanning the sacroiliac joint, both close by and in remote regions, can have significant effects on joint mechanics, giving a valuable rationale for massage therapy treatment.

Posterior sacroiliac ligaments Figure 3: Posterior sacroiliac ligaments 3D anatomy images. Copyright of Primal Pictures Ltd. www.primalpictures.com A great example for understanding the crucial role of massage is simply to look at the many fascial connections that exist in this region. There are fascial connections between the hamstring muscles and the sacrotuberous ligament. Consequently, excess tension in the hamstrings could be transmitted through the sacrotuberous ligament and give adverse pulling force on the sacrum, causing joint dysfunction. There are similar fascial connections between the erector spinae muscles and the posterior sacroiliac ligament complex. Chronic tightness in the lumbar extensor muscles can then be transmitted directly to the sacrum, altering sacroiliac joint mechanics and contributing to pain. Massage treatment of these spinal extensor muscles could be a key factor in normalizing dysfunctional joint mechanics.

There are also fascial connections between the gluteus maximus and the sacrotuberous ligament. The gluteus maximus also has fascial continuity with the lower lumbodorsal fascia which blends into the latissimus dorsi. All of these fascial connections could have beneficial or detrimental effects on sacroiliac joint mechanics. With the numerous fascial connections in this region, it is clear that massage therapy treatment of these soft tissues can play a key role in maintaining optimal joint mechanics of the sacroiliac joint. Yet, without a solid grounding in the complex anatomy and biomechanics in this region it may be difficult to achieve proper interventions.

Movement specialists are still developing working models that accurately convey the complex anatomical and biomechanical relationships in this region. Yet we now understand much more about sacroiliac joint mechanics than we did just a short time ago. The massage therapist who has a better understanding of the joint structure and function along with numerous fascial connections in this region will be so much more effective in helping clients who suffer from these common complaints.

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