We’ve Heard So Much of the ‘CORE’, What About the ‘SLINGS’?
Ever wondered how a belly-dancer is able to move and control her hips effortlessly to the rhythm? She will need to have good control of her lower spine, pelvis and its supporting muscles systems, in particular the “myofascial slings".
Stability of Pelvic Girdle / Sacroiliac Joints
The pelvis consist of the sacrum (triangular base of the spine) and 2 iliums and they are connected to one another via the sacroiliac (SI) joints. The SI joints need to be stable for the pelvis to function normally, so that they can act as shock absorbers between the lower limbs and spine, and to act as a proprioceptive feedback mechanism for coordinated movement and control between trunk and lower limbs. The SI joints (pelvic girdle) achieve stability via:
Form Closure: The shape, structure and congruency of the sacroiliac bones and associated sacral ligaments provide the passive stability (i.e. 2 lego pieces fitted together).
Force Closure: External forces exerted by muscle systems, through their attachment into connective tissue (ligaments and fascia), to compress and stabilize the sacroiliac joints and hence the pelvic girdle. Adequate force closure is vital to allow for movement of the sacrum during activities such as, walking, transferring, stair use, and bending.
The combination of form and force closure is known as the “self-bracing” or “self-locking mechanism” of the SI joint. Form and force closure should be balanced. If a person lacks form closure, perhaps because genetics or anatomy, they will require more stability from muscles that assist in force closure. This is where myofascial slings come into play.
The ‘slings’ that provide force closure and stability in the pelvic girdle include the anterior oblique, posterior oblique and the posterior longitudinal slings.
Anterior Oblique Sling includes the pectorals, external and internal obliques and transverse abdominis. When this group of muscles contract, it provides stability by acting like an abdominal binder, compressing the entire pelvic girdle, especially the front, securing the symphysis pubis.
Posterior Oblique Sling includes the latissimus dorsi,the contralateral/ opposite gluteus maximus and biceps femoris. This sling provides stability by simultaneous contraction of the latissimus dorsi and contralateral gluteus maximus. They also act on the sacrotuberous ligaments thereby compressing the SI joint.
Longitudinal Sling includes the deep multifidus muscles (attached to the sacrum), the deep layer of the thoracolumbar fascia and the sacrotuberous ligament via the long head of the biceps femoris muscle. Contraction of the deep multifidus muscle will rotate the sacrum forward thereby increasing the tension of the ligaments surrounding the sacroiliac joints, and ‘lock the joints in”, thus increasing its stability. Also, as with the contraction of the deep multifidus muscles, the tension of the thoracolumbar fascia increases, giving rise to a “pumping up” phenomenon which in turn increases the compression of SI joints.
Failure of any of the myofascial slings to secure pelvic stability can lead to lumbo-pelvic pains and dysfunctions. This is especially apparent in expectant women and women following childbirth in whom posterior pelvic pain (PPP) and symphysis pubis dysfunction (SPD) are common. Athletes involved in high-impact activities who have lumbo-pelvic pains from walking, lunging and landing from jumps, often suffer from dysfunction of these myofascial slings. This is due to overloading of the ligaments of the pelvis and/or lumbo-pelvic junction (including the sacroliliac joints) during activities in which loads have to be transferred between legs and trunk, thereby injuring the lower back and pelvis.
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