Sacroiliac joint dysfunction can occur as an isolated condition, or associated with other spinal disorders. Torsion injuries can cause damage to the disc annulus, facet joints, lamina, pedicle and ligaments, as well as to the sacroiliac joint.
Common associated conditions of sacroiliac joint dysfunction:
Torsion or axial rotation causes the facets to flex and laterally bend towards the side of the rotation crushing the facet articular surfaces on the rotation side and distracting the capsule with tearing or avulsion on the side opposite the rotation.
The lateral portion of the facet joint is long and slender, making it easily deformed. Torsion causes facet impingement on the torsion side. Distraction on the opposite side can stretch the nerve root. Therefore, neural arch deformation can cause bilateral nerve root entrapment.
Torsion causes annular tears which can weaken the annulus leading to an annular bulge, or herniation, of the nucleolus pulposis. The iliolumbar ligament can become taut due to sub-luxation of the sacroiliac joint. Its fibers are attached to the transverse process of L4, and chronic tension can lead to bulging of the disc. It is not uncommon to see an L4 annular bulge on the MRI of a patient who has chronic sacroiliac joint instability.
Effect on muscle and piriformis syndrome
Janda, an expert on muscle imbalance, has pointed out that postural muscles become facilitated and tighter, and phasic muscles become inhibited and weaker as the result of articular dysfunction. With long-standing dysfunction, anatomic changes in the muscle bundles can take place that are irreversible. Ther piriformis is one of the most adversely affected muscle in chronic sacroiliac instability (piriformis syndrome). Pelvic wall muscle spasm, or contracture, may lead to pelvic floor dysfunction. Other muscles affected include the iliopsoas, hamstrings, adductors, gluteus, quadratus lamborum, and the tensor facscia lata.
Effect on nerves
Due to long-standing spasm, or secondary fibrosis, the chronically shortened piriformis can entrap neurovascular structures that accompany it through the greater sciatic foramen (superior and inferior gluteal nerves, the sciatic nerve and the pudendal nerve. The lateral femoral cutaneous nerve passes just medial to the anterior superior iliac spine. It can be injured as it passes form the pelvis to the thigh by changes in anatomic positioning associated with sacroiliac joint subluxation (meralgia paresthetica).
Pubic symphysis instability
With chronic sacroiliac joint instability the contralateral sacroiliac joint and the pubic symphysis may destabilize.