Sacroiliac joint

 ( Joints ) 

• Anterior sacroiliac ligament
• Interosseous sacroiliac ligament
• Posterior sacroiliac ligament
• Sacrotuberous ligament
• Sacrospinous ligament

The anterior ligament is not much of a ligament at all and in most cases is just a slight thickening of the anterior joint capsule. The anterior ligament is thin and not as well defined as the posterior sacroiliac ligaments.

The posterior sacroiliac (SI) ligaments can be further divided into short (intrinsic) and long (extrinsic). The dorsal interosseous ligaments are very strong ligaments. They are often stronger than bone, such that the pelvis may actually fracture before the ligament tears. The dorsal sacroiliac ligaments include both long and short ligaments. The long dorsal sacroiliac joint ligaments run in an oblique vertical direction while the short (interosseous) runs perpendicular from just behind the articular surfaces of the sacrum to the ilium and functions to keep the sacroiliac joint from distracting or opening. The sacrotuberous and sacrospinous ligaments (also known as the extrinsic sacroiliac joint ligaments) limit the amount the sacrum flexes.

The ligaments of the sacroiliac joint loosen during pregnancy due to the hormone relaxin; this loosening, along with that of the related symphysis pubis, permits the pelvic joints to widen during the birthing process. The long SI ligaments may be palpated in thin persons for pain and compared from one side of the body to the other; however, the reliability and the validity of comparing ligaments for pain have currently not been shown. The interosseous ligaments are very short and run perpendicular from the iliac surface to the sacrum, they keep the auricular surfaces from abducting or opening/distracting.

The motions of the sacroiliac joint

• Anterior innominate tilt of both innominate bone on the sacrum (where the left and right move as a unit)
• Posterior innominate tilt of both hip bones on the sacrum (where the left and right move together as a unit)
• Anterior innominate tilt of one innominate bone while the opposite innominate bone tilts posteriorly on the sacrum (antagonistic innominate tilt) which occurs during gait
• Sacral flexion (or nutation) Motions of the sacrum occur simultaneous with motion of the ilium so you must be careful in the description of these as isolated motions.
• Sacral extension (or counter-nutation).

The sacroiliac joints like all spinal joints (except the atlanto-axial) are bicondylar joints, meaning that movement of one side corresponds to a correlative movement of the other side.

Common mechanical problems of the sacroiliac joint are often called sacroiliac joint dysfunction (also termed SI joint dysfunction; SIJD). Sacroiliac joint dysfunction generally refers to pain in the sacroiliac joint region that is caused by abnormal motion in the sacroiliac joint—either too much or too little motion. It typically results in inflammation of the SI joint, or sacroiliitis.

• Mechanical SIJ dysfunction usually causes a dull unilateral low back pain.
• The pain is often a mild to moderate ache around the dimple or posterior superior iliac spine (PSIS) region.
• The pain may become worse and sharp while doing activities such as standing up from a seated position or lifting the knee towards the chest during stair climbing.
• Pain is typically on one side or the other (unilateral PSIS pain), but the pain can occasionally be bilateral.
• When the pain of SIJ dysfunction is severe (which is infrequent), there can be referred pain into the hip, groin, and occasionally down the leg, but rarely does the pain radiate below the knee.
• Pain can be Referred pain from the SIJ down into the buttock or back of the thigh, and rarely to the foot.
• Low back pain and stiffness, often unilateral, that often increases with prolonged sitting or prolonged walking.
• Pain may occur during sexual intercourse; however, this is not specific to just sacroiliac joint problems.

Given the inherent technical limitations of the visible and palpable signs from these sacroiliac joint mobility maneuvers, another broad category of clinical signs has been described called provocative maneuvers. These maneuvers are designed to reproduce or increase pain originating from within the sacroiliac joint. When the provocative maneuvers reproduce pain along the typical area, it raises suspicion for sacroiliac joint dysfunction. However no single test is very reliable in diagnosing of sacroiliac joint dysfunction. Weakness, numbness, or the loss of a related reflex may indicate nervous system damage.

The current gold standard for diagnosis of sacroiliac joint dysfunction emanating within the joint is sacroiliac joint injection confirmed under fluoroscopy or CT-guidance using a local anesthetic solution. The diagnosis is confirmed when the patient reports a significant change in relief from pain and the diagnostic injection is performed on 2 separate visits. Published studies have used at least a 75 percent change in relief of pain before a response is considered positive and the sacroiliac joint deemed the source of pain.

Women are considered more likely to suffer from sacroiliac pain than men, mostly because of structural and hormonal differences between the sexes, but so far no credible evidence exists that confirms this notion. Female anatomy often allows one fewer sacral segment to lock with the pelvis, and this may increase instability.

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