Subluxation -- a less than full dislocation of a joint -- occurs when movement of a joint goes beyond its maximum range causing the bones to move out of alignment. Subluxations commonly occur in the sacroiliac (SI) joint, which is formed by the bottom of your spine and your pelvis. Causes of SI subluxation include trauma, poor posture, pregnancy and arthritis.
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SI subluxation is usually due to trauma. Unexpected jarring-type accidents, such as slips and falls or tripping, are the most common traumas leading to SI subluxation. Car accidents can also cause SI subluxations. Sports injuries, depending on the nature of the impact, can cause subluxations. A subluxated SI joint can affect surrounding blood flow, nerve function and muscle tension. SI joints can become completely dislocated with extreme trauma, but subluxation is much more common. Most SI subluxations cannot be detected with X-rays, however medical examination can reveal an unleveled pelvis.
Poor posture, which causes micro-trauma over longer periods of time, is the second most common cause of SI subluxation. Sitting in a car or at a desk for hours at a time creates too much forward bending, straining the ligaments that hold your SI joints together. Sleeping facedown, often creates too much backward bending, which causes compression in the SI joint. Leg-crossing while sitting or laying faceup can also strain ligaments and misalign your SI joints.
Another common cause of sacroiliac subluxation is pregnancy. Hormones released in a pregnant woman's body allow ligaments to loosen, which prepares the pelvis for childbirth. Relaxation of the SI ligaments allows for too much movement in the joints and can lead to increased stresses and abnormal wear in these joints. In addition, the increased weight and altered walking pattern associated with pregnancy also places stress on the SI joints.
Both osteoarthritis -- the wear and tear type -- and inflammatory types of arthritis can cause SI joint problems. SI subluxations created from mild to moderate arthritis can create popping or clicking sounds, although severe arthritis often leads to complete SI fusion.