The word "subluxation" is derived from Latin and means "less than full dislocation of a joint." More specifically, a subluxation occurs when movement of a joint goes beyond its maximum passive range so that the alignment between the joint surfaces is distorted. Unlike a full dislocation, partial contact is maintained between the articulating bones with subluxations. Subluxations commonly occur in the sacroiliac (SI) joint, which is formed by the union of the sacrum---the triangular bone at the base of the spine---and the ilium, which is the main bone of the pelvis. Causes of SI subluxation include trauma, poor posture, pregnancy, arthritis and imbalance issues.
Trauma
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 because of the compressional force transmitted into the joint, which either slightly misaligns or "jams" it. Car accidents can cause SI subluxations also, but this force is usually of a shearing nature. Sports injuries, depending on the nature of the impact, can cause subluxations from either compressional or shearing forces. 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, although motion palpation can reveal joint dysfunction, and visual examination can reveal an unleveled pelvis.
Poor Posture
Poor posture is essentially "micro trauma" over longer periods of time and is the next most common cause of SI subluxation. The SI joints can be subluxated by too much sustained flexion, extension or torsion. Sitting in a car or at a desk for hours at a time creates too much flexion, which causes straining of posterior ligaments. Sleeping prone, or facedown, often creates too much extension, which causes compression in the SI joint. Leg-crossing while sitting or laying supine, or faceup, often creates too much torsion, which strains ligaments and misaligns the SI joint surface.
Pregnancy
Another common cause of sacroiliac subluxation and dysfunction is pregnancy. Hormones, such as relaxin, that are released in a pregnant woman's body allow ligament laxity, which prepares the pelvis for childbirth. Relaxation of the SI ligaments allows for hypermobility in the joints and can lead to increased stresses and abnormal wear. In addition, the increased weight and altered gait pattern associated with pregnancy also places stress on the SI joints.
Arthritis
Both osteoarthritis---the "wear and tear" type---and inflammatory types of arthritis---such as gout, psoriasis, rheumatoid arthritis and ankylosing spondylitis---cause SI joint destruction. Joint destruction, evidenced by bone spurs and joint space reduction on x-rays, invariably cause misalignments and dysfunction. SI subluxations created from mild to moderate arthritis can become unstable with movement and often create popping or clicking sounds, although severe arthritis often leads to complete SI fusion.
Imbalance
Any condition that causes an abnormal walking pattern increases stress on the SI joints, which can lead to subluxation over time. This includes short leg issues from deformity, injury, pregnancy or chronic leg-crossing; obesity; and any sort of limping due to pain in the hip, knee, ankle or foot.
References
- "Chiropractic Management of Spine Related Disorders"; Meridel I. Gatterman, D.C.; 2001
- "Special Tests for Orthopedic Examination, Third Edition"; Jeff G. Konin, Ph.D., A.T.C., P.T. et al.; 2006
- Wheeless' Online Textbook of Orthopaedics: Sacroiliac Joint
