Posted by Brendan Hill on Saturday, August 9, 2014
You may have heard talk of Tiger Woods and his sacrum in the last few days and on how it 'popped out' and what not. What ever it was that caused his back to spasm it wasn't the sacrum as they don't just pop out. So here is some info on the sacrum and what it gets up to.
The sacrum is a triangular shaped bone which is made up of 5 fused vertebrae (S1-S5). In children these vertebrae are not fused but become so by around age 20 or even later in some people. It is at the bottom of the spine and lies between the fifth segment of the lumbar spine (L5) and the coccyx (tailbone). It is broad and thick at the top and it gets thinner and smaller as you move down. It is wedged between parts of the ilium portion of the two innominate bones and that’s where you find the sacroiliac joints (SIJ).The SIJ is joined together by strong ligaments and on average there is only 2-3 mm of movement here, so it is a joint that is for stability not mobility. The sacrum supports the spine and is supported in turn by an ilium on each side. The joint is a strong, weight bearing joint with irregular elevations and depressions that produce interlocking of the two bones.
The sacrum and the two innominate bones make up the pelvis. When standing it supports the weight of the body nice and evenly (see the red arrows in the picture). When you sit down more weight of the upper body is placed on the lumber spine and pelvic region which may lead to pain in that area. Dysfunction can occur in the SIJ if there is too much movement (Hypermobility) or too little movement (Hypomobility).
That’s just a introduction the sacrum and what it get up to. Hope you found it slightly interesting!