In degenerative disc disease there is narrowing of the disc between vertebrae. Degenerative Disc Disease can cause sciatic in a few ways:
Spondylolisthesis is a condition in which a vertebrae has slipped out of position. This can cause compression at of the nerve. Spondylolithesis can be caused at birth, degenerately (such as above with degenerative disc disorder) or by extreme force.
Stenosis means narrowing. Lumbar stenosis can be either central - narrowing of the spinal canal in the lumbar vertebrae or foraminal - narrowing of pathway where the nerves exit. This condition causes compression on the sciatic nerve and is usually positional, meaning that being in an awkward position can cause the sciatic pain and moving positions can relieve pain.
Sacroiliitis is inflammation in the sacroiliac (SI) joint. Sacroiliitis can affect the sciatic nerve in a couple of ways
1. Inflammatory mediators released from the SI joint can inflame/irritate the nerve.
2. Oedema (swelling) from the inflammation can compress the nerve.
Sacroiliitis itself can be caused by a range of different things. Pregnancy and heavy lifting being two common ways. In pregnancy a hormone call relaxin is released in order to allow ligaments in the pelvis and ilium to move more freely. This can cause instability around the sacrum and lead to sacroiliitis.
If you remember from the anatomy , the sciatic nerve runs behind the piriformis muscle, or at times through it. If the piriformis muscle goes into spasm then it can cause compression on the sciatic nerve. Piriformis syndrome is more common in women and in runners.
Occasionally, a tumour may cause sciatica - it all depends on the location. For example, a tumour in the femur or pelvis may cause compression of the sciatic nerve.
Obesity may be seen as a cause because it is a risk factor for some of the above mentioned pathologies, such as degenerative disc disease, or disc herniation.
There are other causes of Sciatica, but these are the ones that I would say are most common. It's important to note that sciatica does not always present itself in the same way. As was mentioned above, the exact symptoms you get depend on where the nerve is compromised. It's also interesting to note that not all sciatica will come with low back pain. For example, some people with sacroiliitis will have absolutely no back pain, but yet have pain that radiates from the buttocks down the leg.
Sciatic can have a combination of the following signs and symptoms. The symptoms you get will depend on the cause and where the sciatic nerve is compromised.
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