There are several reasons for sciatica to occur. Often, sciatica results from a degenerative spine condition, such as a herniated disc or bone spur. When damaged disc material or excess bony growth is positioned in such a way that it exerts pressure on the sciatic nerve, painful symptoms can arise. Similarly, sciatica can be caused by a traumatic injury, such as a pelvic fracture, or by spasms of the piriformis muscle (located in the buttock region) in the pelvic region.