Ultimately every case of sciatica results from pressure on the sciatic nerve or one of it’s nerve roots. This can be from direct physical pressure from a damaged disc, as a result of swelling from an injury, from arthritis in the spine or more serious pathologies. We will look below at some of the most common causes of Sciatica.
Disc Herniation (Slipped Disc)
Intervertebal disc herniation is the most common cause of sciatica, being present in about 90% of cases.
The spinal discs are the shock absorbers of the spine with a strong cartilage external casing (annulus fibrosis) and a gel-like centre (nucleus pulposus). The discs separate the vertebrae, leaving space for the nerve roots to exit the spinal column. The discs cushion the spine from compressive forces. Discs are commonly damaged by rotational and compressive movements.
Disc herniation occurs when the gel center of the disc ruptures through the external ring of cartilage. The resulting extrusion of gel compresses the nerve root causing sciatica. The extruded gel also causes an inflammatory reaction which further compresses the nerve root in its confined space within the spinal canal.
Discs can be injured due to a trauma from a car accident, a fall or blow to the spine or long term wear and tear. Sciatica can then be subsequently triggered by very small movements like bending forward or a simple stumble or jolt. This is why Sciatica sometimes appears to start after a very simple activity where in fact the disc may have been injured for some time already and was gradually buging and swelling to the point where a simple lift/jolt/sneeze etc triggered the Sciatica episode.
As the spine gets older, the vertebral bones lose their smooth contours and become a little rough resulting in tiny bone spurs that can pinch the nerves. That coupled with worn discs can cause a narrowing of the nerve canal called ‘stenosis’. Stenosis is a common feature of arthritis of the spine and can cause sciatica in patients over 50 but can sometimes be seen occasionally in younger patients also.
Sometimes an enlarged or swollen muscle in the buttock can compress the Sciatic nerve. This is called Pseudo-Sciatica or Piriformis syndrome and is easily corrected in most cases.
Osteoarthritis of the hip can often cause pain radiation into the thigh which many people confuse with Sciatica. Careful examination allows us to differentiate between the two conditions and treat accordingly. Where hip surgery is required, referral to an appropriate Orthopaedic surgeon is made without delay.
Rare but more serious causes of sciatica include bone infections, bone tumors, nerve or spinal cord tumours, bone fracture due to trauma, severe osteoporosis or cancer. I would like to emphasize that these are extremely rare but nonetheless every patient that presents with sciatica must be thoroughly assessed to rule out any serious issues.