01/01/2026
The most common causes of sciatica all involve something narrowing space around the nerve roots or sciatic nerve and irritating this very sensitive structure.
Slipped (herniated) disc
A herniated or “slipped” lumbar disc occurs when the soft inner material of an intervertebral disc bulges or leaks backward and presses on a nearby nerve root that contributes to the sciatic nerve.
This is considered the single most frequent anatomical cause of sciatica, especially in younger and middle‑aged adults.
Spinal degeneration and narrowing
With age or overload, discs lose water and height, bringing vertebrae closer together and encouraging bone spurs and facet joint arthrosis, which can narrow the spinal canal or foramina (exit tunnels for the nerves).
This degeneration can cause lumbar spinal stenosis or foraminal stenosis, both of which may compress the nerve roots and produce classic radiating leg pain.
Sacroiliac joint dysfunction
Dysfunction or inflammation of the sacroiliac (SI) joint can irritate nearby L5–S1 nerve roots or even the sciatic nerve itself, creating sciatica‑like pain into the buttock and sometimes down the leg.
Distinguishing SI‑joint‑related sciatica from lumbar disc causes can be challenging and often requires a mix of clinical tests and, when needed, imaging.
Myofascial causes (glute trigger points, piriformis)
Trigger points or tightness in the deep gluteal muscles, including piriformis, can compress or sensitize the sciatic nerve along its path, leading to referred buttock and leg pain even without spinal pathology.
These myofascial sources are real but still less common than disc herniation and degenerative spinal narrowing, so clinicians usually rule out spinal nerve‑root compression first.
Encouraging people to see a physio or spine specialist when they have persistent radiating leg pain helps identify which of these mechanisms is driving their sciatica and guides appropriate treatment.