The nerve roots that exit the spine to form the sciatic nerve are extremely sensitive, and the inner portion of the disc that may herniate or extrude contains proteins that are inflammatory and can easily irritate the nerve. Therefore, if some of the inner portion of the disc (the nucleus) comes too close to the nerve, the nerve may be irritated and become inflamed, causing sciatic pain - or sciatica.
The sciatica symptoms one feels (sciatic nerve pain, numbness, tingling, weakness) tend to be different depending on where the pressure on the nerve occurs. The patient’s pain and sciatica symptoms can usually be traced to where the injured/irritated nerve originates in the lower back.
Sciatica from L4 nerve root (usually the L3-L4 level)
The patient may have reduced knee-jerk reflex. Symptoms of sciatica stemming from this level of the lower back may include: pain and/or numbness to the medial lower leg and foot; weakness may include the inability to bring the foot upwards (heel walk).
Sciatica from L5 nerve root (usually the L4-L5 level)
The patient may have weakness in extension of the big toe and potentially in the ankle (called foot drop). Symptoms of sciatica originating at this level of the lower back may include: pain and/or numbness to the top of the foot, particularly in the web between the great toe (big toe) and the second toe.
Sciatica from S1 nerve root (the L5-S1 level)
The patient may have reduced ankle-jerk reflex. Symptoms of sciatica originating at this level of the spine may include: pain and/or numbness to the lateral or outer foot; weakness that results in difficulty raising the heel off the ground or walking on the tiptoes.
Pressure on the sacral nerve roots from sacroiliac joint dysfunction
Symptoms may include: a sciatica-like pain or numbness that is often described as a deep ache, inside the leg more so than a linear, well-defined geographic area of pain/numbness found in true sciatica.
Pressure on the sciatic nerve from the piriformis muscle
This pressure on the sciatic nerve can tighten and irritate the sciatic nerve (called piriformis syndrome). Symptoms of piriformis syndrome may include: a sciatica-like pain and/or numbness in the leg, usually more intense above the knee, which usually starts in the rear rather than the low back, often sparing the low back of symptoms or signs. Piriformis syndrome can mimic the signs and symptoms of sciatica pain from a disc herniation and is part of the differential diagnosis of possible causes of sciatica.
To clarify terminology, the term sciatica is often used to indicate any form of pain that radiates into the leg.
If the sciatic nerve is pinched and the pain in the leg is from the nerve (radicular pain) then this is a correct use of the term sciatica.
If the pain is referred to the leg from a joint (referred pain) then using the term sciatica is technically incorrect.
