The pain runs from the buttock down the back of the thigh, some days reaching the calf, and many people immediately think of a herniated disc. The first question they ask the doctor is often whether they will need surgery. Disc herniation is indeed a common cause. Even so, inside the buttock and around the pelvis there are several other structures that can cause pain along exactly the same path.
The path of the sciatic nerve
The sciatic nerve is formed from nerve roots in the low back and the sacrum. It leaves the pelvis through a deep bony notch beneath the gluteal muscles, runs close to the piriformis muscle, then travels down the back of the thigh. Above the back of the knee, one of its branches curves around to the outer side of the knee and becomes the peroneal nerve.
The name sciatica only describes the route the pain takes. It does not yet tell you at which section the nerve is irritated, whether at the root next to a lumbar disc or along the stretch that passes through the buttock. In musculoskeletal problems, pain felt in one place with its source somewhere else is a common story.
Places that can cause the same kind of spreading pain
Nerve roots in the low back
A herniated disc or a narrowed spinal canal can press on a nerve root. The pain usually comes with numbness along a strip down the leg. If the compression lasts long enough, a group of leg muscles may weaken and the tendon reflexes may decrease.
The piriformis muscle, deep in the buttock
The piriformis lies beneath the gluteus maximus, stretching from the sacrum to the top of the thigh bone, and the sciatic nerve runs right next to it. When the muscle is tight or irritated, the pain can also spread down the leg.
Piriformis syndrome was described long ago, yet it is still debated today. A review of 55 studies by Hopayian and colleagues (2010) found that the most common features were buttock pain, tenderness when pressing over the greater sciatic notch, and pain that gets worse with sitting and when the piriformis is stretched. A case in which the piriformis tightened up to compensate for the pelvis is told in our article buttock pain and neck pain spreading to the shoulder.
The sacroiliac joint
The sacroiliac joint connects the sacrum to the two hip bones and lies beneath the two small dimples just above the buttocks. In a study from 2000, Slipman’s group followed 50 people whose pain had been confirmed as coming from this joint with a diagnostic injection. Among them, 94% had buttock pain, half had pain spreading down the leg, 28% had pain below the knee and 14% had pain all the way to the foot.
One person can have trouble in two places at once, for example a sacroiliac joint that is not working properly, forcing the piriformis to tighten up to hold things in place.
A scan showing a herniation still has to match the examination
Disc bulges on magnetic resonance imaging (MRI) are fairly common, even in people who have never had back pain, as our overview of back pain pointed out. The doctor reads the scan together with where the pain is and what the examination shows. If the scan shows a herniation but the examination findings point to the buttock or the sacroiliac joint, those places have to be considered as well.
A herniation can also shrink on its own. A pooled analysis of 31 studies in people treated conservatively who had at least two scans (Chiu and colleagues, 2015) found that the herniation regressed in 96% of sequestrations (free fragments), 70% of extrusions, 41% of protrusions and 13% of bulges.
At the clinic, we see that most people with new sciatica and no serious signs tend to improve gradually over a few weeks. This is an observation from our consultations; we have not collected statistics on it. So the doctor usually examines carefully and treats first, without rushing to order a scan. Whether or not to operate is decided by a spine surgeon.
How the doctor narrows down the source of pain
The doctor asks what the pain started after, and whether sitting or standing makes it worse. The examination includes the straight leg raise, tendon reflexes, sensation, muscle strength, pressing over the sciatic notch, rotating the hip to stretch the piriformis and stress tests of the sacroiliac joint, along with the four examinations of traditional medicine (looking, listening and smelling, asking, and touching, including the pulse).
You lie face down. The doctor presses gently on one side of the sacrum in one direction at a time, and after each press tests a leg muscle again, using Applied Kinesiology muscle testing to tell the sources of pain apart. If pressing in one direction makes a strong muscle go clearly weak, the sacroiliac joint on that side is a suspect.
The doctor will recommend an MRI if your leg is getting weaker, a reflex is lost, the pain does not ease after a course of treatment, or the examination findings do not fit together. Some people also need electromyography (EMG).
When sciatica becomes an emergency
A few signs should not be waited out. If you have pain spreading down the leg along with numbness in the saddle area (around the anus, the genitals and the inner thighs), cannot pass urine, or lose control of your bladder or bowels, go to the emergency department right away. A leg that gets weaker day by day also needs immediate care. The bundle of nerve roots at the lower end of the spinal cord may be compressed, and this needs to be treated early. Fever, weight loss, or pain that gets worse at night are reasons to see a doctor soon.
Treatment that follows the source of pain
If the examination shows that the pelvis or the sacroiliac joint is not working properly, the doctor corrects it with Applied Kinesiology techniques, for example placing wedge blocks under the pelvis while you lie down.
A trial by Tu’s group (2024) included 216 people with chronic sciatica from a herniated disc; each person received 10 sessions of acupuncture over 4 weeks. In the real acupuncture group, the leg pain score (on a 100 mm scale) fell by 30.8 mm, compared with 14.9 mm in the sham acupuncture group, and this difference lasted until week 52. There were no serious adverse events. The study looked only at pain from disc herniation and says nothing about the piriformis or the sacroiliac joint.
For people whose pain gets worse in cold, damp weather, which traditional medicine calls the wind–cold–dampness pattern (风寒湿 / 風寒濕, fēng hán shī) of zuo gu feng (“sitting-bone wind”, 坐骨风 / 坐骨風, zuò gǔ fēng), where qi and blood in the low back and buttock are blocked, the doctor uses moxibustion (warming points with burning mugwort). Others have a long-standing Liver–Kidney deficiency pattern (肝肾虚 / 肝腎虛, gān shèn xū), so the herbal decoction is modified to fit the pattern. You will also be shown exercises suited to the source of your pain.
If you have had buttock pain spreading down your leg for a few weeks, your first consultation with Dr. Dinh Ngoc Duc (MD, MSc in Traditional Medicine) usually opens with a small step. The doctor asks you to put one finger on the most painful spot in your buttock, then trace the path of the pain down the thigh and into the calf. Only after the neurological examination and muscle testing does the question of whether you need a scan come up.
Worth keeping
- Write down the path of your pain: where it starts, how far down it goes, and whether numbness comes with it;
- Notice what makes the pain worse, such as sitting for a long time, bending forward, coughing or getting up from a chair;
- Keep walking gently during the day, rather than lying in bed for days waiting for the pain to pass;
- If you have had an MRI, bring the image disc as well, not just the written report;
- Numbness in the saddle area, trouble with your bladder or bowels, or a leg that keeps getting weaker means going to the emergency department right away.
References
- Hopayian K, Song F, Riera R, Sambandan S. The clinical features of the piriformis syndrome: a systematic review. Eur Spine J. 2010;19(12):2095-2109. https://doi.org/10.1007/s00586-010-1504-9
- Slipman CW, Jackson HB, Lipetz JS, Chan KT, Lenrow D, Vresilovic EJ. Sacroiliac joint pain referral zones. Arch Phys Med Rehabil. 2000;81(3):334-338. https://doi.org/10.1016/s0003-9993(00)90080-7
- Chiu CC, Chuang TY, Chang KH, Wu CH, Lin PW, Hsu WY. The probability of spontaneous regression of lumbar herniated disc: a systematic review. Clin Rehabil. 2015;29(2):184-195. https://doi.org/10.1177/0269215514540919
- Tu JF, Shi GX, Yan SY, Ni GX, Yu FT, Cai GW, et al. Acupuncture vs sham acupuncture for chronic sciatica from herniated disk: a randomized clinical trial. JAMA Intern Med. 2024;184(12):1417-1424. https://doi.org/10.1001/jamainternmed.2024.5463
