Piriformis

The piriformis is a small muscle deep in the buttock, underneath the gluteus maximus. It starts on the front of the sacrum, the triangular bone at the base of the spine, passes out of the pelvis through an opening called the greater sciatic foramen and attaches to the top of the thigh bone, the greater trochanter (TeachMeAnatomy).

What does the piriformis do?

It belongs to a group of small, deep muscles whose main job is to turn the thigh outwards. The piriformis also helps move the thigh out to the side, and together with its neighbours it helps hold the ball of the thigh bone in the hip socket (TeachMeAnatomy).

Anatomists use it as a landmark. Nerves and blood vessels are named by whether they leave the pelvis above or below it, and the sciatic nerve, the largest nerve of the leg, usually enters the buttock directly below it as a flat band about 2 cm wide (TeachMeAnatomy).

That arrangement varies. In a meta-analysis of 44 cadaver studies, the sciatic nerve ran undivided below the piriformis in 90% of cases. In more than 10% of people, the nerve or one of its branches passed through or above the muscle instead (Poutoglidou et al., 2020).

Why the piriformis comes up when you sit all day

Because the nerve lies so close to it, the piriformis is a natural suspect when a deep buttock ache spreads down the back of the leg, and sitting is part of the picture. In the case reports collected by two systematic reviews, pain made worse by sitting was one of the most common features in people diagnosed with piriformis syndrome (Hopayian et al., 2010; Hopayian & Danielyan, 2018).

That doesn’t make every sore buttock after a long day at a desk a piriformis problem. Pain running from the buttock down the leg is called sciatica, and the NHS lists a slipped disc (herniated disc) as its most common cause (NHS). For the ache of long sitting more generally, see lower back pain from sitting.

Is piriformis syndrome real? What the evidence says

Piriformis syndrome means sciatica caused by the piriformis compressing the sciatic nerve. It has been described for more than 70 years and is still controversial, partly because most of what is written about it comes from case series and narrative reviews (Hopayian et al., 2010).

What the reviews found:

• Four features come up again and again: buttock pain, tenderness near the notch in the pelvis where the nerve leaves, pain made worse by sitting, and pain that increases with movements that tighten the muscle (Hopayian et al., 2010).
• The tests are unproven. The 2018 update concluded that the muscle can cause sciatica, but that nobody knows how often it does among people with back pain and sciatica, or how accurate the clinical tests are. The two larger studies it found were at high risk of bias (Hopayian & Danielyan, 2018).
• A broader label is gaining ground. Some specialists now speak of deep gluteal syndrome: buttock pain from the sciatic nerve being trapped outside the spine and pelvis, where several structures besides the piriformis can be involved (Martin et al., 2015).

Treatment research is thin too. A 2026 review found 12 studies with 572 people with clinically diagnosed piriformis syndrome. Stretching combined with other treatments generally did better than stretching alone, but only four studies were randomised, the samples were small and few followed people up for long (Aali et al., 2026).

Stretches for the deep hip muscles are shown on the hip stretches and pigeon pose pages.

When to see a doctor

See a GP if sciatica has not improved after a few weeks of home treatment, is getting worse or is stopping you doing your normal activities. Go to A&E or call 999 if you have sciatica on both sides, severe or worsening weakness or numbness in both legs, numbness around your genitals or bottom, or new problems peeing or controlling your bowels (NHS). The full list is in red flags.

Bavelu’s Hips and Lower Back session, designed and filmed by physiotherapists, includes a deep hip and glute stretch.