Piriformis

Origin, Insertion, Action, Innervation

Origin: Anterior surface of the sacrum (segments S2–S4), sacrotuberous ligament, and the margin of the greater sciatic notch
Insertion: Superior border of the greater trochanter of the femur (via a rounded tendon)
Action:
Primary: External (lateral) rotation of the hip
Abduction of the hip when the hip is flexed past 60 degrees (the fiber direction reverses its rotational role at deeper flexion angles — this is clinically relevant for testing)
Stabilization of the femoral head in the acetabulum during gait
Innervation: Nerve to piriformis from the sacral plexus (S1, S2)

Note on action reversal: When the hip is flexed past approximately 60 degrees, piriformis shifts from an external rotator to an internal rotator and abductor. This reversal explains the FAIR test position (see Assessment).

Palpation Guide

Client position: Sidelying, affected side up. The hip should be in slight flexion (approximately 45 degrees) with the knee flexed. A pillow between the knees keeps the pelvis neutral and reduces gluteus medius tension, improving access to piriformis beneath.
Landmark sequence:

Locate the PSIS — the bony prominence at the base of the spine, approximately at the level of the S2 spinous process. You can find it by following the iliac crest posteriorly to its termination.
Locate the greater trochanter — the large bony prominence on the lateral hip. With the client sidelying, it is the most prominent point on the lateral thigh.
Draw an imaginary line from the PSIS to the superior border of the greater trochanter. Piriformis runs deep to gluteus maximus along this line.
Palpate approximately one-third of the way from the PSIS toward the greater trochanter. Press through gluteus maximus — piriformis lies deep, against the posterior pelvis. You must sink through the thick gluteal tissue to reach it.
The muscle feels like a firm, rounded cord running diagonally from the sacrum toward the greater trochanter, approximately the diameter of your thumb.

Tissue feel: Piriformis feels ropy and distinct from the broader, flatter gluteus maximus overlying it. In a hypertonic state, it feels like a taut cable under the gluteal mass — tender and resistant to compression. The client often recognizes the tenderness immediately ("that's the spot").
Confirmation test: Maintain your palpating finger on the suspected muscle. Ask the client to externally rotate the hip against your resistance (you resist at the ankle or knee). You should feel the muscle contract directly under your finger. If you feel broad gluteal contraction instead, you are still in gluteus maximus — sink deeper.
Common errors:
Not going deep enough — this is the most common error. Students palpate gluteus maximus and believe they have found piriformis. Piriformis lies on a deeper plane, against the posterior wall of the pelvis. You must compress through the full thickness of gluteus maximus to reach it.
Wrong line — the piriformis runs from the sacrum (not the iliac crest) to the greater trochanter. If your line starts at the iliac crest, you are on gluteus medius.
Confusing piriformis with the other deep six rotators — the obturator internus and gemelli lie inferior to piriformis. If your palpation point is more than halfway from PSIS to greater trochanter, or if it is inferior to your imaginary line, you may be on obturator internus or gemelli rather than piriformis. Piriformis is the most superior of the deep six.

Trigger Point Referral

Common TrP locations: The primary TrP is located in the belly of the muscle, approximately one-third of the distance from the sacral attachment toward the greater trochanter — the same point used in the palpation guide.
Referral pattern: Pain in the ipsilateral buttock (the primary area), the posterior hip joint region, and down the posterior thigh. In some clients, the referral extends to the proximal posterior leg. The pattern follows the course of the sciatic nerve, which is what makes it so easily confused with radiculopathy.
Clinical significance: This referral mimics L5/S1 sciatica almost exactly — it is the most common pseudo-sciatica source (see Clinical Notes for differential).

Trigger point referral diagram — coming soon

Image coming soon. For visual reference, see [Piriformis at TriggerPoints.net](http://www.triggerpoints.net/muscle/piriformis).

Clinical Notes

Common conditions:

The primary cause of piriformis-syndrome — compression of the sciatic nerve by a hypertonic or structurally variant piriformis. Presents as buttock pain with or without posterior leg radiation, worsened by sitting and internal rotation.
Key differential in sciatica — true sciatica involves nerve root compression at the spine (disc herniation, foraminal stenosis); pseudo-sciatica from piriformis involves compression at the greater sciatic notch. The clinical distinction depends on SLR (positive in true sciatica, negative in piriformis syndrome) and the FAIR test (positive in piriformis syndrome).
Relevant to lower-crossed-syndrome — in Janda's lower crossed pattern, hip flexors and erector spinae tighten while gluteals and abdominals weaken. When gluteus medius is weak, piriformis compensates as a hip stabilizer during gait, leading to overuse and hypertonicity.
Can contribute to hip-labral-injury — chronic piriformis tightness alters hip biomechanics, increasing compressive and shearing forces on the acetabular labrum.

What you'll typically find:

Piriformis is hypertonic in clients who sit for prolonged periods — the muscle is compressed against the chair and simultaneously held in a shortened position. Office workers, drivers, and students are the most common presentations.
The muscle often feels like a taut, tender cord deep to gluteus maximus. Clients frequently describe a "deep ache" in the buttock that they cannot reach themselves.
Bilateral involvement is common but usually asymmetric — one side is worse, often correlating with leg-crossing habit, wallet-in-back-pocket sitting, or underlying pelvic obliquity.

Sciatic nerve relationship:

In approximately 88% of the population, the sciatic nerve passes inferior to the piriformis through the greater sciatic foramen. In approximately 12%, the nerve passes through the muscle belly (the peroneal division splits through and the tibial division passes beneath). This anatomical variant predisposes the individual to piriformis syndrome because even normal-range muscle contraction can compress the nerve.
When the sciatic nerve is compressed by piriformis, the client may report numbness, tingling, or burning down the posterior thigh and into the leg — identical to radicular symptoms from a disc herniation.

Treatment effects:

Responds well to sustained compression on the TrP followed by slow, deep longitudinal stripping along the muscle's fiber direction (from sacrum toward greater trochanter).
Because piriformis lies deep to gluteus maximus, the overlying tissue must be warmed and released first. Start with broad effleurage and myofascial release of the gluteal region before attempting direct piriformis work.
During sustained compression on the TrP, the client may report referral down the posterior leg — this confirms you are on the right point and that the TrP is active. Maintain compression until the referral diminishes.
Post-treatment, the client may experience deep soreness in the buttock for 24–48 hours. Warn them this is expected.

Cautions:

The sciatic nerve itself lies immediately deep to piriformis. Do not use aggressive or percussive techniques directly over the nerve's course — sustained compression and slow stripping are preferred over rapid cross-fiber or percussive work in this region.
The superior and inferior gluteal neurovascular bundles exit through the greater sciatic foramen above and below piriformis respectively. Avoid prolonged deep compression directly over the sciatic notch.
In clients with radicular symptoms, confirm the source before treating aggressively. If SLR is positive (suggesting disc involvement), piriformis work may worsen symptoms by compressing an already-irritated nerve.

Postural significance:

Piriformis tightens for two primary reasons: (1) prolonged sitting compresses and shortens it, and (2) weakness in gluteus medius forces piriformis to compensate as a hip stabilizer during single-leg stance (gait). In the second scenario, strengthening gluteus medius is essential — without it, piriformis release will not hold.

Clinical pearl:

If piriformis release does not hold between sessions, check the contralateral quadratus lumborum (QL). Pelvic obliquity from a tight QL on one side drops the contralateral ilium, altering the biomechanics of the opposite hip and forcing piriformis to work harder as a stabilizer. Treating the piriformis alone addresses the symptom; treating the contralateral QL addresses the cause.

Assessment

FAIR test (Flexion, Adduction, Internal Rotation):

Client supine. Flex the hip to 60 degrees, adduct it across midline, and internally rotate. This position stretches piriformis (because its action reverses to abduction and external rotation at this flexion angle). A positive test reproduces the client's buttock pain or posterior leg symptoms. Compare bilaterally.

Resisted external rotation:

Client supine with the hip and knee flexed to 90 degrees. Resist external rotation at the ankle (push the foot medially while the client pushes laterally). Pain in the deep buttock or weakness compared to the contralateral side suggests piriformis involvement.

Piriformis length test (hip internal rotation in flexion):

Client prone with the knee flexed to 90 degrees. Passively internally rotate the hip (let the foot fall laterally — this internally rotates the femur). A tight piriformis will limit internal rotation compared to the contralateral side. Normal hip IR is approximately 35–45 degrees. Less than 30 degrees with reproduction of buttock symptoms suggests piriformis tightness.

Related special orthopedic tests:

Straight leg raise (SLR) — to differentiate true sciatica (positive SLR, nerve root compression) from pseudo-sciatica (negative SLR, piriformis compression). A negative SLR with a positive FAIR test is the classic piriformis syndrome presentation.
Slump test — supplementary neurodynamic test for sciatic nerve tension; positive in both true and pseudo-sciatica, so it does not differentiate, but a negative slump with a positive FAIR is strongly suggestive of piriformis syndrome.

Muscle Groups

Deep six hip external rotators (anatomical):

Hip external rotators (functional):

Piriformis (this article)
obturator-internus
obturator-externus
gemellus-superior
gemellus-inferior
quadratus-femoris
gluteus-maximus (powerful external rotator, especially from flexion)
sartorius (assists external rotation)

Related Muscles

Synergists for hip external rotation:

obturator-internus — lies immediately inferior to piriformis at the greater sciatic notch
gemellus-superior and gemellus-inferior — bracket the obturator internus tendon; treated as a functional unit
quadratus-femoris — most inferior of the deep six; runs from ischial tuberosity to intertrochanteric crest
gluteus-maximus — powerful external rotator, especially from flexion; overlies piriformis

Antagonists (hip internal rotation):

gluteus-medius (anterior fibers) — primary internal rotator of the hip
tensor-fasciae-latae — assists internal rotation and hip flexion

Key Takeaways

The key differential: negative SLR + positive FAIR test = piriformis syndrome; positive SLR = true nerve root compression.
In 12% of the population, the sciatic nerve passes through the muscle belly — even normal contraction can compress the nerve.
Two causes of chronic piriformis tightness: prolonged sitting and gluteus medius weakness. Address the cause or release will not hold.
If release does not hold, check the contralateral QL — pelvic obliquity forces the opposite piriformis to compensate.
Warm and release gluteus maximus before attempting direct piriformis work.