Piriformis
Updated: Oct 5
Piriformis is a thick, flat, triangular muscle located deep in the buttock, although it is the most superficial of the deep lateral hip rotators. Its shape resembles a pear seed—hence the name piriformis, from the Latin piri (pear) and formis (shaped like). The muscle belongs to a functional group of six small but important muscles specialised in external rotation and stabilisation of the hip. The others are obturator internus and externus, superior and inferior gemellus, and quadratus femoris¹.
Piriformis is particularly relevant clinically because it often lies in close anatomical contact with the sciatic nerve, which passes immediately below the muscle—or, in some people, through or above it—as it leaves the pelvis through the greater sciatic foramen. Piriformis is therefore both an important landmark in the gluteal region and a potential source of sciatica-like pain, known as piriformis syndrome².
Origin and insertion
Piriformis originates from the anterior surface of the sacrum, between the second and fourth sacral foramina (S2–S4), and to a lesser extent from the sacrotuberous ligament and the margin of the greater sciatic foramen. It runs laterally and leaves the pelvis through the greater sciatic foramen, inserting on the superior and medial aspect of the greater trochanter of the femur³.
The muscle therefore runs from a medial and anterior position in the pelvis to a lateral and posterior position in the gluteal region, forming a distinct diagonal line beneath gluteus maximus. Its location makes it readily identifiable in cross-section and during palpation towards the sacrum.
Innervation and blood supply
Piriformis is supplied by a dedicated nerve called the nervus musculi piriformis, which arises from the anterior rami of S1 and S2⁴. It is a specialised branch of the sacral plexus rather than one of the usual peripheral nerves supplying the lower limb.
Blood is supplied by several branches of the arteria iliaca interna, including:
Arteria glutea superior
Arteria glutea inferior
Arteria pudenda interna⁵
This combined blood supply reflects the muscle’s location at the boundary between the vascular territories of the pelvis and gluteal region.
Relationships with other structures
Piriformis acts as an anatomical dividing line in the gluteal region. Structures above the muscle are described as suprapiriform, and those below it as infrapiriform. This division applies to:
Nerves: for example, the superior gluteal nerve above the muscle, and the sciatic and inferior gluteal nerves below it
Arteries: with corresponding names and courses⁶
Because the sciatic nerve passes below piriformis in most people, a tight or irritated muscle can compress the nerve and cause radiating leg pain—a central feature of piriformis syndrome.
Piriformis is an important dynamic stabiliser of the hip, with several roles that depend on joint position. Its main functions involve external rotation, abduction and stabilisation of the femur within the acetabulum, contributing to both static and dynamic activities. A particularly interesting feature of piriformis is that its function changes according to hip joint angle—especially whether or not the hip is flexed¹.
Primary functions at the hip
When the hip is in neutral or extension, piriformis primarily acts as:
An external rotator of the femur
A stabiliser of the hip, keeping the femoral head centred within the acetabulum
A weak posterior tilter of the pelvis through its pull on the sacrum
When the hip is flexed beyond 60–90 degrees, the muscle fibres’ line of pull changes relative to the joint’s axis of rotation. Piriformis then acts as:
An abductor of the thigh
A contributor to internal rotation (although this action is weak and debated)²
This functional shift occurs because the muscle rotates around the hip and changes its line of pull during flexion—an example of how a muscle can perform different functions depending on joint position.
Functional role during movement
Piriformis is activated during many movements, particularly in the following situations:
Walking: stabilises the hip during stance and controls rotation during push-off.
Single-leg standing: works with gluteus medius and minimus to maintain pelvic stability.
Stair climbing and lunges: acts as a stabiliser to prevent medial collapse at the hip and knee.
Rotation and sports involving rotational movements: provides precise control of the hip during rapid changes of direction³.
Interaction with other muscles
Piriformis is one of the six deep lateral hip rotators:
Obturator internus
Obturator externus
Gemellus superior
Gemellus inferior
Quadratus femoris
Together they form a muscular ‘cap’ around the posterior aspect of the hip that:
Resists unwanted internal rotation
Reinforces passive hip stability
Works with gluteus maximus during extension
Piriformis also interacts with gluteus medius og minimus to balance rotational forces in the frontal plane, and with iliopsoas and the adductor group as antagonistic and synergistic partners.
Piriformis and pelvic control
Piriformis also plays an indirect role in pelvic control, particularly through its sacral origin and attachment to the sacrotuberous ligament. It contributes to:
Stabilisation of the sacroiliac joint
Force transfer between the lower limb and trunk
Regulation of sacral tilt during asymmetrical loading
This is important in functional movements requiring controlled weight transfer, such as walking on uneven ground or carrying a load while standing on one leg.
Clinical relevance within movement chains
Piriformis may become overactive or compensatory when:
Gluteus medius or minimus is weak
Lumbopelvic control is poor
The adductors are shortened
Overactivity may cause myofascial pain or pressure on the sciatic nerve, contributing to piriformis syndrome. This is discussed further in part 3.
Piriformis syndrome
Piriformis syndrome is a neuromuscular condition in which piriformis irritates or compresses the sciatic nerve. This may cause pain radiating down the back of the thigh, often incorrectly attributed to sciatica caused by spinal nerve-root involvement.
Typical symptoms:
Deep, aching buttock pain
Worsening with sitting, walking or hip flexion
Radiation along the course of the sciatic nerve, often not extending below the knee
Tenderness over the greater sciatic foramen
A positive FAIR test (flexion, adduction, internal rotation)
The syndrome often develops as a result of:
A tight or overactive piriformis
Weak gluteal muscles
Pelvic or lumbar dysfunction
Excessive repetitive loading through running, cycling or rotation
Anatomical variations and risk factors
In most people, the sciatic nerve passes below piriformis, but in 10–15% of the population, part or all of the nerve may pass through the muscle. This increases the risk of compression⁴. Other risk factors include:
Prolonged sitting
Poor posture and reduced pelvic control
Trauma or scar tissue around the gluteal region
Clinical examination
Palpation:
Indirect palpation through gluteus maximus, immediately over the greater sciatic foramen
Pain reproduction is common in piriformis syndrome
Special tests:
FAIR test
Purpose: to reproduce pain associated with piriformis syndrome
Procedure: the patient lies on their side with the affected leg uppermost and the hip flexed approximately 60–90°; adduction and internal rotation are then applied
Interpretation: the test is positive if it causes pain or radiation in the buttock or posterior thigh
Evidence: frequently used clinically, but with moderate specificity and sensitivity
Piriformis stretch test
The patient lies supine with the affected leg crossed over the opposite knee and the hip and knee flexed
Downward pressure on the knee provokes stretch-related buttock pain
Treatment and physiotherapy
Treatment strategies vary according to the cause and severity, but the main aims are to reduce muscle tension, improve gluteal activation, and restore normal mobility and strength balance.
1. Manual treatment and stretching techniques:
Piriformis stretching in flexion and adduction, lying or sitting
Trigger-point treatment
Sacroiliac joint mobilisation when pelvic asymmetry is also present
2. Exercises:
Relaxation and control exercises for gluteus medius and minimus
Progression to strengthening of the hip extensors and stabilisers
Dynamic rotational control, for example through standing rotation exercises
3. Neuromotor training:
Focus on the hip–knee–foot chain during functional activities
Walking and stair climbing with an emphasis on symmetry and control
4. Other modalities:
TENS for pain relief
Ultrasound or heat as adjuncts for acute muscle spasms
Differential diagnoses
Piriformis syndrome should be distinguished from:
Lumbar radiculopathy with reduced strength, sensation or reflexes
Proximal hamstring tendon irritation
Gluteal bursitis
Trochanteric tendinopathy
MRI or ultrasound is rarely used to establish the diagnosis, but may be useful when a structural cause is suspected.
Exercises for piriformis
Background and clinical relevance
Piriformis plays an important role in hip stabilisation and external rotation of the femur, particularly during walking, rotation and rising to stand. In impaired function, such as piriformis syndrome, increased piriformis activity has been documented as compensation for weakness of gluteus medius and minimus¹. This may lead to sciatic nerve compression, reduced hip stability and pain in the buttock and lower limb².
Several EMG studies have investigated piriformis activation during different exercises. The literature also supports the use of stretching and neuromuscular control as part of treatment³.
1. Piriformis stretching
Supine piriformis stretch ("figure 4 stretch")
Research: a 2010 study found significantly increased hip mobility after six weeks of daily piriformis stretching in patients with non-radicular buttock pain⁴.
Clinical use: effective in reducing muscle tone and irritation around the sciatic nerve in piriformis syndrome.
Dosage: 30 seconds × 3, once or twice daily.
Modified seated stretch
Often used clinically for patients with limited mobility. Studies have found that both seated and supine variations increase hip abduction and external rotation without provoking symptoms⁵.
2. Movement control and stability
Clamshell with a resistance band
Research: EMG studies have shown low-to-moderate piriformis activation (20–30% MVIC) and high gluteus medius activation (60–80%)⁶.
Clinical relevance: improves hip stability and reduces piriformis overcompensation associated with gluteus medius weakness.
Dosage: 12–15 repetitions × 2–3 sets, three times per week.
90/90 hip mobility drill
Recommended in recent clinical guidelines as part of neuromuscular control and rotational hip mobility training⁷.
Increases movement tolerance and improves joint positioning during internal and external rotation.
3. Activation and selective strengthening
Standing external rotation with a resistance band, targeting piriformis
Research: a study published in Journal of Orthopaedic & Sports Physical Therapy (JOSPT, 2016) found that standing external rotation with a resistance band produces targeted piriformis activation (35–40% MVIC) while placing little load on surrounding structures⁸.
Clinical value: suitable in later rehabilitation to restore function without provoking the sciatic nerve.
Single-leg glute bridge
Research: although gluteus maximus is the main muscle activated, piriformis has also been shown to act as a synergistic rotator and hip extensor⁹.
Clinical relevance: improves hip control within the lumbopelvic chain and supports the transition to functional strengthening.
4. Evidence-based approach to piriformis syndrome
According to a systematic review by Boyajian-O’Neill et al. in American Family Physician (2008), treatment of piriformis syndrome should include:
Stretching: reduces muscular irritation and compression.
Strengthening exercises: restores balance in the hip musculature.
Neuromuscular training: improves movement patterns and reduces overuse.
A more recent review by Probst et al. (2020) also highlights that piriformis can easily become overactive in compensation, and that an appropriate rehabilitation programme must emphasise gluteal function and movement control¹⁰.
Summary
Piriformis should not be trained solely for isolated strength, but should be included in comprehensive hip and pelvic rehabilitation. The evidence supports:
Stretching for symptom relief and mobility
Selective activation through external rotation and control exercises
Gluteus medius and minimus strengthening to reduce compensatory loading
Gradual exposure to functional loading, including stairs, walking and rotation
References:
Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders.
Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier.
Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier.
Jeremy J. MD: Piriformis. Radiopaedia.org (accessed 15/02/2016).
Dissector Answers - Pelvic Neurovasculature. The University of Michigan (accessed 15/02/2016).
Swenson R. DC, MD, PhD: The gluteal region. O'Rahilly 2008 (accessed 15/02/2016).
