Deep Six Rotators Muscle Anatomy

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Piriformis	Origin: Anterior surface of the sacrum around S2-S4; gluteal surface of the ilium; sacrotuberous ligament Insertion: Greater trochanter of the femur, on the medial side of the superior aspect Action: Laterally rotates the thigh at the hip joint; abducts the thigh when the hip is flexed past about 60 degrees; stabilises the head of the femur in the acetabulum Innervation: Superior gluteal nerve; ventral rami of S1 and S2 Blood Supply: Superior gluteal, inferior gluteal, and internal pudendal arterial branches
Superior gemellus	Origin: Ischial spine Insertion: Medial surface of the greater trochanter Action: Lateral rotation of the hip; assists abduction when the hip is flexed Innervation: Primarily the nerve to obturator internus (L5, S1); additionally the nerve to quadratus femoris (L5, S1) in some individuals Blood Supply: Inferior gluteal and internal pudendal/gemellar branches; possible superior gluteal contribution
Obturator internus	Origin: Pelvic surfaces of the ilium and ischium; obturator membrane Insertion: Medial surface of the greater trochanter of the femur, specifically the trochanteric fossa Action: Laterally rotates the hip joint; stabilises the hip joint; assists hip abduction when the hip is flexed Innervation: Nerve to obturator internus (L5, S1) Blood Supply: Obturator, inferior gluteal, and internal pudendal branches
Inferior gemellus	Origin: Ischial tuberosity Insertion: Medial surface of the greater trochanter, near the trochanteric fossa, via the obturator internus tendon Action: Lateral rotation of the hip; assists abduction when the hip is flexed Innervation: Nerve to quadratus femoris (L5, S1) Blood Supply: Inferior gluteal and medial circumflex femoral arterial contributions (descriptions vary)
Quadratus femoris	Origin: Ischial tuberosity Insertion: Quadrate tubercle and just below it Action: Hip lateral rotation; hip stabilisation Innervation: Nerve to quadratus femoris (L5, S1) Blood Supply: Inferior gluteal artery as the main supply; medial circumflex femoral artery as a supplemental supply
Obturator externus	Origin: Obturator foramen and obturator membrane Insertion: Trochanteric fossa of the greater trochanter Action: Hip lateral rotation; hip stabilisation; potentially assists hip adduction when the hip is flexed Innervation: Posterior division of the obturator nerve (L3, L4) Blood Supply: Anterior branch of the obturator artery and medial circumflex femoral artery

Last updated: 8 June 2026 Estimated Reading Time: 15 min

Location & Overview

The deep six rotators are six short muscles located in the posterior hip region: piriformis, superior gemellus, obturator internus, inferior gemellus, quadratus femoris, and obturator externus. They are commonly grouped together because they all contribute to lateral rotation of the hip and help stabilise the femoral head in the acetabulum, the socket of the hip joint.^[1,2]

Most of the deep six group lies deep in the gluteal region, beneath gluteus maximus and close to the posterior capsule of the hip joint. Piriformis, obturator internus, the two gemelli, and quadratus femoris form a deep posterior layer. Obturator externus is slightly different: it is often described anatomically with the medial thigh because it is supplied by the obturator nerve, but it is still part of the functional deep-six lateral-rotator group because it passes to the proximal femur and helps rotate and stabilise the hip.^[1,2]

Piriformis leaves the pelvis through the greater sciatic foramen. Obturator internus leaves through the lesser sciatic foramen and then turns around the ischium before joining the gemelli. Superior gemellus and inferior gemellus sit above and below the obturator internus tendon, forming a combined unit that is sometimes called triceps coxae. Quadratus femoris lies inferior to that unit, while obturator externus passes deep to quadratus femoris toward the trochanteric fossa.^[1,2]

The close relationship between piriformis and the sciatic nerve is clinically important because the nerve may pass below, through, or around the muscle depending on the person. Smoll (2010) reviewed 18 cadaveric studies and estimated piriformis and sciatic nerve anomaly prevalence at 16.9%.^[3] Ollivier et al. (2026) reviewed 26 studies and reported sciatic nerve variation relative to piriformis in 14.5% of lower limbs.^[4]

Deep six rotators of the hip — Here, we can see the six deep hip lateral rotators together: piriformis, superior gemellus, obturator internus, inferior gemellus, quadratus femoris, and obturator externus.

Piriformis muscle from a posterior view — Here, we can see the piriformis muscle from a posterior view.

Superior gemellus muscle from a posterior view — Here, we can see the superior gemellus muscle from a posterior view.

Obturator internus muscle from a posterior view — Here, we can see the obturator internus muscle from a posterior view.

Inferior gemellus muscle from a posterior view — Here, we can see the inferior gemellus muscle from a posterior view.

Quadratus femoris muscle from a posterior view — Here, we can see the quadratus femoris muscle from a posterior view.

Obturator externus muscle from a posterior view — Here, we can see the obturator externus muscle from a posterior view.

Origin & Insertion

The deep six rotators attach from the pelvis to the proximal femur. Their origins differ across the sacrum, ischium, obturator membrane, and obturator foramen, but most of their insertions converge around the greater trochanter and trochanteric fossa. That arrangement gives the group short, deep lines of pull close to the hip joint, making them suited to joint control as well as rotation.^[1,2]

Piriformis Origin & Insertion

Piriformis originates from the anterior surface of the sacrum around S2-S4. It also has attachments from the gluteal surface of the ilium and the sacrotuberous ligament. Its tendon inserts on the greater trochanter of the femur, on the medial side of the superior aspect.^[5]

Piriformis origin marked in red on the anterior sacrum — This image shows the main origin of the piriformis muscle on the anterior surface of the sacrum, marked in red.

Piriformis origin marked in red on the gluteal surface of the ilium — This image shows another origin of the piriformis muscle on the gluteal surface of the ilium, marked in red.

Piriformis origin marked in red on the sacrotuberous ligament — This image shows the sacrotuberous ligament, another origin point of the piriformis muscle, marked in red.

Piriformis insertion on the greater trochanter — This image shows the insertion of the piriformis muscle on the greater trochanter of the femur.

Superior Gemellus Origin & Insertion

Superior gemellus originates from the ischial spine and inserts on the medial surface of the greater trochanter. It lies directly above obturator internus and blends functionally with the obturator internus tendon.^[2,6]

Superior gemellus origin marked in red — Here, we can see the origin of the superior gemellus marked in red on the ischial spine.

Superior gemellus insertion marked in blue — Here, we can see the insertion of the superior gemellus marked in blue on the medial surface of the greater trochanter.

Obturator Internus Origin & Insertion

Obturator internus originates from the pelvic surfaces of the ilium and ischium and from the obturator membrane. Its tendon leaves the pelvis through the lesser sciatic foramen and inserts on the medial surface of the greater trochanter of the femur, specifically the trochanteric fossa.^[2,7]

Obturator internus origin marked in red — Here, we can see the origin of the obturator internus muscle marked in red on the pelvic surfaces of the ilium and ischium.

Obturator membrane from a posterior view — Here, we can see the obturator membrane, which is another origin point of the obturator internus muscle.

Obturator internus insertion marked in blue — Here, we can see the insertion of the obturator internus muscle marked in blue on the trochanteric fossa.

Inferior Gemellus Origin & Insertion

Inferior gemellus originates from the ischial tuberosity. The inferior gemellus tendon blends with the obturator internus tendon and inserts on the medial surface of the greater trochanter, near the trochanteric fossa. It sits inferior to obturator internus and superior to quadratus femoris, helping reinforce the obturator internus tendon region.^[2,6]

Inferior gemellus origin marked in red — Here, we can see the origin of the inferior gemellus muscle marked in red on the ischial tuberosity.

Inferior gemellus insertion marked in blue — Here, we can see the insertion of the inferior gemellus muscle marked in blue on the medial surface of the greater trochanter, near the trochanteric fossa.

Quadratus Femoris Origin & Insertion

Quadratus femoris originates from the ischial tuberosity and inserts on the quadrate tubercle of the femur and the area just below it. The quadrate tubercle is located on the intertrochanteric crest on the posterior side of the proximal femur.^[1,2]

Quadratus femoris origin marked in red — Here, we can see the origin of the quadratus femoris muscle marked in red on the ischial tuberosity.

Quadratus femoris insertion marked in blue — Here, we can see the insertion of the quadratus femoris muscle marked in blue on the quadrate tubercle and the area just below it.

Obturator Externus Origin & Insertion

Obturator externus originates from the obturator foramen and obturator membrane. Its tendon passes beneath the neck of the femur and inserts on the trochanteric fossa of the greater trochanter.^[2,7]

Obturator externus origin marked in red — Here, we can see the obturator externus origin marked in red on the obturator foramen.

Obturator membrane from an anterior view — Here, we can see the obturator membrane, which is another origin point of the obturator externus muscle.

Obturator externus insertion marked in blue — Here, we can see the obturator externus insertion marked in blue on the trochanteric fossa of the greater trochanter.

Action & Function

The shared action of the deep six rotators is lateral rotation of the hip. Lateral rotation turns the front of the thigh and knee outward. The group is especially useful when the hip is extended, but the exact contribution of each muscle changes with hip position.^[1,2]

Person demonstrating hip external rotation — This image shows an example of hip external rotation, which involves rotating the leg from the hip joint outward. External rotation is also referred to as lateral rotation.

Piriformis, superior gemellus, obturator internus, and inferior gemellus can assist with hip abduction when the hip is flexed. Hip abduction means moving the thigh away from the midline of the body. The individual gemellus muscles are small, so their abduction contribution is secondary compared with larger hip abductors.^[2,6]

Person demonstrating hip abduction — This image shows an example of hip abduction, which involves moving the leg out to the side. **Piriformis, obturator internus, superior gemellus, and inferior gemellus** can assist abduction when the hip is flexed.

Obturator externus also contributes to hip lateral rotation and stabilisation. Some descriptions note that it may assist hip adduction when the hip is flexed, although the literature is not completely consistent on that point. Hip adduction means moving the thigh back toward the midline.^[7,2]

Person demonstrating hip adduction — This image shows an example of hip adduction, which involves moving the leg toward the body’s midline. **Obturator externus** may weakly assist hip adduction when the hip is flexed.

These muscles also help stabilise the hip joint by compressing and controlling the femoral head within the acetabulum. Parvaresh et al. (2019) examined 10 human cadaver hips and reported that the short external rotators have short fibres and architecture consistent with an important stabilising role around the hip.^[8]

Vaarbakken et al. (2015) also showed that the mechanical role of quadratus femoris and obturator externus changes with hip position. Their cadaveric measurements support the idea that these muscles should not be reduced to one simple movement label in every joint position.^[9]

Innervation

Deep six innervation is split across several nerves. Piriformis is supplied by the superior gluteal nerve and the ventral rami of S1 and S2. Older summaries may use the phrase “nerve to piriformis”, but anatomical studies also support superior gluteal nerve and ventral ramus supply.^[10,5]

Obturator internus is supplied by the nerve to obturator internus, with L5 and S1 roots. Superior gemellus is also primarily supplied by the nerve to obturator internus, and may receive an additional nerve to quadratus femoris contribution in some individuals.^[2,6]

Nerve to the obturator internus — This image shows the nerve to the obturator internus, which supplies **obturator internus** and primarily supplies **superior gemellus**.

Inferior gemellus and quadratus femoris are supplied by the nerve to quadratus femoris, with L5 and S1 roots. Aung et al. (2001) reported that superior gemellus can receive dual innervation from both the nerve to obturator internus and the nerve to quadratus femoris, which helps explain why innervation descriptions may vary between sources.^[11]

Obturator externus is supplied by the posterior division of the obturator nerve, with L3 and L4 roots. This is one reason obturator externus is often described with the medial thigh muscles by compartment, even though it is included functionally in the deep six rotator group.^[7,2]

Blood Supply

The deep six rotators do not share one single artery. Their arterial supply comes from the gluteal, internal pudendal, obturator, and medial circumflex femoral systems around the posterior pelvis and proximal thigh.^[1,2]

Piriformis is supplied by branches of the superior gluteal, inferior gluteal, and internal pudendal arteries. Obturator internus receives arterial supply from obturator, inferior gluteal, and internal pudendal branches. Superior gemellus is supplied by inferior gluteal and internal pudendal/gemellar branches, with possible superior gluteal contribution. Inferior gemellus has varying descriptions in the literature, with some descriptions listing the inferior gluteal artery as supplying both gemelli and others listing the inferior gemellus as supplied mainly by the medial circumflex femoral artery.^[12,6,7,1] The discrepancy is anatomically plausible because the deep branch of the medial circumflex femoral artery passes anterior to the conjoint tendon of inferior gemellus, obturator internus, and superior gemellus, while the inferior gluteal artery supplies neighbouring deep gluteal muscles and participates in nearby posterior hip arterial anastomoses.^[13] Because published descriptions vary, the inferior gemellus is best described as receiving contributions from the inferior gluteal and medial circumflex femoral arterial systems rather than from one consistently agreed-upon single source.

Quadratus femoris is supplied mainly by the inferior gluteal artery, with supplemental contribution from the medial circumflex femoral artery. Obturator externus is supplied by the anterior branch of the obturator artery and the medial circumflex femoral artery.^[1,7]

Arteries of the lower limb — This image shows the arteries of the lower limb. The deep six rotators receive arterial supply from several pelvic and proximal thigh arterial systems, including gluteal, internal pudendal, obturator, and medial circumflex femoral branches.

References

[1] Standring S, editor. Gray’s anatomy: the anatomical basis of clinical practice. 42nd ed. Amsterdam: Elsevier; 2021.
[2] Dalley AF 2nd, Agur AMR. Moore’s clinically oriented anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.
[3] Smoll NR. Variations of the piriformis and sciatic nerve with clinical consequence: a review. Clin Anat. 2010 Jan;23(1):8-17. doi:10.1002/ca.20893. PMID:19998490.
[4] Ollivier I, Dannhoff G, Garnon J, Koch G, Clavert P. Anatomical variations of the sciatic nerve and its relationship to the pelvic bone: a systematic review. Surg Radiol Anat. 2026 Jan 29;48(1):50. doi:10.1007/s00276-026-03818-w. PMID:41612052.
[5] Chang C, Jeno SH, Varacallo M. Anatomy, Bony Pelvis and Lower Limb, Piriformis Muscle. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2022.
[6] Lezak B, Massel DH. Anatomy, Bony Pelvis and Lower Limb, Gemelli Muscles. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2023.
[7] Larson MR, Ryan W. Anatomy, Abdomen and Pelvis, Obturator Muscles. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2023.
[8] Parvaresh KC, Chang C, Patel A, Lieber RL, Ball ST, Ward SR. Architecture of the short external rotator muscles of the hip. BMC Musculoskelet Disord. 2019 Dec 20;20(1):611. doi:10.1186/s12891-019-2995-0. PMID:31862009.
[9] Vaarbakken K, Steen H, Samuelsen G, Dahl HA, Leergaard TB, Stuge B. Primary functions of the quadratus femoris and obturator externus muscles indicated from lengths and moment arms measured in mobilized cadavers. Clin Biomech (Bristol, Avon). 2015 Mar;30(3):231-237. doi:10.1016/j.clinbiomech.2015.02.004. PMID:25697090.
[10] Iwanaga J, Eid S, Simonds E, Schumacher M, Loukas M, Tubbs RS. The majority of piriformis muscles are innervated by the superior gluteal nerve. Clin Anat. 2019 Mar;32(2):282-286. doi:10.1002/ca.23311. PMID:30408241.
[11] Aung HH, Sakamoto H, Akita K, Sato T. Anatomical study of the obturator internus, gemelli and quadratus femoris muscles with special reference to their innervation. Anat Rec. 2001 May 1;263(1):41-52. doi:10.1002/ar.1075. PMID:11331970.
[12] Chang C, Jeno SH, Varacallo M. Anatomy, Bony Pelvis and Lower Limb, Piriformis Muscle. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2023.
[13] Gautier E, Ganz K, Krügel N, Gill T, Ganz R. Anatomy of the medial femoral circumflex artery and its surgical implications. J Bone Joint Surg Br. 2000;82(5):679-683.

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Deep Six Rotators Muscle Anatomy

Location & Overview