Deep hip rotators

Function

Six small muscles under the gluteus maximus

Six muscles lie deep to the gluteus maximus (the large muscle of the buttock) and rotate the thigh outward at the hip¹. They are the piriformis, the obturator internus, the obturator externus, the superior gemellus, the inferior gemellus and the quadratus femoris¹. The two gemelli are small muscle bundles that act as accessories to the obturator internus tendon⁷. That tendon lies in a groove between them⁷.

Each muscle starts on the pelvis and ends on the femur, the thigh bone⁷. Four end on the greater trochanter, the bony bump at the outer hip, at the top of the thigh bone⁷.

Muscle	Starts on	Ends on
Piriformis	The front of the sacrum, the triangle-shaped bone at the base of the spine7	The upper border of the greater trochanter7
Obturator internus	Inside the pelvis, on the pubis, the ischium and the inner surface of the hip bone7	The inner surface of the greater trochanter7
Superior gemellus	The ischial spine, a point of bone on the ischium7	The inner surface of the greater trochanter, with the obturator internus tendon7
Inferior gemellus	The upper part of the ischial tuberosity, the “sitting bone”7	The inner surface of the greater trochanter, with the obturator internus tendon7
Quadratus femoris	The outer border of the ischial tuberosity7	A line on the back of the femur7
Obturator externus	The outer surface of the front wall of the pelvis, on the pubis and the ischium7	The trochanteric fossa, a hollow on the femur7

The pubis is the bone at the lower front of the pelvis. The ischium is the lower rear part of the hip bone, which carries the sitting bone. The two gemelli join the obturator internus to form one conjoined tendon⁸. The piriformis tendon is often partly blended with that shared tendon⁷.

How their job changes as the hip bends

A classic anatomy text describes the deep muscles as powerful outward rotators of the thigh⁷. It says they stop rotating and become abductors when the thigh is flexed (bent) in sitting⁷. Abductors move a limb away from the midline of the body. The text names one exception: the obturator externus keeps turning the thigh bone outward⁷.

One study measured outward rotation torque (turning force) in 15 fresh-frozen cadaver hips². For the piriformis, the obturator internus and their conjoined tendon, it peaked at 15° of hip flexion and fell as the hip flexed further². The torque of the obturator externus rose with flexion instead². At 75° of flexion or more, the obturator externus had the highest outward rotation torque of the short rotators². On average it was 2.18 times that of the conjoined tendon at 90° and 3.80 times at 105°².

At 75° of flexion or more, the obturator externus had the highest outward rotation torque of the short rotators.

What recordings from the working muscles show

The table shows recordings of three of these muscles made with fine-wire electrodes, very thin wire sensors placed into a muscle to record its activity^9,10,11.

Muscle	Who was recorded	When it was most active
Obturator internus	Ten participants	In isometric (held, with no joint movement) hip extension, then outward rotation, then abduction9
Quadratus femoris	10 healthy participants	In maximal isometric outward rotation and the clam movement10
Piriformis	Eleven healthy men	In prone (face-down) hip extension with the hip rotated outward, of seven hip movements11

Whether they steady the joint

In 10 cadaver hips, each deep rotator had a relatively small force-producing cross-section and short fibres¹². Some sources suggest these muscles help hold the femoral head (the ball at the top of the thigh bone) in its socket^3,12,13:

• The authors of the 10-hip study pointed to the large combined cross-section and short fibres of the gemelli and obturators¹². They concluded that these suggest the muscles mainly stabilise the hip joint more than they rotate it¹².
• A narrative review is a summary of research written without a set, checkable search method. One proposed that the quadratus femoris, gemelli and both obturators, with three other deep muscles, may be the hip’s primary stabilisers³. It also noted that research on hip muscles is limited³.
• The obturator externus tendon is described as passing like a sling under the neck of the femur¹³. A string-model study of 18 fresh cadaver hips concluded that it helps hold the femoral head in the socket¹³.

Two modelling studies of 12 participants each, which estimate forces with a model rather than measuring them, tested the idea^4,14. In one, of walking and squatting, simulated maximal activation of the six muscles pointed the hip contact force more towards the centre of the socket¹⁴. The other modelled walking⁴. Hip stiffness in the forward-backward plane was 0.8% lower with the muscles switched off and 3.2% higher with them fully on⁴. Those authors said this casts doubt on the muscles’ assumed role as hip stabilisers⁴.

The authors of the obturator internus recordings raised a doubt of their own⁹. They said the muscle’s direction-specific activity questions a general hip-stabilising role⁹.

Breakdown

Strains in kicking sports

Tears of the obturator externus and internus are uncommon injuries, known mostly from a few case reports in high-level athletes⁵. Three reports describe them^5,15,16:

• One series covered four seasons in four teams of the Spanish first division⁵. In it, 16 professional soccer players had an obturator muscle tear confirmed by MRI, a scan that shows soft tissue⁵. Twelve tears were of the obturator externus and four of the obturator internus⁵. The main complaint was pain at the front of the hip⁵.
• In a case series of three professional soccer players with obturator externus injuries, two were hurt by long-distance shooting and one by long-distance passing¹⁵.
• A report of two cases described obturator internus strains in young male athletes in kicking sports¹⁶. One was a sudden strain alongside a strain of the adductor longus, one of the hip adductors¹⁶. The other was an overuse injury of both obturator internus muscles¹⁶.

The authors of the three-player series wrote that few studies describe injuries to the deep hip rotators¹⁵. They gave two reasons: such injuries are either under-reported, or mistaken for hamstring, adductor or quadriceps injuries¹⁵.

The quadratus femoris and the ischiofemoral space

The ischiofemoral space is the gap between the ischium and the femur¹⁷. One MRI study measured it in 12 hips of nine women, aged 30 to 71, with hip pain and abnormal quadratus femoris signal¹⁷. Their gap averaged 13 mm, against 23 mm in 11 control hips¹⁷.

In those 12 hips, the quadratus femoris showed oedema (swelling caused by fluid) in every one¹⁷. It showed a partial tear in 33%¹⁷. The nearby hamstring tendons showed oedema in 50%¹⁷.

A meta-analysis, which pools earlier studies, compared 217 hip MRIs with ischiofemoral impingement (pinching of soft tissue in that gap) and 140 control hips¹⁸. The space was about 15 mm in the impingement cases, against 26 mm¹⁸. In the five studies it pooled, 133 of the 154 people with the condition were female¹⁸.

In people with hip joint conditions

Two small studies looked at these muscles in people with a hip joint condition^20,21.

The first was an MRI study of 12 people with a one-sided tear of the hip labrum and 12 matched healthy people²⁰. A labrum is a rim of tough tissue around the edge of a joint socket. Piriformis and quadratus femoris cross-sectional area did not differ between groups²⁰.

The second was a fine-wire study of squatting²¹. It compared 15 people with femoroacetabular impingement syndrome, a hip condition, with 14 healthy controls²¹. Unlike the controls, the impingement group activated the obturator internus on the way down about as much as on the way up²¹.

Recovery

Return to play after a strain

In the series of 16 professional soccer players with obturator muscle tears, the mean time back to play was 11.5 days⁵. In the case series of three players with obturator externus injuries, all three were playing again after 10 days¹⁵.

How their size changes with sport and training

One study scanned 46 elite Australian Football League players by MRI three times in a season²². Piriformis cross-sectional area, the size of a slice cut straight across the muscle, increased significantly between each scan²². Players whose piriformis grew less had slightly higher odds of sustaining an injury²².

The same study tested motor control training, exercise that trains how the deep trunk muscles are switched on and coordinated²². Two 30-minute sessions a week for 7 to 8 weeks were reported to increase piriformis size in players with low back pain²².

An MRI study compared 33 professional ballet dancers with 33 athletes matched for age and sex, at a single point in time²³. Piriformis, gemelli and quadratus femoris cross-sectional areas were similar in the two groups, and unrelated to hip pain²³.

Connections

The sciatic nerve

The sciatic nerve is the large nerve that runs from the lower back down the back of the thigh. It leaves the pelvis below the piriformis⁷. In the upper part of its course it rests on the obturator internus, the gemelli and the quadratus femoris, covered by the gluteus maximus⁷.

Common peroneal nerve is another name for the common fibular nerve. Two meta-analyses pooled how often the nerve takes this usual path, and how often one part of it pierces the muscle^6,24:

Meta-analysis	Nerve passes as one trunk below the piriformis	Common peroneal part passes through the piriformis
44 cadaver studies	90%6	8%6
45 studies, 7,068 lower limbs	85.2%24	9.8%24

A 2010 systematic review described piriformis syndrome as sciatica (pain along the sciatic nerve) caused by the piriformis compressing the nerve²⁵. It noted that the condition remained controversial after more than 70 years²⁵.

The nerves that supply them

The obturator externus is supplied through the obturator nerve, a nerve that runs to the inner-thigh muscles⁷. One nerve supplies the obturator internus and the superior gemellus⁷. Another supplies the quadratus femoris and the inferior gemellus⁷. The piriformis has a nerve that may be double⁷.

Exercises and stretches

Related exercise pages: side-lying hip abduction and running^10,26. A muscle MRI study of 10 healthy, active people compared exercises²⁶. The clamshell, and side-lying hip abduction with outward rotation, activated the obturator internus more than a single-leg bridge or reverse clamshell²⁶. The clamshell is a side-lying exercise that opens the knees apart with the hips and knees bent. In 10 healthy participants, quadratus femoris activity was very high in the stance phase of running, when the foot is on the ground¹⁰.

Related stretch page: the figure-4 stretch²⁷. In 17 hips from nine embalmed cadavers, strings run along the short outward rotators were displaced significantly in each of four stretch positions tested²⁷. The authors wrote that there was limited research showing how well common stretches work on these muscles²⁷.

Sources

1. Betts JG, Young KA, Wise JA, Johnson E, Poe B, Kruse DH, Korol O, Johnson JE, Womble M, DeSaix P (2022). Anatomy and Physiology 2e. OpenStax. Link
2. Ito Y, Suzuki D, Kizawa F, Kanaizumi A, Hiraiwa T, Tamura T, Kawaguchi Y, Nagoya S (2025). Comparison of External Rotation Torque of Short External Rotator Muscles in Hip Flexion Position. Journal of Orthopaedic Research. doi:10.1002/jor.70005 PMID 40524428
3. Retchford TH, Crossley KM, Grimaldi A, Kemp JL, Cowan SM (2013). Can local muscles augment stability in the hip? A narrative literature review. Journal of Musculoskeletal & Neuronal Interactions. PMID 23445909
4. Meinders E, Pizzolato C, Goncalves BAM, Lloyd DG, Saxby DJ, Diamond LE (2022). The Deep Hip Muscles are Unlikely to Stabilize the Hip in the Sagittal Plane During Walking: A Joint Stiffness Approach. IEEE Transactions on Biomedical Engineering. doi:10.1109/tbme.2021.3114717 PMID 34559628
5. Wong-On M, Turmo-Garuz A, Arriaza R, Gonzalez de Suso JM, Til-Perez L, Yanguas-Leite X, Diaz-Cueli D, Gasol-Santa X (2018). Injuries of the obturator muscles in professional soccer players. Knee Surgery, Sports Traumatology, Arthroscopy. doi:10.1007/s00167-017-4453-6 PMID 28188336
6. Poutoglidou F, Piagkou M, Totlis T, Tzika M, Natsis K (2020). Sciatic Nerve Variants and the Piriformis Muscle: A Systematic Review and Meta-Analysis. Cureus. doi:10.7759/cureus.11531 PMID 33354475
7. Gray H; Lewis WH (editor) (1918). Anatomy of the Human Body. Lea & Febiger, Philadelphia (20th edition). Link
8. Lezak B, Massel DH (2026). Anatomy, Bony Pelvis and Lower Limb, Gemelli Muscles. StatPearls. PMID 32491352
9. Hodges PW, McLean L, Hodder J (2014). Insight into the function of the obturator internus muscle in humans: observations with development and validation of an electromyography recording technique. Journal of Electromyography and Kinesiology. doi:10.1016/j.jelekin.2014.03.011 PMID 24788026
10. Semciw AI, Freeman M, Kunstler BE, Mendis MD, Pizzari T (2015). Quadratus femoris: An EMG investigation during walking and running. Journal of Biomechanics. doi:10.1016/j.jbiomech.2015.05.029 PMID 26116043
11. Morimoto Y, Oshikawa T, Imai A, Okubo Y, Kaneoka K (2018). Piriformis electromyography activity during prone and side-lying hip joint movement. Journal of Physical Therapy Science. doi:10.1589/jpts.30.154 PMID 29410588
12. Parvaresh KC, Chang C, Patel A, Lieber RL, Ball ST, Ward SR (2019). Architecture of the Short External Rotator Muscles of the Hip. BMC Musculoskeletal Disorders. doi:10.1186/s12891-019-2995-0 PMID 31862009
13. Gudena R, Alzahrani A, Railton P, Powell J, Ganz R (2015). The anatomy and function of the obturator externus. Hip International. doi:10.5301/hipint.5000249 PMID 25952918
14. Meinders E, Pizzolato C, Gonçalves B, Lloyd DG, Saxby DJ, Diamond LE (2022). Activation of the deep hip muscles can change the direction of loading at the hip. Journal of Biomechanics. doi:10.1016/j.jbiomech.2022.111019 PMID 35248802
15. Rhim HC, Gureck AE, Jang KM (2022). Acute Obturator Externus Injury in Professional Soccer Players: A Case Series. Medicina (Kaunas). doi:10.3390/medicina58091145 PMID 36143822
16. Byrne C, Alkhayat A, O'Neill P, Eustace S, Kavanagh E (2017). Obturator internus muscle strains. Radiology Case Reports. doi:10.1016/j.radcr.2016.10.020 PMID 28228895
17. Torriani M, Souto SC, Thomas BJ, Ouellette H, Bredella MA (2009). Ischiofemoral impingement syndrome: an entity with hip pain and abnormalities of the quadratus femoris muscle. American Journal of Roentgenology. doi:10.2214/ajr.08.2090 PMID 19542413
18. Singer AD, Subhawong TK, Jose J, Tresley J, Clifford PD (2015). Ischiofemoral impingement syndrome: a meta-analysis. Skeletal Radiology. doi:10.1007/s00256-015-2111-y PMID 25672947
19. Maraş Özdemir Z, Aydıngöz Ü, Görmeli CA, Sağır Kahraman A (2015). Ischiofemoral Space on MRI in an Asymptomatic Population: Normative Width Measurements and Soft Tissue Signal Variations. European Radiology. doi:10.1007/s00330-015-3625-3 PMID 25680726
20. Mendis MD, Wilson SJ, Hayes DA, Hides JA (2020). Hip muscle atrophy in patients with acetabular labral joint pathology. Clinical Anatomy. doi:10.1002/ca.23429 PMID 31301249
21. Diamond LE, van den Hoorn W, Bennell KL, Wrigley TV, Hinman RS, O'Donnell J, Hodges PW (2019). Deep hip muscle activation during squatting in femoroacetabular impingement syndrome. Clinical Biomechanics. doi:10.1016/j.clinbiomech.2019.07.017 PMID 31351343
22. Leung FT, Mendis MD, Stanton WR, Hides JA (2015). The relationship between the piriformis muscle, low back pain, lower limb injuries and motor control training among elite football players. Journal of Science and Medicine in Sport. doi:10.1016/j.jsams.2014.06.011 PMID 25027772
23. Emery S, Cook J, Ferrar K, Mayes S (2021). Deep hip external rotator muscle size in ballet dancers compared to non-dancing athletes, and associations to pain. Physical Therapy in Sport. doi:10.1016/j.ptsp.2021.06.010 PMID 34237542
24. Tomaszewski KA, Graves MJ, Henry BM, Popieluszko P, Roy J, Pękala PA, Hsieh WC, Vikse J, Walocha JA (2016). Surgical anatomy of the sciatic nerve: A meta-analysis. Journal of Orthopaedic Research. doi:10.1002/jor.23186 PMID 26856540
25. Hopayian K, Song F, Riera R, Sambandan S (2010). The clinical features of the piriformis syndrome: a systematic review.. European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society. doi:10.1007/s00586-010-1504-9 PMID 20596735
26. Kim S, Burland JP, Morgan KD, DiStefano LJ, Boling MC, Glaviano NR (2026). Superficial and Deep Gluteal Muscle Activation During Common Therapeutic Exercises: A Muscle Functional Magnetic Resonance Imaging Analysis.. Sports Health. doi:10.1177/19417381251372979 PMID 40977436
27. McGovern RP, Kivlan BR, Martin RL (2017). LENGTH CHANGE OF THE SHORT EXTERNAL ROTATORS OF THE HIP IN COMMON STRETCH POSITIONS: A CADAVERIC STUDY.. International journal of sports physical therapy. doi:10.26603/ijspt20171068 PMID 29234558

Every source the library cites

Changes

• October 7, 2026 First published.