The internal obturator muscle or obturator internus muscle originates on the medial surface of the

obturator membrane The obturator membrane is a thin fibrous sheet, which almost completely closes the obturator foramen. Its fibers are arranged in interlacing bundles mainly transverse in direction; the uppermost bundle is attached to the obturator tubercles and ...

, the

ischium The ischium () form ...

near the membrane, and the rim of the pubis. It exits the

pelvic cavity The pelvic cavity is a body cavity that is bounded by the bones of the pelvis. Its oblique roof is the pelvic inlet (the superior opening of the pelvis). Its lower boundary is the pelvic floor. The pelvic cavity primarily contains the reproducti ...

through the

lesser sciatic foramen The lesser sciatic foramen is an opening (foramen) between the pelvis and the back of the thigh. The foramen is formed by the sacrotuberous ligament which runs between the sacrum and the ischial tuberosity and the sacrospinous ligament which runs ...

. The internal obturator is situated partly within the

lesser pelvis The pelvic cavity is a body cavity that is bounded by the bones of the pelvis. Its oblique roof is the pelvic inlet (the superior opening of the pelvis). Its lower boundary is the pelvic floor. The pelvic cavity primarily contains the reproducti ...

, and partly at the back of the

hip-joint In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...

. It functions to help laterally rotate femur with hip extension and abduct femur with hip flexion, as well as to steady the femoral head in the acetabulum.

Structure

Origin

The internal obturator muscle arises from the inner surface of the antero-lateral wall of the

pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

. It surrounds the

obturator foramen The obturator foramen (Latin foramen obturatum) is the large opening created by the ischium and pubis bones of the pelvis through which nerves and blood vessels pass. Structure It is bounded by a thin, uneven margin, to which a strong membran ...

. It is attached to the

inferior pubic ramus In vertebrates, the pubic region ( la, pubis) is the most forward-facing (ventral and anterior) of the three main regions making up the coxal bone. The left and right pubic regions are each made up of three sections, a superior ramus, inferior ra ...

and

ischium The ischium () form ...

, and at the side to the inner surface of the

hip bone The hip bone (os coxae, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the Ilium (bone), ...

below and behind the

pelvic brim The pelvic brim is the edge of the pelvic inlet. It is an approximately Mickey Mouse head-shaped line passing through the prominence of the sacrum, the arcuate and pectineal lines, and the upper margin of the pubic symphysis. Structure The pel ...

. It reaches from the upper part of the

greater sciatic foramen The greater sciatic foramen is an opening (foramen) in the posterior human pelvis. It is formed by the sacrotuberous and sacrospinous ligaments. The piriformis muscle passes through the foramen and occupies most of its volume. The greater sci ...

above and behind to the

below and in front. It also arises from the pelvic surface of the

. This is except in the posterior part, from the tendinous arch which completes the canal for the passage of the obturator vessels and nerve, and to a slight extent from the

obturator fascia The obturator fascia, or fascia of the internal obturator muscle, covers the pelvic surface of that muscle and is attached around the margin of its origin. Above, it is loosely connected to the back part of the arcuate line, and here it is conti ...

, which covers the muscle.

Passage

The fibers converge through the

. These end in four or five tendinous bands, which are found on the deep surface of the muscle. These bands are reflected at a right angle over the grooved surface of the ischium between its spine and tuberosity. The

obturator nerve The obturator nerve in human anatomy arises from the ventral divisions of the second, third, and fourth lumbar nerves in the lumbar plexus; the branch from the third is the largest, while that from the second is often very small. Structure The o ...

passes on the superficial surface of the internal obturator muscle. The

pudendal nerve The pudendal nerve is the main nerve of the perineum. It carries sensation from the external genitalia of both sexes and the skin around the anus and perineum, as well as the motor supply to various pelvic muscles, including the male or fem ...

passes on the lateral surface of the internal obturator muscle and the

coccygeus muscle The coccygeus muscle or ischiococcygeus is a muscle of the pelvic floor, located posterior to levator ani and anterior to the sacrospinous ligament. Structure The coccygeus muscle is posterior to levator ani and anterior to the sacrospino ...

. The sciatic nerve passes superficial to the internal obturator muscle on the posterior surface.

Insertion

The tendon inserts on the

greater trochanter The greater trochanter of the femur is a large, irregular, quadrilateral eminence and a part of the skeletal system. It is directed lateral and medially and slightly posterior. In the adult it is about 2–4 cm lower than the femoral head.Stan ...

of the proximal

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...

Nerve supply

The internal obturator muscle is supplied by the

obturator internus nerve The nerve to obturator internus, also known as the obturator internus nerve, is a nerve that innervates the obturator internus and gemellus superior muscles. Structure The nerve to obturator internus originates in the lumbosacral plexus. It ar ...

( L5, S1, and S2). Obturator internus muscle

Bursa/bands

This bony surface is covered by smooth cartilage, which is separated from the tendon by a

bursa ( grc-gre, Προῦσα, Proûsa, Latin: Prusa, ota, بورسه, Arabic:بورصة) is a city in northwestern Turkey and the administrative center of Bursa Province. The fourth-most populous city in Turkey and second-most populous in the ...

, and presents one or more ridges corresponding with the furrows between the tendinous bands. These bands leave the pelvis through the lesser sciatic foramen and unite into a single flattened tendon, which passes horizontally across the capsule of the hip-joint, and, after receiving the attachments of the superior and

inferior gemellus muscle The gemelli muscles are the inferior gemellus muscle and the superior gemellus muscle, two small accessory fasciculi to the tendon of the internal obturator muscle. The gemelli muscles belong to the lateral rotator group of six muscles of the hip ...

s, is inserted into the forepart of the medial surface of the greater trochanter above the

trochanteric fossa In mammals including humans, the medial surface of the greater trochanter has at its base a deep depression bounded posteriorly by the intertrochanteric crest, called the trochanteric fossa. This fossa is the point of insertion of four muscles. Mov ...

. A bursa, narrow and elongated in form, is usually found between the tendon and the capsule of the hip-joint. It occasionally communicates with the bursa between the tendon and the ischium.

Function

The internal obturator muscle helps to support the

urinary bladder The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...

as part of the

pelvic floor The pelvic floor or pelvic diaphragm is composed of muscle fibers of the levator ani, the coccygeus muscle, and associated connective tissue which span the area underneath the pelvis. The pelvic diaphragm is a muscular partition formed by the lev ...

Additional images

File:Obturator internus muscle.jpg, Obturator internus muscle File:Slide10A.JPG, Obturator internus muscle

References

External links

* - "Gluteal Region: Muscles" * - "The Female Pelvis: Muscles" * * (, ) * ()
Int. J. Morphol., 25(1):95-98, 2007
{{Authority control Hip muscles Hip lateral rotators Deep lateral rotators of the hip Muscles of the lower limb