The external obturator muscle, obturator externus muscle (; OE) is a flat, triangular muscle, which covers the outer surface of the anterior 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 is sometimes considered part of the
medial compartment of thigh
The medial compartment of thigh is one of the fascial compartments of the thigh and contains the hip adductor muscles and the gracilis muscle.
The obturator nerve is the primary nerve supplying this compartment. The obturator artery is the bloo ...
,
and sometimes considered part of the
gluteal region.
Structure
It arises from the margin of bone immediately around the medial side of the
obturator membrane and surrounding bone, viz., from the
inferior pubic ramus, and the ramus of the
; it also arises from the medial two-thirds of the outer surface of the
obturator membrane, and from the tendinous arch which completes the canal for the passage of the obturator vessels and nerves.
The fibers springing from the pubic arch extend on to the inner surface of the bone, where they obtain a narrow origin between the margin of the foramen and the attachment of the obturator membrane.
The fibers converge and pass posterolateral and upward, and end in a tendon which runs across the back of the neck of the femur and lower part of the capsule of the hip joint and is inserted into the
trochanteric fossa of the femur.
Relations
The obturator vessels lie between the muscle and the obturator membrane; the
anterior branch of the obturator nerve
The anterior branch of the obturator nerve is a branch of the obturator nerve found in the pelvis and leg.
It leaves the pelvis in front of the obturator externus and descends anterior to the adductor brevis, and posterior to the pectineus and add ...
reaches the thigh by passing in front of the muscle, and the
posterior branch by piercing it.
Variation
In 33% of people a
supernumerary muscle is found between the
adductor brevis and
minimus
The Minimus books are a series of school textbooks, written by Barbara Bell, illustrated by Dr. Helen Forte, and published by the Cambridge University Press, designed to help children of primary school age to learn Latin. The books espouse some of ...
. While this muscle, when present, is similar to its neighbouring adductors, it is formed by separation from the superficial layer of the external obturator, and is thus not
ontogenetically related to the
adductor muscles of the hip
The adductor muscles of the hip are a group of muscles mostly used for bringing the thighs together (called adduction).
Structure
The adductor group is made up of:
*Adductor brevis
*Adductor longus
*Adductor magnus
* Adductor minimus This is o ...
. This muscle originates from the upper part of the
inferior pubic ramus from where it runs downwards and laterally. In half of cases, it inserts into the anterior surface of the insertion
aponeurosis
An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join musc ...
of the adductor minimus. In the remaining cases, it is either inserted into the upper part of the
pectineal line or the posterior part of the
lesser trochanter.
It has been demonstrated by the course of the
posterior branch of obturator nerve that the obturator externus is divided into a superior
muscle fascicle and a main belly. The supernumerary muscle described above originates from the superior fascicle, while an anomalous fascicle — also derived from the external obturator — originates from the main belly. The "original" external obturator, i.e. without these supernumerary muscular parts, actually occurs in only 20% of cases, and apparently the external obturator readily undergoes
ontogenetic variations.
Function
The external obturator muscle acts as the lateral rotator of the hip joint. As a short muscle around the hip joint, it stabilizes the hip joint as a postural muscle. It also helps to abduct the hip joint when in flexion.
Additional images
File:Obturator externus.png, Muscles of the back of thigh, with insertion of obturator externus muscle labeled in purple
File:Gray235.png, Right hip bone. External surface
File:Gray344.png, Structures surrounding right hip-joint
File:Gray433.png, Deep muscles of the medial femoral region
File:Slide2gen.JPG, Obturator externus muscle.Deep dissection.Anterior view.
File:Slide8A.JPG, Obturator externus muscle
File:Slide1BIBI.JPG, Muscles of Thigh. Anterior views.
See also
References
External links
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* ()
PTCentral
{{Authority control
Hip muscles
Deep lateral rotators of the hip
Hip lateral rotators
Medial compartment of thigh
Muscles of the lower limb