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| External obturator muscle | |
|---|---|
 The obturator externus and nearby hip muscles (posterior view) | |
 The obturator externus. Anterior-Inferior view | |
| Details | |
| Origin | Obturator foramen andobturator membrane |
| Insertion | Trochanteric fossa offemur |
| Artery | Obturator artery |
| Nerve | Posterior branch of obturator nerve (third and fourthlumbar nerves) |
| Actions | Abductthigh,laterally rotatesthigh |
| Identifiers | |
| Latin | musculus obturatorius externus |
| TA98 | A04.7.02.031 |
| TA2 | 2636 |
| FMA | 22299 |
| Anatomical terms of muscle | |
Theexternal obturator muscle orobturator externus muscle (/ˌɒbtjʊəˈreɪtərɪkˈstɜːrnəs/; OE) is a flat, triangular muscle, which covers the outer surface of the anterior wall of thepelvis.
It is sometimes considered part of themedial compartment of thigh,[1] and sometimes considered part of thegluteal region.[2]
It is also considered to be part of the short external rotators of the hip, along with thegemellus superior and inferior,piriformis, andquadratus femoris.[3]
It arises from the margin of bone immediately around the medial side of theobturator membrane and surrounding bone, viz., from theinferior pubic ramus, and the ramus of theischium; it also arises from the medial two-thirds of the outer surface of theobturator 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 thetrochanteric fossa of the femur.
The obturator vessels lie between the muscle and the obturator membrane; theanterior branch of the obturator nerve reaches the thigh by passing in front of the muscle, and theposterior branch by piercing it.
In 33% of people, asupernumerary muscle is found between theadductor brevis andminimus. 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 notontogenetically related to theadductor muscles of the hip. This muscle originates from the upper part of theinferior pubic ramus from where it runs downwards and laterally. In half of cases, it inserts into the anterior surface of the insertionaponeurosis of the adductor minimus. In the remaining cases, it is either inserted into the upper part of thepectineal line or the posterior part of thelesser trochanter.[4]
It has been demonstrated by the course of theposterior branch of obturator nerve that the obturator externus is divided into a superiormuscle 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 undergoesontogenetic variations.[5]
The external obturator muscle acts as a lateral rotator of the hip joint. As a short muscle around the hip joint, it stabilizes the hip joint as a postural muscle.[6] It also helps to abduct the hip joint when in flexion.[7] And it helps to stabilise the head of the femur in the socket during flexion and internal rotation as its posterior fibers reinforce the posterior capsule of hip joint.[8]
This article incorporates text in thepublic domain frompage 477 of the 20th edition ofGray's Anatomy(1918)
