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Obturator Externus Muscle

Musculus obturatorius externus

For medical students2 min readUpdated 2026-10-10

The obturator externus muscle (m. obturator externus) is a key deep muscle of the pelvic girdle. Its primary biomechanical role is lateral rotation of the thigh, along with assisting in hip adduction.

OriginExternal surface of the obturator membrane, pubis, and ischium
InsertionTrochanteric fossa (*fossa trochanterica*)
BiomechanicsLateral rotation of the thigh, assists in adduction
InnervationObturator nerve (*n. obturatorius*, L₃–L₄)
Blood supplyObturator artery, medial femoral circumflex artery

Topography and Attachment Sites

The obturator externus muscle originates from a complex of pelvic structures. Its primary fixation site is the external surface of the obturator membrane. In addition, its muscle fibers take origin from adjacent areas of two pelvic bones:

From here, the muscle fibers course laterally and posteriorly to insert onto the femur. The final insertion site is the trochanteric fossa (fossa trochanterica).

Biomechanics and Functions

From a biomechanical perspective, the m. obturator externus performs two main functions:

  1. Lateral rotation of the thigh (external rotation/supination) — its primary role.
  2. Assisting in hip adduction — functioning as a synergist to other hip adductors.

Interestingly, the inferior gemellus muscle (m. gemellus inferior) also inserts into the trochanteric fossa (fossa trochanterica) and similarly contributes to lateral rotation of the thigh. Thus, these muscles work together to ensure external rotation of the lower limb.

Blood Supply and Innervation

Proper muscle function requires adequate blood flow and neural control. For the obturator externus, these are supplied as follows:

Frequently asked questions

What other muscles, besides the obturator externus, insert into the trochanteric fossa?

In addition to the obturator externus, two other muscles insert into the trochanteric fossa (fossa trochanterica):

  • Inferior gemellus muscle (m. gemellus inferior) — inserts into the fossa in conjunction with the tendon of the obturator internus.
  • Obturator internus muscle (m. obturator internus / m. obturatorius internus) — inserts into the trochanteric fossa after exiting the lesser pelvic cavity.
Which specific muscles are synergized by the obturator externus during thigh adduction?

During hip adduction, the obturator externus acts as a synergist to the primary and secondary adductor muscles:

  • Adductor longus (m. adductor longus)
  • Adductor magnus (m. adductor magnus)
  • Adductor brevis (m. adductor brevis)
  • Gracilis (m. gracilis)
  • Pectineus (m. pectineus)
How does the origin of the obturator externus differ from that of the obturator internus?

The origins differ based on which surface of the pelvic bone and obturator membrane they arise from:

FeatureObturator externus muscle (m. obturatorius externus)Obturator internus muscle (m. obturatorius internus)
OriginExternal surface of the obturator membrane and adjacent margins of the pubic and ischial bones (surrounding the obturator foramen)Internal surface of the obturator membrane and surrounding pelvic bone around the obturator foramen (anterolateral wall of the true pelvis)
Where does the obturator externus muscle originate?

It originates from the external surface of the obturator membrane, as well as the adjacent parts of the pubic and ischial bones.

Where does the m. obturator externus insert?

The muscle inserts into the trochanteric fossa (fossa trochanterica) on the proximal femur.

Which other muscle attaches to the trochanteric fossa and shares a similar function?

The inferior gemellus muscle (m. gemellus inferior) also attaches to the trochanteric fossa and laterally rotates the thigh.

Which arteries supply the obturator externus muscle?

Blood supply is provided by the obturator artery (a. obturatoria) and the medial femoral circumflex artery (a. circumflexa femoris medialis).

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