Topography and attachment points
The obturator externus muscle originates from a complex of pelvic structures. The main fixation zone is the external surface of the obturator membrane. In addition, the muscle bundles attach to the adjacent areas of two pelvic bones:
- pubic bone;
- ischium.
Next, the muscle fibers run laterally and attach to the femur. The final attachment site (insertion) is the trochanteric fossa — fossa trochanterica.
Biomechanics and functions
From a biomechanical standpoint, m. obturator externus performs two main functions:
- Lateral rotation of the thigh (supination) is its primary purpose.
- Participation in thigh adduction — the muscle acts as a synergist to other thigh adductors.
Interestingly, the inferior gemellus muscle (m. gemellus inferior), which is also responsible for lateral rotation of the thigh, attaches to the trochanteric fossa (fossa trochanterica) as well. Thus, these muscles work together to ensure supination of the lower limb.
Blood supply and innervation
For stable muscle function, adequate blood flow and nerve control are essential. In the case of the obturator externus muscle, these tasks are distributed as follows:
- Innervation is provided by the obturator nerve — n. obturatorius, whose fibers originate from the spinal nerves of segments L₃–L₄.
- Blood supply is provided by two sources simultaneously: the obturator artery (a. obturatoria) and the medial femoral circumflex artery (a. circumflexa femoris medialis).
Briefly: answers to topical questions
Which other muscles, besides the obturator externus, attach to the trochanteric fossa?
In addition to the obturator externus, two other muscles attach to the trochanteric fossa (fossa trochanterica).
- Inferior gemellus muscle (m. gemellus inferior) — attaches to the fossa together with the obturator internus muscle.
- Obturator internus muscle (m. obturator internus / m. obturatorius internus) — attaches to the trochanteric fossa after exiting the lesser pelvis cavity.
Which specific muscles does the obturator externus act as a synergist with during thigh adduction?
During thigh adduction, the obturator externus acts as a synergist to the primary and other accessory adductor muscles.
- Adductor longus muscle (m. adductor longus).
- Adductor magnus muscle (m. adductor magnus).
- Adductor brevis muscle (m. adductor brevis).
- Gracilis muscle (m. gracilis).
- Pectineus muscle (m. pectineus).
How does the origin of the obturator externus differ from that of the obturator internus?
The origins of these muscles differ in the surface of the pelvic bone and obturator membrane from which they arise.
| Characteristic | Obturator externus muscle (m. obturatorius externus) | Obturator internus muscle (m. obturatorius internus) |
|---|---|---|
| Origin | External surface of the obturator membrane and adjacent parts of the pubic and ischial bones (circumference of the obturator foramen) | Internal surface of the obturator membrane and pelvic bone around the foramen obturatum (anterolateral wall of the pelvis) |
Class and exam questions
Where is the origin of the obturator externus muscle located?
It originates on the external surface of the obturator membrane, as well as from the adjacent parts of the pubic and ischial bones.
What structure does m. obturator externus attach to?
The muscle attaches to the trochanteric fossa (fossa trochanterica) on the femur.
What other muscle attaches to the trochanteric fossa and performs a similar function?
The inferior gemellus muscle (m. gemellus inferior) also attaches to the fossa trochanterica and laterally rotates the thigh.
Which arteries supply blood to the obturator externus muscle?
Blood supply is provided by the a. obturatoria and a. circumflexa femoris medialis.
What else to study on this topic
- Inferior gemellus muscle (m. gemellus inferior) and its role in thigh rotation
- Anatomy of the trochanteric fossa (fossa trochanterica)
- Topography of the obturator nerve (n. obturatorius)
- Medial femoral circumflex artery: branches and anastomoses
- Deep layer of pelvic muscles
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