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Obturator Externus Muscle Anatomy

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Quick Overview View Flashcards
Origin
  • Obturator foramen
  • Obturator membrane
Insertion
  • Trochanteric fossa of the greater trochanter
Action
  • Hip lateral rotation
  • Hip stabilization
  • Potentially assists with adduction when the hip is flexed
Innervation
  • Posterior division of the obturator nerve (L3, L4)
Blood Supply
  • Anterior branch of the obturator artery
  • Medial circumflex femoral artery
Last updated: Estimated Reading Time: 5 min

Location & Overview

The obturator externus is a flat, fan-shaped muscle located deep in the medial compartment of the thigh. It originates on the anterior side of the obturator foramen of the pelvis. As it extends laterally, it passes posteriorly beneath the neck of the femur, lying deep to the quadratus femoris muscle.[1,2]

The primary function of the obturator externus is to act as a lateral rotator of the hip joint and to stabilize the femoral head within the acetabulum. It is one of the short, deep lateral rotators of the hip, often referred to as the “deep six”. This group comprises the piriformis, superior gemellus, obturator internus, inferior gemellus, quadratus femoris, and obturator externus.[1,2]

Obturator externus, posterior view
Pictured here, we can see the obturator externus muscle from a posterior view.
Deep six hip external/lateral rotators
Pictured here are the deep six hip external rotator muscles: the piriformis, gemellus superior, gemellus inferior, obturator internus, obturator externus, and quadratus femoris. These muscles play an important role in stabilizing the hip joint and facilitating hip lateral rotation.

Origin & Insertion

The obturator externus originates from the bony margins of the obturator foramen, which is a large opening in the pelvis situated between the pubis and ischium bones. This foramen is covered by the obturator membrane, a thin sheet of connective tissue that stretches across the opening, giving an additional area for the obturator externus to originate from. The muscle fibers of the obturator externus then converge into a tendon that courses posterolaterally beneath the neck of the femur. This tendon attaches to the trochanteric fossa, a shallow depression on the medial aspect of the greater trochanter. The greater trochanter is a prominent bony projection located at the upper part of the femur, serving as a major attachment point for several muscles.[1,2,3]

Obturator externus origin marked in red
Here, we can see the obturator externus origin marked in red on the obturator foramen. The obturator externus also originates on the obturator membrane, displayed below.
Obturator membrane seen from an anterior view
Here, we can see the obturator membrane, another origin point of the obturator externus muscle.
Obturator externus insertion marked in blue
Here, we can see the obturator externus insertion marked in blue on the trochanteric fossa of the greater trochanter.

Action & Function

Contraction of the obturator externus primarily produces lateral rotation, also known as external rotation, of the thigh at the hip joint. This action causes the leg to rotate so that the knee turns outward. Additionally, when the hip is flexed, the obturator externus may contribute to adduction, drawing the thigh toward the midline of the body. There is conflicting information in the literature regarding its ability to contribute to adduction. The obturator externus also plays an important role in stabilizing the hip joint, helping the femoral head remain securely within the acetabulum.[1,2,3]

Image of a person demonstrating the movement of external rotation.
This image shows an example of hip external rotation, which involves rotating the leg from the hip joint outward (laterally). External rotation is also referred to as lateral rotation. The opposite of external rotation is internal rotation (medial rotation). External rotation of the hip joint is the primary action of the obturator externus, alongside hip stabilization.
Image of a person demonstrating the movement of hip adduction.
This image shows an example of hip adduction, which involves moving the leg toward the body’s midline. The opposite of hip adduction is hip abduction. The obturator externus can weakly assist with hip adduction, but only when the hip is flexed.

Innervation

The obturator externus is innervated by the posterior division of the obturator nerve, specifically the spinal roots L3 and L4. Originating from the lumbar plexus, the obturator nerve divides into anterior and posterior branches near the obturator foramen.[3,1,2]

obturator nerve
Here, we can see the obturator nerve, which innervates the obturator externus muscle.

Blood Supply

Arterial supply to the obturator externus is primarily via the anterior branch of the obturator artery. Additional vascular supply comes from the medial circumflex femoral artery, which usually arises from the profunda femoris artery, although it can also arise directly from the femoral artery. These vessels join together near the obturator externus muscle.[3]

References

  1. [1] Dalley AF II, Agur AMR. Moore’s Clinically Oriented Anatomy. 9th ed. Wolters Kluwer Health; 2022.
  2. [2] Standring S. (2015). Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edn. Amsterdam: Elsevier
  3. [3] Larson MR, Ryan W. Anatomy, Abdomen and Pelvis, Obturator Muscles. (Updated 2023 Jan 17). In: StatPearls (Internet). Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK589636/

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