Obturator Externus: Origin, Insertion, Nerve & Hip Stability

The Obturator Externus is a flat, triangular muscle that covers the outer surface of the anterior pelvic wall. Although it is located deep in the upper medial thigh (making it anatomically close to the adductors), its primary function groups it with the short external rotators of the hip.

[Image of Obturator Externus muscle anatomy]

Quick Anatomy Snapshot

Origin (Proximal)	External surface of the Obturator Membrane and the surrounding bone (ramus of pubis and ischium).
Insertion (Distal)	Trochanteric Fossa of the Femur (a deep pit at the root of the Greater Trochanter).
Nerve Supply	Obturator Nerve (Posterior Division) - L3, L4.
Blood Supply	Obturator Artery and Medial Circumflex Femoral Artery.
Primary Actions	External Rotation: Rotates the thigh laterally. Adduction: Assists weakly in adduction. Stabilization: Supports the head of the femur in the acetabulum.

Deep Dive: The Hidden Rotator

The Obturator Externus is often overlooked because it lies deep behind the Pectineus and Adductor muscles. However, its unique path makes it functionally significant.

1. The "Hammock" Under the Neck

After originating from the pelvis, the tendon passes backwards, winding under the neck of the femur and behind the hip joint to reach the Trochanteric Fossa. This path creates a sling or hammock effect, supporting the femoral neck from below.

2. Relationship with Obturator Nerve

The Obturator Nerve is the defining landmark for this muscle. The nerve exits the obturator canal superior to the muscle. It then divides into two branches:
• The Anterior Branch passes in front of the Obturator Externus.
• The Posterior Branch usually pierces or passes behind the Obturator Externus.

Physio Corner: Clinical Relevance

💪 Functional Fact: While the Gluteus Maximus is the power rotator, the Obturator Externus is the fine-tuner. It is crucial for stabilizing the hip joint during single-leg stance, preventing the femoral head from migrating superiorly.

Palpation

Palpation is nearly impossible due to its depth. It is covered by the Pectineus, Adductor Longus, and Iliopsoas tendon. Tenderness deep in the groin that worsens with passive internal rotation of the hip may suggest Obturator Externus pathology.

⚠️ Clinical Pathology: Deep Gluteal/Groin Pain
Pathology of the Obturator Externus is increasingly recognized as a source of chronic hip pain. It can suffer from impingement (Ischiofemoral Impingement) where the muscle gets crushed between the Ischium and the Lesser Trochanter during extension and adduction.

Manual Muscle Testing (MMT)

It is impossible to isolate the Obturator Externus from the other external rotators (Gemelli, Obturator Internus, Quadratus Femoris).

Testing Tip: Testing external rotation with the hip flexed to 90 degrees (sitting) biases the Obturators and Gemelli over the Gluteus Maximus.

Step-by-Step Procedure (External Rotation)

Grade	Patient Action & Resistance
Grade 3, 4, 5 (Against Gravity)	Position: Short sitting (legs dangling). Action: Patient moves the foot medially (rotating the thigh out). Resistance: Applied above the medial malleolus, pushing the foot laterally. Grade 3: Full range. Grade 4/5: Holds against resistance.
Grade 2 (Gravity Eliminated)	Position: Supine. Leg extended and internally rotated. Action: Patient rolls the leg outward. Result: Full range of external rotation.

Frequently Asked Questions

Is it an adductor or a rotator?

Anatomically, it is located in the adductor region (medial thigh). Functionally, it is a Lateral Rotator. It does assist with adduction, but rotation is its primary role.

Why is it called "Externus"?

Because it originates on the External (outer) surface of the obturator membrane. The Obturator Internus originates on the Internal (pelvic) surface of the same membrane.

Does it pass through the Sciatic Foramen?

No. The Obturator Internus passes through the Lesser Sciatic Foramen. The Obturator Externus stays anterior and passes under the hip joint capsule. It does not exit the pelvis via the sciatic foramina.

Test Your Knowledge: Obturator Externus Quiz

1. Where does the Obturator Externus insert?

2. Which nerve supplies the Obturator Externus?

3. What is the primary action of this muscle?

4. Where does the Obturator Externus originate?

5. The tendon passes ________ the neck of the femur.

6. Which artery supplies this muscle?

7. True or False: The Obturator Externus passes through the Lesser Sciatic Foramen.

8. The Obturator Externus lies deep to which muscle?

9. Which movement stretches the Obturator Externus?

10. Ischiofemoral Impingement involves compression of this muscle between which two bones?

References

• Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2018). Clinically Oriented Anatomy. 8th ed. Philadelphia: Wolters Kluwer.
• Standring, S. (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice. 41st ed. Elsevier.
• Kendall, F. P. (2005). Muscles: Testing and Function, with Posture and Pain. 5th ed. Lippincott Williams & Wilkins.