The obturator internus muscle is a key pelvic muscle responsible for lateral rotation of the thigh. It originates on the internal surface of the pelvis, takes a complex path through the lesser sciatic foramen, and inserts onto the femur, playing a vital role in lower limb biomechanics.
Topography and Course of the Obturator Internus Muscle
The anatomy of the obturator internus muscle (m. obturatorius internus) is characterized by its unique trajectory, as its muscle fibers change direction upon exiting the pelvic cavity.
Origin: The fibers arise from the inner surface of the obturator membrane and the surrounding bone structures of the obturator foramen (foramen obturatum).
Course: The muscle courses posteriorly out of the pelvic cavity, passing through the lesser sciatic foramen (foramen ischiadicum minus) and smoothly looping around the lesser sciatic notch.
Insertion: The muscle tendon reaches the trochanteric fossa (fossa trochanterica) on the medial surface of the greater trochanter of the femur, where it securely anchors.
Function, Innervation, and Blood Supply
From a biomechanical standpoint, the primary function of the obturator internus muscle is lateral rotation of the lower limb. When it contracts, it laterally rotates the thigh.
Nerve regulation and blood supply are provided by the following structures:
Innervation: Supplied by the nerve to the obturator internus (n. obturatorius internus). This nerve arises from the ventral rami of spinal nerves at the lumbar and sacral levels (L₅–S₂).
Blood Supply: Arterial blood is supplied by two main sources: the obturator artery (a. obturatoria) and the inferior gluteal artery (a. gluteal inferior).
Articularis Genus Muscle
When studying the muscles of the lower limb, it is also worth noting the articularis genus muscle (m. articularis genus), which performs a specialized protective function for the knee joint.
Origin: The muscle originates from the anterior surface of the distal third of the femur.
Insertion: Its fibers blend directly into the capsule of the knee joint.
Function: During knee extension, the muscle contracts and pulls the articular capsule proximally. This action prevents the capsule from becoming impinged between the articulating bone surfaces.
Innervation: Supplied by the femoral nerve (n. femoralis).
Blood Supply: Supplied by genicular branches (aa. geniculares) from the genicular arterial anastomotic network.
Mnemonic
To remember the path of the m. obturatorius internus, picture it "locking" the pelvis from the inside, then exiting through a "small" door (foramen ischiadicum minus) to the outside to rotate the thigh.
Frequently asked questions
What structures pass through the lesser sciatic foramen?
The lesser sciatic foramen transmits the obturator internus muscle and the pudendal neurovascular bundle.
Obturator internus muscle (m. obturatorius internus) — exits the pelvic cavity toward the posterior aspect;
Pudendal neurovascular bundle — loops around the ischial spine and re-enters the pelvis (into the ischioanal fossa). It consists of:
Internal pudendal artery (a. pudenda interna);
Internal pudendal veins (vv. pudendae internae);
Pudendal nerve (n. pudendus).
Which fascia covers the obturator internus muscle within the lesser pelvis?
The obturator internus muscle is covered on its pelvic side by the parietal pelvic fascia (fascia pelvis parietalis).
This fascia covers the parietal and pelvic floor muscles, including the m. obturatorius internus. Over the obturator internus muscle, it is particularly thickened and forms the obturator fascia.
On which surface of the femur does the articularis genus muscle originate?
The articularis genus muscle originates on the anterior surface of the distal third of the femur.
Through which opening does the obturator internus muscle leave the pelvic cavity?
It exits the pelvis through the lesser sciatic foramen (foramen ischiadicum minus).
Where does the m. obturatorius internus insert?
Its tendon inserts into the trochanteric fossa (fossa trochanterica) of the femur.
Go deeper
Structure of the obturator membrane and borders of the obturator foramen
Borders and contents of the lesser sciatic foramen
Anatomy of the trochanteric fossa
Formation and branching of the nerve to the obturator internus (L₅–S₂)
Genicular arterial network and branches of the genicular arteries