Obturator Internus

Origin, Insertion, Action, Innervation

Origin: Internal surface of the obturator membrane and the surrounding margins of the obturator foramen; also the pelvic surface of the ischium and pubis
Insertion: Medial surface of the greater trochanter of the femur (superior to the trochanteric fossa), via a tendon that passes between the two gemelli
Action:
Primary: External (lateral) rotation of the hip
Abduction of the hip when the hip is flexed (similar to piriformis)
Stabilization of the femoral head in the acetabulum
Innervation: Nerve to obturator internus from the sacral plexus (L5, S1, S2)

Palpation Guide

Client position: Sidelying, affected side up, with the hip in approximately 45 degrees of flexion and a pillow between the knees.
Landmark sequence:

Locate the greater trochanter laterally and the ischial tuberosity inferiorly. The obturator internus tendon runs between these two landmarks.
Locate the PSIS and draw an imaginary line to the greater trochanter — piriformis runs along this line. Obturator internus lies immediately inferior to this line.
Palpate in the space between the ischial tuberosity and the greater trochanter, slightly inferior to the piriformis line. Press through gluteus maximus — obturator internus lies deep, against the posterior pelvis.
The tendon is narrower than piriformis and runs between the two gemelli, which bracket it like bread around a filling.

Tissue feel: The tendon feels like a firm, narrow cord running from the region of the ischium toward the trochanter. It is difficult to distinguish from the gemelli flanking it without resisted testing. In hypertonicity, the region between piriformis and quadratus femoris feels like a continuous band of taut, tender tissue.
Confirmation test: Maintain your palpating finger in position. Ask the client to externally rotate the hip against resistance. You should feel a deep contraction. To differentiate from piriformis (just superior), note your palpation position — if you are inferior to the piriformis line, you are more likely on obturator internus.
Common errors:
Confusing with piriformis — piriformis is the most superior of the deep six; obturator internus lies directly inferior. If your palpation point is on the direct PSIS-to-trochanter line, you are likely on piriformis.
Not going deep enough — like all deep six muscles, obturator internus is under the full thickness of gluteus maximus.

Trigger Point Referral

Common TrP locations: In the tendon region as it wraps over the ischium, approximately midway between the ischial tuberosity and the greater trochanter.
Referral pattern: Deep aching in the posterior hip joint and buttock, particularly in the region between the ischial tuberosity and greater trochanter. Can refer toward the coccyx.
Clinical significance: The obturator internus TrP produces deep hip joint pain that the client may describe as feeling "inside the joint," mimicking hip osteoarthritis or labral pathology. In clients with deep posterior hip pain and negative imaging, palpate the deep six rotators before assuming intra-articular pathology.

Trigger point referral diagram — coming soon

Image coming soon. For visual reference, see [Obturator Internus at TriggerPoints.net](http://www.triggerpoints.net/muscle/obturator-internus).

Clinical Notes

Common conditions:

Contributes to conditions/piriformis-syndrome differential — obturator internus hypertonicity can compress the sciatic nerve or its branches in the same region as piriformis, producing similar symptoms. In some clients with "piriformis syndrome" that does not respond to piriformis treatment alone, the obturator internus is the actual compressor.
Relevant to conditions/hip-osteoarthritis differential — deep rotator hypertonicity produces hip pain that mimics joint pathology. Assess the deep six before concluding the pain is articular.
Can contribute to pelvic floor dysfunction — the obturator internus forms part of the lateral pelvic wall, and its internal surface is related to the pelvic floor musculature. Chronic hypertonicity can affect pelvic floor tension.

What you'll typically find:

Obturator internus is hypertonic alongside the other deep six in clients who sit for prolonged periods — the external rotators are compressed against the chair. It is almost never involved in isolation; when you find one deep six muscle in spasm, check them all.
The tendon region where it wraps over the ischium is often the most tender point — mechanical stress from the 90-degree turn creates vulnerability at this location.
Clients often cannot point to exactly where the pain is — they gesture vaguely toward the deep buttock, saying it feels "deep inside."

Treatment effects:

Responds to sustained compression at the tendon region between the ischial tuberosity and greater trochanter. Because the muscle is deep to gluteus maximus, warm the overlying tissue first.
The deep six rotators are best treated as a group — strip from piriformis superiorly through the gemelli and obturator internus to quadratus femoris inferiorly, rather than targeting individual muscles.
Use sidelying position with the hip flexed to approximately 45 degrees, which opens the space between piriformis and the ischial tuberosity, improving access.

Cautions:

The sciatic nerve passes through this region (inferior to piriformis, superficial to the deep rotators). Radiating symptoms down the leg during treatment indicate sciatic nerve compression — lighten pressure.
The pudendal nerve and internal pudendal vessels pass medial to the obturator internus tendon at the lesser sciatic notch. Deep medial pressure near the ischium can affect these structures.

Clinical pearl:

When treating the deep six, the obturator internus tendon is the most reliable anatomical "anchor" for orientation. Find the ischial tuberosity, move laterally toward the trochanter, and you will cross the obturator internus tendon. Piriformis is above this point, quadratus femoris is below, and the gemelli are flanking it.

Assessment

Resisted external rotation:

Client supine with hip and knee flexed to 90 degrees. Resist external rotation at the ankle (push the foot medially). Pain deep in the buttock implicates the deep six rotators as a group — this test cannot reliably isolate obturator internus from the other rotators.

Log roll test:

Client supine with the leg extended and relaxed. Gently roll the entire leg internally and externally by rotating at the hip. Pain or restriction with this passive movement in the mid-range suggests deep rotator involvement. This is a low-load test that does not stress the capsule as much as the FAIR test.

Muscle Groups

Deep six hip external rotators (anatomical):

Hip external rotators (functional):

Related Muscles

Functional unit — obturator internus and gemelli:

anatomy/muscles/gemellus-superior — brackets the obturator internus tendon superiorly; often considered a functional unit
anatomy/muscles/gemellus-inferior — brackets the obturator internus tendon inferiorly

Adjacent deep six:

anatomy/muscles/piriformis — lies immediately superior; the most commonly treated deep six muscle
anatomy/muscles/quadratus-femoris — lies inferior to gemellus inferior

Antagonists (hip internal rotation):

anatomy/muscles/gluteus-medius (anterior fibers) — primary internal rotator
anatomy/muscles/gluteus-minimus — assists internal rotation
anatomy/muscles/tensor-fasciae-latae — assists internal rotation

Key Takeaways

Obturator internus lies immediately inferior to piriformis — when piriformis treatment fails, check the other deep six, especially obturator internus.
The 90-degree turn of the tendon over the ischium creates a mechanical stress point that is often the most tender location.
Treat the deep six as a group — they rarely present in isolation.
Deep hip pain that feels "inside the joint" may be deep rotator TrPs rather than articular pathology.