Fridays fact: Obturator Internus and its link to the pelvic diaphragm.

I have just run my first anatomy quiz, and one of the common questions that tripped people up was on obturator internus.

Obturator internus is one of the deep six muscles, which are the lateral rotators of the hip. As a group, they laterally rotate the thigh at the hip joint as well as helping to stabilise the hip.

The main muscles that form the pelvic diaphragm are the obturator internus, piriformis, levator ani and coccygeus. They form the floor and the walls of the pelvic diaphragm. Obturator internus connects into the pelvic floor, and forms part of the lateral wall of the pelvis and is covered by obturator fascia. The pelvic diaphragm attaches along the lateral pelvic walls to a thickened band in the obturator fascia called the tendinous arch of the levator ani.

The obturator internus begins inside the pelvis, surrounding the obturator foramen and makes a 90 degrees turn to exit through the lesser sciatic foramen on its way to the greater trochanter. Its tendon is sandwiched between the gemellus superior and inferior, and all three tend to blend as they attach into the greater trochanter. It doesn’t look like much when you see the tendon going to the greater trochanter, but from the inside of the pelvis, it is pretty spectacular.

In dissection, when the obturator Internus is removed from its pelvic attachment on the deep surface, you see strong, shiny tendinous bands that make up the muscle.

Function: it creates lateral rotation but also restrains medial rotation. When the foot is planted, it will rotate the pelvis to the opposite side, as well as helping to stabilise the hip joint.

Clinical practice: Obturator internus can often be overlooked in clinical practice as clients will come in complaining of pain near the hamstring attachment, groin pain or that it feels like it is deep to the gluteal fold. These symptoms can sometimes be hard to distinguish from hamstring problems or Adductor Magnus. It is also an important factor in treating pelvic floor dysfunction.

Too much tension in the obturator can also create symptoms of urinary frequency and urgency, pain in the pelvic floor, sits bone, hip and tail bone. Easing tension in the obturator internus can allow your pelvic diaphragm to work more effectively and in turn, give lift and support to the pelvic organs.

Diving further down the rabbit hole:

The obturator fascia forms a canal called Alcock’s canal, which encloses the pudendal vessels and the pudendal nerve and cross the obturator internus muscle. However, the pudendal nerve can sometimes get trapped in the obturator fascia, leading to many types of pelvic issues such as Neuralgia or severe pelvic pain. Pudendal neuralgia is a painful, uncomfortable pelvic condition which affects bladder, bowel and sexual function in both men and women.