HAC's Senior Anatomy and Physiology Instructor Finds Ways To Make Anatomy Memorable
Mastering anatomy can be tedious, but with a little imagination, we can find ways to look at the human body that makes it easier to remember, and even master, this complex subject matter. So, for our first-ever lesson in "Danatomy", we are going to discuss the "deep six" muscles of the buttock. This muscle group is particularly useful to demonstrate how we can shift our point of view just a bit to enhance our understanding.
Most know this group because of the piriformis muscle and its relationship to the largest nerve in the human body called the sciatic (ischiatic) nerve. But remembering the other five muscles is often challenging at best. Why is remembering a muscle a difficult thing? Well, unless you grew up speaking Latin or Greek, my guess is that the nouns and adjectives that characterize these muscles are brand new words that you rarely, if ever, say or hear outside of an anatomy class or hospital setting. The absence of this common linguistic context and regular use make it difficult place this information into lasting memory.
Allow me to prove my point. The "deep six" muscles are piriformis, quadratus femoris, gemellus superior, gemellus inferior, obturator internus, and obturator externus. That is a lot of Latin for just six muscles. Translation, however, is the secret to remembering these muscles. So what if these muscles were all named with everyday English words? Here is what they would be called: the PEAR, the SQUARE, the TWINS, and the COVERS.
To elaborate, piriformis is named for being shaped like a pear. It is large at its base (upon the front outer edge of the lowest bone of the spinal column) with a proportionally rotund belly that quickly narrows as its fibers converge on to the top of a large bony knob upon the body's largest bone, the femur. In textbooks, it is listed as originating on the anteriolateral surface of the sacrum and inserting along the superior border of the greater trochanter of the femur. It is known best to medical professionals for its potential to compress or impinge the sciatic nerve and it is the most easily palpated muscle of the group.
The quadratus femoris is geometrically rectangular, or "square" in shape and has one margin anchored to the outer edge of the lower pelvic bone and the other margin rooted into a line that runs between the two trochanters of the femur. The top and bottom margins are not attached to bone but clearly distinguish the muscle from the others in the group. In textbooks, it is listed as originating on the lateral border of the ischial tuberosity and inserting along the intertrochanteric crest.
The gemellus superior and inferior muscles, sometimes referred to as the gemelli are the upper twin and lower twin, respectively. If you are familiar with the astrology or astronomy of gemini you know "the twins". Gemelli and gemini are the same words. There are very few differences in their size, shape, or appearance. Both start on the lower pelvic bone and end along the inner margin of the upper projection of the knob of the thigh bone. In textbooks gemellus superior is listed as originating from the spine of the ischium and inserting into the medial surface of the greater trochanter. Inferior gemellus has a broader origin upon the ischial tuberosity and inserts with gemellus superior on the medial surface of the greater trochanter. They are not readily discernible through palpation.
The final two muscles of the group, and arguably the most difficult to understand, are the obturator internus and externus muscles. To grasp these two muscles literally you would have to dissect away other muscles and tissues and expose the obturator foramen. To grasp the muscles figuratively you need to know what the obturator foramen is and why it has that name. A foramen is a hole found within a bone. All bones have them for blood vessels and many of the more common foramina have nerves exiting through the holes along with the blood vessels. The obturator foramen is a hole created by the joining and eventual fusion between the groin bone known as pubis and the "sit" bone known as ischium. This hole is anything but open. In fact, a connective tissue membrane and the two muscles surrounding either side of it obstruct, or cover the hole.
Obturator internus is found obstructing, or covering, the inner rim of the foramen and is listed in textbooks as originating on the ischiopubis ramus and obturator membrane whereas the obturator externus covers the outer rim of the foramen and is listed as originating along the outer rim of ischiopubis ramus and obturator membrane. Their insertions are slightly different. Obturator internus inserts with the gemelli on the medial surface of the greater trochanter. Obturator externus inserts posteriorly in a small depression between the top of the greater trochanter and the neck of the femur known as the trochanteric fossa of the femur.
All six work as a group to laterally rotate the hip which will make the toes point away from the midline. They are basically a collective that work on the greater trochanter to oppose the gluteus minimus which pulls the front of the greater trochanter in the opposite direction. The "deep six" are homologous in their action to the posterior rotator cuff muscles of the glenohumeral joint. Simply translated, they compare to the back side cuff muscles of the shoulder.
So how can you use this to help your bodywork? Remember, these are deep to gluteus maximus so if you can visualize the muscles and the direction of their muscle fibers you can introduce techniques to improve upon them even if you cannot tell that you are directly palpating them. When dysfunction exists that correlates to a single muscle of the group expect it to affect all of the muscles of the group. When all else fails open up your textbooks to get a better picture of how the "deep six" orient. You can use any anatomy textbook but my favorites include Netter's Atlas of Human Anatomy, Andrew Biel's Trail Guide to the Body, and Gray's Anatomy.
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