Gluteal Region

Gluteal Region
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Introduction: Since we are learning about the gluteals this seems like the perfect
place to discuss enemas. Enema discussions are considered out of place at
birthday parties, baptisms, elevator rides, bank lines, and the DMV. By definition,
an enema is liquid injected into the rectum, presumably for some therapeutic
purpose. Like a bidet on steroids. I’ll wait if you need to look up the word
“bidet”. As it turns out, enemas can serve a variety of purposes. There are ones to
clean the rectum, to evacuate the contents of the rectum, to illuminate the lower
GI tract for radiological examination, to relieve flatulence and to provide
nutrients. (Outside of these reasons, you would have to consult a textbook on
deviant behavior or abnormal psychology and while these notes are adventurous
I’m not ready to go there.) So, depending on what the clinician is attempting to
accomplish you may see a variety of different ingredients making up the enema.
For radiology, a suspension of barium is what is used. To clean the rectum you
have the aptly named soapsuds enema, consisting of warm water and soap. (And
yes we are talking about soft soap, not a bar of soap) What goes into an enema
that is intended to evacuate the contents of the rectum? There is a recipe in
Dorland’s Illustrated Medical Dictionary (1951) for a turpentine enema, no, do
not try this at home, it contains1 pint soapsuds containing 2 oz. olive oil and 1 oz.
turpentine. I saved the most curious for last and that is the nutritive enema. Going
back to Dorland’s, you have the eponymously named Ewald’s enema consisting
of eggs, wheat flour boiled in a 20 percent grape sugar solution and red wine. Or,
Leube’s enema that contains boiled meat, fat and pancreatin.
Gluteus Maximus: Originating at the sacrum and the sacrotuberous ligament you
can follow the muscle fibers in an inferolateral direction to their insertion on the
iliotibial band and to a lesser extent the gluteal tuberosity. Remember that the
gluteal tuberosity is no more than an elevated portion of the superior aspect of the
linea aspera. Gluteus maximus is an external rotator and extensor of the hip. It’s
function as a hip extensor is optimized when the hip is already in a position of
flexion. Example: Go to the stairs and place one foot two stairs up. Now use that
same lower extremity to bring your weight up to that 2nd stair all the while
palpating your gluteus maximus. Ignore those who make comments about your
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experiment, they are probably liberal arts majors who can’t tell an epiploic
appendage from the vermiform appendix. Now, walk back to the lab and keep one
hand on maximus. Not as much of a contraction in walking as in stair climbing.
That’s because the hamstrings, which are also extensors of the hip are doing the
work in combination with the momentum of your body. Interesting note,
according to the 1881 work by Luther Holden Landmarks Medical & Surgical
“the buttocks appear firm and globose in the vigourous and loose and flaccid in
the infirm”. I think this would make an excellent sign to place above either the
door of McDonalds or the treadmill in the gym.
Sacrotuberous Ligament: If you were able to prevent the destruction of this
ligament while reflecting G.Maximus, you have come a long way since the first
time you used that scalpel. It runs between the ischial tuberosity and the sacrum.
If you reflected this ligament with the G.Maximus then I ask you to avoid
working as a PA in a surgical setting for the safety of your patients. You
remember from our discussion of the pelvis that this ligament along with the
sacrospinous ligament close the borders of the greater and lesser sciatic foramen
started by the greater and lesser sciatic notch.
Gluteus Medius: An abductor and internal rotator of the thigh that is important in
normal gait. Its importance lies not so much in the fact that this muscle abducts
the thigh while you walk as much as it prevents the hip from adducting while you
walk. This muscles ability to hold the pelvis level during unilateral stance is what
is being evaluated during the Trendelenberg Test. In this test it is an isometric
contraction resisting adduction of the hip as opposed to a concentric contraction
producing hip abduction. See me for a demonstration if necessary. The
demonstration is included in the lab fee.
Gluteus minimus: On its superficial surface you will find the superior gluteal
nerve and artery that supply both the gluteus medius and minimus. Gluteus
minimus has the same actions as the gluteus medius.
Piriformis: This is the muscle you should be using for orientation in this region as
the neurovascular structures that emerge from the greater sciatic foramen are
named in relation to this muscle. Its nerve supply is the nerve to piriformis
(S1,S2) and its actions are determined by the position of the hip. The position of
the hip influences this muscle’s actions because it changes the orientation of
piriformis’s fibers in relation to the axis of rotation of the hip joint.
Superior Gluteal Nerve: (L4,L5,S1) This nerve can be found exiting the pelvis by
way of the greater sciatic foramen, superior to the piriformis muscle. From there it
can be seen traveling between the gluteus medius and gluteus minimus. What you
may not see is that it continues anteriorly to innervate tensor fascia lata. Or
perhaps your dissection was aggressive enough to expose this. Take note of the
fact that L5 is the primary nerve root involved in the motor function of these
muscles.
Inferior Gluteal Nerve: (L5,S1,S2) This nerve can be found exiting the pelvis by
way of the greater sciatic foramen, inferior to the piriformis muscle. From this
point it immediately enters the gluteus maximus separating into several branches.
This is the only muscle it innervates.
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Superior, Middle and Inferior Cluneal Nerves: Now, while these were not
mentioned in lecture and not dissected in the lab that does not mean you should
entirely ignore them. (Don’t say “yes it does” if you are reading this to a
classmate) You may hear of them in a clinical setting, so here is what you should
know to keep from looking inexperienced in front of other professionals. These
are the cutaneous nerves of the buttocks. The superior and middle cluneals come
from posterior primary rami. Remember what that implies? (I’m glad you didn’t
say that they can’t contain motor neurons because only a rookie confuses
posterior roots with posterior rami.) The posterior rami are associated with the
deep (true) back muscles. Dr. Hurley mentioned back at the start of the semester
how the sensory distribution of these nerves was approximately a hands breadth
on either side of the vertebral column. Well, it continues inferiorly as far as the
middle of the buttocks. The Inferior cluneals issue from anterior rami, and they
are sensory to the inferior portion of the buttocks.
Obturator Internus and the Gemelli Muscles: Because the two gemelli muscles
insert on the tendon of the obturator internus you may hear this group of muscles
described as the triceps coxae. Actually the only place you would possibly hear
this is during a round of anatomy jeopardy being played in my office. You can
find the tendon of obturator internus exiting the pelvis through the lesser sciatic
foramen. The superior gemellus can be seen attaching to the ischial spine and the
inferior gemellus from the ishial tuberosity. Both, as mentioned earlier, attach to
the tendon that runs between them. Actions are like those of piriformis and for the
same reasons. Interesting note, as these muscles all fuse as one tendon laterally,
they act simultaneously, independent action is not an option for any of these three.
Quadratus Femoris: This quadrangular muscle travels in the transverse plane
between the ischial tuberosity and the quadrate tubercle (found on the
intertrochanteric crest of the femur). This muscle is a lateral rotator of the hip and
is best seen when the hip is medially rotated, thus stretching the muscle.
Posterior Femoral Cutaneous Nerve: (S1,S2,S3) Look once again to the greater
sciatic foramen to find where this nerve comes into view. It travels next to the
sciatic nerve, deep to gluteus maximus, but superficial to the lateral rotators of the
hip and continues inferiorly down the posterior thigh to the popliteal fossa. If you
recall the inferior cluneal nerves, these are actually branches of PFCN. The
caliber of the nerve tends to taper off fairly quickly, so your best strategy is to
follow it from superior to inferior as opposed to the other way.
Sciatic Nerve: (L4,L5,S1,S2,S3) Exiting through the greater sciatic foramen,
inferior to piriformis and about 2 cm in diameter, this is the most important
individual nerve in the lower extremity. I will discuss it in more detail in future
dissections, as far as this dissection is concerned, it is not innervating any of the
gluteal musculature.
Sacrotuberous Ligament: Attaching the sacrum to the ishial tuberosity this
ligament serves as a medial point of attachment for the gluteus maximus.
Sacrospinous Ligament: From the sacrum to the ischial spine. You can see this
ligament dividing the greater and lesser sciatic foramen. Not enough information?
Follow superior gemellus medially and look through all the fat, it is a thick tough
ligament with a white / silvery appearance. There is a muscle that has similar
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attachments and is just deep to this ligament, it is called the coccygeous recall that
we had talked about it during our conversation concerning the pelvis.
Nerve to Obturator Internus: (L5,S1,S2) In the area you are likely to see it,
(exiting the greater sciatic foramen) this nerve is supplying the superior gemellus,
once it enters the perineum by way of the lesser sciatic foramen it will innervate
obturator internus.
Internal Pudendal Artery: This is a branch of the internal iliac artery and you will
see it traveling medial to the n. to obturator internus as the two of them pass
superficial to the sacrospinous ligament.
Pudendal Nerve: (S2,S3,S4) This nerve travels a similar course superficial to the
sacrospinous ligament as the two previously mentioned structures. Remember it is
the principal nerve to the perineum.
No discussion of the gluteal region would be complete without some mention of
the contribution that this part of the anatomy has made to the arts. The sculpture you see
below (A) is called the Callipygean Venus (Roman) or Aphrodite Kallipygos (Greek).
Rendered during the Hellenistic period of Greek art history, the word Callipygean means
‘of the beautiful buttocks’.
The other sculpture is titled “Venus Pudica” and there are several examples of
females assuming this demure pose in art and they are described the same way. The word
pudica comes from the Latin pudendum meaning “that of which one ought to be
ashamed”. As anatomists we recognize the term as the nerve that is one of the primary
nerve supplies of the genitals, the pudendal nerve. The only shame you should feel about
the pudendal nerve is if you cut it in today’s dissection.
A
B