Donor Positioning: Maintain the same position that was used for the sciatic nerve block.
USE THE SAME SIDE OF THE DONOR AS YOU DID FOR THE ANTERIOR APPROACH
Before attempting this procedure explore every detail of the web exercise “Gluteal Region” under the “Exercises” resource.
Incision: Make a curved incision that begins at the posterior superior spine. It should arc superiorly to your spine-to-trochanter line drawn for the sciatic nerve block. The incision should continue through a point that is two finger-breadths medial to the greater trochanter and down the shaft of the femur to the crease between the gluteal region and the thigh.
1. Deepen the incision to the level of the deep fascia and use retractors to expose as much of the underlying muscles as possible.
2. Incise the fascia lata on the lateral aspect of the thigh to reveal the vastus lateralis. Lengthen the fascial incision superiorly in line with the original skin incision. Split the fibers of the gluteus maximus by blunt dissection (see figure below and note that the artist has switched sides of the body). Some students find themselves superiolateral to the gluteus maximus and miss the hip as a result. Consult an atlas to be sure you have identified the gluteus maximus and be sure you are splitting fibers (not cutting across them).
Which arteries supply the gluteus maximus?
Where do they originate, and how do they get to the gluteus maximus?
Retract the fibers of the split gluteus maximus and the deep fascia of the thigh. Under this you will find the tip of the greater trochanter, where a number of muscles attach.
You already encountered the gluteus maximus and minimus during the last procedure. Unlike those muscles, the remaining 4 muscles are lateral (external) rotators. Two of these are worth remembering: the piriformis and the tendon of the obturator internus. You will explore these muscles in a moment.
3. To widen your view, do the following non-surgical procedure: Gently sweep your hand under the lateral border of the gluteus maximus to free it from the underlying muscles. If helpful, you may make a relaxing incision along the iliac crest to widen your exposure. Place a blunt probe under the superior portion of the gluteus maximus and against the iliac crest. Using the probe as a shield to protect underlying structures, use sharp dissection to divide the muscle from the iliac crest for 3-5 cm. Similarly, place the probe under the inferior portion of the gluteus maximus against the sacrum to make a relaxing incision along the sacrum to widen your exposure. Detach the muscle for 3-5 cm being careful not to cut any underlying tendons, nerves or vessels. Gently reflect the gluteus maximus and observe how you are restricted by the superior and inferior gluteal neurovascular bundle. Note that with your surgical incision, the fibers of the gluteus maximus are split superiolateral to the neurovascular bundles that you observe.
(This is also why intramuscular injections are made in the superiolateral quadrant of the gluteal region.) Since this would be a muscle splitting procedure, there is minimal damage to the fibers of the gluteus maximus or the terminal branches of nerves that are running parallel to these fibers.
4. The sciatic nerve, encased in fat, exits the greater sciatic foramen deep to the piriformis muscle. Confirm that the piriformis muscle also passes through the greater sciatic foramen. As the nerve travels inferiorly, it lies superficial to the 3 inferior most muscles that attach to the greater trochanter. Try and palpate the nerve as it emerges from under the piriformis and travels inferiorly. In a surgical procedure, we would not dissect the fat around the nerve as it may cause unnecessary bleeding, but for this lab you should clean the fat around the nerve.
5. Let’s do a brief digression to understand what we are looking at. Rotate the hip to confirm the action of the external (lateral) rotators.
Should the tension on the muscles increase or slacken when you laterally rotate the hip?
Clean these muscles to confirm that the piriformis enters the greater sciatic foramen, but the tendon of the obturator internus enters the lesser foramen.
Which two ligaments form the borders of the lesser sciatic foramen?
Which one separates the greater from the lesser sciatic foramen?
6. Find the pudendal vessels and nerve hooking over the sacrospinous ligament by extending your dissection medially (surgeons would not want to go this far medial!).
7. Now, return to the surgical procedure. Internally (medially) rotate the hip to move the insertion of the small external rotators as far away as possible from the sciatic nerve. Detach the muscles (including the piriformis muscle) close to their femoral insertion and reflect them back onto the sciatic nerve. These external rotators are used to protect the sciatic nerve during the rest of the surgery.
8. After cleaning and retracting the gluteus minimus anteriorly, you should now be able to see the posterior aspect of the hip joint capsule. You can cut it open with a longitudinal or T-shaped cut. You can dislocate the hip now by internally rotating the hip. If you need to see more of the hip, you can cut the quadratus femoris and the tendinous insertion of the gluteus maximus. Congratulations, you have now reached the posterior aspect of the hip!!
9. So let's recap the functional deep anatomy of the posterior hip. Sketch out a posterior view of the pelvis and proximal femur and sketch in the following structures:
a. Sacrotuberous ligament
b. Sacrospinous ligament
d. Sciatic Nerve
e. Superior and Inferior Gluteal Nerves
f. Pudendal Nerve
g. Superior and Inferior Gluteal Arteries
Summary of Lab 12 Click here or Objectives above
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