Download Posterior Leg Dissection

20140918_Dissection Posterior Leg Dissection
1. Remove the fat off the gluteus maximus to help define its diagonal appearance
2. Cut along the lateral edge of the gluteus
a. Make sure you are above the
i. Greater trochanter
ii. vastus lateralis
b. Fold it over to reveal the sciatic and posterior femoral cutaneous
c. Look for the nerves. These can either be laying on the sacrum or be lifted
up as part of the folded over gluteus. Many of these nerves will appear to
curve up and around the Ischial Tuberosity and the muscles that attach to
it. Palpate the Ischial tuberosity so you know where it is.
d. Digitally dissect to define the nerves.
i. Sciatic nerve
ii. Posterior Femoral Cutaneous Nerve
1. This can be seen rising up to the gluteal flap that you have
raised
2. Try to follow it along the inner surface of the fascia lata a
ways don to the popliteal fossa
iii. Inferior Cluneal Nerves
1. These are nerves that are smaller and come off sooner that
n the rise of the posterior femoral cutaneous nerve and are
more medial to it
iv. Pudendal Vessels and Nerve
1. These are up higher on the spine and sometimes like to
stick to the raised flap instead of laying on the spine where
they normally rest
v. Piriformis
1. Note the Superior and Inferior Gluteal Vessels above and
below the piriformis. These can be cut to allow you to fold
over the gluteus more.
2. Be careful as it is easy with this muscle to create new
anatomy as the muscle can be rather friable
3. The lines of Labat define the position of the piriformis
3. Feel the ischial Tuberosity and remember that this is where the biceps femoris,
semitendinosus and semimembranosus insert
a. The posterior femoral cutaneous nerve curves around the bicep femoris
below the ischial tuberosity
b. Continue to dissect the posterior femoral cutaneous away from the
underside of the fascia lata and follow it down to about the popliteal fossa
and do not go any further because its attachment here helps with the
demonstration later
4. The gluteus is allowed to stay on so we can use it as a cover to keep the nerves
moist and prevent them from drying out.
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9.
a. Once you know where the sciatic and piriformis are you can take a scalpel
and cut the gluteus off the sacrum cephalad to them to release it so that the
gluteus can be folded over more medially to give you room to work
Look at a skeleton and get oriented to the ischial tuberosity, the greater and lesser
sciatic notch.
a. Lesser sciatic foramen through which the tendon of the internal obturator
passes over with the gemellus muscles. The notch is turned onto the
Foramen by the Sacrospinal Ligament.
b. Greater sacral foramen where the piriformis and the sciatic nerve pass.
The notch is turned into the foramen by the Sacrotubular Ligament.
Define the Lesser Sciatic Foramen. Push your finger into the lesser foramen and
feel for what is a tight tendon superiorly or above your finger. This is the
sacrotubular ligament
a. Use your Metz to poke through and open a hole below the ligament but
above the other tissue which is the tendon of the internal Obturator
b. Push your finger through into the pelvis to help you further define where
the Tendon of the Internal Obturator
c. Be careful as the pudendal vessels and nerve are in this area
d. The Sacrospinal ligament is the extension of the spine that rises up to the
sacrum and is where the pudendal vessels and nerve rest
Define the Tendon of the Internal Obturator
a. which comes out of the pelvis through this foramen and attaches to the
greater trochanter. Use the Metz to help you find the cephalad and caudad
edge of the tendon. You may have to poke and spread the teeth of the
Metz in line with the path of the tendon to define it.
b. At a certain point you should be able to put the Metz under the tendon to
know that you got it. It is usually about 1cm wide. It is about 1cm wide
and fairly tough so you can try to poke the Metz through the tissue on
either side of the tendon and then when you do you will be touching bone
on either side
c. Note that this tendon as the tendon and the gemellus muscles form a kind
of sling for the sciatic which leads to its sessile appearance on ultrasound
at this level.
Quadratus Femoris.
a. Now find the quadratus femoris. It’s the next muscle down or Caudad
from the Tendon and Gemellus Muscles
b. Note how wide it is, usually about 3 to 4cm.
c. Note that this muscle kind of dives down toward land lower on the Ischial
tuberosity and with the muscles that insert onto the tuberosity form a kind
of wedge. This is the area where on ultrasound the sciatic appears more
triangular
d. Push your finger down into the wedge area
Adductor Magnus
a. Then note the transition from the quadratus femoris to the adductor. There
is usually a little step down.
b. Then take a look across the table to note the change in elevation of the
sciatic as it exits the greater sacral foramen and descends as it goes caudad
to the area of the adductor. This should help you know how to direct the
probe to better see the sciatic with the ultrasound
10. Define the Biceps Femoris.
a. Use digital dissection to follow along the biceps femoris staying above the
biceps femoris muscle and separate away the fascia lata
b. Digitally dissect the fascia lata off the biceps femoris and try to define its
medial border
c. Be careful not to remove the fascia lata that holds the Posterior Femoral
Cutaneous Nerve
d. Note the small and long head
e. On ultrasound the long head is against the probe
f. The short head is along the side of the ultrasound picture
g. Note the IlioTibial Tract along the lateral aspect of the thigh
11. Now follow the sciatic nerve down and digitally dissect to define the Tibial and
Common Peroneal
a. Note the sheath around theses nerves. It is very thin and transparent in
many specimens.
b. Help to define the nerves and see if you can find the Lesser saphenous
vein coming up to join the medial sural cutaneous nerve
12. Common Peroneal
a. Try to keep the connection between the long and short head of the biceps
s=together and find the common peroneal nerve on the inside of the long
head
b. Now go to the inside or medial edge of the biceps femoris and about 5 to
10cm above this and feel for a bump that represents the nerve and dissect
it out
c. Then feel the fibular head and note that this is the path of the common
peroneal
d. Cut through the tissue a little and spread it open as the nerve is usually in
line with this tendon of the biceps femoris and follows it in a straight line
to the neck of the head of the fibula
e. As you go down the common peroneal be aware a branch that will occur
This is the lateral sural nerve
f. Continue to dissect both the common peroneal and the lateral sural
cutaneous nerve
g. An alternate technique. You can also dissect up from the area of the
fibular head but definitely stay just at the fascia otherwise your Metz
might cut the Lateral Sural Cutaneous nerve
h.
13. Nerve to the Short head of the Biceps Femoris
a. digitally dissect up the common peroneal cephalad to find the little nerve
going to the short head of the biceps femoris. This is the only innervation
of the muscles in the thigh by the common peroneal . all others are
innervated by the tibial portion of the sciatic
b. Once you have found this you can follow this down a ways
14. Fibular Head
a. Return to the fibular head and feel it so you can define its medial and
lateral extent
b. Continue to follow the common peroneal and remove enough fascia to
demonstrate the tight area here and the common peroneal wrapping around
the neck of the fibula
15. Medial Sural Cutaneous Nerve
a. When you pull up the fascia over the calf try too find a nerve on the
medial side. This is the medial sural nerve and this will join the lateral
sural nerve and the lesser saphenous vein to form the common sural nerve
b. Follow this nerve up to the tibial nerve
c. Follow it down to the formation of the sural nerve
16. Sural Nerve
a. The lesser Saphenous vein and the sural nerve travel together other resting
place in between the lateral malleolus and the calcaneal or Achilles tendon
b. Note where they exit the overlying fascia about 10cm above the heel
17. Tendons of the Semitendinosus, Gracilis and Sartorius
a. Clean up the tendons near the knee of the semitendinosus, gracilis and
Sartorius
b. Find the saphenous nerve and make sure it is not cut while you clean up
this area as you may have to cut away some fat to help define things and
clean it
c. If you can show the pes anserinus
18. Ischial Tuberosity and the insertion of the muscles
a. Help define the semitendinosus muscle and semimembranosus muscle
and the biceps femoris in the insertion at the ischial tuberosity
b. Note the membranous portion and ribbon like nature of the
semimembranosus
19. Define the popliteal artery and vein
a. Define the adductor and the hiatus and the tendon of the adductor
b. Also follow the semitendinosus and semimembranosus up to the ischial
tuberosity and clear away some of the tissue so it can be seen better. Note
the ribbon thin semimembranosus near the ischial tuberosity
20. Ultrasound Views Review the different ultrasound views while looking at the
anatomy
a. High Sciatic vs. Labat
b. Sciatic at level of the Tendon of the External Oblique and Gemellus
Muscles
c. Sciatic level at the Quadratus femoris and the underlying lesser trochanter
d. Sciatic at subgluteal
e. Popliteal
f. Popliteal at the point of separation of the nerves with the underlying vein
g. Sural and lesser Saphenous Vein
IMG_7153 Sciatic GOOD
IMG_9316 Sciatic Bilateral Flipped.MOV
IMG_5198.MOV Posterior Leg How to Dissect
20120919_sacrum sciatic ilio ing hypo this file is a very good review of the anatomy
on both right and left but I make some mistakes in calling out the anatomy and don’t
name others but overall it is a great review using many videos
IMG_4977 This video might not be a good one to post on the site but shows that the
posterior femoral nerve comes up along the lateral aspect of the biceps femoris muscle as
it goes towards the surface layers