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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. 5. 6. 7. 8. 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