Back of the thigh posterior cutaneous nerve of

Back of the thigh

posterior cutaneous nerve of the thigh Gluteus Maximus S 1, 2, 3 Greater sciatic foramen Gluteal branch Perineal branches Piriformis posterior cutaneous nerve of thigh

Posterior cutaneous nerve of the thigh (S 1, 2, 3) * Origin; is a combined dorsal and ventral branch of the sacral plexus. * Course and relations; - It comes out from the greater sciatic foramen below the piriformis. - It descends under cover of the gluteus maximus then under cover of the deep fascia in the back of the thigh. - It pierces the deep fascia covering the popliteal fossa and terminates by supplying the skin of the upper part of the calf. * Branches: 1 - Gluteal branch to skin of lower part of the gluteal region. 2 - Perineal branch; to the skin of the perineum. 3 - Cutaneous branches: to the back of the high, roof of the popliteal fossa and upper part of the calf.

Hamstring Muscles 1 - Biceps femoris 2 - Semimembranosus 3 - Semitendinosus 4 - Ischial part of adductor magnus - Muscles of the posterior compartment of the thigh. - Hamstrings because they have a long course from origin to insertion form cord (string) descending down to the popliteal region (Ham). - Origin ischial tuberosity. - Nerve: sciatic nerve except short head biceps. 4 4 23 1

Semitendinosus Semimembranosus Biceps femoris Long head Short head

Origin of hamstring M Superior Lateral Medial Inferior Ling head of biceps & semitendinosus Subcutaneous part in sitting position Semimembranosus Ischial part of adductor Magnus

• Insertion of hamstring M 1 - Biceps apex of the head and styloid process of the fibula. 2 - Semitendinosus (S. G. S) into upper part of the medial surface of the tibia behind the sartorius and gracilis. 3 - Semimembranosus groove on the back of the medial condyle of the tibia.

Biceps Femoris ** Origin: by two heads: 1 - Long head, common origin with the semitendinosus from lower medial part of the upper area of the isthial tuberosity. 2 - Short head; lower part of the linea aspera and upper part of the lateral supracondylar line. ** Insertion: apex of the head and styloid process of the fibula. ** Nerve supply: 1 - Long head by sciatic nerve. 2 - Short head by common peroneal nerve. ** Actions: 1 - Extension of the hip Joint (long head). 2 - Flexion of the knee joint. 3 - Only Lateral rotator of the semi flexed leg.

Semitendinosus ** Origin: common origin with the long head of biceps femoris from lower medial part of upper area of the ischial tuberosity. ** Insertion: (S. G. S) into the upper part of the medial surface of the tibia behind the sartorius and gracilis. • Semimembranosus ** Origin: upper lateral part of upper area of ischial tuberosity. ** Insertion: 1 - groove on the back of the medial condyle of the tibia. 2 - Some fibers are reflected upwards and laterally to form the posterior oblique ligament of the knee joint. ** Actions of both Semi: 1 - Extension of the hip Joint. 2 - Flexion of the knee joint. 3 - Medial rotation of the semi flexed leg.

Sciatic nerve

Common peroneal part of sciatic nerve sacral plexus L 4 L 5 S 1 S 2 Thickest nerve of the body Sciatic nerve S 3 Tibial part of sciatic nerve

Surface anatomy of sciatic nerve 1 1 2 2 3 3 ** Surface anatomy: It is marked by a line joining 3 points; 1 - A point at the junction of the upper 1/3 and lower 2/3 of a line between the posterior superior iliac spine (PSIS) and ischial tuberosity (Exit from greater sciatic foramen). 2 - A point midway between the ischial tuberosity and greater trochanter. 3 - A point in the back of the thigh at the apex of the popliteal fossa where divided into tibial and common peroneal nerves

** Course and relations: - It leaves the pelvis through the greater sciatic foramen below the piriformis, undercover of gluteus maximus. . - It descends in the following structures from above downward (sciatic bed); 1 - Superior gemellus muscle. 2 - Obturator internus muscle. 3 - Inferior gemellus muscle. 4 - Quadratus femoris muscle. 5 - Adductor magnus.

** Variation of the sciatic nerve: - The nerve may leave the pelvis as two separate parts: a- Tibial nerve passes below the piriformis muscle and takes course of the sciatic nerve. b- Common peroneal nerve passes either 1 - Below the piriformis muscle. . 2 - Through the piriformis muscle. 3 - Above the piriformis muscle. • Branches of sciatic nerve A- Muscular to Hamstring muscles B- Terminal: tibial and common peroneal nerve 1 2 - Note sciatic nerve innervates hamstring muscles High up in the thigh, so its lesion in the middle of thigh, hamstring escape from paralysis - All muscular branches arise from medial side of nerve except branch to the short head of the biceps, so its lateral border is therefore the side of relative safety in its operative exposure. 3

** Effects of Injury of the sciatic nerve 1 - Motor; foot drop (resulting from the effect of gravity) a- Paralysis of the hamstring muscles. c- Complete paralysis of all muscles of the leg and foot. 2 - Sensory; Loss of cutaneous sensations of the leg and foot except a- Medial side of leg and foot supplied by saphenous nerve. b- Upper part of calf supplied by posterior cutaneous nerve of the thigh. ** Intramuscular Injections in the upper outer quadrant of the glutea. I region to avoid Injection in the sciatic nerve. ** During an above knee amputation, The nerve is accompanied by an artery called companion artery of sciatic nerve (a branch from inferior gluteal artery). This artery must be ligated to avoid severe bleeding.

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