What is the origin & root value of Sciatic nerve?
Origin: Sciatic nerve arises from the lumbosacral plexus.
Root value: ventral rami of L4-S3 spinal nerves.
Describe the course of Sciatic nerve?
Course:
- It arises in the pelvis and then leaves the pelvis through the greater sciatic foramen inferior to the piriformis.
- In the gluteal region it lies successively on ischium, obturator internus, quadrates femoris.
- It then passes midway between the greater trochanter and ischial tuberosity to enter the posterior compartment of thigh.
- Here it lies on the adductor magnus and is crossed by the long head of biceps femoris.
- It usually divides into tibial and common peroneal nerves at the superior angle of popliteal fossa.
Enumerate the branches of Sciatic nerve.
- Has no branches in the gluteal region.
- Tibial part of sciatic nerve supplies all the hamstring muscles e. semitendinosus, semimebranosus, biceps femoris (long head) and ischial part of adductor magnus except short head of biceps femoris in the posterior compartment of thigh.
- Common peroneal part of sciatic nerve suppliesshort head of biceps femoris.
Applied Aspects
Sciatic nerve injury leads to foot drop
Foot drop is a gait abnormality in which the forefoot cannot be lifted off the ground . This occurs due to inability to dorsiflex the ankle and the toes. as a result of paralysis of the muscles of the anterior compartment of leg. Although, the most common cause of paralysis of muscles of anterior compartment of leg is injury to common peroneal nerve (a branch of sciatic nerve) as it winds around the neck of fibula as the nerve is quite superficial.here., injury to sciatic nerve ( as in posterior dislocation of hip joint) and to the deep peroneal nerve ( it supplies all the muscles of the anterior compartment of leg and is a branch of common peroneal nerve) also results in foot drop.
Compression of sciatic nerve results in ‘sleeping foot’.
Safe quadrant in gluteal region for giving intramuscular injections.
Intramuscular injection enables a large amount of a drug to be introduced at once but absorbed gradually. The injection site must be carefully selected to avoid injury to the underlying large vessels and nerves. In the gluteal region are given in its upper and outer quadrant to avoid injury to sciatic nerve.
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