sciatic nerve

Question 1

Explain the origin, root value, course, distribution, and termination of the sciatic nerve. Also explain the applied anatomy associated with the sciatic nerve.

Answer 1

O ⇒ Ventral Rami of L4, L5, S1, S2, S3

Course in the Pelvis:
1. Lies in front of the piriformis, under cover of its fascia

Course in the gluteal region:
2. Leaves the pelvis through the greater sciatic foramen below the piriformis
3. Runs downwards with a slight lateral convexity b/w ischial tuberosity and greater trochanter

Course in the thigh:
4. Enters the back of the thigh at the lower border of the gluteus maximus
5. Runs vertically downwards lying b/w the adductor magnus anteriorly and long head of biceps femoris posteriorly
6. Keeps travelling until the superior angle of the popliteal fossa

T ⇒ Superior angle of the popliteal fossa by dividing into the tibial and common peroneal nerves

Distribution:
1. Articular branches to the hip joint arise in the gluteal region
2. Muscular branches have:
- Tibial part of sciatic nerve → Supplies semitendinosus, semimembranosus, long hea dof biceps femoris, and ischial head of adductor magnus (medial side)
- Common peroneal part → supplies only the short head of biceps femoris

Question 2

clinical

Answer 2

Clinical Anatomy:

1. Sciatic Nerve Injury
   - Due to badly placed intramuscular injections in the gluteal region. It should be in the upper lateral quadrant to avoid sciatic nerve.
   - Common peroneal part of the sciatic nerve lies superficially and as a result is the most affected during lesion of sciatic nerve
   - Posterior discolaction of hip joint can also damage the sciatic nerve. Mostly due to motor vehicle accident and trauma (femoral head on sciatic nerve)
2. Effects of sciatic nerve injury
   Motor ⇒
   - Marked wasting of muscles below the knee
   - Weak flexion of knee
   - Weak extension of hip
   - Foot drop. Since all muscles below the knee are paralyzed and the weight of the foot causes it to assume plantar flexed position.
   Sensory ⇒
   - Sensation is also lost below the knee except for narrow area down the medial side of lower part of leg and along the medial border of foot (Supplied by saphenous nerve)
3. Sciatica
   - Condition in which patients have pain along the sensory distribution of sciatic nerve and its terminal branches. Mainly the common peroneal nerve.
   - Pain is experienced in the posterior aspect of the thigh, the posterior and lateral sides of the leg and the lateral part of foot.
   - Caused by prolapse of intervertebral disc with pressure on one or more roots. Pressure on the sacral plexus or sciatic nerve by intrapelvic tumor. Inflammation of the sciatic nerve or its terminal branches