- origin: sacral plexus (L4-S3)
- course: exits the pelvis through the greater sciatic foramen to enter the leg between ischial tuberosity and femoral greater trochanter, then courses inferiorly through the posterior compartment of the thigh
- major branches
- motor supply: see motor supply of the sciatic nerve
- sensory supply: no direct sensory function. Indirect sensory supply to the foot (plantar surface: tibial nerve, dorsal surface: common peroneal nerve) and the leg (except its inner side, which is supplied by the saphenous nerve)
The nerve forms from the anterior divisions of the L4-S3 roots (which form the tibial component) and posterior divisions of the L4-S2 roots (which form the common peroneal component) of the sacral plexus.
It descends midway in between the greater trochanter of the femur and the tuberosity of the ischium and in the posterior compartment of the thigh to the apex of the popliteal fossa, where it divides into two large terminal branches:
- upper part: posterior surface of the ischium, nerve to quadratus femoris, obturator internus, the gemelli
- lower part: adductor magnus
- upper part: gluteus maximus
- lower part: long head of biceps femoris (crosses obliquely)
The nerve gives off articular and muscular branches before dividing into two terminal branches - the tibial nerve and the common peroneal nerve.
The sciatic nerve supplies the following muscles:
- biceps femoris: supply to short head arises from the common peroneal part, supply to long head arises from the tibial part
- semitendinosus: arises from the tibial part
- semimembranosus: arises from the tibial part
- adductor magnus: arises from the tibial part
The division of the sciatic nerve into the common peroneal and tibial nerves may take place at any point between the sacral plexus and the lower third of the thigh. When it occurs at the sacral plexus, the common peroneal nerve usually pierces the piriformis muscle.
A range of other variants exist based on the relationship to the piriformis muscle.
- Division in the pelvis with
- Common peroneal nerve piercing piriformis muscle and tibial nerve exiting below (mentioned above)
- Common peroneal nerve traveling above piriformis muscle and tibial nerve below
- Common peroneal nerve traveling above piriformis muscle and tibial nerve piercing pirformis muscle
- Both common peroneal nerve and tibial nerve traveling below piriformis muscle separately
- Sciatic nerve courses over piriformis muscle
- Sciatic nerve pierces piriformis muscle
- appears as a hypoechoic round structure, situated deep to piriformis and gluteus maximus muscles
Pain and functional symptoms may be caused by a compression or irritation of the sciatic nerve. This may be caused by: