The following course is an interactive teaching module on the sciatic nerve. Complete the six sections of the module at your own pace. On completing each section you will be directed to the section to complete next.
At the end of this module you should be able to confidently describe the anatomy and function of the sciatic nerve. In addition to this, you should be able to apply this knowledge to multiple choice and problem solving questions.
Roots of the sciatic nerve
Figure 1: Formation of sciatic nerve form the rami of L4, L5, S1, S2, S3.
The sciatic nerve is the largest nerve in the human body .
It is a thickened and flattened nerve of approximately 2cm in width.
It is formed by the ventral rami of L4, L5, S1, S2, S3 (Figure 1).
The sciatic nerve provides a direct nerve supply to the posterior thigh and an indirect supply to all compartments of the leg and foot.
Overview of the anatomical course of the sciatic nerve
Figure 2: Simplified diagram of the lower limb illustrating the course of the sciatic nerve in the lower limb.
The sciatic nerve is a continuation of the lumbosacral plexus.
It divides into tibial (L4, L5, S1-3) and common peroneal (L4, L5, S1-2) in the posterior thigh (figure 2).
The sciatic nerve normally divides into tibial and common peroneal nerves at the junctions of the middle and lower thirds of the thigh, proximal to the apex of the popliteal fossa.
The tibial nerve then continues in the posterior compartment of the leg giving rise to its terminal branches: medial and lateral plantar nerves.
The common peroneal nerve wraps round the head of the fibula before dividing into superficial and deep peroneal nerves.
Surface markings of the sciatic nerve
Figure 3: Posterior aspect of hemisected bony pelvis, illustrating the relations of the sciatic nerve to bony features of the pelvis.
Knowledge of the surface markings of the sciatic nerve are important in a clinical setting to ensure safe intramuscular injection and successful sciatic nerve block.
Descriptions of the surface markings of the sciatic nerve vary between anatomical textbooks.
Gray's anatomy describe that the sciatic nerve can be marked on the skin by a point midway between the posterior superior iliac spine and the ischial tuberosity. It then courses outwards and downwards to be marked by a point half way between the greater trochanter and ischial tuberosity (figure 3).
The sciatic nerve is formed by the ventral rami of which spinal nerves?
- L3, L4, L5, S1, S2
- L4, L5, S1, S2
- L4, L5, S1, S2, S3
- L3, L4, L5, S1
The sciatic nerve supplies which compartments in the lower limb?
- Posterior thigh, posterior leg and foot
- Anterior and posterior thigh
- Anterior thigh and all compartments of the leg
- Posterior thigh, all compartments of the leg and foot
The sciatic nerve divides into which two named nerves?
- Femoral nerve
- Tibial nerve
- Superficial peroneal nerve
- Deep peroneal nerve
- Common peroneal nerve
When performing a sciatic nerve block, a surface marking for the sciatic nerve can be made between which two bony features? (See figure 4 to aid your answer)
Figure 4: Posterior aspect of hemisected bony pelvis. Labels for two important bony features for the surface marking of the sciatic nerve have been removed.
- Ischial tuberosity
- Lesser trochanter
- Greater trochanter
- Anterior superior iliac spine