What is the origin and composition of the sciatic nerve?

The sciatic nerve originates from the sacral plexus, specifically from spinal nerve roots L4, L5, S1, S2, and S3. It is composed of two main parts: the tibial part (from ventral divisions) and the common peroneal part (from dorsal divisions).

Where does the sciatic nerve exit the pelvis and what is its course?

It exits the pelvis through the greater sciatic foramen, located below the piriformis muscle. Its course then descends between the greater trochanter and ischial tuberosity, deep to gluteus maximus, and runs in the posterior thigh deep to the long head of biceps femoris before dividing in the popliteal fossa.

What muscles does the sciatic nerve innervate?

It gives muscular branches to several muscles in the posterior thigh: from the medial side, it innervates semitendinosus, semimembranosus, long head of biceps femoris, and the ischial head of adductor magnus; from the lateral side, it innervates the short head of biceps femoris (the only lateral branch).

Where does the sciatic nerve divide into its terminal branches?

The sciatic nerve divides into its two terminal branches—the tibial nerve and the common peroneal nerve—at the superior angle of the popliteal fossa.

What is the clinical significance of the 'safe vs unsafe side' of the sciatic nerve?

The lateral side of the sciatic nerve is considered safe during procedures because it has no major muscular branches. In contrast, the medial side is unsafe as it gives off muscular branches and is more vulnerable to injury.

How can compression of the sciatic nerve cause symptoms like 'sleeping foot'?

Compression of the sciatic nerve, often at the gluteal-thigh junction from prolonged sitting on a hard surface, can lead to transient paresthesia (tingling or numbness), commonly referred to as 'sleeping foot'.

Why is it important to avoid the sciatic nerve during injections in the gluteal region?

To prevent nerve injury, injections should be administered in the upper lateral gluteal quadrant, as this area avoids the sciatic nerve's course, which is located more medially and inferiorly.

Sciatic Nerve (L4–S3) – Course & Clinical Notes

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