Relevant Anatomy for Sciatic Nerve Block
Sciatic Nerve begins in the lower back and runs through the buttock and down the lower limb. It is the longest and widest single nerve in the human body, going from the top of the leg to the foot on the posterior aspect. The sciatic nerve supplies nearly the whole of the skin of the leg, the muscles of the back of the thigh, and those of the leg and foot. It is derived from spinal nerves L4 through S3. It contains fibres from both the anterior and posterior divisions of the lumbosacral plexus. The sciatic nerve is formed from the L4 to S3 segments of the sacral plexus, a collection of nerve fibres that emerge from the sacral part of the spinal cord. The fibres unite to form a single nerve in front of the piriformis muscle. The nerve passes beneath the piriformis and through the greater sciatic foramen, exiting the pelvis. From here, it travels down the posterior thigh to the popliteal fossa. The nerve travels in the posterior compartment of the thigh behind the adductor magnus muscle, and is itself in front of the one head of the biceps femoris muscle. At some point between the pelvis and popliteal fossa, the nerve divides into its two branches
- The tibial nerve, which travels down the posterior compartment of the leg into the foot.
- The common peroneal nerve, which travels down the anterior and lateral compartment of the leg into the foot.
The sciatic nerve is the largest nerve in the human body.
The sciatic nerve innervates the skin of the foot, as well as the entire lower leg (except for its medial side). The skin to the sole of the foot is provided by the tibial nerve, and the lower leg and upper surface of the foot via the common fibular nerve. The sciatic nerve also innervates muscles. In particular:
- Via the tibial nerve, the muscles in the posterior compartment of the leg and sole of the foot.
- Via the common fibular nerve, the muscles in the anterior and lateral compartments of the leg
Lumbar Plexus – Structure and Branches – Anatomy
Sciatic nerve block anatomy and approaches PDFOpen PDF
Single Injection Subgluteal Sciatic Nerve Block
Tips for Sciatic Nerve Block
• A pillow may be placed between the legs at the level of the knee.
• Appropriate positioning is critical to establish the proper site for the introduction of the needle.
• Already at this level, the sciatic nerve is separated into the common peroneal and the tibial nerves, and the posterior femoral cutaneous nerve of the thigh has branched.
• The stimulation of the sciatic nerve is almost always preceded by the stimulation of the gluteus maximus.
• A bone contact usually indicates that the needle is too lateral.
• Stimulation of the piriformis muscle indicates that the needle is too cephalad.
• A motor response at the level of the toes increases the likelihood of success.
• When patients complain of pelvic discomfort, it suggests that the needle is too anterior and is going through the greater sciatic notch.
• Because the sciatic nerve is found at a depth of 8 to 13 cm, no redirection of the needle should be attempted after it passes the skin to avoid bending the needle.
• This approach can be uncomfortable for the patient and therefore requires appropriate local anesthesia with a 38-mm needle and an appropriate sedation.
• This approach is not recommended in anticoagulated patients.
• A new posterior approach has been described in adults: The patient is positioned either prone or in the lateral position. The site of introduction of the needle is 10 cm lateral from the midpoint of the intergluteal sulcus.
Nysora Article on Sciatic Nerve block anterior approachOpen PDF
Continuous Sciatic Nerve Block
Continuous Sciatic nerve block article andre boezart NYSORA