Sciatic Nerve Block

  • Originates from the lumbosacral plexus (L4-S3) and enters the gluteal region through the greater sciatic foramen, between two muscle planes
  • The anterior muscle plane is formed by the obturator internus and inferior gemellus muscles
  • The posterior (more superficial muscle plane) by the gluteus maximus muscle


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Sciatic Nerve

Anatomy

Finding the Sciatic Nerve

  • Greater Trochanter and Ischial Tuberosity- defined boundaries, lateral and medial respectively
  • In addition identification will define the depth of the plane for the sub-gluteal space 

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Sciatic Nerve Block

  • Gluteal region- the sciatic nerve is not easily identified by ultrasonography because of its depth
  • Lower in the subgluteal region, the sciatic nerve is more superficial, usually within 5 cm from the skin surface, and can be blocked more easily

Sciatic Nerve

  • Curved 5- to 7-MHz transducer (usually choose low frequency)
  • Transverse view 
  • Patient is positioned semiprone with the limb to be blocked uppermost
  • Bony landmarks- the greater trochanter of the femur laterally and the ischial tuberosity medially

Sciatic Nerve Block

  • 1 to almost 2 cm in width, and at times be less than 3 cm below the skin surface 
  • Often appears hyperechoic and elliptical deep to the distal gluteus maximus muscle and lateral to the biceps femoris muscle 
  • Usually surrounded by a well-defined border, presumably the aponeurosis of the surrounding muscles

Sciatic Nerve Block Applications

  • The transgluteal sciatic nerve block (TGSNB) is a procedure that can provide effective analgesia for lower extremity pain.
  • Clinical response to ultrasound-guided TGSNB performed by emergency physicians for acute pain control of sciatic back pain through a series of cases.

Tips

  • Less gain applied to the image is better than more gain 
  • Always try to follow the same survey pattern – find the trochanter, find the ischial tuberosity, place your probe in between, angle fore and aft, establish the target depth 

  • If you cannot immediately find the sub-gluteal space using the method described above, try lowering the frequency of the probe you're using 
  • If your machine supports focus points, move the focus points down a centimeter or two 

Tips

  • Always remember to focus your attention more medial than lateral (you know where medial is because you can find the ischial tuberosity with the ultrasound) 
  • Make sure your depth of scan is deep enough to cover the target depth 
  • If possible try repositioning the patient's leg into a more flexed position at the hip 

Tips

  • You can try making various adjustments in the machine controls, such as; gray maps, edge enhancement, filters, total gain control, frequencies, focus 
  • When all else fails reset all controls back to their defaults, start your survey pattern again

First ID the Greater Trochanter

The Ischial Tuberosity

Between the Boundaries

 Place your fingers midway along a line drawn between the trochanter and the ischial tuberosity as shown 

Injectate


  • 4ml Normal Saline
  • 4ml Bupivicaine 0.25%
  • 4mg Dexamethasone
  • 10-20mg Depomedrol

Sciatic nerve block

References

and Interesting Articles

  • Rodziewicz TL, Stevens JB, Ajib FA, et al. Sciatic Nerve Block. [Updated 2022 Jun 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470391/
  • D'Souza RS, Hooten WM. Neurolytic Blocks. 2022 May 2. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 30726045.


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