A 3-dimensional ultrasound study of local anesthetic spread during lateral popliteal nerve block: what is the ideal end point for needle tip position?

Reg Anesth Pain Med. Nov-Dec 2012;37(6):627-32. doi: 10.1097/AAP.0b013e31826af511.


Background and objectives: Recent clinical trials suggest that subfascial (sometimes termed subepineural) injections result in faster block onset and success compared with conventional techniques. This prospective, randomized, observer-blinded study measured and compared the 3-dimensional spread pattern and volume of perineural local anesthetic (LA) in contact with the sciatic nerve after subfascial versus extrafascial lateral popliteal injections.

Methods: Sixty patients were randomly assigned to either the subfascial or the extrafascial injection group. All patients received a single-injection, US-guided lateral popliteal sciatic nerve block for postoperative pain. Depending on group assignment, the needle tip was placed outside or beneath the sciatic fascial sheath for a single injection of 30 mL of ropivacaine 0.5%. Using 3-dimensional ultrasound imaging, postblock scans were acquired to quantify the volume and spread pattern of perineural LA around the sciatic nerve in each group.

Results: The mean LA perineural volume for the extrafascial group was 1.48 (SD, 0.50) mL versus a mean of 5.57 (SD, 1.68) mL for the subfascial group, P < 0.05. The mean distance of longitudinal perineural LA spread (along the length of the nerve) for the subfascial group was 66% greater than that observed using the conventional technique (9.3 vs 5.6 cm, P < 0.01). Complete sensory block to pinprick for the extrafascial group was 63% versus 90% (P < 0.05) for the subfascial group.

Conclusions: Placement of the needle tip beneath the complex fascial sheath of the sciatic nerve resulted in significantly greater perineural local anesthetic volume following a single-injection lateral popliteal approach at the nerve bifurcation and was associated with greater sensory blockade and a characteristic laminar LA spread pattern.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Amides / administration & dosage
  • Anesthetics, Local / administration & dosage*
  • Fascia / diagnostic imaging
  • Female
  • Humans
  • Imaging, Three-Dimensional*
  • Injections / methods
  • Male
  • Middle Aged
  • Nerve Block / methods*
  • Pain Measurement
  • Pain, Postoperative / prevention & control
  • Prospective Studies
  • Ropivacaine
  • Sciatic Nerve / diagnostic imaging*
  • Single-Blind Method
  • Ultrasonography, Interventional*


  • Amides
  • Anesthetics, Local
  • Ropivacaine