Ultrasound-guided popliteal sciatic nerve blockade in the severely and morbidly obese: a prospective and randomized study

J Anesth. 2016 Jun;30(3):397-404. doi: 10.1007/s00540-016-2143-z. Epub 2016 Feb 9.


Purpose: Limited research data exist regarding optimal block techniques in the severely and morbidly obese patient population. We compared two approaches to sciatic nerve blockade at the popliteal fossa in severely and morbidly obese patients. The purpose of this study was to identify differences in pain scores, block onset characteristics, and adverse events between the proximal (prebifurcation) and the distal (postbifurcation) sites.

Methods: Patients with a body mass index ≥35 scheduled for unilateral foot surgery with a popliteal block were randomized to receive an ultrasound-guided popliteal block proximal or distal to the bifurcation of the sciatic nerve. The primary endpoint was numerical rating scale (NRS) scores in the post anesthesia care unit (PACU).

Results: Thirty patients were enrolled in each group for a total of 60 participants. Patients in the distal group had lower NRS scores upon entry into the PACU (0.70 ± 1.91) compared with the proximal group (2.17 ± 3.37), had a faster onset of sensorimotor blockade, and were less likely to require a repeat block procedure, conversion to general anesthesia, or local anesthetic supplementation by the surgical team. There was no difference in block procedure times or incidence of nerve injury between the two groups.

Conclusions: The distal approach to the popliteal block provided several intraoperative and analgesic benefits without a difference in block procedural times in the severely and morbidly obese. It is a cost-free intervention that results in a higher likelihood of a successful block in a population where avoidance of opioids is desirable.

Keywords: Foot (or) ankle surgery; Postoperative pain; Regional anesthesia; Sciatic (or) popliteal block; Severe (or) morbid obesity.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Aged
  • Anesthesia, General
  • Anesthetics, Local / administration & dosage
  • Ankle / surgery
  • Body Mass Index
  • Endpoint Determination
  • Female
  • Foot / surgery
  • Humans
  • Male
  • Middle Aged
  • Nerve Block / adverse effects
  • Nerve Block / methods*
  • Obesity, Morbid / diagnostic imaging*
  • Pain Measurement
  • Pain, Postoperative / epidemiology
  • Pain, Postoperative / prevention & control
  • Prospective Studies
  • Sciatic Nerve / diagnostic imaging*
  • Sciatic Nerve / injuries
  • Ultrasonography, Interventional / methods*


  • Anesthetics, Local