title: Ultrasound guided injection inside the common sheath of the sciatic nerve at division level has a higher success rate than an injection outside the sheath.
abstract: OBJECTIVE
  The recommendations for the level of injection and ideal placement of the needle tip required for successful ultrasound-guided sciatic popliteal block vary among authors. A hypothesis was made that, when the local anesthetic is injected at the division of the sciatic nerve within the common connective tissue sheath, the block has a higher success rate than an injection outside the sheath.
  
  
  METHODS
  Thirty-four patients scheduled for hallux valgus repair surgery were randomized to receive either a sub-sheath block (n=16) or a peri-sheath block (n=18) at the level of the division of the sciatic nerve at the popliteal fossa. For the sub-sheath block, the needle was advanced out of plane until the tip was positioned between the tibial and peroneal nerves, and local anesthetic was then injected without moving the needle. For the peri-sheath block, the needle was advanced out of plane both sides of the sciatic nerve, to surround the sheath. Mepivacaine 1.5% and levobupivacaine 0.5% 30mL were used in both groups. The progression of motor and sensory block was assessed at 5min intervals. Duration of block was recorded.
  
  
  RESULTS
  Adequate surgical block was achieved in all patients in the subsheath group (100%) compared to 12 patients (67%) in the peri-sheath group at 30min. Sensory block was achieved faster in the subsheath than peri-sheath (9.1±7.4min vs. 19.0±4.0; p<.001).
  
  
  CONCLUSIONS
  Our study suggests that for successful sciatic popliteal block in less than 30min, local anesthetic should be injected within the sheath.
authors.affiliation: Department of Anesthesiology, Hospital Clínic Barcelona, Barcelona, Spain. Electronic address: analopez@clinic.ub.es.
authors.forename: A M
authors.initials: AM
authors.lastname: Lopez
authors.affiliation: Department of Anesthesiology, Hospital Clínic Barcelona, Barcelona, Spain.
authors.forename: X
authors.initials: X
authors.lastname: Sala-Blanch
authors.affiliation: Department of Anesthesiology, Hospital Clínic Barcelona, Barcelona, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Castillo
authors.affiliation: Department of Anesthesiology, St Luke's-Roosevelt Hospital, College of Physicians and Surgeons, Columbia University, New York, USA.
authors.forename: A
authors.initials: A
authors.lastname: Hadzic
mesh_terms: D000779:Anesthetics, Local / Q000008:administration & dosage*; D002045:Bupivacaine / Q000008:administration & dosage / Q000031:analogs & derivatives; D006215:Hallux Valgus / Q000601:surgery; D006801:Humans; D007267:Injections / Q000379:methods; D000077554:Levobupivacaine; D008619:Mepivacaine / Q000008:administration & dosage; D009186:Myelin Sheath / Q000000981:diagnostic imaging; D009407:Nerve Block / Q000379:methods*; D012584:Sciatic Nerve / Q000000981:diagnostic imaging; D018084:Ultrasonography, Interventional
chemical_list: D000779:Anesthetics, Local; D000077554:Levobupivacaine; D008619:Mepivacaine; D002045:Bupivacaine
keywords: Bloqueo ciático poplíteo; Ecografía; Intraneural injection; Inyección intraneural; Sciatic popliteal nerve block; Ultrasound