title: Soft tissue landmark for ultrasound identification of the sciatic nerve in the infragluteal region: the tendon of the long head of the biceps femoris muscle.
abstract: OBJECTIVE
  The sciatic nerve block represents one of the more difficult ultrasound-guided nerve blocks. Easy and reliable internal ultrasound landmarks would be helpful for localization of the sciatic nerve. Earlier, during ultrasound-guided posterior approaches to the infragluteal sciatic nerve, the authors recognized a hyperechoic structure at the medial border of the long head of biceps femoris muscle (BFL). The present study was performed to determine whether this is a potential internal landmark to identify the infragluteal sciatic nerve.
  
  
  METHODS
  The depth and the thickness of this hyperechoic structure, its relationship with the sciatic nerve and the ultrasound visibility of both were recorded in the proximal upper leg of 21 adult volunteers using a linear ultrasound probe in the range of 7-13 MHz. The findings were verified by an anatomical study in two cadavers.
  
  
  RESULTS
  The hyperechoic structure at the medial border of the BFL extended in a dorsoventral direction between 1.4+/-0.6 cm (mean+/-SD) and 2.8+/-0.8 cm deep from the surface, with a width of 2.2+/-0.9 mm. Between 2.6+/-0.9 and 10.0+/-1.5 cm distal to the subgluteal fold, the sciatic nerve was consistently identified directly at the ventral end of the hyperechoic structure in all volunteers. The anatomical study revealed that this hyperechoic structure corresponds to tendinous fibres inside and at the medial border of the BFL.
  
  
  CONCLUSIONS
  The hyperechoic BFL tendon might be a reliable soft tissue landmark for ultrasound localization of the infragluteal sciatic nerve.
authors.affiliation: Department of Anesthesiology, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands. j.bruhn@anes.umcn.nl
authors.forename: J
authors.initials: J
authors.lastname: Bruhn
authors.forename: N
authors.initials: N
authors.lastname: Moayeri
authors.forename: G J
authors.initials: GJ
authors.lastname: Groen
authors.forename: A
authors.initials: A
authors.lastname: VAN Veenendaal
authors.forename: M J
authors.initials: MJ
authors.lastname: Gielen
authors.forename: G J
authors.initials: GJ
authors.lastname: Scheffer
authors.forename: G-J
authors.initials: GJ
authors.lastname: VAN Geffen
mesh_terms: D000328:Adult; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D008867:Microtomy; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging*; D009407:Nerve Block / Q000379:methods*; D012584:Sciatic Nerve / Q000000981:diagnostic imaging*; D013710:Tendons / Q000000981:diagnostic imaging*; D013848:Thigh / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D014463:Ultrasonography