• Wan Yi Wong, Siska Bjørn, Jennie Maria Christin Strid, Jens Børglum, and Thomas Fichtner Bendtsen.
• From the *Department of Anesthesiology, Intensive Care and Pain Medicine, Tan Tock Seng Hospital, Singapore; †Department of Anesthesiology and Intensive Care Medicine, Aarhus University Hospital, Aarhus, Denmark; and ‡Department of Anesthesiology and Intensive Care Medicine, Zealand University Hospital, University of Copenhagen, Copenhagen, Denmark.
• Reg Anesth Pain Med. 2017 Mar 1; 42 (2): 241-245.

Background And ObjectivesThe precise location of the adductor canal remains controversial among anesthesiologists. In numerous studies of the analgesic effect of the so-called adductor canal block for total knee arthroplasty, the needle insertion point has been the midpoint of the thigh, determined as the midpoint between the anterior superior iliac spine and base of patella. "Adductor canal block" may be a misnomer for an approach that is actually an injection into the femoral triangle, a "femoral triangle block." This block probably has a different analgesic effect compared with an injection into the adductor canal. We sought to determine the exact location of the adductor canal using ultrasound and relate it to the midpoint of the thigh.MethodsTwenty-two volunteers were examined using ultrasound. The proximal end of the adductor canal was identified where the medial border of the sartorius muscle intersects the medial border of the adductor longus muscle. The distal end of the adductor canal is the adductor hiatus, which was also visualized ultrasonographically.ResultsThe mean distance from the anterior superior iliac spine to the midpoint of the thigh was 22.9 cm (range, 20.3-24.9 cm). The mean distance from the anterior superior iliac spine to the proximal end of the adductor canal was 27.4 cm (range, 24.0-31.4 cm). Consequently, the mean distance from the midpoint of the thigh to the proximal end of the adductor canal was 4.6 cm (range, 2.3-7.0 cm).ConclusionsIn all volunteers, the midpoint of the thigh was proximal to the beginning of the adductor canal, suggesting that an injection performed at this level is in fact a femoral triangle block.

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