Background and objectives For pain relief after total knee arthroplasty (TKA), an injection at the midthigh level may produce analgesia inferior to that of a femoral nerve block as the anterior femoral cutaneous nerves (intermediate femoral cutaneous nerve (IFCN) and medial femoral cutaneous nerve (MFCN)) are not anesthetized. The IFCN can be selectively anesthetized in the subcutaneous tissue above the sartorius muscle and the MFCN by an injection in the proximal part of the femoral triangle (FT). The primary aim was to investigate the area of cutaneous anesthesia in relation to the surgical incision for TKA and anteromedial knee area after intermediate femoral cutaneous nerve blockade (IFCNB) in combination with an injection in the proximal or distal part of the FT (proximal vs distal femoral triangle block (FTB)).
Methods The study was carried out as two separate investigations: first, dissection of nine cadaver sides to verify a technique for IFCNB; second, a volunteer study with 40 healthy volunteers. The surgical midline incision for TKA was drawn bilaterally. All volunteers received an active distal FTB combined with a placebo proximal FTB on one side and vice versa on the other side. All volunteers were randomized to an active IFCNB on one side and placebo IFCNB on the contralateral side.
Results Identification of IFCN was successful in all cadaver sides. Fifteen out of 20 volunteers had complete anesthesia of the incision line after IFCNB combined with proximal FTB, which was significantly higher compared with proximal FTB alone and with distal FTB+IFCNB. A gap at the anteromedial knee area was present in 2/20 volunteers with proximal FTB compared with 17/20 with distal FTB when all volunteers had active IFCNB.
Conclusion Ultrasound-guided blockade of the IFCN and MFCN anesthetize the surgical midline incision and the anteromedial area of the knee relevant for TKA. In contrast, an injection at the midthigh level produces insufficient cutaneous anesthesia not covering the areas of interest.
Trial registration number EudraCT: 2018-004986-15.
- regional anesthesia
- lower extremity
- postoperative pain
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Contributors SB contributed to the conception and the design of the study protocol; recruited the study subjects; conducted the trial; acquired, analyzed and interpreted the data; and authored the initial manuscript. TDN contributed to the conception and the design of the study protocol; conduction of the trial; and the acquisition, analysis and interpretation of data. BM contributed to the design of the dissection study, performed dissections and contributed to the data collection and interpretation of dissection data. RH performed dissections and contributed to the data collection and interpretation of dissection data. TFB contributed to the conception and the design of the study protocol; recruitment of study subjects; conduction of the trial; and the acquisition, analysis and interpretation of data. All authors read and revised the manuscript critically, approved the final version and agreed to be accountable for all aspects of the work.
Funding The study was funded by The Salling Foundation, The Toyota Foundation, Knud and Edith Eriksen's Memorial Foundation, Helga and Peter Korning’s Foundation and Aarhus University Research Foundation. The content is solely the responsibility of the authors.
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval This double-blind, randomized, placebo-controlled volunteer trial was conducted in accordance with the Declaration of Helsinki and was approved by the Danish Medicines Agency (2019023631), The Central Denmark Region Committees on Health Research Ethics (1-10-72-366-18) and the Danish Data Protection Agency.
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement Data are available upon reasonable request.