An iliopsoas plane block does not cause motor blockade—A blinded randomized volunteer trial

Background A femoral nerve block relieves pain after total hip arthroplasty, but its use is controversial due to motor paralysis accompanied by an increased risk of fall. Assumedly, the iliopsoas plane block (IPB) targets the hip articular branches of the femoral nerve without motor blockade. However, this has only been indicated in a cadaver study. Therefore, we designed this volunteer study. Methods Twenty healthy volunteers were randomly allocated to blinded paired active vs. sham IPB (5 mL lidocaine 18 mg/mL with epinephrine vs saline). The primary outcome was reduction of maximal force of knee extension after IPB compared to baseline. Secondary outcomes included reduction of maximal force of hip adduction, and the pattern of injectate spread assessed with magnetic resonance imaging. Results Mean (confidence interval) change of maximal force of knee extension from baseline to after IPB was −9.7 N (−22, 3.0) ( P = .12) (n = 14). The injectate was consistently observed in an anatomically well‐defined closed fascial compartment between the intra‐ and extra‐pelvic components of the iliopsoas muscle anterior to the hip joint. Conclusion We observed no significant reduction of maximal force of knee extension after an IPB. The injectate was contained in a fascial compartment previously shown to contain all sensory branches from the femoral nerve to the hip joint. The clinical consequence of selective anesthesia of all sensory femoral nerve branches from the hip could be a reduced risk of fall compared to a traditional femoral nerve block. Registration of Trial : The trial was prospectively registered in EudraCT (Reference: 2018‐000089‐12, https://www.clinicaltrialsregister.eu/ctr-search/search?query=2018-000089-12 ).