Ultrasound-guided abdominal wall infiltration versus freehand technique in anterior cutaneous nerve entrapment syndrome (ACNES): randomized clinical trial

BACKGROUND: The optimal technique of abdominal wall infiltration for chronic abdominal wall pain due to anterior cutaneous nerve entrapment syndrome (ACNES) is unknown. The aim of this study was to compare pain reduction after an abdominal wall anaesthetic injection by use of an ultrasound-guided technique (US) or given freehand (FH). METHODS: In this multicentre non-blinded randomized trial, adult patients with ACNES were randomized (1:1) to an US or a FH injection technique. Primary outcome was the proportion of injections achieving a minimum of 50 per cent pain reduction on the Numeric Rating Scale (range 0–10) 15–20 min after abdominal wall infiltration (‘successful response’). Secondary outcomes were treatment efficacy after 6 weeks and 3 months, and the influence of the subcutaneous tissue thickness on treatment outcome. RESULTS: Between January 2018 and April 2020, 391 injections (US = 192, FH = 199) were administered in 117 randomized patients (US = 55, FH = 62; 76.0 per cent female, mean age 45 years). The proportion of successful responses did not significantly differ immediately after the injection regimen (US 27.1 per cent versus FH 33.2 per cent; P = 0.19) or after 3 months (US 29.4 per cent versus FH 30.5 per cent; P = 0.90). Success was not determined by subcutaneous tissue thickness. CONCLUSION: Pain relief following abdominal wall infiltration by a US or FH technique in ACNES is similar and not influenced by subcutaneous tissue thickness. REGISTRATION NUMBER: Dutch Clinical Trial Register NL8465.