King's Mill anterior-posterior and transverse versus paracervical block in operative outpatient hysteroscopy: a randomised trial.

Abstract

BACKGROUND: Pain control during operative outpatient hysteroscopy remains a clinical challenge, with the paracervical block (PCB) showing inconsistent efficacy. The King's Mill Anterior-Posterior and Transverse (KAPT) block targets the Lee-Frankenhauser plexus within the uterosacral ligament complex, where the highest density of uterine and cervical sensory fibres lies. We compared the KAPT block with the PCB in operative outpatient hysteroscopy. METHODS: Single-centre, participant- and outcome assessor-blinded randomised controlled trial in a UK district general hospital. Forty-eight women undergoing operative outpatient hysteroscopy were randomised 1:1 to the KAPT block or the PCB, each delivered with 10 ml of prilocaine. Pain was measured on a 10-point Visual Analogue Scale (VAS) during the procedure and 10 minutes post-procedure (co-primary endpoints), and during cervical dilatation (exploratory). Analyses used the Mann-Whitney U test on an intention-to-treat basis, with Hodges-Lehmann median differences, percentile bootstrap 95% confidence intervals, and a hierarchical fixed-sequence testing strategy. RESULTS: Median intra-procedural VAS was 1 (IQR 0 to 3) with the KAPT block versus 2 (IQR 1 to 6) with the PCB (Hodges-Lehmann median difference -1.00, 95% CI -3.00 to 0.00; p = 0.040). At 10 minutes post-procedure, median VAS was 0 (IQR 0 to 1.25) versus 2 (IQR 0 to 3.25) (median difference -1.00, 95% CI -2.00 to 0.00; p = 0.011). Both co-primary endpoints reached significance under hierarchical testing. Cervical dilatation pain did not differ significantly (p = 0.146). Satisfaction was 100% in both arms; willingness to recommend was 100% (KAPT) versus 95.8% (PCB). No serious adverse events occurred. CONCLUSIONS: The KAPT block was associated with lower intra-procedural and post-procedural pain than the PCB, with effect sizes consistent with a clinically meaningful difference. These findings support the KAPT block as a superior, anatomically targeted alternative to the PCB and justify evaluation in a larger multicentre trial.Trial registration: ISRCTN15619382.