Underpowered study design invalidates conclusions of LTAP versus LWI in peritoneal endometriosis surgery

Sir,

We read with great interest the prospective, randomized, double‐blinded trial by Terho et al. recently published in Acta Obstetricia et Gynecologica Scandinavica, comparing laparoscopically guided transversus abdominis plane block (LTAP) and local wound infiltration (LWI) for postoperative analgesia in laparoscopic peritoneal endometriosis surgery. ¹ The authors concluded that LTAP provides no opioid‐sparing benefit and yields equivalent analgesia, recovery, and safety compared with LWI. However, we highlight a fatal methodological flaw that fundamentally undermines the validity of this conclusion: a severely underpowered study design caused by unrealistic sample size calculation.

The sample size was estimated assuming LTAP would reduce opioid consumption by 50%, using a historical control where LWI resulted in 15.4 ± 9.2 mg morphine equivalents. ¹ In the actual study, the LWI group consumed 27.5 ± 19.3 mg—nearly double the value used for power analysis—with high interindividual variability in both groups. ¹ This critical mismatch meant the final sample of 46 patients lacked statistical power to detect genuine between‐group differences, exposing the trial to a high risk of Type II error.

Patients with endometriosis‐related chronic preoperative pain have well‐established higher postoperative opioid requirements due to peripheral and central sensitization. ² , ³ The authors did not account for this population‐specific pain phenotype in their power calculation. A valid non‐inferiority or equivalence comparison requires prospective sample size estimation based on real‐world data from endometriosis cohorts rather than historical controls from general laparoscopic surgery.

The high opioid consumption in both groups may have masked potential analgesic differences. Given the discrepancy between the assumed and observed opioid use, the negative findings should be interpreted with appropriate caution. We believe this methodological perspective may help inform the design of subsequent analgesia studies in this unique patient population.

AUTHOR CONTRIBUTIONS

All authors contributed equally to the manuscript and read and approved the final version of the manuscript.

FUNDING INFORMATION

This research was funded by a grant from the Zhejiang Provincial Medical and Health Plan (2022KY1159, 2025KY1423, 2025KY1417, and 2025HY1019). Key Technology Breakthrough Program of “Ningbo Sci‐Tech Innovation Yongjiang 2035” (No. 2024Z222). Ningbo Municipal Specialized Training Program for Young Technical Backbone Talents in Health (Yongweifa 2024–102‐77). Ningbo High‐Level Medical and Health Team Major Tackling Project and the Talent Development Program (2022020405). Ningbo Municipal Key Modern Medical Discipline Development Project (2026‐A36).

CONFLICT OF INTEREST STATEMENT

The authors certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.

DATA AVAILABILITY STATEMENT

Not applicable.