Comparing 2-Hz and 100-Hz Electroacupuncture for Postoperative Musculoskeletal Pain: Protocol for a 2 × 2 Prospective Randomized Crossover Trial

BACKGROUND: Postoperative pain after musculoskeletal surgery impedes early rehabilitation and reduces quality of life. Electroacupuncture is used as an adjunct for analgesia, but the optimal stimulation frequency and short-term response trajectory have not been established. OBJECTIVE: The aim of this study is to compare frequency-dependent relative analgesic responses to bilateral ST36 to SP9 electroacupuncture at 2 Hz and 100 Hz and generate effect size and variability estimates to inform future definitive trials. METHODS: This single-center, frequency-masked, active-comparator, 2 × 2 prospective randomized crossover trial will enroll 30 adults (aged 19-80 years) experiencing pain (numerical rating scale [NRS] score≥4) after musculoskeletal surgery. Participants will undergo two 15-minute electroacupuncture sessions at bilateral ST36 to SP9 (2 Hz and 100 Hz) separated by a washout period of at least 7 days. Participants will not be informed of the assigned stimulation frequency or treatment sequence. RESULTS: Participant recruitment began in September 2025, and data collection is expected to be completed by August 2026. Data analysis will begin after database finalization in late 2026, with primary findings submitted for publication in April 2027. The primary outcomes are baseline-adjusted changes in pain NRS scores at 15 minutes and 2 hours after each intervention. Secondary outcomes include pain NRS scores immediately after and at 1, 4, and 24 hours after electroacupuncture; pain location and quality; photoplethysmography-derived pulse rate variability, used as a surrogate for heart rate variability; radial pulse tonometry parameters; and wrist-worn activity metrics. CONCLUSIONS: This protocol describes an active-comparator crossover trial designed to estimate relative immediate and short-term analgesic responses to 2-Hz vs 100-Hz electroacupuncture and associated physiological measures in postoperative musculoskeletal pain. Because the trial does not include a sham, usual care, or no-additional-electroacupuncture control arm, it will not determine the absolute efficacy of electroacupuncture or separate specific effects from nonspecific contextual or placebo effects. Results from this trial will help optimize stimulation parameters and outcome assessments for larger, definitive efficacy trials. TRIAL REGISTRATION: Clinical Research Information Service KCT0011009; https://tinyurl.com/54phyep7. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/91706.