Movement-Evoked Pain After Mastectomy with Interpectoral and Pectoserratus Plane Blocks with or Without an Additional Superficial Serratus Plane Injection: A Retrospective Cohort Study

Background and Objectives: Movement-evoked pain captures pain experienced during postoperative activity and complements assessment of pain at rest after mastectomy. We evaluated whether the combined strategy of interpectoral and pectoserratus plane blocks with an additional superficial serratus plane injection was associated with lower movement-evoked pain during the first 24 postoperative hours. Materials and Methods: This single-centre retrospective cohort study included adults undergoing unilateral mastectomy from January 2023 through December 2025. Patients received interpectoral and pectoserratus plane blocks alone or the same strategy plus a superficial serratus plane injection. The primary outcome was movement-evoked numeric rating scale pain at 2, 6, 12, and 24 h. Repeated pain scores were analysed using covariate-adjusted linear mixed-effects models, with unadjusted models and inverse probability of treatment weighting as complementary analyses. Results: Among 216 patients assessed, 169 were included (81 interpectoral–pectoserratus; 88 combined strategy). Mean total bupivacaine doses were 66.39 mg and 110.06 mg, respectively. The adjusted mean between-group difference in movement-evoked pain, averaged across four assessments and expressed as interpectoral–pectoserratus minus combined strategy, was 2.09 points (95% CI 1.87–2.32); the unadjusted difference was 2.13 points (95% CI 1.90–2.36). The adjusted resting pain difference was 1.59 points (95% CI 1.38–1.80). Weighted estimates were similar. Rescue tramadol was administered to 13.6% and 8.0% of patients, respectively (p = 0.319). No block-related complications were documented. Conclusions: The combined strategy was associated with lower recorded movement-evoked and resting pain but involved approximately 66% more bupivacaine and a greater total injectate volume. These observational findings cannot establish whether the additional injection site provides an analgesic benefit independent of the higher local anaesthetic dose and volume.