Clinical efficacy of ultrasound-guided serratus posterior superior intercostal plane block in unilateral cervicothoracic myofascial pain syndrome: a retrospective study

BACKGROUND: Myofascial pain syndrome (MPS) of the cervicothoracic region is a common cause of chronic neck and upper back pain that often shows limited response to conservative therapies. The recently described serratus posterior superior intercostal plane block (SPSIPB) targets the fascial plane between the serratus posterior superior and intercostal muscles and may provide effective regional analgesia. However, its long-term clinical efficacy in MPS has not been systematically evaluated. This study aimed to investigate the effectiveness and safety of ultrasound-guided SPSIPB in patients with unilateral cervicothoracic MPS. METHODS: This single-center retrospective cohort study evaluated the effectiveness of ultrasound-guided SPSIPB in patients with unilateral cervicothoracic MPS. A total of 75 patients treated between June 2024 and May 2025 were included. Pain intensity (Numerical Rating Scale [NRS]) was assessed at baseline, 1 h, 4 weeks, 12 weeks, and 6 months. Functional disability (Neck Disability Index [NDI]) and quality of life (EQ-5D-5 L) were evaluated in a predefined subset. A linear mixed-effects model including all available observations was used for primary analysis, with post-baseline co-interventions incorporated as a time-varying covariate. Sensitivity analyses included per-protocol, complete-case, and conservative missing-not-at-random (MNAR) approaches. RESULTS: NRS scores decreased significantly over time, with the greatest reduction observed at 1 h and continued improvement at 6 months (adjusted mean change - 2.73, 95% CI - 3.18 to - 2.28; p < 0.001). Clinically meaningful improvement, defined as ≥ 50% reduction in NRS, was observed in 90.7%, 34.7%, and 28.0% of patients at 1 h, 4 weeks, and 6 months, respectively. Functional disability improved significantly, with NDI reductions of - 7.83, - 7.37, and - 6.67 at 4 weeks, 12 weeks, and 6 months, respectively (all p < 0.001). EQ-5D-5 L scores also improved significantly across all follow-up time points (all p < 0.001). Sensitivity analyses demonstrated consistent findings across all models, including conservative MNAR assumptions. No major complications were observed. CONCLUSIONS: Ultrasound-guided SPSIPB was associated with rapid pain reduction and continued improvements in disability and quality of life up to six months in this retrospective cohort. No major complications were documented. These findings support further prospective controlled evaluation of SPSIPB as a potential interfascial approach for cervicothoracic MPS.