PRP vs PRP+Betamethasone vs Betamethasone Injection for Upper Trapezius Myofascial Pain: A 3-Arm RCT

Myofascial pain syndrome (MPS) is a common musculoskeletal condition caused by active trigger points (TrPs) - hypersensitive, painful nodules within taut bands of skeletal muscle. The upper trapezius muscle is among the most frequently affected sites. Trigger point injection (TPI) is a widely used minimally invasive treatment for MPS refractory to conservative care. However, the optimal injectate remains debated. Corticosteroids (e.g., betamethasone) provide rapid anti-inflammatory relief but their long-term benefit over local anesthetic alone has not been consistently demonstrated. Platelet-rich plasma (PRP), an autologous concentrate rich in growth factors (PDGF, IGF-1, VEGF, EGF), promotes tissue repair and has shown superior pain relief over lidocaine at 4 weeks in masseteric MPS (Sakalys et al., 2020). The combination of betamethasone and PRP has shown superior outcomes over betamethasone alone in frozen shoulder models (p\<0.001); however, no study has evaluated this combination in upper trapezius MPS. This 3-arm, prospective, randomized, assessor-blind, controlled trial will compare: (A) PRP + bupivacaine, (B) PRP + betamethasone + bupivacaine, and (C) betamethasone + bupivacaine + saline (volume-matched control) in 150 patients with single active TrP in the upper trapezius. Primary outcome is VAS pain change at 3 months. Secondary outcomes include pressure pain threshold (PPT), cervical range of motion (ROM), rescue analgesic use, recurrence rate, and adverse events at 1 week, 4 weeks, 3 months, and 6 months. All injections are performed by the same investigator using a palpation-guided fanlike technique. Outcome assessments are conducted by a separate blinded evaluator. The study follows CONSORT 2010 and SPIRIT 2013 reporting guidelines

STUDY DESIGN Single-center, prospective, 3-arm randomized controlled trial. Randomization: computer-generated block randomization (block size 6, 1:1:1 ratio) using sealed opaque envelopes. Patient and assessor blinded; injecting physician unblinded (PRP preparation technically precludes blinding). INTERVENTIONS Group A (PRP): 2 mL autologous leukocyte-poor PRP + 1 mL bupivacaine 0.5% \[total 3 mL\] Group B (Combination): 1 mL PRP + 1 mL bupivacaine 0.5% + 1 mL Diprospan (betamethasone dipropionate 5 mg + betamethasone sodium phosphate 2 mg) \[total 3 mL\] Group C (Control): 1 mL Diprospan + 1 mL bupivacaine 0.5% + 1 mL normal saline \[total 3 mL\] All groups receive equal injection volume (3 mL) to control for volume confounding. PRP PREPARATION SOP 10 mL peripheral venous blood collected into citrate tube. First centrifuge: 1500 rpm, 10 min. Second centrifuge: 2500 rpm, 10 min. LP-PRP fraction collected. No activator. Applied within 30 min. Platelet concentration, leukocyte content, and preparation parameters recorded per ISTH/ISGP classification. INJECTION TECHNIQUE Palpation-guided, fanlike distribution, 25G 1.5-inch needle, 30-degree angle. Local twitch response documented. No ultrasound guidance. OUTCOME ASSESSMENTS T0 (baseline): VAS, PPT (algometer, kg/cm²), cervical ROM (digital goniometer), randomization + injection T1 (week 1): VAS, PPT, adverse events T2 (week 4): VAS, PPT, ROM, rescue analgesics T3 (month 3 - PRIMARY): VAS, PPT, ROM, rescue analgesics, patient satisfaction (Likert) T4 (month 6): VAS, PPT, ROM, recurrence evaluation, patient satisfaction STATISTICAL ANALYSIS Primary: Repeated measures ANOVA with Greenhouse-Geisser correction; post-hoc Tukey HSD with Bonferroni adjustment. ITT analysis; missing data: multiple imputation (MICE, m=20). Per-protocol as sensitivity analysis. Recurrence: Kaplan-Meier + log-rank test. Software: SPSS v26.

Inclusion Criteria: 1\. Age 18-65 years 2. Presenting to the Orthopedics and Traumatology outpatient clinic with neck/shoulder pain 3. Diagnosis of upper trapezius MPS confirmed by Simons \& Travell criteria: presence of (a) taut band, (b) local tenderness, (c) referred pain pattern, and (d) local twitch response 4. Single active trigger point in the upper trapezius muscle 5. Symptom duration ≥ 4 weeks 6. Pain intensity VAS ≥ 4 (moderate-to-severe pain) 7. Inadequate response to ≥4 weeks of conservative treatment (physical therapy and/or oral analgesics) 8. Ability to provide written informed consent Exclusion Criteria: 1\. Multiple active trigger points 2. Fibromyalgia (2010 ACR criteria) 3. Cervical radiculopathy or myelopathy 4. Trigger point injection in the same region within the past 3 months 5. Coagulopathy or anticoagulant/antiplatelet therapy 6. Known allergy or contraindication to corticosteroids, local anesthetics, or PRP components 7. Active infection (systemic or local) 8. Pregnancy or lactation 9. Thrombocytopenia (platelet count \< 100,000/μL) 10. Malignancy 11. Inability to cooperate or provide written informed consent