Brief Summary

Myofascial pain syndrome (MPS) is a common musculoskeletal condition characterized by active trigger points (TrPs), which are hypersensitive, painful nodules within taut bands of skeletal muscle. The upper trapezius muscle is one of the most frequently affected sites. Trigger point injection (TPI) is a widely used minimally invasive treatment for patients who are refractory to conservative management.

Corticosteroids provide rapid anti-inflammatory effects, whereas platelet-rich plasma (PRP) has regenerative properties through growth factors that may support tissue healing. Despite their widespread use, the optimal injectate for TPI remains unclear. Additionally, the potential benefit of combining PRP with corticosteroids has not been adequately studied in upper trapezius MPS.

This study is a single-center, prospective, randomized, assessor-blinded controlled trial designed to compare the clinical effectiveness of three injection protocols: (1) PRP plus bupivacaine, (2) PRP plus betamethasone plus bupivacaine, and (3) betamethasone plus bupivacaine with saline (volume-matched control). A total of 150 patients with a single active trigger point in the upper trapezius will be included.

The primary outcome is pain intensity measured by the visual analog scale (VAS) 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 technique, and outcome assessments are conducted by a blinded evaluator.

Study Design

This is a single-center, prospective, three-arm randomized controlled trial. Randomization will be performed using a computer-generated block randomization method (block size: 6, allocation ratio 1:1:1) with sealed opaque envelopes. Patients and outcome assessors will be blinded to group allocation. The injecting physician will not be blinded due to the nature of PRP preparation.

Interventions

Group A (PRP group):

2 mL autologous leukocyte-poor PRP + 1 mL bupivacaine 0.5% (total 3 mL)

Group B (Combination group):

1 mL PRP + 1 mL bupivacaine 0.5% + 1 mL betamethasone (total 3 mL)

Group C (Control group):

1 mL betamethasone + 1 mL bupivacaine 0.5% + 1 mL normal saline (total 3 mL)

All groups receive equal injection volumes to avoid volume-related bias.

PRP Preparation

Ten milliliters of peripheral venous blood will be collected into a citrate-containing tube. The first centrifugation will be performed at 1500 rpm for 10 minutes, followed by a second centrifugation at 2500 rpm for 10 minutes. One milliliter of leukocyte-poor PRP will be obtained. No activator will be used. The preparation will be applied within 30 minutes. Platelet concentration and preparation parameters will be recorded.

Injection Technique

Trigger point injections will be performed using a palpation-guided technique without ultrasound assistance. A 25G needle will be inserted at approximately 30 degrees into the trigger point. Local twitch response will be documented during the procedure.

Outcome Assessments

Baseline (T0):

VAS, PPT (algometer), cervical ROM (digital goniometer)

1 week (T1): VAS, PPT, adverse events 4 weeks (T2): VAS, PPT, ROM, rescue analgesic use 3 months (T3 - Primary endpoint): VAS, PPT, ROM, rescue analgesic use, patient satisfaction 6 months (T4): VAS, PPT, ROM, recurrence evaluation, patient satisfaction Statistical Analysis

The primary analysis will be conducted using repeated measures ANOVA with Greenhouse-Geisser correction. Post hoc comparisons will be performed using Tukey HSD with Bonferroni adjustment. Intention-to-treat analysis will be applied. Missing data will be handled using multiple imputation. A per-protocol analysis will be performed as a sensitivity analysis. Recurrence rates will be analyzed using Kaplan-Meier survival analysis and log-rank testing. Statistical analyses will be performed using SPSS version 26.

Inclusion Criteria:

• Age between 18 and 65 years
• Presentation to the Orthopedics and Traumatology outpatient clinic with neck and/or shoulder pain
• Diagnosis of upper trapezius myofascial pain syndrome based on Simons and Travell criteria, including:
• Presence of a taut band
• Local tenderness
• Referred pain pattern
• Local twitch response
• Presence of a single active trigger point in the upper trapezius muscle
• Symptom duration ≥ 4 weeks
• Pain intensity ≥ 4 on the visual analog scale (VAS)
• Inadequate response to at least 4 weeks of conservative treatment (physical therapy and/or oral analgesics)
• Ability to provide written informed consent

Exclusion Criteria:

• Presence of multiple active trigger points
• Diagnosis of fibromyalgia according to ACR 2010 criteria
• Cervical radiculopathy or myelopathy
• Trigger point injection in the same region within the past 3 months
• Coagulopathy or current anticoagulant or antiplatelet therapy
• Known allergy or contraindication to corticosteroids, local anesthetics, or PRP components
• Active infection (systemic or local)
• Pregnancy or lactation
• Thrombocytopenia (platelet count < 100,000/µL)
• Malignancy
• Inability to cooperate or provide informed consent

Participants are blinded to treatment allocation; all injections appear identical in volume (3 mL) and technique. The outcomes assessor (who performs VAS, PPT, and ROM measurements) is a separate physician blinded to group assignment and not present during injections. The injecting investigator is unblinded due to the technical requirement of PRP preparation.