Comparative Efficacy of Scalene versus Scapular Approach for Ultrasound-Guided Corticosteroid Hydrodissection in Dorsal Scapular Nerve Entrapment: A Randomized Controlled Trial

Background: Dorsal scapular nerve (DSN) entrapment is a common cause of chronic interscapular pain. Ultrasound-guided corticosteroid hydrodissection is an effective intervention, but no randomized controlled trial has directly compared the efficacy of the proximal (scalene) and distal (scapular) injection approaches. Methods: In this multicentre, prospective, randomized controlled study conducted across seven centers in Egypt, patients and outcome assessors were blinded; proceduralists could not be blinded due to inherent technical differences. Sixty patients with electrodiagnostically-confirmed DSN entrapment were randomly assigned to receive a single ultrasound-guided hydrodissection injection of triamcinolone acetonide (40 mg) and lidocaine in 10 mL saline. Group I (n=30) received the injection at the DSN within the middle scalene muscle, while Group II (n=30) received it below the levator scapulae muscle. The primary outcome was the Visual Analog Scale (VAS) for pain at rest. Secondary outcomes included VAS during movement, Fatigue Assessment Scale (FAS), patient satisfaction, and motor distal latency, assessed at baseline, 1, and 3 months. Results: The groups were well-matched at baseline. The scalene group demonstrated a significantly greater reduction in pain at rest at both 1 month (Z = 6.68, p < 0.001) and 3 months (Z = 6.68, p < 0.001). Similar significant differences favoring the scalene group were observed for pain during movement and fatigue scores at all follow-ups (p < 0.001). Patient satisfaction was significantly higher in the scalene group at all follow-ups (p < 0.001). No significant between-group difference was found in motor distal latency, and no major complications occurred. Conclusion: Ultrasound-guided corticosteroid hydrodissection administered at the middle scalene muscle resulted in significantly greater short-term improvement in pain, fatigue, and patient satisfaction over three months compared to the distal scapular approach. The scalene approach may be considered more effective for short-term management, though longer-term studies are needed to confirm durability. Keywords: dorsal scapular neuropathy, ultrasonography, interventional, nerve block, hydrodissection, middle scalene muscle, randomized controlled trial, pain management