Case Report: Ultrasound-guided hydrodissection targeting the subsynovial connective tissue with dynamic ultrasound assessment in refractory carpal tunnel syndrome: a report of two cases.

Carpal tunnel syndrome is established to be caused by compression of the median nerve. However, recent studies have highlighted fibrosis of the subsynovial connective tissue and consequent restriction of median nerve sliding as a key pathophysiological mechanism. In this case report, we present the results of dynamic ultrasound assessment conducted on two patients with persistent symptoms, with a mixture of polydeoxyribonucleotide (PDRN) 7 mg and 5% dextrose in water (5DW) applied to perform a more extensive ultrasound-guided hydrodissection procedure targeting the subsynovial connective tissue area between the median nerve and the flexor tendons in addition to the conventional area around the median nerve. After treatment, both patients showed a decrease in Boston Carpal Tunnel Questionnaire scores, while dynamic ultrasound evaluation revealed morphological and cross-sectional changes in the median nerve during finger flexion. No adverse events or symptom recurrence were observed during the procedure or throughout the follow-up period. This report highlights an expanded ultrasound-guided hydrodissection approach that targets not only the conventional perineural spaces but also the subsynovial connective tissue-containing intertendinous space in refractory carpal tunnel syndrome. As such, this procedure could represent a non-surgical alternative for patients with carpal tunnel syndrome who do not respond to conventional conservative treatment.