Introduction
Carpal tunnel syndrome (CTS) is the most prevalent peripheral compressive neuropathy.1Although the exact pathophysiology remains nebulous, the prevailing theory is that progressive ischemic and strangulation of the median nerve (MN) develop in the high pressure of the intracarpal tunnel.2, 3
Nerve hydrodissection (HD), a method used to abridge adhesions by dissecting the anatomic spaces with fluid injection,4 was recently found to facilitate ultrasound-guided nerve injection for treating entrapment neuropathy.5-8 The therapeutic rationale is to detach nerve from surrounding compressive tissue, increasing the blood flow, and allowing the nerve impulses to re-pass.5-8 Research published in 2019 demonstrated the efficacy of HD to treat mild-to-moderate CTS.9Despite the positive clinical effects of HD for CTS, whether the injection technique would influence the duration of the HD effect is still unknown.
Currently, the two main methods of ultrasound-guided perineural injection for CTS, short- or long-axis approaches, are broadly applied in clinical practice.10-13 The method of long-axis injection may directly separate the MN from the flexor retinaculum (FR) with more contact area.14 In contrast to long-axis injection in which only the FR is hydrodissected from the MN, the operator can simultaneously hydrodissect the FR and subsynovial connective tissue (SSCT) through the short-axis approach. Furthermore, the short-axis approach could provide more accuracy with a lesser incidence of nerve injury because the operator can clearly identify the MN between the FR and SSCT with ultrasound guidance.15 However, due to inconsistent results from published studies, controversy continues about the optimal strategy between short- and long-axis injection for CTS.12, 13, 16-18In our clinical practice, both short- and long-axis injections were effective for HD in patients with CTS. Moreover, we observed that hydrodissecting both the FR and the SSCT seemed to enhance the therapeutic benefits of HD, based on patients’ clinical presentations. Thus, we hypothesized that short-axis HD may have equivalent or superior efficacy than long-axis HD for treating CTS. Hence, this trial aimed to compare short- and long-axis approaches in patients with mild-to-moderate CTS.