Does it Matter the Volume of Injectate on the Outcome of Ultrasound-guided Perineural Injection for Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) is an entrapment neuropathy affecting the median nerve with a lifetime prevalence of about 8% in the adult population. Carpal tunnel syndrome (CTS) occurs with the symptoms of intermittent nocturnal paresthesia and dysesthesia, followed by loss of sensation, weakness, and thenar muscle atrophy in later stages.

Although the etiology of CTS is multifactorial, compression of the median nerve in a space-limited osteofibrous canal at wrist level was proposed.

The gold standard of diagnosis is electrophysiological study, but ultrasonography was applied in recent decades for a better approach to the morphology change of the median nerve.Nerve hydrodissection (HD) is a widely used technique that involves the injection of fluid to separate the nerve from the surrounding structures.

HD is now considered a novel approach for the treatment of CTS with safe and outstanding long-term effects. A potential benefit of HD is to release the pressure on the "free nerves supplying the main nerves," called "nervi nervorum." Early, the compression of the vasa nervorum would affect venous outflow, causing the accumulation of toxins in the affected part. Then, the lymphatic drainage, located outside the epineurium, would undergo compressive effects.

HD can also decrease the gliding resistance of the median nerve within the carpal tunnel, which is considered a principal patho-mechanical cause of nerve injury.

Hydrodissection HD of the entrapped median nerve is considered a safe and efficacious approach for treatment of mild to moderate CTS and could be offered to patients with severe CTS if surgery is refused or can't be done due to other medical comorbidities. The use of US-guided HD could improve symptom severity, functional status, and the US parameters of nerve entrapment. HD has a long-term efficacy outcome; 88.6% of patients reported an effective outcome, and this may vary according to the initial severity status.

Different types of injectants are available and studied, with no clear indication of use for each type. However, PRP, D5W, and HA were more efficient than NS as regards subjective and objective improvement. PRP and HA were more effective for long-term nerve recovery, while HA was preferred for the earliest response. So, we recommend making the choice based on every patient's severity scale and electrophysiological scales, which means that for patients with mild forms and severe pain.

Injection of a large volume could be a better option in order to dissect a larger area, provide a better environment for the nerve repair mechanisms, and release the vascular and neural compressive elements.