While the gold standard of carpal tunnel release (CTR) is open surgery, new and less invasive procedures have emerged. Sonographically-guided percutaneous surgery is the newest technique described.

The aim of this study was to quantify whether percutaneous incision of the transverse carpal ligament (TCL) can lead to anatomical modification and how these changes may explain postoperative clinical manifestations.

In a prospective, non-controlled study, 21 patients with carpal tunnel syndrome (CTS) confirmed by electromyography were assessed. These patients were evaluated preoperatively and postoperatively after ultrasound-guided percutaneous CTR at 1,3,6 months.

Clinical and ultrasound evaluation were performed.

Sonographic measurements consisted in median nerve cross sectional areas (CSA) over and at the carpal tunnel (CT), interapophyseal distance between the hook of the hamate and the trapezium tubercle to assess the opening of the CT and distance between the TCL and the CT bottom to assess bowstringing effect.

Clinical assessment consisted in: pillar pain (PP), grip strength, key pinch, and other variables.

A three-dimensional surface scan was obtained: we measured the antero-posterior thickness of the hand and CSA at CT level in transversal plane, to quantify the swelling of the palm heel at the four perioperative time.

Ultrasound measurements showed a significant difference between preoperative and postoperative states for most of the collected datas. However, no significant difference was found for the trapezio-hamatal inter-apophyseal distance.

Almost all clinical quantitative variables showed significant changes between each perioperative time. The comparison of variables at one month postoperatively showed a significant correlation between grip and key pinch strength.

There was a highly significant correlation between PP and thickness of the hand at CT level at each perioperative time.

The lack of significant change in inter-apophyseal distance before and after surgery suggests an absence of opening of the carpal arch postoperatively in this sample.

Because the grip strength improved few weeks after the surgery with persistant increased distance between the CT bottom and the TCL, bowstringing does not appear to be the cause of strength loss observed after CTR.

A significant link between PP and the swelling at the palm heel was observed post-operatively, however this effect remains difficult to be distinguished from the effect of time alone.

We can conclude that there are some anatomical changes after percutaneous sonographically guided CTR.

Postoperative outcome is favorable: we observe the regain of force at 3 months and a diminution of the swelling of the hand at 6 months.