Ultra-minimally invasive sonographically guided carpal tunnel release: anatomic study of a new technique.

Objectives: The purposes of this study were to measure a safe zone and a path for ultra-minimally invasive sonographically guided carpal tunnel release with a 1-mm incision in healthy volunteers and then test the procedure in cadavers.

Methods: First, a previously reported sonographic zone was defined as the space between the median nerve and the closest ulnar vascular structure. Axially, the safest theoretical cutting point for carpal tunnel release was set by bisecting this zone. Magnetic resonance imaging was used for axially determining the limits of the sectors (origin at the cutting point) that did not enclose structures at risk (arteries and nerves) and coronally for determining whether our release path could require directions that could potentially compromise safety (origin at the pisiform's proximal pole). Second, in cadavers, we performed ultra-minimally invasive sonographically guided carpal tunnel release from an intracarpal position through a 1-mm antebrachial approach. Efficacy (deepest fibrous layer release rate), safety (absence of neurovascular or tendon injury), and damage to any anatomy superficial to transverse carpal ligament were assessed by dissection.

Results: All 11 of our volunteers (22 wrists) had safe axial sectors located volar and radially of at least 80.4º (considered safe). Release path directions were theoretically safe (almost parallel to the longitudinal axis of the forearm). In 10 cadaver wrists, ultra-minimally invasive sonographically guided carpal tunnel release was effective (100% release rate) and safe without signs of intrusion into the superficial anatomy.

Conclusions: Ultra-minimally invasive sonographically guided carpal tunnel release in a safe sonographic zone may be feasible The technique preserves the superficial anatomy and diminishes the damage of a surgical approach.