Incidental Guyon's canal release during attempted endoscopic carpal tunnel release: an anatomical study and report of two cases.

Two patients were found to have a partial release of Guyon's canal after attempted endoscopic carpal tunnel release. This resulted in significant morbidity from ulnar nerve injury and required open neurolysis of the ulnar nerve and carpal tunnel release. In order to determine how this error could be made, we performed an endoscopic carpal tunnel release on two cadaveric specimens with subsequent dissection, and found that Guyon's canal could be entered with relative ease through the standard portals. If, however, one is aware of this potential complication, uses the ulnar bursa overlying the flexor tendons as a guide, and makes a positive identification of the transverse fibers of the transverse carpal ligament, this mistake can be avoided.