Intraoperative transverse carpal muscle during endoscopic carpal tunnel release: a case report.

We encountered the aberrant muscle called transverse carpal muscle (TCM) anterior to the transverse carpal ligament (TCL) during endoscopic carpal tunnel release (ECTR) for a 56-year-old female with left carpal tunnel syndrome (CTS). Our ECTR technique started with making the distal portal and the anomalous muscle emerged in the portal. We changed ECTR to open carpal tunnel release to clarify the anatomy around TCL to avoid iatrogenic tendon and neurovascular injuries. The TCM does not necessarily exist bilaterally, and our case has also it unilaterally, because the TCM was not observed during the ECTR on the opposite side. Distal incision first ECTR technique enabled us to find the TCM which we could not encounter if conventional ECTR was performed.