During surgical exposure of the carpal tunnel it is possible to injure the neurovascular structures closely related to the flexor retinaculum, such as the superficial palmar arch and the communicating branch between the ulnar and median nerves. Because of the importance of these structures and with the purpose of increasing knowledge of anatomical details concerning to their location, a biometric study was performed on the retinaculum and the communicating branch, and between the communicating branch and the distal wrist crease, as well as between the retinaculum and the superficial palmar arch. We dissected 56 hands from 28 Brazilian formalin-preserved cadavers of both sexes (24 male) at the Federal University of São Paulo–Escola Paulista de Medicina, Brazil. The communicating branch was observed in 96.4% of cases and the superficial palmar arch in 78.6%. The communicating branch was found between the common palmar digital nerve of the 4th interosseous space (from the ulnar nerve) to the homonymous nerve of the 3rd interosseous space (from the median nerve). In males, the distance between the distal wrist crease and the site where the communicating branch originates from the ulnar component had an average of 33.9±5.5 mm on the right side and 30.2±8.2 mm on the left. The distance between the distal wrist crease and the junction of the communicating branch with the common palmar digital nerve of the 3rd interosseous space was 43.6±6.9 mm on the right and 40.2±6.2 mm on the left side. Conversely, in 14.8% of cases (1 female), the communicating branch was observed to emerge from the common palmar digital nerve of the 3rd interosseous space. The distance between the retinaculum and the superficial palmar arch in the axial line of the 4th metacarpal bone was on average 7.3±4.3 mm on the right and 8.3±3.5 mm on the left side. At the same level, the distance between the retinaculum and the communicating branch was 6.2±3.7 mm on the right side and 5.1±2.8 mm on the left. These results can be used as a reference during surgical procedures in the palmar region.
