Laminar configuration of the transverse carpal ligament.

We investigated the laminar configuration of the transverse carpal ligament, using 77 hands from 44 donated cadavers. According to the running directions and attachments of the fiber bundles composing the ligament, we identified four basic bundle patterns: proximal transverse, distal transverse, radial oblique, and ulnar oblique. Although these patterns often coexisted and the bundles were somewhat intermingled, a specific pattern was very evident in several laminae. Laminae with the distal transverse bundle pattern were the thickest and were reinforced by additional fibers which originated from the palmar aponeurosis and were deeply inserted into the lamina. Based on the laminar configurations of the superficial and deep layers and their composite fiber bundles, we classified the ligaments into four types. Type I, in which distal transverse and ulnar oblique laminae predominated in every layer, was the most common (44.2%), while another large group (41.6%) exhibited type II ligaments, comprising distal transverse and ulnar oblique laminae in the superficial layer and proximal transverse and radial oblique laminae in the deep layer. Thus, in almost half of the patients (type II), the strong distal transverse lamina is likely to be excised during the final step of endoscopic carpal tunnel release because of its superficial localization. This could be a major reason for the frequent occurrence of incomplete release. Moreover, the almost universal superficial ulnar oblique bundle pattern (observed in type I, II, and III ligaments), predisposes to scarring, which may cause radial shifting of the ulnar neurovascular bundle and may affect the palmar branch of the median nerve. We conclude that the interindividual variability seen in the results of endoscopic carpal tunnel release, including minor complications, depends partly on configurational variations in the laminar arrangement of the transverse carpal ligament.