The transverse carpal ligament is thought to have an important role in the pulley system for the digital flexor tendons at the wrist [16]. This ligament prevents bowstringing of the digital flexor tendons and allows maximum finger flexion while the wrist is flexed. A fresh-frozen cadaver study demonstrated approximately 5 mm of palmar displacement of the flexor digitorum tendons after TCL release [17]. Other MRI studies have demonstrated significant volar displacement of the median nerve (3.3 mm) and flexor digitorum tendons (2.4 mm) in both neutral and flexed wrist positions after open TCL release [18]. Palmar displacement of the flexor digitorum tendons has been shown to increase the distance between the tendons and the center of rotation of the wrist, thus increasing the amount of flexor tendon excursion necessary to achieve fingertip-palm contact during wrist flexion. This increase in excursion was less in the ECTR group than in the open TCL release group and was noted after 20–30 degrees of wrist flexion as tendon bowstringing occurred [19]. Although power grasping is usually performed with the wrist in extension, many of the activities of daily living require wrist flexion [20]; thus, palmar displacement of the flexor digitorum tendons after TCL release could affect some postoperative activities.

The incidence of trigger finger within a year of open TCL release has been reported to range from 5.9 to 22% [21, 22]. One cause of this phenomenon is thought to be increased friction at the A1 pulley due to the increased entrance angle of the flexor tendons [22]. In a cadaver study, TCL release changes the entrance angle of the flexor tendons to the A1 pulley in all five fingers, especially the middle finger (Fig. 25.2) [23]. In the case of the flexor pollicis longus tendon , the mean entrance angle to the A1 pulley was 10°. The release of only the TCL caused the entrance angle to increase to a mean of 20°. Additional release of the distal forearm fascia caused a further increase in the entrance angle to a mean of 28°. In the other fingers, TCL release increased the mean entrance angles to the A1 pulley by 12, 27, 12, and 3° in the index, middle, ring, and little fingers, respectively. Additional release of the distal forearm fascia further increased these angles by 4, 4, 9, and 2°, respectively.

Approximately two-thirds of the thenar muscles, and almost half of the hypothenar muscles , originate on the volar surface of the TCL [24]. Release of the TCL causes palmar displacement of some of the sites of origin of the thenar and hypothenar muscles and thus shortens their length [25]. The muscle shortens by as much as 25% in the superficial head of flexor pollicis brevis, 20% in the ulnar part of abductor pollicis brevis, 20% in opponens pollicis, and 10% in opponens digiti minimi [26]. After TCL release, the forces associated with gripping and pinching will be transmitted preferentially to the thenar and hypothenar muscles that originate from the carpal bones rather than the TCL; this could lead to increased stress on the origins of these muscles and may cause pain [24]. Release of the TCL may also change pisotriquetral joint alignment and tracking of the pisiform, which induces pain at the base of the hypothenar area [27].