Ligaments are passive brakes which authorize movements inside and between the rows and maintain the spacial coherence of the carpus [61]. They allow intra-row movements, which are adaptative for congruence movements, and inter-row movements which are efficient movements to mobilize the hand [17]. The limit of range depends on their length. For didactic reasons, intrinsic and deep extrinsic ligaments (Fig. 7) and extrinsic superficial ligaments will be separately represented (Fig. 8).

The scapholunate ligament links both bones (Fig. 7-1). The fibres which constitute the ligament are not symmetrically distributed. The dorsal part of the ligament is the most fibrous and thickest and also the most resistant [62]. It is considered as the main stabilizer of the scapholunar couple. It is always injured in scapholunar instability [63–65]. This ligamentous injury involves an increase flexion of the scaphoid from 3° to 6° [47–50, 62, 66], an extension of the lunate of 5° [50] and a dorsal translation of the scaphoid’s proximal pole more than 2 mm [62]. Tang also noticed a possible displacement of the rotation centre of the wrist [67].

The radioscapholunate ligament (Fig. 7-2) is thin; it is a neurovascular pedicle [62, 68] and not a real ligament.

The lunotriquetral ligament (Fig. 7-3). Its fibres are asymmetric too. On the palmar part, these fibres are thicker and resist to traction. They lock up the ­palmar translation of the lunate. Dorsal fibres are the most torsion resistant. They lock up both the lunate’s dorsal translation and the torsion by differential flexion-extension between the two bones [41]. When the ligament is injured, it engenders a lunotriquetral instability with VISI and sometimes a gap with supination of the triquetrum [42].

The palmar scaphotriquetral ligament (Fig. 8-4) avoids palmar scaphotriquetral dissociation and indirectly scapholunate dissociation. It probably maintains the head of the capitate when the wrist extends [66].

The radioscaphocapitate ligament (Fig. 8-5) is a powerful palmar ligament ensuring carpal cohesion. It is tensed against the scaphoid tubercle which lifts it in radial inclination of the wrist (Fig. 9). It avoids the dorsal translation of the proximal scaphoid pole and is a secondary stabilizer of the scapholunate couple [63]. If it is injured, it can be responsible for the scaphoid’s instabilities with DISI and scapholunar gap [64].

The scaphotrapezial ligament (Fig. 7-6) is V pattern ligament attached to the radial side of the scaphoid, the proximal point and at distal joint on the palmar and radial sides of the trapezium [68]. It is another secondary stabilizer of the scapholunar couple together with the radioscaphocapitate ligament. For Moritomo et al., it is also one of the points where the scaphoid’s flexion-extension axis passes through [69] (Fig. 10). The injury of this ligament after that of the scapholunar ligament worsens the instability of the scapholunar space.

The scaphocapitate ligament (Fig. 7-7) is the second element which stabilizes the scaphoid with the distal carpal row [68]. It also plays a part in the materialization of the scaphoid’s flexion-extension axis (Fig. 10).

The triquetocapitate ligament (Fig. 7-8) is tensed from the radial angle distal from the triquetrum to the ulnar part of the capitate’s body [68]. It takes ­attachment from the hamate bone, and its fibres go to the ulnotriquetral ligament to describe the ulnocapitate ligament. It is the ulnopalmar stabilizer of the mediocarpal space.

The long radiolunotriquetral ligament (Fig. 8-18) is the palmar part of Kuhlmann’s triquetral sling [8, 61]. It prevents the ulnar translation of the carpal bones. When this ligament is injured, the perilunar region becomes deeply unstable and thus promotes the perilunar dislocation of the carpal bones [7].

The dorsal radiocarpal ligament (Fig. 8-15) is radiolunotriquetral. It is the dorsal part of Kuhlmann’s triquetral sling [8, 11, 61]. It is a secondary stabilizer of the carpal bones. When it is injured, it is as destabilizing for the carpus as when the radioscaphocapitate and scaphotrapezial palmar bundles are injured [65]. The dorsal radiocarpal ligament is injured in more than 50 % of the carpal instabilities, often in association with the interosseous scapholunar ligament, but it may be the only ligament to be injured [70].

The dorsal intercarpal ligament (Fig. 8-16) links the triquetrum and the distal scaphoid and continues on the trapezium and the trapezoid in half of the cases. It is the last secondary stabilizer of the carpal bones [65]. For Viegas, this ligament constitutes, together with the dorsal radiocarpal ligament, a dorsal V-shaped radioscaphoidal ligament with a transversal orientation [47]. The resulting length varies, but the ligament is always tensed. A direct radioscaphoid ligament would be either lax, to allow the flexion of the wrist, and inefficient or tensed in a neutral position, preventing flexion and giving stiffness. This transversal V-shaped ligament remains tensed whatever the position of flexion or extension of the wrist thanks to the movement of the branches of the V which modify the angle (Fig. 11) and whatever the radioulnar inclination of the wrist as it goes together with the linked movements of flexion/extension of the scaphoid.

The transverse anterior annular ligament of the carpal bones (Fig. 8-17) completes the system. If it were sectioned, there would be an extension of the scaphoid of 58 % during the carpal ulnar drift and probably an increase of the restraints on the other ligaments [48].

To sum up, the scapholunar instability is often the result of an interosseous injury. The problem increases if other ligaments, mainly the palmar secondary stabilizers (radioscaphocapitate ligament or scaphotrapezial ligament) or the dorsal secondary stabilizers (dorsal radiocarpal or dorsal intercarpal), are affected [63–65, 71].

If the ligamentous injury starts at the distal pole of the scaphoid and affects the STT ligamentous system, there is also a destabilizing of the scaphoid, what can lead to STT arthritis if no surgical repair is made [72]. This situation of distal scaphoidal ligamentous injury can be compared to the partial osseous resections which are used in scaphotrapezial arthritis [73]. The distal scaphoidal resection separates the scaphoid from the trapezium and the trapezoid. It engenders a DISI in half of the cases [74], but the isolated trapeziectomy does not destabilize the wrist. The injury of the scaphotrapezial ligament only seems to have no impact on the scaphoid’s stability. It must be linked with a scaphotrapezoidal ligamentous injury or maybe a scaphocapitate ligamentous injury to produce a scaphoidal destabilization by its distal pole.

The lunotriquetral instability is linked to an injury of the lunotriquetral ligament, the palmar radiolunotriquetral ligament and the dorsal radiocarpal ligament [7, 42]. It is often associated to an ulnocarpal hyper pressure or to an injury of the TFCC. There may be a responsibility of the injured triquetrocapitate and palmar scaphotriquetral ligaments, but this has not been studied yet.

A ligamentous injury is not necessarily unstable at once. If one of the restraints of the different compartments is affected, there is often merely an occult ligamentous laxity, which can only be seen by arthroscopy. However, the repetition of ­movements in a wrist where there is such a laxity can engender a real instability by the fatigability of previously sane restraints. Berger asserted that carpal destabilization is linked to the number of cycles of movements imposed to the wrist. This assertion is checked for the scapholunar compartment [63–65] and for the lunotriquetral compartment [42].

The peripheral tendons come stabilizing the wrist with the carpal ligaments. The carpal motors muscles and tendons are the flexor carpi radialis and the flexor carpi ulnaris, the extensor carpi radialis brevis and longus and the extensor carpi ulnaris. Their direction is mostly axial (Fig. 12). This layout makes them play a role in the cohesion of the carpal bones. Intracarpal pressures are mainly due to the traction impressed on the hand by the motor tendons. The traction strengths stiffen the tendons which become like the bars of a cage around the carpal bones [51].

Schematically, there are four muscular groups, often contracting two by two, surrounding the wrist [75]. The action of the palmaris longus is insignificant. The radial and ulnar flexors and extensors act two by two and simultaneously, in the elementary movements of the carpus. For instance, the neutral extension of the wrist is the result of the simultaneous contraction of the radial and ulnar carpal extensors (Table 1). The dart thrower’s motion (DTM) is produced by the alternative contraction of flexor carpi ulnaris and the extensor carpi radialis longus and brevis [76].