of Normal Anatomy and Injuries of Extrinsic Ligaments

Fig. 1

Palmar extrinsic ligaments : Radioscaphocapitate (RSC) and long radiolunate (RL) ligaments. Notice the (normal) interruption of the fibres on the lunate attachment with a separated palmar lunotriquetral (LT ) bundle, which corresponds to an anatomic variation (a, b). R radius, L lunate, S scaphoid. (a) On a cadaveric specimen (Courtesy of David Connell, London), (b) normal MR appearance on a thin slice (1 mm thick) obtained in 3D gradient echo sequence, (c) partial rupture of the RSC and RL ligaments, (d) drawing which shows the trajectory of these two ligaments together with the radioscapholunate ligament (RSL) and the inconstant short radiolunate ligament (SRL), (e) normal arthroscopic view, (f) arthroscopic view of the injured RSC and RL ligaments showing synovitis filling the interligamentous sulcus

The radioscaphocapitate ligament (RSC) extends from the styloid process of the radius; it cravats the scaphoid waist (what enables to maintain the position of the scaphoid as it acts like a seat belt) to insert on the palmar side of the capitate. It acts like a spindle around which revolves the scaphoid and is paramount in the scaphoid stability [13–16].

The radiolunotriquetral ligament (RLT) or long radiolunate ligament is paralleled to the radioscaphocapitate ligament, extends from the anterior margin and from the styloid process of the radius to the radial margin of the palmar surface of the lunate and obliquely connects on the palmar side of the triquetrum (where it is covered up by the ulnotriquetral ligament). The fibres of this ligament can interrupt at the lunate attachment and thus create two ligamentous structures, the long radiolunate and the palmar lunotriquetral. The RLT ligament is the longest of the wrist [17–20].

The radioscapholunate ligament (or ligament of Testut) originates between the long and short portions of the radiolunate ligament and has its fibres embedded in the interosseous scapholunate ligament. It is deeper than the RSC and RLT ligaments. It is rather considered as a synovial fold which retains a neurovascular bundle. It corresponds to the anterior brake of the lunate and is used as a reference in arthroscopy to point out the scapholunate ligament [21].

In case of injury, the signal of these ligaments can increase and the ligaments can lose their sharp outlines on the thin sections obtained in 3D sequence (Fig. 1). A fibrous thickening (with decreased signal intensity on T2) can also be described in chronic partial ruptures (Fig. 2). Moreover a cyst can sometimes appear and develop itself in the ligaments or anterior to it, and be associated to a chronic ligamentous rupture (Figs. 3 and 4) [22].

Fig. 2

Chronic fibrous thickening of the radioscaphocapitate ligament (a, b, arrows) of a gymnast who suffered from midcarpal pain. The presence of an associated rupture of the intrinsic scapholunate ligament results in a rotatory subluxation of the scaphoid (with a horizontal orientation of the latter), which is clearly pointed out on the thin sagittal slices (2 mm thick) in proton density (a) and T2 (b). The ligament seems to be thickened and presents a heterogeneous signal in proton density and weak in T2; it has irregular outlines. Compare with the contralateral wrist (c, d) where the ligament seems normal (arrow), as well as the scaphoid axis

Fig. 3

Synovitis with chronic cystic distension around the radioscapholunate ligament in a patient complaining of palmar radiocarpal pain. On anterior coronal section (of a 3D gradient echo sequence) (a, b), a cystic distension with a chronic multilobular aspect is put forward at the level of the radioscapholunate ligament (RSL). The radiolunotriquetral (RLT, a) and radioscaphocapitate ligaments (RSC, b) are continuous

Fig. 4

Thickening of the radioscapholunate ligament and surrounding synovitis associated with a rupture of the intrinsic scapholunate ligament. The patient is a 40-year-old gardener who developed a localised palmar distension after he had pruned trees; he had already fallen from a ladder 4 years before as his wrist was in dorsal hyperflexion. The coronal slices in proton density (a, b) and T2 (d, e) reveal the presence of a fluid distension with a cystic aspect at the level of the palmar fibres of the scapholunate and the radioscapholunate ligament with a widening of the scapholunate space. The rupture of the palmar bundle of the intrinsic ligament is confirmed on the transverse section (c) on which the ligament has an increased signal intensity, is thickened and has blurred contours in comparison with the normal ligament of the contralateral uninjured wrist (f); the dorsal bundle was also torn (not shown) (c circle, torn palmar bundle of scapholunate ligament; f circle, normal palmar bundle of scapholunate ligament). The radioscapholunate ligament appears thickened with a heterogeneous signal on the sagittal section (h) (arrow), whereas the contralateral sagittal section is normal (g). Arthroscopy (i) reveals the presence of an important synovitis associated with a rupture of the palmar fibres of the scapholunate ligament with partly detached strips. These strips can also be seen on the sagittal section (h) at the level of the anterior radiocarpal space, ahead of the tilted lunate (compare to the normal contralateral sagittal section) (g). R radius, L lunate, S scaphoid

These three palmar ligaments can be visualised by arthroscopy. It is however necessary to precise that the extrinsic ligamentous structures are only reachable during arthroscopic examination for their very short intra-articular part.

The general configuration of the palmar ligaments has a “V” structure which is weaker at one point, a triangular area in the capsule, so-called space of Poirier. This space is situated between the two palmar arcs with a V shape, above the lunocapitate joint where the lunate can dislocate [23].

The short radiolunate ligament, which is not described by all the researchers, is close to the palmar fibres of the triangular fibrocartilaginous complex. It is an anterior capsular thickening. Its origin is usually described on the palmar and ulnar rim of the distal part of the radius and the ligament inserts at the proximal part of the palmar surface of the lunate. This ligament stabilises the lunate [23] (Fig. 1).

The distal palmar ligamentous group (with a reversed V shape) is composed of the intrinsic triquetrocapitate ligament on the medial side and of the extrinsic radioscaphocapitate ligament and of the intrinsic scaphocapitate ligament on the lateral side. This group stabilises the capitate and thus the distal row of the carpal bones. The intrinsic triquetrocapitate and scaphocapitate ligaments form the arc-shaped ligament of the wrist or volar arcuate ligament (terminology used by hand surgeons) which is an important palmar midcarpal stabiliser. Theumann et al. identified it as the palmar scaphotriquetral ligament [7, 24] (Fig. 5).

Fig. 5

Image showing the components of the arc-shaped (intrinsic midcarpal): triquetrocapitate (TC) and scaphocapitate (SC) ligaments

2 Palmar Ulnocarpal Ligaments

The proximal palmar ligamentous group (with a reversed V shape) is made of the extrinsic ulnotriquetral and ulnolunate ligaments, on the medial side and of the extrinsic radiolunotriquetral ligament on the lateral side. This group stabilises the lunate and thus the proximal row of the carpal bones.

The ulnocarpal ligaments originate on the anterior rim of the palmar radioulnar ligament or of the triangular fibrocartilage or the base of the styloid process of the ulna (according to the different authors). The ulnolunate ligament is situated next to the short radiolunate ligament following the same direction and then is inserted on the palmar side of the lunate. The ulnotriquetral ligament originates medial to the former and inserts on the triquetrum [25] (Fig. 6).