Anatomy and Lesions of the Extrinsic Ligaments

Fig. 1

The plane of extrinsic wrist ligaments, (a) palmar and (b) dorsal views. 4 Scaphotriquetral ligament, 5 Radioscaphocapitate ligament, 15 dorsal radiocarpal ligament, 16 dorsal intercarpal ligament, 17 annular anterior carpal ligament, 18 long radiolunate ligament

On arthroscopic examination of the radiocarpal joint, the RSC is most radial (Fig. 2). Its fibres are obliquely oriented from radial to ulnar, and it is separated from its neighbouring radiolunotriquetral by a hiatus – the interligamentary sulcus which allows testing of both ligaments using the hook palpation (Fig. 3).

Fig. 2

Arthroscopic view of the radiocarpal interval left wrist. Right to left: RSC ligament, interligamentary sulcus and RLT ligament

Fig. 3

Arthroscopic view of the left radiocarpal interval. Probing RLT (which is lax stage 2). Probe is in the interligamentary sulcus. Hemorrhagic synovitis in the radial part of the RSC ligament

The radiolunotriquetral ligament (RLT) is also very strong and usually composed of two bands: the long radiolunate (LRL) radially and the short radiolunate (inconstant) (SRL) separated by the radioscapholunate (Fig. 1). It is almost parallel to the RSC and usually divided into two parts: a proximal purely radiolunate half and the distal palmar lunotriquetral. The SRL fibres cross with those of the ulnotriquetral.

It traces a proximal inverted ‘V’ with the anterior ulnocarpal where the apex of the V represents the triquetral and lunate insertions.

It forms the palmar part of the triquetral sling [21] and contributes to the stabilization of the lunate, preventing its dorsal flexion and palmar translation. It prevents the ulnar translation of the carpus, and its injury destabilizes the perilunate region. On arthroscopic assessment, the radiolunotriquetral ligament RLT is the ulnar neighbour of the RSC. It links the anterior border of the scaphoid fossa of the radius to the triquetrum, and its fibres are more oblique than those of the RSC (Fig. 2). On its way, it also inserts onto the anterior horn of the lunate.

The radioscapholunate ligament (RSL) or ligament of Testut is quite a lax fibrous structure (Fig. 4). According to Berger, ‘the RSL ligament is not a real ligament in the biomechanical or the histological sense of the term’. It can be considered as a mesocapsule. It contains terminal branches of the anterior interosseous nerve and rami from the radial arcade [19, 20].

Fig. 4

The plane of extrinsic and intrinsic wrist ligaments, (a) palmar and (b) dorsal views. 1 Scapholunate, 2 radioscapholunate, 3 lunotriquetral, 6 scaphotrapezial, 7 scaphocapitate, 8 triquetrohamatocapitate, 9 capitotrapezial, 10 capitotrapezoidal, 11 capitohamatal, 12 short radiolunate, 13 ulnolunate, 14 ulnotriquetral

It serves as an arthroscopic landmark for the scapholunate ligament which is sometimes difficult to identify without probing which depresses it (Fig. 4). It is characterized by its vertical fibres which extend along the scapholunate crest of the radius. It is the most superficial from the scope and can sometimes obscure the anterior part of the radiocarpal joint like a veil (Fig. 5).

It is more lax than the previous ligaments and feels always more so on probe palpation.

3.2 The Anterior Ulnocarpal Plane

This is formed by the RLT ligament, the proximal palmar ‘V’ ligament (Fig. 1), which is formed of the ulnolunate UL and lunotriquetral LT ligaments. It inserts on the proximal part of the anterior portion of the TFCC and the ulnar styloid. It contributes to the stabilization of the lunotriquetral complex and TFCC tension. The ulnolunate ligament may sometimes share fibres with the short RL ligament.

Fig. 5

Arthroscopic view of the right radiocarpal interval. Left to right: LRTL (long radiotriquetral) and hemorrhagic synovitis on the RSL ligament

Ulnarly, the anterior floor is composed of less distinctly individualized ligaments (Fig. 6). The difference in obliquity distinguishes between the UL and UT ligaments which appear to be intimately attached to the TFCC and represent an extension of this structure. They are also palpated by the probe.

Fig. 6

Arthroscopic view of the left ulnocarpal interval: 3 years after shortening osteotomy described by Milch, ‘scarring’ chondritis triquetrum. Ulnocarpal ligaments stretched with no clear separation between the UT and the UL

4 The Anterior Midcarpal Plane and the Scaphotrapeziotrapezoid Complex

The anterior midcarpal plane is formed of a combination of extrinsic and intrinsic ligaments. It includes the distal part of the RSC ligament; the intraarticular midcarpal part of the RSC forming the distal palmar ‘V’ is visible through the standard arthroscopic portals.

Thus, the RMC and UMC classic midcarpal portals give direct access to the intraarticular part of the RSC and TC ligaments.

The midcarpal part of the radioscaphocapitate ligament is easily identified (Fig. 7) by the same obliquity of fibres as its radiocarpal portion. It is easily accessible to the probe.

Fig. 7

Arthroscopic view of the right midcarpal interval: stage 1 laxity of the midcarpal portion of the RSC

The anterior midcarpal plane also includes the triquetrocapitate TC (Fig. 4) and the palmar scaphotriquetral STP (Fig. 1) ligaments.

The TC extends from the distal radial angle of the triquetrum to the ulnar cortex of the capitate [19]. It forms the distal and ulnar part of the palmar midcarpal ‘V’ and is the palmar ulnar stabilizer of the midcarpal joint. On arthroscopic examination, it is discernible from the RSC by the inverted obliquity of its fibres.

Described in 1994, the STP ligament prevents scaphotriquetral palmar dissociation and thus indirectly scapholunate dissociation. It probably supports the head of the capitate during wrist extension [20]. It is extraarticular and inaccessible to arthroscopic examination.

The anterior midcarpal plane also includes the scaphotrapeziotrapezoid complex. It is strictly palmar and is composed of three distinct exclusively intrinsic structures: the palmar scaphotrapezial ligament (STz) and radially a scaphocapitate ligament (SC) and a capitotrapezoid ligament (CTzo) distal to the scaphoid (Fig. 4). The STz ligament seems to act as a secondary stabilizer to the scapholunate complex along with the RSC and the dorsal intercarpal ligament (DIC) [11–13]. The two ligaments materialize the flexion-extension axis of the scaphoid (Fig. 8). This axis passes through the waist of the capitate [16, 17]. The SC ligament is also an important stabilizer of the scaphoid [19].

Fig. 8

Plate of extrinsic wrist ligaments: the scaphotrapezial STz and scaphocapitate SC tracethe axis of flexion-extension of the scaphoid

The SC ligament is accessible only when the distal scaphocapitate interval is open, i.e., in a pathological situation of instability (Fig. 9).

Fig. 9

Arthroscopic view of left midcarpal interval. Scope through RMC, probe through MC 1–3. Enlarged distal scaphocapitate interval allowing palpation of SC ligament

The CTz ligament is inaccessible to arthroscopic examination, and the STz is not accessible through the dorsal midcarpal ptortals. It is possible to introduce the probe through an MC 1–3 portal in the distal anatomical snuffbox taking care to avoid the dorsal recurrent branch of the radial artery. Recently, we use standard portals (scope through RMC and probe through MC). The probe crosses up the scope into the midcarpal joint and goes to palpate the STz ligament in the STT joint. The scope is slid through the MCR along the scaphoid to visualize the scaphotrapeziotrapezoid junction.

5 The Dorsal Plane

The dorsal plane is formed by two ligaments forming a sloping ‘V’ open radially with the point inserted on the triquetrum. Viegas describes it as a radioscaphoid ligament which relays on the triquetrum [4]. It is distinguished by the constant tension of its branches whatever the opening angle of the ‘V’ and whatever the movement of the wrist (in the sagittal or the frontal plane). Thus, in ulnar inclination, the ‘V’ opens and the dorsal ligament plane participates in the verticalization of the scaphoid, while the triquetrum passes under the hamate (Fig. 10) [26].