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The so-called intrinsic ligamentous structures, scapholunate and pyramido-lunate are implied in the instabilities which are said to be dissociative. Just like ‘noninvasive’ imagery (MRI and arthroscanner), arthroscopy is a means to study these ligamentous structures. It has even been reported that the arthroscanner has an excellent ‘sensitiveness’ to detect breaches in the interosseous ligaments [1]. Nevertheless, arthroscopy’s superiority is to be found in the dynamic aspect of this exam, which not only enables to study the mechanical qualities of these ligaments but also to analyse the consequences of a ligamentous lesion resorting to dynamic tests. Only one diagnostic stage is enough to prove a ligamentous injury and, even more ­important, to demonstrate the consequences of this injury on the dynamics of the carpal bones, asserting or invalidating the existence of an instability or a dissociation. To end up, the same exam enables to accurately analyse the chondral impact of the instability and thus contributes to evaluate how long it has been lasting. The quality of the ligamentous stumps can also be studied to judge whether a fixing by direct suture is possible or not. For all these reasons, arthroscopy remains the gold standard to diagnose dissociative instabilities.

1 Anatomic Reminder: Intrinsic Ligaments

1.1 The Scapholunate Ligament

The scapholunate ligament [2, 3] is a ligament covered up with synovial tissue and tensed between the scaphoid and the lunate. It is divided into three sections: the posterior, the proximal and the anterior section. The posterior section, which is made of transverse conjunctive fibres, is the strongest. This section links the radial side of the posterior horn of the lunate to the dorso-ulnar part of the proximal pole of the scaphoid. Some fibres, which come from the extrinsic intercarpal ligament and from the radiocarpal articular capsule, are getting into it. The proximal section is avascularized and has little conjunctive tissue. A fibrocartilage is unequally dispatched on its length. The absence of fibrocartilage makes this part of the ligament thin, and degenerative perforations are possible. The anterior section is stronger as it has more conjunctive tissue. It is as strong as the posterior section.

1.2 The Triquetrolunate Ligament

The triquetrolunate ligament links the lunate to the triquetrum. The constitution of the ligament is more or less the same as that of the scapholunate ligament: it is divided into three parts and one-third of it has a real subordinate mechanical role.

2 The Role of the Intrinsic Ligamentous Structures in the Etiopathogeny of Dissociative Instabilities

2.1 Scapholunate Dissociative Instability

Most authors agree on the fact that the apparition of a dissociative instability needs the combination of an intrinsic and an extrinsic ligamentous injury. However, opinions still diverge on the nature of the extrinsic injuries which must be combined to the rupture of the interosseous ligament. For some authors, it is the ligamentous complex of the STT joint which plays the main role. Indeed, it maintains the distal pole of the scaphoid in place [4, 5]. Other authors underlined the role of the volar or dorsal extrinsic ligamentous structures [6]. Short and Werner [7], after an experimental study consisting in sequential ligamentous sections followed by cyclic and repetitive motions of the wrist, assert that the scapholunate interosseous ligament is the ‘primary’ stabilising structure of the scapholunate couple while the extrinsic structures (radioscaphocapitate ligaments and STT ligamentous complex) are the ‘secondary’ stabilisers. The same authors also mentioned that the dorsal ligamentous plane plays a part in the stabilisation of the scapholunate couple and thus assert the alteration of the scapholunate kinematic in case of capsulotomy which gets over this dorsal extrinsic ligamentous plan [8]. If nowadays it is difficult to accurately define which extrinsic ligaments are responsible for the apparition of an instability, it is partly because it is difficult to reproduce the effects of a traumatic rupture in an experiment. On the contrary, retrospective clinical studies are faced with the methodological difficulty which consists in separating the ligamentous injuries at the origin of the instability from those which are associated to it by chance [9].

2.2 Pyramido-Lunate Dissociative Instability

Once again, the triquetrolunate interosseous ligament embodies the ‘main ligamentous bolt’ as it maintains the spatial cohesion between the semilunate and the triquetrum. The anterior third of this ligament plays the most important part [10].

3 Practice of a Diagnostic Arthroscopy in Search of a Scapholunate Dissociative Instability (Study of Intrinsic Ligaments)

3.1 Portals for the Diagnostic Exploration of Dissociative Instabilities

The usual portals which are used to make a diagnostic arthroscopy of the wrist are enough to estimate the intrinsic ligaments and to make dynamic tests. The SLIOL is correctly analysed by the combination of the 3/4, 4/5 and 6u portals. The arthroscope is first placed in the 3/4 portal and the hook palpator in the 4/5 portal. The 6u portal is used to let the washing fluid go out. To explore the triquetrolunate joint space, you will just have to exchange the instruments and to place the arthroscope in the 4/5 portal. The resort to a volar portal has been evoked to allow a more complete exploration of the SLIOL. Abe et al. [11, 12] insists on the interest of such a volar portal to explore the anterior third of the SLIOL.

3.2 Study and Palpation of the Intrinsic Ligamentous Structures

3.2.1 Intrinsic Ligaments

The scapholunate and pyramido-lunate interosseous ligaments must be explored. For each of these ligaments, only the anterior two-thirds will be reachable to study and palpation, considering the posterior point of penetration of the arthroscope.

3.2.2 The Scapholunate Interosseous Ligament

It is looked for in the ‘roof’ during the exam of the carpal condyle and the arthroscope is introduced by the 3/4 portal. When it is healthy, it can be difficult to find since it is covered up with a layer of articular cartilage which is the continuity of the scaphoid and the semilunate. Palpation is the best means to locate it as it is in a zone where tonus is diminished at the level of the anteroposterior crest of separation from the scaphoidal and lunar fossas and the deep radioscapholunate ligament (ligament of Testut) (Fig. 1). The whole ligament has to be analysed in search for injuries of the mid-third or the anterior third. Traumatic injuries lie in the insertion zone on the scaphoid, right inside the ligament or, more rarely, where the lunate inserts itself. Apart from typical ligamentous breaches and tears (Fig. 2), it is also necessary to recognise a healed ligament, which takes the shape of a zone of fibrous continuity, where it is not possible to introduce the hook but where the tonus and the normal consistency of the interosseous ligament are not restored.

Fig. 1
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Localisation of the scapholunate interosseous ligament thanks to palpation. The ligament is found during the exam of the radiocarpal interval: tonus in the interval between the scaphoid and semilunate is diminished. S scaphoid, L lunate

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Fig. 2
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Breach of the scapholunate interosseous ligament: the hook is introduced in the breach inside the ligament. S scaphoid, L lunate

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3.2.3 The Pyramido-Lunate Interosseous Ligament

It is more difficult to locate than the previous one as there is no topographic reference. To locate it, the arthroscope has to be reintroduced by the 4/5 portal, and once again, palpation with the hook is often necessary.

3.3 Practice of Arthroscopic Dynamic Tests [13]

3.3.1 Dissociative Scapholunate Instabilities

Before any dynamic test, it is necessary to reduce the tension on the finger traps so as not to distort the interpretation by the artificial tension impressed on the extrinsic ligamentous structures induced by distraction. At the beginning of our experiment, we systematically used dynamic tests in the radiocarpal joint. The examining hook was introduced in a ligamentous breach and moved axially to try and separate the scaphoid from the semilunate, or the lunate from the triquetrum. In the same way, we made an ‘arthroscopic test of Watson’ as we dorsally pushed on the tubercle of the scaphoid to try and put forward a rotatory subluxation of the proximal pole of the scaphoid. Retrospectively, it becomes obvious that the analysis of these tests’ results is difficult, especially when the interval contains post-traumatic ligament remnants. Thus, these tests have now been abandoned and replaced by the midcarpal dynamic tests which interpretation is far easier.

In the midcarpal space, it is also possible to use the hook to estimate the stability of the scapholunate or the pyramido-lunate couples. To make these tests, the arthroscope is introduced by one of the midcarpal portals (RMC or UMC), and it visualises the junction of the scapholunate or pyramido-lunate distal facets. Normally, it is impossible to slip the hook in the interosseous scapholunate and pyramido-lunate intervals. When there is no instability, the hook can definitely not penetrate into the interosseous interval. If there is an instability, the hook can be pushed into the interosseous interval, towards the midcarpal. The axial movements that are impressed on it manage to move both osseous pieces apart (Figs. 3 and 4). The interosseous interval opens and makes the remnants of the interosseous ligament visible at the floor.

Figs. 3 and 4
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Practice of dissociative dynamic tests in the scapholunate interval: the hook is introduced by the UMC portal and pushed towards the scapholunate interval. Axial movements are created to try and create a diastasis in the scapholunate interval. In the case of dissociative instability, the opening of the interval becomes clearly visible (see text)

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At a further stage of instability, these dynamic manoeuvres with the hook even allow an opening which is wide enough to let the arthroscope go from the radiocarpal to the midcarpal space, through the ligamentous breach (Figs. 5, 6 and 7). However, this is only possible when the instability is further in the spectrum of injuries and can usually be established by a radiographic diagnosis.

Figs. 5, 6 and 7
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Midcarpal view of the scapholunate base during dissociative tests: (Fig. 5) The scapholunate interval is perfectly congruent and ‘continent’. If there is a breach in the SLIOL, there is no instability. (Fig. 6) Moderate opening of the interval under the twisting motion applied to the hook. (Fig. 7) The interval is clearly opened and leaves the remnants of the SLIOL visible at the floor. The arthroscope easily goes from the midcarpal to the radiocarpal joint, through the ligamentous breach (see text). S scaphoid, L lunate, T triquetrum, H hamate, RSCL radioscaphocapitate ligament

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3.4 Meaning of the Dynamic Arthroscopic Tests in the Dissociative Scapholunate Instabilities

These manoeuvres and dynamic tests thus enable to put forward a deficiency in the ligamentous devices. The surgeon indirectly analyses the effects of intrinsic and/or extrinsic possible ligamentous injuries on the carpal stability. Throughout our experiment, thanks to these dynamic arthroscopic tests, it has been made possible to point out an early instability before it creates abnormalities in the dynamic or a fortiori static radiographic results [14, 15]. It is easy to understand the higher ‘sensitiveness’ of arthroscopy as far as dissociative instabilities are concerned since this exam enables to make a test of direct dissociation and impress constraints on the bones (under the effect of the twisting motion applied to the hook). On the contrary, in a dynamic radiographic study, the component of dissociation is indirectly induced under the effect of axial compression which is itself induced by fist clenching. Scapholunate dissociative instability is probably an entity with various declinations following a vast spectrum of injuries. The distinction between a static and a dynamic instability only is not sufficient to make the vastness of this spectrum clear. If the conditions in which radiographic images are made are perfectly standardised, correlations can be established between the severity of ligamentous injuries seen in arthroscopy and their radiographic interpretation [16].

3.5 Dynamic Arthroscopic Tests in Pyramido-Lunate Dissociative Instabilities

The practice of these tests has been deduced from what was observed in the scapholunate interval. In that case, the absence of ligamentous injury does not let the hook penetrate into the triquetrolunate interosseous interval. Instability is established after an abnormal opening of the interosseous interval impressed by the twisting motion applied to the hook (Fig. 8).

Fig. 8
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Dynamic testing in the interval between lunate and triquetrum (midcarpal joint). L lunate, T triquetrum, H hamate, C capitate

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3.6 Other Ligamentous Structures

During a diagnostic arthroscopy, our clinical practice systematically consists in the inspection and the palpation of the extrinsic ligamentous structures. Through the classic dorsal portals, it is possible to inspect and palpate the short intra-articular section of the extrinsic anterior ligamentous plane, while the dorsal plane escapes from a ‘normal’ arthroscopy (that is to say, by a dorsal portal). Despite this systematic testing, the information we have is not sufficient to confirm or to contradict one or other etiopathogenic theories relating to the participation of these structures in the birth of dissociative instabilities.

3.7 Study of the Chondral Effect of the Instability

The initial diagnostic arthroscopy is also the best moment to establish an assessment of the chondral effect of a dissociative instability. If this method is not really interesting on the triquetrolunate side as the TL dissociative instability is not said to be very arthrogen, it is paramount on the scapholunate side. The inspection and the accurate palpation of the stylo interval or radioscaphoidal joint enable to detect an early chondrite or arthrosis which testifies to the oldness of the instability. As a matter of fact, deep radioscaphoidal chondral injuries have sometimes been diagnosed while the patient just mentioned a unique and recent trauma. The search for the chondral effect is useful to detect ruptures with multiple stages which are classic phenomena of scapholunate instabilities.

4 Arthroscopy to Analyse the Severity and the Oldness of a Scapholunate Instability

Considering the performances of arthroscopy as far as diagnostic evaluation is concerned, it became obvious to use it to establish a score of severity, especially in the case of scapholunate instability which is now known to be a vast spectrum of ­injuries and not a binary entity. The arthroscopic classification of instabilities that we use is reproduced below [15, 17]. The other existing classification was made by Geissler [18, 19].

5 Arthroscopy to Treat Early Stages of Scapholunate Instability

A mere arthroscopic debridement has often been mentioned as a means to treat the isolated injuries of the scapholunate or pyramido-lunate interosseous ligaments [20, 21]. However, it is still difficult to make a distinction between what can be granted to the debridement itself and what is the consequence of the effects of immobilisation which is associated to it or the mid-term spontaneous evolution towards indolence, which is often observed in the context of scapholunate dissociation, a fortiori when a scapholunate and/or scaphocapitate broaching has also been made. Most of the studies published refer to the development of a mere functional score (Mayo wrist score or else) to judge of the efficiency of arthroscopy on the long term.

Arthroscopic severity score for scapholunate instability (Dautel)

Stage 0: Absence of instability, normal wrist as far as the scapholunate kinetics is concerned. This stage is a means to list the SLIOL breaches without instability

Stage 1: The tip of the hook can be introduced in the scapholunate interval. Normal radiography

Stage 2: Moderate opening of the scapholunate interval with the use of the twisting motion applied to the hook

Stage 3: Clear opening of the scapholunate interval, possibility to introduce the arthroscope from the radiocarpal to the midcarpal space

This type of scoring can judge the global function and the comfort but remains unable to analyse the consequences of arthroscopy on wrist stability. The same can be said of the ligamentous electro-thermocoagulation techniques which are still used but for which there is no proof of real efficiency.