Treatment Alternatives for the Different Stages of Scapholunate (SL) Instability
Stage 1 (Partial SL Ligament Injury)
Proprioception reeducation of the flexor carpi radialis (FCR) muscle
Percutaneous K-wire fixation
Arthroscopic debridement of the unstable portions of the torn ligament
Electrothermal SL ligament shrinkage
Stage 2 (Complete SL Ligament Injury, Repairable)
Direct repair of the dorsal SL ligament plus percutaneous K-wire fixation
Reattachment of avulsed ligaments with anchor sutures
Stage 3 (Complete SL Ligament Injury, Nonrepairable, Normally Aligned Scaphoid)
Reconstruction of the dorsal SL ligament with portions of adjacent ligaments
Stage 4 (Complete SL Ligament Injury, Nonrepairable, Reducible Rotary Subluxation of the Scaphoid)
Tendon reconstruction of the scaphoid stabilizers (Brunelli’s technique, three-ligament tenodesis)
Reduction association of the SL joint (RASL procedure)
Stage 5 (Complete SL Ligament Injury with Irreducible Malalignment but Normal Cartilage)
Radius–SL fusion plus distal scaphoidectomy
Stage 6 (Complete SL Ligament Injury with Irreducible Malalignment and Cartilage Degeneration)
Scaphoidectomy plus midcarpal (MC) (“four corner”) fusion
Total wrist fusion
From a biomechanical point of view, a joint is stable when it is capable of bearing physiologic loads without yielding. For the wrist to be considered stable, not only must it be able to maintain normal carpal relationships under load in the neutral position, but also throughout its entire range of motion. When a stable wrist is loaded, the joint contact forces induce certain rotations of the carpal bones in specific directions, but the overall joint congruency is always preserved. , When the load is released, the original carpal alignment is reestablished. Furthermore, when a stable wrist moves, the resultant carpal motion is smooth and predicable, without sudden changes in position or orientation. Indeed, a snapping or clunking while moving the wrist often indicates instability in kinematic terms. In short, the term instability is to be understood as the lack of stability; that is, the inability to carry physiologic load without yielding (kinetic stability) and/or the incapability of moving smoothly, without sudden, abrupt carpal bone displacements (kinematic stability). , When defining stability , however, it is important to note that a mechanically unstable wrist is not always a clinical problem; not unusually, hyperlax individuals may exhibit clunking and malalignment in their wrists and yet be completely asymptomatic. Indeed, for a wrist to be considered clinically unstable, it must have a mechanical instability (kinetic and/or kinematic) inducing symptoms (e.g., pain, lack of strength, a giving way sensation).
Based on this definition, carpal instability is a term synonymous with symptomatic dysfunction of the wrist, and this obviously may result from a large variety of conditions. Any modification of the shape of the wrist bones or of the linkages between them may alter the mechanical equilibrium of forces that is essential for the wrist to behave normally and generate instability. Of the many clinical conditions resulting in carpal instability, some are nontraumatic in nature (e.g., bone necrosis, infections, chronic inflammation, tumors), whereas others are the consequence of injury. Management of nontraumatic carpal instabilities, as well as those resulting from fractures of the radius or the carpal bones, are discussed elsewhere in this book. This chapter covers only ligament-related carpal instabilities.
As stated, many traumatic conditions involving rupture or stretching of wrist ligaments may result in an unstable carpus. Classifying such diversity of problems is difficult and probably unnecessary. , In fact, not a single classification can be thorough enough to allow categorizing all types of ligament-related carpal instabilities and yet simple enough to be easily remembered and used clinically. To overcome this, Larsen and co-workers developed a useful system to analyze each carpal instability case to rationalize its treatment. According to this scheme, any carpal instability can be described according to six independent parameters ( Table 74-1 ).
When ligament disruption has been diagnosed early (acute injury), the healing potential of the ligament is likely to be optimal. Between 1 and 6 weeks (subacute injury), the ligaments may not heal as well as a consequence of retraction and necrosis of their remnants. After 6 weeks (chronic cases), primary ligament healing, although possible, is very unlikely. The exception would be when the ligament is detached but not ruptured, in which case, good chances of healing exist beyond the time limit expressed for midsubstance ruptures, if properly reattached.
If carpal incongruity appears only under certain loading conditions, the case is less severe than if the malalignment is permanent. Based on this, five levels of instability exist: (1) predynamic instability when there is a partial ligament tear that is only symptomatic under stress but without malalignment; (2) dynamic instability when there are episodic instances of carpal subluxation only under certain loading conditions; (3) static reducible instability when there is permanent carpal malalignment owing to rupture of both primary and secondary carpal stabilizers, the subluxation being easily reducible; (4) static irreducible instability when joint deformity or intra-articular fibrosis does not allow reduction of the subluxation; and (5) static arthritic instability when a chronic subluxation has induced degenerative changes in the joint cartilage.
Although most ligament disruptions are caused by trauma, some diseases may also cause ligament insufficiency. Although traumatic ruptures tend to heal well if diagnosed and treated early, ruptures caused by rheumatoid arthritis very rarely heal, even if carefully repaired. Other etiologies include congenital defects, infections, and iatrogenically inflicted defects.
It is important always to explore under fluoroscopy all unstable wrists to identify where the major dysfunction is located. This may not always coincide with the location of the initial ligament injury. Whether there is a predominant monoarticular dysfunction or a more extended problem is also an important feature to highlight.
Several patterns of carpal malalignment exist. The most common are (1) dorsal intercalated segment instability when the lunate, understood as an intercalary segment between the distal row and the radius, appears abnormally extended ; (2) volar intercalated segment instability (VISI) when the lunate appears rotated into an abnormal flexion ; (3) ulnar translocation when the proximal row is (or can be passively) displaced toward the ulnar side beyond the normal limits ; (4) radial translocation when the proximal row is or can be translocated radially beyond normal ; (5) dorsal translocation when the proximal or distal rows are or can be passively displaced in a dorsal direction ; and (6) palmar translocation when the carpus is subluxable palmarly.
Four major patterns of carpal instability have been described: (1) carpal instability dissociative (CID), when there is a major derangement (fracture and/or ligament disruption) within or between bones of the same carpal row; (2) carpal instability nondissociative (CIND), when the linkage between bones of the same row is preserved, yet there is dysfunction at the radiocarpal level, at the MC level, or at both levels; (3) carpal instability complex, when there are features of both CID and CIND types; and (4) carpal instability adaptive when the malalignment is an adaptation to an abnormally tilted distal radial fracture or malunion.
What follows is a review of the diagnosis and treatment of the three most common post-traumatic ligament-related carpal instabilities: SL dissociation (SLD), lunotriquetral (LT) dissociation, and palmar MC instability.
Scapholunate dissociation (SLD) describes the dysfunction that results from rupture of the links that connect the scaphoid to the lunate (primary stabilizers) and to the distal row (secondary stabilizers). Although the condition was already recognized by Destot in 1910, it was not until the publication by Linscheid and associates in 1972 that the clinical features of SLD were widely acknowledged. In some publications, the term rotary subluxation of the scaphoid has been used as a synonym of SLD; this term, however, should only be used in advanced cases in which both the SL ligaments and the scaphotrapezial-trapezoidal (STT) and scaphocapitate (SC) ligaments have failed, resulting in substantial carpal collapse with the scaphoid rotating into flexion and pronation. , If only the proximal SL ligaments (primary stabilizers) are disrupted, the scaphoid may appear normally aligned, with the secondary stabilizers (STT and SC ligaments) preventing carpal collapse (dynamic instability). In such circumstances, the case can be categorized as SLD but not as a rotary subluxation of the scaphoid.
Pathomechanics of SLD
Most SLDs are the consequence of a twisting injury to the wrist involving loaded hyperextension, ulnar deviation, and MC supination. Most often, this is the result of a motorcycle accident (head-on collision with the hand grasping the handlebar) or a fall from a height on the outstretched hand. There is a spectrum of injuries, from minor SL sprains to complete perilunar dislocations, all being different stages of the same pathomechanical event, as described by Mayfield and associates.
The mechanical consequences of the loss of the different scaphoid stabilizers have been investigated by different authors. , Partial tears of the SL membrane may be symptomatic despite minimal kinematic alteration (predynamic instability). Complete rupture of the SL membrane and ligaments, by contrast, may create substantial alteration of both kinematic and kinetic behavior of the carpus, but not necessarily a permanent malalignment (dynamic instability). In fact, as stated previously, permanent rotary subluxation of the scaphoid plus carpal collapse (static instability) is only seen if both the primary (SL) and secondary (STT and SC) ligaments have failed. Injury to the secondary stabilizers rarely occurs acutely, but as a result of the stress imposed by the distal row on the proximally unconstrained scaphoid. In such circumstances, the loaded lunate and triquetrum tend to rotate into abnormal extension (dorsal intercalated segment instability), supination, and radial deviation, whereas the scaphoid tends to collapse around the radioscaphocapitate ligament into abnormal flexion, ulnar deviation, and pronation ( Fig. 74-1 ).
When the scaphoid has collapsed in such a rotatory fashion, its proximal pole has a propensity to sublux dorsoradially ( Fig. 74-2 ). This creates increased compressive and shear stress on the dorsal and lateral corner of the scaphoid fossa, explaining the early development of degenerative changes at that level. The lunate, by contrast, even if abnormally extended, maintains normal congruency with the lunate fossa, and this explains why the radiolunate joint is so seldom affected by the degeneration process. The term scapholunate advanced collapse (SLAC) has been proposed to refer to this clinical condition in which there has been a progression of degenerative changes from an isolated radial styloid-scaphoid impingement (stage 1), to complete radioscaphoid osteoarthritis (stage 2) and MC arthritis (stage 3).
After a thorough evaluation of the patient’s history, with special emphasis on the mechanism of injury, the clinical examination needs to be exhaustive, systematic, and bilateral. The external appearance of a wrist with SLD often is not particularly dramatic: swelling is generally moderate and motion may be almost normal. Palpation of areas of maximal tenderness is one of the keys in the diagnosis of this pathology, especially in patients with chronic SLD. If sharp pain is elicited by pressing the area just distal to Lister’s tubercle, the probability of an SLD problem is high.
A useful maneuver to investigate scaphoid instability is the scaphoid shift test, described by Watson and associates. If the SL ligaments are torn, pressure on the palmar-distal scaphoid tuberosity while the wrist is moved from neutral to radial deviation induces a dorsal subluxation of the proximal pole of the scaphoid out of the radius, inducing pain. When pressure is released, a clunking may occur, indicating self-reduction of the scaphoid. This test is very sensitive but poorly specific. Comparison with the contralateral normal side is important.
Static SLD may be easily suspected by evaluating standard posteroanterior (PA) and lateral radiographs. Three major features define the lesion: (1) an increased asymmetrical SL joint space greater than 5 mm; (2) the scaphoid has a foreshortened appearance in the PA view, with the scaphoid tuberosity being projected in the form of a radiodense circle or ring over the distal two thirds of the scaphoid; and (3) on the lateral projection, the SL angle is greater than 70 degrees, being asymmetrical relative to the other side.
Because dynamic SLD is difficult to diagnose with standard radiographs, when the condition is suspected, wrist evaluation under fluoroscopy is recommended. The patient is to actively move the wrist while the examiner looks for any abnormal SL gap appearing in some wrist position. Passively stressing the joint (traction or axial compression) in different wrist positions may also be of help.
Injecting dye in the joint and analyzing postinjection MRI or computed tomography scans may also be useful to diagnose SLD. When interpreting these scans, however, care must be taken not to confuse degenerative perforations of the proximal carpal membranes with true ligament ruptures. One must also be aware that such abnormalities may be bilateral, with only one side being symptomatic. Because of these limitations, the use of these methods has diminished in favor of arthroscopy, certainly the gold standard technique in the diagnosis of intracarpal derangements, , as it is discussed in Chapter 77 .