There is no clear consensus on what constitutes acute, subacute, and chronic injuries. Whichever criteria are used, the principle aim is to define the potential for healing of the native ligament.

Larsen et al. classified carpal instability in a temporal way. Acute was defined as less than a week old, subacute was defined as between 1 and 6 weeks, and chronic was described as more than 6 weeks old [22].

Geissler and Haley defined an acute injury as up to 3–4 weeks old. Subacute was defined as an injury more than 3–4 weeks old and up to 6 months old. A chronic injury was defined as symptoms present greater than 6 months [23].

The current trend has been to consider injuries as “chronic” at an earlier time point due to the observed poorer outcomes in terms of radiographic maintenance of SL gap after direct ligament repair, at relatively early intervals after the apparent index injury.

This lack of consensus as to what constitutes an acute injury means that algorithms for management based on temporal classification remain inconsistent.

Clinically we can define four types of instability: (1) predynamic instability; (2) dynamic instability; (3) reducible static instability; (4) nonreducible instability [24]. Predynamic instability was initially termed by Kirk Watson [7] and applies to instability that may be observed clinically on physical examination but not by radiographic studies, and corresponds to a Geissler grade I or II instability [23]. Dynamic SL instability is applied to a complete SL ligament tear, but the secondary scaphoid stabilizers remain intact [25]. SL instability can be observed radiographically under loaded conditions or in specific wrist positions, “clenched fist” or loading the wrist in ulnar deviation. Static reducible SL dissociation occurs when the ligament tear is chronic and irreparable; the secondary stabilizers are insufficient and a DISI deformity results; carpal subluxation is reducible [24].

A structural classification can be based on imaging studies, or arthroscopic or open operative evaluation. Imaging studies may be static X-ray films, stress/positional radiographs, fluoroscopy, ultrasound, or MRI.

The key to treatment of SL ligament complex pathology is recognition of what is normal and what is pathological anatomy. Both the radiocarpal and midcarpal spaces must be evaluated arthroscopically when carpal instability is suspected. Wrist arthroscopy is usually not considered complete if the midcarpal space has not been evaluated, particularly with a suspected diagnosis of carpal instability.

The SLL is best visualized with the arthroscope in the 3-4 portal. It should have a concave appearance as viewed from the radiocarpal space (Fig. 10.2). In the midcarpal space, the SL interval should be tight and congruent without any step-off (Fig. 10.3). This is in contrast to the lunotriquetral (LT) interval, in which a 1-mm step off occasionally is seen which is considered normal and slight motion is seen between the lunate and triquetrum. When it tears, the SLIL hangs down and blocks visualization with the arthroscope in the radiocarpal space from the 3-4 portal. The normal concave appearance between the carpal bones becomes convex. However, the degree of rotation of the carpal bones and any abnormal motion or separation is best appreciated from the unobstructed view available in the mid-carpal space.

A spectrum of injury to either the SL or LT interosseous ligament is possible. The interosseous ligament appears to attenuate and then tear from volar to dorsal. Geissler devised an arthroscopic classification of carpal instability and suggested management of acute lesions to the interosseous ligament (Table 10.2) [23, 25]. The management options as listed from this original article have evolved as the understanding of the compromise of ligament healing potential over time has changed.

In Grade I injuries, there is loss of the normal concave appearance of the scaphoid and lunate as the interosseous ligament bulges with the convex appearance (Fig. 10.4). Evaluation of the SL interval from the midcarpal space shows the SL interval still to be tight and congruent. These mild Grade I injuries usually resolve with simple immobilization.

In Grade II injuries, the interosseous ligament bulges similarly to grade I injuries as seen from the radiocarpal space. In the midcarpal space, the SL interval is no longer congruent. The scaphoid flexes and its dorsal lip is rotated distal to the lunate (Fig. 10.5). This can be better appreciated with the arthroscope placed in the ulnar midcarpal portal looking across the wrist to assess the wrist to assess the amount of flexion to the scaphoid. This is analogous to the dorsal translation of the proximal pole of the scaphoid that can be identified on sagittal plane MRI imaging (Fig. 10.1).

In Grade III injuries, the interossesous ligament starts to separate, and a gap is seen between the scaphoid and lunate from both the radiocarpal and midcarpal space. A 1 mm probe may be passed through the gap and twisted between the scaphoid and lunate from both the radiocarpal and midcarpal spaces (Fig. 10.6). Sometimes the gap between the scaphoid and lunate is not visible until the probe is used to push the scaphoid away from the lunate. A portion of the dorsal SLIL may still be attached.

In Grade IV injuries, the interosseous is completely torn, and a 2.7 mm arthroscope may be passed freely from the midcarpal space to the radiocarpal space between the scaphoid and lunate (the drive-through sign) (Fig. 10.7). This corresponds to the widened SL gap seen on plain radiographs with a complete SL dissociation.

This surgery may be appropriate for acute lower grade injuries.

The wrist is evaluated arthroscopically for direct visualization of SLL injury and indirect evidence of disordered intercarpal mechanics. Arthroscopic assessment is achieved through the preferred means of arthroscopy and traction. The wrist may be suspended at approximately 10 lbs of traction in a traction tower [27, 28]. Alternately traction may be applied with the forearm horizontal using a variety of traction devices [28, 29]. The 3-4 portal is the most ideal viewing portal for visualization of the SLL. A working 4-5 or 6-R portal is also used. The wrist is systematically evaluated from radial to ulnar. The SL interval is probed. The degree of injury may not be fully appreciated until the tear is palpated with a probe (Fig. 10.8). Torn fibers of the SLL, if present, are then debrided with the arthroscope in the 6-R portal, and a shaver inserted into the 3-4 portal. A probe is inserted into the SL interval to note particularly any gap between the scaphoid and lunate. Following arthroscopic debridement of a torn SLL from the radiocarpal space, the midcarpal space is then evaluated. The arthroscope is initially placed in the radial midcarpal space. Close attention is paid to any rotational displacement of the scaphoid with the dorsal lip being rotated distal to that of the lunate. This may be best visualized with the arthroscope placed in the ulnar midcarpal portal. Also, any gap where the probe or arthroscope itself can be passed between the scaphoid and lunate is identified. If this is achieved easily then there are serious doubts as to whether closed pinning is appropriate [28].

Patients with a Grade II lesion may be most ideally suited for arthroscopic-assisted reduction and pinning although efficacy of this treatment must me be interpreted in the context of the interval since injury, which will affect the healing potential. Alternate treatment options with arthroscopic capsular abrasion or shrinkage have also been advocated for Grade II pathology particularly in more chronic injury and will be discussed later. Use of closed pinning for Grade III injuries is difficult to justify based on current literature.

For arthroscopic pinning the arthroscope is placed in the 3-4 portal after the midcarpal space has been evaluated in patients who have an acute or perhaps subacute Grade II SLIL injury. A 0.045 Kirschner wire (k-wire) is inserted through a soft tissue protector or through a 14-G needle placed dorsally in the anatomic snuff-box to the scaphoid. A soft tissue protector may be used in order to avoid injury to the sensory branches of the radial nerve. A small incision is made, and blunt dissection is continued down with a hemostat; a soft tissue protector may be placed directly on the scaphoid.

The k-wire can then be seen as it enters the scaphoid with the surgeon looking down the radial gutter with the arthroscope. In an easier alternative technique, the wrist is taken out of traction and the k-wires can be positioned under fluoroscopic control. If there is concern regarding the reduction then placing the arthroscope in the ulnar mid-carpal portal during stabilization allows the surgeon to look across the wrist to better judge the rotation of the scaphoid in relation to the lunate.

Additionally, a probe may be inserted through the radial midcarpal space to control the palmar flexion of the scaphoid. The wrist may be extended and ulnar deviated to help further reduce the palmar flexion of the scaphoid. After the first wire is placed controlling the reduction, an additional wire may be placed in the SL interval. Placement of wires between scaphoid and capitate remains controversial. A scapho-capitate wire gives excellent control of scaphoid rotation but some authors have questioned the advisability of violating the uninjured scapho-capitate articulation. In addition, immobilization of the midcarpal joint through scapho-capitate wires may be considered undesirable in the context of renewed interest in the “Dart throwing” plane of motion.

The k-wires are best buried under the skin as this avoids secondary infection and need for premature removal. The wrist is immobilized in a below elbow thermoplastic splint. Gentle inner range radiocarpal flexion-extension range of motion exercise is usually possible, as restricted by the wires. The k-wires are then removed in theater after 6–8 weeks. Grip strength exercises for the wrist are initiated at 3 months.

Treatment for patients with Grade III and Grade IV injuries to the SLL, either acute, subacute, or chronic remains unclear. Results of closed treatment for higher-grade injuries have largely been unsatisfactory [30] and the dichotomy between repair and reconstruction has remained difficult to clarify. There has undoubtedly been a trend toward earlier adoption of reconstruction for higher-grade injuries.

Whipple reviewed the results of arthroscopic management of SL instability, utilizing the previously described techniques in patients who were followed for 1–3 years [31]. In his series, patients were classified into two distinct groups of 40 patients each, according to the duration of symptoms and the radiographic SL gap. Thirty-three patients (83 %) who had a history of instability for 3 months or less and had less than 3 mm side-to-side difference in the SL gap had maintenance of the reduction and symptomatic relief. When symptoms were present for greater than 3 months and there was more than a 3 mm side-to-side SL gap only 21 patients (53 %) had symptomatic relief following arthroscopic reduction and pinning. Patients with less than 3 months symptoms duration and 3 mm side-to-side SL gap were followed for 2–7 years. Whipple found that 85 % continued to maintain their stability and comfort in his series. This report emphasized the need for early diagnosis and intervention prior to the onset of fixed carpal alignment and diminished capacity for ligamentous healing.

Patients with acute Grade III and Grade IV injuries to the SLIL are best treated with open repair or reconstruction. The efficacy of direct repair remains controversial; however, there is little doubt that the trend is toward earlier adoption of reconstructive techniques rather than direct repair due to the strong impression that complete ruptures lose the capacity for primary healing very soon after injury. The critical interval has not been defined and indeed it may be that once a complete rupture of the SLIL has occurred the potential for healing may be compromised. Furthermore the tear morphology may influence the healing potential. When the ligament is avulsed from either the scaphoid or lunate, it may have a greater capacity to heal than a midsubstance rupture. Prior to arthrotomy, the wrist is evaluated arthroscopically for any additional injuries, including potential cartilaginous loose bodies, triangular fibrocartilage complex tears, and possible injury to the LT interosseous ligament. Open repair is undertaken through a dorsal 3-4 extensor compartment approach. A Berger ligament sparing arthrotomy [32] is preferred by the authors. It is essential that an intraoperative assessment is made as to the healing potential of the residual ligament and alternate reconstructive or salvage procedures undertaken if the residual ligament is of poor quality or there is concern regarding the cartilage surfaces of the carpus and radius.

Restraint of scaphoid flexion has long been identified as a desirable intervention in the treatment of SL pathology [33–35]. The dorsal subluxation of the proximal scaphoid and loss of congruence of the distal pole in relation to the radial styloid have long been considered the principal initial biomechanical abnormalities requiring intervention. Procedures that restrict scaphoid flexion have been advocated as an alternative to repair or reconstruction. There is no consensus as to when such alternate stabilizing procedures should be undertaken in preference to repair or other reconstructive options.