Introduction

Treatment of scapholunate instability due to rupture of the scapholunate interosseous ligament remains a challenge, with no predictable or reproducible procedure. The natural progression of SL instability has been documented, and in the last 30 years several treatments have been described to halt the ensuing pathomechanics.¹ Soft-tissue reconstructions include capsulodesis procedures such as the Blatt procedure or the Szabo modification, which uses the dorsal intercarpal ligament. These techniques do not reduce the scapholunate (SL) interval, but are nonetheless thought to provide symptomatic relief.^2,3 Brunelli has described a tenodesis of the scaphotrapezial joint using a strip of the FCR tendon, but long-term follow-up is lacking.⁴

Bone procedures include arthrodesis of the scaphoid and lunate (which has a high complication and nonunion rate) and the scaphotrapezialtrapezoid arthrodesis advocated by Watson.^5,6 Results of this procedure have not been reproducible, and there is the suggestion of progressive arthrosis and limitation of motion over time. Unfortunately, both soft and bony techniques will ultimately impair grip strength and total arc of motion at the expense of scaphoid stabilization.²

Herbert initially described a surgical technique involving open reduction and reattachment of the ligament to the bone, combined with Herbert screw fixation across the scapholunate joint. The screw is normally left in situ for 12 to 18 months, allowing sufficient time for ligament healing and restoration of carpal stability.⁷

Rosenwasser and colleagues recently popularized this technique and endeavored to create a stable fibrous pseudarthrosis between the scaphoid and lunate by reducing and stabilizing the SL joint (or reduction association of the scaphoid-lunate RASL) with a Herbert bone screw (HBS). Long-term data is not available on this procedure, but early results are encouraging.⁸ The procedure they describe uses both dorsal and radial incisions for joint preparation and reduction (as well as screw placement). Further experience with the procedure led us to develop an arthroscopic (ARASL) technique, which minimizes the tissue trauma and facilitates precise reduction of the joint and placement of the screw.

At the fifty-fifth annual meeting of the American Association of Hand Surgery (January 1996, Palm Springs, CA), a group of hand surgeons were presented with the scenario of a 34-year-old laborer who had suffered a scapholunate interosseous ligament (SLIL) tear. Nearly all believed surgical intervention was necessary. However, half of the group opted for a soft-tissue reconstruction and the other half recommended a bony procedure. The mixed consensus suggests that no clear mode of treatment or solution is suitable to this day, leaving the door open for new techniques to control the scaphoid.

History and Literature Review

As early as 1978, Palmar and colleagues tried to treat scapholunate instability with a tenodesis technique using the ERCL or ERCB. The reports led to modifications of the procedure by Glickel⁷ and Almquist. However, the intervention often demonstrated a loss of grip strength and wrist motion of 20 to 25% (while many still complained of pain). By 1985, Watson described fusion of the scaphoid, trapezium, and trapezoid bones (triscaphe arthrodesis) to control scaphoid rotation (with improved results in grip strength).

Other authors were not able to duplicate his clinical results, and Watson modified the procedure by including a generous radial styloidectomy to prevent radioscaphoid arthrosis.⁶ However, by spanning the proximal and distal carpal rows mobility was decreased 40% and complications often included nonunion. Although a fusion procedure was generally considered if the SL gap was >4mm, or if the scaphoid was nonreducible, many believed that post-traumatic arthritis was inevitable with limited arthrodeses due to the abnormal wrist kinetics.

Blatt subsequently used the dorsal capsule to tether the distal pole of the scaphoid in extension, whereas Szabo and colleagues demonstrated success utilizing the dorsal intercarpal ligament.⁹ Although motion appears to improve at the expense of grip strength, these reconstructions tend to fail over time (as evidenced by radiographic carpal collapse and SL widening). Long-term outcomes are not well documented, but there is cause for concern that late degeneration may occur (because the abnormal carpal alignment is not corrected). Overall, the results are variable (with soft-tissue reconstructions wherein mobility decreases 10 to 44% and strength decreases to 13 to 35% of the contralateral limb).² Despite symptomatic improvement, Moran et al. recorded a 15% loss of motion and 20% decrease in grip strength with dorsal capsulodesis (with radiographic alignment lost at two-year follow-up).³

In 1991, Hom and Ruby attempted limited arthrodesis of the scaphoid and lunate with high rates of nonunion. However, the pseudoarthrosis rendered many patients symptom free.⁵ This led to Rosenwasser to decribe the RASL procedure with encouraging clinical results in early 2000 (American Society for Surgery of the Hand meeting, October 2000, Seattle, WA). The RASL has been reported to minimize the loss of grip strength and mobility 10 to 15%. The technique uses a cannulated Herbert screw to stabilize the scaphoid and lunate.

The dumbbell-shaped screw allows for some rotation, while restoring the scapholunate interval and preventing AP translation at the joint. The RASL requires two incisions: one to perform the reduction and a second for a radial styloidectomy.⁸ Shortly thereafter, the ARASL technique was developed using three portals to achieve similar results. Performing this procedure arthroscopically facilitates both establishing the initial diagnosis of a scapholunate injury as well as visualizing the adequacy of reduction of the scapholunate subluxation during HBS screw placement.

Anatomy and Biomechanics

The SLIL is an important intrinsic restraint that allows the scaphoid and lunate to seamlessly rotate in unison during wrist motion. As the wrist palmar or dorsiflexes, the scaphoid moves in concert with the lunate. As the wrist deviates ulnarly or radially, the scaphoid and lunate extend and flex (respectively).¹⁰ If there is an isolated SLIL rupture, the extrinsic ligamentous complex maintains the position of the scaphoid and lunate, albeit with added stress, because the two bones are no longer internally coupled. Attrition of the extrinsic restraints occurs over time, and ultimately the SL interval widens and a dorsal intercalated segment instability (DISI) pattern appears. It is important to understand that both the intrinsic SLIL and extrinsic restraints have to be compromised in order to observe radiographic abnormalities. However, symptoms can still be present despite the lack of radiographic findings. One of the advantages of using the arthroscope is the ability to assess the integrity of the SLIL.

The SLIL consists of three segments, with the ligament being the strongest and thickest dorsally. The volar portion is less robust, and the mid-substance is the weakest (being comprised of fibrocartilagenous material).² The volar extrinsic ligaments include the radioscaphocapitate (RSC), long and short radiolunate ligaments (LRL, SRL), and the ulnotriquetral and ulnolunate ligaments. The RSC acts as a fulcrum for the scaphoid to flex and extend. Dorsally, the radiocarpal (DRC) and dorsal intercarpal (DIC) ligaments are stout restraints that prevent dorsal translation of the carpal bones.¹⁰ When the SLIL, along with any of the external ligaments, is injured the scaphoid is free to flex over the RSC and pronate. During the ARASL, adequate reduction of the rotary subluxation is achieved by dorsiflexion and supination of the scaphoid at the same time the lunate is palmar flexed. If the SL instability is allowed to go untreated, the abnormal kinematics that ensue will lead to a scapholunate advanced collapse (SLAC) deformity.¹

Indications

The ARASL is indicated in cases where there is clinical and radiographic evidence of SL instability. Upon physical examination, tenderness over the dorsum of the scapholunate joint as well as a positive scaphoid shift test (Watson test) is suggestive of SL instability. The Mayfield classification for radial-sided injuries (stage 1) is a useful method to stratify which patients require surgical intervention. Stage 1 injuries are subdivided into four classes with respect to the severity of injury to both the intrinsic and extrinsic restraints.

Class A injuries are the least severe (in which no radiographic signs are present). However, there is clinical suspicion of SL injury. Generally, this represents a partial simple tear of the intrinsic SL ligament and can often be treated conservatively. Class B is considered a “dynamic” state in which stress radiographic views reveal SL widening consistent with an injury to both the intrinsic and extrinsic restraints. Class C demonstrates a static SL gap on radiographs. Such injuries can be further classified into flexible and fixed deformities (Figure 9.1a and b).

FIGURE 9.1 AP and lateral radiographs show a diastasis (Terri-Thomas) sign at the scapholunate interval, characteristic of a scapholunate ligament rupture. The lesion would be classified as CID (carpal instability dissociative) because of the disruption within the proximal carpal row. The diastasis suggests a Geissler grade IV ligament injury. DISI (dorsal intercalated segment instability) is seen on the lateral view, with the scapholunate angle of 90 degrees.

Patients with a class A or “predynamic” state can be treated with splinting, pain medication, or cortisone injection until symptoms improve. However, attrition of the extrinsics may develop in which the patient will progress to class B. Patients who present with classes B and C injuries require surgical intervention to control the scaphoid instability and are candidates for the ARASL procedure. Some of the alternative methods of treatment may be contraindicated in the presence of radiocarpal arthritis. However, an early SLAC wrist does not preclude one from undergoing the ARASL coupled with a radial styloidectomy. Patients with stage II SLAC wrist have demonstrated symptomatic improvement in our small series, and the ARASL can be performed prior to considering a salvage procedure. Absolute contraindications include SLAC wrists beyond stage II.

Technique

Preparation

The procedure is usually performed under regional anesthesia, with the patient in the supine position. An arthroscopy traction tower is used. Important landmarks include Lister’s tubercle, the radial styloid, the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) tendons, and the extensor carpi ulnaris tendon. Low-pressure inflow is used to prevent extravasation into the subcutaneous tissues.

The arthroscopic RASL procedure begins by creating a 3-/,4 portal between the third and fourth extensor compartments and a radial midcarpal portal. The arthroscope is initially inserted into the 3-/,4 portal for inspection of the scapholunate interval and radiocarpal joint. The midcarpal portal, which is located one centimeter distal to the 3-/,4 portal, is then used to evaluate the distal aspect of the scapholunate joint and to confirm the presence of instability. This is more easily seen from the midcarpal portal, in that the torn ligament remnants may obscure the view from the 3-/,4 portal.

Once the diagnosis is confirmed and a “drive-through” sign is seen (Figure 9.2), the arthroscope is placed in the radial midcarpal portal. A 2.9-mm shaver is placed in the 3-/,4 portal. The adjacent articular surfaces of the scaphoid and lunate are denuded of cartilage and excoriated until punctate bleeding is seen. The surfaces are not, however, completely decorticated.

FIGURE 9.2 Radial midcarpal and 3-4 radiocarpal portals are established. With the arthroscope in the radial midcarpal portal, the ligament rupture is confirmed and a 2.9-mm shaver is placed in the 3-4 portal and used to excoriate the opposing surfaces of the scaphoid and lunate. Ideally, punctate bleeding should be seen, but the bones should not be decorticated because this will adverse affect the purchase of the screw.

Reduction Procedure

Step 1

Once the surfaces are prepared, a trial reduction is performed. A .062 Swanson pin is placed in the distal pole of the scaphoid. The wire should be placed in the distal pole so that it will not interfere with placement of the screw. The wrist is then flexed and a second .062 wire is inserted into the lunate so that when the wrist is then extended impingement of the K-wire on the dorsal lip of the radius holds the lunate in flexion. In chronic cases, mobilization of the distal pole of the scaphoid may be necessary. This can be accomplished by placing the arthroscope in the radial midcarpal portal and creating an additional palmar portal at the scaphotrapezial joint to permit localized soft-tissue debridement and mobilization.

Step 2

Next, a 1-/,2 portal is created just dorsal to the APL tendon. This will allow for insertion of the cannulated HBS screw guide wire. The subcutaneous tissues are spread to the capsule, and small Ragnell retractors are used to introduce a protective cannula. The entrance position of the 0.35-mm guide wire may be observed from either the 3-/,4 portal or under fluoroscopic control (Figure 9.3).

FIGURE 9.3 In chronic injuries, mobilization of the distal pole of the scaphoid may be necessary to anatomically reduce the joint. The shaver may be placed in a 1-2 portal or a palmar scaphotrapezial portal can be made for the shaver. Once mobilized, a .062 K-wire is placed in the distal pole of the scaphoid. The wrist is flexed and a second .062 K-wire is placed in the lunate. When the wrist is dorsiflexed, this pin impinges on the dorsal lip of the radius, stabilizing the lunate in flexion. The joint is then reduced by dorsiflexing and supinating the scaphoid (the supination is critical to an anatomic reduction). The scaphoid is then pinned to the capitate and the radius and the lunate is also pinned to the radius to help stabilize the reduction as the guide wire is passed into the lunate.

The .035 Kirschner (K)-wire should enter near the waist of the scaphoid, in the mid portion of the bone on the lateral projection. The guide wire should exit just beneath the subchondral surface at the medial edge of the scaphoid. The exit of the pin can be observed from the 3-4 or radial midcarpal portal. The position of the guide wire is absolutely critical to the success of the operation. This may be the most time-consuming part of the operation, but mal-positioning is the most common cause of failure.

Step 3

Once the correct position is confirmed, the pin is withdrawn slightly so as not to interfere with the reduction (Figure 9.4a). The scapholunate joint is anatomically reduced by levering the K-wire in the distal pole dorsally and rotating the pin to supinate the scaphoid. The scaphoid and lunate are then firmly fixed by pinning them to the radius and capitate (Figure 9.4b). Confirming again that an anatomic reduction has been achieved, the guide pin is advanced across the scapholunate joint and advanced to the proximomedial corner of the lunate.

FIGURE 9.4 (A) The position of the guide wire is observed from the radial midcarpal portal. (B) It should pass just beneath the subchondral bone of the scaphoid and lunate and reach the proximomedial pole of the lunate. (C) The drill is then used, taking care not to force the bones apart when drilling the lunate cortex, and the screw is advanced.

The reduction is checked with the arthroscope, and the position of the wire and the carpal alignment are checked with the image intensifier. If correct, the length of the screw is determined by placing a second K-wire against the scaphoid from the 1-2 portal immediately adjacent to the guide wire. The pin is advanced to the surface of the scaphoid, and the difference between the two wires is the length inside the bones. The screw length is 4 to 5 mm less than this distance. A second wire may now be inserted parallel to the guide wire to further stabilize the joint. The guide wire is advanced out of the lunate to prevent inadvertent withdrawal during drilling.

Step 4

Next, a new cannulated drill is used. The two scaphoid cortices are perforated. Power may be desirable to penetrate the lunate cortex to avoid pressure that could distract the joint. Once in the lunate, the drill should be advanced by hand up to the medial corner of the lunate. The position is confirmed with the image intensifier and the scapholunate joint is checked to ensure there has been no distraction (Figure 9.4c). It is helpful to compress the joint with the .062 pins during drilling to prevent distraction.

Step 5

Once the drilling is completed, the screw is inserted. If the joint is well reduced, the standard compression screw is used. However, if there is any distraction the high-compression HBS screw can be used to compensate. The screw is advanced until it is barely beneath the subchondral surface of the scaphoid (Figure 9.5a through c). Motion is checked with the image intensifier while the position of the screw and reduction of the joint are confirmed. The instruments are then withdrawn and the portals closed. A short arm cast is applied.

FIGURE 9.5 Improper positioning of the screw. Incomplete reduction and incorrect choice of hardware are the most common causes of failure. (A) The correct position of the screw. (B) The screw is placed too proximally in the scaphoid. In addition, the screw does not have enough step-off between the threaded and central diameters, increasing the chance of “pull-out.” (C) The scapholunate joint is inadequately reduced, making it impossible for the screw to reach the proximal-medial corner of the lunate without entering the midcarpal joint. If the guide wire cannot be advanced from the waist of the scaphoid to the proximal-medial corner of the lunate without transgressing the midcarpal joint, either the SL joint is mal-reduced or the guide wire is being directed too distally.

Postoperative Care

Exercises are initiated for the fingers immediately after surgery. Use for light activities (such as typing, writing, and eating) is encouraged. Postoperatively, cast removal occurs at three weeks and gentle range-of-motion exercises are begun. Use, as tolerated, is permitted—except for heavy gripping, lifting, and contact sports, which are prohibited until week six.

Results

A total of seven patients (five males and two females, ages 28 to 77) were included in our study. Four patients had static deformities, whereas three had progressed to an SLAC pattern. Two patients had stage II, and one patient had a stage III SLAC pattern. Total arc of wrist motion was reduced 22.5% at a mean follow-up of 19 months. One patient, who had the SLAC III wrist, experienced a poor result (with a 47% reduction in wrist range of motion and persistent pain). This patient opted for the ARASL prior to having a salvage procedure to minimize her worsening mobility. Without this poor result, the mean reduction in wrist range of motion for the remaining six patients was 17.6%. Radiographically, the mean SL distance was reduced from 4.2 to 1.75 mm and the mean SL angle was reduced from 81.6 to 61.8 degrees.

The ARASL allows for wrist movement to begin more rapidly than the open procedure postoperatively and overall morbidity is minimized. Arthroscopic screw insertion is as precise as its counterpart open procedure, with the advantage of decreased soft-tissue damage. The key to a successful result, regardless of technique, lies within proper screw placement. We have seen fantastic results when the hardware is positioned perfectly. Unfortunately, with the slightest malpositioning the results have been less than favorable.