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