Screw Fixation: Reduction and Association of the Scapholunate (RASL) Procedure

38 Screw Fixation: Reduction and Association of the Scapholunate (RASL) Procedure

Indications

Subacute to chronic scapholunate (SL) dissociation
Static or dynamic SL instability
Irreparable scapholunate interosseous ligament (SLIL)
No SL advanced collapse wrist or advanced osteoarthritis of the radiocarpal joint
Focal radial styloid-scaphoid arthritis is not a contraindication.

Technique

6 cm longitudinal dorsal incision just ulnar to Lister’s tubercle

Oblique retinaculum incision between third and fourth dorsal compartment, retract extensor pollicis longus (EPL) radially, retract extensor indicis pro-prius (EIP) and extensor digitorum communis (EDC) ulnarly.

Longitudinal incision in capsule, retract to visualize scaphoid and lunate

Insert two 0.062 in. Kirschner wires into the scaphoid and lunate to use as joysticks for reduction. The Kirschner wire in the scaphoid is placed distal and directed proximally in the palmar-flexed scaphoid. The Kirschner wire is placed as proximal as possible and directed distally in the dorsiflexed lunate. Placement of the Kirschner wires is planned to allow the Herbert screw fixation after SL reduction (Fig. 38-1A,B).
Use the joysticks to spread the SL joint and allow dechondrification of the contacting surfaces (Fig. 38-2).
A second 5 cm longitudinal incision is made on the midaxial border of the radius palmar to the first dorsal compartment from 2 cm proximal to the radial styloid to the level of the scaphotrapezial joint (Fig. 38-3). Take care to avoid injury to the radial sensory nerve and dorsal branch of the radial artery.
Open the first dorsal compartment and retract abductor pollicis longus (APL) and extensor pollicis brevis (EPB). Make a longitudinal incision in the radio-scaphoid-capsular ligament. Develop this in continuity as a sleeve for repair. Dissect subperiosteally to expose the radial styloid.
Perform a radial styloidectomy with an osteotome, with care to preserve the radioscaphocapitate ligament. Reduce the scaphoid and lunate with the Kirschner wire joysticks and maintain with a Kocher clamp (Fig. 38-4). Extend the scaphoid and flex the lunate to entirely close the SL gap and cover the head of the capitate.
The Herbert jig is placed through the radial incision and the hook is brought across the dorsoulnar aspect of the lunate under direct vision. Do not violate the lunotriquetral (LT) ligament. The position of the screw should be as central as possible in both the scaphoid and the lunate. The tip of the jig should be at the proximal apex of the lunate when reduced. Alternatively, one can place a guide wire freehand for the Herbert-Whipple cannulated (Zimmer, Warsaw, Indiana) screw system.
Once the proper position is established and the starting point determined, drill, measure, tap, and insert the correct length Herbert screw. The unthreaded portion of the screw should lie between the two bones. The average length is 22 to 28 mm (Fig. 38-5).
Once the screw is inserted and the jig and Kirschner wires are removed, the wrist may be taken through a full range of motion to confirm that it is unrestricted and that SL reduction is maintained. Confirm with intraoperative imaging. You will note obligatory rotation between the scaphoid and lunate about the instant center of rotation.
Both dorsal and radial capsular incisions are closed without imbrication to avoid the capsulodesis effect.
Repair the dorsal retinaculum and close both incisions in standard fashion. Apply a sterile bulky dressing and a palmar gauntlet split.