39 Four-Corner Fusion
Wrist arthritis is a clinical entity with multiple etiologies, including osteoarthritis, rheumatoid disease, scaphoid nonunion, and scapholunate dissociation. The stability of the wrist is secondary to the anatomical relationship of the carpal bones and their ligamentous connections, with the scaphoid serving an important role between the proximal and distal rows.1 An injury to the scaphoid is the most common cause of noninflammatory arthritis2 and carpal instability.3 Pathological carpal bone orientation secondary to carpal instability leads to a dissipation of the normal stored potential energy within the wrist,4 , 5 abnormal shear forces, and eventual cartilage degeneration.3 A loss of the normal relationship between the scaphoid and the lunate due to either a scaphoid nonunion or a scapholunate dissociation leads to pathological carpal motion and a predictable pattern of carpal degeneration, which have been termed scaphoid nonunion advanced collapse (SNAC) and scapholunate advanced collapse (SLAC) arthritis, respectively.3 , 6 The treatment options for SLAC/SNAC arthritis vary depending on the stage of degeneration and the arthritic pattern within the carpus, and they are aimed at pain relief and restoring function. When the arthritis affects the radioscaphoid joint and, to a lesser degree, the capitolunate joint, a fusion of the lunate, triquetrum, capitate, and hamate (i.e., a four-corner fusion) combined with an excision of the scaphoid, can provide a stable, pain-free wrist while permitting a limited range of motion of the wrist ( Fig. 39.1 ).7
Unlike its alternative, a four-corner fusion has the advantage of creating a pain-free construct while still allowing for native radiocarpal motion. Studies comparing proximal row carpectomies (PRCs) versus four-corner fusions have shown slightly better motion following a PRC, but maintenance of carpal height and equivalent grip strengths with a four-corner fusion.3 , 8 – 11 One of the reasons for choosing to do a partial wrist arthrodesis instead of the simpler PRC is the perceived durability of the radiolunate joint. From a functional standpoint, wrist extension is more important than wrist flexion. Approximately 30 to 35 degrees of wrist extension has been shown to be sufficient to accomplish most activities of daily living.12 , 13 Various studies have shown that after a four-corner fusion, the total arc of motion can range from 60 to 100 degrees, with at least 30 degrees of wrist extension.7 , 8 , 14 – 17
Patients with advanced wrist arthritis typically present with pain during wrist motion and with loading, as well as limited function. They should initially be treated with conservative measures that include bracing, activity modification, and antiinflammatory medications. The surgical treatment for SLAC/SNAC arthritis should be considered in patients with continued wrist pain after a failure of these conservative measures. The treatment options for SLAC/SNAC arthritis vary depending on the stage of degeneration and the arthritic pattern within the carpus. When the degeneration affects only the radioscaphoid joint (stage I and II SLAC wrists, stage I SNAC wrist), a four-corner fusion along with a PRC is a popular surgical option. When the degeneration extends to the capitolunate joint (stage III SLAC wrist, stage III SNAC), treatment is generally limited to a four-corner fusion or, in rare instances, total wrist arthrodesis.8 , 18 , 19 The indications for a four-corner fusion with or without a scaphoid excision also include isolated arthritis of the radioscaphoid or capitolunate joints,3 as well as chronic perilunar instability20 and severe midcarpal instability.21 , 22
Contraindications to a four-corner fusion include SLAC or SNAC wrist with radiolunate articular degeneration and ulnocarpal translation, frequently due to an incompetent long radiolunate ligament, where there is a disruption of the normal congruity of the radiolunate joint.17 In these cases a total wrist arthrodesis is the only effective treatment except in the rare cases of isolated radiolunate arthritis or radioscapholunate arthritis when a radioscapholunate fusion with excision of the distal pole of the scaphoid is a viable option.17 , 18
▪ Surgical Technique
The procedure is performed with the patient in a supine position using regional or general anesthesia and an arm tourniquet. A dorsal longitudinal incision is made in line with the third metacarpal starting at the carpometacarpal joint and extending proximal to the Lister tubercle. Alternatively, a dorsal transverse incision distal to the radial styloid, or a more extensile T-shaped incision may be used. Sharp dissection is carried down to the extensor retinaculum. The subcutaneous tissue is elevated off the retinaculum, which is then incised taking care to protect the radial and ulnar sensory nerves. The extensor carpi radialis longus and brevis and the extensor pollicis longus tendons are transposed radially ( Fig. 39.2 ). The extensor communis and the extensor indicis proprius are retracted ulnarly, exposing the Lister tubercle and the dorsal aspect of the carpus. The terminal branch of the posterior interosseous nerve is identified in the floor of the fourth compartment and resected. The ligament-sparing approach described by Berger et al is used to expose the car-pus.23 A transverse capsular incision is made centered over the capitolunate joint, in line with the dorsal intercarpal ligament along with an oblique incision parallel to the dorsal radiocarpal ligament, then a radially based capsular flap is elevated ( Fig. 39.3 ). The Lister tubercle is removed with a rongeur, and bone graft for the fusion is harvested from the distal radius metaphysis. In the presence of radioscaphoid arthritis, the scaphoid is excised sub periosteally with the use of a K-wire as a joystick ( Fig. 39.4 ). Care is taken to preserve the radioscaphocapitate and long radiolunate ligaments to prevent ulnocarpal translation.24 , 25 After scaphoid excision the lunate, capitate, hamate, and triquetrum are exposed. The lunate is often tilted into a dorsal intercalated segmental instability (DISI) position. Any abnormal dorsal tilt of the lunate must be corrected and provisionally fixed. A large Kirschner wire is placed into the lunate and used as a joystick to assist in its reduction. With the lunate held in a neutral position, a Kirschner wire is placed through the distal radius into the volar lunate to lock this position, while avoiding interference with the position of the implant ( Fig. 39.5 ). Care is taken to center the capitate over the lunate and to correct any ulnar drift of the proximal carpal row. The four carpal bones are stabilized in a reduced position with K-wires. These must be placed relatively volarly in order not to interfere with the reaming. The final fixation can be performed using multiple Kirschner wires, powered staples, headless screws, or a circular plate ( Figs. 39.6 and 39.7 ). The use of a circular plate is preferred by the senior author (APW) because it provides immediate rigid fixation, a recessed fixation device, and circumferential compression. Many circular recessed plates are available from a variety of manufacturers, all of which evolved from the introduction of the Spider plate in 1997 (KMI, Carlsbad, CA). Proper seating of the plate is required to diminish the risk of impingement on the dorsal lip of the radius with wrist extension and to minimize sensory nerve irritation ( Fig. 39.8A,B ).
While placing traction on the hand, the intercarpal articulations between the four carpal bone are denuded down to bleeding cancellous bone using a rongeur. A plate-specific rasp is then centered over the four-corner junction and hand reaming is performed until the rasp is seated below the dorsal lip of the lunate. This enables recession of the circular plate below the dorsal lip of the lunate to prevent impingement or the dorsal radius with wrist extension ( Figs. 39.9 and 39.10 ). In the case of a type II lunate, the center of the rasp should be centered at the articulation between the lunate and the hamate. The pressure of the rasper may need to be higher on the lunate to prevent over-reaming the distal carpal row because the lunate is typically harder than the capitate or hamate. The position of the triquetrum is checked before rasping because it tends to migrate laterally. A small curette is used to remove debris from the articulations. Substantial amounts of bone graft are then packed into the articulations. The circular plate is then placed such that at least one and preferably two screws can be placed into each of the four carpal bones. The holes are drilled and measured followed by the insertion of self-tapping screws. The screws are inserted and tightened in a clockwise fashion starting radially to maximize compression. Intraoperative fluoroscopy is used to confirm adequate carpal alignment, plate position, and screw lengths. Extra attention should be focused on the length of the triquetral screws to ensure that they do not impinge on the pisotri-quetral joint. The space between the radial styloid and the trapezium is then probed with the wrist in neutral and in radial deviation to check for styloid impingement. If this space appears tight, a radial styloidectomy is performed. The surrounding area and the center of the plate are covered with high-quality bone graft. The provisional fixation Kirschner wire is removed. The wound is irrigated, and the capsule and retinaculum are closed with absorbable sutures. The extensor pollicis longus is transposed dorsal to the retinaculum. The skin is then closed with nylon sutures. The tourniquet is deflated, and the wrist is covered with a compressive dressing and short arm splint with the wrist in neutral. Finger motion and tendon gliding exercises are encouraged immediately postoperatively. Approximately 7 to 10 days postoperatively, the sutures are removed, and the patient is placed in a short arm cast for total of 3 to 5 weeks. Serial radiographs are taken to monitor union of the arthrodesis, and strenuous activity is limited until union is achieved.