▪ The Scaphoid Nonunion Advanced Collapse Wrist

Several authors have reported a clear correlation between scaphoid nonunion and the development of arthritic changes in the wrist. Ruby et al2 demonstrated that osteoarthritic changes of the wrist develop 97% of the time after at least 5 years after the onset of a scaphoid nonunion, and they concluded that all patients with a scaphoid nonunion should be advised that arthritic change is a “likely eventuality.” Mack et al3 and Inoue and Sakuma4 similarly demonstrated a high probability of degenerative change, with a strong correlation between duration of nonunion and presence of arthritis. Scaphoid nonunion advanced collapse, or “SNAC,” as coined by Krakauer et al5 in 1994, has a characteristic progressive arthritic pattern, similar to that seen in SLAC. Because the scapholunate ligament is intact in a SNAC wrist, however, the carpus is better able to withstand axial loading; thus there is less proximal migration of the capitate. The resultant shear force on the capitate is more distal and radial than in a SLAC wrist, and there are greater loads applied to the radial and distal aspect of the scaphoid nonunion. Concurrently, the distal scaphoid moves independently from the proximal pole, which is still attached to the lunate. This culminates in arthritis between the distal scaphoid and the radial styloid, the extent of which is partially determined by the site of nonunion; specifically, proximal and middle third nonunions demonstrate early arthritic change that is limited to the radioscaphoid joint, whereas distal third nonunions have been shown to result primarily in lunocapitate joint changes.6 Stage I SNAC wrist is defined as an isolated radial styloid arthritis due to this styloid–scaphoid impingement. Later stages of SNAC involve the radioscaphoid, scaphocapitate, and capitolunate articulations, and eventually culminate in pancarpal arthritis.

In light of the clear association of a chronic scaphoid nonunion with progressive radiocarpal and midcarpal arthritis, certainly the recommended treatment for the majority of acute displaced and comminuted scaphoid fractures as well as any proximal pole fracture is open reduction and internal fixation (ORIF), with or without bone graft. Once SNAC arthritis develops, it is unlikely that an acceptable result will be obtained with a simple ORIF. Numerous surgical treatments have been reported for early-and late-stage SNAC wrist, and several are described in earlier chapters. These include proximal row carpectomy,7 ^– 9 limited intercarpal arthrodesis,10 ^, 11 scaphoid excision and intercarpal arthrodesis, and total wrist arthrodesis. More limited procedures have also been described. Malerich et al12 reported a case series of 19 patients who underwent an open distal scaphoid pole excision, and at an average follow-up of over 4 years, grip strength and wrist range of motion increased by 134% and 85%, respectively. Soejima et al13 also reported nine patients treated with distal scaphoid resection for scaphoid nonunion with either intercarpal or radioscaphoid arthritis. Good or excellent results were noted in all nine patients at an average follow-up of 28.6 months. Ruch et al14 performed an arthroscopic distal scaphoid excision and a radial styloidectomy on three patients with scaphoid avascular necrosis and early-stage SNAC wrist. Using this less invasive technique, they report complete relief of all patients’ mechanical pain and satisfaction with the surgery at a 2-year follow-up.

▪ Indications

The most frequent indication for radial styloidectomy is isolated arthritis between the scaphoid and the radial styloid. This entity is most commonly seen in cases of radial styloid malunion or early SLAC or SNAC wrist in which the arthritis is limited to degenerative changes at the styloid–scaphoid joint. Radial styloidectomy has also been described as an adjunct procedure for stages IIIb and IV Kienböck disease,15 ^, 16 and also for radial styloid malunion. Additionally, radioscaphoid impingement may occur with radial deviation of the wrist following triscaphe fusion,17 four-quadrant fusion,18 and proximal row carpectomy19 This is considered an indication for styloidectomy as an adjunct procedure if impingement is noted at the time of the index reconstructive procedure.