Arthroscopic radial styloidectomy

Pathophysiology

An isolated tear of the scapholunate interosseous ligament (SLIL) changes carpal loading and kinematics even without demonstrable radiographic abnormalities. It can lead to attenuation of the secondary stabilizers and progressive dissociation and rotation of the scaphoid and the lunate. With axial loading over time, the capitate migrates proximally, further driving the scaphoid and lunate apart like a wedge. This results in midcarpal instability, loss of carpal height, and changes in the radiocarpal, intercarpal, and midcarpal joint contact areas and loads. These lead to a predictable scapholunate advanced collapse (SLAC) arthritis as described by Watson et al. This begins with radial styloid beaking and radial styloid-scaphoid joint narrowing (stage 1), then progresses proximally to alter the radial scaphoid facet proximal pole scaphoid articulation (stage 2), and finally to the midcarpal capitolunate joint (stage 3). A stage 4 was described recently, which includes the addition of radiolunate osteoarthritis (OA) or pancarpal OA.

Vender et al. noted that a longstanding scaphoid nonunion leads to a similar sequence of arthritic degeneration known as scaphoid nonunion advanced collapse (SNAC) ( Video 18-1 ). It differs, however, in that the articulation between the proximal scaphoid fragment and radius is spared from arthritic changes. The distal scaphoid fragment is no longer attached to the dorsal intercarpal (DIC) ligament, which allows it to fall into flexion, which causes incongruity between the distal scaphoid fragment and the corresponding articular surface of the radius. The site of initial degenerative change is between the radius and distal scaphoid fragment (stage 1), which stops at the site of nonunion. Narrowing of the lunocapitate joint (stage 2) occurs next, and with advanced midcarpal arthritis, narrowing of the capitate-distal scaphoid fragment (stage 3) occurs. The proximal radius scaphoid fragment and radiolunate joints remain normal, even with severe arthritis. These joints are preserved because both are spherical in nature, allowing perpendicular cartilage loading in all positions, and because the proximal scaphoid fragment is still attached to the lunate via an intact SL ligament.

In a study of 104 scaphoid nonunions, Inoue et al. noted a prevalence of arthritis in 22% of cases if the nonunion was 1 to 5 years old, 75% of cases in nonunions that were 5 to 9 years old, and 100% of cases in nonunions that were 10 years old or more. Osteoarthritic changes occurred initially at the scaphoid–radial styloid joint, which were manifested by radial styloid pointing and/or dorsal radioscaphoid osteophyte formation, later progressing to the midcarpal joint. OA at the scaphoid–radial styloid joint was significantly associated with a dorsal intercalated segmental instability (DISI) deformity. The overall incidence of DISI deformity of the wrist was 56%, and the frequency of DISI pattern increased with a longer duration of nonunion. There was no correlation between symptoms of pain and the severity of arthritis or the duration of nonunion, but there was a good correlation between the duration of nonunion and reduced grip strength or decreased wrist motion.

Nakamura et al. categorized scaphoid nonunions into 2 types based on 3-D CT scans: a volar type, in which the distal fragment overlaps the proximal fragment volarly; and a dorsal type, in which the distal fragment overlaps the proximal fragment dorsally.

Moritiomo et al. demonstrated that the fracture location of a scaphoid nonunion relates to the fracture displacement, development of DISI deformity, and changes in the contact area of the bones in the radiocarpal joint. Eleven patients with scaphoid nonunions were examined with 3-D CT scans. Two patterns of displacement of scaphoid nonunions were demonstrated: 1 volar and 1 dorsal. In the volar type, the distal fragment was displaced volarly relative to the proximal fragment and became close to the radial styloid with the proximal fragment extended, resulting in a humpback deformity. All patients with a volar-type scaphoid nonunion had a DISI deformity. Only a few of the patients with a dorsal-type scaphoid nonunion, mostly in longstanding nonunions, had a DISI deformity. The fracture line was generally distal to the dorsal apex of the ridge of the scaphoid in the volar-type fractures and proximal in the dorsal-type fractures. The location of the dorsal apex of the ridge of the scaphoid coincides with the location of the attachment of the proximal part of the DIC ligament, which is just distal to the attachment of the dorsal component of the SLIL. These ligaments, along with the dorsal radiocarpal ligament (DRCL), probably afford indirect dorsal stability of the scaphoid. In the volar-type scaphoid nonunion, the fracture line is distal to the attachment of the DIC ligament and the dorsal component of the SLIL, which may affect the stability of the distal fragment. This could explain why the proximal pole extends and the distal pole flexes, resulting in a DISI deformity in the volar-type scaphoid nonunion.

In the dorsal-type scaphoid nonunion, the ligamentous attachments remain on the distal fragment, which may offer some additional stability or ability for the distal fragment to resist flexion forces. In the cases with a longstanding scaphoid nonunion, however, even the dorsal-type scaphoid nonunion can develop a DISI deformity with degenerative changes at the articulation between the proximal fragment of the scaphoid and the capitate. They also looked at the proximity map, which is the visual representation of the distance from one bone to the nearest neighboring bone and gives a qualitative assessment of the inferred contact area between the bones. In the volar-type scaphoid nonunion, the proximity map of the distal fragment of the scaphoid on the radius shifted radially compared with a normal wrist, placing it closer to the radial styloid. They called this the styloid pattern ( Fig. 18.1 A–C). In the dorsal-type scaphoid nonunion, the proximity map of the distal fragment of the scaphoid on the radius shifted dorsally compared with a normal wrist, placing it closer to the dorsal lip of the scaphoid fossa of the radius. They called this the dorsal lip pattern .

Oka et al. studied the wrist kinematics in 13 patients with scaphoid nonunions during wrist flexion-extension and radioulnar deviation. Two clear patterns of interfragmentary motion of the scaphoid emerged based on the fracture location. In the mobile-type scaphoid nonunion (7 cases), the fracture was located distal to the apex of the scaphoid dorsal ridge and the distal scaphoid was unstable relative to the proximal scaphoid. The distal fragment showed a “book-opening” motion from wrist flexion to extension. In the stable-type scaphoid nonunion (6 cases), the fracture was located proximal to the scaphoid apex, and the interfragmentary motion was considerably less than with the distal type. In the displaced distal scaphoid fractures, the proximal fragment of the scaphoid, lunate, and triquetrum rotated into extension and supination. The distal fragment of the scaphoid and capitate translated dorsally without notable rotation. Most distal scaphoid nonunions had a DISI deformity pattern, whereas this occurred in only 1 case of a proximal fracture.

Diagnosis

The diagnosis of SLAC or SNAC wrist arthritis is made by history, physical examination, and radiographs. The wrist examination often reveals a joint effusion, dorsal-radial wrist swelling, and tenderness over the radioscaphoid joint. There may or may not be a positive scaphoid shift test. Chronic synovitis over the snuffbox may be misdiagnosed as a ganglion cyst. Wrist motion may be decreased, depending on the stage of degeneration. The definitive diagnosis is made radiographically. Standard posteroanterior, oblique, and lateral views should be performed. Marked changes as seen in SLAC and SNAC are easily identified. An AP grip view and radioulnar deviation views can magnify any SL diastasis. An MRI and/or CT scan may be useful to evaluate any midcarpal joint changes and DISI deformity, and to determine whether there is a styloid pattern or dorsal lip pattern of impingement.