SLAC and SNAC Wrist



This chapter reviews the etiology, evaluation, and treatment of the most common forms of posttraumatic arthritis of the wrist: scapholunate advanced collapse (SLAC) and scaphoid nonunion advanced collapse (SNAC). Their radiographic appearance and progression are classic and predictable, but clinical symptoms do not always correlate with the radiographic findings. Common treatment recommendations include splinting, activity modification, nonsteroidal anti-inflammatory drugs (NSAIDs), and steroid injections. When conservative treatments are not successful, surgical procedures are available to provide pain relief and maintain some degree of wrist motion; the most common procedures are proximal row carpectomy and limited wrist arthrodesis.


Radiographic findings support the diagnosis and stage of disease, but final staging is confirmed during surgery.

Conservative therapies should be exhausted before offering surgical treatment.

The goal of surgical treatment is to provide pain relief while preserving wrist motion.

The various surgical options should be considered, taking into account the patients’ needs and desires.


Wrist Denervation:

  • Preoperative local anesthetic injections help predict postoperative pain relief.

Proximal Row Carpectomy:

  • Evaluate head of capitate intraoperatively for arthritic changes, and be prepared to alter procedure if necessary.

  • Maintain integrity of volar extrinsic wrist ligaments because these are important for stability.

  • Check for impingement on radial styloid with radial deviation.

Scaphoid Excision and Limited Wrist Fusion (Capito-hamate-lunotriquetral or Capitolunate):

  • Treatment typically indicated in Stage III disease or Stage II disease in a manual laborer.

  • Preserve volar extrinsic wrist ligaments during scaphoid removal.

  • Establish collinear alignment of capitate on lunate prior to definitive fixation.

  • Check for impingement on radial styloid in radial deviation and on distal radius in wrist extension.




Multiple forms of wrist arthritis can lead to pain and loss of motion. SLAC (scaphoid lunate advanced collapse) and SNAC (scaphoid nonunion advanced collapse) are the most common patterns seen. The scaphoid accounts for 95% of degenerative/traumatic arthritis in the wrist, with 55% involving the radioscaphoid joint (SLAC pattern). This is not surprising because the most common ligamentous injury involving the wrist is the scapholunate ligament rupture. The predictable sequence of degenerative changes following scapholunate dissociation is a result of articular alignment problems in the scaphoid, lunate, and radius. A disruption in the biomechanical relationship of the proximal carpal row, as occurs with scapholunate ligament disruption or scaphoid fracture, allows the unrestrained scaphoid (or distal pole in a scaphoid fracture) to assume a flexed position. This creates an abnormal wear pattern between the scaphoid and the radius. The radiolunate joint is usually spared (until the latest stages of arthritis), creating the potential for future motion-preserving reconstructive procedures.

Although the true natural history of untreated scapholunate ligament injuries and scaphoid fractures is unknown (a prospective study would be unethical and those who present late are generally only the symptomatic patients, rather than all patients with these injuries), the predictable and progressive nature of the resulting degenerative changes is well accepted. This pattern of wrist osteoarthritis has been termed scapholunate advanced collapse wrist by Watson and Ballet. Their evaluation of 4,000 wrist radiographs clearly establishes the pattern of sequential changes now reflected in their staging system ( Fig. 5-1 ). In normal wrist biomechanics, the proximal carpal row moves in balanced equilibrium with the scaphoid linking the proximal and distal carpal rows. With normal kinematics, the scaphoid tries to assume a flexed posture. The longitudinal force of the capitate is positioned eccentrically in the lunate, creating a force causing the lunate and thus the triquetrum to extend. As long as the link between the scaphoid and lunate is intact these forces counteract each other, keeping the proximal row in alignment. When the link is disrupted, either through SL ligament disruption or scaphoid fracture, the scaphoid is allowed to flex without restraint and the lunate and triquetrum are allowed to extend. This carpal alignment pattern can be visualized on a lateral wrist radiograph and is termed DISI (dorsal intercalated segment instability) deformity. The shape of the lunate fossa of the radius allows the lunate to assume this extended posture without altering the normal contact and wear patterns, which explains the preservation of the radiolunate joint, even in advanced cases of SLAC pattern arthritis. The natural shape of the scaphoid and the scaphoid fossa of the radius, however, require precise alignment for smooth congruous motion. When the normal alignment is disrupted, an abnormal wear pattern develops between the scaphoid and radius.

Figure 5-1

Schematic diagram of progressive arthritic changes seen in SLAC arthritis. A: Stage I—Involvement of the radial styloid and styloscaphoid region. B: Stage II—Involvement of the radioscaphoid joint. C: Stage III—Involvement of the capitolunate joint.

With chronic scapholunate ligament dissociation, these abnormal wear patterns progress to arthritis in a predictable and well-described pattern. The first radiographic changes begin at the most radial portion of the radioscaphoid joint between the radial styloid and the radial portion of the scaphoid, near the waist (Stage I). These changes then progress proximally to involve the proximal pole of the scaphoid and the scaphoid fossa of the radius (Stage II). The cartilage space is lost, resulting in sclerosis, followed by the development of osteophytes and subchondral cysts. The degenerative process next moves to the capitolunate articulation of the midcarpal joint. With the collapse of the scaphoid into a flexed position, it no longer spans across both the proximal and distal carpal rows. The resulting loss of this important buttress allows collapse of the normal carpal relationships. As wrist height decreases, the capitate head migrates proximally between the dissociating scaphoid and lunate. The extended posture of the lunate creates abnormal wear and degeneration between the head of the shifting capitate and the distal lunate, resulting in midcarpal arthritis (Stage III). The lunate eventually becomes fixed in an extended position, creating a static DISI deformity and further compromising wrist motion.

Scaphoid nonunion can lead to a similar progressive pattern of arthritis. When a scaphoid fracture does not heal, the scaphoid assumes a collapsed posture around the fracture site. The distal unrestrained scaphoid portion flexes, while the proximal scaphoid portion, through the intact scapholunate ligament, follows the lunate into extension. This, along with resorption of the bone edges along the volar aspect of the fracture, will produce a characteristic humpback deformity. The extended lunate (now with the extended proximal scaphoid fragment) creates a DISI deformity visible on a lateral wrist radiograph. From the resulting joint incongruities associated with the nonunion and from the altered stress patterns resulting from loss of the biomechanical balance, degenerative arthritic changes termed scaphoid nonunion advanced collapse wrist will develop. The SNAC and SLAC patterns have some subtle differences. Stage I SNAC has the same degenerative pattern as seen in the SLAC wrist scenario, and preliminary changes involve the radial styloid and the distal styloscaphoid regions. In contrast to the SLAC pattern of arthritis, since the link between the proximal scaphoid and lunate remains intact (SL ligament intact), the proximal radioscaphoid joint is preserved and the degenerative changes progress to the midcarpal joint. Changes are first noted along the proximal scaphocapitate joint (Stage II), followed by the capitolunate joint (Stage III) ( Fig. 5-2 ).

Figure 5-2

Schematic diagram of progressive arthritic changes seen in SNAC arthritis. A: Stage I—Involvement of the radial styloid and the styloscaphoid region. B: Stage II—Involvement of the proximal scaphocapitate joint. C: Stage III—Involvement of the capitolunate joint.

In general, there are two surgical treatment options once arthritic changes have developed: proximal row carpectomy and limited wrist arthrodesis. There is ongoing controversy as to which procedure is best and both have their advocates and detractors. These treatment options do not change significantly through most stages of the arthritic process; therefore, conservative treatment should be instituted prior to performing a reconstructive procedure. In other words, delay of definitive surgical intervention once arthritis has developed does not seem to burn any bridges. Conservative measures include splinting, the use of nonsteroidal anti-inflammatory drugs (NSAIDs), steroid injections, and occasionally a steroid dose pack. In addition, surgical procedures directed at pain relief without addressing the underlying arthritic process may play a temporizing role in selected patients.


The history and physical examination, supplemented with plain radiographs, are typically adequate for diagnosis and treatment. These radiographic images should be evaluated to rule out other sources of wrist pathology. Typical radiographic findings include either a scapholunate diastasis or scaphoid fracture with varying degrees of arthritic degeneration, as described earlier. Further diagnostic studies add little to the decision-making process. The most common clinical symptoms in a patient with wrist arthritis are loss of motion, swelling, and pain, especially with activity. Point tenderness over the scapholunate interval or radiocarpal joint, and crepitus with wrist motion, further support the diagnosis. Most patients will report some relief of discomfort with activity modification, NSAIDs, splinting, and an intraarticular injection of lidocaine/steroid. Further treatment is directed by recalcitrant symptoms, most notably pain, and the desire for a definitive procedure.

The goals of surgical treatment include pain relief, motion preservation, strength preservation, and longevity. Wrist denervation may be effective in relieving, although not eliminating, symptoms and is discussed in more detail in Chapter 3 . In symptomatic patients who do not want to go through an extensive surgical procedure and recovery time, radial styloidectomy (with excision of the distal scaphoid in the SNAC wrist) may provide good temporary pain relief with a minimal recovery period when the arthritis is confined to the radial styloid. When definitive treatment is desired, the scaphoid is removed and the wrist is reconstructed by either excision of the remainder of the proximal carpal row (proximal row carpectomy) or a midcarpal fusion, either involving the capitolunate joint by itself or the capito-hamate-lunate-triquetrum articulations. Both procedures remove the arthritic scaphoid and thus provide pain relief and preserve some motion through the radiolunate joint. Although the motion is not that of an uninjured wrist, the literature illustrates it is adequate for most activities. Ryu and colleagues evaluated the range of motion required for daily activities. Ideal wrist motion is in the range of 60 degrees of flexion, 60 degrees of extension, 20 degrees of radial deviation, and 40 degrees ulnar deviation. Although the motion required for work and recreational activities may be in this range, the amount of motion required to perform activities of daily living is much less, and the amount of motion used to accomplish these activities is typically greater than that which is really needed.


The treatment options are basically the same for a wrist with SLAC or SNAC patterns of arthritis. Because these are chronic degenerative processes, there is no urgency for surgical intervention and conservative options should be exhausted. I usually offer patients a steroid injection into the radiocarpal joint and a splint for immobilization because this will decrease the synovitis in the wrist and often improve symptoms, regardless of whether patients have early or advanced arthritic changes. This is completed using a mixture of local anesthetic and steroids (I prefer 40 mg of triamcinolone and 10 mg of plain 1% lidocaine). This is injected dorsally into the radiocarpal joint at the soft spot just proximal to the scapholunate interval (corresponding to the 3-4 arthroscopic portal). This often will provide significant pain relief and, in some cases, at least temporary complete resolution of symptoms. More likely, the symptoms will improve for a time, only to return once the body has absorbed the injected steroids. The fact that patients often present with advanced radiographic changes but only recent development of symptoms, however, demonstrates that significant pathologic changes in the joint do not necessarily correlate with severity of symptoms. In a patient with advanced, longstanding arthritis, but minimal symptoms until a recent inciting event, a steroid injection will often get them back to their previous status, eliminating, or at least delaying, the need for surgical intervention.

When conservative treatment does not relieve symptoms, several surgical options are available and are similar, whether the arthritis is an SLAC or an SNAC pattern. The stage of the disease does, however, influence these options. For early Stage I disease, radial styloidectomy (and possibly excision of the distal scaphoid in SNAC arthritis) is the simplest option. The advantage of this procedure is the minimal recovery time and minimal immobilization. Although this is typically not a definitive procedure, it may provide a pain-free interval and enable the patient to continue to work. Partial wrist denervation with removal of the posterior interosseous nerve (PIN) and anterior interosseous nerve (AIN) through a single dorsal incision can provide pain relief with minimal added morbidity. Prior to the procedure, local anesthetic blocks can be administered to predict the potential effectiveness of the denervation procedure.

The more traditional procedures for SLAC and SNAC arthritis involve limited wrist arthrodesis and proximal row carpectomy (PRC). These procedures involve excision of the scaphoid but vary in the management of the remainder of the proximal row. When the deformity is limited to the radioscaphoid joint (Stage I and II), and the extrinsic volar wrist ligaments are competent, a proximal row carpectomy may be performed. This procedure takes advantage of the preserved lunate fossa of the radius and capitate head by allowing the head of the capitate to articulate in the lunate fossa of the radius. The complex wrist joint is thus converted into a ball and socket type of joint with slightly mismatched articular surfaces and altered carpal kinematics. Although this would seem suboptimal, it is an effective procedure with both short- and long-term results illustrating its effectiveness and reliability. When the midcarpal joint (the capitate head) is involved, the PRC becomes less predictable but can still be performed with interposition of a capsular flap between the arthritic head of the capitate and the lunate fossa of the radius. Alternatively, the SLAC wrist procedure (scaphoid excision and arthrodesis of the capitato-hamate-lunato-triquetrum joints) can be performed for Stage I and II deformities suitable for PRC but has typically been recommended for Stage III deformity (capitate head involvement). This procedure still requires a normal radiolunate joint but is not affected by midcarpal involvement because this area is included in the arthrodesis. A similar strategy to stabilize the midcarpal joint following scaphoid excision is to fuse only the capitolunate joint, leaving the hamate and triquetrum out of the fusion mass. This can be performed with or without excision of the triquetrum. Advocates of capitolunate arthrodesis cite preservation of the ulnar midcarpal joint and decreased amount of bone graft required as benefits of this procedure when compared to the four-bone fusion. When the triquetrum is excised, the ligamentous constraint between the capitate and hamate will prevent proximal migration of the hamate. In addition, this has been shown in the cadaver model to allow for significant increase in radial deviation, but at the cost of grater contact pressures in the radiolunate joint. The clinical significance of this has not been determined, but the assumption is the potential progression to radiographic and possibly clinical symptoms of arthritis. The benefits of the capitolunate arthrodesis are limited to the technical portions of the procedure because the postoperative recovery and motion are similar.

As described previously, the typical SLAC and SNAC patterns of arthritis spare the lunate fossa of the radius. If, however, on intraoperative inspection of the lunate fossa, significant arthritic changes are noted, a limited wrist arthrodesis will not be successful. In this case, total wrist fusion would be the procedure of choice. The possibility of shifting the surgical plan based on intraoperative findings should, of course, be discussed beforehand.


Radial Styloidectomy

When performed as an isolated procedure, I prefer a volar approach along the region of the radial artery. After incising through the skin, the radial artery is identified and mobilized in an ulnar direction. The dissection is then carried to the tip of the radial styloid and the first dorsal compartment tendons are mobilized, exposing the radial styloid. Removal of the distal 3 to 4 mm of the radial styloid is completed with a sharp osteotome, taking care not to disrupt the volar radiocarpal wrist ligaments. Their origin is typically several millimeters from the tip of the arthritic styloid and almost always less than 1 cm. The incision is closed and the patient is placed in a volar plaster wrist splint for comfort. Alternatively, this procedure can be performed arthroscopically through a 1-2 portal for the shaver and the 3-4 portal for the scope. The amount of bone removed and the origin of the volar wrist ligaments can be visualized to ensure their preservation. At the first postoperative visit (approximately 1 week), the patient is fitted with a custom orthoplast splint and allowed to return to activities as tolerated.

Distal Scaphoid Excision Combined with Radial Styloidectomy (SNAC Arthritis)

When the radial styloidectomy is performed in conjunction with other procedures, the procedure is completed through the standard dorsal approach. A longitudinal incision is made over the third dorsal compartment, just ulnar to Lister’s tubercle. Subcutaneous flaps are elevated at the level of the extensor retinaculum. The third compartment is opened and the extensor pollicis longus (EPL) tendon is mobilized in a radial direction. The second and fourth compartment tendons are elevated off the wrist capsule and a ligament-sparing capsulotomy, as described by Berger, Bishop, and Bettinger, is performed. The attachments of the dorsal intercarpal ligament are removed from the distal scaphoid and the distal scaphoid is removed by circumferential dissection, taking care to minimize trauma to the volar wrist capsule and the volar radioscaphocapitate ligament. With the degenerative changes occurring around the scaphoid, as typically exist with a SNAC wrist, it is often difficult to remove and may require sectioning with an osteotome or oscillating saw. Fluoroscopy should be used to confirm the correct level prior to cutting and that the entire distal pole has been removed.

The radial styloid can now be visualized and removed in a similar manner as previously described, again taking care to preserve the radioscaphocapitate ligament. The patient is placed in a volar thumb spica plaster splint, which is converted to an orthoplast thumb spica splint at the first postoperative visit, and allowed to resume activities as tolerated.

Partial Wrist Denervation

Partial wrist denervation, as described by Weinstein and Berger, is completed with a longitudinal incision between the radius and ulna, beginning 2 cm proximal to the ulnar head. The digital extensor communis tendons are elevated and retracted in a radial direction, exposing the dorsal surface of the interosseous membrane. The PIN is identified and a 2-cm segment is sharply excised. The posterior interosseous artery is protected and a longitudinal incision is made through the interosseous membrane. The anterior interosseous artery and nerve are identified along the pronator quadratus muscle. The AIN is followed and a 2-cm segment is removed distal to the last motor branch. The wound is closed and a soft dressing or volar wrist splint is applied. The patient is allowed to resume activities as tolerated.

Proximal Row Carpectomy

The procedure can be performed through either a longitudinal or a transverse incision ( Fig. 5-3 ). Flaps are elevated off the extensor retinaculum and the third dorsal compartment is opened. The EPL tendon is retracted in a radial direction. The second and fourth compartment tendons are elevated off the wrist capsule. Along the radial aspect of the floor of the fourth compartment, the terminal portion of the posterior interosseous nerve is identified and a 2-cm segment is excised. A ligament-sparing capsulotomy is performed, exposing the carpus. The lunate fossa and the midcarpal joint are inspected. If they are free of arthritic changes, the procedure proceeds. If however, arthritic changes in the proximal capitate are noted, the surgeon must decide whether to change the procedure to a limited wrist arthrodesis or proceed with a PRC and use a capsular flap as interposition material between the arthritic head of the capitate and the lunate fossa as previously discussed.

Jan 26, 2019 | Posted by in ORTHOPEDIC | Comments Off on SLAC and SNAC Wrist

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