Scaphoid Nonunion Advanced Collapse (SNAC)

Watson Classification for SNAC Wrist:

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Comparison with SLAC Staging:

Both SNAC and SLAC follow the same arthritic progression pattern. The only difference is the initiating event: SNAC from scaphoid nonunion, SLAC from scapholunate ligament injury. Treatment algorithms are identical.

PA View Findings:

Scapholunate widening or Terry-Thomas sign if concurrent SL injury. Scaphoid nonunion line with sclerosis or cystic change. Shortened scaphoid with humpback deformity. Radioscaphoid joint space narrowing in Stage II or III. Styloid spurring in Stage I or higher.

Lateral View Findings:

DISI pattern - increased scapholunate angle greater than 70 degrees. Increased capitolunate angle greater than 30 degrees (normal is less than 15 degrees). Volar flexion of distal scaphoid fragment.

CT Scan:

Best for assessing nonunion site, bone stock, and cystic changes. Essential for surgical planning - defines fragment size and quality. 3D reconstruction helpful for complex cases.

MRI:

Assesses proximal pole vascularity - important for reconstruction planning. Identifies early AVN before radiographic changes. Limited role once SNAC established.

Non-operative Management:

• Activity modification
• NSAIDs, wrist splinting
• Corticosteroid injections (temporary relief)
• Rarely successful long-term once SNAC established

Non-operative management is primarily for patients who are poor surgical candidates or those with minimal symptoms. It does not alter the natural history of progression.

Operative Management - Decision Algorithm:

Surgical Options by Stage:

Proximal Row Carpectomy (PRC):

Removes the scaphoid, lunate, and triquetrum. The capitate head articulates with the lunate fossa of the radius creating a neoconcentric joint. Simpler procedure with no fusion to heal but requires pristine capitate head.

Scaphoid Excision and Four-Corner Fusion (SE4CF):

Removes the scaphoid and fuses capitate, lunate, hamate, and triquetrum into a single unit. This unit articulates with the preserved radiolunate joint. More complex with fusion site to heal but works even with capitate damage.

Total Wrist Arthrodesis:

Complete fusion of radiocarpal and midcarpal joints. Used for failed motion-preserving surgery, pancarpal arthritis, or high-demand patients requiring maximum strength.

Wrist denervation (PIN ± AIN neurectomy):

A pain-relieving option that preserves ALL wrist motion and does not "burn bridges" to later salvage. Partial denervation resects the terminal articular branches of the posterior interosseous nerve (PIN) in the floor of the fourth dorsal compartment, often combined with the anterior interosseous nerve (AIN); total (Wilhelm) denervation is more extensive. It treats pain only — it does NOT correct the carpal malalignment or instability, so it suits patients who prioritise retaining motion, are lower-demand, or want a temporising measure. A diagnostic local-anaesthetic block of the PIN/AIN that abolishes the pain predicts a good response and is used for selection. Pain relief can be incomplete or diminish over time, after which a standard salvage (PRC/SE4CF/fusion) remains available.

Limited (alternative) intercarpal fusions:

Scaphoid excision + four-corner fusion is the standard, but to reduce nonunion, hardware impingement and stiffness, several limited variants are used: scaphoid excision + capitolunate (two-corner) fusion (± triquetrum excision), and three-corner fusion (capitate-lunate-triquetrum, excising the hamate). These remove fewer/awkward joints from the fusion mass and may preserve slightly more radiocarpal motion; comparative outcomes are broadly similar to SE4CF, and the choice is driven by surgeon preference and fixation method. All depend, like SE4CF, on a spared radiolunate joint.