SNAC and SLAC of the wrist

SLAC of the wrist is a disorder resulting from altered stress around an unstable scaphoid, while SNAC results from a scaphoid fracture non-union.

Scapholunate advanced collapse (SLAC) and scaphoid non union advanced collapse (SNAC) are the most common patterns (55%) of wrist osteoarthritis.

See Also: Wrist Anatomy

SLAC of the wrist:

SLAC of the wrist stands for Scaphoid Lunate Advanced Collapse.

It has been proposed by Watson and associates to define the progression of degenerative changes secondary to SL (Scapholunate) dissociation.

Causes of SLAC

1. Traumatic: Scapholunate ligament rupture.
2. calcium pyrophosphate dihydrate crystal deposition disease (CPPD): Pyrophosphate leading to SLL 1 tear.
3. Preiser’s disease: Idiopathic avascular scaphoid necrosis.
4. Kienböck’s disease: Avascular necrosis of the lunate.
5. Intra-articular fractures: Involving the radioscaphoid or capitolunate joint.

Clinically:

• Difficulty bearing weight with the hand.
• Pain in region of scapholunate interval.
• Progressive weakness of affected hand.
• Wrist stiffness.
• Watson scaphoid shift test is used to examine the patient with SLAC of the wrist.

See Also: Watson scaphoid shift test

Stages of SLAC of the wrist:

There were only 3 stages of SLAC of the wrist identified by Watson, then a recent investigation by Lluch identified five stages of this degenerative.

Stages	Degenerative Changes Location
I	Radioscaphoid joint
II	Scaphocapitate joint
III	Lunocapitate joint
IV	Triquetrohamate joint
V	Radiolunate joint

SLAC Treatment:

Nonoperative:

In mild disease:

• Non-steroidal anti-inflammatory drugs (NSAIDs)
• Wrist splinting.
• Corticosteroid injections.

Operative Treatment:

Stage	Procedure
Stage I	– Radial styloidectomy + scaphoid stabilization. – Posterior interosseous nerve and anterior interosseous nerve denervation
Stage II	– Proximal row corpectomy – Scaphoid excision and Four-corner fusion
Stage III	– Scaphoid excision and Four-corner fusion – Wrist arthrodesis

SNAC of the wrist:

SNAC stands for Scaphoid Nonunion Advanced Collapse. It was first described by Vender et al. in 1987

It’s a characteristic progression of posttraumatic osteoarthrosis that result from untreated, chronic scaphoid nonunion. The radioscaphoid joint is affected first, followed by the scaphocapitate and lunocapitate; the radiolunate joint is spared the longest

Stages of SNAC:

Stages	Degenerative Changes Location
I	Radioscaphoid joint arthritis
II	Involvement of Scaphocapitate joint
III	Lunocapitate joint

SNAC Treatment

Nonoperative Treatment:

Nonoperative Treatment for SNAC of the wrist is indicated in patients with low functioning demands.

Operative Treatment:

Stage	Procedure
Stage I	– Radial styloidectomy + scapholunate reduction and stabilization.
Stage II	– Proximal row corpectomy – Four-corner fusion – Wrist arthrodesis
Stage III	– Proximal row corpectomy – Four-corner fusion – Wrist arthrodesis

In stage I, the earliest osteoarthritic changes will differ among SLAC and scaphoid nonunion advanced collapse (SNAC) wrists.
In SLAC of the wrists, osteoarthritis includes the proximal scaphoid and the dorsal rim of the radius.
In SNAC of the wrists, osteoarthritis develops between the distal scaphoid and the radial styloid, while the proximal fragment of the scaphoid remains free of pathology.

References

• Kompoliti E, Prodromou M, Karantanas AH. SLAC and SNAC Wrist: The Top Five Things That General Radiologists Need to Know. Tomography. 2021 Sep 23;7(4):488-503. doi: 10.3390/tomography7040042. PMID: 34698283; PMCID: PMC8544666.
• Vender M.I., Watson H.K., Wiener B.D., Black D.M. Degenerative change in symptomatic scaphoid nonunion. J. Hand Surg. 1987;12:514–519. doi: 10.1016/S0363-5023(87)80198-3.
• Watson HK, Ballet FL: The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis, J Hand Surg Am 9:358–365, 1984.