Causes / typical injury mechanism: Scaphoid nonunion advanced collapse (SNAC) describes a specific, predictable pattern of arthritis within the wrist that follows a nonunion of the scaphoid. The mechanism of scaphoid fracture and subsequent nonunion is highly varied but typically results from trauma involving an axial load across a hyper-dorsiflexed, pronated, and ulnarly deviated wrist. The arthritic changes begin at the radial side of the scaphoid and radial styloid and eventually progress to pancarpal / midcarpal arthritis.

Classic history and presentation: Patients will present with stiffness in extension and radial deviation, reduced grip strength, and reduced pinch strength greater than 6 months following scaphoid fracture with subsequent nonunion.

Prevalence: Scaphoid fractures have a prevalence of 8 per 100 000 females, 38 per 100 000 males. Ninety-seven percent of those who develop subsequent nonunion develop SNAC within 5 years.

• Age – Third decade of life
• Sex / gender – 2:1 male to female

Risk factors: Scaphoid nonunion, male sex, smoking, preexisting arthritis, proximal pole necrosis, delayed presentation following scaphoid fracture.

Pathophysiology: Altered biomechanics of the carpus following scaphoid nonunion lead to altered loading properties and a predictable pattern of carpal arthritis.

Radiographic classification system:

• Stage 1: Arthritic changes begin at the radial side of the scaphoid and radial styloid
• Stage 2: Additional scaphocapitate arthritis
• Stage 3: Periscaphoid arthritis