Scapholunate Advanced Collapse (SLAC) wrist follows a highly predictable pattern of progressive joint destruction. Which specific carpal articulation is characteristically spared from osteoarthritis in this condition, allowing for salvage procedures like a four-corner fusion?

Explanation:
The correct option is c. SLAC wrist begins with an untreated scapholunate ligament tear. The scaphoid flexes, causing point loading and initial osteoarthritis at the radial styloid (Stage I), progressing to the entire radioscaphoid facet (Stage II). The capitate then migrates proximally between the dissociated scaphoid and lunate, destroying the capitolunate joint (Stage III). However, because the short radiolunate ligament almost always remains perfectly intact, the lunate maintains its congruency within the lunate fossa of the distal radius. Therefore, the radiolunate joint is remarkably spared. A four-corner fusion (capitate, hamate, lunate, triquetrum) with scaphoid excision capitalizes on this spared joint, preserving functional wrist flexion/extension. Reference: Watson HK, Ballet FL. The SLAC wrist: scapholunate advanced collapse pattern of osteoarthritis. J Hand Surg Am.