Dorsal intercalated segment instability (DISI) is characterized by the tear of the scapholunate ligament, leading to specific deformities of the wrist. Which deformity occurs in DISI, and which ligament is primarily affected?

A) "Swan neck" deformity; Triangular fibrocartilage complex (TFCC)
B) "Boutonniere" deformity; Extensor retinaculum
C) "Signet ring" deformity; Scapholunate ligament
D) "Humpback" deformity; Lunotriquetral ligament

In Dorsal Intercalated Segment Instability (DISI), the deformity that occurs is the 'Signet ring' deformity, which implicates the scapholunate ligament as the primarily affected ligament. This describes option (C) 'Signet ring' deformity; Scapholunate ligament.

Explanation:

In the context of wrist injuries, Dorsal Intercalated Segment Instability (DISI) is characterized by a specific deformity of the wrist, which is typically associated with a tear of the scapholunate ligament. The deformity that occurs in DISI is the "Signet ring" deformity, which indicates that the correct option is:

(C) "Signet ring" deformity; Scapholunate ligament

The scapholunate ligament is responsible for maintaining the proper alignment and motion between the scaphoid and lunate bones of the wrist. When it is torn, the result is a DISI deformity, characterized by a dorsiflexed lunate on lateral X-ray and associated carpal instability. Other mentioned deformities and ligaments, such as the swan neck deformity, boutonniere deformity, and humpback deformity, are associated with different conditions and different ligaments.