The scapholunate ligament maintains the proximal pole of the scaphoid adjacent to the lunate (scapholunate gap) and stabilizes the palmar rotation force of the scaphoid against the dorsal rotation force of the lunate (scapholunate angle). This structure is injured when the wrist hyperextension mechanism that might result in a scaphoid fracture instead disrupts the adjacent scapholunate ligament. This may occur as a partial tear with pain but no instability, best treated by arthroscopic debridement. More complete injuries may result in dynamic scapholunate instability, with normal plain x-rays, but pain with use and increase in the scapholunate gap with wrist in ulnar deviation with a strongly clenched fist. Complete disruption of the scapholunate ligament results in an instability pattern visible on plain x-rays with widening of the scapholunate gap, palmar flexion of the scaphoid and dorsiflexion of the lunate - referr ed to as scapholunate dissociation with DISI (Dorsal Intercalary Segment Instability). Acute repair of scapholunate injuries associated with instability may be possible, and many surgeons augment this with some form of wrist capsulodesis. Results of repair are unpredictable and often disappointing if delayed months after the initial injury. Over time, the abnormal position of the scaphoid and lunate result in degenerative changes at the radioscaphoid, midcarpal, and then radiolunate joints and, referred to as scapholunate advanced collapse or SLAC wrist (Fig. 9a). Salvage procedures include, among others, proximal row carpectomy, scaphoid excision with midcarpal fusion, and full wrist fusion.

Scapholunate Ligament Injuries
 

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