Presentation
Fell on an outstretched hand 7 months ago, delay in seeking treatment.
Patient Data
scaphoid waist nonunion fracture associated with volar subluxation of the distal scaphoid fragment producing a secondary humpback-type deformity
bone marrow edema/bruise along with scaphoid proximal and distal poles
stretched but intact dorsal fibers of the scapholunate ligament
abnormally increased fluid signal and fibers discontinuity along with scapholunate ligament membranous and volar side fibers could be due to partial tearing
the lunate is dorsally tilted and associated with increased capitolunate angle measuring about 54o (normal <30o) and scapholunate angle measuring about 95o (normal <60o) suggesting dorsal intercalated segment instability (DISI)
Case Discussion
Imaging findings are consistent with the scaphoid waist nonunion fracture producing a humpback deformity and associated with dorsal intercalated segment instability (DISI).
Humpback deformity of the scaphoid results from volar angulation of the proximal and distal poles of the scaphoid in the setting of scaphoid fracture through the waist 1. The dorsal component forms a 'humpback', which can be palpated.
Dorsal intercalated segment instability (DISI) is a form of carpal instability featuring dorsal tilt of the lunate. It occurs mainly after the disruption of the scapholunate ligament and is more often encountered than volar intercalated segment instability (VISI).
On the sagittal MRI images with the wrist in a neutral position, DISI typically demonstrates dorsal tilt of the lunate with both of the following presents:
scapholunate angle >60º: a sign of scapholunate ligament dissociation
capitolunate angle >30º: the capitate is displaced posteriorly compared to the distal radius