Scaphoid Length Loss Following Nonunion Is Associated with Dorsal Intercalated Segment Instability

Abstract

Background Dorsal intercalated segment instability (DISI) in scaphoid nonunions is frequently attributed to fracture location relative to ligamentous attachments onto the scaphoid apex. We hypothesize scaphoid length loss to have a stronger correlation with DISI deformity than fracture location in patients with scaphoid nonunion. Questions/Purposes To investigate the correlation between (1) scaphoid length loss, (2) fracture location relative to the scaphoid apex, and (3) type of nonunion (Herbert classification) and DISI deformity in skeletally mature patients with scaphoid nonunion. Patients and Methods Twenty-seven cases of computed tomography (CT)-confirmed scaphoid nonunion (>6 months) were retrospectively included. Our primary outcome was the degree of DISI as measured by the radiolunate (RL) angle on CT. Scaphoid length loss was expressed as height-to-length (H/L) ratio. Fracture location was classified as proximal or distal to the scaphoid apex. Nonunions were classified as fibrous unions (type D1) or pseudoarthrosis (type D2). The correlation between RL angle, H/L ratio, fracture location, and nonunion type was evaluated. Results H/L ratio was the only factor associated with the degree of DISI as measured by RL angle. As scaphoid length loss increased (increasing H/L ratio), the RL angle increased. There was no significant difference in RL angle between fractures located proximal (30 degrees) or distal (28 degrees) to the scaphoid apex, or type D1 (31 degrees) versus type D2 (28 degrees) nonunions. There was no correlation between patient age, sex, or wrist side affected and RL angle. Conclusions Scaphoid length loss, rather than fracture location, is correlated to the degree of DISI deformity in patients with scaphoid nonunion. This highlights the importance of restoring scaphoid height when planning scaphoid nonunion reconstruction. Level of Evidence Level III, diagnostic study.

Keywords: DISI; dorsal intercalated segment instability; height-to-length ratio; nonunion; scaphoid.

Fig. 1

Flowchart of patient selection and inclusion. *Medical imaging archives were electronically only accessible from 2012 onward.

Fig. 2

(A) Scaphoid nonunion with fracture location distal to the scaphoid apex and good preservation of height. CT reconstruction along the scaphoid axis ( left ) and sagittal view ( right ) of a scaphoid nonunion distal to the scaphoid apex with good preservation of scaphoid height (H/L ratio 0.63) and limited DISI deformity (RL angle 23 degrees). Note the absence of bone resorption at the nonunion site, suggesting a fibrous integrity (Herbert type D1). (B) Scaphoid nonunion with fracture location proximal to the scaphoid apex with scaphoid shortening and increased radiolunate angle. CT reconstruction along the scaphoid axis ( left ) and sagittal view ( right ) of a scaphoid nonunion proximal to the scaphoid apex with scaphoid shortening (H/L ratio 0.90) and a greater degree of DISI deformity (RL angle 38 degrees). Note the scalloping and bone resorption suggesting a pseudoarthrosis (Herbert type D2) leading to the clear humpback deformity.