Evaluation of the sigmoid notch with computed tomography following intra-articular distal radius fracture

A classification system for disruption patterns of the sigmoid notch of the radius associated with distal radius fractures has not been established. Using plain x-rays and corresponding computed tomography (CT) scans we characterized and quantified the types of sigmoid notch involvement in 20 consecutive distal radius fractures with radiocarpal joint extension. Plain radiographs revealed fracture extension into the sigmoid notch in only 7 cases (35%) and the CT scans demonstrated fracture extension into the sigmoid notch in 13 cases (65%). Of the 13 fractures with sigmoid notch involvement, 9 (69%) were displaced and 4 (31%) were nondisplaced. Sigmoid notch articular step-off (n = 7) and gapping (n = 9) were detectable on the CT scans but not on the x-rays. Plain x-rays appear to underestimate sigmoid notch involvement following distal radius fractures. In addition, CT appears to be a superior diagnostic modality for quantifying sigmoid notch fracture step-off and articular gapping.