Figure 4.

Measurement of the articular involvement of posterior malleolar fractures on 3D CT image is shown. (a) When using 3D CT linear measurement method, on the lateral border of the tibial plafond, if we assume the distance between front and back points of the residual articular surface is i and the distance between posterior malleolar fracture line and back point is ii, then the percentage of involved articular surface is ii/i + ii. (b) When using 3D CT surface measurement method, the surface boundary of the posterior malleolar fragment (ii) and residual articular surface (i) was delineated manually. Each surface area was calculated automatically by the software. Then, the ratio of the involved fragment area is ii/i + ii.