Abstract:

Objective　To provide anatomical basis for lag screw internal fixation for acetabular posterior column fracture via the lesser sciatic notch.　Methods　Pelvic CT scanning data from 60 adults（30 males and 30 females）were imported into Mimics14.1 for 3D image reconstruction. The direction of longitudinal axis of the acetabular posterior column was observed in the three-dimensional pelvic model, screw placement was simulated, and the point where the screw pieced out was determined. Measurements were made about the length of the longitudinal axis, α angle between the longitudinal axis and the frontal plane, and β angle between the long axis and the sagittal plane.　Results　The point where the longitudinal axis of the acetabular posterior column  terminated inferiorly was located at the midpoint of the sciatic notch, and the point where it  terminates superiorlyat the midpoint between the rear end of arcuate line and anterior superior spine. The length of the longitudinal axis was (105.04±4.29) mm (male) and(101.80±3.20)mm (female), α angle 33.41°±2.18° (male) and 31.56°±2.71°(female), β angle 21.74°±1.19°(male) and 19.15°±1.24°(female). The bone cortex thickness at the screw entrance point was(5.54±0.46)mm, and that of lateral pelvic and of acetabular side was (1.45±0.13)mm and(1.04±0.10)mm, respectively.　Conclusions　The three-dimensional reconstruction model for simulation of lag screw internal fixation via the lesser sciatic notch is a speedy and accurate way for measurement of the screw path parameters as well as for preoperative evaluation. Using the model to place screws for fixation of posterior column fracture proves easy and safe.

Key words: Acetabulum, Posterior column fracture, Lag screws, Internal fixation