Percutaneous retrograde screw fixation for posterior column fractures of acetabulum: a study by virtual three-dimensional model

Abstract

Objective To provide evidence of applied anatomy for the placement of pereutaneoas retrograde lag screws in the treatment of posterior column fractures of acetabulum. Methods Virtual three-dimensional models were reconstructed from computed tomography (CT) scans obtained from 60 adult patients without any bony problem. Virtual cylindrical implants were placed intraosscously into the posterior column of acetabulum. The maximum diameter, length and insertion direction were determined for screws.The distance between the insertion point (A) of virtual cylindrical implant and the distal end of the ischiadic tuberosity (B) was measured. In the same model, cross-sections of the pelvic posterior column was made at interval of 1 cm to measure their diameters. Results One hundred and twenty (58 male, 62 female) hemi-pelvic models were obtained. The mean maximum diameter of virtual cylindrical implant was 13. 16 ±1.45 mm and the mean angles to the transverse, coronal and sagittal planes were 72.02°± 6. 05°, 14. 71°±6. 98° and 8.61°±3.96° respectively. The insertion point was on the central line between the medial and lateral margins of ischiadic tuberosity. The distance between points A and B was 15.18 ± 1.97 mm. The smallest diameter of the posterior column was larger than the maximum diameter of the corresponding virtual cylindrical implant. Differences in the diameter, length, angle to sagittal plane of virtual cylindrical implant between the male and female were of statistical significance ( P ＜ 0. 001 ). Conclusions The posterior column can accommodate screws of 7.3 mm, but the insertion angle should vary from the male to female. The screw size for percutaneous fixation of posterior column fractures of aeetabulum should not be based solely on the measurement of cross-sectional diameter. Key words: Acetabulum; Fracture fixation, internal; Anatomy