Development and preliminary validation of guide apparatus for retrograde lag screw fixation of posterior column acetabular fracture

Abstract

Objective To devise the guide apparatus for percutaneous retrograde lag screw fixation of fracture in posterior column of the acetabulum and validate its feasibility and accuracy.Methods Based on spiral CT data of bilateral hemi-pelvis in 33 normal adults,three-dimensional pelvic models were reconstructed using Mimics 10.01 software.Virtual cylindrical implants were placed along the axis connecting the center of ischial tuberosity and the midpoint of most prominent bony points on anterior superior iliac spine and on posterior superior iliac spine and related anatomical parameters were measured.The guide apparatus was developed according to the measuring results and validated in Mimics software,pelvic specimens and cadaveric specimens.Results There was no implant failure.Mean distance between the most prominent bony points on anterior superior iliac spine and on posterior superior iliac spine was (156.26 ±7.28) mm in males,while (151.38 ±8.11) mm in females (t =2.574,P＜0.05) ; mean length of the virtual cylinder was (139.53 ± 7.56) mm in males,but (125.15 ± 11.17) mm in females (t =5.992,P ＜ 0.05) ; mean maximum diameter of the virtual cylinder was (12.19 ± 1.97) mm in males,while (10.19 ± 2.14) mm in females (t =3.923,P ＜ 0.05).In testifying safety of the guide apparatus,all obtained good results.Conclusions Posterior column screws can be placed along the axis.The guide apparatus based on the entry results of posterior column lag screws can assist percutaneous lag screw placement accurately. Key words: Acetabulum ; Fracture fixation, internal; Bone screws