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Published on: May 20, 2019
Magic screw fixation for acetabular posterior column fractures: a CT-based digital anatomical study and biomechanical
Min Wu1, Xiangqin Yang1, Yan Huang1
1Department of Radiology, The People's Hospital of Yubei District of Chongqing City, Yubei District, Chongqing, 401120, China.
Objective:
To explore and quantify the key parameters for placement of the magic screw (MS) in the acetabulum posterior column and compare the biomechanical stability of MS, retrograde lag screw (RLS), single reconstruction plate screw system (SRPS), and double reconstruction plate screw system (DRPS) in the fixation of acetabular posterior column fractures (APCF).
Methods:
A total of 120 pelvic CT datasets from healthy adults (60 males, 60 females) were retrospectively analyzed for three-dimensional reconstruction and virtual MS placement, with gender differences in key placement parameters measured and verified by senior orthopedic surgeons. A finite element model of APCF was established to compare the biomechanical properties of MS, RLS, SRPS, and DRPS under three physiological loading modes, with von Mises stress and maximum displacement as key evaluation indices.
Results:
The MS skin entry point (~ 30 mm posterior to ASIS) showed no gender differences in anteroposterior (males 32.92 ± 5.35 mm vs. females 29.51 ± 11.50 mm, P > 0.05) or craniocaudal (males 7.51 ± 5.51 mm vs. females 7.26 ± 5.69 mm, P > 0.05) distances from anterior superior iliac spine (ASIS); most points (58% males, 67% females) clustered in the ASIS lateral-superior region (P = 0.346). Males had significantly larger maximum screw diameter (7.02 ± 0.91 mm vs. 6.41 ± 0.78 mm, P < 0.001) and longer corridor length (76.21 ± 8.80 mm vs. 63.93 ± 7.88 mm, P < 0.001) than females, while insertion angles (medial ~ 52°, posterior ~ 56°) were gender-uniform (P > 0.05). All fixation methods exhibited stress levels below bone/implant yield strength. MS fixation had lower maximum displacement than SRPS and DRPS under superior-inferior (0.057 mm vs. 0.102 mm/0.070 mm) and lateral-medial (0.751 mm vs. 1.300 mm/0.897 mm) loading, with stress distribution comparable to RLS and superior to plate-based methods.
Conclusions:
Standardized anatomical parameters (ASIS-based entry point with approximately 52° medial and 56° posterior insertion angles) enable gender-neutral initial MS localization, while screw diameter and length should be gender-specific. Biomechanically, MS fixation demonstrates comparable or superior stability to conventional methods for APCF, suggesting its potential as a minimally invasive alternative. Future multicenter clinical trials are required to validate its clinical translation potential.
