[Comparison of the stability of dual INFIX and INFIX combined with sacroiliac screw fixation for C1 type pelvic fractures].

OBJECTIVE

To evaluate the biomechanical stability of dual anterior subcutaneous internal fixation (INFIX) in pelvic C1 fractures by finite element analysis, and to compare it with INFIX combined with sacroiliac screws to determine whether it is sufficient to replace the combined fixation of anterior and posterior rings.

METHODS

The pelvic CT data of a 43-year-old female volunteer were imported into the computer and the normal pelvic model and pelvic C1 fractures model were constructed using Mimics, Workbench and other software. The latter was fixed with dual INFIX and INFIX combined with sacroiliac screws, respectively. First, the effectiveness of the normal pelvic model in anatomical landmarks, stress conduction and displacement distribution was verified. Then, a vertical downward load of 500 N was applied to the two internal fixation models to simulate the standing and sitting positions of the human body, and the displacement of the anterior and posterior ring fractures ends, the stress of the internal fixation and the stress of the nail channel in the bone were collected.

RESULTS

The model passed the validity verification. The maximum displacement of the anterior and posterior ring fractures in the standing dual INFIX group were 0.861 mm and 4.128 mm, respectively, which were both smaller than the 0.152 mm and 0.293 mm in the combined fixation group. The displacement of the posterior ring fractures in the sitting dual INFIX group was 3.757 mm, which was larger than the 0.560 mm in the combined fixation group, while the maximum displacement of the anterior ring fractures was 0.221 mm, which was not much different from the 0.194 mm in the combined fixation group. The maximum stress of internal fixation in the standing dual INFIX group was greater than that in the combined fixation group, while the opposite was true in the sitting position. The maximum stress of each internal fixation was lower than the yield strength of titanium alloy 790 MPa. The maximum stress of the nail channel in the standing and sitting daul INFIX groups was lower than that in the combined fixation group, and the stress of all nail channels was lower than the strength limit of bone 290 to 540 MPa.

CONCLUSION

The stability of dual INFIX fixation in anterior and posterior ring fractures is generally inferior to that of INFIX combined with sacroiliac screw fixation. Although simple dual INFIX fixation can share part of the load for the posterior ring, the posterior ring will still have a large displacement, so the fixation of the posterior ring is very important. In addition, the fixation strength and stability of dual INFIX in the anterior ring are better than INFIX. When INFIX cannot provide sufficient strength to stabilize the anterior ring fractures, dual INFIX will be a good choice.