Proper detailed parameters for S1 sacral alar iliac screw placement in the Chinese population, a 3D imaging study

Software-assisted preoperative planning of S1 Alar Iliac screws: a 3D morphometric and anatomical study

PURPOSE

S1 alar iliac (S1AI) trajectory has gained popularity as a salvage technique for revision surgeries and failed constructs in the lumbopelvic region. This study aims to investigate the morphometry of this new trajectory based on 3D models. The possible role of gender, ethnicity and view angle (surgeon's vs. radiologist's) was investigated.

METHODS

Computed tomography-driven virtual 3D models of spinopelvic region were created applying Materialize MIMICS software, and assessed for coronal and sagittal radiographic versus surgeon's view angles, and morphometry of the screw trajectory. Independent-samples t test was used to analyze the results. P value was set at <  = 0.05. The Statistical Package for the Social Sciences Software (SPSS version 24.0) was used for the statistical analysis.

RESULTS

A total of 164 3D models were simulated with a total 328 screws inserted satisfactorily within the S1AI trajectory. S1AI instrumentation was feasible in 96.48%. The mean radiological coronal angle was 50.619' ± 8.590' and the mean coronal angle for surgeons' perspective was 10.263' ± 5.860'. The mean radiological and surgeon's perspective sagittal angles were found to be 44.532' ± 6.424' and 31.164' ± 5.455', respectively. A statistically significant difference was found between anatomical and surgeon's perspective trajectories. Neither the pelvic laterality nor the gender influence the screw angles, length and diameter in radiological versus surgeon's view angles.

CONCLUSION

Preoperative 3D modeling would be an invaluable adjunct to increase the accuracy of S1AI screw placement. Surgeon's perspective of the trajectory differs from standard CT sections and should be considered in preoperative planning.

Three-dimensional digital anatomical measurement of modified sacroiliac screws

Purpose

To rebuild a model of the pelvis and effectively simulate the trajectory of modified sacroiliac screws, we measured the parameters of each screw and screw channel and assessed the safety and feasibility of the parameters in adults.

Method and materials

One hundred (50 males and 50 females) normal adult pelvic computed tomography (CT) images were randomly selected and imported into Mimics software to rebuild the three-dimensional pelvis model. In these models, each ideal channel of modified screws was simulated, and then we obtained the precise parameters of screws and channels using Mimics and Three-matic software.

Results

The results of the comparison (right vs. left) showed that there were no significant differences in any of the angles, radius or M1SI parameters (the first modified sacroiliac). However, one parameter (BS) of M2SI (the second modified sacroiliac), two parameters (AP and BS) of M3SI (the third modified sacroiliac), and three parameters (AP, BS, L) of M4SI (the fourth modified sacroiliac) were statistically significant (P < 0.05). The result of comparison (between genders) showed that there were no significant differences in M1SI and M2SI; in contrast, the radius, length and the α angle of M3SI and M4SI were significantly different between genders (P < 0.05), and the radius of M4SI required special attention. If the radius of the limiting screw channel was > 3.50 mm, 52 cases (52%, 24 males and 28 females) could not complete the M4SI screw placement among 100 samples. If the radius of the limiting screw channel was > 3.0 mm, a total of 10 cases (10%, 2 males and 8 females) could not complete the M4SI screw placement.

Conclusion

Through the measurement of 100 healthy adult real three-dimensional pelvic models, we obtained the parameters of each modified sacroiliac screw and measured the three angles of each screw based on international coordinates for the first time, which can instruct clinical application.

The three-dimensional printed template guided technique for S2 alar iliac screw placement and a comparison with freehand technique

PURPOSE

Sacropelvic fixation continues to present challenges when involved in the adult spinal deformity correction. The S2 alar iliac (S2AI) fixation is commonly used in sacropelvic fixation. Several techniques, including intraoperative navigation and freehand technique, were used for S2AI screws placement. The aim of this study is to analyze the anatomic parameters for S2AI screw trajectory in Asian population and introduce a novel technique described as a three-dimensional printed template guided technique (TGT). Meanwhile, the accuracy and safety of this technique were compared with the conventional freehand technique.

METHODS

The S2AI trajectory parameters were measured in 100 Asian adult volunteers. Parameters were compared between different genders. Forty-eight adult patients who underwent S2AI screw placement were reviewed: 28 patients received freehand technique and 20 patients received TGT technique. Postoperative computed tomography was used to assess the accuracy of screw trajectory and cortex violation-related complications were recorded.

RESULTS

The cephalocaudal angles (CAs), maximal length of screw pathway, narrowest width of pathway within the iliar teardrop, distance from the center of teardrop to sciatic notch, and distance of the start point distal to S1 dorsal foramen showed significant gender-related difference (p < 0.05). All 48 patients were placed S2AI screws bilaterally (40 screws in TGT vs. 56 screws in freehand). One screw penetrated iliac cortex in the TGT group but 10 screws penetrated iliac cortex in the freehand group (3% vs. 17.9%) (p < 0.05).

CONCLUSION

Approximately 30-35° of CA and 39° mediolateral angle are appropriate for S2AI screw placement in Asian patients. Either freehand or TGT technique is safe for S2AI screw placement. TGT technique is more accurate compared with the conventional freehand technique.

TRIAL REGISTRATION

This is a retrospective study.

S3 Sacral-Alar Iliac Screw: A Salvage Technique for Pelvic Fixation in Complex Deformity Surgery

Sacral-alar iliac (SAI) screws constitute a relatively new technique for pelvic fixation. Since their initial description in 2007, SAI screws have gained wide popularity among the spine surgery community. In 2013, we first described the possibility of using both S1 and S2 SAI screws for pelvic fixation in revision surgeries for adult degenerative scoliosis. Although a previous radiological study has suggested the feasibility of S3 and S4 SAI screws, to the best of our knowledge, there has been no report in the literature on the clinical use of such techniques. In this brief technical note, we present the first clinical report of the use of S3 SAI screws as a salvage method for pelvic fixation in a patient with suboptimal anatomy that prevented proper placement of S1 and S2 SAI screws. We also discuss the recommended anatomical entry points and trajectory of such screws.