Biomechanical study of three kinds of internal fixation for the treatment of sacroiliac joint disruption using biomechanical test and finite element analysis

Finite element analysis of modified pedicle screw fixation and traditional lumbopelvic fixation for the treatment of sacroiliac joint disruption

INTRODUCTION

The modified pedicle screw fixation (PSF) was designed to simulate an integrated framework structure to ameliorate the resistance to vertical and shearing forces of the disrupted sacroiliac complex, and the aim of this study was to compare the biomechanical characteristics of PSF and traditional lumbopelvic fixation (LPF) for the treatment of sacroiliac joint disruption.

METHODS

The digital computer simulation model of an intact spine-pelvis-femur complex with main ligaments was built from clinical images. A left sacroiliac joint disruption model was mimicked by removing the concerned ligaments. After model validation, the two fixation models (modified PSF and traditional LPF) were established, and assembled with the disruption model. Under five loading scenarios (compression, flexion, extension, right bending, and left twisting), the finite element simulation was implemented. The maximum von Mises stress (VMS) of internal fixations and pelvises, maximum deformations on the Z-, Y-, X-axes and overall deformation of the sacrum were evaluated and compared.

RESULTS

Under all loading conditions, the maximum VMS of internal fixations and pelvises in the modified PSF model were lower than those in the traditional LPF model. Under flexion, right bending, and left twisting, the maximum Z-axis deformation of the sacrum for the modified PSF model was smaller than that of the traditional LPF model. For compression, the maximum Y-axis deformation of the sacrum was smaller than that of the traditional LPF model. During various loading modes, the maximum X-axis, and overall deformations of the sacrum for the modified PSF model were smaller than those in the traditional LPF model.

CONCLUSIONS

Compared with the traditional LPF, the modified PSF shows superior biomechanical stability, with satisfied resistance to vertical and shearing forces, which might be potentially suitable for treating sacroiliac joint disruption.

[Effectiveness of sacroiliac screw implantation assisted by three-dimensional printed faceted honeycomb guide plate in treatment of posterior pelvic ring fracture]

Objective

To investigate the effectiveness of sacroiliac screw implantation assisted by three-dimensional (3D) printed faceted honeycomb guide plate in the treatment of posterior pelvic ring fracture.

Methods

The clinical data of 40 patients with posterior pelvic ring fractures treated with sacroiliac screw implantation between December 2019 and December 2022 were retrospectively analyzed. Among them, 18 cases were treated with sacroiliac screws fixation assisted by 3D printed faceted honeycomb guide plate (guide plate group), and 22 cases were treated with sacroiliac screws percutaneously fixation under fluoroscopy (conventional group). There was no significant difference in baseline data ( P>0.05) such as gender, age, time from injury to operation, and Dennis classification between the two groups. The implantation time, frequency of C-arm X-ray fluoroscopy, frequency of guide pin adjustment of each sacroiliac screw, and postoperative complications and bone healing were recorded. Majeed score was used to evaluate the functional recovery at 6 months after operation, and CT was used to observe whether the screw penetrated the bone cortex. The deviation between the virtual position and the actual position of the screw tip, the sacral foramen, and the screw entry point was measured on the sagittal CT images of the guide plate group.

Results

The number of screws implanted in S 1 and S 2 vertebral bodies was 14 and 16 respectively in the guide plate group, and 17 and 18 respectively in the conventional group. The implantation time of each sacroiliac screw, the frequency of C-arm X-ray fluoroscopy, and the frequency of guide pin adjustment in S 1, S 2, and all vertebrae in the guide plate group were significantly less than those in the conventional group ( P<0.05). Patients in both groups were followed up 8-48 months, with an average of 19.7 months. There was no incision infection, screw displacement, or internal fixation loosening in both groups. Callus growth was observed in all patients at 12 weeks after operation, and bone healing was achieved in all patients. The healing time ranged from 12 to 24 weeks, with an average of 15.7 weeks. No sacroiliac screw penetrated the bone cortex in the guide plate group; 2 patients in the conventional group had sacroiliac screws penetrating the bone cortex without damaging blood vessels or nerves. In the guide plate group, the deviation between the virtual position and the actual position of the screw tip, the sacral foramen, and the screw entry point were (2.91±1.01), (2.10±0.74), and (1.67±0.70) mm, respectively, with an average deviation of (2.19±1.22) mm. There was no significant difference in Majeed function evaluation between the two groups at 6 months after operation ( P>0.05).

Conclusion

The application of 3D printed faceted honeycomb guide plate in sacroiliac screw implantation for posterior pelvic ring fracture can shorten the screw implantation time, reduce the frequency of fluoroscopy and guide pin adjustment, and reduce the risk of screw penetration through the bone cortex.

Comparison of mechanical stability of modified pedicle screw fixator and unilateral lumbopelvic fixation for treating sacroiliac joint disruption: A finite element analysis study

Objective

This study aimed to investigate the mechanical stability of a modified pedicle screw fixator and compare it with unilateral lumbopelvic fixation for treating sacroiliac joint disruption using finite element simulation technology.

Methods

The digital model of a normal spine-pelvis-femur containing the main pelvic and lumbar ligaments was established based on computed tomography images. A sacroiliac joint disruption model was built and validated, which was stabilized with the models of a modified pedicle screw fixator or unilateral lumbopelvic fixation. A 400 N follower loading was applied to the lumbar vertebrae for the 2 fixation models to analyze displacement and stress distribution. In addition, the construct stiffness was calculated.

Results

The peak amounts of sacral vertical displacement, horizontal displacement, posterior displacement, and overall displacement were 0.70 mm, 0.17 mm, 0.73 mm, and 0.88 mm, respectively, in the modified pedicle screw fixator model, which were less than those in the unilateral lumbopelvic fixation model (1.17 mm, 0.31 mm, 2.21 mm, and 2.29 mm, respectively). Compared with unilateral lumbopelvic fixation, the percentage decreases of the modified pedicle screw fixators were 40.2%, 45.2%, 67.0%, and 61.6%, respectively. The peak stress of the internal fixation and pelvis in the modified pedicle screw fixator model was 351.23 MPa and 39.91 MPa, which has 15.5% and 70.4% lower than in the unilateral lumbopelvic fixation model. The construct stiffness of the modified pedicle screw fixator (571 N/ mm) was 67% better than that of unilateral lumbopelvic fixation (342 N/mm).

Conclusion

The finite element simulation results showed that the modified pedicle screw fixator model demonstrated smaller sacral displacement, fewer stresses on the internal fixation and bone, and higher construct stiffness compared with the unilateral lumbopelvic fixation model. Thus, the modified pedicle screw fixator may provide biomechanical advantages over unilateral lumbopelvic fixation in the treatment of sacroiliac joint disruption.

Pelvic Ring Fractures: A Biomechanical Comparison of Sacral and Lumbopelvic Fixation Techniques

BACKGROUND CONTEXT

Pelvic ring fractures are becoming more common in the aging population and can prove to be fatal, having mortality rates between 10% and 16%. Stabilization of these fractures is challenging and often require immediate internal fixation. Therefore, it is necessary to have a biomechanical understanding of the different fixation techniques for pelvic ring fractures.

METHODS

A previously validated three-dimensional finite element model of the lumbar spine, pelvis, and femur was used for this study. A unilateral pelvic ring fracture was simulated by resecting the left side of the sacrum and pelvis. Five different fixation techniques were used to stabilize the fracture. A compressive follower load and pure moment was applied to compare different biomechanical parameters including range of motion (contralateral sacroiliac joint, L1-S1 segment, L5-S1 segment), and stresses (L5-S1 nucleus stresses, instrument stresses) between different fixation techniques.

RESULTS

Trans-iliac-trans-sacral screw fixation at S1 and S2 showed the highest stabilization for horizontal and vertical displacement at the sacral fracture site and reduction of contralateral sacroiliac joint for bending and flexion range of motion by 165% and 121%, respectively. DTSF (Double transiliac rod and screw fixation) model showed highest stabilization in horizontal displacement at the pubic rami fracture site, while the L5_PF_W_CC (L5-Ilium posterior screw fixation with cross connectors) and L5_PF_WO_CC (L5-Ilium posterior screw fixation without cross connectors) showed higher rod stresses, reduced L1-S1 (approximately 28%), and L5-S1 (approximately 90%) range of motion.

CONCLUSIONS

Longer sacral screw fixations were superior in stabilizing sacral and contralateral sacroiliac joint range of motion. Lumbopelvic fixations displayed a higher degree of stabilization in the horizontal displacement compared to vertical displacement of pubic rami fracture, while also indicating the highest rod stresses. When determining the surgical approach for pelvic ring fractures, patient-specific factors should be accounted for to weigh the advantages and disadvantages for each technique.

Effects of manipulations of oblique pulling on the biomechanics of the sacroiliac joint: a cadaveric study

BACKGROUND

There are many reports on the treatment of sacroiliac joint dysfunction by manipulation of oblique pulling (MOP). However, the specific mechanism of MOP on the sacroiliac joint remains unclear. This study aimed to investigate the effect of MOP on the biomechanics of the sacroiliac joint and the effect of the anterior sacroiliac ligament on the stability of the sacroiliac joint.

METHODS

First, MOP-F1 (F: force) and MOP-F2 were applied to nine cadaveric pelvises. Then, segmental resection of the anterior sacroiliac ligament was performed. The range of motion of the sacroiliac joint was observed in all procedures.

RESULTS

Under MOP-F1 and F2, the average total angles were 0.84° ± 0.59° and 1.52° ± 0.83°, and the displacements were 0.61 ± 0.21 mm and 0.98 ± 0.39 mm, respectively. Compared with MOP-F1, MOP-F2 caused greater rotation angles and displacements of the sacroiliac joint (p = 0.00 and p = 0.01, respectively). In addition, the rotation angles and displacements of the sacroiliac joint significantly increased after complete resection of the anterior sacroiliac ligament (p = 0.01 and p = 0.02, respectively). The increase was mainly due to the transection of the upper part of the anterior sacroiliac ligament.

CONCLUSIONS

MOP-F2 caused greater rotation angles and displacements of the sacroiliac joint and was a more effective manipulation. The anterior sacroiliac ligament played an important role in maintaining the stability of the sacroiliac joint; the upper part of the anterior sacroiliac ligament contributed more to the stability of the joint than the lower part.

Biomechanical tests and finite element analyses of pelvic stability using bilateral single iliac screws with different channels in lumbo-iliac fixation

BACKGROUND

In lumbo-iliac fixation, the iliac screw can be placed in several locations and directions. There is no uniform standard for the placement of a single iliac screw. Biomechanical tests and finite element analyses were used to compare the effect of bilateral single iliac screws with three channels on pelvic stability to determine the best channel.

METHODS

Five embalmed adult cadaver pelvic specimens were selected. An unstable Tile C1 pelvic injury model was established. Lumbo-iliac fixation for the treatment of left sacral Denis II fracture includes the following: three channels of bilateral, single iliac screws (channel A from posterior superior iliac spine (PSIS) to anterior inferior iliac spine (AIIS), channel B from 1 cm medial and 1 cm caudal of PSIS to AIIS, and channel C from 2 cm below PSIS to AIIS). Biomechanical testing was performed for stiffness evaluations. A finite element model was established to study the stress distribution of the model and the maximum von Mises stress of internal fixation.

RESULTS

Biomechanical tests revealed that under vertical compression loading. The compressive stiffness fixed by channel B (246.15 ± 27.85 N/mm) was better than that fixed by channel A and channel C. Under torsional load, the torsional stiffness fixed by channel B (2.234 ± 0.223 N·m/°) was stronger than that fixed by channel A and channel C. However, there was no significant difference in terms of compressive and torsional stiffness between channel B and channel A (P > 0.05). Finite element analyses conformed that the maximum von Mises stress of the internal fixator fixed in channel B under the conditions of vertical, forwards bending, backwards extension, left bending, left rotating, and right bending (213.98 MPa, 338.96 MPa, 100.63 MPa, 297.06 MPa, 200.95 MPa and 284.75 MPa, respectively) was significantly lower than those fixed in channel A and channel C.

CONCLUSIONS

The construct stiffness of the channel from 1 cm medial and 1 cm caudal of PSIS to AIIS is better than that of the other two channels. This channel has the advantages of good biomechanical stability, small maximum von Mises stress of internal fixation.

Identification of safe channels for screws in the anterior pelvic ring fixation system

Background

Minimally invasive surgery for pelvic fracture using anterior ring internal fixator system is increasing gradually, and the way to insert the fixation screws in the fixation system is the key technical points of the method. However, there have been few studies on insertion of fixation screws for the anterior pelvic ring internal fixator system.

Objective

To identify safe channels for fixation screws in the anterior pelvic fixator system and provide the anatomical basis for insertion of fixation screws in clinical operation.

Methods

Screw insertion was simulated into a total of 40 pelvic finite element models as well as 16 fresh pelvic specimens, and the channel parameters were measured.

Results

Finite elements (male, female) include: screws in ilium: length 114.4 ± 4.1 and 107.6 ± 8.3 mm, respectively; diameter 11.7 ± 0.5 and 10.0 ± 0.6 mm, distance between screw and anterior inferior iliac spine: 5.5 ± 1.0 and 5.6 ± 1.0 mm, angle of coronal plane 55.8° ± 2.4° and 50.6° ± 3.1°, angle of sagittal plane 26.6° ± 1.0° and 24.5° ± 1.9° and angle of horizontal plane 64.9 ± 3.7 and 58.1 ± 3.1; screws in pubis: length 47.0 ± 2.0 and 39.8 ± 3.9 mm, diameter 7.1 ± 0.4 and 6.1 ± 0.4 mm. Specimens (male, female) include: distance between screw and anterior inferior iliac spine: 5.5 ± 0.5 and 5.6 ± 0.7 mm, angle of coronal plane 55.9° ± 1.3° and 50.7° ± 1.5°, angle of sagittal plane 26.7° ± 0.5° and 24.1° ± 0.9° and angle of horizontal plane 64.8° ± 0.6° and 58.8° ± 0.8°. In the comparison between female and male in each group, differences in distances between screws and anterior inferior iliac spine and median line of symphysis pubis (P > 0.05) were not statistically significant; differences in the remaining parameters were statistically significant (P < 0.05).

Conclusions

If surgeons paid attention to sex differences, select screws of appropriate diameter and length and hold the insertion position and direction, screws in the anterior pelvic ring fixation system could be safely inserted.

What happens at the L5/S1 facet joint when implants are placed across the sacroiliac joint?

BACKGROUND

Injuries to the posterior pelvic ring are often stabilized with fixation across the sacroiliac joint (SIJ). However, the compensatory changes at the neighboring L5/S1 facet joint are unknown. The objective of this study was to determine the compensatory change in pelvic kinematics and contact forces at the L5/S1 facet joint after fixation across the sacroiliac joint (SIJ) using a cadaveric model.

METHODS

Five fresh-frozen cadaveric pelvis specimens were dissected to remove non-structural soft tissue. Retroreflective markers were fixed to the L5 body, S1 body and bilateral anterior superior iliac spines to represent the motion of L5, S1 and the ileum, respectively. Pressure sensors were inserted in both L5/S1 facet joints. Testing was performed using a robotic system that applied load to mimic ambulation. Testing was performed prior to SIJ fixation, after unilateral SIJ fixation and bilateral fixation.

RESULTS

Contact force at the L5/S1 facet joint significantly increased by 55% from 48.4 N to 75.2 N following unilateral fixation (p = 0.0161) and increased by 100% to 96.9 N after bilateral fixation (p = 0.0038). Unilateral SIJ fixation increased flexion of the ilium relative to L5 from 1.2° to 2.0° (p = 0.01) and increased axial rotation of L5 relative to S1 from 0.7° to 1.6° (p = 0.001). Bilateral fixation increased flexion of the ilium relative to L5 to 2.0° from 1.2° prior to fixation (p = 0.001), increased axial rotation of L5 relative to S1 to 1.2° from 0.7° prior to fixation (p = 0.002) and increased flexion of L5 relative to S1 to 2.4° from 1.5° prior to fixation (p = 0.04).

CONCLUSION

The L5/S1 facet joint experiences compensatory increased motion under increased contact force after unilateral and bilateral SIJ fixation, possibly predisposing it to adjacent segment arthritis.

LEVEL OF EVIDENCE

V, cadaveric study.

Computer-aided automatic planning and biomechanical analysis of a novel arc screw for pelvic fracture internal fixation

BACKGROUND AND OBJECTIVE

The sacroiliac joint screw is a common fixation method for pelvic posterior ring fractures. The complex anatomical structure around the pelvis makes it impossible to find a suitable fixed path, which increases the difficulty of surgical operation. In this paper, we propose an automatic planning algorithm based on a computer-aided internal arc fixation channel for pelvic fractures for the first time.

METHODS

A channel generation algorithm based on seed derived points was designed, and the optimal channel was selected by scoring rules based on 3D erode algorithm for the generated channel. The biomechanical properties of the internal arc fixation screw and traditional internal straight fixation screw in three postures were compared using biomechanical finite element analysis.

RESULTS

The proposed algorithm verified the existence of a more adaptable internal arc fixation channel and can quantitatively plan a relatively optimal constant-curvature internal arc fixation channel in pelvises of ten adults. Significantly high stresses concentrated around the interaction region between the screws and bone may increase the risk of bone fractures and screw loosening in the long term. The experimental results show that the internal arc fixation screw has better strain and deformation performance than the internal straight fixation screw.

CONCLUSIONS

A novel arc internal fixation method for pelvic fractures was proposed to improve the safety and stability of screw fixation of pelvic fracture. The nonparametric test proved that the sacroiliac dislocation model repaired by internal arc fixation screw was significantly different from that repaired by internal straight fixation screw. The computer-aided automatic planning algorithm provides the possibility of robot-assisted pelvic fracture fixation.

A biomechanical study of the birth position: a natural struggle between mother and fetus

Birth trauma affects millions of women and infants worldwide. Levator ani muscle avulsions can be responsible for long-term morbidity, associated with 13-36% of women who deliver vaginally. Pelvic floor injuries are enhanced by fetal malposition, namely persistent occipito-posterior (OP) position, estimated to affect 1.8-12.9% of pregnancies. Neonates delivered in persistent OP position are associated with an increased risk for adverse outcomes. The main goal of this work was to evaluate the impact of distinct fetal positions on both mother and fetus. Therefore, a finite element model of the fetal head and maternal structures was used to perform childbirth simulations with the fetus in the occipito-anterior (OA) and OP position of the vertex presentation, considering a flexible-sacrum maternal position. Results demonstrated that the pelvic floor muscles' stretch was similar in both cases. The maximum principal stresses were higher for the OP position, and the coccyx rotation reached maximums of 2.17[Formula: see text] and 0.98[Formula: see text] for the OP and OA positions, respectively. Concerning the fetal head, results showed noteworthy differences in the variation of diameters between the two positions. The molding index is higher for the OA position, with a maximum of 1.87. The main conclusions indicate that an OP position can be more harmful to the pelvic floor and pelvic bones from a biomechanical point of view. On the other side, an OP position can be favorable to the fetus since fewer deformations were verified. This study demonstrates the importance of biomechanical analyses to further understand the mechanics of labor.

S2-alar-iliac screw and S1 pedicle screw fixation for the treatment of non-osteoporotic sacral fractures: a finite element study

Background

Five different sacral fracture fixation methods were compared using finite element (FE) analysis to study their biomechanical characteristics.

Methods

Denis type I sacral fractures were created by FE modeling. Five different fixation methods for the posterior pelvic ring were simulated: sacroiliac screw (SIS), lumbopelvic fixation (LPF), transiliac internal fixator (TIFI), S2-alar-iliac (S2AI) screw and S1 pedicle screw fixation (S2AI-S1) and S2AI screw and contralateral S1 pedicle screw fixation (S2AI-CS1). Four different loading methods were implemented in sequence to simulate the force in standing, flexion, right bending and left twisting, respectively. Vertical stiffness, relative displacement and change in relative displacement were recorded and analyzed.

Results

As predicted by the FE model, the vertical stiffness of the five groups in descending order was S2AI-S1, SIS, S2AI-CS1, LPF and TIFI. In terms of relative displacement, groups S2AI-S1 and S2AI-CS1 displayed a lower mean relative displacement, although group S2AI-CS1 exhibited greater displacement in the upper sacrum than group S2AI-S1. Group SIS displayed a moderate mean relative displacement, although the displacement of the upper sacrum was smaller than the corresponding displacement in group S2AI-CS1, while groups LPF and TIFI displayed larger mean relative displacements. Finally, in terms of change in relative displacement, groups TIFI and LPF displayed the greatest fluctuations in their motion, while groups SIS, S2AI-S1 and S2AI-CS1 displayed smaller fluctuations.

Conclusion

Compared with SIS, unilateral LPF and TIFI, group S2AI-S1 displayed the greatest biomechanical stability of the Denis type I sacral fracture FE models. When the S1 pedicle screw insertion point on the affected side is damaged, S2AI-CS1 can be used as an appropriate alternative to S2AI-S1.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02805-8.

Pelvic Reconstruction With a Novel Three-Dimensional-Printed, Multimodality Imaging Based Endoprosthesis Following Enneking Type I + IV Resection

BACKGROUND AND PURPOSE

Pelvic tumor involving Type I + IV resections are technically challenging, along with various reconstructions methods presenting unsatisfactory outcomes and high complication rates. Since predominating studies preferred adopting pedicle screw-rod system (PRSS) to address this issue, we designed a novel three-dimensional-printed, multimodality imaging (3DMMI) based endoprosthesis with patient-specific instrument (PSI) assistance to facilitate the surgical reconstruction of pelvic tumor involving Enneking Type I + IV resection. We aimed to investigate the clinical effectiveness of this novel endoprosthesis and compare it with PRSS in Type I + IV reconstruction.

METHODS

We retrospective studied 28 patients for a median follow-up of 47 months (range, 10 to 128 months) in this study with either 3D-printed endoprosthesis reconstruction (n = 10) or PRSS reconstruction (n = 18) between January 2000 and December 2017. Preoperative 3DMMI technique was used for tumor evaluation, PSI design, virtual surgery, and endoprosthesis fabrication. Clinical, oncological outcomes, functional assessments, and complications were analyzed between the two groups.

RESULTS

Minor surgical trauma with mean operative duration of 251 ± 52.16 minutes (p = 0.034) and median intraoperative hemorrhage of 2000ml (range, 1600, 4000ml) (p = 0.032) was observed in endoprosthesis group. Wide margins were achieved in 9 patients of the endoprosthesis group compared with 10 in the PRSS group (p = 0.09). The 1993 version of the Musculoskeletal Tumor Society score (MSTS-93) was 23.9 ± 3.76 in endoprosthesis group, which was higher than PRSS group (p = 0.012). No statistical significance was found in relapse between two groups (p = 0.36). Complications were observed in two patients in endoprosthesis group compared with 12 patients in PRSS group (p = 0.046).

CONCLUSION

The novel design of this 3D-printed endoprosthesis, together with 3DMMI and PSI assisted, is technically accessible with favorable clinical outcomes compared with PRSS. Further study is essential to identify its long-term outcomes.

Effect of the birthing position on its evolution from a biomechanical point of view

BACKGROUND AND OBJECTIVE

During vaginal delivery, several positions can be adopted by the mother to be more comfortable and to help the labor process. The positions chosen are very influenced by factors such as monitoring and intervention during the second stage of labor. However, there is limited evidence to support the most ideal birthing position. This work aims at contributing to a better knowledge associated with the widening of the pubic symphysis and the biomechanics of flexible and non-flexible sacrum positions that can be adopted during the second stage of labor, as well as their resulting pathophysiological consequences.

METHODS

A validated computational model composed by the pelvic floor muscles attached to the bones, and a fetus head was used to simulate vaginal deliveries. This model was modified to mimic two birthing positions: one that allows the free movement of the coccyx as in flexible sacrum positions and other in which this movement is more restricted as in non-flexible sacrum positions. The widening of the pubic symphysis was also considered to facilitate the passage of the fetus head.

RESULTS

The results obtained showed that, in non-flexible sacrum positions, where the coccyx movement is restricted, occur a rotation of 3.6° of the coccyx and a widening of 6 mm of the pubic symphysis. In contrast, in flexible sacrum positions, where the coccyx is free to move, occur a rotation of 15.7° of the coccyx and a widening of the pubic symphysis of 3 mm, appearing to be more beneficial for the mother's pelvis, but slightly higher stresses were detected in the pelvic floor muscles.

CONCLUSIONS

Globally, the results obtained allow to conclude that different birthing positions lead to changes in the female pelvic space, so certain positions can be adopted by the mother during the second stage of labor to reduce the risk of obstructed labor and the development of several dysfunctions. More specifically, flexible sacrum positions, such as kneeling, standing, squatting and sitting positions, are more beneficial for the bone structure of her pelvis as they allow a higher coccyx movement and lower widening of the pubic symphysis.

A finite element analysis of sacroiliac joint displacements and ligament strains in response to three manipulations

BACKGROUND

Clinical studies have found that manipulations have a good clinical effect on sacroiliac joint (SIJ) pain without specific causes. However, the specific mechanisms underlying the effect of manipulations are still unclear. The purpose of this study was to investigate the effects of three common manipulations on the stresses and displacements of the normal SIJ and the strains of the surrounding ligaments.

METHODS

A three-dimensional finite element model of the pelvis-femur was developed. The manipulations of hip and knee flexion (MHKF), oblique pulling (MOP), and lower limb hyperextension (MLLH) were simulated. The stresses and displacements of the SIJ and the strains of the surrounding ligaments were analyzed during the three manipulations.

RESULTS

MOP produced the highest stress on the left SIJ, at 6.6 MPa, while MHKF produced the lowest stress on the right SIJ, at 1.5 MPa. The displacements of the SIJ were all less than 1 mm during the three manipulations. The three manipulations caused different degrees of ligament strain around the SIJ, and MOP produced the greatest straining of the ligaments.

CONCLUSION

The three manipulations all produced small displacements of the SIJ and different degrees of ligament strains, which might be the mechanism through which they relieve SIJ pain. MOP produced the largest displacement and the greatest ligament strains.

Anterior approach to the sacroiliac joint for pelvic ring fractures: Technical note

Displaced pelvic fractures, combining an anterior lesion and sacroiliac disruption, most often require multiple surgical approaches. The technique we describe here allows these lesions to be treated by a single approach. It combines a Stoppa approach to address the anterior lesion and a pararectus approach to the sacroiliac joint through the same incision under the rectus abdominis muscle. This pararectus approach is done by passing laterally to the external and common iliac vessels. The entire anterior surface of the sacroiliac joint is exposed by the same passage through the abdominal wall. No neurological or vascular complications occurred in a 7-patient case series. Reduction was achieved in all cases. This approach is an interesting alternative to traditional approaches and enriches the surgeon's therapeutic arsenal for managing these complex fractures.

Biomechanics of Anterior Ring Internal Fixation Combined with Sacroiliac Screw Fixation for Tile C3 Pelvic Fractures

Background

Despite the development of minimally invasive techniques for pelvic fractures, performing minimally invasive surgery for Tile C3 pelvic fractures remains challenging. Thus, we propose use of anterior ring internal fixation combined with sacroiliac screw fixation for Tile C3 pelvic fractures.

Material/Methods

A normal pelvic finite element model (model 1) was established. Two-screw, three-screw, and four-screw anterior ring internal fixators and plate combined with sacroiliac screw Tile C3 pelvic fracture models (models 2, 3, 4, and 5, respectively) were also established. A vertical load of 600 N was applied on S1. The distribution of displacement and stress in the standing and sitting positions was compared.

Results

Models 2, 3, 4, and 5 can provide effective fixation. Compared with model 1, in the erect position, the maximum displacement of models 2, 3, 4, and 5 increased by 66.51%, 65.36%, 35.16%, and 35.47% and the maximum stress increased by 201.78%, 130.65%, 100.82%, and 99.03%, respectively. Compared with model 1, in sitting position, the maximum displacement of models 2, 3, 4, and 5 increased by 9.1%, 11.04%, 5.57%, and 8.59% and the maximum stress increased by 157.73%, 118.02%, 98.32%, and 93.16%, respectively.

Conclusions

Anterior ring internal fixators combined with sacroiliac screws can effectively fix Tile C3 pelvic fractures.

Fully threaded sacroiliac lag screws have higher load to failure when compared to partially threaded screws: A biomechanical study

The purpose of this study is to compare biomechanical properties of fully and partially threaded iliosacral screws. We hypothesise that fully threaded screws will have a higher yield force, and less deformation than partially threaded screws following axial loading. Twenty sawbone blocks were uniformly divided to simulate vertical sacral fractures. Ten blocks were affixed with fully threaded iliosacral screws in an over-drilled, lag-by-technique fashion whilst the remaining ten were fixed with partially threaded lag-by-design screws. All screws measured 7.3-mm x 145 mm, and were inserted to a 70% of calculated maximal insertional torque, ensuring uniform screw placement throughout across models. Continuous axial loads were applied to 3 constructs of each type to failure to determine baseline characteristics. Five hundred loading cycles of 500 N at 1 Hz were applied to 4 constructs of each type, and then axially loaded to failure. Force displacement curves, elastic, and plastic deformation of each construct was recorded. Fully threaded constructs had a 428% higher yield force, 61% higher stiffness, 125% higher ultimate force, and 66% lower yield deformation (p < 0.05). The average plastic deformation for partially threaded constructs was 336% higher than fully threaded constructs (p = 0.071), the final elastic deflection was 10% higher (p = 0.248), and the average total movement was 21% higher (p = 0.107). We conclude from this biomechanical study that fully threaded, lag-by-technique iliosacral screws can withstand significantly higher axial loads to failure than partially threaded screws. In addition, fully threaded screws trended towards exhibiting a significantly lower plastic deformation following cyclical loading.

What do we know about the biomechanics of the sacroiliac joint and of sacropelvic fixation? A literature review

The purpose of this review is to summarize the general knowledge about the biomechanics of the sacroiliac joint and sacropelvic fixation techniques. Additionally, this study aims to support biomechanical investigations in defining experimental protocols as well as numerical modeling of the sacropelvic structures. The sacroiliac joint is characterized by a large variability of shape and ranges of motion among individuals. Although the ligament network and the anatomical features strongly limit the joint movements, sacroiliac displacements and rotations are not negligible. Currently available treatments for sacroiliac joint dysfunction include physical therapy, steroid injections, Radio-frequency ablation of specific neural structures, and open or minimally invasive SIJ fusion. In long posterior construct, the most common solutions are the iliac screws and the S2 alar - iliac screws, whereas for the joint fixation alone, mini - invasive alternative system can be used. Several studies reported the clinical outcomes of the different techniques and investigated the biomechanical stability of the relative construct, but the effect of sacropelvic fixation techniques on the joint flexibility and on the stress generated into the bone is still unknown. In our opinion, more biomechanical analyses on the behavior of the sacroiliac joint may be performed in order to better predict the risk of failure or instability of the joint.

Sex-based differences in human sacroiliac joint shape: a three-dimensional morphological analysis of the iliac auricular surface of modern Japanese macerated bones

The human pelvis is one of the skeletons where sex differences are expressed, but few detailed studies have been conducted on sex-related differences in the sacroiliac joint morphology. Therefore, we conducted a three-dimensional morphological analysis evaluation of the sacroiliac joints to clarify the sex-related difference of the joint's morphology. Right-side macerated innominate bones of Japanese males (n = 100) and females (n = 70) whose ages at death were recorded were included in the study. Three-dimensional images were created from the subjects' iliac auricular surface images, and 16 measurement parameters were acquired on the basis of 11 defined measurement points. All measurement parameters were compared between the male and female groups. The values of the measurement parameters indicating the size of the iliac auricular surface were significantly larger in the male group than in the female group. In addition, the angle between the short and long arms of the auricular surface was larger in the male group. Furthermore, on the basis of the corrected values of the physical disparity, the long arm dimension of the iliac auricular surface was larger in the male group, while the short arm dimension was larger in the female group. The sex-based differences in the iliac auricular surface morphology that were confirmed in this study may reflect the sex-based differences in the sacroiliac joint function. The findings of this study may contribute to the elucidation of the pathophysiology of the sacroiliac joint dysfunction that frequently occurs in women.

Relationships between the femoral neck-preserving ratio and radiologic and clinical outcomes in patients undergoing total-hip arthroplasty with a collum femoris-preserving stem

The femoral neck-preserving ratio is crucial in arthroplasty with a collum femoris-preserving (CFP) stem. The aim of our study was to analyze the relationships between the neck-preserving ratio and the short-term radiologic and clinical outcomes of patients who underwent total-hip arthroplasty (THA) with a CFP stem.The data of 325 hips from January 2015 to December 2016 were retrospectively reviewed. The demographic and radiologic data before and after surgery were obtained from patients. The neck-preserving ratio was defined as the ratio of the preserved femoral neck length to the preoperative femoral neck length. Correlations between the neck-preserving ratio and the radiologic and clinical outcomes of patients were analyzed.The mean neck-preserving ratio was 66.38 ± 6.91% in the current study. We divided patients into 3 groups according to the neck-preserving ratio: group A (neck-preserving ratio ≤60.00%), group B (60.00% < neck-preserving ratio < 70.00%), group C (neck-preserving ratio ≥70.00%). Radiologic features, including the neck-shaft angle ratio (0.96 ± 0.05), canal fill ratio (0.64 ± 0.07), anterior-posterior offset ratio (1.04 ± 0.10), and lateral offset ratio (2.55 ± 1.56) (ratios of the postoperative values to the preoperative values), and the prevalence of complications was significantly different among the groups (χ = 21.173, P < .001). In the correlation analysis, we found a moderate negative correlation between the neck-preserving ratio and neck-shaft angle ratio (r = -0.308, P < .001) and a slight positive correlation of the neck-preserving ratio with the anterior-posterior offset ratio (r = 0.415, P < .001) and the lateral offset ratio (r = 0.164, P = .003). In the linear regression analyses, the neck-preserving ratio was significantly linearly correlated with the neck-shaft angle ratio (B = -0.232, 95% confidence interval [CI] = -0.311 to -0.154, P < .001), anterior-posterior offset ratio (B = 0.589, 95% CI = 0.447-0.730, P < .001), and lateral offset ratio (B = 3.693, 95% CI = 1.256-6.131, P = .003). However, there was no significant linear correlation between the neck-preserving ratio and the canal fill ratio (B = 0.073, 95% CI = -0.033 to 0.180, P = .174). Logistic regression analyses also showed that a sufficient neck-preserving ratio was a protective factor for periprosthetic femoral fractures (odds ratio [OR] = 0.924, 95% CI = 0.859-0.994, P = .035), dislocations (OR = 0.892, 95% CI = 0.796-0.999, P = .048), and thigh pain (OR = 0.886, 95% CI = 0.818-0.960, P = .003).For CFP stems, an insufficient neck-preserving ratio is significantly correlated with poor radiologic and clinical outcomes. Therefore, surgeons should be cognizant to preserve a sufficient femoral neck length during surgery to improve the outcomes for patients undergoing THA with CFP stems.

BIOMECHANICAL ANALYSIS OF DIFFERENT SURGICAL STRATEGIES FOR THE TREATMENT OF ROTATIONALLY UNSTABLE PELVIC FRACTURE USING FINITE ELEMENT METHOD

A rotationally unstable pelvic fracture can lead to loss of function and limit moving ability. Immediate fracture fixation is needed for patients with the pelvic fractures. However, it may be difficult to evaluate different surgical strategies for the fracture treatments due to variations in patients’ anatomies and surgical techniques. Thus, the purpose of the present study was to analyze the biomechanical performances of the intact, injured, and treated pelvises based on different physiological movements of the spine using finite element method. Three-dimensional musculoskeletal finite element models of the spine-pelvis-femur complex were developed. The intact pelvis, the rotationally unstable pelvis, and six types of pelvic fixation techniques were analyzed. Additionally, seven types of physiological movements of the spine were also considered. The results showed that the posterior iliosacral screws combined with lower and anterior plate (PIS-LAP) had good fixation stability, lower plate stress, and lower pelvic stress. However, the PIS-LAP increased the stress of the posterior iliosacral screws. The right lateral bending, left lateral bending, and flexion significantly affect all the biomechanical performances compared to the other physiological movements of the spine. The present study can provide engineers and surgeons with the understanding of the biomechanics of various fixation techniques during different physiological movements for the treatment of rotationally unstable pelvic fractures.