Biomechanical study of four kinds of percutaneous screw fixation in two types of unilateral sacroiliac joint dislocation: a finite element analysis

Biomechanical performance evaluation of S2AI combine with LC-2 screw for day II pelvic crescent fracture dislocation via finite element analysis

Plate fixation is a classic method for treating day II crescent fracture dislocation of the pelvic (CFDP). However, due to the advantages of minimally invasive techniques and reduced complications associated with internal fixation percutaneous cannulated screws have emerged as a promising alternative for treating Day II CFDP. In this study, we propose using an S2AI screw combined with an LC-2 screw (S2AI + LC-2) for the treatment of Day II CFDP. The aim of this study was to compare its biomechanical stability with that of two conventional fixation methods using finite element analysis (FEA). A finite element (FE) model of pelvic was developed and validated. Three fixation methods were applied: S1 sacroiliac (SI) screws combined with LC-2 screw (S1 + LC-2), S1 and S2 SI screws combined with LC-2 screw (S1 + S2 + LC-2), and S2AI + LC-2. A 500 N load was applied, and the displacement of the crescent fracture fragments, the stress distribution of the implants, the displacement of the SI joint, and the maximum stress on the bone surrounding the screws were analyzed across the three FE models. After loading 500 N stress, the maximum displacement of the crescent fracture fragment and the maximum stress of bone around the implant in the S2AI + LC-2 group were the smallest in three groups. The displacement of SI joint in S2AI + LC-2 group was less than that in S1 + LC-2 and S1 + S2 + LC-2 (P < 0.001). The maximum stress of implants in each group is smaller than the yield stress of titanium. The maximum stress of the bone around the screws at SI joint in all models lower than the yield strength of cortical bone. The maximum stress of the bone around LC-2 screws in all models lower than the yield strength of cancellous bone. The S2AI + LC-2 group can achieve reliable stability of the SI joint, and the stress on the bone around the screw could be reduced. The S2AI + LC-2 group has good biomechanical stability and can be considered as a new implant to treat Day II CFDP.

Unilateral Lumbo-Pelvic Fixation for Denis Type I Unilateral Sacral Fracture: A Finite Element Analysis

Background

Unilateral sacral fractures with posterior ring instability represent a prevalent type of posterior pelvic ring fracture. While lumbo-pelvic fixation is recognized as a highly stable method, the sufficiency of unilateral lumbo-pelvic fixation (ULF) for such fractures remains under debate.

Purpose

This study aims to assess the biomechanical stability of ULF compared to traditional bilateral lumbo-pelvic fixation (BLF) and triangular osteosynthesis (TO), incorporating clinical observations, and previous biomechanical data.

Methods

We developed a three-dimensional spine-pelvis model to simulate a unilateral sacral fracture with posterior ring instability. The model was used to compare the stability of ULF with BLF and TO, utilizing both newly generated data and ULF models reported in existing literature.

Results

Our findings indicate that BLF and TO provide greater stability than ULF, with BLF emerging as the most stable model. While ULF may be insufficient for immediate postoperative weight-bearing, TO also demonstrated potential risks of instability during rotational and lateral bending movements toward the fracture side.

Conclusion

Despite its application in clinical settings, ULF may not adequately support early postoperative mobility. This study underscores the need for cautious application of ULF and suggests that enhancements such as additional fixation points may be necessary. The results also highlight the importance of tailored postoperative rehabilitation strategies for patients undergoing TO, especially in managing movements that could destabilize the fracture site.

A case report of S1-S3 sacroiliac screw fixation for posterior pelvic ring injury with S1 sacral dysmorphism

INTRODUCTION

There are few reports on the treatment of pelvic posterior ring injury with Sacral 1 - Sacral 3(S1-S3)sacroiliac screw fixation. This article reports a case of pelvic posterior ring injury with S1 sacral dysmorphism treated with S1-S3 sacroiliac screw fixation and reviews the relevant research progress.

PRESENTATION OF THE CASE

A 72-year-old man riding e-bike was struck by a car at a high speed and diagnosed with pelvic fracture. The patient successfully underwent treatment of 3 sacroiliac screws (S1-S3) fixation. Postoperative X-rays and CT scans confirmed that all screws were in good position and located in the bone corridors. Follow up pelvic Majeed score of 96 at 11th month after surgery.

DISCUSSION

Preoperative CT scans of this patient showed that S1 segment was a dysmorphic sacrum with narrow corridor while S2 and S3 segments were wide corridors. S1-S3 sacroiliac screw fixation can be attempted.

CONCLUSION

For patients with posterior pelvic ring injury with S1 sacral dysmorphism, S1-S3 sacroiliac screw fixation may be a better choice.

Bilateral Iliosacral and Transsacral Screws Are Biomechanically Favorable and Reduce the Risk for Fracture Progression in Fragility Fractures of the Pelvis-A Finite Element Analysis

(1) Background: The incidence of fragility fractures of the pelvis (FFP) has increased significantly over the past decades. Unilateral non-displaced fractures, defined as FFP II, are the most common type of fracture. When conservative treatment fails, surgical treatment is indicated. We hypothesize that the use of bilateral SI screws (BSIs) or a transsacral screw (TSI) is superior compared to a unilateral screw (USI) because of a significant reduction in the risk of adjacent fractures and a reduction in fracture progression. (2) Methods: A finite element model of a female pelvic ring was constructed. The ligaments were simulated as tension springs. The load was applied through the sacrum with the pelvis fixed to both acetabula. An FFP IIc was simulated and fixed with either a USI or BSI or TSI. The models were analyzed for a quantitative statement of stress and fracture dislocation. (3) Results: The BSI and TSI resulted in less dislocation compared to the USI. The stress distribution on both sides of the sacrum was favorable in the BSI and TSI groups. The BSI resulted in a higher rotational stability compared to the TSI. (4) Conclusions: The use of either a BSI or TSI for fixation of unilateral FFP is biomechanically favorable compared to the use of a USI. In addition, the use of a BSI or TSI reduces the stress on the contralateral uninjured side of the sacrum. This may reduce the risk of an adjacent fracture or fracture progression.

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.

Comparison of sacroiliac screw techniques for unstable sacroiliac joint disruptions: a finite element model analysis

Vertically unstable pelvic injuries associated with sacroiliac disruption are challenging. Although percutaneous iliosacral fixation using two screws at S1 vertebral body has been shown beneficial, the use of two transiliac screws at S1 has been proposed to increase the fixation strength of the construct. In the herein study, the finite element method (FEM) was performed to analyse the biomechanical behaviour of five different constructions using iliosacral screws only, transiliac screws only, and combining an iliosacral and a transiliac screw. A vertically unstable AO 61C1.2 type pelvic injury was produced for the evaluation of the posterior pelvic displacement and implant stress, and the anterior implant stress using FEM. The symphysis pubis was fixed with a 3.5-mm reconstruction plate in all cases. The model was axially loaded with 800N applied in the centre of S1 body, perpendicular to the ground (Y-axis), simulating the bipodal stance moment. There was a statistically significant reduction in both posterior displacement and implant stresses in the groups fixed with at least one transiliac screw compared to the groups fixed with iliosacral screws. In our FEM study, the construct using two transiliac screws in S1 is biomechanically superior for stabilizing the sacroiliac joint in vertically unstable pelvic ring injuries compared to the other configurations. Lateral displacement, posterior displacement, and von Mises stress were reduced with this construct. A good option can be the use of one iliosacral screw and one transiliac screw in S1.

Biomechanical effects of S1 sacroiliac screws versus S2 sacroiliac screws on sacroiliac screws combined with a lumbar iliac fixation in the treatment of vertical sacral fractures: a biomechanical finite element analysis

OBJECTIVE

To examine the impact of sacroiliac screw position and length on the biomechanical properties of triangular osteosynthesis in treating unilateral vertical sacral fractures and provide a clinical reference.

METHODS

Unilateral Denis type II sacral fractures were modelled using finite elements to represent Tile C pelvic ring injuries. Six sacroiliac screws were used with iliolumbar fixation patterns to fix the sacral fractures, and the sacral stability, maximum pressure, and stress distribution were compared among the internal fixation modalities.

RESULTS

The best vertical stability of the internal fixation model was achieved when the S1 segment was fixed with lengthened sacroiliac screws, followed by when the S1 segment was fixed using normal sacroiliac screws. There was no significant difference in vertical stability between the S1 + S2 dual-segment fixation model and the S1-segment fixation model. The maximum pressure under a vertical force of 600 N showed a trend of L5LS1 < L5NS1 < L5LS12 < L5LS2 < L5NS2 < L5NS12.

CONCLUSIONS

In unilateral vertical sacral fractures (Denis II) treated with triangular osteosynthesis using triangular jointing combined with unilateral iliolumbar + sacroiliac screw fixation, the use of a single lengthened sacroiliac screw for the S1 segment is recommended to achieve the best vertical stability of the sacrum with less maximum compression on the internal fixation components. If it is not possible to apply a lengthened sacroiliac screw, the use of a normal sacroiliac screw for the S1 segment is recommended. Adding an S2 screw does not significantly increase the vertical stability of the sacrum.

Biomechanical comparison of four triangular osteosynthesis fixations for unilateral vertical sacral fractures

To compare the stability and biomechanical characteristics of four commonly used triangular osteosynthesis techniques to treat unilateral vertical sacral fractures and provide a clinical application reference. Finite element models of Tile C-type pelvic ring injury (unilateral Denis II sacral fracture) were produced. In four models, sacral fractures were fixed with a combination of unilateral L5, unilateral L4, and L5 iliac lumbar fixation with lengthened or normal sacroiliac screws. The biomechanical properties of the four fixation models were measured and compared under bipedal stance and lumbar rotation. The fixation stability of the model with the lengthened sacroiliac screw was excellent, and the fracture end was stable. The stability of fixation using unilateral L4 and L5 segments was close to that of unilateral L5 segment fixation. Triangular osteosynthesis transverse stabilization devices using lengthened sacroiliac screws can increase the vertical stability of the sacrum after internal fixation and increase the stability of the fracture. When triangular osteosynthesis lumbar fixation segments were selected, simultaneous fixation of L4 and L5 segments versus only L5 segments did not significantly enhance the vertical stability of the sacrum or the stability of the fracture end.

Finite element analysis of sacral-alar-iliac screw fixation for sacroiliac joint dislocation

The percutaneous sacroiliac (SI) screw is a common fixation option for posterior ring disruption in pelvic fractures. However, SI screw placement is difficult and can injure adjacent neurovascular structures. The sacral-alar-iliac screw (SAI) is a safe, reliable free-hand sacral pelvic fixation technique. To investigate the biomechanical stability of SAI for SI joint dislocation, finite element analysis was performed in unstable Tile-Type B and C pelvic ring injuries. The displacement in S1 (fixation of a unilateral S1 segment with one SI screw), TS1 (fixation of the S1 segment with a transsacra 1 screw), TS2 (fixation of the S2 segment with a transsacra 2 screw), S1AI, and S2AI exceeded the normal SI joint mobility. Sufficient stability after SI joint dislocation was obtained with (TS1 + TS2), (TS2 + S1), (S1AI + S2AI + rod), (S1AI + S2AI), and (S1 + S2AI + S1 pedicle) fixation. The TS1 + TS2 group had the smallest displacement and lowest peak screw stress, followed by (S1 + S2AI + S1 pedicle) placement. Our findings suggest that SAI screws are a valuable option for SI joint dislocation.

Finite Element Analysis and Transiliac-Transsacral Screw Fixation for Posterior Pelvic Ring with Sacrum Dysplasia

OBJECTIVE

Posterior pelvic ring sacroiliac screws are preferred by clinicians for their good biomechanical performance. However, there are few studies on mechanical analysis and intraoperative screw insertion of the dysplastic sacrum and sacroiliac screw. This study investigated the biomechanical performance of oblique sacroiliac screws (OSS) in S1 combined with transiliac-transsacral screws (TTSs) in S2 for pelvic fracture or sacroiliac dislocation with dysplastic sacrum and evaluated the safety of screw placement assisted by the navigation template.

METHODS

Six models were established, including one OSS fixation in the S2 segment, one transverse sacroiliac screw (TSS) fixation in the S2 segment, one TTS fixation in the S2 segment, one OSS fixation in the S1 and S2 segments, one OSS fixation in the S1 segment and one TSS fixation in the S2 segment, one OSS fixation in the S1 segment and one TTS fixation in the S2 segment. Then, finite element analysis (FEA) was performed. Twelve dysplastic sacrum patients with pelvis fracture or sacroiliac dislocation underwent OSS insertion in the S1 combined with TTS insertion in the S2 under the assistance of the patient-specific locked navigation template. Grading and Matta scores were evaluated after surgery.

RESULTS

In the one-screw fixation group, the vertical displacements of the sacrum surface of S2 OSS, S2 TSS and S2 TTS were 1.23, 1.42, and 1.22 mm, respectively, and the maximum stress of screw were 139.45 MPa, 144.81 MPa, 126.14 MPa, respectively. In the two-screw fixation group, the vertical displacements of the sacrum surface of the S1 OSS + S2 OSS, S1 OSS + S2 TSS and S1 OSS + S2 TTS were 0.91, 1.06, and 0.75 mm, respectively, and the maximum stress of screw were 149.26 MPa, 167.13 Pa, 136.76 MPa, respectively. Clinically, a total of 12 TTS and OSS were inserted under the assistance of navigation templates, with a surgical time of 55 ± 7.69 min, bleeding of 57.5 ± 18.15 ml and radiation times of 14.5 ± 4.95. One of the TTS and one of the OSS were grade 1, and the other screws were grade 0. The Matta scores of nine patients were excellent, and three patents were good.

CONCLUSION

OSS in the S1 combined with TTS in the S2 had the best mechanical stability in six models, and it is safe for screw insertion assisted by the patient-specific locked navigation template.

Three-dimensional navigation-guided percutaneous trans-symphyseal screw for mechanically unstable pubic symphysis diastasis

Minimally invasive trans-symphyseal screw (TSS) for pubic symphysis diastasis was recently advocated, and its feasibility and reproducibility under 3D-navigation guidance are explored. Fifteen cases between 2016 and 2021 with a background of pubic symphysis diastasis are reviewed in this case series. Twenty-two TSS were inserted with an average Injury Severity Score of 35.3. Sixty percent received a one-stage procedure including fracture reduction, intra-operative 3D imaging, and planning followed by execution. The mean operative time and blood loss were 132 minutes and 160 ml, respectively. Average fracture healing was 5.8 months with two delayed unions at 9 months. The pubic symphysis distance was maintained in all cases at 6 months post-op. The average Marjeed score, Multicenter Study Group Pelvic Outcome Score, and Numeric pain rating scale were 60.2, 6.5, and 2.7, respectively. We conclude that 3D-navigation-guided percutaneous TSS restores pelvic stability and provides satisfactory pain control, and thus a safe and effective alternative to open reduction internal fixation.

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.

Simultaneous reduction and fixation of concomitant acetabular fracture and ipsilateral sacroiliac joint injury through the pararectus approach: a technical report and early radiological outcome

PURPOSE

Osteosynthesis for acetabular fractures with ipsilateral sacroiliac joint (SIJ) injuries remains challenging for orthopedic surgeons, despite the evolution of surgical approaches, such as the pararectus approach, and treatment sequences. The study aimed to describe the details of the treatment of acetabular fracture with ipsilateral SIJ injury by the pararectus approach and to report its surgical outcomes.

METHODS

We retrospectively assessed patients with acetabular fractures and ipsilateral SIJ injuries undergoing osteosynthesis by the pararectus approach over a three-year period. Evaluation parameters of the quality of reduction of both acetabulum and pelvis injuries were, among others, Matta's criteria, Lefaivre's criteria, inlet/outlet ratios, and maximal gap measured on computed tomography (CT) scans.

RESULTS

Ten patients (seven men and three women) were enrolled. Pelvic ring injuries classified as AO B2.3 and acetabular fractures involving two columns were the most common fractures, accounting for 70% and 60%, respectively. Radiological evaluation for pelvic ring injury revealed three excellent and seven good results according to Matta's criteria, as well as five excellent, three good, and one fair results according to Lefaivre's criteria. Inlet and outlet ratios were between 0.84-1.06 and 0.93-1.60, respectively. The distance of the sacroiliac joints significantly improved postoperatively in both axial and coronal views (P = 0.002). Further, the maximal articular gap and step-off of acetabular fractures on axial, coronal, and sagittal view CT scans showed statistically significant improvements after osteosynthesis.

CONCLUSION

Simultaneous reduction and fixation of acetabular fractures with ipsilateral SIJ injuries using the pararectus approach achieved satisfactory radiological outcomes.

LEVEL OF EVIDENCE

IV.

TRIAL REGISTRATION

Retrospectively registered.

Percutaneous iliosacral screw and trans-iliac trans-sacral screw with single C-arm fluoroscope intensifier is a safe treatment for pelvic ring injuries

To elucidate the accuracy, efficacy, and safety of percutaneous iliosacral screw (ISS) and trans-iliac trans-sacral screw (TITS) insertion using a single C-arm fluoroscopy intensifier. Additionally, the potential risk factors that might cause mal-positioned screws were identified. Patients with pelvic ring injuries who underwent percutaneous screw fixation in a single medical institute were divided into an ISS group (n = 59) and a TITS group (n = 62) and assessed. The angles deviated from ideal orientation (ADIO) of the implanted screw were measured, and potential risk factors for mal-positioned screws were analyzed. Overall, the reduction quality of the pelvic ring was good or excellent in 70 patients (82.4%) by Matta’s criteria and in 48 patients (56.5%) by Lefaivre’s criteria. ADIO measurements of the ISS and TITS groups via multi-planar computed tomography were 9.16° ± 6.97° and 3.09° ± 2.8° in the axial view, respectively, and 5.92° ± 3.65° and 2.10° ± 2.01° in the coronal view, respectively. Univariate statistical analysis revealed body mass index as the single potential risk factor of mal-positioned screws. With careful preoperative planning and intraoperative preparations, placing ISS and TITS under the guidance of single C-arm fluoroscopy intensifier is a reliable and safe technique. Caution should be exercised when performing this procedure in patients with a high body mass index.

Comparison of Outcomes Following TiRobot-Assisted Sacroiliac Screw Fixation with Bone Grafting and Traditional Screw Fixation without Bone Grafting for Unstable Osteoporotic Sacral Fracture: A Single-Center Retrospective Study of 33 Patients

BACKGROUND This retrospective study from a single center aimed to compare patient outcomes following TiRobot-assisted sacroiliac screw fixation and bone grafting with traditional screw fixation without bone grafting in 33 patients with unstable osteoporotic sacral fracture (UOSF). MATERIAL AND METHODS Patients with UOSF were included and divided into 2 groups: a TiRobot-assisted surgical group with 18 patients (robot-aided sacroiliac screw fixation and bone grafting) and a standard surgical group with 15 patients (free-hand screw fixation without bone grafting). T values of bone mineral density (BMD) £-2.5 standard deviation (SD) were diagnosed as osteoporosis. Screw positioning and fracture healing time were evaluated. Functional outcomes were investigated at the final follow-up. RESULTS There were no statistically significant differences in screw positioning; however, there were satisfactory positioning rates in 94.4% (17/18) of patients in the TiRobot-assisted surgical group and 73.3% (11/15) in the standard surgical group. The advantages with TiRobot on surgical time of screw placement, fluoroscopy frequency, and total drilling times were noted (P=0.000). The nonunion rates were 5.6% (1/18) in the TiRobot-assisted surgical group and 33.3% (5/15) in the standard group (P=0.039). Healing time in the union cases had a significant difference (P=0.031). Functional outcome scores in the TiRobot-assisted surgical group were superior to that in the standard group (P=0.014). CONCLUSIONS The findings showed that TiRobot-assisted sacroiliac screw fixation and bone grafting was a safe and effective surgical treatment option that had a reduced radiation dose and improved fracture healing, when compared with standard screw fixation without bone grafting.

Biomechanical study of transsacral-transiliac screw fixation versus lumbopelvic fixation and bilateral triangular fixation for "H"- and "U"-type sacrum fractures with traumatic spondylopelvic dissociation: a finite element analysis study

Objective

To compare the biomechanical stability of transsacral-transiliac screw fixation and lumbopelvic fixation for “H”- and “U”-type sacrum fractures with traumatic spondylopelvic dissociation.

Methods

Finite element models of “H”- and “U”-type sacrum fractures with traumatic spondylopelvic dissociation were created in this study. The models mimicked the standing position of a human. Fixation with transsacral-transiliac screw fixation, lumbopelvic fixation, and bilateral triangular fixation were simulated. Biomechanical tests of instability were performed, and the fracture gap displacement, anteflexion, rotation, and stress distribution after fixation were assessed.

Results

For H-type fractures, the three kinds of fixation ranked by stability were bilateral triangular fixation > lumbopelvic fixation > transsacral-transiliac screw fixation in the vertical and anteflexion directions, bilateral triangular fixation > transsacral-transiliac S1 and S2 screw fixation > lumbopelvic fixation in rotation. The largest displacements in the vertical, anteflexion, and rotational directions were 0.57234 mm, 0.37923 mm, and 0.13076 mm, respectively. For U-type fractures, these kinds of fixation ranked by stability were bilateral triangular fixation > lumbopelvic fixation > transsacral-transiliac S1 and S2 screw fixation > transsacral-transiliac S1 screw fixation in the vertical, anteflexion, and rotational directions. The largest displacements in the vertical, anteflexion, and rotational directions were 0.38296 mm, 0.33976 mm, and 0.05064 mm, respectively.

Conclusion

All these kinds of fixation met the mechanical criteria for clinical applications. The biomechanical analysis showed better bilateral balance with transsacral-transiliac screw fixation. The maximal displacement for these types of fixation was less than 1 mm. Percutaneous transsacral-transiliac screw fixation can be considered the best option among these kinds of fracture fixation.

Quantitative evaluation of the sacroiliac joint fixation in stress reduction on both sacroiliac joint cartilage and ligaments: A finite element analysis

BACKGROUND

The sacroiliac joint fixation is the last resort for patients with prolonged and severe joint pain. Although the clinical results of anterior fixations are conclusive, there exist several inevitable drawbacks with the surgical method such as the difficulty performing the surgery due to the presence of many organs. The posterior fixation technique has thus been developed to overcome those inconveniences. This study aims to assess in silico the mechanical environment following posterior and anterior fixations, focusing on stresses in both the sacroiliac cartilage and dorsal ligamentous part, as well as loads experienced by the pelvic ligaments.

METHODS

Sacroiliac joint cartilage, dorsal ligamentous part stresses and pelvic ligaments loads were evaluated with three types of fixation models. A vertical load of 600 N was applied, equally distributed via both acetabula when standing and sitting.

FINDINGS

Results show that the anterior sacroiliac joint fixation reduced von Mises stresses in the cartilage and dorsal ligamentous part and decreased ligaments loads more extensively than the posterior fixation when compared to the untreated model as a reference. However, the posterior fixation still remains the desirable and preferential treatment.

INTERPRETATION

The anterior sacroiliac joint fixation showed better performances compared to the posterior one; however, the lower invasive aspect of the latter is a fundamental clinical advantage which also has the possibility to be improved by considering various screws and cages configurations. This study provides a beneficial suggestion to improve the current fixation technique.

Three-dimensional finite element analysis with different internal fixation methods through the anterior approach

BACKGROUND

With the modernization of society and transportation in the last decades in China, the incidence of high-energy trauma increased sharply in China, including that of acetabular fractures.

AIM

To establish different finite element models for acetabular posterior column fractures involving the quadrilateral area of the acetabulum.

METHODS

The three-dimensional models of the normal and fractured pelvis and the five internal fixations were established using the computed tomography data of the pelvis of a living volunteer. After the vertebral body model was inserted in the way of origin matching and all cancellous bones were copied using the duplicated cancellous bone model as the subtractive entity, the Boolean operation was performed on the pelvis model to obtain the model of the complete pelvis cortical and cancellous bones.

RESULTS

In the standing position, the maximum stress was 46.21 MPa. In the sitting position, the sacrum bore the simulated gravity load at the upper end. When comparing the five fixations, there were no significant differences in the stress mean values among groups (sitting: P = 0.9794; standing: P = 0.9741). In terms of displacement, the average displacement of the internal iliac plate group was smaller than that of the spring plate group (P = 0.002), and no differences were observed between the other pairs of groups (all P > 0.05). In the standing position, there were no significant differences in the mean value of displacement among the groups (P = 0.2985). It can be seen from the stress nephogram of the internal fixations in different positions that the stress of the internal fixation was mainly concentrated in the fracture segment.

CONCLUSION

There were no significant differences among the fixations for acetabular posterior column fractures involving the quadrilateral area of the acetabulum.

A biomechanics study on ligamentous injury in anterior-posterior compression type II pelvic injury

Background

Anterior-posterior compression (APC) type II pelvis fracture is caused by the destruction of pelvic ligaments. This study aims to explore ligaments injury in APC type II pelvic injury.

Method

Fourteen human cadaveric pelvis samples with sacrospinous ligament (SPL), sacrotuberous ligament (SBL), anterior sacroiliac ligament (ASL), and partial bone retaining unilaterally were acquired for this study. They were randomly divided into hemipelvis restricted and unrestricted groups. We recorded the separation distance of the pubic symphysis and anterior sacroiliac joint, external rotation angle, and force when ASL ruptured. We observed the external rotation damage to the pelvic bone and ligaments.

Result

When ASL failed, there was no significant difference in pubic symphysis separation (28.6 ± 8.4 mm to 23.6 ± 8.2 mm, P = 0.11) and anterior sacroiliac joint separation (11.4 ± 3.8 mm to 9.7 ± 3.9 mm, P = 0.30) between restricted and unrestricted groups. The external rotation angle (33.9 ± 5.5° to 48.9 ± 5.2°, P < 0.01) and force (553.9 ± 82.6 N to 756.6 ± 41.4 N, P < 0.01) were significantly different. Pubic symphysis separation between two groups ranged from 14 to 40 mm. In the restricted group, both SBL and SPL were injured. SPL ruptured first, and then SBL and the interosseous sacroiliac ligament were damaged while the posterior ligament remained unharmed. In the unrestricted group, interosseous sacroiliac ligament and posterior sacroiliac ligaments were damaged, while SBL and SPL were not. When the ASL, SBL, and SPL all failed, pubic symphysis and anterior sacroiliac joint separation between two groups increased significantly (from 28.6 ± 8.4 to 42.0 ± 7.6 mm, 11.4 ± 3.8 to 16.7 ± 4.2 mm respectively, all P < 0.05).

Conclusion

Pelvic external rotation injury is either hemipelvic restricted or unrestricted, which can result in different outcomes. When the ASL ruptures, the unrestricted group needs greater external rotation angle and force, without SBL or SPL injury, while both SBL and SPL were injured in another group. When ASL fails in two groups, pubic symphysis separation fluctuates considerably. Finally, when the ASL ruptures, SBL and SPL may be undamaged.

Robot-assisted S2 screw fixation for posterior pelvic ring injury

BACKGROUND

Percutaneous sacroiliac screw is one of the main methods to treat unstable posterior pelvic ring injury. However, complexity of pelvic anatomical structure increases the difficulty and risk with freehand operation. Besides, S2 screw fixation began to receive attention. The purpose of the current study was to evaluate the safety, accuracy, efficiency and clinical outcome of robot-assisted S2 screw fixation for posterior pelvic ring injury.

METHODS

We reviewed 128 cases of unstable posterior pelvic ring injury treated by percutaneous sacroiliac screw fixation in our hospital from January 2016 to January 2020. All cases were divided into robot-assisted S1 group (RAS1), robot-assisted S2 group (RAS2), freehand group S1 group (FHS1) and freehand group S2 group (FHS2). The mean times of fluoroscopy per screw and adjustment per guide wire were used to evaluate radiation exposure and the efficiency of screw placement, respectively. The final position of the screw was evaluated with postoperative CT to illustrate security and accuracy. 108 patients (84.38%) were followed up for 5~24 months and the Majeed scores were compared among groups.

RESULTS

A total of 180 screws were inserted. In comparison of the mean times of fluoroscopy per screw and adjustment per guide wire, RA group was significant less than FH group, further comparison revealed that freehand S2 placement need more fluoroscopy and adjustment times compared with freehand S1 placement, but for robot-assisted procedure, there was no difference between placing S1 and S2. Screw penetration was found in the FHS1(3/48) and FHS2(2/14) and none in RAS1 or RAS2, which means robot-assisted groups were more safety and accurate (P<0.001). The mean Majeed score in RAS1 (83.33±13.47) and RAS2 (82.32±11.42) was higher than in FHS1 (80.43±12.25) and FHS2 (75.08±18.47), but this difference failed to reach significant.

CONCLUSION

Compared with the freehand operation, TiRobot increased the safety and accuracy, reduced radiation exposure, and improved the efficiency. TiRobot could reduce the risk of S2 placement and provide a safe and feasible way for clinical practice.

Placas anteriores são mais efetivas do que parafusos iliossacrais na fixação da articulação sacroilíaca? Estudo Biomecânico

Introduction  Sacroiliac joint dislocations are caused by high energy trauma and commonly treated with the iliosacral screw fixation or the anterior plating of the sacroiliac joint (SIJ). However, there is a lack of consensus regarding which procedure is the most successful in treating sacroiliac joint dislocations. This aims to compare stiffness and maximum load of pelvises with sacroiliac joint dislocations treated with both procedures in a synthetic bone model.

Methods  Synthetic pelvises were mounted and divided into 2 treatment groups ( n  = 5): a model with two orthogonal plates placed anteriorly to the SIJ (PPS group) and another with two iliosacral screws fixating the SIJ (SPS group), both with pubic symphysis fixation. The maximum load supported by each sample was observed and the stiffness was calculated from the curve load vs displacement. The mean values of load to failure and stiffness for each group were compared with the Mann-Whitney U test ( p  < 0.05 was considered significant for all analysis).

Results  The mean load to failure supported by the PPS group was 940 ± 75 N and the SPS was 902 ± 56 N, with no statistical difference. The SPS group showed higher values of stiffness (68.6 ± 11.1 N/mm) with statistical significant difference in comparison to the PPS sample (50 ± 4.0 N/mm). The mode of failure was different in each group tested.

Conclusion  Despite lower stiffness, the anterior plating fixation of the sacroiliac joint can be very useful when the iliosacral screw fixation cannot be performed. Further studies are necessary to observe any differences between these two procedures on the clinical and surgical setting.

Three-Dimensional Finite Element Analysis of the Effects of Ligaments on Human Sacroiliac Joint and Pelvis in Two Different Positions

To present the ligament effects on sacroiliac joint (SIJ) stability and human pelvis biomechanical characteristics in two different positions by using three-dimensional (3D) finite element (FE) models of pelvis. Based on the computed tomography (CT) data of human pelvis, three-dimensional FE models of human pelvis in sitting and standing positions were established, which include the bone (sacrum, ilium, and coccyx) and six ligaments (sacroiliac, sacrospinous, sacrotuberous, inguinal, superior pubic, and arcuate pubic ligaments). 600 N vertical load was applied at the upper surface of sacrum to analyze the stress and displacement distribution of pelvis and SIJ. The simulation results demonstrated that the maximum stresses of sacrum and ilium on SIJ contact surface were 5.63 MPa and 7.40 MPa in standing position and 7.44 MPa and 7.95 MPa in sitting position. The stresses of ligament dysfunction group were higher than that of health group, which increased by 22.6% and 35.7% in standing position and 25.2% and 43.6% in sitting position in sacrum and ilium. The maximum displacements located on the upper surface of sacrum, which were 0.13 mm and 1.04 mm in standing and sitting positions. Ligaments dysfunction group increased 30.7% and 9.6% than health group in standing and sitting positions. The integral displacement of pelvis was greater in sitting position. The location of stress concentration and displacement distribution of pelvic bone are closely resembled previous research results in two different positions. The simulation results may provide beneficial information and theoretical models for clinical research of pelvic fracture, joint movement, and ligament functional injuries, and so on.

Gradient Biomineralized Silk Fibroin Nanofibrous Scaffold with Osteochondral Inductivity for Integration of Tendon to Bone

Enthesis injury repair remains a huge challenge because of the unique biomolecular composition, microstructure, and mechanics in the interfacial region. Surgical reconstruction often creates new bone-scaffold interfaces with mismatched properties, resulting in poor osseointegration. To mimic the natural interface tissue structures and properties, we fabricated a nanofibrous scaffold with gradient mineral coating based on 10 × simulated body fluid (SBF) and silk fibroin (SF). We then characterized the physicochemical properties of the scaffold and evaluated its biological functions both in vitro and in vivo. The results showed that different areas of SF nanofibrous scaffold had varying levels of mineralization with disparate mechanical properties and had different effects on bone marrow mesenchymal stem cell growth and differentiation. Furthermore, the gradient scaffolds exhibited an enhancement of integration in the tendon-to-bone interface with a higher ultimate load and more fibrocartilage-like tissue formation. These findings demonstrate that the silk-based nanofibrous scaffold with gradient mineral coating can regulate the formation of interfacial tissue and has the potential to be applied in interface tissue engineering.

Biomechanics of the Sacroiliac Joint: Surgical Treatments

BACKGROUND

Fixation is one of the most common surgical techniques for the treatment of chronic pain originating from the sacroiliac joint (SIJ). Many studies have investigated the clinical outcomes and biomechanics of various SIJ surgical procedures. However, the biomechanical literature points to several issues that need to be further explored, especially for the devices used in minimally invasive surgery of the SIJ. This study (part II) aims to assess biomechanical literature to understand the existing information as it relates to efficacies of the surgical techniques and the gaps in the knowledge base. Part I reviewed basic anatomy and mechanics of the SIJ joint, including difference between males and females, and causes of pain emanating from these joints.

METHODS

A thorough literature review was performed pertaining to studies related to SIJ fixation techniques and the biomechanical outcomes of the surgical procedures.

RESULTS

Fifty-five studies matched the search criteria and were considered for the review. These articles predominantly pertained to the biomechanical outcomes of the minimally invasive surgery with different instrumentation systems and surgical settings.

CONCLUSIONS

The SIJ is one of the most overlooked sources of lower back pain. The joint is responsible for the pain in 15% to 30% of people suffering from lower back pain. Various studies have investigated the clinical outcomes of different surgical procedures intended to improve the pain and quality of life following surgery. The data show that these techniques are indeed effective. However, clinical studies have raised several issues, like optimal number and positioning of implants, unilateral versus bilateral placements, adjacent segment disease, implant designs, and optimal location of implants with respect to variations in bone density across the SIJ. Biomechanical studies using in vitro and in silico techniques have addressed some of these issues. Studies also point out the need for additional investigations for a better understanding of the underlying mechanics for the improved long-term surgical outcomes. Further long-term clinical follow-ups are essential as well. This review presents pertinent findings.

Comparison of Biomechanical Performance of Five Different Treatment Approaches for Fixing Posterior Pelvic Ring Injury

Background

A large number of pelvic injuries are seriously unstable, with mortality rates reaching 19%. Approximately 60% of pelvic injuries are related to the posterior pelvic ring. However, the selection of a fixation method for a posterior pelvic ring injury remains a challenging problem for orthopedic surgeons. The aim of the present study is to investigate the biomechanical performance of five different fixation approaches for posterior pelvic ring injury and thus provide guidance on the choice of treatment approach in a clinical setting.

Methods

A finite element (FE) model, including the L3-L5 lumbar vertebrae, sacrum, and full pelvis, was created from CT images of a healthy adult. Tile B and Tile C types of pelvic fractures were created in the model. Five different fixation methods for fixing the posterior ring injury (PRI) were simulated: TA1 (conservative treatment), TA2 (S1 screw fixation), TA3 (S1 + S2 screw fixation), TA4 (plate fixation), and TA5 (modified triangular osteosynthesis). Based on the fixation status (fixed or nonfixed) of the anterior ring and the fixation method for PRI, 20 different FE models were created. An upright standing loading scenario was simulated, and the resultant displacements at the sacroiliac joint were compared between different models.

Results

When TA5 was applied, the resultant displacements at the sacroiliac joint were the smallest (1.5 mm, 1.6 mm, 1.6 mm, and 1.7 mm) for all the injury cases. The displacements induced by TA3 and TA2 were similar to those induced by TA5. TA4 led to larger displacements at the sacroiliac joint (2.3 mm, 2.4 mm, 4.8 mm, and 4.9 mm), and TA1 was the worst case (3.1 mm, 3.2 mm, 6.3 mm, and 6.5 mm).

Conclusions

The best internal fixation method for PRI is the triangular osteosynthesis approach (TA5), followed by S1 + S2 screw fixation (TA3), S1 screw fixation (TA2), and plate fixation (TA4).

Space available for trans-sacral implants to treat fractures of the pelvis assessed by virtual implant positioning

INTRODUCTION

The use of trans-sacral implants to treat fractures of the sacrum is limited by the variable pelvic anatomy. We were interested in how many trans-sacral implants can be placed per pelvis? If a trans-sacral implant cannot be placed in S1, where is the cortex perforated, and is the use of sacroiliac screws safe in these pelves?

MATERIALS AND METHODS

3D pelvic models were created from CT scans of 156 individuals without fractures (92 European and 64 Japanese, 79 male and 77 female, mean age 66.7 ± 13.7 years). Trans-sacral implants with a diameter of 7.3 mm were positioned virtually with and without a surrounding safe zone of 12 mm diameter.

RESULTS

Fifty-one percent of pelves accommodated trans-sacral implants in S1 with a safe zone. Twenty-two percent did not offer enough space in S1 for an implant even when ignoring the safe zone. Every pelvis had sufficient space for a trans-sacral implant in S2, in 78% including a safe zone as well. In S1, implant perforation was observed in the sacral ala and iliac fossa in 69%, isolated iliac fossa perforation in 23% and perforation of the sacral ala in 8%. Bilateral sacroiliac screw placement was always possible in S1.

CONCLUSIONS

The use of trans-sacral implants in S1 requires meticulous preoperative planning to avoid injury of neurovascular structures. S2 more consistently offers space for trans-sacral implants.

Comparative Study of Percutaneous Sacroiliac Screw with or without TiRobot Assistance for Treating Pelvic Posterior Ring Fractures

Objectives

To analyze the curative effect of TiRobot surgical robotic navigation and location system‐assisted percutaneous sacroiliac screw fixation and percutaneous sacroiliac screw by traditional fluoroscopy, and to summarize the safety and benefits of TiRobot.

Methods

A total of 91 patients with pelvic posterior ring fractures from December 2015 to February 2018 were included in this study. According to the surgical methods selected by the patients, the patients were divided into a TiRobot surgical robotic navigation and location system group (TiRobot group) and a percutaneous sacroiliac screw fixation group (traditional group). Statistical indicators included the number of sacroiliac screws, the time of planning the sacroiliac screw path, fluoroscopy frequency, fluoroscopy time, operation time, length of incision, blood loss, anesthesia time, the healing process of skin incisions, and fracture healing time. Fracture reduction was evaluated according to the maximum displacement degree at the inlet and outlet view X‐ray or CT. Matta standard was used to evaluate fracture reduction. At the last follow‐up, the Majeed function system was used to evaluate the function.

Results

All patients were followed up for 8 to 32 months. A total of 66 sacroiliac screws were implanted in the TiRobot group. A total of 43 sacroiliac screws were implanted in the traditional group. There were statistically significant differences in terms of fluoroscopy frequency, fluoroscopy time, operation time, incision length, anesthesia time, and blood loss between the two groups; the TiRobot group was superior to the traditional group. The healing time of the TiRobot group and the traditional group was 4.61 ± 0.68 months (range, 3.5–6.3 months) and 4.56 ± 0.78 months (range, 3.4–6.2 months), respectively, and there was no statistical difference. Postoperatively, by Matta standard, the overall excellent and good rate of fracture reduction was 89.28% and 88.57%, respectively. At the last follow‐up, by Majeed function score, the overall excellent and good rate was 91.07% and 91.43%. There was no statistical difference between the two groups.

Conclusion

Sacroiliac screw implantation assisted by TiRobot to treat the posterior pelvic ring fractures has the characteristics of less trauma, shorter operation time, and less blood loss. TiRobot has the characteristics of high safety and accuracy and has great clinical application value.

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.

In Silico Pelvis and Sacroiliac Joint Motion: Refining a Model of the Human Osteoligamentous Pelvis for Assessing Physiological Load Deformation Using an Inverted Validation Approach

Introduction. Computational modeling of the human pelvis using the finite elements (FE) method has become increasingly important to understand the mechanisms of load distribution under both healthy and pathologically altered conditions and to develop and assess novel treatment strategies. The number of accurate and validated FE models is however small, and given models fail resembling the physiologic joint motion in particular of the sacroiliac joint. This study is aimed at using an inverted validation approach, using in vitro load deformation data to refine an existing FE model under the same mode of load application and to parametrically assess the influence of altered morphology and mechanical data on the kinematics of the model. Materials and Methods. An osteoligamentous FE model of the pelvis including the fifth lumbar vertebra was used, with highly accurate representations of ligament orientations. Material properties were altered parametrically for bone, cartilage, and ligaments, followed by changes in bone geometry (solid versus 3 and 2 mm shell) and material models (linear elastic, viscoelastic, and hyperelastic isotropic), and the effects of varying ligament fiber orientations were assessed. Results. Elastic modulus changes were more decisive in both linear elastic and viscoelastic bone, cartilage, and ligaments models, especially if shell geometries were used for the pelvic bones. Viscoelastic material properties gave more realistic results. Surprisingly little change was observed as a consequence of altering SIJ ligament orientations. Validation with in vitro experiments using cadavers showed close correlations for movements especially for 3 mm shell viscoelastic model. Discussion. This study has used an inverted validation approach to refine an existing FE model, to give realistic and accurate load deformation data of the osteoligamentous pelvis and showed which variation in the outcomes of the models are attributed to altered material properties and models. The given approach furthermore shows the value of accurate validation and of using the validation data to fine tune FE models.

Robot-assisted Minimally-invasive Internal Fixation of Pelvic Ring Injuries: A Single-center Experience

Objective

To investigate the indications, surgical strategy and techniques, safety, and efficacy of robot‐assisted minimally‐invasive internal fixation of pelvic ring injuries.

Methods

The clinical data of 86 patients with anterior and posterior pelvic ring injuries who underwent robot‐assisted minimally‐invasive internal fixation were retrospectively analyzed. The patients included 57 men and 29 women aged between 22 and 75 years, with an average age of (40.2 ± 13.6) years. According to the Tile classification, there were 5 (5.8%) type A2, 48 (55.8%) type B, and 33 (38.4%) type C fractures. The surgical plans were formulated based on the injury type of the pelvic ring, the effectiveness of the reduction, and the integrity of the osseous channel. Posterior pelvic ring injuries were treated with robot‐assisted percutaneous cannulated screw fixation of the sacroiliac joint. Anterior pelvic ring injuries were treated with robot‐assisted percutaneous cannulated screw fixation of the pubic ramus, INFIX fixation, or a “hybrid” fixation. The surgical complications and the efficacy of the surgical treatments were analyzed.

Results

A total of 274 screws were inserted with robotic assistance, of which 262 screws were successfully inserted to a satisfactory position on the first attempt. The number of screws placed per person was 3.2 on average, and the average operation time was 175 min (35–280 min). Fluoroscopies were performed an average of 29.1 times (range, 9–63 times), and it took 6.1 s to place each screw. There were 13 unsatisfactory guiding needle placements during the surgeries, among 7 of which cutting or penetration of the cortex was re‐planned until satisfactory insertions; 1 penetrated the pubic cortex, causing hemorrhage of the “crown of death,” and was changed to “hybrid surgery”. The robot‐assisted surgical wounds all healed by primary intention with satisfactory position and precision of screw insertions. All patients were followed up for 3–6 months, with an average of 4.2 months. There were two postoperative fixation failures, in which both patients had separated symphysis pubes after hybrid surgery. The average Majeed score at the last follow‐up was 92.4 points.

Conclusions

Robot‐assisted surgery is accurate and minimally invasive, with a high success rate for one‐time screw placement and satisfactory clinical results. The indications and surgical strategy should be rigorously selected, the level of surgical techniques mastered, and the operating procedures standardized, all of which may help to prevent surgical complications. Robot‐assisted surgery provides a novel modality for the minimally‐invasive treatment of pelvic ring injuries.

In-silico pelvis and sacroiliac joint motion-A review on published research using numerical analyses

BACKGROUND

Computational models of the human pelvis have become highly useful tools to assess mechanisms of injury, diagnostics and treatment options. The purpose of this systematic literature review was to summarize existing pelvic computer models, to assess their comparability and the measures taken for experimental validation.

METHODS

Research on virtual simulations of the posterior pelvis and sacroiliac joint available from the ISI Web of Knowledge, PubMed and Scopus databases available until January 2018 were included.

FINDINGS

From a total of 3938 articles, 33 studies matched the criteria. Thirteen studies reported on experimental biomechanics, of which seven were parametric. Thirteen studies focused on pelvic injury and surgery, three were clinical case reports. One study assessed the effects of lumbar surgery on the sacroiliac joint, three studies on diagnostics and the non-surgical treatment of the sacroiliac joint. The mode of load application, geometry, material laws and boundary conditions varied vastly between the studies. The majority excluded the lumbosacral transition as part of pelvic biomechanics, and used isotropic linear elastic material properties. Outcomes of the analyses were reported inconsistently with negative impact on their comparability, and validation was commonly conducted by literature with varying agreement of the loading conditions.

INTERPRETATION

Comparability and validation are two major issues of present computational biomechanics of the pelvis. These issues diminish the transferability of the in-silico findings into real-life scenarios. In-vitro cadaveric models remain the realistic standard to account for the present computational analyses which simplify the complex nature of musculoskeletal tissues of the pelvis.

A systematic review of the morphology and function of the sacrotuberous ligament

The sacrotuberous ligament (STL) has been linked to conditions such as pelvic girdle pain and pudendal nerve entrapment, yet its contribution to pelvic stability is debated. The purpose of this review was to explore the current understanding of the STL and highlight any gaps in knowledge regarding its anatomy and function. A systematic search of the literature was conducted, focussing on the morphology and attachments of the STL, the relationship of the STL with surrounding structures, and its neurovascular supply and function. A total of 67 papers and four textbooks were obtained. The attachment sites of the STL are largely consistent; however, the extent of its connections with the long head of biceps femoris, gluteus maximus, piriformis, the posterior layer of the thoracolumbar fascia, and sacrospinous ligament are unclear. Morphometric parameters, such as mean STL length (6.4-9.4 cm), depth (0.3-0.4 cm), and width (1.8-3.5 cm, at its mid-point) are variable within and between studies, and little is known about potential side-, age-, or sex-related differences. The STL is pierced in several sites by the inferior and superior gluteal arteries, but information on its innervation pattern is sparse. Functionally, the STL may limit sacral nutation but it appears to have a limited contribution to pelvic stability. Some morphological aspects of the STL warrant further investigation, particularly its connections with surrounding structures, innervation pattern and function. Knowledge of the detailed anatomy and function of this ligament is important to better understanding its role in clinical conditions. Clin. Anat. 32:396-407, 2019. © 2018 Wiley Periodicals, Inc.

Effects of Cutting the Sacrospinous and Sacrotuberous Ligaments

The sacrospinous (SS) and sacrotuberous (ST) ligaments form a complex at the posterior pelvis, with an assumed role as functional stabilizers. Experimental and clinical research has yielded controversial results regarding their function, both proving and disproving their role as pelvic stabilizers. These findings have implications for strategies for treating pelvic injury and pain syndromes. The aim of the present simulation study was to assess the influence of altered ligament function on pelvis motion. A finite elements computer model was used. The two-leg stance was simulated, with the load of body weight applied via the fifth lumbar vertebra and both femora, allowing for nutation of the sacroiliac joint. The in-silico kinematics were validated with in-vitro experiments using the same scenario of load application following SS and ST transection in six human cadavers. Modeling of partial or complete ligament failure caused significant increases in pelvis motion. This effect was most pronounced if the SS and ST were affected with 164% and 182%, followed by the sacroiliac and iliolumbar ligaments with 123% and 147%, and the pubic ligaments with 113% and 119%, for partial and complete disruption, respectively. Simultaneous ligament transection multiplied the effects on pelvis motion by up to 490%. Unilateral ligament injury altered the motion at the pelvis contralaterally. The experiments presented here provide strong evidence for the stabilizing role of the SS and ST. A fortiori, the instability resulting from partial or complete SS and ST injury merits consideration in treatment strategies involving these ligaments as important stabilizers. Clin. Anat. 32:231-237, 2019. © 2018 Wiley Periodicals, Inc.

Biomechanical evaluation of sacroiliac joint fixation with decortication

BACKGROUND CONTEXT

Fusion typically consists of joint preparation, grafting, and rigid fixation. Fusion has been successfully used to treat symptomatic disruptions of the sacroiliac joint (SIJ) and degenerative sacroiliitis using purpose-specific, threaded implants. The biomechanical performance of these systems is important but has not been studied.

PURPOSE

The objective of this study was to compare two techniques for placing primary (12.5 mm) and secondary (8.5 mm) implants across the SIJ.

STUDY DESIGN

This is a human cadaveric biomechanical study of SIJ fixation.

MATERIALS AND METHODS

Pure-moment testing was performed on 14 human SIJs in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) with motion measured across the SIJ. Specimens were tested intact, after destabilization (cutting the pubic symphysis), after decortication and implantation of a primary 12.5-mm implant at S1 plus an 8.5-mm secondary implant at either S1 (S1-S1, n=8) or S2 (S1-S2, n=8), after cyclic loading, and after removal of the secondary implant. Ranges of motion (ROMs) were calculated for each test. Bone density was assessed on computed tomography and correlated with age and ROM. This study was funded by Zyga Technology but was run at an independent biomechanics laboratory.

RESULTS

The mean±standard deviation intact ROM was 3.0±1.6° in FE, 1.5±1.0° in LB, and 2.0±1.0° in AR. Destabilization significantly increased the ROM by a mean 60%-150%. Implantation, in turn, significantly decreased ROM by 65%-71%, below the intact ROM. Cyclic loading did not impact ROM. Removing the secondary implant increased ROM by 46%-88% (non-significant). There was no difference between S1-S1 and S1-S2 constructs. Bone density was inversely correlated with age (R=0.69) and ROM (R=0.36-0.58).

CONCLUSIONS

Fixation with two threaded rods significantly reduces SIJ motion even in the presence of joint preparation and after initial loading. The location of the secondary 8.5-mm implant does not affect construct performance. Low bone density significantly affects fixation and should be considered when planning fusion constructs. Findings should be interpreted in the context of ongoing clinical studies.

Robot-assisted percutaneous screw placement combined with pelvic internal fixator for minimally invasive treatment of unstable pelvic ring fractures

Purpose

The purpose of this study was to investigate the safety and efficacy of the combination of robot‐assisted percutaneous screw placement and pelvic internal fixator (INFIX) for minimally invasive treatment of unstable anterior and posterior pelvic ring injuries.

Methods

From September 2016 to June 2017, twenty‐four patients with unstable anterior and posterior pelvic ring injuries were treated with TiRobot‐assisted percutaneous sacroiliac cannulated screw fixation on the posterior pelvic ring combined with robot‐assisted pedicle screw placement in the anterior inferior iliac spine along with INFIX on the anterior pelvic ring. The results of the treatment, including surgery duration, fluoroscopy frequency, total drilling, amount of blood loss, fracture healing time, and postoperative functional outcomes were recorded and compared with another 21 similar patients who underwent conventional manual positioning surgery.

Results

The TiRobot group incurred significantly shorter duration of surgery; less fluoroscopy frequency, intraoperative bleeding, and total drilling than in the conventional group (P < 0.05). Postoperative radiological follow‐up showed that all screws were in the safe area and no screw penetrated the cortex. All wounds healed by primary intention and no iatrogenic damage to the blood vessels, nerves, and organs occurred. Patients showed good tolerance to INFIX and reported no discomfort. The mean follow‐up duration was 5.4 months; the fractures were all healed, no loss of reduction occurred, and the mean Majeed score at the last follow‐up did not show any difference.

Conclusion

TiRobot‐assisted percutaneous screw placement combined with INFIX for the anterior and posterior pelvic ring injuries is accurate, safe, less invasive, and shows satisfactory efficacy, suggesting it is a better method for minimally invasive treatment of unstable pelvic ring fractures.

Management of the open book APC II pelvis: Survey results from pelvic and acetabular surgeons in the United Kingdom

The results of this questionnaire show that the opinion of pelvic and acetabular surgeons in the UK and Republic of Ireland vary as to the best method of fixation for APC II pelvic injuries. A single anterior plate and single sacroiliac joint (SIJ) screw was the most popular fixation method, chosen by 34%. 74% favour a single, opposed to two orthogonal anterior plates. Posterior fixation supplementing anterior plating is preferred by 63% of surgeons, 58% use a single versus 42% two SIJ screws. Case by case assessment and intraoperative screening to assess stability is essential when considering whether to stabilise the SIJ.

Critical dimensions of trans-sacral corridors assessed by 3D CT models: Relevance for implant positioning in fractures of the sacrum

Trans-sacral implants can be used alternatively to sacro-iliac screws in the treatment of osteoporosis-associated fragility fractures of the pelvis and the sacrum. We investigated trans-sacral corridor dimensions, the number of individuals amenable to trans-sacral fixation, as well as the osseous boundaries and shape of the S1 corridor. 3D models were reconstructed from pelvic CT scans from 92 Europeans and 64 Japanese. A corridor of <12 mm was considered critical for trans-sacral implant positioning, and <8 mm as impossible. A statistical model of trans-sacral corridor S1 was computed. The limiting cranio-caudal diameter was 11.6 mm (±5.4) for S1 and 14 mm (±2.4) for S2. Trans-sacral implant positioning was critical in 52% of cases for S1, and in 21% for S2. The S1 corridor was impossible in 26%, with no impossible corridor in S2. Antero-superiorly, the S1 corridor was limited not only by the sacrum but in 40% by the iliac fossa. The statistical model demonstrated a consistent oval shape of the trans-section of corridor S1. Considering the variable in size and shape of trans-sacral corridors in S1, a thorough anatomical knowledge and preoperative planning are mandatory using trans-sacral implants. In critical cases, S2 is a veritable alternative. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2577-2584, 2017.

Biomechanical study of different fixation techniques for the treatment of sacroiliac joint injuries using finite element analyses and biomechanical tests

The pelvis is one of the most stressed areas of the human musculoskeletal system due to the transfer of truncal loads to the lower extremities. Sacroiliac joint injury may lead to abnormal joint mechanics and an unstable pelvis. Various fixation techniques have been evaluated and discussed. However, it may be difficult to investigate each technique due to variations in bone quality, bone anatomy, fracture pattern, and fixation location. Additionally, the finite element method is one useful technology that avoids these variations. Unfortunately, most previous studies neglected the effects of the lumbar spine and femurs when they investigated the biomechanics of pelvises. Thus, the aim of this study was to investigate the biomechanical performance of intact, injured, and treated pelvises using numerical and experimental approaches. Three-dimensional finite element models of the spine-pelvis-femur complex with and without muscles and ligaments were developed. The intact pelvis, the pelvis with sacroiliac joint injury, and three types of pelvic fixation techniques were analyzed. Concurrently, biomechanical tests were conducted to validate the numerical outcomes using artificial pelvises. Posterior iliosacral screw fixation showed relatively better fixation stability and lower risks of implant failure and pelvic breakage than sacral bar fixation and a locking compression plate fixation. The present study can help surgeons and engineers understand the biomechanics of intact, injured, and treated pelvises. Both the simulation technique and the experimental setup can be applied to investigate different pelvic injuries.

[Percutaneous internal fixation of pelvic fractures. German version]

BACKGROUND

Percutaneous internal fixation of pelvic fractures is increasing in popularity with multiple new techniques reported.

OBJECTIVES

The purpose of this article is to outline the imaging, indication, planning, equipment, surgical technique and complications of these methods.

METHODS

A review of the literature is provided and the techniques for anterior and posterior pelvic stabilization are discussed.

RESULTS

High-quality preoperative CT scans are essential in planning for this technique. The anterior internal fixator ("InFix") is an effective method for stabilizing the anterior ring and should be usually used in conjunction with posterior fixation. Good technique avoids neurovascular injury, which can be a devastating complication. The retrograde anterior column screw (RACS) is a technique that can be used in most patients, although in smaller patients smaller screw diameters may be needed. The entry point for the screw is more lateral in women than men. Iliosacral screws (ISS) are an effective method of posterior stabilization and can be placed using 2D or 3D fluoroscopy, computer navigation or CT navigation.

CONCLUSION

Percutaneous fixation of pelvic fractures requires high-quality imaging and can be aided by computer navigation. Safe techniques are reproducible; however, not all patients and fracture patterns can be treated using these techniques.

Comparison of Biomechanical Characteristics and Pelvic Ring Stability Using Different Fixation Methods to Treat Pubic Symphysis Diastasis: A Finite Element Study

The intention of this study was to compare the biomechanical characteristics using 5 internal fixation methods used clinically to stabilize a pubic symphysis diastasis (PSD, Tile type B1).A 3-dimensional finite element model of PSD was simulated using 5 implants, including single superior plate (Single-Plate), superior and anterior plate (Dual-Plate), single cannulated screw (Single-Screw), crossed dual cannulated screws (Cross-Screw), and parallel dual cannulated screws (Para-Screw). Three loads were distributed in all models, including dual-leg standing, single-leg stance, and rotation. To evaluate the biomechanical properties, the construct stiffness, the stress distribution, and the von Misses stress were recorded and analyzed. To evaluate pelvic ring stability, the micromotion of the pubic symphysis and iliosacral joint was analyzed.Disruption of pubic symphysis dramatically decreased the pelvic ring stability. Cross-screw and Para-Screw showed higher stiffness than other methods. All implants endured the maximum von Misses stress under single-leg stance. For Plate-Screw system, the maximum stress occurred at a place where it strides over pubic symphysis and adjacent Plate-Screw interface. The single implant and Para-Screw had a tendency to fail. Para-Screw showed the best fixation effect under dual-leg conditions. Cross-screw showed superior antishearing force capacity under single-leg stance. Dual-Plate provided maximum antihorizontal rotation. Para-Screw provided the maximum stabilization for the posterior pelvic ring.This study showed the biomechanical advantages of dual-implant for PSD only from the finite element view. The Para-Screw provided high construct stiffness under 3 load conditions. The single implant and Para-Screw had a tendency to fail. The better anterior and posterior pelvic stabilization were obtained by the dual-implant fixation than other methods. Therefore, the Cross-Screw and Dual-Plate fixation methods should be preferred in the treatment of pubic symphysis from the finite element view.

Functional Outcome With Percutaneous Ilio-sacral Screw Fixation For Posterior Pelvic Ring Injuries In Patients Involved In Heavy Manual Laboring

INTRODUCTION

Unstable posterior pelvic ring injuries are best treated with operative methods due to better post-op functional score. Our patient cohort was involved in heavy manual laboring frequently required ground level work in their activities of daily living. There are very few outcome studies dealing exclusively with such patients.

MATERIALS & METHODS

Forty one patients who were treated with percutaneous sacroiliac screw fixation under fluoroscopic guidance and were followed-up for at least one year were analyzed retrospectively for functional outcome using the Majeed score.

RESULTS

Twenty one (51.22%) and thirteen (31.70%) patients were found to be in excellent and good categories respectively and majority of the patients (thirty/73.17%) were able to return to their original occupation with or without minor adjustments.

CONCLUSION

Percutaneous ilio-sacral screw fixation for posterior pelvic unstable injuries is an acceptable mode of treatment in patients involved in heavy manual laboring.

Comparison of reconstruction plate screw fixation and percutaneous cannulated screw fixation in treatment of Tile B1 type pubic symphysis diastasis: a finite element analysis and 10-year clinical experience

Objective

The objective of this study is to compare the biomechanical properties and clinical outcomes of Tile B1 type pubic symphysis diastasis (PSD) treated by percutaneous cannulated screw fixation (PCSF) and reconstruction plate screw fixation (RPSF).

Materials and Methods

Finite element analysis (FEA) was used to compare the biomechanical properties between PCSF and RPSF. CT scan data of one PSD patient were used for three-dimensional reconstructions. After a validated pelvic finite element model was established, both PCSF and RPSF were simulated, and a vertical downward load of 600 N was loaded. The distance of pubic symphysis and stress were tested. Then, 51 Tile type B1 PSD patients (24 in the PCSF group; 27 in the RPSF group) were reviewed. Intra-operative blood loss, operative time, and the length of the skin scar were recorded. The distance of pubic symphysis was measured, and complications of infection, implant failure, and revision surgery were recorded. The Majeed scoring system was also evaluated.

Results

The maximum displacement of the pubic symphysis was 0.408 and 0.643 mm in the RPSF and PCSF models, respectively. The maximum stress of the plate in RPSF was 1846 MPa and that of the cannulated screw in PCSF was 30.92 MPa. All 51 patients received follow-up at least 18 months post-surgery (range 18–54 months). Intra-operative blood loss, operative time, and the length of the skin scar in the PCSF group were significantly different than those in the RPSF group. No significant differences were found in wound infection, implant failure, rate of revision surgery, distance of pubic symphysis, and Majeed score.

Conclusion

PCSF can provide comparable biomechanical properties to RPSF in the treatment of Tile B1 type PSD. Meanwhile, PCSF and RPSF have similar clinical and radiographic outcomes. Furthermore, PCSF also has the advantages of being minimally invasive, has less blood loss, and has shorter operative time and skin scar.