Biomechanical analysis of the fixation systems for anterior column and posterior hemi-transverse acetabular fractures

Inclined angles of acetabular quadrilateral plate: digital measurement and clinical application of the new anatomical concept

PURPOSE

Matta scoring standard is one of the most frequently used postoperative imaging evaluations for acetabular fracture reduction, but has obvious shortcomings. This study, for the first time, proposed the concept of inclined angles of acetabular quadrilateral plate. The purpose of this study was to investigate the normal range of the inclined angles in adults by digital measurement and explore the feasibility of using them to evaluate the reduction quality of acetabular quadrilateral fractures after surgery.

METHODS

Firstly, the pelvic CT three-dimensional reconstruction data of 40 healthy adults including 20 males and 20 females were collected. The normal range of the anterior, middle, and posterior inclined angles were measured via Mimics software. Secondly, a modified Matta criteria that combined the classic Matta criteria and evaluation criteria of the inclined angles was proposed. And we classified modified Matta criteria into three grades including excellent, good and poor. Finally, a total of 125 cases with quadrilateral plate fractures was included and the postoperative CT data were analyzed by using both the classic Matta criteria and our modified Matta criteria. Then, the accuracy and consistency of both criteria to evaluate postoperative hip function was investigated.

RESULTS

The average anterior inclined angle: male (97.11° ± 2.59°), female (90.63° ± 2.09°); middle inclined angle: male (105.57° ± 1.93°), female (100.64° ± 2.46°); and posterior inclined angle: male (112.62° ± 2.54), female (106.37° ± 2.53°). Whether in males or in females, the anterior, middle, and posterior inclined angles showed a progressively increasing trend. All the three inclined angles in males were all significantly larger than those in females (p < 0.05). Among 125 cases with quadrilateral plate fractures, 101 cases (80.8%) were graded as excellent, 18 cases (14.4%) as good, and 6 cases (4.8%) as poor according to the classic Matta criteria. While based on modified Matta criteria, there were excellent in 37 cases (29.6%), good in 76 cases (60.8%), and poor in 12 cases (9.6%). According to the Harris hip score system, the functional outcomes were excellent in 59 cases (47.2%), good in 26 cases (20.8%), fair in 24 cases (19.2%), and poor in 16 cases (12.8%). Our results showed that among the cases evaluated as excellent according to the classic Matta criteria and modified Matta criteria, the excellent-to-good rates of hip function were 70.3% and 78.4%, respectively. And among the cases evaluated as poor according to the modified Matta criteria, the fair-to-poor rate of hip function was 75%, while this value was 50% for classic Matta criteria. Both differences were statistically significant (p < 0.05).

CONCLUSION

Inclined angles of the quadrilateral plate could be used to assess the quality of fracture reduction and provide a basis for evaluating the rotational displacement of fracture blocks in the quadrilateral plate, which compensates the shortage of classic Matta criteria.

Biomechanical study of different fixation constructs for anterior column and posterior hemi-transverse acetabular fractures: a finite element analysis

BACKGROUND

To compare the biomechanical properties and stability, using a finite element model, of four fixation constructs used for the treatment of anterior column and posterior hemi-transverse (ACPHT) acetabular fractures under two physiological loading conditions (standing and sitting).

METHODS

A finite element model simulating ACPHT acetabular fractures was created for four different scenarios: a suprapectineal plate combined with posterior column and infra-acetabular screws (SP-PS-IS); an infrapectineal plate combined with posterior column and infra-acetabular screws (IP-PS-IS); a special infrapectineal quadrilateral surface buttress plate (IQP); and a suprapectineal plate combined with a posterior column plate (SP-PP). Three-dimensional finite element stress analysis was performed on these models with a load of 700 N in standing and sitting positions. Biomechanical stress distributions and fracture displacements were analysed and compared between these fixation techniques.

RESULTS

In models simulating the standing position, high displacements and stress distributions were observed at the infra-acetabulum regions. The degree of these fracture displacements was low in the IQP (0.078 mm), as compared to either the IP-PS-IS (0.079 mm) or the SP & PP (0.413 mm) fixation constructs. However, the IP-PS-IS fixation construct had the highest effective stiffness. In models simulating the sitting position, high fracture displacements and stress distributions were observed at the regions of the anterior and posterior columns. The degree of these fracture displacements was low in the SP-PS-IS (0.101 mm), as compared to the IP-PS-IS (0.109 mm) and the SP-PP (0.196 mm) fixation constructs.

CONCLUSION

In both standing and sitting positions, the stability and stiffness index were comparable between the IQP, SP-PS-IS, and IP-PS-IS. These 3 fixation constructs had smaller fracture displacements than the SP-PP construct. The stress concentrations at the regions of quadrilateral surface and infra-acetabulum suggest that the buttressing fixation of quadrilateral plate was required for ACPHT fractures.

Biomechanical evaluation of a healed acetabulum with internal fixators: finite element analysis

BACKGROUND

Treatment of complicated acetabular fracture with internal fixation usually has high risk of failure because of unbefitting fixation. However, evaluation of the biomechanical effect of internal fixation under physiological loading for fracture healing is still generally rarely performed. The purpose of this study is to analyze the biomechanical characteristics of a healed acetabulum with designed internal fixators under gait and to explore the biomechanical relationship between the healed bone and the internal fixator.

METHODS

A patient-specific finite element model of whole pelvis with designed internal fixators was constructed based on the tomographic digital images, in which the spring element was used to simulate the main ligaments of the pelvis. And the finite element analysis under both the combination loading of different phases and the individual loading of each phase during the gait cycle was carried out. The displacement, von Mises stress, and strain energy of both the healed bone and the fixation were calculated to evaluate the biomechanical characteristics of the healed pelvis.

RESULTS

Under the combination loading of gait, the maximum difference of displacement between the left hip bone with serious injury and the right hip bone with minor injury is 0.122 mm, and the maximum stress of the left and right hemi-pelvis is 115.5 MPa and 124.28 MPa, respectively. Moreover, the differences of average stress between the bone and internal fixators are in the range of 2.3-13.7 MPa. During the eight phases of gait, the stress distribution of the left and right hip bone is similar. Meanwhile, based on the acetabular three-column theory, the strain energy ratio of the central column is relatively large in stance phases, while the anterior column and posterior column of the acetabular three-column increase in swing phases.

CONCLUSIONS

The acetabular internal fixators designed by according to the anatomical feature of the acetabulum are integrated into the normal physiological stress conduction of the pelvis. The design and placement of the acetabular internal fixation conforming to the biomechanical characteristics of the bone is beneficial to the anatomical reduction and effective fixation of the fracture, especially for complex acetabular fracture.

New screw technique for posterior column and ischial fixation from the anterior approach for acetabular fractures

Management of the ischial fragment in acetabular fractures is a considerable problem. In this report, we presented how to drill or screw around the posterior column and ischium from the anterior approach using a novel 'sleeve guide technique' and the difficulty of plating. A sleeve, drill, depth gauge and driver from DepuySynthes were prepared. The portal was about 2-3 cm inside the anterior superior iliac spine opposite to the side of the fracture. The sleeve was inserted to the screw point around quadrilateral area through the retroperitoneal space. Drilling, measuring screw length by a depth gauge and the screwing were performed through the sleeve. Case 1 used a one-third plate and case 2 used a reconstruction plate. With this technique, the approach angles to the posterior column and ischium were inclined, and plating and screw insertion could be performed with a low risk of organ injury.

A novel anatomical self-locking plate fixation for both-column acetabular fractures

PURPOSE

To compare the stability of the posterior anatomic self-locking plate (PASP) with two types of popular reconstruction plate fixation, i.e. double reconstruction plate (DRP) and cross reconstruction plate (CRP), and to explore the influence of sitting and turning right/left on implants.

METHODS

PASP, DRP and CRP were assembled on a finite element model of both-column fractures of the left acetabulum. A load of 600 N and a torque of 8 N·m were loaded on the S1 vertebral body to detect the change of stress and displacement when sitting and turning right/left.

RESULTS

The peak stress and displacement of the three kinds of fixation methods under all loading conditions were CRP > DRP > PASP. The peak stress and displacement of PASP are 313.5 MPa and 1.15 mm respectively when turning right; and the minimal was 234.0 Mpa and 0.619 mm when turning left.

CONCLUSION

PASP can provide higher stability than DRP and CRP for both-column acetabular fractures. The rational movement after posterior DRP and PASP fixation for acetabular fracture is to turn to the ipsilateral side, which can avoid implant failure.

Biomechanical analysis of fixation methods in acetabular fractures: a systematic review of test setups

Purpose

Optimal anatomical reduction and stable fixation of acetabular fractures are important in avoiding secondary dislocation and osteoarthritis. Biomechanical studies of treatment options of acetabular fractures aim to evaluate the biomechanical properties of different fixation methods. As the setup of the biomechanical test can influence the experimental results, this review aimed to analyze the characteristics, comparability and clinical implications of studies on biomechanical test setups and finite element analyses in the fixation of acetabular fractures.

Methods

A systematic literature research was conducted according to the PRISMA guidelines, using the PubMed/MEDLINE and Web of Science databases. 44 studies conducting biomechanical analyses of fixation of acetabular fractures were identified, which met the predefined inclusion and exclusion criteria and which were published in English between 2000 and April 16, 2021. The studies were analyzed with respect to distinct parameters, including fracture type, material of pelvis model, investigated fixation construct, loading direction, loading protocol, maximum loading force, outcome parameter and measurement method.

Results

In summary, there was no standardized test setup within the studies on fixation constructs for acetabular fractures. It is therefore difficult to compare the studies directly, as they employ a variety of different test parameters. Furthermore, the clinical implications of the biomechanical studies should be scrutinized, since several test parameters were not based on observations of the human physiology.

Conclusion

The limited comparability and restricted clinical implications should be kept in mind when interpreting the results of biomechanical studies and when designing test setups to evaluate fixation methods for acetabular fractures.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00068-022-01936-9.

Prediction of fracture initiation and propagation in pelvic bones

The objective is developing an XFEM model that is capable of predicting different types of fracture in the pelvic bone under various loading conditions. Previously published mechanical and failure characteristics of cortical and cancellous tissues were implemented and assigned to an intact pelvic bone with specified cortical and cancellous tissues. Various loading conditions, including combined load directions, were applied to the acetabulum to model different types of fracture (e.g., anterior/posterior wall fracture and transverse fracture) in the pelvic bone. The predicated types of fracture and the maximum force at fracture were compared to those acquired from previously published experimental tests. Anterior/posterior wall fracture and transverse fracture were the most common types of fractures determined in the simulations. The XFEM simulations were able to predict similar fractures to those reported in the experimental tests. The maximum fracture force in the XFEM model was found to be 18.6 kN compared to 8.85 kN reported in the previous experimental tests. The results revealed that different types of fracture in the pelvic bones can be caused by the various loading conditions in unstable high-rate impact loads. Using proper mechanical and failure behaviors of cortical and cancellous tissues, XFEM modeling of pelvic bone is capable of predicting bone fracture. In future work, the XFEM models of cancellous and cortical tissues can be assigned to other bones in human body skeleton so that the failure mechanism in such bones can be investigated.

Finite Element Analysis of a Novel Anatomical Locking Guide Plate for Anterior Column and Posterior Hemi-Transverse Acetabular Fractures

Purpose

The increasing worldwide prevalence of anterior column-posterior hemi-transverse fracture (ACPHTF) brings formidable challenges to orthopaedic surgeons. Our newly-designed locking plate had previously demonstrated promising effects in ACPHTF, but evidence of their direct comparison with conventional internal fixations remains lacking. In this study, we aimed to compare our novel plate with the traditional devices via finite element analysis.

Methods

The ACPHTF model was created based on a 48-year-old volunteer’s CT data, and then fixed in three different internal fixations: an anterior column locking plate with posterior column screws, double column locking plates, and our novel anatomical locking plate. These models were next loaded with a downward vertical force of 200 N, 400 N and 600 N, and the stress peaks and displacements of three different sites were recorded and analyzed.

Results

We first tested the rigidity and found that our newly-designed locking plate as well as its matched screws had a greater stiffness especially when they were under a higher loading force of 600 N. Then we evaluated the displacements of fracture ends after applying these fixations. Both our novel plate and DLP showed significantly smaller displacement than LPPCS at the anterior column fracture line and the pubic branch fracture line, while our novel plate was not obviously inferior to DLP in terms of the displacement.

Conclusion

This novel plate demonstrates a distinct superiority in the stiffness over LPPCS and DLP and comparable displacements to DLP in ACPHTF, which suggests this novel anatomical locking guide plate should be taken into consideration in ACPHTF.

Single column plate plus other column lag screw fixation vs. both column plate fixation for anterior column with posterior hemitransverse acetabular fractures - a biomechanical analysis using different loading protocols

OBJECTIVES

Open reduction and internal fixation of both columns is considered the treatment of choice for displaced anterior column with posterior hemitransverse (ACPHT) fractures in non-geriatric patients. Plate fixation of one column combined with lag screw fixation of the other column allows to decrease operative time and approach-related morbidity compared to conventional both column plating. The aim of this biomechanical study was to evaluate whether single column plate plus other column lag screw fixation confers similar stability to both column plate fixation. Physiological loads were simulated using both the single-leg stance (SLS) as well as the sit-to-stand (STS) loading protocols.

METHODS

A clinically relevant ACPHT fracture model was created using fourth-generation composite hemipelves. Fractures were stabilized with three different fixation constructs: (1) anterior column plate plus posterior column screw fixation (AP+PCS), posterior column plate plus anterior column screw fixation (PP+ACS) and anterior column plate plus posterior column plate fixation (AP+PP). Specimens were loaded from 50 to 750 N with a ramp of 100 N/s. Fracture gap motion (FGM) and relative interfragmentary rotation (RIFR) between the three main fracture fragments were assessed under loads of 750 N using an optical 3D measurement system.

RESULTS

STS loading generally resulted in higher mean FGM and RIFR than STS loading in the AP+PCS and AP+PP groups, while no significant differences were found in the PP+ACS group. Compared to conventional both column plate fixation (AP+PP), PP+ACS displayed significantly higher FGM and RIFR between the iliac wing and the posterior column during SLS loading. No significant differences in FGM and RIFR were identified between the AP+PCS and the AP+PP group.

CONCLUSION

Overall, single column plate plus other column lag screw fixation conferred similar stability to conventional both column plate fixation. From a clinical point of view, AP+PCS appears to be the most attractive alternative to conventional AP+PP for internal fixation of ACPHT fractures.

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.

Double column acetabular fractures fixation using a novel dynamic anterior plate-screw system: A biomechanical analysis

BACKGROUND

According to the classification of Judet and Letournel, all double column acetabular fractures will certainly involve the disruption of the quadrilateral plate (QLP). Accurate reduction and reliable fixation of QLP is the key to obtain a normal congruent hip joint and avoid postoperative arthritis. The aims of this study were to assess the biomechanical properties of a novel dynamic anterior plate-screw system (named DAPSQ) and to compare its biomechanical stability with buttress-plate construct.

METHODS

Double column acetabular fractures involving the QLP were created on cadaveric pelvic specimens and subsequently stabilized with (1) a pre-contoured side-specific DAPSQ titanium plate and 4 quadrilateral screws (Group A) or a 12-hole suprapectineal pelvic reconstruction plate combined with a 9-hole 1/3 tube buttress plate (Group B). These constructs were mechanically loaded on ZwickZ 100 testing machine. Construct stiffness and displacement amounts of the two fixation methods in the condition of dynamic axial loading conditions were measured.

RESULTS

As the axial loading force increased from 200 N to 800 N, the longitudinal displacement of each pelvic specimen increased linearly and Group B was found to have significantly higher displacement than Group A (p<0.05). In the 600 N physiological loading, the construct stiffness values of Groups A and B were 139.4 ± 37.4 N/mm and 101±18.3 N/mm, respectively. Group A is 27% stiffer than Group B(p<0.05).

CONCLUSIONS

In this in vitro biomechanical study, DAPSQ plate and quadrilateral screws fixation of a double column acetabular fracture involving the QLP resulted in a better fixation construct than the traditional suprapectineal pelvic reconstruction plate and 1/3 tube buttress plate fixation.

Open reduction and internal fixation of quadrilateral plate fractures in the elderly: association between initial fracture pattern and outcomes

Background

Acetabular fractures with medial displacement of the quadrilateral plate (QLP) are common in the elderly. The presence of QLP fractures greatly increase the surgical difficulty of acetabular fractures. This study aims to evaluate the clinical radiological outcomes of open reduction and internal fixation (ORIF) in QLP fractures in elderly patients and to investigate factors potentially affecting the result.

Methods

We conducted a retrospective study. A series of 37 consecutive patients with acetabular fracture involving the QLP aged 60 years and older who received ORIF between January 2010 and May 2019 were included. QLP fractures were classified according to Walid’s classification system. Radiological outcomes were evaluated using Matta criteria and functional outcomes were assessed using the modified Merle d’Aubigné score. The relationships between Walid’s classification and radiological or functional outcomes were analyzed.

Results

According to Walid’s classification, 18, 13, 6 were classified as QLP1, QLP2 and QLP3, respectively. The average follow-up was 35.5 ± 10.7 months. We obtained anatomic reduction in 48.6 % (18/37) of cases, imperfect reduction in 40.5 % (15/37) of cases, and poor reduction in 10.8 % (4/37) of cases. Excellent-good functional scores were found in 83.7 % (modified Merle d’Aubigné). There were no cases of screw entering the hip, pull-out and loosening or implant failure during the follow-up. Walid’s classification was positively correlated with radiological outcomes of reduction (r = 0.661; P < 0.001), and functional outcomes (r = 0.478; P = 0.003). Unsatisfactory reduction was demonstrated a correlation with the development of post-traumatic arthritis (r =-0.410; P = 0.012).

Conclusions

ORIF may be suggested for quadrilateral plate fractures in the elderly. Walid’s classification system is associated with the reduction quality and functional recovery.

A Post-Traumatic Osteoarthritic Model of Hip Following Fracture of Acetabulum in Rabbit: A Preliminary Study by Macroscopic and Radiographic Assessment

Objective

To develop a post‐traumatic osteoarthritic model of hip following fracture of acetabulum in rabbit for revealing biochemical mechanism of post‐traumatic osteoarthritis.

Methods

A total of 36 mature male New Zealand white rabbits were equally divided into sham group (n = 12), non‐ORIF group (n = 12), and open reduction and internal fixation (ORIF) group (n = 12). Except for the sham group, rabbits had survival surgeries to create acetabular fractures of dorsal wall for simulating dashboard impaction mechanism. The ORIF group received open reduction and internal fixation, while fractures in the non‐ORIF group were left as displaced but transverse fracture and dislocation was reduced. Besides intraoperative appearance and postoperative recovery, macroscopic and radiographic characteristics of the hips were recorded and assessed by a radiographic scoring scale at 3 weeks, 6 weeks, and 6 months, respectively.

Results

Out of 24 modeled acetabula, 21 (87.5%) were pure dorsal wall fractures as proposed and the remaining three were associated fractures (dorsal wall plus transverse fracture) accompanied by dorsal dislocation or not. All hips were stable, and no sciatic nerve injury was observed. One rabbit in the ORIF group died of deep infection 4 days after surgery. Rabbits in the sham and ORIF groups returned to normal gait in 2 weeks, but animals in the non‐ORIF group suffered from limping and restricted movement. As the time progressed, the hips in the non‐ORIF group experienced progressive and severe degeneration which exhibited dramatically malformed and hypertrophic joints at 6 months, but the ORIF group maintained much better morphological structure. Corresponding to morphological changes, the average radiographic scores of the non‐ORIF group increased from 1.25 at 3 weeks to 2.75 at 6 months and showed statistically significant difference when compared to the sham group at all three time points (P = 0.011, 0.011, 0.015, respectively, <0.0167). Although the scores of the ORIF group showed apparent improvements (increased from 0.67 at 3 weeks to 2.00 at 6 months), there was no significant difference between the two modeled groups at all three time points.

Conclusion

The fracture model with high consistency and reproducibility showed progressive post‐traumatic osteoarthritic changes which could be improved by open reduction and internal fixation surgery and provided an alternative selection for investigating potential pathogenesis and pathology of post‐traumatic osteoarthritis following fracture of acetabulum.

Biomechanical comparison of fixation techniques for transverse acetabular fractures - Single-leg stance vs. sit-to-stand loading

OBJECTIVES

To biomechanically compare five different fixation techniques for transverse acetabular fractures using both the single-leg stance (SLS) and the sit-to-stand (STS) loading protocols and to directly compare fracture gap motion (FGM) and relative interfragmentary rotation (RIFR).

METHODS

Transtectal transverse acetabular fractures were created on fourth-generation composite hemipelves in a reproducible manner. Five different fixation techniques were biomechanically assessed using both an SLS and STS loading protocol: anterior plate (AP) only, posterior plate (PP) only, anterior plate plus posterior column screw (AP+PCS), posterior plate plus anterior column screw (PP+ACS) and anterior plus posterior plate (AP+PP). After preconditioning, the specimens were loaded from 50 to 750 N with a ramp of 100 N/s. FGM and RIFR under loads of 750 N were measured using an optical 3D measurement system.

RESULTS

In the three groups of fixation techniques addressing both columns, STS loading resulted in higher mean FGM and in RIFR than SLS loading. No construct failure was observed. In the single plate groups (AP only and PP only), STS loading resulted in failure of all specimens before reaching loads of 750 N, while no failure occurred after SLS loading. No significant differences in FGM and RIFR were found between the double plate (AP+PP) and the single plate plus column screw (AP+PCS and PP+ACS) techniques.

CONCLUSION

SLS loading appeared to overestimate the strength of acetabular fracture fixation constructs and STS loading may be more appropriate to provide clinically relevant biomechanical data. Internal fixation of a single column might not provide adequate stability for transverse fractures, while strength of single plate plus column screw fixation and double plate fixation was comparable.

Personalized Three-Dimensional Printed Anterior Titanium Plate to Treat Double-Column Acetabular Fractures: A Retrospective Case-Control Study

Objective

To compare the clinical efficacy and safety of a personalized three‐dimensional (3D) printed dynamic anterior plate–screw system for the quadrilateral area (DAPSQ) titanium plate and a traditional DAPSQ reconstruction plate in the treatment of double‐column acetabular fractures.

Methods

This was a retrospective case‐control study. From May 2014 to January 2018, 43 patients with double‐column acetabular fractures underwent open reduction and internal fixation. Among these, 20 cases were fixed with a 3D printed DAPSQ plate (3D printed group) and 23 cases were fixed with a DAPSQ reconstruction plate (control group). The 3D printed group comprised 15 men and 5 women, with an average age of 50.1 ± 8.2 years. The control group comprised 16 men and 7 women, with an average age of 51.0 ± 8.6 years. The evaluation index included the surgical data (i.e. blood loss, operating time, duration of hospital stay, and intraoperative and postoperative complications), position and length of implants, reduction quality, hip function, and related complications. The reduction quality was evaluated using the Matta scoring standard and hip function was evaluated using the modified Merle d’Aubigné score.

Results

A total of 43 patients met the inclusion criteria. The mean postoperative follow up was 35.2 months in the 3D printed group and 36.9 months in the control group. There were no significant group differences in demographic data between the two groups. The position and length of the 3D printed implants were generally in accord with preoperative planning using a 3D pelvic model. Patients in the 3D printed group had significantly shorter operation time (223.2 vs 260.5 min, P < 0.05) and less intraoperative blood loss (930.4 vs 1426.1 mL, P < 0.05) compared to the control group. Anatomic, imperfect, and poor reduction was obtained in 13, 5, and 2 cases in the 3D printed group, respectively, and was obtained in 12, 8, and 3 cases in the control group. The modified Merle d’Aubigné scores were excellent in 11 cases, good in seven cases, and fair in two cases in the 3D printed group. They were excellent in 11 cases, good in eight cases, fair in three cases, and poor in one case in the control group. The reduction quality and hip function did not differ within the groups (P > 0.05). The general complication rate in the 3D printed group and the control group was 15% and 26.1%, respectively, but the difference between the two groups was not statistically significant.

Conclusion

Use of a personalized 3D printed DAPSQ plate has potential advantages in reducing the operation time and blood loss during the treatment of double‐column acetabular 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.

Biomechanical Evaluation of a New Fixation Type in 3D-Printed Periacetabular Implants using a Finite Element Simulation

Pelvic implants require complex geometrical shapes to reconstruct unusual areas of bone defects, as well as a high mechanical strength in order to endure high compressive loads. The electron beam melting (EBM) method is capable of directly fabricating complex metallic structures and shapes based on digital models. Fixation design is important during the 3D printing of pelvic implants, given that the fixation secures the pelvic implants to the remaining bones, while also bearing large amounts of the loads placed on the bone. In this study, a horseshoe-shaped plate fixation with a bridge component between two straight plates is designed to enhance the mechanical stability of pelvic implants. The aim of this study is to investigate the biomechanics of the horseshoe-shaped plate fixation in a 3D-printed pelvic implant using a finite element (FE) simulation. First, computed tomography (CT) scans were acquired from a patient with periacetabular bone tumors. Second, 3D FE implant models were created using the patient’s Digital Imaging and Communications in Medicine (DICOM) data. Third, a FE simulation was conducted and the stress distribution between a conventional straight-type plate model, and the horseshoe-shaped plate model was compared. In both of the models, high-stress regions were observed at the iliac fixation area. In contrast, minimal stress regions were located at the pubic ramus and ischium fixation area. The key finding of this study was that the maximal stress of the horseshoe-shaped plate model (38.6 MPa) was 21% lower than that of the straight-type plate model (48.9 MPa) in the iliac fixation area. The clinical potential for the application of the horseshoe-shaped plate fixation model to the pelvic implant has been demonstrated, although this is a pilot study.

Minimally invasive screw fixation is as stable as anterior plating in acetabular T-Type fractures - a biomechanical study

INTRODUCTION

Operative treatments of T-type acetabular fractures are challenging surgical procedures. Open reduction and internal fixation is the standard method for the operative management of these fractures, however this is associated with high blood loss, long hospital stay and longer rehabilitation. Anterior subcutaneous pelvic fixation (internal fixation=INFIX) and retrograde pubic screw fixation have shown promising results in minimally invasive treatment of pelvic ring fractures. For T-type acetabular fractures, however, minimally invasive treatment concepts are still rare. Therefore we performed a mechanical in vitro study to: - investigate the potential favorability of minimally invasive treatment options over the already established open anterior locking plate osteosynthesis of acetabular T-fractures regarding biomechanical stability and post-surgical stiffness; - explore the biomechanical feasibility of the INFIX; - assess its potential ability to reduce the anterior acetabular column.

HYPOTHESIS

A minimally invasive treatment of acetabular T-type fractures is biomechanically equivalent to an open anterior plate osteosynthesis.

METHODS

Twenty-four synthetic hemipelvis specimens with a T-type acetabular fracture were divided in four groups. A posterior column screw was placed in every pelvis of every group. The anterior column was fixed with: - anterior column screw; - anterior column screw incl. INFIX; - INFIX alone; - 14-hole angular stable locking plate (standard fixation method). Displacement of the anterior column was reduced in group 2+3 using the INFIX. All specimens were cyclically loaded with 200N until a maximum of 600N. Movement/displacement of the fracture fragments were detected with a 3D-ultrasound measuring system. Displacement (mm) and Stiffness (N/mm) of the construction were analyzed.

RESULTS

Statistical assessment showed no significant differences between the four fixation types (p>0.05). The 14-whole locking plate (group 4) displayed the overall highest stability with a displacement of 1.3±0.04mm and stiffness of 76.3±2.4N/mm. Anterior screw fixation (group 1) proved to be the minimally invasive fixation method with the least displacement and highest stiffness (1.5±0.2mm, 68.3±6.8N/mm). The combination of an INFIX and an anterior column screw (group 2), showed a mean stiffness of 62.1±6.0N/mm and a mean displacement of 1.7±0.2mm. INFIX only (group 3) presented a displacement of 1.6±0.1mm and a stiffness of 64.5±4.5N/mm.

DISCUSSION

Minimally invasive fixation techniques for T-type acetabular fractures show promising biomechanical stability in non- or slightly displaced fractures. Furthermore, INFIX could be a feasible tool for the reduction of the anterior acetabular column.

LEVEL OF EVIDENCE

III, case control prospective experimental study.

Biomechanical comparison of three different fixation techniques for anterior column posterior hemitransverse acetabular fractures using anterior intrapelvic approach

OBJECTIVES

The aim of this study was to biomechanically compare three different fixation methods for the fixation of anterior column posterior hemitransverse type acetabular fracture (ACPHT).

METHODS

ACPHT fracture models were created on twenty-four foam cortical shell artificial hemipelvis models. Three fixation methods were assessed - Group 1: posterior column lag screws over a suprapectineal plate; Group 2: Posterior column lag screws over a suprapectineal plate and an infrapectineal plate; Group 3: A suprapectineal plate and a vertical infrapectineal plate. Stiffness and displacement amounts of fixation methods under dynamic and static axial loading conditions were measured.

RESULTS

In the dynamic and static tests, Group 3 showed the less stable fixation compared to Group 2. There was no statistically significant difference between the stiffness values of the fixation groups. In the static tests, there was no statistically significant difference between Group 1 and 2, although less displacements were obtained in Group 2.

CONCLUSIONS

A combination of posterior lag screws over a suprapectineal plate and an infrapectineal plate supporting the pelvic brim along both sides of the linea terminalis resulted in a better fixation construct than a suprapectineal plate accompanying with a vertical infrapectineal plate provide better stability with less fracture displacement.