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

Comparative study between anterior symphyseal platting and percutaneous symphyseal screws for treatment of traumatic symphyseal diastasis

PURPOSE

Symphyseal diastasis accounts for 13-16% of pelvic ring injuries. Symphyseal plating via a Pfannenstiel approach was the standard method of fixation for symphysis diastasis. Recently, percutaneous reduction and fixation of pelvic fractures have been employed to treat various pelvic ring and acetabulum injuries. The current study aims to compare the clinical and radiological results of treatment of symphysis pubis diastasis using symphyseal plating and percutaneous symphyseal screws.

METHODS

It is a retrospective study conducted at a trauma centre at academic level I. One hundred and ten patients were identified in our records. Sixty patients were excluded according to our exclusion criteria. Fifty patients were included in this study. Among which were 26 patients treated with anterior symphyseal plating (Group A) and 24 patients treated with percutaneous symphyseal screws (Group B). Posterior pelvic injury was fixated according to the existing pathology. In both groups, we recorded operation time, intraoperative blood loss, length of the incision, number of x-ray shots, changes in symphysis distance (preoperative, immediate postoperative, and in the last follow-up), and time for union. At the last follow-up, the clinical evaluation was conducted using the Visual Analogue Scale (VAS), and the functional evaluation was conducted using the Majeed scoring method for both groups.

RESULTS

All patients have followed up for at least two years. According to the Majeed Score, group A's functional classification was excellent for fourteen patients, good for seven, fair for two, and poor for three cases. Group B's functional classification was excellent for seventeen patients, good for six, and poor for one. The operative time and intraoperative time were significantly different between both groups, while the symphysis diastasis at the last follow-up was insignificant. Five patients in group A showed metal failure in the form of plate breakage, screw loosening, and screw backing out. In Group B, one case showed implant failure and loss of reduction in the form of screw backing out and widening of the symphysis pubis. Two patients in group A had infections at the incision site, which were treated with antibiotics and daily dressings and resolved adequately. No recorded cases of infection in group B.

CONCLUSION

Both techniques showed favourable results. The group with symphyseal plating showed a higher failure rate than the group with percutaneous screw fixation. The symphyseal screw group had shorter operative time, smaller incision, and less intraoperative blood loss than the symphyseal plating group but more radiation exposure. The symphyseal screw technique is a technically demanding technique and requires a high learning curve. It involves more radiation exposure, especially in inexperienced surgeons.

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.

Substitutional semi-rigid osteosynthesis technique for treatment of unstable pubic symphysis injuries: a biomechanical study

BACKGROUND/PURPOSE

The surgical fixation of a symphyseal diastasis in partially or fully unstable pelvic ring injuries is an important element when stabilizing the anterior pelvic ring. Currently, open reduction and internal fixation (ORIF) by means of plating represents the gold standard treatment. Advances in percutaneous fixation techniques have shown improvements in blood loss, surgery time, and scar length. Therefore, this approach should also be adopted for treatment of symphyseal injuries. The technique could be important since failure rates, following ORIF at the symphysis, remain unacceptably high. The aim of this biomechanical study was to assess a semi-rigid fixation technique for treatment of such anterior pelvic ring injuries versus current gold standards of plate osteosynthesis.

METHODS

An anterior pelvic ring injury type III APC according to the Young and Burgess classification was simulated in eighteen composite pelvises, assigned to three groups (n = 6) for fixation with either a single plate, two orthogonally positioned plates, or the semi-rigid technique using an endobutton suture implant. Biomechanical testing was performed in a simulated upright standing position under progressively increasing cyclic loading at 2 Hz until failure or over 150,000 cycles. Relative movements between the bone segments were captured by motion tracking.

RESULTS

Initial quasi-static and dynamic stiffness, as well as dynamic stiffness after 100,000 cycles, was not significantly different among the fixation techniques (p ≥ 0.054).). The outcome measures for total displacement after 20,000, 40,000, 60,000, 80,000, and 100,000 cycles were associated with significantly higher values for the suture technique versus double plating (p = 0.025), without further significant differences among the techniques (p ≥ 0.349). Number of cycles to failure and load at failure were highest for double plating (150,000 ± 0/100.0 ± 0.0 N), followed by single plating (132,282 ± 20,465/91.1 ± 10.2 N), and the suture technique (116,088 ± 12,169/83.0 ± 6.1 N), with significantly lower values in the latter compared to the former (p = 0.002) and no further significant differences among the techniques (p ≥ 0.329).

CONCLUSION

From a biomechanical perspective, the semi-rigid technique for fixation of unstable pubic symphysis injuries demonstrated promising results with moderate to inferior behaviour compared to standard plating techniques regarding stiffness, cycles to failure and load at failure. This knowledge could lay the foundation for realization of further studies with larger sample sizes, focusing on the stabilization of the anterior pelvic ring.

Percutaneous Fixation for Traumatic Symphysis Pubis Disruption-Are the Results Superior Compared to Open Techniques? A Systematic Review and Meta-Analysis of Clinical and Biomechanical Outcomes

INTRODUCTION

Open reduction and reconstruction plate and screws fixation (RPSF) is considered the gold standard for the treatment of traumatic symphysis pubis diastasis (SPD). Percutaneous cannulated screw fixation (PCSF) has recently gained popularity as it may reduce operative time and morbidity. The current systematic review aims to compare the clinical and radiological outcomes of PCSF and RPSF in traumatic SPD and analyze the biomechanical effectiveness of PCSF.

MATERIAL AND METHODS

The Medline, Scopus, and Cochrane databases were searched until February 2023. The primary outcomes were the incidence of implant failure and revision surgery and the amount of displacement of symphysis pubis. Secondary outcomes were the intraoperative blood loss, the scar length, the operative time, the wound infection, and the patients' functional improvement.

RESULTS

Six clinical trial studies with a total of 184 patients and nine biomechanical studies were included. There was no significant difference between the two groups regarding the incidence of implant failure, the prevalence of revision surgery, and the amount of postoperative loss of reduction (p > 0.05 for all outcomes). The intraoperative blood loss (14.9 ± 4.2 mL for PCSF versus 162.7 ± 47.6 mL for PCSF, p < 0.001) and the incision length (1.7 ± 0.9 mL for PCSF versus 8 ± 1.4 mL for PCSF, p < 0.001) were significantly lower after PCSF. The mean operative time was 37 ± 19.1 min for PCSF and 68.9 ± 13.6 min for RPSF (p < 0.001). The infection rate was less frequent in the PCSF group (3% for PCSF versus 14.3% for RPSF, p = 0.01). One clinical trial reported better functional recovery after PCSF. In all biomechanical studies, the threshold for implant failure was beyond the applied forces corresponding to daily activities.

CONCLUSIONS

PCSF for traumatic SPD is associated with less operative time, less blood loss, and a lower infection rate when compared to conventional plate techniques without increasing the incidence of postoperative fixation failure and revision surgery. Moreover, PCSF has been proven to be biomechanically sufficient for stabilization. Therefore, it should be considered an efficient and viable alternative for the reconstruction of SPD when closed reduction can be adequately achieved.

Percutaneous screw fixation of the pubic symphysis versus plate osteosynthesis: a biomechanical study

Objectives: To compare the stability of screw fixation with that of plate fixation for symphyseal injuries in a vertically unstable pelvic injury (AO/Tile 61-C1) associated with complete disruption of the sacroiliac joint and the pubic symphysis. Methods: Eight fourth-generation composite pelvis models with sacroiliac and pubic symphyseal disruption (Sawbones, Vashon Island, WA) underwent biomechanical testing simulating static single-leg stance. Four were fixed anteriorly with a symphyseal screw, and 4 with a symphyseal plate. All had single transsacral screw fixation posteriorly. Displacement and rotation were monitored at both sacroiliac joint and pubic symphysis. Results: There was no significant difference between the 2 groups for mean maximum force generated. There was no significant difference in net displacement at both sacroiliac joint and pubic symphysis. There was significantly less rotation but more displacement in the screw group in the Z-axis. The screw group showed increased stiffness compared with the plate group. Conclusions: This is the first biomechanical study to compare screw versus plate symphyseal fixation in a Tile C model. Our biomechanical model using anterior and posterior fixation demonstrates that symphyseal screws may be a viable alternative to classically described symphyseal plating.

A Morphologic Analysis of the Pubic Symphysis Using CT and MRI

INTRODUCTION

The goal of this study was to investigate prevalence and morphometric parameters of pubic ligaments and the interpubic disk and its cavity using imaging methods for use in clinical medicine.

METHODS

Pubic symphysis morphology was investigated in 652 patients (348 women and 304 men), from which 449 CT scans and 203 MR scans were available. The average age of men was 48 years and women 39 years. Investigated parameters included dimensions of the interpubic disk, visibility and width of the reinforcing ligaments, and visibility, dimensions, and location of the symphysial cavity. The results were compared with MR scans of 20 healthy volunteers and 21 dissected anatomic specimens.

RESULTS

The craniocaudal, ventrodorsal, and mediolateral diameters of the pubic disk were 36 to 37.7, 14.8 to 15.2, and 2.2 to 4.2 mm in women and 42 to 42.3, 18.6 to 19, and 2.4 to 4.5 mm in men, respectively. Higher age correlated with shorter mediolateral diameter and larger craniocaudal and ventrodorsal diameters. The superior pubic ligament was visible in 93.1% of men (1.44 mm thick) and in 100% of women (1.7 mm); the inferior pubic ligament in 89.7% of men (1.74 mm) and 88% of women (1.95 mm), the anterior pubic ligament in 96.6% of men (1.5 mm) and 82% of women (1.34 mm); and the posterior pubic ligament in 65.5% of men (1.18 mm) and 63.7% of women (0.83 mm). A symphysial cavity was found in 24% of men and 22.9% of women, with craniocaudal, ventrodorsal, and mediolateral dimensions of 13, 10.7, and 3.2 mm in men and 9.5, 10.7, and 3 mm in women, respectively.

CONCLUSION

The presented morphologic parameters provide an anatomic reference for diagnostics of pathologic conditions of the pubic symphysis. The following anatomic structures should be added to the official anatomic terminology: symphysial cavity (cavitas symphysialis), retropubic eminence (eminentia retropubica), anterior pubic ligament (ligamentum pubicum anterius), and posterior pubic ligament (ligamentum pubicum posterius).

LEVEL OF EVIDENCE

II-III.

Biomechanical in vitro analysis of a novel flexible implant for pubic symphysis disruption using an ultra-high molecular weight polyethylene fiber cord

BACKGROUND

Plate osteosynthesis depicts the gold standard to surgically treat pubic symphysis disruptions. However, high rates of implant failure after plate osteosynthesis are reported, probably because of the iatrogenic arthrodesis of this fibrocartilaginous joint. Therefore, flexible implants for treatment of pubic symphysis disruptions appear to be a sensible solution.

METHODS

In this biomechanical screening study, we designed and investigated a flexible implant, which consists of two plates connected with an ultra-high molecular weight polyethylene fiber cord. We mechanically tested eye splices as a possible fixation method of the cords by performing tensile load to failure tests. Afterwards, we developed a biomechanically appropriate plate design and cord routing between the plates. Finally, we biomechanically tested the flexible implant under tensile and shear loading until failure.

FINDINGS

When fixing a 1 mm ultra-high molecular weight polyethylene fiber cord with eye splices, a load at failure of 1570.74 N was detected under tensile loading. None of the eye splices failed but the cords itself ruptured. The load at failure of the designed cord routing in criss-cross technique and fixation within the plates amounts 4742.09 N under tensile and 2699.77 N under shear load.

INTERPRETATION

We developed a novel flexible implant for repair of pubic symphysis disruptions using ultra-high molecular weight polyethylene fiber cords connected to osteosynthesis plates. We identified eye splices as a mechanically optimal fixation method and proved that the ultra-high molecular weight polyethylene fiber cord routing and fixation of the flexible implant clearly withstands physiological forces acting on the pubic symphysis.

Biomechanical evaluation of seven fixation methods to treat pubic symphysis diastasis using finite element analysis

Background

Pubic symphysis diastasis (PSD) hinders the connection between bilateral ischia and pubic bones, resulting in instability of the anterior pelvic ring. PSD exceeding 25 mm is considered disruptions of the symphyseal and unilateral/bilateral anterior sacroiliac ligaments and require surgical intervention. The correct choice of fixation devices is of great significance to treat PSD. This study aimed to evaluate the construct stability and implant performance of seven fixation methods to treat PSD using finite element analysis.

Methods

The intact skeleton-ligament pelvic models were set as the control group. PSD models were simulated by removing relevant ligaments. To enhance the stability of the posterior pelvic ring, a cannulated screw was applied in the PSD models. Next, seven anterior fixation devices were installed on the PSD models according to standard surgical procedures, including single plates (single-Plate group), single plates with trans-symphyseal cross-screws (single-crsPlate group), dual plates (dual-Plate group), single cannulated screws, dual crossed cannulated screws (dual-canScrew group), subcutaneous plates (sub-Plate group), and subcutaneous pedicle screw-rod devices (sub-PedRod group). Compression and torsion were applied to all models. The construct stiffness, symphyseal relative micromotions, and von Mises stress performance were recorded and analyzed.

Results

The construct stiffness decreased dramatically under PSD conditions. The dual-canScrew (154.3 ± 9.3 N/mm), sub-Plate (147.1 ± 10.2 N/mm), and sub-PedRod (133.8 ± 8.0 N/mm) groups showed better ability to restore intact stability than the other groups (p < 0.05). Regarding regional stability, only single-plate fixation provided unexpected regional stability with a diastasis of 2.1 ± 0.2 mm (p < 0.001) under a compressive load. Under a rotational load, the single-crsPlate group provided better regional angular stability (0.31° ± 0.03°, p < 0.001). Stress concentrations occurred in the single-Plate, sub-Plate, and sub-PedRod groups. The maximum von Mises stress was observed in the single-plate group (1112.1 ± 112.7 MPa, p < 0.001).

Conclusion

The dual-canScrew fixation device offers ideal outcomes to maintain stability and prevent failure biomechanically. The single-crsPlate and dual-Plate methods effectively improved single-Plate device to enhance regional stability and disperse stresses. The subcutaneous fixation devices provided both anterior pelvic ring stability and pubic symphysis strength.

Percutaneous screw fixation of pubic symphysis disruption: A preliminary report

BACKGROUND

Percutaneous techniques are commonly used to treat pelvic ring disruptions but are not mainstream for fixation of pubic symphysis disruption worldwide. Potential advantages include less blood loss and lower risk of surgical site infection, especially in the morbidly obese or multiply injured patient. This study was performed to describe the clinical and radiographic outcomes of patients after percutaneous reduction and screw fixation of pubic symphysis disruption and to evaluate the preliminary safety and efficacy of this technique and its appropriateness for further study as an alternative method of fixation.

METHODS

A retrospective review was performed to identify all patients who underwent percutaneous fixation of pubic symphysis disruption by two surgeons at an academic Level I trauma center over a 3-year period. Patients underwent percutaneous reduction and fixation of the pubic symphysis using 1 or 2 fully or partially threaded 5.5, 6.5, or 7.3 mm cannulated screws in a transverse or oblique configuration. Associated posterior ring injuries were fixed with trans-sacral and/or iliosacral screws. The primary outcome of interest was loss of reduction, defined as symphysis distance greater than 15 mm measured on final AP pelvis radiograph. Secondary outcomes collected by chart review were operative time, blood loss, vascular or urologic injury, sexual dysfunction, infection, implant loosening or breakage, and revision surgery.

RESULTS

Twelve patients met criteria and primary and secondary outcomes were collected. Mean clinical and radiographic follow-up were 15 months each. One patient lost reduction. Mean operative time and blood loss were 124 min and 29 cc, respectively. No vascular or urologic injuries occurred. Two patients reported sexual dysfunction. No patients became infected or required revision surgery. Four patients underwent implant removal. Seventeen additional patients were excluded due to short follow-up and limited outcomes were collected. Two of these patients lost reduction. Three underwent implant removal.

CONCLUSION

These data support percutaneous reduction and screw fixation of pubic symphysis disruption as a potentially safe and effective method of treatment that warrants further investigation.

Danger zone - The spermatic cord during anterior plating of the symphysis pubis

BACKGROUND

Distances between anatomic landmarks and anatomic structures at risk are often underestimated by surgeons.

PURPOSE

The goal of the study was to evaluate the distances between anatomic landmarks and the spermatic cord in case of anterior plating of the symphysis.

METHODS

A total of 25 pelves (50 hemipelves) of male embalmed cadavers were dissected. A 5-hole 3.5mm locking compression plate (Synthes GmbH) was fixed from directly anterior on the symphysis. Measurements were taken 1) distance between the tips of both pubic tubercles, 2) horizontal interval between the lateral border of the plate and the medial margin of the SC (bilateral), 3) distances between the medial border of the SC and the tip of the pubic tubercle (bilateral), 4) distances between the medial border of the SC and the lateral basis of the pubic tubercle (bilateral).

RESULTS

The distance between the pubic tubercles was 60.3mm in average (SD: 5.7). The interval between the lateral border of the plate and the medial margin of the SC was on average 4.5mm (SD: 1.9) on the right and 4.7mm (SD: 2.6) on the left side. The distance between the tip of the pubic tubercle and the medial border of the SC was in average 11.2mm (SD: 2.7) on the right, and 11.0mm (SD: 2.7) on the left side. The average distance between the medial border of the SC and the lateral basis of the pubic tubercle was 8.1mm (SD: 2.4) on the right and 8.2 mm (SD: 2.4) on the left side.

CONCLUSION

The SC is at risk not only during dissection but also during anterior plating of the symphysis, because of its close relation to the SC.

CLINICAL RELEVANCE

Average distances between the palpable pubic tubercle and the SC are below one finger breadth (as reference).

Symphyseal plate with trans-symphyseal cross-screws for fixation of tile-type B1 pelvic ring injuries: radiological and functional evaluation

INTRODUCTION

Failure to neutralize the different physiological forces acting on the inferior as well as the superior regions of the pubic symphysis, the long healing time, is blamed for the repeated failures of conventional superior symphyseal plating.

MATERIAL AND METHODS

A three years prospective case series study between January 2017 and December 2019 was done, to evaluate the radiological and the functional outcomes, using Matta/Tornetta and Majeed criteria respectively, of the combination of trans-symphyseal cross-screws configuration and superior symphyseal plate in Tile-type B1 pelvic injuries.

RESULTS

Thirty patients, 18 with anteroposterior compression type II and 12 with type III, with a mean follow-up of 20 months ±5 were included. Radiologically, 26 (86.6%) cases showed an excellent, one (3.3%) good and three (10%) fair outcome. Clinically, excellent outcome in 26 (86.6%) cases, good in two (6.6%) cases, and fair in two (6.6%). Intra-operative drill bit breakage occurred in three (10%) cases and was the only reported technical complication. Significant re-displacement was reported in three (10%) cases.

CONCLUSION

The open trans-symphyseal cross-screws for fixation of the superior symphyseal plate is a simple, efficient, and safe technique with the biomechanical advantages of an extra-fixation point to the inferior symphysis together with a long and a strong bony anchorage.

What's New in Percutaneous Pelvis Fracture Surgery?

Percutaneous reduction and fixation of pelvic ring fractures is now widely accepted as a safe and effective treatment method. The only exception remains reduction and fixation of pubic symphyseal injuries. Several units from China and one from Spain have published clinical and biomechanical studies supporting percutaneous reduction and fixation of the pubic symphysis with various screw configurations. The initial clinical results are promising. Biomechanical data show there is little difference between plate and screw fixation. We review the current literature and also present a case performed by ourselves using this novel technique.

Influence of pubic symphysis stiffness on pelvic load distribution during single leg stance

This study focuses on the influence of the softening and stiffening of pubic symphysis on the load distribution within the bones of the pelvic ring under the physiological loadings of the single leg stance. Muscle forces and joint reaction forces were first determined by inverse dynamics and applied to a linear finite element model of the pelvis. With normal pubic symphysis stiffness, high Von Mises stresses are located on the anterior surface to the sacrum around the sacroiliac joint and on the superior ramus, both on the side of the weight-bearing leg. Softening of the pubic symphysis redirects the load backward, decreases the stresses at the anterior pelvis, and increases them at the posterior pelvis. A stiffening of the pubic symphysis redirects the load forward, increases the load on the posterior pelvis, and decreases them at the anterior pelvis. This investigation highlights the significance of the pubic symphysis on the load distribution of the pelvis and in maintaining the integrity of the structures. Its role should not be neglected when analyzing the pelvis.

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).

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.

Finite element analysis of the pelvis including gait muscle forces: an investigation into the effect of rami fractures on load transmission

BACKGROUND

The objective of the study is to investigate the load transmission within the pelvic ring under physiological loading during gait and to correlate these results with clinical findings. In a second approach, we analysed how load distribution is altered by fractures of the anterior pelvic ring.

METHODS

Muscle forces and joint reaction forces are calculated by inverse dynamics and implemented in a finite element pelvis model including the joints.

RESULTS

With the intact configuration and according to the moment of the gait, left and right superior and inferior rami show the highest stresses of the model, corresponding to the typical location of an anterior pelvic ring fracture. A superior ramus fracture induces larger stresses to the lower ramus and a slight increase of stresses on the posterior structures. A total disruption of anterior rami redirects the loads to the back of the pelvis and introduces significantly higher stresses on the posterior structures.

CONCLUSIONS

This investigation enhances the understanding of the biomechanics of the pelvis and highlights the important role of the rami in load carrying and in maintaining integrity of the pelvic ring.

Bernese-type triple pelvic osteotomy through a single incision in children over five years: a retrospective study of twenty eight cases

INTRODUCTION

Bernese-type triple pelvic osteotomy (BTPO) combines periacetabular and triple innominate osteotomy techniques. However, studies that evaluate the clinical and radiographic outcomes of BTPO are scarce. The aim of this study is to report on the clinical and radiographic outcomes of ambulatory children with developmental dysplasia of the hip (DDH) or Legg-Calvé-Perthes disease (LCPD) managed with BTPO that were older than five years of age at the time of surgery.

MATERIALS AND METHODS

We retrospectively reviewed the records of 27 consecutive patients with DDH or LCPD (mean age 7.6 ± 1.8; 28 hips) who were treated with the reported technique. All patients had regular clinical and radiographic follow-up. Post-operatively, changes in the acetabular index (AI) and centre-edge angle of Wiberg (CEA) were measured in all patients. The presence/absence of avascular necrosis of the femoral epiphysis was also noted in patients with DDH. Final radiographic results were evaluated with the Severin and Stulberg classifications. The Harris hip score was used in the functional evaluation of all patients.

RESULTS

In patients with DDH, the mean age at the time of surgery was 7.5 ± 1.8 years and the mean follow-up time was 22.2 ± 10.7 months. Prior to surgery, the mean AI was 37.9° ± 7.6°. At their final follow-up visit, the mean AI and CEA were 10.8° ± 5.4° and 40.9° ± 8.6°, respectively. Moreover, 66.7% of hips (14/21) were graded as Severin type I, and 33.3% (7/21) were graded as type II. The overall AVN rate was 14.3% (3/21). The mean Harris score was 92.1 ± 7.7. In patients with LCPD, the mean age at the time of surgery was 7.9 ± 1.8 years, and the mean follow-up time was 18.4 ± 6.1 months. Prior to surgery, 85.7% of hips were graded as Herring C, and 14.3% were graded as grade B. Prior to surgery, the mean AI and CEA were 19.4° ± 5.3° and 19.1° ± 12.6°, respectively. At the final follow-up visit, the mean AI and CEA were 5.8° ± 3.4° and 50.3° ± 12.0°, respectively, and 57.1% of hips were graded as Stulberg II. The mean Harris score was 94 ± 5.4. Ischial osteotomy non-unions were recorded in three patients (10.7%).

CONCLUSIONS

BTPO through a modified anterior Smith-Peterson approach is an alternative treatment for DDH and LCPD in older children who are skeletally immature. It not only provides for a large acetabular correction but also achieves good biomechanical stability.

Three-dimensional reduction and finite element analysis improves the treatment of pelvic malunion reconstructive surgery: A case report

RATIONALE

Pelvic malunion is a rare complication and is technically challenging to correct owing to the complex three-dimensional (3D) geometry of the pelvic girdle. Hence, precise preoperative planning is required to ensure appropriate correction. Reconstructive surgery is generally a 2- or 3-stage procedure, with transiliac osteotomy serving as an alternative to address limb length discrepancy.

PATIENT CONCERNS

A 38-year-old female patient with a Mears type IV pelvic malunion with previous failed reconstructive surgery was admitted to our department due to progressive immobilization, increasing pain especially at the posterior pelvic arch and a leg length discrepancy. The leg discrepancy was approximately 4 cm and rotation of the right hip joint was associated with pain.

DIAGNOSIS

Radiography and computer tomography (CT) revealed a hypertrophic malunion at the site of the previous posterior osteotomy (Mears type IV) involving the anterior and middle column, according to the 3-column concept, as well as malunion of the left anterior arch (Mears type IV).

INTERVENTIONS

The surgery was planned virtually via 3D reconstruction, using the patient's CT, and subsequently performed via transiliac osteotomy and symphysiotomy. Finite element method (FEM) was used to plan the osteotomy and osteosynthesis as to include an estimation of the risk of implant failure.

OUTCOMES

There was not incidence of neurological injury or infection, and the remaining leg length discrepancy was ≤ 2 cm. The patient recovered independent, pain free, mobility. Virtual 3D planning provided a more precise measurement of correction parameters than radiographic-based measurements. FEM analysis identified the highest risk for implant failure at the symphyseal plate osteosynthesis and the parasymphyseal screws. No implant failure was observed.

LESSONS

Transiliac osteotomy, with additional osteotomy or symphysiotomy, was a suitable surgical procedure for the correction of pelvic malunion and provided adequate correction of leg length discrepancy. Virtual 3D planning enabled precise determination of correction parameters, with FEM analysis providing an appropriate method to predict areas of implant failure.

Biomechanical characteristics of fixation methods for floating pubic symphysis

Background

Floating pubic symphysis (FPS) is a relatively rare injury caused by high-energy mechanisms. There are several fixation methods used to treat FPS, including external fixation, subcutaneous fixation, internal fixation, and percutaneous cannulated screw fixation. To choose the appropriate fixation, it is necessary to study the biomechanical performance of these different methods. The goal of this study was to compare the biomechanical characteristics of six methods by finite element analysis.

Methods

A three-dimensional finite element model of FPS was simulated. Six methods were used in the FPS model, including external fixation (Ext), subcutaneous rod fixation (Sub-rod), subcutaneous plate fixation (Sub-plate), superior pectineal plate fixation (Int-sup), infrapectineal plate fixation (Int-ifa), and cannulated screw fixation (Int-scr). Compressive and rotational loads were then applied in all models. Biomechanical characteristics that were recorded and analyzed included construct stiffness, micromotion of the fracture gaps, von Mises stress, and stress distribution.

Results

The construct stiffness of the anterior pelvic ring was decreased dramatically when FPS occurred. Compressive stiffness was restored by the three internal fixation and Sub-rod methods. Unfortunately, rotational stiffness was not restored satisfactorily by the six methods. For micromotion of the fracture gaps, the displacement was reduced significantly by the Int-sup and Int-ifa methods under compression. The internal fixation methods and Sub-plate method performed well under rotation. The maximum von Mises stress of the implants was not large. For the plate-screw system, the maximum von Mises stress occurred over the region of the fracture and plate-screw joints. The maximum von Mises stress appeared on the rod-screw and screw-bone interfaces for the rod-screw system.

Conclusions

The present study showed the biomechanical advantages of internal fixation methods for FPS from a finite element view. Superior stabilization of the anterior pelvic ring and fracture gaps was obtained by internal fixation. Subcutaneous fixation had satisfactory outcomes as well. Sub-rod fixation offered good anti-compression, while the Sub-plate fixation provided favorable anti-rotational capacity.

Newly designed anterolateral and posterolateral locking anatomic plates for lateral tibial plateau fractures: a finite element study

BACKGROUND

Lateral column tibial plateau fracture fixation with a locking screw plate has higher mechanical stability than other fixation methods. The objectives of the present study were to introduce two newly designed locking anatomic plates for lateral tibial plateau fracture and to demonstrate their characteristics of the fixation complexes under the axial loads.

METHODS

Three different 3D finite element models of the lateral tibial plateau fracture with the bone plates were created. Various axial forces (100, 500, 1000, and 1500 N) were applied to simulate the axial compressive load on an adult knee during daily life. The equivalent maps of displacement and stress were output, and relative displacement was calculated along the fracture lines.

RESULTS

The displacement and stresses in the fixation complexes increased with the axial force. The equivalent displacement or stress map of each fixation under different axial forces showed similar distributing characteristics. The motion characteristics of the three models differed, and the max-shear stress of trabecula increased with the axial load.

CONCLUSIONS

These two novel plates could fix lateral tibial plateau fractures involving anterolateral and posterolateral fragments. Motions after open reduction and stable internal fixation should be advised to decrease the risk of trabecular microfracture. The relative displacement of the posterolateral fragments is different when using anterolateral plate and posterolateral plate, which should be considered in choosing the implants for different posterolateral plateau fractures.