Finite element analysis of different configurations of fully threaded cannulated screw in the treatment of unstable femoral neck fractures

Finite Element Analysis of Six Internal Fixations in the Treatment of Pauwels Type III Femoral Neck Fracture

OBJECTIVE

The current investigation sought to utilize finite element analysis to replicate the biomechanical effects of different fixation methods, with the objective of establishing a theoretical framework for the optimal choice of modalities in managing Pauwels type III femoral neck fractures.

METHODS

The Pauwels type III fracture configuration, characterized by angles of 70°, was simulated in conjunction with six distinct internal fixation methods, including cannulated compression screw (CCS), dynamic hip screw (DHS), DHS with de-rotational screw (DS), CCS with medial buttress plate (MBP), proximal femoral nail anti-rotation (PFNA), and femoral neck system (FNS). These models were developed and refined using Geomagic and SolidWorks software. Subsequently, finite element analysis was conducted utilizing Ansys software, incorporating axial loading, torsional loading, yield loading and cyclic loading.

RESULTS

Under axial loading conditions, the peak stress values for internal fixation and the femur were found to be highest for CCS (454.4; 215.4 MPa) and CCS + MBP (797.2; 284.2 MPa), respectively. The corresponding maximum and minimum displacements for internal fixation were recorded as 6.65 mm for CCS and 6.44 mm for CCS + MBP. When subjected to torsional loading, the peak stress values for internal fixation were highest for CCS + MBP (153.6 MPa) and DHS + DS (72.8 MPa), while for the femur, the maximum and minimum peak stress values were observed for CCS + MBP (119.3 MPa) and FNS (17.6 MPa), respectively. Furthermore, the maximum and minimum displacements for internal fixation were measured as 0.249 mm for CCS + MBP and 0.205 mm for PFNA. Additionally, all six internal fixation models showed excellent performance in terms of yield load and fatigue life.

CONCLUSION

CCS + MBP had the best initial mechanical stability in treatment for Pauwels type III fracture. However, the MBP was found to be more susceptible to shear stress, potentially increasing the risk of plate breakage. Furthermore, the DHS + DS exhibited superior biomechanical stability compared to CCS, DHS, and PFNA, thereby offering a more conducive environment for fracture healing. Additionally, it appeared that FNS represented a promising treatment strategy, warranting further validation in future studies.

Biomechanical Stability of Femoral Neck System for Pauwels Type III Femoral Neck Fractures Based on Different Reduction Quality

To further investigate the biomechanics of a femoral neck system (FNS) for Pauwels type III femoral fractures based on three different reductions.We constructed three different reduction (anatomical reduction, negative buttress reduction, and positive buttress reduction) models of Pauwels type III femoral neck fractures. Then, three cannulated screws (3CS), dynamic hip screws (DHS), dynamic hip screws combined with an anti-rotation screw (DHS + ARS), one-hole femoral neck system (1HFNS), and two-hole femoral neck system (2HFNS) were assembled with the reduction models, respectively, to simulate the internal fixation surgical procedure. All models had a load of 2100 N in line with the femoral mechanical axis applied. The implant stress, the head and implant displacements, and the rotational angles of all models were recorded and analyzed.Compared to 3CS and 2HFNS, 1HFNS had higher implant stress (higher than 92.5 MPa and 46.3 MPa, respectively) and displacement (higher than 0.9 mm and 0.8 mm, respectively) in the anatomical reduction. 2HFNS exhibited the highest stress values (225.5 MPa) in the anatomical reduction but the lowest values (159.8 MPa) in the positive buttress reduction when compared to the other implants. 2HFNS showed the best rotational stability in the negative and positive buttress reduction (rotational angels of 0.8° and 0.6°, respectively).Based on the outcome of this computational study, it might be concluded that 2HFNS was an alternative fixation for the treatment of Pauwels type III femoral neck fracture, especially when anatomical reduction cannot be perfectly attained. More relevant clinical and biomechanical studies are needed in the future.

Single-plane osteotomy model is inaccurate for evaluating the optimal strategy in treating vertical femoral neck fractures: A finite element analysis

BACKGROUND AND OBJECTIVES

The conventional method for simulating vertical femoral neck fractures (vFNFs) is via a vertical single-plane osteotomy (SPO) across the entire femur. However, the accuracy of SPO for evaluating the optimal internal fixation strategy (IFS) and the appropriate assessment parameters is not clear. This study thus aimed to examine the accuracy of SPO in evaluating IFSs and to identify appropriate evaluation parameters using finite element analysis.

METHODS

Eighty patient-specific finite element models were developed based on CT images from eight vFNF patients. The natural fracture model was built using structural features of the affected side, while the SPO was simulated on the healthy side. Five different IFSs were applied to both the natural fracture and SPO groups. Thirteen parameters, including stress, displacement, and stiffness, were subjected to a two-way repeated measures ANOVA to determine the effect of IFSs and fracture morphology on stability. A Pearson correlation analysis was performed on varied parameters with various IFSs to identify independent parameters. Based on these independent parameters, the entropy evaluation method (EEM) score was used to rank the performance of IFSs for each patient.

RESULTS

Eight of the thirteen parameters were significantly influenced by IFSs (p < 0.05), two by fracture morphology (p < 0.01), and none by the interaction between IFS and fracture morphology. In the natural fracture group, parameters including screw stress and displacement, bone cut rate (BCR), and compression effects varied independently with distinct IFSs. In the SPO group, trunk displacement, BCR, cut-out risk, and compression effects parameters changed independently. The BCR of the Alpha strategy was significantly higher than that of the Inverted strategy in the natural fracture group (p = 0.002), whereas the opposite was observed in the SPO group (p = 0.016). Regarding compression effects, two IFS pairings in the natural fracture group and seven IFS pairings in the SPO group exhibited significant differences. None of the five IFSs achieved the optimal EEM score for each patient.

CONCLUSIONS

The single-plane osteotomy model may have limitations in assessing IFSs, particularly when the bone cut rate and compression effects are the main influencing factors. Parameters of the screw stress and displacement, BCR, and compression effects appear to be relevant in evaluating IFSs for natural fracture models. It indicates that individualized natural fracture models could provide more comprehensive insights for determining the optimal IFS in treating vFNFs.

The significance of reduction of valgus-intercalated femoral neck fracture with valgus angle > 15°and the selection of internal fixation by finite element analysis

BACKGROUND

Currently, consensus is lacking on the necessity of internal fixation after reducing valgus-intercalated femoral neck fractures with abduction > 15°. This study employs finite element analysis to compare the biomechanical differences between the femoral neck dynamic cross nail system (FNS) and inverted cannulated screw (ICS), aiming to provide a foundation for clinical procedures.

METHODS

Human femur CT scan data were processed using MimICS21.0 and Geomagic 2021 software, imported into Solidworks2021 to create fracture models, based on Garden I abduction and Valgus-intercalated femoral neck fractures. The internal fixation model was divided into two groups: A-Anatomic reduction group; B-Valgus-intercalated femoral neck fracture group. ANSYS software facilitated meshing, material assignment, and data calculation for stress and displacement comparisons when ICS and FNS were applied in reduction or non-reduction scenarios.

RESULTS

Without internal fixation, peak femur stress in both groups was 142.93 MPa and 183.62 MPa. Post FNS fixation, peak stress was 254.11 MPa and 424.81 MPa; peak stresses for the two FNS models were 141.26 MPa and 248.33 MPa. Maximum displacements for the two FNS groups were 1.91 mm and 1.26 mm, with peak fracture-end stress at 50.751 MPa and 124.47 MPa. After ICS fixation, femur peak stress was 204.76 MPa and 274.08 MPa; maximum displacements were 1.53 mm and 1.15 mm. ICS peak stress was 123.88 MPa and 174.61 MPa; maximum displacements were 1.17 mm and 1.09 mm, with peak fracture-end stress at 61.732 MPa and 104.02 MPa, respectively.

CONCLUSIONS

Our finite element study indicates superior mechanical stability with internal fixation after reducing valgus-intercalated femoral neck fractures (> 15°) compared to in situ fixation. Additionally, ICS biomechanical properties are more suitable for this fracture type than FNS.

[Translated article] The configuration of the screws in the osteosynthesis of fractures of the femoral neck does not influence the functional or mechanical outcomes

BACKGROUND AND OBJECTIVE

Synthesis with cannulated screws is one of the accepted methods in femoral neck fractures, although its optimal configuration is a subject in continuous debate. The main objective was to compare the results of the patient with a femoral neck fracture fixed with three screws in triangle and inverted triangle configuration in the frontal plane.

MATERIALS AND METHODS

Retrospective and comparative study of 53 patients with femoral neck fracture, operated between 2015 and 2022 with fixation with three cannulated screws, 22 with a triangle configuration (triangle group) and 31 in an inverted triangle (inverted triangle group). Functionality was evaluated using the modified Merlé d'Aubigné scale, walking ability using the Koval scale, as well as postoperative complications.

RESULTS

On the Merlé d'Aubigné scale, the mean score was 16.7 in the triangle group and 16.1 in the inverted triangle group (p=.259). On the Koval scale, a significant decrease was observed, going from 1.6 preoperative mean to 2.2 after surgery (p=.000), finding no differences between groups. There were six postoperative complications in the triangle group and three in the inverted triangle group (p=.140).

CONCLUSION

The configuration of the screws in the femoral neck, both in the form of a triangle and an inverted triangle, did not influence the functional or mechanical outcomes of the patients with a femoral neck fracture fixed with three cannulated screws.

The configuration of the screws in the osteosynthesis of fractures of the femoral neck does not influence the functional or mechanical outcomes

BACKGROUND AND OBJECTIVE

Synthesis with cannulated screws is one of the accepted methods in femoral neck fractures, although its optimal configuration is a subject in continuous debate. The main objective was to compare the results of the patient with a femoral neck fracture fixed with three screws in triangle and inverted triangle configuration in the frontal plane.

MATERIALS AND METHODS

Retrospective and comparative study of 53 patients with femoral neck fracture, operated between 2015 and 2022 with fixation with three cannulated screws, 22 with a triangle configuration (triangle group) and 31 in an inverted triangle (inverted triangle group). Functionality was evaluated using the modified Merlé d'Aubigné scale, walking ability using the Koval scale, as well as postoperative complications.

RESULTS

On the Merlé d'Aubigné scale, the mean score was 16.7 in the triangle group and 16.1 in the inverted triangle group (P=.259). On the Koval scale, a significant decrease was observed, going from 1.6 preoperative mean to 2.2 after surgery (P=.000), finding no differences between groups. There were six postoperative complications in the triangle group and three in the inverted triangle group (P=.140).

CONCLUSION

The configuration of the screws in the femoral neck, both in the form of a triangle and an inverted triangle, did not influence the functional or mechanical outcomes of the patients with a femoral neck fracture fixed with three cannulated screws.

Biomechanical effects of internal fixation with self-lock compression anti-rotation blade for Pauwels type III femoral neck fractures: a comparative finite element analysis

BACKGROUND

Self-lock compression anti-rotation blade (SCAB) is a novel internal fixation implant for femoral neck fractures (FNF). We conducted this finite element analysis study to evaluate the biomechanical performances of SCAB combined with a cannulated screw for fixation of Pauwels type III FNF.

METHODS

Three finite element models of Pauwels type III FNF treated with various internal fixations were established: a: the inverted triangular parallel cannulated screw (3CS) model, b: the biplane double-supported screw fixation (BDSF) model, c: the SCAB combined with a cannulated screw model. Displacement and Von Mises stress of femurs and internal fixations under increasing loads as well as the average stress on fracture surfaces and maximum displacements on the X and Z axis of proximal fracture fragments at maximum load were measured and compared.

RESULT

The SCAB-based internal fixation exhibited superior biomechanical performances compared with 3CS and BDSF configurations, as the former resulted in lower parameters including displacement of the femur, Von Mises stress of internal fixation, stress on fracture surfaces as well as X and Z axis displacement of fracture fragments.

CONCLUSION

Internal fixation using SCAB combined with a cannulated screw for Pauwels type III FNFs shows enough stability, with satisfied resistance to varus and shearing forces, which may provide a new option for the treatment of FNFs.

Biomechanical evaluation of two modified intramedullary fixation system for treating unstable femoral neck fractures: A finite element analysis

Purpose: The existing implants for fixation of femoral neck fractures have poor biomechanical stability, so the failure rate is high. We designed two modified intramedullary implants for treating unstable femoral neck fractures (UFNFs). We tried to improve the biomechanical stability of fixation by shortening the moment and reducing stress concentration. Each modified intramedullary implant was compared with cannulated screws (CSs) through finite element analysis (FEA). Methods: Five different models were included: three cannulated screws (CSs, Model 1) in an inverted triangle configuration, the dynamic hip screw with an anti-rotation screw (DHS + AS, Model 2), the femoral neck system (FNS, Model 3), the modified intramedullary femoral neck system (IFNS, Model 4), and the modified intramedullary interlocking system (IIS, Model 5). Three-dimensional (3D) models of femur and implants were constructed by using 3D modelling software. Three load cases were simulated to assess the maximal displacement of models and fracture surface. The maximal stress at the bone and implants was also evaluated. Results: FEA data showed that Model 5 had the best performance in terms of maximum displacement while Model 1 had the worst performance for this index under axial load of 2100 N. With respect to Maximum stress, Model 4 had the best performance while Model 2 had the worst performance under axial load. The general trends under bending and torsion load were consistent with that under axial load. Our data demonstrated that the two modified intramedullary implants exhibited the best biomechanical stability, followed by FNS and DHS + AS, and then three cannulated screws in axial, bending, and torsion load cases. Conclusion: The two modified intramedullary designs showed the best biomechanical performance among the five implants included in this study. Therefore, this might provide some new options for trauma surgeons to deal with unstable femoral neck fractures.

Finite element analysis of coronoid prostheses with different fixation methods in the treatment of comminuted coronoid process fracture

BACKGROUND

Comminuted fractures of the coronoid process significantly compromise the stability and function of the elbow joint. Reconstruction of the coronoid process with a prosthesis has been suggested as an alternative to restore the architecture. The purpose of this study was to investigate the strength and stability of various methods for the fixation of a coronoid prosthesis by finite element analysis.

MATERIALS AND METHODS

A coronoid prosthesis was designed based on the morphological information from computed tomography images acquired from 64 subjects in whom the top 40% of the coronoid process height was replaced. Four methods for the fixation of the prosthesis were suggested: (1) a double 2.0-mm fixation bolt, anterior to posterior; (2) a double 2.5-mm fixation bolt, anterior to posterior; (3) a single 4.0-mm fixation bolt, posterior to anterior; (4) a single 4.5-mm fixation bolt, posterior to anterior. The integrated prosthesis-bone constructs were analyzed via the finite element analysis of 10 simulated proximal ulna models with loading applied along the axis of the humerus and with three different elbow flexion angles (30°, 90°, and 130°). The maximum principal stress and the total deformation were quantified and compared.

RESULTS

A coronoid prosthesis was developed. The maximum principal stress of the fixation bolts occurred around the neck of the fixation bolt. For a comparison of the strengths of the four fixation methods, the maximum principal stress was the lowest for fixation using a single 4.5-mm fixation bolt. The value of the maximum principal stress significantly decreased with increased elbow flexion angle for all fixation methods. The maximum deformation of the fixation bolts occurred at the head of the fixation bolt. For a comparison of the maximum deformations in the four fixation methods, the maximum deformation was the lowest for fixation using a single 4.5-mm fixation bolt. The value of the maximum deformation significantly decreased with increased elbow flexion angle for all fixation methods.

CONCLUSIONS

The present study suggested that fixation of a coronoid prosthesis with a single 4.5-mm fixation bolt from posterior to anterior is an excellent option in terms of the strength and stability. Level of Evidence Experimental study.

Reoperation rate and implants’ position variation features of displaced femoral neck fractures with sliding compression or length-stable fixation in young and middle-aged population

Introduction

Sliding compression fixation and length-stable fixation are two basic internal fixation concepts in the treatment of displaced femoral neck fractures. In this study, we aimed to compare the reoperation rates for different methodologies of internal fixation for femoral neck fractures in young and middle-aged population.

Materials and methods

This a retrospective study. A total of 215 patients with displaced femoral neck fractures treated with cannulated screw fixation were enrolled and divided into the sliding compression and length-stable groups according to the fixation pattern. The occurrence of and reason for revision surgery within one year were recorded. Forty-five patients with complete CT data (including CT scanning on the first postoperative day and at the last follow up) were selected from the total sample. A newly established computerized image processing method was used to evaluate variations in the spatial location of screws.

Results

The reoperation rate was significantly higher in the length-stable group (23.8%) than in the sliding compression group (7.3%). The rate of revision surgery due to nonunion was also higher in the length-stable group (11.4%) than in the sliding compression group (1.8%). However, no significant difference was observed in terms of joint penetration or soft tissue irritation. The sliding compression group (6.58 ± 3.18 mm) showed higher femoral neck shortening than length-stable group (4.16 ± 3.65 mm). When analyzing the spatial variations, a significantly greater screw withdrawal distance was observed in the sliding compression group than in the length-stable group, but with a smaller rotation angle.

Conclusion

Length-stable internal fixation of displaced femoral neck fractures may lead to an increased reoperation rate in young and middle-aged population.

Trial registration

Name of the registry: Chinese Clinical Trial Registry.

Trial registration number: ChiCTR2000032327.

Trial registration date: 2020–4-26.

[Research progress of femoral neck system in treatment of femoral neck fracture in young and middle-aged patients]

Objective

To summarize the research progress of femoral neck system (FNS) in the treatment of femoral neck fracture in young and middle-aged patients.

Methods

The literature on FNS at home and abroad in recent years was extensively reviewed, and the results of mechanical and clinical studies on FNS were summarized based on clinical experience.

Results

FNS has good mechanical stability, which can reduce complications such as femoral neck shortening, internal fixation failure, and varus caused by mechanical instability. At present, FNS is mainly selected for comparison with cannulated compression screws and dynamic hip screws in clinical research. The results show that FNS has the advantages of minimally invasive, short operation time, less intraoperative fluoroscopy, earlier postoperative weight-bearing and fracture healing, and better hip function recovery.

Conclusion

As a new internal fixator, FNS has achieved satisfactory results in the current research. FNS has good mechanical advantages, which is beneficial to fracture healing and the recovery of hip joint function after operation. However, whether FNS can reduce the incidence of nonunion and osteonecrosis of the femoral head remains to be further clarified.

Finite element analyses of lateral condyle fracture fixation in paediatrics regarding configuration of Kirschner-wire

Background

This study aimed to discover the most stable outcome among different Kirschner-wire (K-wire) configurations for fixation of a lateral condyle fracture (Milch type II) in different loads of stress by using finite element analyses (FEA).

Methods

The right humerus of a 6-year-old boy with a lateral condyle fracture (Milch type II), was modelled with a computer aided engineering. Using FEA, peak von Mises stress and stiffness were evaluated first for a single K-wire fixation by varying the angle (0, 5, 10, 15, 20, 25, 30 degrees). Then, based on the single K-wire result, assessment of peak von Mises stress and stiffness were evaluated via FEA for two- or three-wire fixation under various configurations (two convergent, two parallel, three divergent).

Results

Single K-wire fixation by 5 and 25 degrees had the lowest peak von Mises stress. The fracture site showed higher stiffness at 0, 5 and 15 degrees. Considering the collected results and clinical situation, 5 degree K-wire was selected for the FEA of multiple K-wire fixation. For multiple K-wire fixation, three divergent (5–20-35 degrees) K-wires showed better stability, both in peak von Mises stress and stiffness, than any two-K-wire configurations. Among two K-wire fixations, two divergent (5–50 degrees) K-wires provided the lowest von Mises stress in varus and valgus while two divergent (5–65 degrees) K-wires showed better results in flexion, extension, internal and external rotation, and both configurations showed similar results in stiffness.

Conclusions

We successfully created a paediatric lateral condyle fracture (Milch type II) model which was used to conduct FEA on different K-wire configurations to achieve stability of the fracture. Our results show that an initial K-wire inserted at 5 degrees, followed by the insertion of a second divergent wire at either 45 or 60 degrees provides the most stability in two K-wire fixations in this type of fracture repair.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05897-3.

Biomechanical study on parallel cannulated compression screw combined with medial buttress plate fixation and F-type cannulated compression screw fixation in Pauwels III femoral neck fracture：A finite element analysis

OBJECTIVES

Pauwels III fracture is a kind of femoral neck fractures, in which the angle of the fracture line in the coronal plane and the upper edge of the acetabulum is more than 50°. Internal fixation for the treatment of femoral neck fractures is largely performed by cannulated compression screw (CCS), dynamic hip screw, or locking plate. This study aims to compare the biomechanical properties of parallel CCS combined with medial buttress plate fixation and F-type CCS fixation in the treatment of Pauwels III femoral neck fracture by finite element modeling and to determinate the most suitable procedure for such fractures.

METHODS

A 52-year-old male volunteer, 176 cm in height and 72 kg in weight, with no history of hip joint, was selected. X-ray and CT examination confirmed that the morphology and bone condition of the right hip of the volunteer were normal. A simulation model of Pauwels III femoral neck fracture was established from the collected CT data of the right proximal femur of the volunteer by the finite element method. Four internal fixations were developed to treat the finite element model: Three CCSs in an inverted triangular parallel configuration combined with medial buttress plate model served as Group A, 2 CCSs in a vertical parallel configuration combined with medial buttress plate model served as Group B, 2 CCSs in a horizontal parallel configuration combined with medial buttress model served as Group C, and the "F" shaped CCS model served as Group D. The distribution of stress, the peak stress, the distribution and maximum of displacement of internal fixations and fracture ends in different models were evaluated.

RESULTS

For Groups A, B, C, and D, the peak stresses on the internal fixation were 362.74, 586.84, 558.25, and 208.66 mPa, respectively, all of which occurred near the fractures and the stress distribution in Group D was the most uniform. The maximum displacements of internal fixations in Groups A, B, C, and D were 0.39, 0.45, 0.44, and 0.41 mm, respectively; the peak stresses on the fracture ends were 70.62, 98.48, 55.84, and 65.39 mPa, respectively, all of which were concentrated on the base of femoral neck and lateral cortex of the femoral shaft, and the stresses of Groups C and D were more evenly distributed than those of Groups A and B. The maximum displacements of fracture ends in Groups A, B, C, and D were 0.44, 0.52, 0.50, and 0.44 mm, respectively.

CONCLUSIONS

The biomechanical stability of F-type CCS fixation is similar to that of 3 CCSs in an inverted triangular parallel configuration combined with medial buttress plate, with a better dispersion of stress. F-type CCS fixation may be a well option for the treatment of femoral neck fracture of Pauwels III.

Biomechanical study of anterior and posterior pelvic rings using pedicle screw fixation for Tile C1 pelvic fractures: Finite element analysis

Objective

The purpose of this study was to analyse the biomechanical characteristics of pedicle screws with different placement methods and diameters in the treatment of Tile C1 pelvic fractures by finite element simulation technology and to compare them with the plate fixation model to verify the effectiveness of pedicle screw fixation.

Methods

A three-dimensional digital model of a normal pelvis was obtained using computed tomography images. A finite element model of a normal pelvis containing major ligaments was built and validated (Model 1). Based on the verified normal pelvis finite element model, a Tile C1 pelvic fracture model was established (Model 2), and then a plate fixation model (Model 3) and a pedicle screw fixation model with different screw placement methods and diameters were established (Models 4–15). For all pelvic fracture fixation models, a vertical load of 500 N was applied on the upper surface of the sacrum to test the displacement and stress distribution of the pelvis in the standing state with both legs.

Results

The finite element simulation results showed the maximum displacement of Model 1 and Models 3–15 to be less than 1 mm. The overall maximum displacement of Models 4–15 was slightly larger than that of Model 3 (the maximum difference was 177.91×10⁻³ mm), but the maximum displacement of iliac bone and internal fixation in Models 4–15 was smaller than that of Model 3. The overall maximum stress (maximum stress of the ilium) and maximum stress of internal fixation in Models 4–15 were less than those in Model 3. The maximum displacement difference and maximum stress difference at the fracture of the pubic ramus between each fixed model were less than 0.01 mm and 1 MPa, respectively. The greater the diameter and number of pedicle screws were, the smaller the maximum displacement and stress of the pelvic fracture models were.The maximum displacement and stress of the pelvic fracture models of the screws placed on the injured side of the pubic region were smaller than the screws on the healthy side.

Conclusion

Both the anterior and posterior pelvic rings are fixed with a pedicle screw rod system for treatment of Tile C1 pelvic fractures, which can obtain sufficient biomechanical stability and can be used as a suitable alternative to other implants.The greater the diameter and number of pedicle screws were, the greater the pelvic stability was, and the greater was the stability of the screws placed on the injured side of the pubic region than the screws on the healthy side.

Finite element analysis of necessity of reduction and selection of internal fixation for valgus-impacted femoral neck fracture

This study compared the biomechanical characteristics of different treatment strategies based on finite element analysis. Posterior tilt and valgus angle were measured on X-ray from ten valgus-impacted femoral neck fractures, and 7 finite element models that were generated to compare the stress and displacement. The results showed that in the intact femur, von Mises stress was concentrated at the medial and inferior sides of the femoral neck. In valgus-impacted femoral neck fractures, von Mises stress was at the same locations but was 5.66 times higher than that in the intact femur. When 3 cannulated screws were used for internal fixation, anatomic reduction diminished the stress at the fracture end from 140.6 to 59.14 MPa, although displacement increased from 0.228 to 0.450 mm. When the fracture was fixed with a sliding hip screw (SHS) + cannulated screw, there was less stress at the fracture end and greater displacement with anatomic reduction than that without reduction (stress: 15.9 vs 37.9 MPa; displacement: 0.329 vs 0.168 mm). Therefore, the SHS + cannulated screw has superior biomechanical stability than 3 cannulated screws, and is recommended following anatomic reduction to treat valgus-compacted femoral neck fractures.

Comparison between headless cannulated screws and partially threaded screws in femoral neck fracture treatment: a retrospective cohort study

The choices of the treatments for femoral neck fractures (FNF) remain controversial. The purpose of this study is to evaluate the prognoses of the variable pitch fully threaded headless cannulated screws (HCS) in the fixation of femoral neck fractures and to compare them with those of partially threaded cannulated screws (PCS). Between 1st January 2012 and 31st December 2016, there were 89 patients with the main diagnose of FNF who accepted the treatment of closed reduction cannulated screw fixation in Peking University People’s Hospital. 34 cases of PCS and 23 cases of HCS met the criterion. The characteristics, prognoses and the imaging changes of all cases were described and the differences between the two groups were compared. Statistical analyses were performed using SPSS version 23.0 (SPSS Inc., USA). Mann–Whitney U test, Analysis of Variance and Chi-square test were used. Statistical significance was defined as P value (two sided) less than 0.05. There was no significant difference in the general characteristics, fracture classifications and reduction quality between the two groups. HCS group had a significant lower angle decrease rate (30.4% vs. 58.8%, P = 0.035), femoral neck shortening rate (26.1% vs. 52.9%, P = 0.044) and screw back-sliding rate (21.7% vs. 50.0%, P = 0.032), but a higher screw cut-out rate (21.7% vs. 0.0%, P = 0.008). In non-displacement fracture subgroup, HCS had significant higher Harris Score (92 vs. 90, P = 0.048). Compared with PCS, HCS had a lower screw back-sliding rate, femoral shortening rate, angle decrease rate and similar function score, but would result in more screw cut-outs in displaced FNF. As a conclusion, HCS should not be used in displaced FNF due to its higher screw cut-out rate, and its potential advantage in non-displaced FNF needs to be further proved. Further qualified investigations with a larger scale of patients and longer follow-up are needed in the future.

Comparison of oblique triangular configuration and inverted equilateral triangular configuration of three cannulated screws in treating unstable femoral neck fracture: A finite element analysis

BACKGROUND

The cross-sectional area of three parallel screws might affect the stability of the internal fixation of femoral neck fractures. The screws fixed in the oblique-triangle configuration (OTC) were assumed to have a larger cross-sectional area, but the biomechanical stability has not yet been validated. In this study, finite element analyses were performed to compare the biomechanical properties of the internal fixation fixed by the OTC and the traditional Inverted Equilateral Triangle Configuration (IETC).

METHOD

Pauwels type III fracture was established on the three-dimensional femoral model and three cannulated screws with the OTC and traditional IETC methods were applied. The oblique-triangle configuration with the largest area inscribed the femoral neck isthmus by the three screws was determined, the area and circumference of the cross-section formed by the OTC and IETC model were compared. Stress, strain, and displacement peaks of the two configuration models under different loads were compared. Twelve pairs of nodes on the fracture ends were selected and the displacement of the fracture ends was evaluated through the displacement between these nodes.

RESULTS

The area and circumference of the cross-section formed by the OTC were larger than those in the IETC model. The degree of stress dispersion around the screw holes in the OTC model was better than that of the IETC, but the stress distribution order of the three screws in the two models was consistent. The maximum stress, strain, displacement, and displacement of the fracture end in the OTC model were smaller than those in the IETC model. The stress, strain, displacement, and fracture end displacement peaks of the two fixed models gradually increase with the increase of loads.

CONCLUSION

The oblique-triangle configuration showed superior mechanical properties than the IETC in finite element analyses. This study suggests that when three screws are fixed in parallel method, the larger the cross-sectional area of the screw configuration, the better stability of the internal fixation might be obtained. Furthermore, the biomechanical properties of various spatial configurations and screw holes of the three parallel screws need to be considered before clinical practice.

Stochastic Strength Analyses of Screws for Femoral Neck Fractures

This paper represents a multidisciplinary approach to biomechanics (medicine engineering and mathematics) in the field of collum femoris fractures, i.e., of osteosyntheses with femoral/cancellous screws with full or cannulated cross-sections. It presents our new numerical model of femoral screws together with their stochastic (probabilistic, statistical) assessment. In the first part of this article, the new simple numerical model is presented. The model, based on the theory of planar (2D) beams on an elastic foundation and on 2nd-order theory, is characterized by rapid solution. Bending and compression loadings were used for derivation of a set of three 4th-order differential equations. Two examples (i.e., a stainless-steel cannulated femoral screw and full cross-section made of Ti6Al4V material) are presented, explained, and evaluated. In the screws, the internal shearing forces, internal normal forces, internal bending moments, displacement (deflections), slopes, and mechanical stresses are calculated using deterministic and stochastic approaches. For the stochastic approach and a “fully” probabilistic reliability assessment (which is a current trend in science), the simulation-based reliability assessment method, namely, the application of the direct Monte Carlo Method, using Anthill software, is applied. The probabilities of plastic deformations in femoral screws are calculated. Future developments, which could be associated with different configurations of cancellous screws, nonlinearities, experiments, and applications, are also proposed.

The oblique triangle configuration of three parallel screws for femoral neck fracture fixation using computer-aided design modules

Closed reduction and internal fixation with three cannulated compression screws is a common method for treating femoral neck fractures in young and middle-aged patients. Protocols including the inverted triangle configuration and dispersion of the screws still needed further supports. The purpose of this study was to explore a novel oblique triangle configuration (OTC) of three screws in fixing femoral neck fractures based on the morphology of the femoral neck isthmus (FNI). The computer-aided design modules were used to explore the ideal spatial configuration with largest triangle by three parallel screws. A univariate evaluation model was established based on the oval-like cross-section of the FNI. When the three screws were positioned by the OTC, Inverted Equilateral Triangle Configuration (IETC), and the Maximum Area Inverted Isosceles Triangle Configuration (MA-IITC) respectively, the proportion of area and circumference in the cross-section of FNI and the changing trend of proportion were compared under various torsion angles, eccentricity, and cross-sectional area of FNI. The area and circumference ratios of the parallel screws using the OTC method were significantly higher than in the IETC and MA-IITC groups. In the univariate evaluation model, the OTC area ratio and circumference ratio remained stable under the different femoral neck torsion angles, FNI cross-sectional area, and eccentricity. The OTC method provided an ideal spatial configuration for the FNA fixation with the largest area using three parallel screws. The position of the posterior screw was also away from the metaphyseal artery, potentially reducing the possibility of vascular injury and screw penetrating.

Fixation effects of different types of cannulated screws on vertical femoral neck fracture: A finite element analysis and experimental study

Femoral neck fractures (FNFs) in young patients usually result from high-energy violence, and the vertical transcervical type is typically challenging for its instability. FNFs are commonly treated with three cannulated screws (CS), but the role of screws type on fixation effects (FE) is unclear. The purpose of this study was to evaluate the FE of ten types of CS with different diameters, lengths, depths, and pitches of thread via finite element analysis which was validated by a biomechanical test. Ten vertical FNF models were grouped, fixed by ten types of CS, respectively, all in a parallel, inverted triangular configuration. Their FE were scored comprehensively from six aspects via an entropy evaluation method, as higher scores showed better results. For partial-thread screws, thread length and thread shape factor (TSF) are determinative factors on stability of FNF only if thread depth is not too thick, and they have less cut-out risk, better compression effects and better detached resistance of fracture than full-thread screws, whereas full-thread screws appear to have better shear and shortening resistance. A combination of two superior partial-thread screws and one inferior full-thread screw for vertical FNF may get optimal biomechanical outcomes. The type of cannulated screw is important to consider when treating vertical FNF.

Biomechanical study of two alternative methods for the treatment of vertical femoral neck fractures - A finite element analysis

BACKGROUND

No consensus has been reached for the treatment of vertical femoral neck fractures (vFNFs). Recently, two alternative methods were invented to treat vFNFs, one of which is a new plate with a sliding groove, which was designed as a substitution of the medial buttress locking plate to combine with cannulated compression screws (CCS) for reducing the breakage possibility of the proximal locking screw during the bone healing. Another one is the femoral neck system (FNS), which was believed with biomechanical superiority. This study aims to compare the biomechanics of these two new implants with three previous methods via finite element analysis (FEA) to validate whether they are suitable for the treatment of vFNFs.

METHODS

Five 70-degree Pauwels type III transcervical FNFs (vFNFs, AO/OTA 31B2.3^r) models were built and fixed by CCS augmented with the newly designed sliding groove buttress plate (CCS+BS) and FNS. For comparison, models fixed by three parallel cannulated compression screws (CCS), biplane double-supported screw fixation (BDSF), CCS augmented with a medial buttress locking plate (CCS+BL) were also built. A 2100N load was applied along with the mechanical axis. Parameters of the maximal stress as well as the maximal displacement of the implants and bone, the maximal relative displacement of interfragments, and the stiffness, were analyzed to compare the biomechanical characteristics of the five models.

RESULTS

CCS+BS and CCS+BL showed stronger fixation strength with improved stiffness (1012.05N/mm, 1092.04N/mm), reduced maximal displacement of the implants (1.976mm, 1.838mm) and bone (2.075mm, 1.923mm), when compared with CCS (925.11N/mm, 2.158mm and 2.270mm) and BDSF (842.36N/mm, 2.299mm and 2.493mm). While FNS showed the weakest stiffness (593.22N/mm) and largest maximal displacement of the implants (3.234mm) and bone (3.540mm) among the five models.

CONCLUSIONS

CCS+BS has a better biomechanical performance than CCS and BDSF, which offers a new choice to deal with vFNFs. The construction stability of FNS is weaker than CCS, BDSF, and CCS+BL, indicating that this method may not as stable as reported in the previous study.

Modified F configuration in the treatment of Pauwels type III femoral neck fracture: a finite element analysis

Background

The optimal treatment of Pauwels type III femoral neck fracture (FNF) in young patients remains a worldwide challenge in orthopedic surgery.

Methods

Finite element models of four internal fixations were developed to treat Pauwels type III FNF: a: the traditional inverted triangular parallel cannulated screw (PCS) model, b: the F-technique cannulated screw model, c: the modified F-technique cannulated screw model using a fully threaded screw instead of a partially threaded distally, d: the dynamic hip screw coupled with derotational screw (DHS + DS) model. Under the same conditions, finite element analyses were carried out to compare the displacement and von Mises stress distribution of four internal fixations and femurs, the maximum crack distances of the fracture surfaces, Z axis displacements of four models as well as the stress distribution in the subtrochanteric region.

Results

The modified F-technique configuration resulted in a more stable fixation as compared to the other three configurations, with respect to the maximum displacement and stress peaks of femur and internal fixations, the maximum crack distances of the fracture surfaces, Z axis displacements of four configurations as well as the stress distribution in the subtrochanteric region.

Conclusions

Our results suggested that modified F-technique configuration show a better performance in resisting shearing and rotational forces in treating Pauwels type III FNF compared to those using traditional inverted triangular PCS, the F-technique configuration or DHS + DS, providing a new choice for the treatment of FNFs.

The Effect on the Fracture Healing following Femoral Neck Shortening after Osteoporotic Femoral Neck Fracture Treated with Internal Fixation: Finite Element Analysis

Objective

To evaluate the stress status of fracture site caused by femoral neck shortening and to analyze the stress of fracture site and the implants from the finite element point of view.

Methods

CT scan data of hip of a normal adult female were collected. Three-dimensional reconstruction MICs and related module function simulation was used to establish the postoperative shortening model of femoral neck fracture with Pauwels angle > 50°, which was treated with cannulated screws. The models were divided into four groups: normal femoral neck, shortening in 2.5 mm, shortening in 7.5 mm, and shortening in 12.5 mm. The finite element analysis software msc.nastran2012 was used, and the data of maximum stress and stress nephogram of fracture site and implants were carried out.

Results

From normal femoral neck to shortening in 12.5 mm of the femoral neck, the maximum tensile stress increased gradually in the fracture site above the cannulated screws while compressive stress decreased gradually in the fracture site below the cannulated screws, and the maximum stress of the cannulated screws increased gradually with obvious stress concentration at the screw holes in the fracture site, and the peak value of stress concentration was about 179 MPa.

Conclusion

The biomechanical environment of the fracture site changed by femoral neck shortening. With the increasing of femoral neck shortening, the stress of the fracture site and implants would be uneven; then, the stability of fracture site would become worse, and the possibility of implant sliding or even breakage would be increased.

How to choose the suitable FNS specification in young patients with femoral neck fracture: A finite element analysis

BACKGROUND

Consensus regarding the optimal approach for the treatment of femoral neck fractures remains lacking. A new internal fixation femoral neck system (FNS) was developed and used in clinical practice. We aimed to investigate the biomechanical outcomes of different types of FNS in the treatment of unstable femoral neck fractures.

METHOD

In this study, we constructed three different types of unstable femoral neck fractures of Pauwels classification with angles of 50°, 60°, and 70°. We set up four test groups, namely, the one-hole plated FNS group, two-hole plated FNS group, inverted cannulated screw group and triangle cannulated screw group. Under 2100 N axial loads, displacements and the von Mises stress of the femur and internal fixation components were measured for each fracture group.

RESULTS

When the Pauwels angle was 50°or 60°, the one-hole locking plated FNS was as superior as the two-hole plated FNS in terms of femur and internal fixation displacement, and the inverted cannulated screw had slightly better stability than the triangular cannulated screw. However, when the angle increases to 70°, the two-hole locking plate has the minimum displacement, followed by the triangular cannulated screw and inverted cannulated screw, which is the worst displacement for the single-hole locking plate. Regardless of the angle, the two sets of FNS have higher internal fixation stress than the two sets of cannulated screws, which is approximately 1.6-3.0 times that of the cannulated screw group.

CONCLUSION

From the perspective of biomechanics, we suggest that when the angle of the fracture line is less than 60°, both single-hole locking plated or double-hole locking plated FNS can be used to treat unstable femoral neck fractures. However, when the angle of the fracture line is greater than 70°, we recommend using a double-hole locking plated FNS. This result needs further verification in further clinical studies.

A Postoperative Displacement Measurement Method for Femoral Neck Fracture Internal Fixation Implants Based on Femoral Segmentation and Multi-Resolution Frame Registration

Femoral neck fractures have a high incidence in the geriatric population and are associated with high mortality and disability rates. With the minimally invasive nature, internal fixation is widely used as a treatment option to stabilize femoral neck fractures. The fixation effectiveness and stability of the implant is an essential guide for the surgeon. However, there is no long-term reliable evaluation method to quantify the implant’s fixation effect without affecting the patient’s behavior and synthesizing long-term treatment data. For the femur’s symmetrical structure, this study used 3D convolutional networks for biomedical image segmentation (3D-UNet) to segment the injured femur as a mask, aligned computerized tomography (CT) scans of the patient at different times after surgery and quantified the displacement in the specified direction using the generated 3D point cloud. In the experimental part, we used 10 groups containing two CT images scanned at the one-year interval after surgery. By comparing manual segmentation of femur and segmentation of femur as a mask using neural network, the mask obtained by segmentation using the 3D-UNet network with symmetric structure fully meets the requirements of image registration. The data obtained from the 3D point cloud calculation is within the error tolerance, and the calculated displacement of the implant can be visualized in 3D space.

Migration Measurement of Pins in Postoperative Recovery of the Proximal Femur Fractures Based on 3D Point Cloud Matching

Background and objectives: Internal fixation is one of the most effective methods for the treatment of proximal femur fractures. The migration of implants after the operation can seriously affect the reduction of treatment and even cause complications. Traditional diagnosis methods can not directly measure the extent of displacement. Methods: Based on the analysis of Hansson pins, this paper proposes a measurement method based on three-dimensional matching, which uses computerized tomography (CT) images of different periods of patients after the operation to analyze the implants' migration in three-dimensional space with the characteristics of fast speed and intuitive results. Results and conclusions: The measurement results show that the method proposed in this paper has more minor errors, more flexible coordinate system conversion, and more explicit displacement analysis than the traditional method of manually finding references in CT images and measuring displacement.

Influence of the proximal screws of buttress plates on the stability of vertical femoral neck fractures: a finite element analysis

Background

The treatment of vertical femoral neck fractures (vFNFs) in young patients remains challenging, with a high complication rate by using traditional techniques. The use of cannulated screws (CSs) combined with a buttress plate represents an alternative approach for treating vFNFs. However, the biomechanical influence of the use or non-use of the proximal screws of buttress plates on vFNFs stability remains unclear. This study aims to analyse the biomechanics of buttress plate fixation with or without the use of proximal screws through finite element analysis (FEA) to further understand this approach.

Methods

We built five vFNFs (Pauwels angle 70°) finite element models treated using three cannulated screws (CS group) or three cannulated screws plus a locking buttress plate (buttress group). In the buttress group, use or non-use of proximal screws was carried out on two types of plates (4-hole & 6-hole). The following seven parameters were analysed to compare biomechanical properties of the five models: the stiffness; the maximal stress of the plate system (plate and screws), CSs and bone (MPS, MCS, MBS); the maximal displacement of internal fixations (plate system & CSs) and bone (MIFD, MBD); and the maximal relative displacement of interfragments (MID).

Results

Compared with CS model, the buttress models exhibited improved biomechanical properties, with increased stiffness and decreased MCS, MBS, MIFD, MBD and MID. The models fixed using buttress plates combined with a proximal screw showed greater stiffness (+ 3.75% & + 8.31% vs + 0.98% & + 4.57%) and MPS (795.6 & 947.2 MPa vs 294.9 & 556.2 MPa) values, and smaller MCS, MBS, MIFD, MBD and MID (− 3.41% to − 15.35% vs − 0.07% to − 4.32%) values than those using the same length plates without a proximal screw.

Conclusions

Based on the FEA results, buttress plates can improve construct mechanics, help to resist shear force and prevent varus collapse; under the modelling conditions, the use of a proximal screw on buttress plate may be a key technical feature in improving anti-shearing ability; additionally, this screw may be essential to reduce stress and prevent re-displacement of cannulated screws and fracture fragments.

Biomechanical evaluation of internal fixation implants for femoral neck fractures: A comparative finite element analysis

BACKGROUND AND OBJECTIVE

It remains controversial regarding the optimal type of fixation implant for the treatment of femoral neck fractures (FNFs). Biomechanical rational for implant choices can benefit from the integration of finite element analysis (FEA) in device evaluation and design improvement. In this study, we aim to evaluate biomechanical performance of several internal fixation implants for Pauwels type III FNFs under physiological loading conditions using FEA, as well as to assess the biomechanical contribution of medial buttress plate (MBP) augmentation.

METHODS

Several fixation styles for FNFs have been analyzed numerically by the finite element method. Five groups of models were developed with different FNFs fixation implants, including dynamic hip screw (DHS), cannulated screws (CSs), proximal femoral nail antirotation (PFNA), DHS with MBP augmentation (DHS+MBP), and CSs with MBP (CSs+MBP). For each group, four FE models were established to evaluate strain in bone and stress in devices during walking and stair climbing conditions, which simulated the hip contact force using static and dynamic loadings respectively.

RESULTS

No notable differences were observed in peak strain within implanted bone and maximum stress values of the device between DHS and CSs. The implanted femur with PFNA was in a lower state of bone strain and implant stress. Although the buttress plate did not decrease peak bone strain, it alleviated stress concentration on device, especially for CSs under dynamic loadings.

CONCLUSIONS

Compared to the other fixation styles, the PFNA showed biomechanical advantages of decreasing risk of implant failure and bone yielding. The MBP augmentation provided an additional load path to bridge fracture fragments, which reduced failure risk of DHS and CSs, especially during dynamic loading scenarios. Although further studies are needed for patients with other types of FNFs, our findings may provide valuable references for device design optimization in terms of complex physiological loadings, as well as for clinical decision making in surgical treatment of FNFs.

Finite element modeling of proximal femur with quantifiable weight-bearing area in standing position

Background

The positional distribution and size of the weight-bearing area of the femoral head in the standing position as well as the direct active surface of joint force can directly affect the result of finite element (FE) stress analysis. However, the division of this area was vague, imprecise, and un-individualized in most studies related to separate FE models of the femur. The purpose of this study was to quantify the positional distribution and size of the weight-bearing area of the femoral head in standing position by a set of simple methods, to realize individualized reconstruction of the proximal femur FE model.

Methods

Five adult volunteers were recruited for an X-ray and CT examination in the same simulated bipedal standing position with a specialized patented device. We extracted these image data, calculated the 2D weight-bearing area on the X-ray image, reconstructed the 3D model of the proximal femur based on CT data, and registered them to realize the 2D weight-bearing area to 3D transformation as the quantified weight-bearing surface. One of the 3D models of the proximal femur was randomly selected for finite element analysis (FEA), and we defined three different loading surfaces and compared their FEA results.

Results

A total of 10 weight-bearing surfaces in 5 volunteers were constructed, and they were mainly distributed on the dome and anterolateral of the femoral head with a crescent shape, in the range of 1218.63–1,871.06 mm². The results of FEA showed that stress magnitude and distribution in proximal femur FE models among three different loading conditions had significant differences, and the loading case with the quantized weight-bearing area was more in accordance with the physical phenomenon of the hip.

Conclusion

This study confirmed an effective FE modeling method of the proximal femur, which can quantify the weight-bearing area to define a more reasonable load surface setting without increasing the actual modeling difficulty.

A quantitative biomechanical study of positive buttress techniques for femoral neck fractures: a finite element analysis

Background:

Refractory femoral neck fractures cannot be anatomically reduced by closed traction reduction which may affect fracture healing. We evaluated the biomechanical effects of positive, negative, and anatomic reduction of various degrees of displacement in Pauwels I femoral neck fractures by a finite element analysis.

Methods:

Five reduction models of Pauwels type I femoral neck fracture were established using the Mimics 17.0 (Materialize, Leuven, Belgia) and Hypermesh 12.0 (Altair Engineering, Troy, MI, USA). According to the degree of fracture displacement, there were three models of positive support, an anatomic reduction model, and a negative 2 mm reduction model. Finite element analysis was conducted using the ABAQUS 6.9 software (Simulia, Suresnes, France). The von Mises stress distribution and the stress peak of internal fixation in different models, the displacement between fracture blocks, and the principal strain of the femoral neck cancellous bone model were recorded under the axial stress of 2100 N.

Results:

The peak von Mises stress on screw of each model was located at the thread of the screw tip. The peak von Mises stress was the lowest at the tip of the anatomic reduction model screw (261.2 MPa). In the positive 4 mm model, the von Mises stress peak was the highest (916.1 MPa). The anatomic reduction model showed the minimum displacement (0.388 mm) between fracture blocks. The maximum displacement was noted in the positive 4 mm model (0.838 mm). The displacement in the positive 3 mm model (0.721 mm) was smaller than that in the negative 2 mm model (0.786 mm). Among the five models, the strain area of the femoral neck cancellous bone was mainly concentrated around the screw hole, and the area around the screw hole could be easily cut.

Conclusions:

Compared with negative buttress for femoral neck fracture, positive buttress can provide better biomechanical stability. In Pauwel type I fracture of femoral neck, the range of positive buttress should be controlled below 3 mm as far as possible.

Finite element analysis of a new plate for Pauwels type III femoral neck fractures

Background

Method

Result

Conclusion

Stability evaluation of anterior external fixation in patient with unstable pelvic ring fracture: a finite element analysis

Background

The pelvic ring fractures (PRF) are commonly induced by the high-energy impact and will lead to unstable and sever injures. This study is aimed to explore the stability of anterior external fixation in treating pelvis fracture and evaluate the possibility for these kinds of patients to reduce bedridden time.

Methods

A patient with Tile B3 pelvis fracture was chosen in the research and the corresponding digital model was reconstructed according to the CT images and 3D scanning. Four angles of pelvis under vertical compression were employed in the finite element (FE) analyses. The stress distribution and micro-motion displacement were calculated to validate the instability of pelvis.

Results

The stress applied on the pelvis was ranged from 4.296 to 8.364 MPa in all postures. The stress applied on pins was less than 7.011 MPa during reclining, and reached 28.29 MPa when standing. The micro-motion displacement in reclining posture was ranged from 0.005 to 0.087 mm. The value increased to more than 1mm in standing posture.

Conclusions

It was safety for patients with pelvis fracture to sit vertical or recline on the bed during nursing or having treatment, but standing or walking will generate inappropriate micro-motion. The existence of external fixation can reduce the possibility of complications caused by long-term bedridden.

Perforated H-beam implant can be used in femoral neck fracture

This biomechanical study evaluated comparison osteosynthesis of the femoral neck fracture model by 3 cannulated screw implants and new perforated H beam implants under different loading conditions with 45 third generation right proximal femur bones. A standardized Pauwels Type 3 of the femoral neck fracture was performed in the femur models. For assessing the rigidity and strength of fixation methods, the proximal femur bones after their osteosynthesis were then mechanically tested in axial compression, and torsional and dynamic axial compression loading. To determine the structural advantage of the new implant system, perforated and nonperforated new implant systems were comparing about pull out performance. When loading the samples, photographs were taken continuously. The reference parameters were described and measured from unloaded and loaded photographs of the static and dynamic tests. There was no significant difference between stiffness values of two fixation methods under static and rotational loading. Under dynamic loading, the displacement of the superior point of femoral head at the fracture line showed a significant decrease between the new implant system and cannulated screws. Comparing the relative motion at the mid line of the fracture in femoral neck between groups, a significant increase was found in H Beam implant group. Perforated H beam implants have similar static and torsion properties with golden standard. Although there was significant difference under dynamic loading which simulate movement early after surgery, the patient was not allowed to move early after surgery in the clinical practice. Therefore, the differences due to the perforated "H" beam implant would not cause clinical insecurity. Therefore, it is assumed that the perforated "H" beam implant can be used for internal fixation as an alternative to cannulated screws in the treatment of instable femoral neck fracture.