In silico biomechanical analysis of Poller screw-assisted small-diameter intramedullary nail in the treatment of distal tibial fractures

doi:10.21203/rs.3.rs-1611097/v1

Download PDF

Research Article

In silico biomechanical analysis of Poller screw-assisted small-diameter intramedullary nail in the treatment of distal tibial fractures

https://doi.org/10.21203/rs.3.rs-1611097/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Objective

To evaluate the biomechanical effects of Poller screws combined with small-diameter intramedullary nails in the treatment of distal tibial fractures at different locations and on different planes.

Methods

Data were acquired from one cadaveric lower limb (male, age 39 years) via computed tomography. Finite element modeling simulated the placement of small-diameter intramedullary nails and poller screws for distal tibial fractures. Nine finite element models were established in this study. The models containing poller screw were set as the experimental group, and the model containing only intramedullary nail was set as the control group.Construct stiffness and directional micro-motion through the fracture were investigated to assess the poller effects of Poller screws. The allowable stress method was used to evaluate the safety of the construct.

Results

Under the load condition of 500N, the mean axial stiffness with IMN only was 973.38 ± 95.65 N/mm, which was significantly less than that in the two PS groups at positions A and B. The axial stiffness means in the sagittal plane group at position A and position B were 2698.84 ± 296.53 N/mm and 2234.47 ± 254.69 N/mm (P༜0.05). The axial stiffness means in the coronal plane group from position A and position B were 2139.50 ± 262.46 N/mm and 2439.53 ± 518.26 N/mm. The shear displacements of position A and position B in sagittal plane group and coronal plane group were 0.410mm ± 0.12mm, 0.487 mm ± 0.06 mm, 0.168mm ± 0.11mm and 0.187mm ± 0.07mm. The above displacements were all smaller than the shear displacements of the models containing only intramedullary nail: 2.10mm ± 0.02mm (P < 0.05). Under physiological load, the stresses of all internal fixation devices and the nail-bone interface were within a safe range.

Conclusion

In the treatment of distal tibial fractures, placing the poller screw in the proximal fracture block can obtain better biomechanical performance.The intramedullary fixation system can obtain higher structural stiffness and reduce the displacement of the fracture end by adding poller screws.

Poller screw

small-diameter intramedullary2

distal tibial fractures3

parallel interfragmentary motion 4

flexible fixation5

Tibial fractures frequently occur at the distal metaphysis, and management of this kind of injury has been the subject of several studies. Complexity with respect to biological and biomechanical aspects, as well as surgical tools and techniques, makes the treatment of these fractures challenging and problematic.[1] Due to advantages including soft tissue preservation, earlier definitive fixation, and weight-bearing, intramedullary nailing has become an increasingly common method of fixation in all tibial fractures regardless of location. There are reports of high rates of malunion with intramedullary nail (IMN) fixation via the traditional infrapatellar approach, 23% are associated with distal tibial fractures.[2] Of the many techniques that have been described, Poller screws (PSs) or Blocking screws are among the methods that can be used to aid satisfactory fracture reduction and biomechanical stability.[3, 4]

The PS technique can narrow the relatively wide medullary cavity near the fracture end and increase the contact area between the IMN and the cortical bone. PSs provide the third fulcrum for the IMN and change its track to improve its stability. Current research mainly focuses on the clinical application and efficacy of the PS, and Hannah et al [5] have also provided a method of preoperative planning for the PS. However, as the third support point of the intramedullary nail in the intramedullary cavity, the PS cannot pass through the IMN like locking screws which can provide strong support for the IMN. So, whether it can be placed in a reasonable position, Providing the correct support for the IMN is the key to using the PS technique. Improper use of poller screws may not only lead to their failure but also cause secondary damage and increase patient suffering. Therefore, it is necessary to further explore the biomechanical performance of PS in the IMN internal fixation system.

In the current study, finite element (FE) models were used to investigate whether the use of a PS technique in distal tibial fractures could provide better biological performance and structural stability. FE-based biomechanical analysis was performed given that screws are anchored in both sites of the fracture and on two anatomical planes. An allowable stress method based on our previous work[6] was used to conduct FE simulation and safety assessment. We hypothesized that the poller effect of PSs is related to their position and plane. Improper placement of the PSs will cause asymmetric interfragmentary motion (IFM) of the distal tibia fracture treated with IMNs. Such improper placement could potentially delay secondary bone healing by inducing asymmetric early IFM.

2.1. FE modeling

Computed tomography was performed on a 39-year-old male cadaver. The whole tibia, distal femoral condyle, and proximal talar condyle were scanned. The slice thickness was 1.25 mm and the plane resolution was 512 x 512 pixels. By processing computed tomography slices in mimics (10.01), 3D models including the tibia, distal femur, and proximal talus were established. Point cloud data of the 3D tibia and its joint samples (talus and distal femur) were then imported into Geomagic warp(2014) to create a solid structure. A transverse 10-mm fracture space 70 mm from the distal tibial articular surface (tibia calcaneal joint) was simulated[7].

Three-dimensional models of IMNs, locking nails, and PSs were prepared in advance and imported into NX8.5 together with the tibia model for assembly. The IMN was placed in the tibial model based on a senior qualified surgeon’s recommendation. The proximal and distal parts were fixed with two screws. All the screws were placed from the inside to the outside. In this study, an experimental group and a control group were set up, and the experimental group was the FE model containing IMN and PS. According to the plane perpendicular to PS, the models were divided into coronal plane group and sagittal plane group. The PS placement was arranged with the fracture line as the boundary, and the distance between screws on the same side was 10 mm and the distance between the screws and the fracture line was also 10 mm. Each group contains four finite element models. The control group was an FE model that only used IMN for internal fixation. A total of nine FE models were set up in this study. (Fig. 1)

2.2. Loading and boundary conditions

To apply loads and boundary conditions the interaction surfaces of proximal talus distal tibia and distal femur proximal tibia were considered. These surfaces were then used to set boundary conditions such as where the load is applied to the proximal tibial meniscus and the range of motion of all nodes on the distal tibial ankle surface is limited. The FE model was loaded under axial force with 500 N, and the axial force was distributed in 60% of the medial plateau and 40% of the lateral tibial plateau[8]. Implants, i.e., IMNs, PSs, and locking screws were considered titanium alloys and modeled as equal diameter, linear elastic, and homogeneous materials with Young's modulus of 110 GPA and a Poisson’s ratio of 0.3. Each part of the tibia was considered to be isotropic homogeneous material and assigned Young's modulus (Table 1). Screws were tied to adjacent bones in all degrees of freedom. For simplicity, a contact case with a penalty function equal to 0.2 is defined at the interface between nail and bone, PS and nail. Notably, there may be initial gaps at the IMN bone and PS nail interfaces, which may contact each other during loading and simulation. All samples meshed with 10-node tetrahedral elements.(Table 2).

2.3.Mechanical experiment validation

This study was verified by literature and biomechanical experiments. The same finite element modeling method was used to carry out biomechanical experiments on three fourth generation composite tibias. (Fig. 5.a)The effectiveness of the finite element method is verified by comparing the axial stiffness of FE model and composite tibia. The specific mechanical experiment verification method is as follows.

The axial stiffness tests were conducted by an electronic universal testing machine (A TES6010, China). The specimens were first pre-loaded with the testing machine in position to control a vertical load of up to 100 N. And then the loader was controlled to press down at a rate of 1 mm/min until the force is up to 1000 N. Loads and displacements were recorded and for at least 90 s after load removal for each repetition. Three loading repetitions were performed for each loading configuration, with the specimen being allowed to recover at least 10 min between replicates. Loads and displacements were collected by sensors. According to the load-displacement data, the slope of the linear region is calculated as the axial stiffness of the sample.

2.4. Data analysis

In order to better evaluate IFM, the fracture gap was marked on the coronal plane and sagittal plane, and the length of the mark was measured to reflect the IFM of the fracture space (Fig. 4.a.b). Nodes of marks on the FE model are pre-labeled for the calculation of line lengths. To better evaluate the effects of the PS on secondary bone healing, the parts of the sagittal plane passing through the fracture space were marked “a" for anterior and “c" for posterior at the outer edges of the tibial cortical bone. Similarly, the part of the coronal plane passing through the fracture space was divided into “b" for lateral and “d" for medial. Statistical analysis of the ratio of a and c and the ratio of b and d was used to calculate the symmetry of the fracture space, to better reflect IFM.

Nine static FE simulations were performed in the current study using Abaqus/Standard 2017 software. The equivalent stress and the positions of the model and template were used in the output measurement of statistical analysis. Mean stiffness and displacement values derived from the two models were compared via one-way analysis of variance, and significant results were followed by a post hoc test with Bonferroni correction. p < 0.05 was considered statistically significant.

3.1. Construct stiffness and shear displacement of the fracture site

The stiffness derived from the FE model was consistent with the experimental stiffness in normal models[7, 9]. Under the load condition of 500N, the mean axial stiffness with IMN only was 973.38 ± 95.65 N/mm, which was significantly less than that in the two PS groups at positions A and B. The axial stiffness means in the sagittal plane group from position A and position B were 2698.84 ± 296.53 N/mm and 2234.47 ± 254.69 N/mm (P༜0.05). The axial stiffness means in the coronal plane group from position A and position B were 2139.50 ± 262.46 N/mm and 2439.53 ± 518.26 N/mm.(Fig. 2.d.e) There was no statistically significant difference between the coronal and sagittal plane groups. In the sagittal plane group, the shear displacement of position A was 0.410mm ± 0.12mm. The value of the shear displacement of position B was 0.487 mm ± 0.06 mm. The shear displacements of positions A and B in the coronal plane group were 0.168mm ± 0.11mm and 0.187mm ± 0.07mm, respectively. The above displacements were all smaller than the shear displacements of the models without PS: 2.10mm ± 0.02mm (P < 0.05) (Fig. 2.a.b)

3.2. Parallel IFM

Axial displacements located at a,b,c, and d were calculated between cortices at the fracture site (Fig. 4.a.b). The ratio of a to c and the ratio of b to d was calculated to indicate the symmetry of the axial displacement at the plane fracture site. An IFM ratio range from 0.90 to 1.10 is usually considered to represent parallel IFM (1.00 represents completely parallel IFM at the fracture site[10–12]. In the IMN model, these 2 ratios are 0.99 and 1.00, respectively. However, the ratios of model A and model B are more dispersed in both the sagittal plane group and coronal plane group. The ratio of B to D showed significant changes, 3.03 and 1.36 in the sagittal plane group and 3.05 and 1.36 in the coronal plane group, respectively.

3.3. Mechanical experiment validation

The biomechanical experimental validation results are presented in Fig. 5.b. In the process of axial compression load from 0N to 1000N, the axial stiffness of the mechanical experiment and FE model group are 838.36 ± 150.52 N/µm and 996.26 ± 139.87 N/µm, respectively.

3.4. Safety assessment

In all nine FE models, the maximum stress was evident at the junction of the locking nail and the IMN. The maximum stress of the PS was located at position B in the sagittal plane group under a load of 500 N, and it was 57.78 MPa. The minimum stress was 31.78 MPa, and it was located at position D in the coronal plane group under a load of 500 N.

When evaluating the structural stability associated with using the PS technique in distal tibial fractures with IMN fixation, we also evaluated the risk of a fracturing of the screws that exhibited the maximum deformation in each model. According to our previous work, the allowable stress of the medical titanium alloy can be calculated using the following formula:

$\left[ \sigma \right]=\frac{{{\sigma _Y}}}{n}$

Thus, the maximum safe stress of the IMN and screws was calculated as:

$$\left[{\sigma }\right]=412.5 \text{M}\text{P}\text{a}$$

The maximum von Mises stress should be less than the allowable stress to ensure structural safety. The maximum von Mises stresses of the models under axial compression loading compared with the allowable stress are shown in Fig. 3.a.b

PS was proposed by krettek et al. in 1991[3], and then applied to the clinical treatment of the tibial metaphyseal fracture. Then in 2004, Hans et al.[13] Simulated the placement of more kinds of PS by establishing a simple model, and further elaborated the mechanical effect of poller screws. Andrew Hannah et al. [13] Proposed a more detailed clinical application method for PS in 2014. However, the above studies did not further elaborate on the biomechanical properties of the PS. In the current study, finite element analysis is used to study the influence of specific factors in a given system to better understand the role of PS in internal fixed structures[14]. Finite element modeling can effectively focus on a single factor and offset the influence of other variables, while clinical research may be affected by several controlled and uncontrolled variables. Therefore, based on the 3D finite element model of proximal tibial extraarticular fracture, using finite element analysis software to evaluate the placement of PS in different positions and planes is helpful to further clarify the biomechanical mechanism of PS.

In the clinical report, the users of the PS are concerned about whether it can achieve a satisfactory reduction effect and provide additional stability during the treatment. The axial stiffness of all FE models with PS combined with IMN was improved compared with only IMN. Compared with the control group, the stiffness of the coronal plane group and sagittal plane group at positions A and B was significantly increased. The results showed that placing PS in the proximal fracture block could obtain better stiffness. The reason for this result may be related to the model setting itself. In this study, the focus of the FE model setting is that after appropriate reduction, the force line has been fully corrected. Compared with the clinical application, the placement of internal fixation in the model is more ideal. In addition, the setting of boundary conditions makes the displacement of the distal tibial fracture block smaller in the whole loading process. Based on the above reasons, the distal fracture block will not be greatly affected during model loading. Under physiological conditions, the force on the proximal tibia is asymmetric, and the internal and external forces are distributed in 60% and 40%[8]. When the IMN can not form a good contact with the isthmus of the tibia, such as the space that may be generated after reaming or the use of a small-diameter intramedullary nail for the treatment of fractures, this asymmetry will be more obvious, which may be one of the reasons why the PS placed in the proximal fracture block can obtain better axial stiffness. Although the differences in the anatomical morphology of the medullary cavity and the gap between the IMN and the medullary cavity may lead to changes in the axial stiffness of internal fixation, it can still show that PS plays a constructive role in maintaining the alignment of nails in the Medullary cavity, thereby enhancing the stability of the bone-implant structure (Fig. 2.d.e). The results of this study, corresponding to the axial stiffness of the bone-implant construct, are in agreement with Hoegel et al.and Amin’s results.[7, 15]

The decrease in IFM is another change observed. Whether in vitro experiments or biomechanical experiments, IFM has been proved to be a mechanical stimulation that directly affects bone healing IFM is one of the main reasons for poor alignment of fractures, which affects the healing of distal tibial fractures[16]. Lindvar et al. [17]reported that the incidence of nonunion caused by improper reduction of IMN was higher than that caused by locking plate, and considered that may be due to shear movement at the end of fracture space. In this experiment, when PS was added, the IFM of all FE models decreased, which is consistent with the results of Amin Baseri et al[7]. The addition of PS can effectively limit the shear displacement of the fracture end and provide more stable conditions for the healing of the fracture end.

However, the change of symmetry of IFM at the fracture end is another result observed. The symmetry of IFM can further affect the formation of callus. Michael bottlang et al.[18] found through animal experimental research that symmetrical axial movement can increase the healing strength by 54% and the load-bearing capacity by 156%. For the intramedullary fixation mode highly dependent on secondary bone healing, the symmetry of IFM is one of the factors that should be considered. In the FE model with more obvious stiffness improvement and IFM reduction in the experimental group, by calculating the ratio of the corresponding line segments, it can be found that the maximum value is 3.03, and the minimum value is 1.36 (Fig. 4.d). This value is 0.99 in the FE model with only IMN. This suggests that good symmetry can be obtained when only IMN is used for internal fixation, while the addition of PS increases the asymmetry of IFM, which may have an impact on fracture healing. In addition, in all FE models, the maximum stress generated by the PS is 57.88 MPa, which is a safe value. However, when the PS is placed on the proximal fracture block, the stress of the whole internal fixation system shows a concentrated trend on the contact surface between IMN and PS, which also poses a certain challenge to the long-term safety of this internal fixation system. Clinically, stress concentration and damage to cell resources in bone marrow and periosteum during PS insertion should be considered adverse effects on its application. In the bone nail structure. It is well known that the lack of cellular resources at the fracture site can lead to delayed healing or even nonunion[19]. Therefore, when PS is used, can be considered as another reason for the delay or non healing of the healing process.

The current study had some inherent limitations. The material properties assigned to cortical bone and cancellous bone may not reflect those of actual bone. In addition, other structures adjacent to the tibia such as soft tissue were not fully considered.

This study confirmed that in the treatment of tibial comminuted fractures that do not involve the surface of the ankle, the insertion of PS at the proximal end of the fracture can safely increase the structural stiffness and effectively reduce the shear IFM of the fracture. However, the effect of the change of axial motion symmetry of shear IFM on secondary fracture healing and the potential risk of stress concentration after PS should also be considered by clinical users.

intramedullary nail: IMN

Poller screws: PS

finite element: FE

interfragmentary motion: IFM

Funding

the Science and Technology Project of Guangdong Province(2016B090917001,2018B090944002); Sanming Project of Medicine in

Shenzhen（SZSM201612019); Supported by Southwest Medical University High-Level Talents (Zhong Shizhen Team) Special Support

Program; General Project of Nature Foundation of Guangdong Province(2020A151501998);

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Ethics approval and consent to participate

Not applicable.

Consent for publication

By submitting my article I agree to pay the APC in full if my article is accepted for publication (unless it is covered by an institutional agreement or a full waiver has been granted).

Competing Interests

The authors declare that they have no competing interests and the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Author contributions

(I)Conception and design: Wenhua Huang, Yuping Deng, Hanbin Ouyang;

(II) Administrative support: Wenhua Huang, Yuping Deng;

(III) Data analysis and interpretation: Jinchuan Tan, Yang Yang, Mian Wang, Xuecheng Huang, Dongliang Zhao, Gang Huang；

(VI) Manuscript writing: Jinchuan Tan, Yang Yang;

(VII) Final approval of manuscript: All authors.

†These authors contributed equally to this work.

Baseri A, Bagheri M A, Rouhi G, Aghighi M R and Bagheri N 2020 Fixation of distal tibia fracture through plating, nailing, and nailing with Poller screws: A comparative biomechanical-based experimental and numerical investigation Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 234 1129-38
Bedi A, Le T T and Karunakar M A 2006 Surgical Treatment of Nonarticular Distal Tibia Fractures J AM ACAD ORTHOP SUR 14 406–16
Bottlang M, Doornink J, Lujan T J, Fitzpatrick D C, Marsh J L, Augat P, von Rechenberg B, Lesser M and Madey S M 2010 Effects of Construct Stiffness on Healing of Fractures Stabilized with Locking Plates Journal of Bone and Joint Surgery 92 12–22
Bottlang M, Lesser M, Koerber J, Doornink J, von Rechenberg B, Augat P, Fitzpatrick D C, Madey S M and Marsh J L 2010 Far Cortical Locking Can Improve Healing of Fractures Stabilized with Locking Plates Journal of Bone and Joint Surgery 92 1652–60
Bottlang M, Schemitsch C E, Nauth A, Routt M, Egol K A, Cook G E and Schemitsch E H 2015 Biomechanical Concepts for Fracture Fixation J ORTHOP TRAUMA 29 S28-33
Deng Y, Ouyang H, Xie P, Wang Y, Yang Y, Tan W, Zhao D, Zhong S and Huang W 2021 Biomechanical assessment of screw safety between far cortical locking and locked plating constructs COMPUT METHOD BIOMEC 24 663–72
Giannoudis P V, Einhorn T A and Marsh D 2007 Fracture healing: The diamond concept INJURY 38 S3-6
Hannah A, Aboelmagd T, Yip G and Hull P 2014 A novel technique for accurate Poller (blocking) screw placement INJURY 45 1011-4
Hans-Werner Stedtfeld T M P L 2004 The Logic and Clinical Applications of Blocking Screws J BONE JOINT SURG AM 17–25
Hoegel F W, Hoffmann S, Weninger P, Bühren V and Augat P 2012 Biomechanical comparison of locked plate osteosynthesis, reamed and unreamed nailing in conventional interlocking technique, and unreamed angle stable nailing in distal tibia fractures J TRAUMA ACUTE CARE 73 933–8
Josten C, Marquass B, Schwarz C and Verheyden A 2010 Marknagelosteosynthese proximaler Tibiafrakturen Der Unfallchirurg 113 21–8
Kawabata Y, Matsuo K, Nezu Y, Kamiishi T, Inaba Y and Saito T 2017 The risk assessment of pathological fracture in the proximal femur using a CT-based finite element method J ORTHOP SCI 22 931–7
Krettek C, Stephan C, Schandelmaier P, Richter M, Pape H C and Miclau T 1999 The use of Poller screws as blocking screws in stabilising tibial fractures treated with small diameter intramedullary nails Journal of bone and joint surgery. British volume 81 963
Lindvall E, Sanders R, DiPasquale T, Herscovici D, Haidukewych G and Sagi C 2009 Intramedullary Nailing Versus Percutaneous Locked Plating of Extra-Articular Proximal Tibial Fractures: Comparison of 56 Cases J ORTHOP TRAUMA 23 485–92
Lujan T J, Henderson C E, Madey S M, Dan C Fitzpatrick and J Lawrence Marsh M B 2010 Locked Plating of Distal Femur Fractures Leads to Inconsistent and Asymmetric Callus Formation J Orthop Trauma. 3 156–62
Metcalf K B, Du J Y, Lapite I O, Wetzel R J, Sontich J K, Dachenhaus E R, Janes J L and Ochenjele G 2021 Comparison of Infrapatellar and Suprapatellar Approaches for Intramedullary Nail Fixation of Tibia Fractures J ORTHOP TRAUMA 35 e45-50
Perren S M 2002 Evolution of the internal fixation of long bone fractures. The scientific basis of biological internal fixation: choosing a new balance between stability and biology J Bone Joint Surg Br 8 1093–110
Raja Izaham R M A, Abdul Kadir M R, Abdul Rashid A H, Hossain M G and Kamarul T 2012 Finite element analysis of Puddu and Tomofix plate fixation for open wedge high tibial osteotomy INJURY 43 898–902
Sonoda N, Chosa E, Totoribe K and Tajima N 2003 Biomechanical analysis for stress fractures of the anterior middle third of the tibia in athletes: nonlinear analysis using a three-dimensional finite element method J ORTHOP SCI 8 505–13

Table1. Materrail properties used in FE analysis and interaction
Materrails	Young’s modulus(Mpa)	Poisions’s ratio
Cortical bone	8000	0.3
Cancellous bone	1500	0.2
Titanium alloy	110000	0.3

Table 2. Number and type of elements used in the FE models of this study.
Parts	Element type	Number of elements	Number of nodes	Approximate element size (mm)
Tibia (nailing)	C3D10	150693	238965	0.8-4.0
Tibia (poller)	C3D10	162563	257095	0.8-4.0
nail	C3D10	65195	108819	0.6-3.0
Screw	C3D10	5777	9296	0.8
Poller screw	C3D10	6783	10805	0.6

No competing interests reported.

Download PDF

Version 1

posted

You are reading this latest preprint version

In silico biomechanical analysis of Poller screw-assisted small-diameter intramedullary nail in the treatment of distal tibial fractures

Status:

Version 1

Abstract

Objective

Methods

Results

Conclusion

Figures

1. Introduction

2. Materials And Methods

2.1. FE modeling

2.2. Loading and boundary conditions

2.4. Data analysis

3. Results

3.1. Construct stiffness and shear displacement of the fracture site

3.2. Parallel IFM

3.3. Mechanical experiment validation

3.4. Safety assessment

4. Discussion

5. Conclusion

Abbreviations

Declarations

References

Tables

Additional Declarations

Status:

Version 1