Biomechanical analysis of the stability of anterograde reamed intramedullary nails in femoral spiral fractures

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Biomechanical analysis of the stability of anterograde reamed intramedullary nails in femoral spiral fractures A. Herrera , J. Rosell , E. Ibarz , J. Albareda , S. Gabarre , J. Mateo , L. Gracia PII: DOI: Reference:

S0020-1383(20)30111-X https://doi.org/10.1016/j.injury.2020.02.034 JINJ 8590

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Injury

Accepted date:

9 February 2020

Please cite this article as: A. Herrera , J. Rosell , E. Ibarz , J. Albareda , S. Gabarre , J. Mateo , L. Gracia , Biomechanical analysis of the stability of anterograde reamed intramedullary nails in femoral spiral fractures, Injury (2020), doi: https://doi.org/10.1016/j.injury.2020.02.034

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Highlights 

Spiral fractures are the most complicated from a biomechanical point of view, because they present high instability.



Intramedullary nailing has emerged as an alternative in the treatment of that type of fractures.



A numerical study of reamed locked intramedullary nails in spiral femoral fractures along zones 2 and 4 of Wiss is done.



Blocked reamed nails can be considered as an appropriate surgical technique in the treatment of spiral femoral fractures.

 Blocked reamed nails provide sufficient stability in order to obtain an adequate fracture healing.

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Biomechanical analysis of the stability of anterograde reamed intramedullary nails in femoral spiral fractures A. Herreraa,b, J. Rosellc, E. Ibarzc,d, J. Albaredaa,b,e, S. Gabarref, J. Mateoa,b,g, L. Graciac,d* a

b

c

Department of Surgery, University of Zaragoza. Zaragoza, Spain

Department of Mechanical Engineering, University of Zaragoza. Zaragoza, Spain d

e

Aragón Health Research Institute. Zaragoza, Spain

Aragón Institute for Engineering Research. Zaragoza, Spain

Department of Orthopaedic Surgery and Traumatology, Lozano Blesa University Hospital. Zaragoza, Spain f

g

Vlaams Instituut voor Biotechnologie, Leuven, Belgium

Department of Orthopaedic Surgery and Traumatology, Miguel Servet University Hospital. Zaragoza, Spain

*

Corresponding author.

E-mail address: [email protected]

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Abstract Femoral shaft fractures present high morbidity and important complications and consequences, being spiral fractures the most complicated from a biomechanical point of view, being unstable and without possibility of getting a good contact between nail and femoral endosteum. Femoral diaphyseal fractures are treated, usually, by means of intramedullary nailing. So, it is necessary to know the osteosynthesis stability and which locking screws combination is optimal. This work studies the use of reamed locked intramedullary nails in spiral femoral fractures located along zones 2 and 4 of Wiss, depending on the spire length, corresponding to 32-A spiral type in AO/OTA classification, which represent a percentage of 23% within the total of diaphyseal fractures. A three-dimensional finite element model of the femur was developed, modeling a spiral fracture with different spiral lengths and gaps. A femoral nail was used, considering two transversal screws both at the proximal and the distal parts. The study was focused on the immediately post-operative stage, verifying the appropriate stability of the osteosynthesis. Reamed intramedullary blocked nails provide appropriate stability of femoral spiral fractures, considering global mobility of femoral head with respect to femoral condyles, relative displacements between fragments at fracture site, stresses at nail and locking screws, and stresses at cortical bone. The obtained results show that the use of blocked reamed nails in spiral femoral fractures can be considered as an appropriate surgical technique, providing sufficient stability in order to obtain an adequate fracture healing.

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Key words Intramedullary nail, Anterograde reamed nail, Femoral spiral fracture, Osteosynthesis, Finite elements

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Introduction Femoral shaft fractures range from 9.9 to12.0 for every 100.000 inhabitants/year [1-3]. Most of fractures are mainly due to high energy traumas (in particular traffic accidents), and are associated with other traumatic injuries affecting to lower limb, chest and head, which can be underdiagnosed [4]. The peak incidence occurs in young people, between 15 and 25 years old, with a percentage of 60% men and 40% women [1-3]. Another possible etiology may be low energy trauma in older people. In this respect, a study in women over the age of 50 and men over the age of 65 (mean age 80.2±10.3, 78.3% of women) was performed [5], analyzing a total of 197 femoral fractures, of which 38% were atypical fractures, caused by certain medications such as bisphosphonates and glucocorticoids. Femoral fractures can be classified depending on their anatomical location at one of the six Wiss’ zones [6], and biomechanically they can be classified as transverse, obliquetransverse, oblique and spiral-type [3]. Depending on the comminution grade, the fractures are classified according to the criterion of Winquist and Hansen, ranging from grade 0 to IV [7]. Considering simultaneously location and fracture type, the classification of AO Foundation [8], later revised by OTA (Orthopaedic Trauma Association) [9], is used. Since the introduction of intramedullary nailing (IM) by G. Küntscher [10], this technique has become the gold standard for treatment of long bone fractures [11]. The subsequent evolution of nail design and materials, and especially the introduction of locked nails in the 1970s, have allowed locked intramedullary nail become the standard of care for most femoral fractures. Its indication has been extended proximally and distally to almost all femoral fractures from the lesser trochanter to the supracondilar areas, zones 2 (subtrochanteric) to 5 (supracondylar) of Wiss [6].

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At present locked intramedullary nailing could be said to be the gold standard for the treatment of femoral fractures. This is a close technique preserving the hematoma at the fracture site, which is a key factor in fracture healing, so intramedullary nailing has a high rate of consolidation (99%) and a low percentage of infection (1%) [6, 7, 12-14]; on the other hand, the implant is easy to remove after fracture healing due to its extrarticular location [12]. Currently controversy about reamed or non-reamed nails is clearly pointed towards reamed and locked nails [15], which allows the insertion of larger diameter nails, a wider contact surface between nail and femoral endosteum, and the use of locking screws of larger size, improving the osteosynthesis stability which is an essential requirement for fracture consolidation [15]. Among the different types of femoral fractures, spiral fractures are the most complicated from a biomechanical point of view, because they are unstable and it is not possible getting a good contact between nail and femoral endosteum, being therefore important to know the osteosynthesis stability and which locking screws combination is optimal. The great diversity of diaphyseal fracture types and size, according to their anatomical location and degree of comminution, makes it difficult the appropriate choice of nailing and locking to ensure stability and to achieve fracture consolidation. In vivo animal experimentation has been used to assess the biomechanical behavior of intramedullary femoral nails. So, in vivo studies in animal models have been published [16], but the results have a difficult extrapolation to humans due to the important anatomical differences and load conditions. With respect to in vitro studies, a unique study was found in the last ten years. In that study [17] the stability of intramedullary flexible nail osteosynthesis with end caps in femoral spiral fractures is analyzed by means of experimental testing using synthetic adolescent-size femoral bone models.

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They conclude that the use of end caps did not improve the stability of the intramedullary flexible nail osteosynthesis. As in vivo animal experimentation and in vitro studies on cadaveric bone or plastic bone models can hardly be applied to humans, due to the differences between in vivo humans and in vivo animals or in vitro behavior. Those difficulties have led to the development of simulation models using the Finite Element Method (FE). Analysis of osteosynthesis by means of FE models enables the assessment of all critical parameters (global stability, local movements at the fracture site and stresses in bone, nail and locking screws). Different FE studies have been published concerning biomechanical behavior of intramedullary nailing in transverse femoral fractures [18-21], even by the own authors [22, 23]. However, studies on more complex fracture types can hardly be found. In this respect, only two studies [24, 25], comparing the biomechanical behavior of composite versus metallic intramedullary nailing system in femoral oblique fractures, has been found. No studies of intramedullary nailing in femoral spiral fractures by means of FE simulation were found in the main medical databases. In this context, the objective of the present work is the study of reamed locked intramedullary nails in spiral femoral fractures located along zones 2 and 4 of Wiss, depending on the spire length, corresponding to 32-A spiral type in AO/OTA classification, simulating also a greater or lesser fracture fragmentation depending on the gap size. These kinds of fractures represent a percentage of 23% within the total of diaphyseal fractures [3].

Material and Methods A three dimensional (3D) finite element model of the femur from 55-year-old male donor was developed (the project “Estudio biomecánico y clínico del enclavamiento 7

centromedular en el tratamiento de las fracturas diafisarias de fémur”, in which is included the present work, was approved by the Ethics Committee of the Institute of Health Sciences of Aragón; protocol number C.P. -C.I. PI 15/0214). The outer geometry of the femur was obtained by means of 3D scanner Roland3D Roland® PICZA (Irvine, California), whereas a set of computed tomography (CT) of the donor’s femur were treated using Mimics® Software (Materialise, Leuven). The CT scans were obtained by means of a TOSHIBA Aquilion 64 scanner (Toshiba Medical Systems, Zoetermeer, Netherlands) (512x512 acquisition matrix, field of view (FOV)=240 mm, slice thickness=0.5 mm, in plane resolution). Once the inner interface between cortical and trabecular bone was delimited by means of an in-house algorithm material properties were assigned to the FE model in I-Deas software [26], using the same methodology of previous studies [27]. The used nail was IM Stryker femoral nail S2/T2 (Stryker, Mahwah, NJ, USA), with a length of 360 mm wall thickness of 2 mm and outer diameter of 13 mm. This reamed anterograde nail uses locking screws of 5 mm of outer diameter, which were geometrically modeled as cylinders of the same diameter. Nail surgery was reproduced in I-Deas in a virtual way, inserting the nail into the femur with the corresponding screws. Subsequently the assembly of the computer aided design (CAD) model was performed under surgeon supervision. Bone, nail and screws were meshed with linear tetrahedra. They were assumed for the bone linear elastic isotropic properties (ECortical=20000 MPa, =0.3; ETrabecular=959 MPa, =0.3 [28]) as reference, with variable values related with the processed CT images. The metallic nail was considered of 316 LVM steel (E=192.36 GPa, =0.3) or Ti-6L-4V (E=113.76 GPa,  =0.34) and metallic screws of 316 LVM steel, both materials assumed to be linear elastic isotropic.

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A sensitivity analysis was performed to determine the minimal size mesh required for an accurate simulation. For this purpose, a mesh refinement was executed in order to achieve a convergence towards a minimum of the potential energy, both for the whole model and for each of its components, with a tolerance of 1% between consecutive meshes. The final models had an average mesh size about 1.5 mm, with about of 220.000 nodes and 1.000.000 elements on average. All the considered fractures were modeled as spiral by means of an irregular surface developed to represent a closer geometry to the actual fracture. Considering that irregular fracture pattern, two different fracture gaps have been studied: 1.0 mm (considered as a non-comminuted fracture) and 3 mm (as the most referenced value found in literature, representing a mid-value between comminuted and non-comminuted fractures). Three lengths of fractures were considered: 120, 150 and 180 mm, respectively (Table 1). The study was focused on the immediately post-operative stage. Thus, the interaction at the fracture site does not take into account any biological healing process. Contact interaction was assumed between the outer surface of the nail and the inner cortex of the intramedullary channel of the femur. Interaction between screws and cortical bone was considered to be bonded, whereas contact between screws a femoral nail was simulated. The selected friction values of bone/nail and nail/screws were 0.1 and 0.15, respectively, in accordance with literature [29-31]. This study considered fully constrained conditions at the condyles and a load case associated with an accidental support of the leg at early post-operative (PO) stage (Fig. 1). This load was quantified to be about 25% the maximum gait load. According to Orthoload’s database [32] the hip reaction force and abductor force (as the prime muscle group), referred to the 45% of gait, correspond to the maximum and most representative load. Muscle attachments areas corresponding to abductor group muscle 9

were determined mimicking anatomy atlas, in the same way that in previous works [22, 23]. The studied femoral nail corresponds to the Stryker S2/T2TM design (Stryker, Mahwah, NJ, USA), considering a length of 380 mm, with a wall thickness of 2 mm and an outer diameter of 13 mm. This nail uses locking screws of 5 mm of outer diameter, which were modeled as cylinders of the same diameter. Two transversal screws (anterior/posterior) were considered at the proximal part and two transversal screws (lateral/medial) at the distal part. The different osteosyntheses included in Table 1 were simulated by means of Abaqus software [33].

Results The FE simulations allowed obtaining the mobility and stress results for the different cases analyzed. The different resulting trends are detailed hereafter.

Trends of the global movement at the femoral head Figure 2 exhibits the global movement of the femoral head for the different fracture gaps, fracture lengths and nail material that were simulated. A higher mobility is produced the higher the gap and fracture length are, and significant difference appears between steel and titanium nails, being the mobility about 38% higher for titanium nails in every considered case.

Stability trends at the fracture site Relative movements at fracture site are processed considering working groups of corresponding nodes located in opposite positions at the fracture focus (Figure 3).

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Figures 4a and 4b show the graphs of relative displacements at fracture site for the different osteosynthesis considered in the study (stainless steel and titanium nails, respectively). As can be seen in Figs. 4a and 4b, relative displacements increase inasmuch as the spiral length grows, practically reaching the same values independently of gap size for spiral lengths of 150 and 180 mm; however, relative movements are higher for a small gap size in the case of spiral length of 120 mm. The same trend appears in both stainless steel and titanium nails. A larger movement is observed for titanium nail with respect to stainless steel nail, being the relative displacement about 59% higher for titanium nail for spiral length of 120 mm, 51% higher for titanium nail for spiral length of 150 mm and 40% higher for titanium nail for spiral length of 180 mm. This trend is due to the higher values of relative displacements obtained as the spiral length increases. Anyway, the obtained values are in a range that can be considered as appropriate for fracture stabilization.

Stress trends in the nail and locking screws Figure 5a shows the maximum values of von Mises stress in the nail for the different fracture gaps, fracture lengths and nail material that were simulated. The maximum von Mises stress value in the nail increases for higher spiral lengths and gap sizes, independently of nail material. The stresses are higher for the stainless steel nail in every of the considered osteosyntheses, with values about 20% for spiral length of 120 mm, 27% for spiral length of 150 mm and 29% for spiral length of 180 mm. Any case, the obtained values are well below those corresponding to the yield strength of both materials, which is logical, considering that only a fraction of the physiological load was considered.

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Figure 5b shows the maximum values of von Mises stress in locking screws for the different fracture gaps, fracture lengths and nail material that were simulated. In this case, an identical trend as in the nails is observed: the maximum von Mises stress value in the locking screws increases for higher spiral lengths and gap sizes, independently of nail material, reaching higher values for the stainless steel nail in every of the considered osteosynthesis, with values about 20% higher. The obtained values are well below those corresponding to the yield strength of locking screws material.

Trends of stresses in cortical bone Figure 6 shows the maximum values of von Mises stress in the cortical bone for the different fracture gaps, fracture lengths and nail material that were simulated. In cortical bone no clear trend appears concerning stresses, except for the case of nail material, producing higher stress values in cortical bone titanium nails. Values of stresses are very similar for spiral lengths of 150 and 180 mm, increasing in the case of spiral length of 120 mm. This could be because for a shorter spiral length the contact area between nail and femoral endosteum is larger, allowing a greater overload on bone. The stresses are about 36% higher for titanium nail in every case. The obtained values are sufficiently low to avoid additional fractures.

Discussion From our knowledge none of the few published works using FE simulation has studied the biomechanical behavior of different types of spiral femur fractures, using rigid blocked nails. We have used blocked reamed nails in our study because it is widely demonstrated in the bibliography the superiority of these over nonreamed nails [4, 6, 7, 11-15]. Although there are controversies about the effects of reaming on the 12

intramedullary circulation [15], other authors have shown that reaming has positive effects on fracture site, such increasing extraosseus circulation [34]. There is no evidence that the increase in intramedullary pressure and the possibility of fatty embolism increase the number of pulmonary complications, including the Acute Respiratory Distress Syndrome (ARDS), provided that the fracture stabilization be done within the first twenty-four hours after the injury [4, 15, 35-39]. The obtained results show that the biomechanical behavior of reamed intramedullary blocked nails is suited for stability of femoral spiral fractures. So, the global mobility of femoral head with respect to femoral condyles is kept within safe values, being lower for stainless steel nails compared to titanium nails, according to their respective stiffness. In the same way, the relative displacements between fragments at fracture site, for the different osteosynthesis considered in the study, falls within the range that can be considered as appropriate for fracture stabilization, with values that provides the adequate mechanical stimulus for fracture healing. On the other hand, stresses at nail and locking screws are well below those corresponding to the yield strength of materials, taking into account that only a fraction of the physiological load was considered. Finally, stresses at cortical bone are sufficiently low to avoid additional fractures. In 1958, prior to the introduction of blocked nails, the Swiss AO proposed the concept of Open Reduction Internal Fixation (ORIF) whit plating for the treatment of fractures, which was the very opposite to the closed reduction and intramedullary nailing, preserving the fracture haematoma, the periosteum and the perifractural soft tissues. Since then design of plates and the basic concepts have evolved [40]. Although present ORIF has new plate models, Locked Plate techniques [41], submuscular plating [42] or bridge plating [43], the versatility of blocked nails prevails due to its shorter

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consolidation time, lower fluoroscopic exposure and less demanding technique, as well as the possibility of earlier loading [41-44]. Accurate fracture reduction is essential in long-range spiral fractures, to avoid shortening and rotational malalignment before placing the distal locking screws [6], which prevent loss of fracture reduction during the consolidation process. In our study we have analyzed different gap in the fracture focus, to simulate the comminution of the fragments. The locked intramedullary nail has achieved a stable fixation in all cases, as mentioned above. We are not agreeing with [45] who indicates that a separation of 1 cm or greater between the fragments impairs the consolidation process because this area of the bone is not properly reamed. Clinical experience with close intramedullary nailing, preserving the hematoma and soft tissues at the fracture site, confirm the good outcomes in this type of fracture as long as fixation provides stability though, in any case may take longer to heal. It should be emphasized that in these cases the locking screws must be static and, progressive weight bearing must be allowed according to the radiographic evolution. Our clinical experience shows that even in the case of spiral comminute complex fractures, including fragmentation, the use of reamed intramedullary blocked nails can be fully effective (Fig. 7). As main limitation of the present study, it should be noted that the applied loads correspond to a fraction of physiological load, considering an accidental foot support at postoperative stage, in which loading is not permitted, but without taking account of possible rotational loads which could compromise the stability.

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Conclusions The use of blocked reamed nails in spiral femoral fractures can be considered as an appropriate surgical technique, providing sufficient stability in order to obtain an adequate fracture healing. Moreover, as the fracture length is increasing stainless steel nails are recommended because of the greater stiffness, providing better stability. Any case, locking screws must be static, preventing any movement at the locking zone.

List of abbreviations CAD: Computer Aided Design CT: Computed Tomography FE: Finite Elements IM: Intramedullary nailing ORIF: Open Reduction Internal Fixation OTA: Orthopaedic Trauma Association PO: Post-operative 3D: Three-Dimensional

Conflict of interest statement The authors have no professional or financial conflicts of interest to discloser.

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Acknowledgements This research has been partially financed by The Fundación Mutua Madrileña (Research Project: AP162632016) and by the Government of Spain, Ministry of Economy and Competitiveness (Research Project: DPI2016-77745-R).

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References [1]

Arneson TJ, Malton III LJ, Lewallen DG, O’Fallon WN. Epidemilogy of diaphyseal and distal femoral fractures in Rochester Minnesota, 1965-1984. Clin Orthop Relat Res 1988; 234: 188-94.

[2]

Bengner U, Ekbon T, Johnell O, Nilsson DE. Incidence of femur and tibial shaft fractures, epidemiology 1950-1983 in Malmo Sweden. Acta Orthop Scand 1990; 61: 251-4.

[3]

Salminen ST, Pihlajamaki HK, Avikainen VJ, Bostman ON. Population based epidemiologic and morphologic study of femoral shaft fractures. Clin Orthop Relat Res 2000; 372: 241-9. doi: 10.1097/00003086-200003000-00026.

[4]

Regel G, Lobenhoffer P, Grotz M, Pape HC, Lehmann U, Tscherne H. Treatment results of patients with multiple trauma: an analysis of 3406 cases treated between 1972 and 1991 at a german level I trauma center. J Trauma 1995; 38(1): 70-8. doi: 10.1097/00005373-199501000-00020.

[5]

Feldstein AC, Black D, Perrin N, Rosales AG, Friess D, Boardman D, Dell R, Santora A, Chandler JM, Rix MM, Orwoll E. Incidence and demography of femur fractures with and without atypical features. J Bone Miner Res 2012; 27(5): 97786. doi: 10.1002/jbmr.1550.

[6]

Wiss DA, Fleming CH, Matta JM, Clark D. Comminuted and rotationally unstable fractures of the femur treated with an interlocking nail. Clin Orthop Relat Res 1986; (212): 35-47. doi: 10.1097/00003086-198611000-00006.

[7]

Winquist RA, Hansen Jr ST. Comminuted fractures of the femoral shaft treated by intramedullary nailing. Orthop Clin North Am 1980; 11 (3): 633-648.

[8]

Muller ME, Nazarian S, Koch P, Schatzker J. The Comprehensive Classification of Fractures of Long Bones. Berlin. Springer-Verlag 1990.

[9]

Orthopaedic Trauma Association Committee for Coding and Classification: Fracture and dislocation compendium. J Orthop Trauma 1996; 10 Suppl 1: v-ix, 1154.

[10] Bick EM. The intramedullary nailing of fractures by G. Küntscher: Translation of article in Archiv für Klinische Chirurgie, 200:443, 1940. Clin Orthop Relat Res 1968; 60: 5-12. [11] Gradl G. Intramedullary nailing of long bone fractures: sixty years of evolution but

what

the

future holds? Injury

10.1016/j.injury.2013.10.046. 17

2014;

45 Suppl 1:

S1-2.

doi:

[12] Winquist RA, Hansen ST Jr, Clawson DK. Closed intramedullary nailing of

femoral fractures: A report of five hundred and twenty cases 1984. J Bone Joint Surg Am 2001; 83-A(12): 1912. [13] Wiss DA, Brien WW, Stetson WB. Interlocked nailing for treatment of segmental

fractures of the femur. J Bone Joint Surg Am 1990; 72(5): 724-8. [14] Winquist RA. Locked Femoral Nailing JAAOS 1993; 1(2): 95-105

[15] Wolinsky P, Tejwani N, Richmond JH, Koval KJ, Egol K, Stephen DJ. Controversies in intramedullary nailing of femoral shaft fractures. Instr Course Lect 2002; 51: 291-303. doi: 10.2106/00004623-200109000-00018. [16] Sha M, Guo Z, Fu J, Li J, Yuan CF, Shi L, Li SJ. The effects of nail rigidity on

fracture healing in rats with osteoporosis. Acta Orthop 2009; 80(1): 135-8. doi: 10.1080/17453670902807490 [17] Kaiser MM, Zachert G, Wendlandt R, Rapp M, Eggert R, Stratmann C, Wessel

LM, Schulz AP, Kienast BJ. Biomechanical analysis of a synthetic femoral spiral fracture model: Do end caps improve retrograde flexible intramedullary nail fixation? J Orthop Surg Res 2011; 18: 6-46. doi: 10.1186/1749-799X-6-46 [18] Bayoglu R, FethiOkyar A. Implementation of boundary conditions in modeling

the femur is critical for the evaluation of distal intramedullary nailing. Med Eng Phys 2015; 37: 1053-1060. doi: 10.1016/j.medengphy.2015.08.007 [19] Chantarapanich

N,

Sitthiseripratip

K,

Mahaisavariya

B,

Siribodhi

P.

Biomechanical performance of retrograde nail for supracondylar fractures stabilization. Med Biol Eng Comput 2016; 54: 939–952. doi: 10.1007/s11517016-1466-0 [20] Chang-Cheng L, Wen-Zhao X, Ya-Xing Z, Zheng-Hua P, Wen-Ling F. Three-

Dimensional Finite Element Analysis and Comparison of a New Intramedullary Fixation with Interlocking Intramedullary Nail. Cell Biochem Biophys 2015; 71: 717-724. doi: 10.1007/s12013-014-0254-4 [21] Shih KS, Hsu CC, Hsu TP, Hou SM, Liaw CK. Biomechanical analyses of static

and dynamic fixation techniques of retrograde interlocking femoral nailing using nonlinear finite element methods. Comput Methods Programs Biomed 2014; 113: 456-464. doi: 10.1016/j.cmpb.2013.11.002 [22] Gabarre S, Albareda J, Gracia L, Puertolas S, Ibarz E, Herrera A. Influence of gap

size, screw configuration, and nail materials in the stability of anterograde reamed

18

intramedullary nail in femoral transverse fractures. Injury 2017; 48 Suppl 6: S40S46. doi: 10.1016/S0020-1383(17)30793-3 [23] Gabarre S, Albareda J, Gracia L, Puertolas S, Ibarz E, Herrera A. Influence of

screw combination and nail materials in the stability of anterograde reamed intramedullary nail in distal femoral fractures. Injury 2017; 48 Suppl 6: S47-S53. doi:

10.1016/S0020-1383(17)30794-5

[24] Samiezadeh S, Tavakkoli Avval P, Fawaz Z, Bougherara H. Biomechanical

assessment of composite versus metallic intramedullary nailing system in femoral shaft fractures: A finite element study. Clin Biomech 2014; 29(7): 803-810. doi: 10.1016/j.clinbiomech.2014.05.010 [25] Samiezadeh S, Tavakkoli Avval P, Fawaz Z, Bougherara H.

An Effective

Approach for Optimization of a Composite Intramedullary Nail for Treating Femoral Shaft Fractures. J Biomech Eng, 2015; 137: 121001-1-121001-9. doi: 10.1115/1.4031766 [26] Siemens,

I-deas®

11

NX

Series

PLM

software

2018

[http://www.plm.automation.siemens.com]. [27] Gabarre S, Herrera A, Mateo J, Ibarz E, Lobo-Escolar A, Gracia L. Study of the

polycarbonate-urethane/metal contact in different positions during gait cycle. Biomed Res Int 2014; 2014: 548968. doi: 10.1155/2014/548968 [28] Herrera A, Panisello JJ, Ibarz E, Cegonino J, Puertolas JA, Gracia L. Long-term

study of bone remodelling after femoral stem: A comparison between Dexa and finite

element

simulation.

J

Biomech

2007;

40:

3615-3625.

doi:

10.1016/j.jbiomech.2007.06.008 [29] Chen SH, Chiang MC, Hung CH, Lin SC, Chang HW. Finite element comparison

of retrograde intramedullary nailing and locking plate fixation with/without an intramedullary allograft for distal femur fracture following total knee arthroplasty. Knee 2014; 21: 224-31. doi: 10.1016/j.knee.2013.03.006 [30] Grant JA, Bishop NE, Gotzen N, Sprecher C, Honl M, Morlock MM. Artificial

composite bone as a model of human trabecular bone: the implant-bone interface. J Biomech 2007; 40: 1158-64. doi: 10.1016/j.jbiomech.2006.04.007 [31] Eberle S, Gerber C, von Oldenburg G, Hungerer S, Augat P. Type of Hip Fracture

Determines Load Share in Intramedullary Osteosynthesis. Clin Orthop Relat Res 2009; 467: 1972-1980. doi: 10.1007/s11999-009-0800-3

19

[32] Orthoload

data

base.

Loading

of

Orthopaedic

Implants

2018.

[https://orthoload.com]. [33] Dassault Systèmes 2018. [http://www.3ds.com].

[34] Bong MR, Kummer FJ, Koval KJ, Egol KA. Intramedullary nailing of the lower extremity: biomechanics and biology. J Am Acad Orthop Surg 2007; 15(2): 97106. doi: 10.5435/00124635-200702000-00004. [35] Nork SE, Agel J, Russell GV, Mills WJ, Holt S, Routt ML Jr. Mortality after reamed intramedullary nailing of bilateral femur fractures. Clin Orthop Relat Res 2003; (415): 272-8. doi: 10.1097/01.blo.0000093919.26658.23 [36] Byrne JP, Nathens AB, Gomez D, Pincus D, Jenkinson RJ. Timing of femoral

shaft fracture fixation following major trauma: A retrospective cohort study of United States trauma centers. PLoS Med 2017; 14(7): e1002336. doi: 10.1371/journal.pmed.1002336 [37] Brumback RJ, Virkus WW. Intramedullary nailing of the femur: reamed versus

nonreamed. J Am Acad Orthop Surg 2000; 8(2): 83-90. doi: 10.5435/00124635200003000-00002. [38] Anwar IA, Battistella FD, Neiman R, Olson SA, Chapman MW, Moehring HD. Femur fractures and lung complications: a prospective randomized study of reaming.

Clin

Orthop

Relat

Res

2004;

(422):

71-6.

doi:

10.1097/01.blo.0000129150.92270.f9. [39] Canadian Orthopaedic Trauma Society. Reamed versus unreamed intramedullary

nailing of the femur: comparison of the rate of ARDS in multiple injured patients. J Orthop Trauma 2006; 20(6): 384-7. [40] Rozbruch SR, Müller U, Gautier E, Ganz R. The evolution of femoral shaft

plating technique. Clin Orthop Relat Res 1998; (354): 195-208. doi: 10.1097/00003086-199809000-00024. [41] Cheng T, Xia RG, Dong SK, Yan XY, Luo CF. Interlocking Intramedullary

Nailing Versus Locked Dual-Plating Fixation for Femoral Shaft Fractures in Patients with Multiple Injuries: A Retrospective Comparative Study. J Invest Surg 2017; 18: 1-10. doi: 10.1080/08941939.2017.1400131 [42] Park KC, Oh CW, Byun YS, Oh JK, Lee HJ, Park KH, Kyung HS, Park BC.

Intramedullary nailing versus submuscular plating in adolescent femoral fracture. Injury 2012; 43(6): 870-5. doi: 10.1016/j.injury.2011.10.032

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[43] Wenda K, Runkel M, Degreif J, Rudig L. Minimally invasive plate fixation in

femoral shaft fractures. Injury 1997; 28 Suppl 1: A13-9. doi: 10.1016/S00201383(97)00074-0. [44] Zlowodzki M, Vogt D, Cole PA, Kregor PJ. Plating of femoral shaft fractures:

open reduction and internal fixation versus submuscular fixation. J Trauma 2007; 63(5): 1061-5. doi: 10.1097/TA.0b013e318154c0b4 [45] Lin SJ, Chen CL, Peng KT, Hsu WH. Effect of fragmentary displacement and

morphology in the treatment of comminuted femoral shaft fractures with an intramedullary nail. Injury 2014; 45(4): 752-6. doi: 10.1016/j.injury.2013.10.015

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Fig. 1. Boundary conditions and loads

Fig. 2. Values of global movements of the femoral head

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Fig. 3. Groups of corresponding nodes located in opposite positions at fracture site

Fig. 4. Graphs of relative displacements at fracture site for the different osteosynthesis considered in the study: a) stainless steel nail; b) titanium nail

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Fig. 5. Maximum values of von Mises stress for the different fracture gaps, fracture lengths and nail material: a) stresses in the nail; b) stresses in the locking screws

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Fig. 6. Maximum values of von Mises stress in the cortical bone for the different fracture gaps, fracture lengths and nail material

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Fig. 7. Spiral comminute complex fracture consolidation: a) fracture before nailing; b) & c) frontal and sagittal images, respectively, with clear signs of consolidation

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Table 1. Different osteosyntheses considered in the study

Fracture length (mm)

Fracture gap (mm)

Fracture model

1.0 120

3.0 1.0

150 3.0 1.0 180 3.0

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Nail and screws

Fracture X-ray