The purpose of this study was to compare the mechanical properties of bone-plate constructs with locking compression plates (LCP) used either with standard screws or with locking screws on an experimental model of comminuted fracture

A. Autefage

Aguila AZ

D. Mathon

Filipowicz D

M. Verset

P. Swider

S. Palierne

English

The purpose of this study was to compare the mechanical properties of bone-plate constructs with LCP plates used either with standard screws or with locking screws on an experimental model of comminuted fracture

Verset, Michaël

Palierne, Sophie

Mathon, Didier

Swider, Pascal

Autefage, André

Open Archive Toulouse Archive Ouverte

Open Archive TOULOUSE Archive Ouverte (OATAO)OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible.This is an author-deposited version published in : http://oatao.univ-toulouse.fr/Eprints ID : 6275To cite this version : Verset, Michaël and Palierne, Sophie and Mathon, Didier andSwider, Pascal and Autefage, André Comparison of the effect oflocking vs standard screws on the mechanical properties of bone-plate constructs in a comminuted diaphyseal fracture model.(2012) In: 21st Annual Scientific Meeting of the European Collegeof Veterinary Surgeons, 5-7 Juil 2012, Barcelona, Spain.Any correspondance concerning this service should be sent to the repositoryadministrator: staff-oatao@inp-toulouse.fr.Title of abstract: Comparison of the effect of locking vs standard screws on the mechanical properties of bone-plate constructs in a comminuted diaphyseal fracture model.  Introduction: Healing of comminuted diaphyseal fractures is a major consideration in veterinary orthopaedics as they are frequently encountered, demonstrate a high rate of complications and their treatment is often challenging. One of the latest available implant in this indication is the Locking Compression Plate (LCP) in which combined holes accept either standard or locking screws. Although there are a few clinical and biomechanical studies comparing LCP plates featuring locking screws with non-locking plates, the real advantage of locking screws remains undefined and unquantified. The purpose of this study was to compare the mechanical properties of bone-plate constructs with LCP plates used either with standard screws or with locking screws on an experimental model of comminuted fracture.  Materials and methods: Twelve pairs of ovine tibia were harvested and packed with gauze soaked in isotonic saline solution before freezing (-24°C). After thawing at room temperature, they were kept moistened throughout the experiment. Inclusion criteria were skeletally mature animals belonging to one single breed, similar size of tibia and absence of bone diseases evaluated on radiographs. They were randomly divided into 2 equal groups. The model of comminuted fracture used was a mid-diaphyseal 5-mm gap created on the left tibia from each pair with an oscillating saw. Fracture was treated with a 8-hole, 4.5-mm, broad stainless LCP plate with 3 bicortical screws in each of the 2 fragments. All plates were similarly contoured to fit the medial side of bone. In group 1 (G1), 4.5 mm self-tapping cortical screws (standard screws) were placed in slightly inner eccentric position (to avoid collapse of the osteotomy site during weight-bearing). In group 2 (G2), 5.0 mm self-tapping locking screws were used. All screws were tightened using a torque-limiting screwdriver at 4 Nm.  Biomechanical evaluations were performed by non-destructive tests at quasi-static displacement rate (1 mm/min) on electromechanical systems. Four-point bending, torsion and axial compression loading conditions were applied one after the other on plated bones and on intact contralateral bones, to serve as a control. Maximum load used for non-destructive tests was about 50% of yield load, as previously assessed by destructive tests on pre-test plated bones. Bending was performed in a latero-medial direction with upper anvils surrounding bone gap (span distance of 30 mm). After embedding of proximal and distal ends in polyurethane casting resin, bones sustained clockwise torsional load, then axial compression load. For bending and compression on plated bones, 2 monocortical 1.5 mm pins were seated through the lateral cortex (2.5 mm outside the edges of bone osteotomy). A laser scan micrometer allowed continuous measurement of width between pins during tests. Crosshead displacement, load, angle of rotation, torque and width between pins were recorded at 10 Hz.  Extrinsic stiffness of bone-plate constructs (K) was calculated (i.e. the slope of the load-crosshead displacement curve). Difference between extrinsic stiffness of contralateral tibia and K was divided by extrinsic stiffness of contralateral tibia to obtain stiffness loss (Kr), expressed as a percentage. Slope of the load-pins displacement curve (S) was also calculated. K and Kr provide information on global mechanical properties of plated or intact bone, whereas S is a reflection of interfragmentary motion during load thus providing information on local mechanical properties close to the osteotomy gap. Results were statistically compared between the 2 groups by a 2-way ANOVA and Tukey's Post Hoc tests, for each loading condition. Significance was set at P<.05.    Results: In 4-point bending tests, there were no significant differences between group 2 and group 1 for K (G2: 321.9 ± 65.2 kN/m, G1: 286.0 ± 36.6 kN/m; P=.85), for Kr (G2: 55.4 ± 10.4%, G1: 64.5 ± 3.9%; P=.07) and for S (G2: 292.0 ± 84.3 N/mm, G1: 271.4 ± 36.2 N/mm; P=.59) (figure 1). In torsion tests, there were no significant differences between group 2 and group 1 for K (G2: 133.3 ± 18.7 Nm/rad, G1: 117.2 ± 18.0 Nm/rad; P=.59) and for Kr (G2: 44.0 ± 10.3%, G1: 55.0 ± 10.6%; P=.10) (figure 2). In axial compression tests, K was significantly lower for group 2 (611.1 ± 104.0 kN/m) than for group 1 (1019.2 ± 249.5 kN/m) (P=.003) (figure 3). Kr was significantly higher for group 2 (66.5 ± 10.3%) than for group 1 (47.7 ± 10.8%) (P=.01). There was no significant difference between group 2 and group 1 for S (G2: 254.6 ± 72.6 N/mm, G1: 438.2 ± 228.3 N/mm; P=.09).  Discussion: Bending stiffness and torsion stiffness were not significantly different using locking screws or standard screws. That is consistent with most other in vitro and ex vivo studies comparing LCP with LC-DCP plates, performed on synthetic bones. Compression stiffness with locking screws was about half compared with standard screws, whereas other studies showed no significant difference or significantly higher stiffness for locking screws. It might be related to 2 phenomena: i) the friction forces induced by the screws which compress the plate onto bone in standard osteosynthesis and ii) the limitation of bone displacement by the eccentric position of standard screws that are blocked on the inner part of the plate hole, under axial compression. Anyway, the significant difference of global mechanical properties seems to have no significant effect on the local mechanical properties. The main limitation of this ex vivo study is the only mechanical evaluation, without assessment of bone healing. It has been previously suggested that use of locking screws leads to preservation of periosteal perfusion, allowing better bone healing. The next step of this study is the assessment of mechanical, radiological and histological properties of bone-plate constructs and of bone callus after osteosynthesis and bone healing obtained with use of LCP plates either with standard screws or with locking screws on the same model of comminuted fracture. It should help to make a rational choice of the type of implant to treat comminuted fractures.  Conclusion: Locking screws had no statistically significant effect on the mechanical properties of LCP-plated bones in 4-point bending and torsion, compared to standard screws. In axial compression, locking screws induced a significant decrease in global mechanical properties without significant decrease in local mechanical properties close to the osteotomy gap.  References: Aguila AZ, et al: In Vitro Biomechanical Comparison of Limited Contact Dynamic Compression Plate and Locking Compression Plate. Vet Comp Orthop Traumatol 2005;18(4):220-226.  Filipowicz D, et al: A Biomechanical Comparison of 3.5 Locking Compression Plate Fixation to 3.5 Limited Contact Dynamic Compression Plate Fixation in a Canine Cadaveric Distal Humeral Metaphyseal Gap Model. Vet Comp Orthop Traumatol 2009;22(4):270-7.  Snow M, et al: A Mechanical Comparison of the Locking Compression Plate (LCP) and the Low Contact-Dynamic Compression Plate (DCP) in an Osteoporotic Bone Model. J Orthop Trauma 2008;22(2):121-5.      Figure 1 Box plots comparing mechanical properties in 4-point bending for the different groups:           a) extrinsic stiffness  b) stiffness loss c) load-pins displacement curve slope Asterisks indicate significant differences between groups (P<.05). Whiskers lower and upper limits = 2.5th and 97.5th percentiles.    Figure 2 Box plots comparing mechanical properties in torsion for the different groups:         a) extrinsic stiffness       b) stiffness loss Asterisks indicate significant differences between groups (P<.05). Whiskers lower and upper limits = 2.5th and 97.5th percentiles.    Figure 3 Box plots comparing mechanical properties in axial compression for the different groups:          a) extrinsic stiffness         b) stiffness loss  c) load-pins displacement curve slope Asterisks indicate significant differences between groups (P<.05). Whiskers lower and upper limits = 2.5th and 97.5th percentiles.  

A Biomechanical Comparison of 3.5 Locking Compression Plate Fixation to 3.5 Limited Contact Dynamic Compression Plate Fixation in a Canine Cadaveric Distal Humeral Metaphyseal Gap Model. Vet Comp Orthop Traumatol

A Mechanical Comparison of the Locking Compression Plate (LCP) and the Low Contact-Dynamic Compression Plate (DCP) in an Osteoporotic Bone Model.

et al:

Comparison of the effect of locking vs standard screws on the mechanical properties of bone-plate constructs in a comminuted diaphyseal fracture model

International audienceThe purpose of this study was to compare the mechanical properties of bone-plate constructs with locking compression plates (LCP) used either with standard screws or with locking screws on an experimental model of comminuted fracture

Verset, Michael

Autefage, Andre

HAL Université de Toulouse, et Toulouse INP

HAL ENVT (Ecole Nationale Vétérinaire de Toulouse)

HAL: Hyper Article en Ligne

Open Archive TOULOUSE Archive Ouverte (OATAO)OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible.This is an author-deposited version published in : http://oatao.univ-toulouse.fr/Eprints ID : 6273To cite this version : Verset, Michaël and Palierne, Sophie and Mathon, Didier andSwider, Pascal and Autefage, André Comparison of the effect oflocking vs standard screws on the mechanical properties of bone-plate constructs in a comminuted diaphyseal fracture model.(2012) In: 37ème Congrès de la Société de Biomécanique, 16-19Oct 2012, Toulouse. Any correspondance concerning this service should be sent to the repositoryadministrator: staff-oatao@inp-toulouse.fr.Comparison of the effect of locking vs standard screws on the mechanical properties of bone-plate constructs in a comminuted diaphyseal fracture model  Keywords: comminuted fracture, locking compression plate   1 Introduction The purpose of this study was to compare the mechanical properties of bone-plate constructs with locking compression plates (LCP) used either with standard screws or with locking screws on an experimental model of comminuted fracture.  2 Methods A model of comminuted fracture (mid-diaphyseal 5-mm gap) was created on ovine tibia and treated with a 8-hole, 4.5-mm, broad stainless LCP plate with 3 bicortical self-tapping screws in each fragment. In group 1 (n=6), 4.5 mm cortical screws were placed in slightly inner eccentric position and in group 2 (n=6), 5.0 mm locking screws were used. Quasi-static non-destructive tests were performed in 4-point bending, torsion and axial compression. A laser scan micrometer continuously measured the width of osteotomy gap. Extrinsic stiffness of bone-plate constructs (K) was calculated, as well as stiffness loss (Kr) compared with contralateral tibia. Slope of the load-gap displacement curve (S) was calculated. Results were statistically compared between the 2 groups by a 2-way ANOVA and Tukey's Post Hoc tests with significance set at P<.05.  3 Results and Discussion In 4-point bending, there were no significant differences between group 2 (G2) and group 1 (G1) for K (G2: 321.9 ± 65.2 kN/m, G1: 286.0 ± 36.6 kN/m), for Kr (G2: 55.4 ± 10.4%, G1: 64.5 ± 3.9%) and for S (G2: 292.0 ± 84.3 N/mm, G1:  271.4 ± 36.2 N/mm). In torsion, there were no significant differences between the 2 groups for K (G2: 122.1 ± 17.1 Nm/rad, G1: 107.3 ± 16.5 Nm/rad) and for Kr (G2: 44.0 ± 10.3%, G1: 55.0 ± 10.6%). That is consistent with most other in vitro and ex vivo studies comparing LCP with non locking (LC-DCP) plates [1] [2].    In compression, group 2 showed significantly lower K (611.1 ± 104.0 kN/m) and higher Kr (66.5 ± 10.3%) than group 1 (1019.2 ± 249.5 kN/m; 47.7 ± 10.8%), whereas other studies showed significantly higher stiffness for locking screws [2] [3]. It might be related to 2 phenomena: i) the friction forces induced by the screws which compress the plate onto bone in standard osteosynthesis and ii) the limitation of bone displacement by the eccentric position of standard screws that are blocked on the inner part of the plate hole, under axial compression. Anyway, there was no significant difference between the 2 groups for S (G2: 254.6 ± 72.6 N/mm, G1: 438.2 ± 228.4 N/mm).  4 Conclusions Locking screws had no statistically significant effect on the mechanical properties of LCP-plated bones in 4-point bending and torsion, compared to standard screws. In axial compression, locking screws induced a significant decrease in global mechanical properties without significant decrease in local mechanical properties close to the osteotomy gap.  References  [1] Aguila AZ, et al, In Vitro Biomechanical Comparison of LC-DCP and LCP. Vet Comp Orthop Traumatol, 2005;18(4):220-226.  [2] Snow M, et al, A Mechanical Comparison of the LCP and the LC-DCP in an Osteoporotic Bone Model. J Orthop Trauma, 2008;22(2):121-5.  [3] Filipowicz D, et al, A Biomechanical Comparison of 3.5 LCP Fixation to 3.5 LC-DCP Fixation in a Canine Cadaveric Distal Humeral Metaphyseal Gap Model. Vet Comp Orthop Traumatol, 2009;22(4):270-7.   

A Biomechanical Comparison of 3.5 LCP Fixation to 3.5 LC-DCP Fixation in a Canine Cadaveric Distal Humeral Metaphyseal Gap Model. Vet Comp Orthop Traumatol,

A Mechanical Comparison of the LCP and the LCDCP in an Osteoporotic Bone Model.

Comparison of the effect of locking vs standard screws on the

mechanical properties of bone-plate constructs in a

comminuted diaphyseal fracture model

Crossref

Computer Methods in Biomechanics & Biomedical Engineering

Comparison of the effect of locking<i>vs</i>standard screws on the mechanical properties of bone-plate constructs in a comminuted diaphyseal fracture model

HAL Descartes

Open Archive TOULOUSE Archive Ouverte (OATAO)OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible.This is an author-deposited version published in : http://oatao.univ-toulouse.fr/Eprints ID : 6272To cite this version : Verset, Michaël and Palierne, Sophie and Mathon, Didier andSwider, Pascal and Autefage, André Comparison of the effect oflocking vs standard screws on the mechanical properties of bone-plate constructs in a comminuted diaphyseal fracture model.(2012) Computer Methods in Biomechanics and BiomedicalEngineering, 15 (supplement). pp. 337-339. ISSN 1025-5842  Any correspondance concerning this service should be sent to the repositoryadministrator: staff-oatao@inp-toulouse.fr.Comparison of the effect of locking vs standard screws on the mechanical properties of bone-plate constructs in a comminuted diaphyseal fracture model  M. VERSET*†, S. PALIERNE†, D. MATHON†, P.SWIDER‡ and A. AUTEFAGE† † Université de Toulouse, INP, ENVT, Unité de Chirurgie, F-31076 ‡ Université de Toulouse, IMFT UMR 5502, F-31056 Keywords: comminuted fracture, locking compression plate   1 Introduction Healing of comminuted diaphyseal fractures is a major consideration in orthopaedics as they are frequently encountered, demonstrate a high rate of complications and their treatment is often challenging. They are often treated by bridging osteosynthesis for which the implant must withstand all weight-bearing forces until sufficient bridging callus is formed. One of the latest available implant in this indication is the Locking Compression Plate (LCP) whose combined holes accept either standard or locking screws. Although there are a few clinical and biomechanical studies comparing LCP plates featuring locking screws with non-locking plates, the real advantage of locking screws remains undefined and unquantified. The purpose of this ex vivo study was to compare the mechanical properties of bone-plate constructs with LCP plates used either with standard screws or with locking screws on an experimental model of comminuted fracture.  2 Methods Twelve pairs of ovine tibia were harvested and packed with gauze soaked in isotonic saline solution before freezing (-24°C). After thawing at room temperature, they were kept moistened throughout the experiment. Inclusion criteria were skeletally mature animals belonging to one single breed, similar size of tibia and absence of bone diseases evaluated on radiographs. They were randomly divided into 2 equal groups. A model of comminuted fracture (mid-diaphyseal 5-mm gap) was created on the left tibia from each pair and treated with a 8-hole, 4.5-mm, broad stainless LCP plate with 3 bicortical self-tapping screws in each fragment. In group 1 (n=6), 4.5 mm cortical screws were placed in slightly inner eccentric position (to avoid collapse of the osteotomy site during weight-bearing). In group 2 (n=6), 5.0 mm locking screws were used. All screws were tightened using a torque-limiting screwdriver at 4 Nm.  Biomechanical evaluations were performed by non-destructive tests at quasi-static displacement rate (1 mm/min) on electromechanical systems. Four-point bending, torsion and axial compression loading conditions were applied one after the other on plated bones and on intact contralateral bones, to serve as a control. Maximum load used for non-destructive tests was about 50% of yield load, as previously assessed by destructive tests on pre-test plated bones. Bending was performed in a latero-medial direction with upper anvils surrounding bone gap. After embedding of proximal and distal ends in polyurethane casting resin, bones sustained clockwise torsional load, then axial compression load. For bending and compression on plated bones, 2 monocortical 1.5 mm pins were seated through the lateral cortex (2.5 mm outside the edges of bone osteotomy). A laser scan micrometer allowed continuous measurement of width between pins during tests. Crosshead displacement, load, angle of rotation, torque and width between pins were recorded at 10 Hz.  Extrinsic stiffness of bone-plate constructs (K) was calculated, as well as stiffness loss (Kr) compared with contralateral tibia. Slope of the load-gap displacement curve (S) was also calculated. K and Kr provide information on global mechanical properties of plated or intact bone, whereas S is a reflection of interfragmentary motion during load thus providing information on local mechanical properties close to the osteotomy gap. Results were statistically compared between the 2 groups by a 2-way ANOVA and Tukey's Post Hoc tests, for each loading condition with significance set at P<.05.  3 Results and Discussion In 4-point bending, there were no significant differences between group 2 (G2) and group 1 (G1) for K (G2: 321.9 ± 65.2 kN/m, G1: 286.0 ± 36.6 kN/m), for Kr (G2: 55.4 ± 10.4%, G1: 64.5 ± 3.9%) and for S (G2: 292.0 ± 84.3 N/mm, G1:  271.4 ± 36.2 N/mm). In torsion, there were no significant differences between the 2 groups for K (G2: 133.3 ± 18.7 Nm/rad, G1: 117.2 ± 18.0 Nm/rad) and for Kr (G2: 44.0 ± 10.3%, G1: 55.0 ± 10.6%) (table 1). Bending stiffness and torsion stiffness were not significantly different using locking screws or standard screws. That is consistent with most other in vitro and ex vivo studies comparing LCP with non locking (LC-DCP) plates [1] [2]. In compression, group 2 showed significantly lower K (611.1 ± 104.0 kN/m) and higher Kr (66.5 ± 10.3%) than group 1 (1019.2 ± 249.5 kN/m; 47.7 ± 10.8%) (table 1, figure 1). Compression stiffness with locking screws was about half compared with standard screws, whereas other studies showed significantly higher stiffness for locking screws [2] [3]. It might be related to 2 phenomena: i) the friction forces induced by the screws which compress the plate onto bone in standard osteosynthesis and ii) the limitation of bone displacement by the eccentric position of standard screws that are blocked on the inner part of the plate hole under axial compression whereas standard screws are usually placed in central position. Anyway, there was no significant difference between the 2 groups for S (G2: 254.6 ± 72.6 N/mm, G1: 438.2 ± 228.4 N/mm), meaning that the significant difference of global mechanical properties seems to have no significant effect on the local mechanical properties (table 1).   Standard screws (G1) Locking screws (G2) K Kr S K Kr S 4-point bending 286 007.22 ± 36 586.22 64.47 ± 3.87 271.35 ± 36.16 321 926.90 ± 65 244.02 55.44 ± 10.39 292.00 ± 84.33 Torsion 107.28 ± 16.46 54.98 ± 10.56  / 122.07 ± 17.10 44.01 ± 10.27  / Axial compression 1.02E+6 ± 249 501.43 47.67 ± 10.77 438.24 ± 228.34 611 057.11 ± 104 012.99 66.50 ± 10.26 254.61 ± 72.56 Table 1 Mechanical properties of bone-plate constructs for each type of condition (mean ± SD)  K = extrinsic stiffness: slope of the graph showing the load or torque over the vertical displacement of the crosshead or the angular displacement of bone (N/m or Nm/rad) Kr = stiffness loss: difference between extrinsic stiffness of the intact contralateral bone and extrinsic stiffness of the operated bone divided by extrinsic stiffness of the contralateral bone (%) S = load-displacement curve slope: slope of the graph showing the load over the displacement of the two pins surrounding the interfragmentrary gap (N/mm)   Figure 1 Box plots comparing mechanical properties in axial compression for the 2 groups: Asterisks indicate significant differences between groups (P<.05). Whiskers lower and upper limits = 2.5th and 97.5th percentiles.  The main limitation to this ex vivo study is the only mechanical evaluation of bone-plate constructs, without assessment of bone healing. Now, bone healing results both of controlled mechanical conditions and of favourable biological conditions at the fracture site. Further in vivo study is needed to compare the biological conditions of bone-plate constructs with LCP plates used either with standard screws or with locking screws. It may be conducted by assessing the mechanical properties of bone callus after bridging osteosynthesis according to the same experimental design.  4 Conclusions Locking screws had no statistically significant effect on the mechanical properties of LCP-plated bones in 4-point bending and torsion, compared to standard screws. In axial compression, locking screws induced a significant decrease in global mechanical properties without significant decrease in local mechanical properties close to the osteotomy gap.  Our mechanical ex vivo study, completed by further in vivo study, should help to make a rational choice of the type of implant to treat comminuted fractures.   References  [1] Aguila AZ, et al, In Vitro Biomechanical Comparison of LC-DCP and LCP. Vet Comp Orthop Traumatol, 2005;18(4):220-226.  [2] Snow M, et al, A Mechanical Comparison of the LCP and the LC-DCP in an Osteoporotic Bone Model. J Orthop Trauma, 2008;22(2):121-5.  [3] Filipowicz D, et al, A Biomechanical Comparison of 3.5 LCP Fixation to 3.5 LC-DCP Fixation in a Canine Cadaveric Distal Humeral Metaphyseal Gap Model. Vet Comp Orthop Traumatol, 2009;22(4):270-7.        a) extrinsic stiffness K b) stiffness loss Kr  *Corresponding author. Email: m.verset@envt.fr 

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Comparison of the effect of locking vs standard screws on the mechanical properties of bone-plate constructs in a comminuted diaphyseal fracture model

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