Evaluation of the mechanical behaviour of the expandable wedge locked nail fixation in retrograde use: A finite element study.

INTRODUCTION: In literature, there have been many studies conducted to research the alternatives of standard interlocking intramedullary nailing. The expandable wedge locked nail fixation, which is thought as a new alternative to the standard interlocking nailing, has been presented in previous numerical studies. The antegrade usage of the wedge locked nail fixation has provided promising results. From this point, the aim of the study is to evaluate mechanical behavior of its retrograde usage on femur models. Additionally, another aim of the study is to investigate the effect of fracture level on mechanical properties of the fixation. MATERIALS AND METHODS: The mechanical behaviors of the wedge locked nail and standard interlocking nail fixations were compared by finite element methods. Sawbones femurs having osteotomies at five different levels to simulate different fractures were fixed with wedge locked nail or interlocking nail by using retrograde approach. With respect to the fracture level, two different nail lengths were used. Axial compression load was applied to fixations. The mechanical behaviors of the fixations were evaluated with respect to stiffness of the fixations and stresses occurred on both implants and bones. RESULTS: Any of the wedge locked nail fixation did not slip at canal. The stress and stiffness results were mostly close with each other for both nail types. The maximum stresses at locking elements or bones contacting these elements increased with decreased distance between the fracture and relevant locking elements. DISCUSSION: The wedge locked nail fixation showed comparable results to the standard interlocking nail fixation with respect to the stiffness and stress. Under axial loading, wedge locked nail provided a secured fixation without any slippage and preserved its position inside the medullary canal. It may be thought as a safe alternative to the standard interlocking nail fixation for retrograde usage. Additionally, according to stress results, it is advised to the surgeons to avoid a close locking to the fracture line.

Which implant is better for the fixation of posterior wall acetabular fractures: A conventional reconstruction plate or a brand-new calcaneal plate?

BACKGROUND: Increased posterior wall acetabular fractures among older adults, require precise treatment to restore stability to the joint, lower the risk of degenerative arthritis, and enhance overall functional recovery. The purpose of this study was to compare the fixation stability and mechanical characteristics of calcaneal buttress plate and conventional reconstruction plate under different loading condition. METHODS: Typical acetabular posterior wall fractures were created on twenty synthetic hemipelvis models. They were fixed with calcaneus plate and reconstruction plate. Dynamic and static tests were performed. Displacements of fracture line and stiffness were calculated. FINDINGS: After dynamic loading, calcaneus plate fixation has significantly less displacement than the reconstruction plate on the superior posterior wall. Under static loading condition, the calcaneus plate group has significantly less displacement than the reconstruction plate group on the inferior posterior part of the fracture. The average stiffness values of the calcaneus plate group and the reconstruction plate group were 265.16±53.98 N/mm and 167.48±36.87 N/mm, respectively and a statistically significant difference was found between the two groups. INTERPRETATION: The calcaneal plate group demonstrated better stability along the fracture line after dynamic and static loading conditions. Especially when the fragment was on the acetabulum's superior posterior, inferior posterior, and inferior rim, Calcaneal buttress plates offer biomechanically effective choices.

Biomechanical performance of talon cannulated compression device in pauwels type III fractures: a comparative study.

INTRODUCTION: Pauwels Type III fractures are unstable and frequently treated with cannulated screws (CS) or dynamic hip screws (DHS). The newly developed talon-cannulated compression devices (TCCD) have the potential to provide rotational stability, mainly through their talon. The study investigates whether TCCD has mechanical advantages over conventional screws or can be as stable as DHS in a reverse triangle configuration for an unstable femoral neck fracture. MATERIAL AND METHODS: After creating a standard Pauwels Type III unstable femoral neck fracture in 36 synthetic femur bones in cortical/hard cancellous bone density, 18 were reserved for dynamic-static tests, and 18 were used for torsional tests. Each group containing 18 synthetic bones was divided into three groups to apply three different fixation materials (CS, DHS, and TCCD), with six models in each group. The displacement amounts after dynamic-static tests were measured using the AutoCAD program according to the reference measurement criteria. During the dynamic tests, a series of photographs were taken. During the static tests, the beginning and post-test photographs were taken. Finally, torsional tests were performed until implant failure occurred in the synthetic femur. RESULTS: In static axial loading tests, TCDD was found to be statistically superior to conventional CS in AL-BL distance (p = 0,014) and CL distance (p = 0,013) measurements, and there was no significant difference between the other groups. There was no significant difference between all groups in dynamic axial compression tests in any points of interest. In torsional tests, TCCD outperformed cannulated screws in stiffness (p = 0,001) and maximum torque (p = 0,001) categories, and they provided statistically significant superiority to DHS in yield torque (p<0,001) category. CONCLUSIONS: Biomechanically, TCCD predominates conventional cannulated screws in femoral neck fractures. TCCD also has superior torsional properties than DHS in the yield torque category. Therefore, TCCD could be the implant of choice for unstable femoral neck fractures.

Talon cannulated compression device as an alternative in the fixation of acetabulum posterior column fractures: A biomechanical study.

To compare the amount of displacement and rigidity at the fracture line under static & dynamic axial loading and torsional stress of conventional cannulated screw (CS), plate screw fixation including inter-fragmentary screw (PL), and talon cannulated compression device or talon screw in other words (TS) in posterior column fracture models. Synthetic hemipelvis bone models presenting a posterior column fracture were used in this study. Group PL, CS, and TS were created with ten bone models prepared for each group for dynamic and static loading tests and another ten for torsional tests. Rigidity and displacement amounts before and after loading were measured at the reference points AL, BL, and CL, located at the acetabulum's top, middle, and bottom, respectively. Torsional tests for each group were used to calculate torsional rigidity and maximum torque values. In dynamic axial loading tests, Group CS showed more displacement than PL at the BL point (p = 0,032) and Group TS at AL (p = 0,032) and CL (p = 0,004) points. In static axial loading tests, Group CS significantly displaced more than TS at AL and CL points (p = 0,05 and p = 0,014, respectively). Group PL and Group TS exhibited similar behavior in dynamic, static axial loading tests and torsional rigidity. The maximum torque that Group PL could withstand was statistically significantly higher than the other two groups (p <0,001). Talon cannulated screws had promising results in posterior column fractures of the acetabulum, which may decline the need for open surgery for stable fixation.

Histological and Biomechanical Effects of Local Anesthetics and Steroids on Achilles Tendon: A Study in Rats.

BACKGROUND: Peritendinous injection of local anesthetics, alone or in combination with corticosteroids, is widely used in the treatment of tendinopathies. Toxicity of local anesthetics has been demonstrated in many cells, including myocytes, chondrocytes, and neurons. Bupivacaine and lidocaine are known to have time- and dose-dependent cytotoxicity in these cells. The effects of these agents on the tendon remain unknown. PURPOSE: To show histological and biomechanical effects after the injection of different local anesthetics and steroids, both single and combined, at different concentrations into the peritendinous sheath of rat Achilles tendon. STUDY DESIGN: Controlled laboratory study. METHODS: In the study, 100 rats were divided into 10 groups with equal body weights. Inflammation was induced in both Achilles tendons of each rat by means of the ball drop technique; 7 hours later, injections were made into the peritendinous sheaths of both Achilles tendons using lidocaine, bupivacaine, and dexamethasone as appropriate for the rat's group. At the end of the first week, the right Achilles tendons of the rats were removed for histological study. Left Achilles tendons were evaluated in terms of biomechanics. RESULTS: Histological findings demonstrated that the group with the most toxicity to the tendon was the group that received injection of dexamethasone alone. The groups with the least toxicity were those receiving dexamethasone combined with low- or high-dose bupivacaine. Biomechanical findings showed that the experimental groups had similar results to each other with the exception of the groups receiving 0.25% bupivacaine alone and dexamethasone alone, in which tendons revealed higher tensile strength. CONCLUSION: Local anesthetic and steroid applications have different histological and biomechanical effects on the tendon. Although the dexamethasone-injected group was the most affected in terms of histology, these changes could not be demonstrated biomechanically. CLINICAL RELEVANCE: In future clinical studies, the effect of steroids on the tendon should be investigated more comprehensively. Whether biomechanical results overlap with histological results should be investigated further.

Mechanical comparison of standard interlocking, clawed, and expandable wedge locked nail fixations: An experimental and numerical study.

INTRODUCTION: Intramedullary nailing has been used as a standard in the treatment of the long bone fractures with its clinical and mechanical advantages. However, using distal locking screws has been associated with longer operative times, higher radiation exposure rates, and complications like breakages of distal screw or nail at the screw hole level. Therefore, attempts to eliminate distal locking screws has been always present for intramedullary nail fixation. With a similar purpose, the present study has been carried out to compare mechanical behaviors of intramedullary nail fixations with different distal locking elements. MATERIALS AND METHODS: In this study, mechanical behaviors of standard interlocking and clawed nail fixations were compared experimentally in the first part. Six fourth generation Sawbones femurs, which have a simulated subtrochanteric fracture, were divided equally and were fixed with standard interlocking and clawed nails. During axial compression tests, experimental strain measurements were taken from all fixations. After validation of numerical models with using experimental strains and stiffnesses, mechanical behaviors of standard interlocking, clawed, and wedge locked nail fixations were compared numerically under axial compression loads. In numerical comparison, the stress-strain distributions were evaluated. RESULTS: Experimental results showed that although that there was no significant difference in stiffnesses, standard nail fixation bore two times higher loads than clawed nail fixations. Under loading, decrease in the distance between fracture surfaces was approximately seven times higher in the clawed nail fixation when compared to standard nail fixations. Numerical results showed that wedge locked nail fixation provided equivalent mechanical behavior to standard interlocking nail. DISCUSSION: In experiments of clawed nail fixation, the high decrease in the distance between fracture surfaces was evidence of the slippage of nail in the medullary canal. For a safe fixation, claws should be deployed when they are completely in contact with the cortical bone, they should be stuck into the bone in a fair amount, and the deployment in the distal third of the femur should be avoided. According to experimentally validated numerical analyses, wedge locked nail fixation may be an alternative for standard interlocking nail fixation if experimental studies support the present results.

The effect of the distance between the end point of the osteotomy and the lateral cortex on the lateral cortical hinge fracture in medial opening-wedge high tibial osteotomy.

Background The purpose of this study was to compare the effects of different distances between the end point of the osteotomy and the lateral cortex on the risk of lateral cortical fracture in the medial opening-wedge high tibial osteotomy (MOWHTO) procedure. Methods Eighteen synthetic tibia models were used. Saw cuts were performed on the test models (n=6 for all groups). Wedge gap distance and wedge opening load were evaluated using compression tests. Findings The mean maximum gap distance without a lateral cortical fracture was 19.90 mm in Group 5, 15.49 mm in Group 10, and 11.23 mm in Group 15. The differences between Group 5 and Group 10, Group 5 and Group 15, and Group 10 and Group 15 were statistically significant. The mean load just before the fracture was 13.24 N in Group 5, 18.31 N in Group 10, and 26.16 N in Group 15. The difference between Group 5 and Group 15 was statistically significant. No significant difference was observed between Group 10 and both Group 5 and Group 15. Interpretation As the end point of the osteotomy is brought gradually closer to the lateral cortex, wider gaps can be opened without a lateral cortical fracture. Thus, higher angle corrections can be achieved more safely by bringing the end point of the osteotomy closer to the lateral cortex, which should be preferred to reduce the risk of a lateral cortical hinge fracture during the MOWHTO procedure, from a clinical viewpoint.

The Effect of Lateralization of a Pelvic Brim Plate on the Fixation of an Anterior Column Fracture: A Biomechanical Analysis.

Objectives Anterior column fractures can be seen as either isolated or accompanied by many types of complex acetabulum fractures. The aim of this study was to biomechanically compare the stability of a standard pelvic brim plate with a more laterally located suprapectineal plate, which is more commonly used in minimally invasive application, on an intermediate height anterior column fracture model under dynamic and static loading. Materials and methods Right side, adult, foam cortical shell artificial hemipelvis models were used (Sawbones, Pacific Research Laboratories, Vashon, WA, USA). Twenty-four (24) pieces of foam cortical shell artificial hemipelvis models were separated into three groups (M, L, and control). In group "M," a suprapectineal plate was placed medially just adjacent to the pelvic brim. In group "L," a laterally located suprapectineal plate was placed 2 cm lateral of the pelvic brim at its most proximal point. Then, dynamic load testing of 1000 cycles between 50 N and 500 N force and a static load test of 1.2 kN at 2 mm/minute were applied. Dynamic and static tests were conducted on an axial compression device. Displacements were measured after dynamic and static loading conditions. Results In the dynamic loading test at the AL point (superior intersection of the fracture line with the acetabular roof), the median displacement was significantly higher in group L than in group M (0.12 (IQR: 0.058-0.8125) mm and 0.04 (IQR: 0.03-0.065) mm (p = 0.02)). There was no other statistically significant difference in the displacement amounts in both dynamic and static loading conditions at other measurement points. The comparison of the stiffness of the M and L groups showed no statistically significant results, while the control group was significantly more rigid than both the M and L groups (p = 0.04 for both). None of the artificial hemipelvis models was found to be fractured at the end of the test. Conclusion Suprapectineal plates, placed on either the medial or lateral aspect of the pelvic brim, may be used for the fixation of anterior column-type fractures to provide rigid fixation and stability. As plate location did not impact stiffness and stability, the results suggest that surgeons have flexibility in determining the fixation based on accessibility, fracture pattern, and surgeon experience.

The effects of pre-stressed rods contoured by different bending techniques on posterior instrumentation of L4-L5 lumbar spine segment: A finite element study.

Posterior pedicle screw instrumentation (PPSI) is a well-known method in lumbar spine surgery. Understanding how PPSI affects the biomechanics of the lumbar spine is an important issue. In particular, during PPSI operations, surgeons bend rods according to the patients' spinal curvatures based on their own experiences. As a result, residual stresses develop on the rods due to this bending. Although many finite element-based biomechanical studies have been performed for PPSI, studies comparing the effects of residual stresses arising from rod contouring on the construct stresses are lacking. Thus, this study aimed to investigate the effects of residual stress in PPSI using rods contoured with a French bender and an in-situ bender, as well as comparing the differences in stress increment with straight and contoured rods for different physiological motions. Accordingly, a finite element (FE) model of the L4-L5 lumbar spine segment was developed for PPSI and the effects of residual stresses on rods were investigated by using different bending methods. In the simulations, it was found that rods contoured with a French bender with residual stress resulted in significantly more increased stress in PPSI compared to those contoured with an in-situ bender. The results of this study emphasize that increased stress in PPSI due to the residual stresses for different physiological motions may increase the risk of PPSI failures. Additionally, the finite element modeling approach employed here could be used as a fundamental tool for further investigations of topics such as PPSI fatigue life and failure studies.

A NEW ANATOMICAL PLATE FOR EXTRA-ARTICULAR DISTAL HUMERAL FRACTURES: BIOMECHANICAL STUDY.

Introduction: We compared the mechanical properties of two fixation techniques for the treatment of extra-articular distal third humeral fractures. Materials and Methods: Two groups were created from twenty-four humeri. Group 1 was instrumented using a new, precontoured, 8-hole (3.5-mm-diameter) locking compression plate (LCP) placed anterolaterally. Group 2 was instrumented using an 8-hole (3.5-mm-diameter) precontoured posterolateral LCP plate placed on the distal humerus. Four-point bending tests and torsion tests were performed until the specimens broke. Results: The four-point bending stiffness test showed that the stiffness of anterolaterally fixed humeri was significantly higher than that of posterolaterally fixed humeri (p<0.05). Torsion testing revealed that posterolateral fixation was associated with better yield strength (p<0.05), but the torsional stiffness did not differ significantly between the two plates (p> 0.05). Conclusions: The anterolateral plate exhibited higher bending stiffness and torsional yield strength than the posterolateral plate. Anterolateral plate fixation can thus be used to manage extra-articular distal humeral fractures. Multiaxial locking screws ensure rigid fixation, allow early elbow motion without olecranon fossa impingement, and prevent iatrogenic injury of the triceps muscle. Level of Evidence I, Therapeutic Studies Investigating the Results of Treatment.

Introdução: Comparamos as propriedades mecânicas de duas técnicas de fixação para o tratamento de fraturas extra-articulares do terço distal do úmero. Materiais e Métodos: Dois grupos foram criados a partir de vinte e quatro úmeros. O Grupo 1 foi instrumentado com uma nova placa de compressão com travamento (LCP) pré-contornada e com oito orifícios (3,5 mm de diâmetro) posicionados anterolateralmente. O Grupo 2 foi instrumentado com uma placa LCP pré-contornada posterolateral com oito orifícios (3,5 mm de diâmetro) colocada na parte distal do úmero. Testes de flexão e testes de torção a quatro pontos foram realizados até que os corpos de prova quebrassem. Resultados: O teste de rigidez à flexão de quatro pontos mostrou que a rigidez dos úmeros fixados anterolateralmente foi significativamente maior do que os úmeros fixados posterolateralmente (p <0,05). O teste de torção revelou que a fixação posterolateral foi associada a melhor força de rendimento (p <0,05), mas a rigidez à torção não diferiu significativamente entre as duas placas (p > 0,05). Conclusões: A placa anterolateral apresentou maior rigidez à flexão e resistência à tração do que a placa posterolateral. A fixação anterolateral da placa pode, portanto, ser usada para tratar fraturas extra-articulares da parte distal do úmero. Os parafusos de travamento multiaxiais garantem uma fixação rígida, permitem o movimento precoce do cotovelo sem causar impacto à fossa do olécrano e previnem lesão iatrogênica do músculo tríceps. Nível de evidência I, Estudos terapêuticos - Investigação dos resultados do tratamento.

Evaluation of the Effects of Transforming Growth Factor-Beta 3 (TGF-ß3) Loaded Nanoparticles on Healing in a Rat Achilles Tendon Injury Model.

BACKGROUND: Achilles tendon (AT) midsubstance injuries may heal suboptimally, especially in athletes. Transforming growth factor-beta 3 (TGF-ß3) shows promise because of its recently discovered tendinogenic effects. Using poly(lactic-co-glycolic acid)-b-poly(ethylene glycol) (PLGA-b-PEG) nanoparticles (NPs) may enhance the results by a sustained-release effect. HYPOTHESIS: The application of TGF-ß3 will enhance AT midsubstance healing, and the NP form will achieve better outcomes. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 80 rats underwent unilateral AT transection and were divided into 4 groups: (1) control (C); (2) empty chitosan film (Ch); (3) chitosan film containing free TGF-ß3 (ChT); and (4) chitosan film containing TGF-ß3-loaded NPs (ChN). The animals were sacrificed at 3 and 6 weeks. Tendons were evaluated for morphology (length and cross-sectional area [CSA]), biomechanics (maximum load, stress, stiffness, and elastic modulus), histology, immunohistochemical quantification (types I and III collagen [COL1 and COL3]), and gene expression (COL1A1, COL3A1, scleraxis, and tenomodulin). RESULTS: Morphologically, at 3 weeks, ChT (15 ± 2.7 mm) and ChN (15.6 ± 1.6 mm) were shorter than C (17.6 ± 1.8 mm) (P = .019 and = .004, respectively). At 6 weeks, the mean CSA of ChN (10.4 ± 1.9 mm2) was similar to that of intact tendons (6.4 ± 1.1 mm2) (P = .230), while the other groups were larger. Biomechanically, at 3 weeks, ChT (42.8 ± 4.9 N) had a higher maximum load than C (27 ± 9.1 N; P = .004) and Ch (29.2 ± 5.7 N; P = .005). At 6 weeks, ChN (26.9 ± 3.9 MPa) had similar maximum stress when compared with intact tendons (34.1 ± 7.8 MPa) (P = .121); the other groups were significantly lower. Histologically, at 6 weeks, the mean Movin score of ChN (4.5 ± 1.5) was lower than that of ChT (6.3 ± 1.8). Immunohistochemically, ChN had higher COL3 (1.469 ± 0.514) at 3 weeks and lower COL1 (1.129 ± 0.368) at 6 weeks. COL1A1 gene expression was higher in ChT and ChN at 3 weeks, but COL3A1 gene expression was higher in ChN. CONCLUSION: The application of TGF-ß3 had a positive effect on AT midsubstance healing, and the sustained-release NP form improved the outcomes, more specifically accelerating the remodeling process. CLINICAL RELEVANCE: This study demonstrated the effectiveness of TGF-ß3 on tendon healing on a rat model, which is an important step toward clinical use. The novel method of using PLGA-b-PEG NPs as a drug-delivery system with sustained-release properties had promising results.

3D porous PCL-PEG-PCL / strontium, magnesium and boron multi-doped hydroxyapatite composite scaffolds for bone tissue engineering.

Bioceramic/polymer composite systems have gained importance in treating hard tissue damages using bone tissue engineering (BTE). In this context, it was aimed to develop 3D porous composite PCL-PEG-PCL scaffolds containing different amounts of B, Sr and Mg multi-doped HA that can provide bone regeneration in the bone defect area and to investigate the effect of both the amount of inorganic phase and the porosity on the mechanical and the biological properties. B-Sr-Mg multi-doped HA and PCL-PEG-PCL copolymer were successfully synthesized. PCL-PEG-PCL composite scaffolds containing different amounts of hydroxyapatite (HA) (10% and 20 wt%) were produced with the desired porosity (50% and 60%) by compression-molding and particulate leaching method. The porosity of the scaffolds was determined between 47% and 59%. HA/PCL-PEG-PCL composite scaffolds were subjected to a 3-week degradation test and showed negligible (0.2-0.5%) degradation. The water uptake percentage of the composite scaffolds with 60% porosity was the highest among all groups. Presence of HA in the scaffolds improved the water adsorption and the mechanical properties. Compressive strength of the scaffolds was between 9.32 and 24.27 MPa and 20% 2Sr0.5BHA scaffolds were found to have the maximum compressive strength. Compressive strength of 50% porous samples was higher than that of 60% porous samples. In the relative cell viability (%) test, the highest viability was observed on the scaffolds with HA and 2Sr0.5BHA. The specific ALP activity level of the cells on the scaffolds containing 2Sr0.5BHA was significantly higher (2.6 times) than that of the control group. The amount of porosity did not make a significant difference in cellular response. It was concluded that PCL-PEG-PCL composite scaffolds with 2Sr0.5BHA have the potential to be used in BTE.

Postfusion effect on pullout strength of pedicle screws with expandablepeek shell and conventional screws.

The pullout performance of various pedicle screws after artificial fusion process was investigated in this study. Normal, cannulated (cemented), novel expandable and normal (cemented) pedicle screws were tested. Polyurethane foams (Grade 10 and Grade 40) produced by casting method were used as test materials. The instrumentation of pedicle screws has been carried out with production of foams, simultaneously. For cemented pedicle screws, 3D models were prepared with respect to the anteriosuperior and oblique radiographs by using PMMA before casting procedure. Pullout tests were performed in an Instron 3369 testing device. Load versus displacement graph was recorded and the ultimate force was defined as the pullout strength sustained before failure of screw. As expected, the pullout strengths of pedicle screws in postfusion are higher than before fusion. Pullout strengths increased significantly by artificial fusion in Grade 10 foams compared to Grade 40 foams. Additionally, while the pullout strengths of normal, cannulated and novel expandable pedicle screws increased by artificial fusion, cemented normal pedicle screws had lower pullout values than before fusion in Grade 40 foams. When the cemented normal pedicle screws are excluded, other screws have almost similar pullout strength level. On the other hand, the pedicle screws have different increasing behaviour also, there is no correlation between each other. As a result, the novel expandable pedicle screws can be used instead of normal and cannulated ones due to their performances in non-cemented usage.

A new anatomical plate for extra-articular distal humeral fractures: biomechanical study / Uma nova placa anatômica para fraturas extra-articulares distais do úmero: estudo biomecânico

ABSTRACT Introduction We compared the mechanical properties of two fixation techniques for the treatment of extra-articular distal third humeral fractures. Materials and Methods Two groups were created from twenty-four humeri. Group 1 was instrumented using a new, precontoured, 8-hole (3.5-mm-diameter) locking compression plate (LCP) placed anterolaterally. Group 2 was instrumented using an 8-hole (3.5-mm-diameter) precontoured posterolateral LCP plate placed on the distal humerus. Four-point bending tests and torsion tests were performed until the specimens broke. Results The four-point bending stiffness test showed that the stiffness of anterolaterally fixed humeri was significantly higher than that of posterolaterally fixed humeri (p<0.05). Torsion testing revealed that posterolateral fixation was associated with better yield strength (p<0.05), but the torsional stiffness did not differ significantly between the two plates (p> 0.05). Conclusions The anterolateral plate exhibited higher bending stiffness and torsional yield strength than the posterolateral plate. Anterolateral plate fixation can thus be used to manage extra-articular distal humeral fractures. Multiaxial locking screws ensure rigid fixation, allow early elbow motion without olecranon fossa impingement, and prevent iatrogenic injury of the triceps muscle. Level of Evidence I, Therapeutic Studies Investigating the Results of Treatment.

RESUMO Introdução Comparamos as propriedades mecânicas de duas técnicas de fixação para o tratamento de fraturas extra-articulares do terço distal do úmero. Materiais e Métodos Dois grupos foram criados a partir de vinte e quatro úmeros. O Grupo 1 foi instrumentado com uma nova placa de compressão com travamento (LCP) pré-contornada e com oito orifícios (3,5 mm de diâmetro) posicionados anterolateralmente. O Grupo 2 foi instrumentado com uma placa LCP pré-contornada posterolateral com oito orifícios (3,5 mm de diâmetro) colocada na parte distal do úmero. Testes de flexão e testes de torção a quatro pontos foram realizados até que os corpos de prova quebrassem. Resultados O teste de rigidez à flexão de quatro pontos mostrou que a rigidez dos úmeros fixados anterolateralmente foi significativamente maior do que os úmeros fixados posterolateralmente (p <0,05). O teste de torção revelou que a fixação posterolateral foi associada a melhor força de rendimento (p <0,05), mas a rigidez à torção não diferiu significativamente entre as duas placas (p > 0,05). Conclusões A placa anterolateral apresentou maior rigidez à flexão e resistência à tração do que a placa posterolateral. A fixação anterolateral da placa pode, portanto, ser usada para tratar fraturas extra-articulares da parte distal do úmero. Os parafusos de travamento multiaxiais garantem uma fixação rígida, permitem o movimento precoce do cotovelo sem causar impacto à fossa do olécrano e previnem lesão iatrogênica do músculo tríceps. Nível de evidência I, Estudos terapêuticos - Investigação dos resultados do tratamento.

Influence of posterior pedicle screw fixation at L4-L5 level on biomechanics of the lumbar spine with and without fusion: a finite element method.

BACKGROUND: Posterior pedicle screw (PS) fixation, a common treatment method for widespread low-back pain problems, has many uncertain aspects including stress concentration levels, effects on adjacent segments, and relationships with physiological motions. A better understanding of how posterior PS fixation affects the biomechanics of the lumbar spine is needed. For this purpose, a finite element (FE) model of a lumbar spine with posterior PS fixation at the L4-L5 segment level was developed by partially removing facet joints (FJs) to imitate an actual surgical procedure. This FE study aimed to investigate the influence of the posterior PS fixation system on the biomechanics of the lumbar spine before and after fusion by determining which physiological motions have the most increase in posterior instrumentation (PI) stresses and FJ loading. RESULTS: It was determined that posterior PS fixation increased FJ loading by approximately 35% and 23% at the L3-L4 adjacent level with extension and lateral bending motion, respectively. This increase in FJ loading at the adjacent level could point to the possibility that adjacent segment disease has developed or progressed after posterior lumbar interbody fusion. Furthermore, analyses of peak von Mises stresses on PI showed that the maximum PI stresses of 272.1 MPa and 263.7 MPa occurred in lateral bending and flexion motion before fusion, respectively. CONCLUSIONS: The effects of a posterior PS fixation system on the biomechanics of the lumbar spine before and after fusion were investigated for all physiological motions. This model could be used as a fundamental tool for further studies, providing a better understanding of the effects of posterior PS fixation by clearing up uncertain aspects.

Numerical evaluation of the mechanical properties of a novel expandable intramedullary nailing: A new alternative to standard interlocking nailing.

INTRODUCTION: There has been a great effort in preventing the disadvantages of distal locking in intramedullary nailing to date. From this scope, a novel expandable nail fixation eliminating distal locking screws has been designed. The primary aim of this numerical parametric study is to investigate mechanical behavior of expandable nail fixation on the fractured femur model under different contact parameters which are effective in maintaining the nail position and to specify the appropriate values of these contact parameters for a safe fixation. The second aim is to compare mechanical behavior of the expandable nail fixation with the standard interlocking nail fixation. MATERIALS AND METHODS: The expandable nail has three wedges which are responsible for distal fixation by compressing the medullary canal in the radial direction. 4th generation Sawbones femur model was used as bone model. A transverse osteotomy with 20 mm gap was created to simulate a subtrochanteric fracture. The fixations have been examined under axial compression with 1200 N and torsion with 7 Nm. In the parametric study, the tightening torque and static friction coefficient in wedge-canal contact were selected as contact parameters. The outputs were stiffnesses of the fixations, equivalent von-Mises stress distribution on the models, and load sharing between the canal and distal locking elements. RESULTS: The results of the parametric study showed that the model with the tightening torque of 3 Nm and friction coefficient of 0.7 was the safest. The load borne by wedges is generally prone to increase with increased tightening torque and friction coefficient. The both fixations showed close stiffness and stress values. CONCLUSION: The tightening torque of the wedge locking mechanism is directly effective in maintaining the nail position constant in canal, and the safety of the fixation is better ensured with increased tightening torque but stress states on bone must be carefully evaluated. The expandable nail provided comparable results to standard interlocking nails with respect to the fixation stiffness, stress, and contact forces. The expandable nailing may be evaluated as an alternative in the fractures of long bones in the case that the numerical results are supported by future experimental studies.

Synthesis and sintering of B, Sr, Mg multi-doped hydroxyapatites: Structural, mechanical and biological characterization.

Hydroxyapatite (HA, Ca10(PO4)6(OH)2) is the main constituent mineral of bone and teeth in mammals. Due to its outstanding biocompatibility and osteoconductive capabilities, it is preferred for bone repair and replacement. Owing to high potential to have excellent biological properties, ternary ions-doped HAs have just begun to be investigated in the biomedical field and preparing multi-doped HAs is a fairly new approach. Boron (B, BO33-), strontium (Sr, Sr2+) and magnesium (Mg, Mg2+) provide a beneficial effect on bone growth, bone strength, biocompatibility and positively affect bone microstructure. The motivation of this study is taking advantages of the potential of the combine effects of these bivalent ions. In this study, 8 different compositions of BO33-, Sr2+, Mg2+ multi-doped HAs were synthesized by microwave irradiation method to investigate the structural, mechanical and biological features of bone substitutes. This is the first time we report the effect of boron, strontium and magnesium ions multi-doping on the structure of HA and its biological properties. Samples were sintered at 700, 900 and 1100 °C. The effect of varying ion contents and sintering temperature on structural and biological properties of the multi-doped samples was investigated. B, Sr and Mg ions were successfully doped into the HA structure according to X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) analyses. A biphasic structure was obtained with increasing amount of ion-doping. Increasing the sintering temperature affected the crystallinity and the density of the samples gradually. Vicker's microhardness and diametral strength of the samples increased at high sintering temperatures. B-Sr-Mg multi-doped HA promoted osteoblast-like Saos-2 cell proliferation, and as the sintering temperatures of the samples increased, the osteogenic differentiation level of the cultured cells also increased. Overall, results showed that the biological properties of HA were improved with the doping of Sr, Mg and B ions, and for bone implant applications samples sintered at 1100 °C were suggested to have potential as a biomaterial.

Could isthmic approach to far lateral disc hernias cause instability?

BACKGROUND: The aim of this study is to investigate the relationship between the degree of instability and the amount of isthmus excised during transpars (isthmic) approach which is accomplished with partial resection of the pars interarticularis used in distal lateral disc herniation. METHODS: Thirty-six ovine lumbar spine segments were used in the study. 25% and 50% of the right side isthmus of each spinal segment were excised. Flexion, lateral bending and axial rotation tests were performed in both groups. FINDINGS: There was no statistically significant difference found between the groups for yield moment, stiffness and ultimate load in flexion tests (p = 0.262, p = 0.749 and p = 0.200, respectively). Statistically significant difference was found between the groups for yield moment, stiffness and maximum load in lateral bending tests (p = 0.016, p = 0.010 and p = 0.016, respectively). There was no statistical difference found between the groups for yield torque and stiffness in axial rotation tests (p = 0.855 and p = 0.314). INTERPRETATION: These results show that a significant loss of resistance especially during the lateral bending loading was occurred with increasing resection portion of isthmus. With the load applied during the lateral bending of the pars interarticularis, the vertebra resected by 50% percent fractured significantly easier in comparison to the vertebra resected by 25% percent. Pars interarticularis is an important structure with an important role in stability. It is presumed that the more defect is created during the drill-up of the pars interarticularis, the more instability will be occurred.

Comparison of various tendon repair techniques in extansor zone 3 injuries: an experimental biomechanical cadaver study.

PURPOSE: To compare five different repair techniques for extensor tendon zone III modified Kessler (MK), double-modified Kessler (DMK), modified Kessler epitendinous (MKE), double-modified Kessler epitendinous (DMKE), and running-interlocking horizontal mattress (RIHM) in terms of shortening, stiffness, gap formation, and ultimate load to failure. METHODS: A total of 35 human cadaver fingers were randomly assigned to five suture techniques with 7 fingers each and were tested under dynamic and static loading conditions. RESULTS: DMK was found to be superior over MK in terms of ultimate load to failure (36 N vs. 24 N, respectively), shortening (1.75 vs. 2.20 mm, respectively) and gap formation. However, these two methods had similar characteristics in terms of stiffness. The addition of epitendinous sutures to the repair methods resulted in approximately 40% increase in ultimate load to failure, whereas epitendinous sutures had no effect on shortening. DMKE was found to be superior over MKE in terms of shortening (1.77 vs. 2.22 mm, respectively). However, these two methods had similar characteristics in terms of mean ultimate load to failure and stiffness. RIHM was found to be superior over the other four methods in terms of ultimate load to failure (89 N), stiffness, and shortening (0.75 mm). CONCLUSION: RIHM was found to be stronger and more durable for extensor tendon zone III than the other techniques in terms of ultimate load to failure and stiffness.

Effect of cortical bone thickness and density on pullout strength of mini-implants: An experimental study.

INTRODUCTION: Anchorage, which is defined as resistance against undesired tooth movements, is one of the most important factors in success of orthodontic treatment. In recent years, mini-implants have been used instead of uncomfortable headgears and Nance appliances. The pullout test is the most common method for measuring the anchorage capacity of mini-implants. The aim of this study was to investigate the effects of cortical bone thickness and cortical layer bone density on pullout strength of mini-implants. METHODS: Mini-implants were placed in polyurethane foam blocks representing 3 different cortical thicknesses (1 mm, 2 mm, and 3 mm) and 3 different cortical bone densities (grade 40, grade 45, and grade 50). Pullout tests were performed with 5 mm/min loading rate. Load vs displacement values were recorded during the tests. RESULTS: Comparing cortical thicknesses on the same bone densities, statistically significant differences were found between 1 mm, 2 mm, and 3 mm thicknesses. Likewise, comparing bone densities on the same cortical thicknesses, statistically significant differences were found among all groups. Spearman rank tests showed that both cortical thickness and cortical bone density are correlated with pullout strength (rs, 0.548; P <0.001 and rs, 0.691; P <0.001, respectively). CONCLUSIONS: Although both factors are positively correlated with pullout strength, the effect of cortical bone density was the dominant factor affecting primary stability.