Abstract This study investigates the biomechanics of the spine after insertion of vertebral body tethering (VBT) with different cord pretensions. For that purpose, a Finite Element model of the average thoracolumbar spine was stepwise calibrated and validated. The VBT instrumentation was inserted in the left side of the L1-L2 segment with different cord pretensions. As a second test, the L1-L2 segment was submitted to an external pure moment of 6 Nm in left and right lateral bending. The range of motion (ROM) for the spine with VBT was determined with respect to its initial post VBT position. Pretension forces of 100 N and 300 N resulted in a change of scoliotic angle of 2.7° and 5.3° to the left side of the spine, respectively. The ROM of the native spine was 4.5° in right lateral bending and reduced to 1.8° and 1.4° for the cases of the spine with a cord pretension of 100 N and 300 N, respectively. In left lateral bending, the absolute ROM of the native spine was 4.6°. For the cases of a cord pretension of 100 N and 300 N, the spine bent 1.9° and 0.8° to the left side from its initial post VBT position, respectively.

RESUMO Objetivo Avaliar e comparar a resistência mecânica e o comportamento em fadiga associados ao uso de três modalidades distintas de conectores de hastes do sistema de fixação vertebral por meio de ensaios mecânicos pré-clínicos in vitro desenvolvidos especificamente para essa aplicação (linear, lateral com conector quadrado e lateral com conector oblíquo). Métodos Foram usadas hastes de Cromo-cobalto de 5,5 mm de diâmetro acopladas a três modalidades de conectores: a) haste lateral com conector oblíquo, b) haste lateral com conector quadrado e c) haste e conector lineares. Foram realizados ensaios mecânicos quase-estáticos e de fadiga sob flexão em quatro pontos. As variáveis medidas foram (I) o momento fletor no limite de escoamento, (II) o deslocamento no limite de escoamento e (III) a rigidez do sistema em flexão e (IV) número de ciclos até a falha do sistema. Resultados O sistema linear apresentou a maior força e o maior momento no limite de escoamento, bem como maior rigidez equivalente à flexão. Todos os corpos de prova com conectores quadrados e oblíquos suportaram 2,5 milhões de ciclos nas condições mínimas e máximas de momento aplicado. Os corpos de prova com conector linear suportaram 2,5 milhões de ciclos com frações de 40,14% do momento fletor no limite do escoamento, porém falharam com níveis de 60,17% e 80,27%. Conclusões Os sistemas com conectores lineares apresentaram maior resistência mecânica quando comparados aos sistemas com conectores quadrados e oblíquos. Todos os sistemas suportaram carregamentos cíclicos que mimetizam as solicitações in vivo. Nível de evidencia V; Pesquisa in vitro.

ABSTRACT Objective Evaluate and compare the mechanical resistance and the fatigue behavior associated with the use of three different modalities of vertebral fixation system rod connectors through in vitro pre-clinical mechanical tests developed specifically for this application (linear, lateral with square connector and lateral with oblique connector). Methods Cobalt chromium rods 5.5 mm in diameter were used and coupled with three types of connectors: a) side rod with oblique connector, b) side rod with square connector, and c) rod and linear connectors. Quasi-static mechanical four-point bending and fatigue tests were performed. The variables measured were (I) the bending moment at the yield limit, (II) the displacement at the yield limit, (III) the rigidity of the system in flexion and (IV) the number of cycles until system failure. Results The linear system presented the greatest force and the greatest moment at the yield limit, as well as the greatest stiffness equivalent to bending. All specimens with square and oblique connectors endured 2.5 million cycles in the minimum and maximum conditions of applied moment. The specimens with linear connector endured 2.5 million cycles with fractions of 40.14% of the bending moment at the yield limit, but failed with levels of 60.17% and 80.27%. Conclusions Systems with linear connectors showed greater mechanical resistance when compared to systems with square and oblique connectors. All systems supported cyclic loads that mimic in vivo demands. Level of evidence V; In vitro research.

RESUMEN Objetivo Evaluar y comparar la resistencia mecánica y el comportamiento de fatiga asociado al uso de tres modalidades distintas de conectores de varilla del sistema de fijación vertebral a través de ensayos mecánicos preclínicos in vitro desarrollados específicamente para esta aplicación (lineal, lateral con conector cuadrado y lateral con conector oblicuo). Métodos Se utilizaron varillas de cromo-cobalto de 5,5 mm de diámetro acopladas a tres tipos de conectores: a) varilla lateral con conector oblicuo, b) varilla lateral con conector cuadrado y c) varilla y conector lineales. Se realizaron ensayos mecánicos y de fatiga cuasi-estáticos y ensayos por flexión de cuatro puntos. Las variables medidas fueron (I) el momento flector en el límite elástico, (II) el desplazamiento en el límite elástico y (III) la rigidez del sistema en flexión y (IV) el número de ciclos hasta la falla del sistema. Resultados El sistema lineal presentó la mayor fuerza y el mayor momento en el límite elástico, así como la mayor rigidez equivalente a la flexión. Todas las probetas con conectores cuadrados y oblicuos soportaron 2,5 millones de ciclos en las condiciones mínimas y máximas de momento aplicado. Las probetas con conector lineal soportaron 2,5 millones de ciclos con fracciones del 40,14% del momento flector en el límite elástico, pero fallaron con niveles de 60,17% y 80,27%. Conclusiones Los sistemas con conectores lineales mostraron mayor resistencia mecánica en comparación con los sistemas con conectores cuadrados y oblicuos. Todos los sistemas admitían cargas cíclicas que imitan las solicitudes in vivo. Nivel de Evidencia V; Investigación in vitro.

Resumo Objetivo: O objetivo do presente estudo foi comparar, in vitro, a taxa de desgaste do polietileno de alto peso molecular reticulado acoplado a cabeças cerâmicas de 36 mm de diâmetro e acoplado a cabeças metálicas de 32 mm de diâmetro. Métodos: Foram realizados ensaios biomecânicos em simulador de desgaste para os pares tribológicos cerâmica-poli (36 mm) e metal-poli (32 mm) a fim de verificar a taxa de desgaste após em 15 × 106 ciclos. Resultados: Na comparação entre as medidas de taxa de desgaste dos conjuntos com cabeças metálicas (média:14,12 mg/MC) e cerâmicas (média:7,46 mg/MC) houve diferença estatitsticamente significativa (p= 0,0005). Conclusão: O presente estudo demonstrou menor taxa de desgaste em conjuntos protéticos que utilizaram o par tribológico cerâmica-polietileno reticulado de 36 mm em comparação aos conjuntos com metal-polietileno reticulado de 32 mm. Tal achado demonstra a eficácia do par tribológico cerâmica-poli, mesmo com a utilização de cabeças de grande diâmetro.

Abstract Objective This study aims to compare the in vitro wear rate of crosslinked, high molecular weight polyethylene coupled to 36-mm diameter ceramic heads and 32-mm diameter metal heads. Methods Ceramic-on-polyethylene (36 mm) and metal-on-polyethylene (32 mm) tribological pairs were submitted to biomechanical tests in a simulator to determine the wear rate after 15 × 106 cycles. Results A statistically significant difference (p= 0.0005) was detected when comparing the wear rate of assemblies with metallic heads (average wear: 14.12 mg/MC) and ceramic heads (average wear: 7.46 mg/MC). Conclusion The present study demonstrated the lower wear rate in prosthetic assemblies using 36-mm crosslinked ceramic-on-polyethylene tribological pairs compared to 32-mm crosslinked metal-on-polyethylene assemblies. This finding demonstrates the effectiveness of ceramic-on-polyethylene tribological pairs, even with large diameter heads.

Abstract In this study, the preparation of a novel functional material for orthopedic implants using compression molding was investigated. The new functional material is envisioned to avoid inflammatory reactions in vivo after prosthesis implantation. Ibuprofen-loaded UHMWPE samples were prepared in two concentrations (3% and 5%) and samples were characterized in terms of physicochemical and mechanical properties. In addition, the drug-release profile was investigated. The manufacturing process resulted in a homogeneous polymer matrix with homogeneous drug dispersion. The addition of ibuprofen had a minor effect on physicochemical properties but a more significant influence on the mechanical behavior of the specimens was observed. Drug release was demonstrated and overall the results obtained showed a positive outcome with regard to the intended use. The properties analyzed remained within an acceptable range for medical application and the drug-release profile obtained for the material developed shows promise for its use as an anti-inflammatory system.

Resumo O objetivo deste estudo foi comparar a resistência à fadiga de dentes restaurados com uma resina composta bulk fill, resina composta convencional de inserção incremental e dentes hígidos sem preparo. Vinte e oito pré-molares maxilares extraídos foram selecionados e divididos em quatro grupos conforme a resina composta e técnica de inserção: controle (C), resina composta convencional com inserção incremental (I) e resina composta bulk fill inserida em três (BF3) ou único incremento (BF1). O preparo das cavidades foi padronizado para todos os grupos. As amostras foram restauradas e submetidas ao testes de resistência à fadiga com uma frequência de 5 Hz. Foram aplicados 5.000 ciclos de carregamento senoidal inicial com valor de força mínima igual a 50 N e força máxima de 200 N. Após, foram aplicados estágios de 30.000 ciclos de carga com a força máxima sendo aumentada gradativamente a cada estágio, para 400, 600, 800, 1000, 1200 e 1400 N. O ensaio foi finalizado ao ser alcançado 185.000 ciclos de carga (número máximo de ciclos de carga), ou na fratura da amostra. A resistência à fadiga foi registrada para comparação usando a curva de sobrevivência de Kaplan-Meier e analisada pelo teste log-rank a um nível de significância de 0.05. As fraturas foram classificadas conforme a posição da falha - acima ou abaixo da junção cemento esmalte (JCE). A análise estatística da curva de sobrevivência de Kaplan-Meier pelo teste log-rank demonstrou diferença significativa entre os grupos (p=0.001). Na análise de fratura somente 28.58% das falhas foram abaixo da JCE para o grupo C, enquanto para os grupos I, BF1 e BF3 foram 42.85%, 85.71% e 85.71%, respectivamente. Os dentes restaurados com a resina composta bulk fill em ambas as técnicas de inserção apresentaram valores de resistência à fadiga similares àqueles dos dentes restaurados com a resina composta convencional pela técnica incremental. Entretanto, dentes hígidos mostraram uma menor porcentagem de fraturas abaixo da JCE e maior resistência à fadiga.

Abstract The aim of this study was to compare the fatigue resistance of restored teeth with bulk fill composite resin, conventional composite resin with incremental insertion and unprepared sound teeth. Twenty-eight extracted maxillary premolars were selected and divided into 4 groups based on composite resin and insertion technique: control (C), conventional composite resin with incremental insertion (I) and bulk fill composite resin with three (BF3) or single increment (BF1). The restored specimens were submitted to fatigue resistance test with a 5 Hz frequency. An initial application of 5,000 sinusoidal load cycles with a minimum force of 50 N and a maximum force of 200 N was used. Next, were applied stages of 30,000 load cycles with the maximum force increasing gradually: 400, 600, 800, 1000, 1200 and 1400 N. The test was concluded when 185,000 load cycles were achieved or the specimen failed. The fatigue resistance data were recorded for comparison, using the Kaplan-Meier survival curve and analyzed by log-rank test at 0.05 significance. Fractures were classified based on the position of the failure - above or below the cementoenamel junction (CEJ). Statistical analysis of the Kaplan-Meier survival curve and log-rank test showed a significant difference between groups (p=0.001). The fracture analysis demonstrated that only 28.58% of failures were below the CEJ in group C, while for groups I, BF1 and BF3 they were 42.85%, 85.71% and 85.71%, respectively. Teeth restored with composite bulk fill in both techniques present similar fatigue resistance values compared with those restored with a conventional incremental insertion of composite, while the fatigue strength values of unprepared sound teeth were higher. Furthermore, unprepared sound teeth showed a lower percentage of fractures below the CEJ.

Abstract Introduction The method of graft fixation is critical in anterior cruciate ligament (ACL) reconstruction surgery. Success of surgery is totally dependent on the ability of the implant to secure the graft inside the bone tunnel until complete graft integration. The principle of EndoButton is based on the cortical suspension of the graft. The Cross-Pin is based on graft expansion. The aim of this study was to evaluate the biomechanical performance of EndoButton and Bio Cross-Pin to fix the hamstring graft at femoral side of porcine knee joints and evaluate whether they are able to support of loading applied on graft during immediate post-operative tasks. Methods Fourteen ACL reconstructions were carried out in porcine femurs fixing superficial flexor tendons with Titanium EndoButton (n = 7) and with 6 × 50 mm HA/PLLA Bio Cross-Pin (n = 7). A cyclic loading test was applied with 50-250 N of tensile force at 1 Hz for 1000 cycles. The displacement was measured at 20, 100, 500 and 1000 load cycles to quantify the slippage of the graft during the test. Single-cycle load-to-failure test was performed at 50 N/mm to measure fixation strength. Results The laxity during cyclic loading and the displacement to failure during single-cycle test were lower for the Bio Cross-Pin fixation (8.21 ± 1.72 mm) than the EndoButton (11.20 ± 2.00 mm). The Bio Cross-Pin (112.22 ± 21.20 N.mm–1) was significantly stiffer than the EndoButton fixation (60.50 ±10.38 N.mm–1). There was no significant difference between Bio Cross-Pin (failure loading: 758.29 ± 188.05 N; yield loading: 713.67 ± 192.56 N) and EndoButton strength (failure loading: 672.52 ± 66.56 N; yield loading: 599.91 ± 59.64 N). Both are able to support the immediate post-operative loading applied (445 N). Conclusion The results obtained in this experiment indicate that the Bio Cross-Pin technique promote stiffer fixation during cyclic loading as compared with EndoButton. Both techniques are able to support the immediate post-operative loading applied.

Introduction Although there has been significant progress in the design of implants for osteosynthesis, the occurrence of failures in these medical devices are still frequent. These implants are prone to suffer from fretting corrosion due to micromotion that takes place between the screw heads and plate holes. Consequently, fretting corrosion has been the subject of research in order to understand its influence on the structural integrity of osteosynthesis implants. The aim of this paper is to correlate the surface finish characteristics of bone plate-screw systems with fretting corrosion. Methods The surface finish (machined and polished) of five specimens taken from three commercial dynamic compression plates (DCP) were evaluated. For testing, the specimens were fixed with bone screws, immersed in a solution of 0.90% NaCl and subjected to a rocking motion with an amplitude of 1.70 mm and frequency of 1.0 Hz for 1.0 × 106 cycles, according to the ASTM F897 standard. Both, plate and screws were manufactured in Brazil with ASTM F138 stainless steel. Results Flaws on the hole countersink area and on the screw thread of some specimens were identified stereoscopically. At the end of the test all the specimens showed evidence of fretting corrosion with an average metal loss of 4.80 mg/million cycles. Conclusion An inadequate surface finish in some areas of the plates and screws may have favored the incidence of damage to the passive film, accelerating the fretting corrosion at the interfaces between the plate hole countersink and the screw head. Keywords Osteosynthesis, DCP, Bone plate, Screw, Fretting corrosion, Stainless steel.

Introduction The rupture of the anterior cruciate ligament (ACL) is the most common type of knee injury. Reconstructive surgery is the ‘gold standard’ treatment. During the immediate post-operative period, the fixation of the graft is entirely dependent on the ability of the grafted implant to be secured inside the bone tunnel under the cyclical loads associated with daily tasks. Poor fixation can lead to graft slippage, thus impairing the healing and integration of the graft. The aim of this study was to evaluate the biomechanical performance of tendon graft fixation devices with metallic and bioabsorbable interference screws. Methods Twenty ACL reconstructions were carried out in porcine tibias using deep flexor tendons to fix 9 × 20 mm metallic (n=10) and PLLA 70/30 bioabsorbable screws (n=10). To verify the ability of a construct to resist immediate postoperative (PO) rehabilitation protocols for immediate load bearing, a cyclic loading test was applied with 50-250 N of tensile force at 1 Hz for 1000 cycles, and the displacement was measured at 10, 50, 100, 500 and 1000 load cycles to quantify the slippage of the graft during the test. After the cyclic loading test, a single-cycle load-to-failure test was applied. Results The slippage of the graft using metallic screws did not differ (P = 0.616) from that observed when using bioabsorbable screws. Conclusion The results obtained in this experiment indicate that metallic screws may promote a similar amount of graft slippage during low cyclic loading as bioabsorbable screws. Additionally, there was no difference in the biomechanical performance of these two types of screws during high failure loads.

The purpose of this study was to evaluate the influence of buccal and lingual wall thickness on the fatigue resistance of molars restored with CAD/CAM ceramic inlays. Forty human third molars were selected and divided into 4 groups, according to the remaining surrounding wall thickness chosen for inlay preparation (n = 10): G1, 2.0 mm; G2, 1.5 mm; G3, 1.0 mm; G4, 0.5 mm. All inlays were made from feldspathic ceramic blocks by a CAD/CAM system, and cemented adhesively. After 1 week stored in distilled water at 37 °C, the specimens were subjected to fatigue testing under the following protocol: 5Hz; pre-load of 200 N for 5,000 cycles, followed by increasing loads of 400, 600, 800, 1000, 1200 and 1400 N for 30,000 cycles each. The specimens were cycled until failure or completion of 185,000 cycles. The survival rate of the groups was compared using the Kaplan-Meier survival curves (p > 0.05). All specimens withstood the fatigue protocol (185,000 cycles), representing a 100% survival rate. The Kaplan-Meier survival curves showed no difference between groups. It can be concluded that the remaining tooth wall thickness did not influence the fatigue resistance of molars restored with CAD/CAM ceramic inlays.

OBJETIVO: Por ser a articulação mecanicamente mais solicitada de nossa estrutura e pelo grande número de lesões associadas, motivaram a construção de um modelo tridimensional da articulação do joelho humano para simular a cinemática da articulação e obter as solicitações mecânicas nos principais ligamentos durante o movimento de flexão do joelho. Essas informações podem futuramente ser empregada como ferramenta de apoio à decisão médica em ortopedia, fornecendo subsídios na escolha do procedimento cirúrgico. MÉTODOS: Método dos Elementos Finitos foi utilizado para construir um modelo biomecânico, tridimensional, da articulação do joelho. Nesse modelo com seis graus de liberdade é aplicado movimento de flexão/extensão sendo os demais cinco graus de liberdade governados pelas interações entre os componentes da articulares. RESULTADOS: Foram obtidas informações dos movimentos, das rotações interna/externa e adução/abdução, das translações anterior/posterior, lateral/medial e superior/inferior e dos esforços nos quatro principais ligamentos articulares, no decorrer de um amplo movimento de flexão/extensão. Estes valores foram comparados, de forma qualitativa, com valores equivalentes obtidos na literatura. CONCLUSÃO: A análise de resultados permitiu observar que vários aspectos cinemáticos são satisfatoriamente reproduzidos. A pré-carga inicial dos ligamentos e o posicionamento das inserções ligamentares no modelo mostraram-se variáveis relevantes nos resultados.

OBJECTIVE: The knee joint is the part of our structure upon which most mechanical demands are placed and a large number of lesions are associated to it. These factors motivated the construction of a three-dimensional model of the human knee joint in order to simulate joint kinematics and obtain the mechanical demands on the main ligaments during knee flexion movements. METHODS: The finite elements method was used to build a three-dimensional, biomechanical model of the knee joint. In this model with six degrees of freedom, the flexion/extension movement is applied, while the other five degrees of freedom are governed by the interactions between joint components. RESULTS: Data was collected on the movements, on the internal/external and adduction/ abduction rotations, on the anterior/posterior, lateral/medial and upper/lower translations, and on the forces acting upon the four main joint ligaments, during a wide flexion/extension movement. These values were qualitatively compared with comparable values available in the literature. CONCLUSIONS: It was observed through an analysis of the results that several kinematic aspects are satisfactorily reproduced. The initial pre-load of the ligaments and the positioning of the ligament insertions in the model were shown to be relevant variables in the results.