Static tensioning promotes hamstring tendons force relaxation more reliably than cycling tensioning.

BACKGROUND: Graft elongation might be a major reason for increased anterior laxity after anterior cruciate ligament (ACL) reconstruction. This study analyzed the force relaxation values and their stabilization when single strands of the gracilis and semitendinosus tendons underwent cyclic and static tensioning at 2.5% strain level, and compared the efficiency of static and cyclic tensioning in promoting force relaxation. METHODS: Eighteen gracilis tendons and 18 semitendinosus tendons from nine male cadavers (mean age: 22.44years) were subjected to 10 in vitro cyclic loads at 2.5% strain level, or to a static load at 2.5% strain level. RESULTS: During cyclic loading, the reduction in force values tended to stabilize after the sixth cyclic load, while, in the case of static loading, this stabilization occurred by the second minute. Comparing static and cyclic loading, the gracilis tendon had similar mechanical responses in both conditions, while the semitendinosus tendon showed greater force relaxation in static compared with cyclic loading. CONCLUSIONS: Considering that the semitendinosus tendon is the main component of the hamstring graft, its biomechanical response to loading should guide the tensioning protocol. Therefore, static tensioning seems more effective for promoting force relaxation of the semitendinosus tendon than cyclic tensioning. The gracilis tendon showed a similar mechanical response to either tensioning protocols.

Experimental Model for Sutureless Proximal Anastomosis by the Viabahn Open Revascularization TEChnique (VORTEC).

Introduction: In the treatment of complex aneurysms, debranching is an extra-anatomical revascularization of visceral arteries followed by endograft coverage of the thoracoabdominal aorta. It eliminates the need for a thoracotomy and aortic clamping, but requires the performance of several technically demanding visceral anastomosis. In 2008, Lachat described visceral revascularization with the use of a sutureless distal anastomosis, performed by the telescoping of an endograft in the visceral branch, named VORTEC (Viabahn Open Revascularization TEChnique). Objective: An experimental model was created to test the feasibility and short term results of performing a telescoped proximal anastomosis to the abdominal aorta. Methods: Swine model. The abdominal aorta was dissected and ligated between the renal arteries and the iliac vessels. Three centimeters bellow the renal arteries a Viabahn endograft was telescoped for 2 cm into the proximal aorta. The other extremity was conventionally anastomosed to the distal aorta. Patency, sealing and tensile strength of the anastomosis were tested. Results: Time for performing the telescoped anastomosis was shorter (5.4±2.8 min versus 10.3±3.4 min, P<0.05). All grafts were patent and both types of anastomosis presented no bleeding. Immediate tensile strength showed a higher strength of the conventional suture (22.7 x 14.3 N, P<0.09). After 30 days there was no pseudo-aneurysms and the strength of the conventional and VORTEC anastomosis were similar (37.3 x 40.8 N, respectively, P=0.17). Conclusion: Telescoped proximal anastomosis by the technique of VORTEC is feasible. After 30 days the tensile strength of the both anastomosis were similar.

Primary fixation of mini slings: a comparative biomechanical study in vivo.

INTRODUCTION AND OBJECTIVES: The mini sling concept for stress urinary incontinence is an anatomical approach that involves placing a midurethral low-tension tape anchored to the obturator internus muscles bilaterally. They overcome the blind passage of long needles and all the related complications. There are many different devices available and because these are outpatient procedures, primary fixation plays an important role in the outcome. The objective is to evaluate the primary fixation of the various devices of attachment of the commercially available mini-slings through biomechanical tests. MATERIALS AND METHODS: A total of 45 Wistar rats were divided in 3 groups of 15 rats each. They underwent 5 subcutaneous implantation of different mini slings and one polipropilene mesh (control), as follows: TVT-Secur® (Gynecare, USA), Type 1 polypropylene mesh (control); Ophira Mini Sling System ® (Promedon, Argentina), Tissue Fixation System ® (TFS PTY, Australia), Zipper Sling ® and ″T device″ (Prosurg, USA). The abdominal wall was removed on bloc at different times after implant for biomechanical evaluation, which consisted in application of unidirectional force to the extremity of the fixation system or mesh, until it was completely removed from the tissue using a tension meter (Nexygen 3.0 Universal Testing Machine-LLOYD Instruments). The force was measured in Newtons (N). RESULTS: There was significant difference in the resistance to extraction among the different fixation systems. At 7 days the Ophira Mini Sling System ® presented the best fixation and ″T dispositive″ the worst. CONCLUSION: Ophira mini sling System ® presented the best primary fixation at 7°, 14° and 30° days. The impact of this feature in the clinical setting needs to be verified.

Primary fixation of mini slings: a comparative biomechanical study in vivo

INTRODUCTION AND OBJECTIVES: The mini sling concept for stress urinary incontinence is an anatomical approach that involves placing a midurethral low-tension tape anchored to the obturator internus muscles bilaterally. They overcome the blind passage of long needles and all the related complications. There are many different devices available and because these are outpatient procedures, primary fixation plays an important role in the outcome. The objective is to evaluate the primary fixation of the various devices of attachment of the commercially available mini-slings through biomechanical tests. MATERIALS AND METHODS: A total of 45 Wistar rats were divided in 3 groups of 15 rats each. They underwent 5 subcutaneous implantation of different mini slings and one polipropilene mesh (control), as follows: TVT-Secur® (Gynecare, USA), Type 1 polypropylene mesh (control); Ophira Mini Sling System® (Promedon, Argentina), Tissue Fixation System® (TFS PTY, Australia), Zipper Sling® and "T device" (Prosurg, USA). The abdominal wall was removed on bloc at different times after implant for biomechanical evaluation, which consisted in application of unidirectional force to the extremity of the fixation system or mesh, until it was completely removed from the tissue using a tension meter (Nexygen 3.0 Universal Testing Machine - LLOYD Instruments). The force was measured in Newtons (N). RESULTS: There was significant difference in the resistance to extraction among the different fixation systems. At 7 days the Ophira Mini Sling System® presented the best fixation and "T dispositive" the worst. CONCLUSION: Ophira mini sling System® presented the best primary fixation at 7º, 14º and 30º days. The impact of this feature in the clinical setting needs to be verified.

Nitrogen availability, leaf life span and nitrogen conservation mechanisms in leaves of tropical trees

Evergreen species of temperate regions are dominant in low-nutrient soils. This feature is attributed to more efficient mechanisms of nutrient economy. Nevertheless, the cashew (Anacardium occidentale- Anacardiaceae), a deciduous species, is native to regions in Brazil with sandy soil, whilst the annatto (Bixa orellana- Bixaceae), classified as an evergreen species native to tropical America, grows spontaneously in regions with more humid soils. Evergreens contain robust leaves that can resist adverse conditions for longer. The physical aspects of the leaves and mechanisms of nutrient economy between the two species were compared, in order to verify whether the deciduous species had more efficient mechanisms that might explain its occurrence in regions of low soil fertility. The mechanisms of nitrogen economy were also compared for the two species at available concentrations of this nutrient. The following were analysed: (i) leaf life span, (ii) physical leaf characteristics (leaf mass per area, and rupture strain), (iii) nitrogenous compounds (nitrogen, chlorophyll, and protein), (iv) nitrogen conservation mechanisms (nitrogen resorption efficiency, resorption proficiency, and use efficiency), and (v) nitrogen conservation mechanisms under different availability of this mineral. The higher values of leaf mass per area and leaf rupture strain found in A. occidentale were related to its longer leaf life span. A. occidentale showed lower concentrations of nitrogen and protein in the leaves than B. orellana. Under lower nitrogen availability, A. occidentale had higher nitrogen resorption proficiency, nitrogen use efficiency and leaf life span than B. orellana. These characteristics may contribute to the adaptation of this species to sandy soils with low nitrogen content.

Perenifólias de clima temperado são dominantes em solos pouco férteis. Essa característica é atribuída a mecanismos mais eficientes de economia de nutrientes. O cajueiro (Anacardium occidentale - Anacardiaceae), uma espécie decídua, é nativo de região do Brasil com solos arenosos, enquanto que o urucuzeiro (Bixa orellana - Bixaceae), uma perenifólia, nativa da América tropical, é espontâneo em regiões com solo mais úmido e fértil. As perenifólias apresentam folhas robustas, adaptadas a resistir a adversidades por mais tempo. Compararam-se aspectos físicos das folhas e mecanismos de economia de nutrientes entre as duas espécies, a fim de verificar se a espécie decídua apresenta mecanismos mais eficientes, que expliquem sua ocorrência em locais pouco férteis. Foram também comparados os mecanismos de economia de nitrogênio sob disponibilidades diferentes deste nutriente. Foram avaliados: (i) longevidade foliar, (ii) características físicas das folhas (massa por área e tensão de ruptura), (iii) concentração de compostos nitrogenados nas folhas (nitrogênio, clorofila e proteínas), (iv) mecanismos de conservação de nitrogênio (eficiência de reaproveitamento, proficiência de reaproveitamento e eficiência do uso), (v) mecanismos de conservação de nitrogênio sob disponibilidades diferentes deste elemento. A maior longevidade foliar de A. occidentale foi relacionada a valores maiores de massa foliar específica e tensão de ruptura foliar. A. occidentale apresentou menores concentrações de nitrogênio e proteínas. Sob menor disponibilidade de nitrogênio A. occidentale apresentou maiores valores de proficiência de reaproveitamento e eficiência do uso de nitrogênio e maior longevidade foliar. Essas características podem ter contribuído para a adaptação dessa espécie a locais com solos arenosos mais pobres em nitrogênio.

Nitrogen availability, leaf life span and nitrogen conservation mechanisms in leaves of tropical trees

Evergreen species of temperate regions are dominant in low-nutrient soils. This feature is attributed to more efficient mechanisms of nutrient economy. Nevertheless, the cashew (Anacardium occidentale- Anacardiaceae), a deciduous species, is native to regions in Brazil with sandy soil, whilst the annatto (Bixa orellana- Bixaceae), classified as an evergreen species native to tropical America, grows spontaneously in regions with more humid soils. Evergreens contain robust leaves that can resist adverse conditions for longer. The physical aspects of the leaves and mechanisms of nutrient economy between the two species were compared, in order to verify whether the deciduous species had more efficient mechanisms that might explain its occurrence in regions of low soil fertility. The mechanisms of nitrogen economy were also compared for the two species at available concentrations of this nutrient. The following were analysed: (i) leaf life span, (ii) physical leaf characteristics (leaf mass per area, and rupture strain), (iii) nitrogenous compounds (nitrogen, chlorophyll, and protein), (iv) nitrogen conservation mechanisms (nitrogen resorption efficiency, resorption proficiency, and use efficiency), and (v) nitrogen conservation mechanisms under different availability of this mineral. The higher values of leaf mass per area and leaf rupture strain found in A. occidentale were related to its longer leaf life span. A. occidentale showed lower concentrations of nitrogen and protein in the leaves than B. orellana. Under lower nitrogen availability, A. occidentale had higher nitrogen resorption proficiency, nitrogen use efficiency and leaf life span than B. orellana. These characteristics may contribute to the adaptation of this species to sandy soils with low nitrogen content.

Perenifólias de clima temperado são dominantes em solos pouco férteis. Essa característica é atribuída a mecanismos mais eficientes de economia de nutrientes. O cajueiro (Anacardium occidentale - Anacardiaceae), uma espécie decídua, é nativo de região do Brasil com solos arenosos, enquanto que o urucuzeiro (Bixa orellana - Bixaceae), uma perenifólia, nativa da América tropical, é espontâneo em regiões com solo mais úmido e fértil. As perenifólias apresentam folhas robustas, adaptadas a resistir a adversidades por mais tempo. Compararam-se aspectos físicos das folhas e mecanismos de economia de nutrientes entre as duas espécies, a fim de verificar se a espécie decídua apresenta mecanismos mais eficientes, que expliquem sua ocorrência em locais pouco férteis. Foram também comparados os mecanismos de economia de nitrogênio sob disponibilidades diferentes deste nutriente. Foram avaliados: (i) longevidade foliar, (ii) características físicas das folhas (massa por área e tensão de ruptura), (iii) concentração de compostos nitrogenados nas folhas (nitrogênio, clorofila e proteínas), (iv) mecanismos de conservação de nitrogênio (eficiência de reaproveitamento, proficiência de reaproveitamento e eficiência do uso), (v) mecanismos de conservação de nitrogênio sob disponibilidades diferentes deste elemento. A maior longevidade foliar de A. occidentale foi relacionada a valores maiores de massa foliar específica e tensão de ruptura foliar. A. occidentale apresentou menores concentrações de nitrogênio e proteínas. Sob menor disponibilidade de nitrogênio A. occidentale apresentou maiores valores de proficiência de reaproveitamento e eficiência do uso de nitrogênio e maior longevidade foliar. Essas características podem ter contribuído para a adaptação dessa espécie a locais com solos arenosos mais pobres em nitrogênio.

Cyclic-loading of the human gracilis and semitendinosus muscle tendons: study of young adult cadavers.

During knee ligament reconstruction, the tendon graft is tensioned to prevent the occurrence of excessive graft elongation during the postoperative period. Tensioning may be achieved by applying a cyclic or static load to the graft during fixation. Although this procedure is part of the surgery, there is no consensus in international literature regarding ideal tension levels to be used in this procedure. This study was conducted on 10 tendons of the human gracilis muscle and 10 tendons of semitendinosus muscle removed from five male cadavers whose mean age was 20.8 years. These tendons underwent 10 in vitro strain cycles at three levels of deformation (2.5, 3, and 4%) and the value of the deforming load used for each cycle was recorded. The statistical analysis demonstrated that in order to attain the same level of deformation during the 10 cycles there was a reduction in the value of strain applied to the graft, observed at the three levels of deformation. It was concluded that the semitendinosus tendon presents a more uniform mechanical behavior and that there is a need for new graft tensioning protocols that consider the force associated with deformation.

Elongamento do enxerto de tendões do músculo grácial e semitendinoso humanos: estudo realizado em cadáveres de adultos jovens / Graft semitendinosus and gracilis human muscle tendons elongation: a study carried out on young adult human cadavers

Na cirurgia de reconstrução do ligamento cruzado anterior do joelho, os enxertos de tendões autólogos são a principal opção como substitutos ligamentares. Entretanto, uma das razões da falha da reconstrução ligamentar com tecidos moles é o estiramento ou elongamento do enxerto com o tempo. Neste trabalho, foram ensaiados oito tendões do músculo grácil e oito do músculo semitendinoso humanos, obtidos de quatro cadáveres do sexo masculino, com idade média de 24,5 anos. Cada tendão foi submetido a uma deformação relativa constante de 2,5 por cento durante 600 s, com registro contínuo do relaxamento de força. A seguir, o tendão retornava ao seu comprimento inicial e era mantido num período de repouso de 300 s. Após este intervalo, um segundo ensaio, semelhante ao primeiro, era realizado. A velocidade de carregamento empregada foi de 10 por cento do comprimento inicial do corpo de prova por segundo. Foram obtidos valores de força inicial, com 300 s e 600 s nos dois ensaios. A análise estatística sugere um comportamento mecânico mais uniforme para o tendão do músculo semitendinoso quando comparado ao tendão do músculo grácil.