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.

Highly purified collagen coating enhances tissue adherence and integration properties of monofilament polypropylene meshes.

INTRODUCTION AND HYPOTHESIS: Complications related to tissue integration of polypropylene implants used in the treatment of pelvic organ prolapse are relatively prevalent. Collagen, a biocompatible, less immunogenic material with modulating properties on the inflammatory process, may improve polypropylene integration. The objective was to study biomechanical and histological effects of monofilament polypropylene mesh coated with purified collagen gel. METHODS: Forty rats were implanted with two fragments of polypropylene mesh in their abdominal walls (one on each side of the linea alba). One of the fragments had a collagen gel coating (group I) while the other one did not (group II). The animals were euthanized at 7, 14, 90, and 180 days after implantation and their abdominal walls were excised for analysis. RESULTS: The biomechanical study showed that mesh adherence to neighboring tissue increased significantly in group II (p < 0.05). Acute (p < 0.001) and chronic (p = 0.004) inflammatory responses as well as granulation tissue formation (p = 0.001) were less intense in group II at 7 and 14 days. Granulomatous inflammation and foreign body reaction was less significant at 7 days in group II (p = 0.029 and p < 0.001). The birefringence analysis showed higher mean brightness density in the late phase of implantation in group II meshes (p = 0.000). CONCLUSION: Polypropylene mesh coated with purified collagen gel increases adherence to tissue, promotes a less intense and lasting inflammatory response and triggers a greater organization and packing arrangement of collagen fibers in the late phase of implantation.

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.