Carlos Alberto Moro

Mechanical resistance of peripheral nerve repair with biological glue and with conventional suture at different postoperative times.

Regardless of its type, the repair of a peripheral nerve must ideally permit early motion of the affected limb and resist disruption by the tensile forces generated throughout the healing process and regeneration. A comparative study of the mechanical resistance of the repair of the sciatic nerve with biological glue and conventional microsurgical suture over time was undertaken in 48 rats. Both right and left sciatic nerves were exposed simultaneously and repaired at random with the glue on one side and conventional suture on the opposite side. Mechanical resistance of the repair was evaluated in situ with a universal testing machine using a hooklike accessory applied proximally to the repair site, immediately and at 7, 14, and 28 days postoperatively. A load was applied at the rate of 2 mm/min till rupture. The resistance of both types of repair significantly increased up to day 14 ( P < 0.001), and the repair with the glue was significantly less resistant than repair with conventional suture immediately postoperatively ( P < 0.001) and on day 7 ( P = 0.03). Resistance became equivalent for the two types of repair on days 14 ( P = 0.67) and 28 ( P = 0.34). The change in resistance of both types of repair with time was in accordance with the power function numeric formula.

Uma nova pinça regulável para a produção de lesões por esmagamento do nervo ciático do rato

Objective: A new adjustable pinch has been developed for producing a crush injury, with a previously known load of 5 kg, on a 5 mm-long segment of the nerve. Methods: Stainless steel was the material selected for building the pinch due its durability and possibility of sterilization with anti-septic substances, which are often corrosive. The crushing load of the pinch is adjustable by increasing or decreasing the tension of the spring by means of a screw used for calibration, which is performed by a load cell. Result: This pinch has been used in a few experimental investigations and was shown to be as efficient as both the universal testing machine and the dead weight machine, previously used. Conclusion: The developed pinch has the advantages of being portable and user-friendly. In addition, the pinch is cheap and allows for the standardization of the applied load.

Estabilização primária da diáfise umeral: estudo experimental de diferentes métodos de osteossíntese

OBJECTIVE: The purpose of this study was to assess primary stabilization of humeral shaft fractures using three different methods of fixation, represented by a DCP type plate, applied as a bridge plate, an uncommon synthesis material named SPS®, not previously described in literature and also used as a bridge plate, and a third type of material constituted by an intramedullary nail, with an uncommon locking provided by a distal cortical screw and a proximal Ender-type wire. MATERIAL AND METHOD: Twenty-one pairs of human humeri were divided into three groups, each using one type of material for fixation, the bones of which were osteotomized, stabilized and submitted to nondestructive flexion-compression and torsion assays up to 200 N and 100 N respectively, and, in a crossing mechanism, the groups were again submitted to other torsion and flexion-compression assays, supported by statistical analysis. RESULTS: The bridge-DCP group showed good resistance to the applied forces, similarly to the SPS® group, which, although presenting greater deflection, showed great elastic capacity. The intramedullary nail group showed good results in the flexion-compression assay due to the tutor mechanism of the intramedullary nails, but did not show resistance to the torsion forces.

Tension band wire fixation for valgus osteotomies of the proximal femur: A biomechanical study of three configurations of fixation

BACKGROUND A variety of techniques can be used to achieve stabilization of femoral valgus osteotomies in children, but what is lacking is a versatile fixation system that associates stability and versatility at different ages and for different degrees of deformity. METHODS Mechanical tests of three configurations used to fix femoral valgus osteotomies, based on the tension band wire principle, were carried out. A 30 degrees wedge valgus osteotomy was performed at the subtrochanteric level in 60 swine femurs and fixed with three different systems. In Group 1, two Kirschner wires (K wire) were introduced from the tip of the greater trochanter to the medial cortex, crossing the osteotomy. A flexible steel wire was anchored to the K wires into holes in the lateral cortex and tightened to form a tension band. The same setup was used in Group 2, but two additional smooth K wires were inserted into the lateral surface of the greater trochanter and driven to the femoral head with the distal extremities bent and tied around the bone shaft. In Group 3, the fixation was similar to that in Group 2, but the ascending K wires were introduced below the osteotomy level, crossing the osteotomy. Mechanical tests in bending-compression and torsion were used to access the stability. FINDINGS The torsional relative stiffness was 116% greater for Group 3 (0.27 Nm/degree) and no significant difference was found between Group 1 (0.10Nm/degree) and Group 2 (0.12 Nm/degree). The average torque was 103% higher for Group 3 (1.86 Nm). Stiffness in bending-compression was significantly higher in Group 3 (508 x 10(3) N/m) than in Group 1 (211 x 10(3) N/m) and Group 2 (219 x 10(3) N/m). INTERPRETATION Fixation as used in Group 3 was significantly more stable, both in torsion and bending-compression tests, than the other two techniques.

Torsional force applied to the tibia of living lambs in an attempt to change the bone rotational axis

PURPOSE To evaluate the effects of torsional force on the rotational axis of living lamb tibias. METHODS An external fixator device was designed to apply rotation to the tibias of lambs. Once a week, the bone distal extremity was rotated 2º. After achieving ~20º of internal rotation, the turning was discontinued and the device was maintained in situ for one month and euthanasia occurred in group A (n=10) after this. In group B (n=9) euthanasia occurred three months after removing the device. Computed tomography scans evaluated the rotational angle; dual-energy X-ray absorptiometry assessed the bone mineral density, and conventional and polarized light microscopy studied the bone microstructure. RESULTS In group A, the mean angle of the external rotation in the control tibias was 24º and 8º in the twisted tibias (p<0.0001); in group B, the angle was 23º (control) and 7º (twisted, p<0.0001), with no differences between groups A and B (p=0.9567). The BMD increased in the twisted tibias in group A (p<0.0001) and in group B (p=0.0023), with no between-group differences (p>0.05). Microscopically, the twisted tibias showed asymmetrical subperiosteal bone deposition on the lateral cortex surface. CONCLUSION Gradual torsion applied to the immature tibia significantly modified its rotational axis.

Desenvolvimento e desempenho de um fixador flexível na consolidação de fraturas diafisárias transversais provocadas iatrogênicamente na tíbia de carneiros

An experimental study was carried out to verify the development and performance of a flexible external fixator on the bone healing process of the tibia of sheep submitted to a transverse diaphyseal osteotomy. It was used twenty Santa Ines sheep with average weigh of 37kg divided in groups, according to the period of postoperative observation of 30, 45, 60 and 90 days. At the end, the animals were sacrificed and the tibiae were removed for study of transverse callus volumetric by computed tomography and destructive mechanical testing. The results had shown that the formation of voluminous callus occurred, thus characterizing the occurrence of displacement of axial load to the focus of the osteotomy, promoted by the used external fixator used. The mechanical testing showed that the comparisons between the respective intact and operated groups were significantly different (P<0.05) except for the group with 90 days, which demonstrated equivalent stiffness when compared to normal bone. In none of the animals there was development of pseudarthrosis or non-union of the bone. Given the results, it was conclude that the use of the flexible fixator covered in this research for treatment of long bones fractures in medium animals was easy to apply, reproducible and recommended.