Tomaz Puga Leivas

EXPERIMENTAL DETERMINATION OF BONE CORTEX HOLDING POWER OF ORTHOPEDIC SCREW

Cylindrical specimens of bone measuring 15 mm in diameter were obtained from the lateral cortical layer of 10 pairs of femurs and tibias. A central hole 3.2 mm in diameter was drilled in each specimen. The hole was tapped, and a 4.5 mm cortical bone screw was inserted from the outer surface. The montage was submitted to push-out testing up to a complete strip of the bone threads. The cortical thickness and rupture load were measured, and the shear stress was calculated. The results were grouped according to the bone segment from which the specimen was obtained. The results showed that bone cortex screw holding power is dependent on the bone site. Additionally, the diaphyseal cortical bone tissue is both quantitatively and qualitatively more resistant to screw extraction than the metaphyseal tissue.

Análise comparativa da resistência de fêmures de cães após a confecção de janelas ósseas circular e quadrada

With the purpose of evaluating the weakness caused by holes in the cortical bone, the authors performed circular holes in the diaphysis cortical bone of eight femurs from dog carcasses, and square holes in the diaphysis cortical bone of the contralateral femurs, the diagonals being similar to the diameters. The specimens were submitted to torsion stress test in a mechanical test machine to determine maximum torque and rigidity to torsion. Maximum mean torque for the femurs with circular holes was 13.65 ± 5.12 Nm and mean rigidity was 1.18 ± 0.45 Nm/degree, while the femurs with square holes showed maximum mean torque of 13.39 ± 5.23 Nm and mean rigidity of 1.05 ± 0.41 Nm/degree. The resistance to torsion stress in femurs with circular or square holes was very similar and the statistical analysis did not show a significant difference (p = 0.05).

Análise comparativa das propriedades mecânicas do ligamento da patela e do tendão calcâneo

Traction tests were performed in specimens obtained from 25 human cadavers, with the purpose of comparing the mechanical properties of the patellar ligament and the calcaneus tendon. Age range of donors was 58 ± 14 years (33-85). There were 19 (76%) males and 6 (24%) females; 23 whites (92%) and 2 blacks (8%). The 10-mm central portion of the specimens was tested at a load application rate level of 30 mm/min. The cross-sectional area of the specimens was obtained so that their structural and material properties could be studied. The following variables were studied: ultimate load (N), stress (MPa), elasticity modulus (Mpa), energy (Nm), absolute (mm) and specific strain (%), yield point (N), yield point stress (MPa). Statistical analysis revealed that both the patellar ligament and the calcaneus tendon, the ultimate load, proportionality limits and ultimate stress, were similar (p>0.05). The other variables showed significant differences (p<0.05). Energy and strain values were higher in the calcaneus tendon. The elasticity modulus, significantly higher in the patellar ligament (p< 0.05) was the variable that best characterized the mechanical behavior of both materials.

Estudo mecânico de implante para fixação do segmento lombossacro da coluna vertebral

This work consists of a mechanical analysis of the resistance and critical points of a stainless steel device for lumbossacral spinal fixation. The device was fixed into a wooden model representing the spinal lumbossacral segment. The experiment comprised seven tests of flexo-compression, seven tests of axial rigidity, seven tests of radial rigidity, and one destructive test. The critical points are the intersection of the pedicular screws threads and the attrition rate between the vise and the rod. The results demonstrated the device to be efficient and safe when used in human beings.

Measurement of the concentration and size of aerosol particles and identification of the sources in orthopedic surgeries

In this study, the measurement of the concentration and size of particles and the identification of their sources were carried out at five orthopedic surgeries. The aerosol concentration and particle size distribution, ranging from 0.3 μm–10 μm, were measured and related to the type of indoor activity. The handling of surgical linen and gowns, handling of the patient, use of electrosurgical apparatus, use of a bone saw, handling of equipment, and cleaning of the room were identified as the most important sources of particles, with each of these activities posing different risks to the health of the patients and workers. The results showed that most of the particles were above 0.5 μm and that there was a strong correlation among all particles of sizes above 1 μm. Particles with diameters in the range of 0.3 μm–0.5 μm had a good correlation only with particles in the ranges of 0.5 μm–1.0 μm and 1.0 μm–3.0 μm in three of the surgeries analyzed. Findings led to the conclusion that most of the events responsible for generating aerosol particles in an orthopedic surgery room are brief, intermittent, and highly variable, thus requiring the use of specific instrumentation for their continuous identification and characterization.

Estudo da rigidez do ligamento cruzado anterior do joelho e dos enxertos para sua reconstrução com o ligamento patelar e com os tendões dos músculos semitendíneo e grácil

Com o objetivo de avaliar a rigidez do ligamento cruzado anterior e dos enxertos preparados para sua reconstrucao a partir da porcao central do ligamento patelar e dos tendoes dos musculos semitendineo e gracil duplos, oriundos dos mesmos joelhos, o autor utiliza 20 joelhos de cadaveres humanos, frescos, todos masculinos, com idade media de 32,2 ± 8,9 anos, variando de 17 a 47 anos. As estruturas analisadas foram submetidas a tres ensaios mecânicos de tracao, com intervalos de 10 minutos para recuperacao, em maquina Kratos K-5002 (eletromecânica), com velocidade de 20 mm/min ate atingir 147,15 N (15 kgf), mantendo-as alongadas por um periodo de 15 minutos. Todas as estruturas observadas apresentam um aumento da rigidez aos sucessivos testes realizados, exceto entre o 2o e o 3o teste do ligamento cruzado anterior onde nao apresentou diferenca estatistica. A analise estatistica permite concluir que os ciclos sucessivos dos ensaios mecânicos determinam um aumento da rigidez dos enxertos analisados.

Axial compressive strength of human vertebrae trabecular bones classified as normal, osteopenic and osteoporotic by quantitative ultrasonometry of calcaneus

Abstract : Biomechanical assessment of trabecular bone microarchitecture contributes to the evaluation of Introductionfractures risk associated with osteoporosis and plays a crucial role in planning preventive strategies. One of the most widely clinical technics used for osteoporosis diagnosis by health professionals is bone dual-energy X-ray absorptiometry (DEXA). However, doubts about its accuracy motivate the introduction of congruent technical analysis such as calcaneal ultrasonometry (Quantitative Ultrasonometry - QUS). Methods: Correlations between Bone Quality Index (BQI), determined by calcaneal ultrasonometry of thirty (30) individuals classified as normal, osteopenic and osteoporotic, and elastic modulus (E) and ultimate compressive strength (UCS) from axial compression tests of ninety (90) proof bodies from human vertebrae trabecular bone, which were extracted from cadavers in the twelfth thoracic region (T 12 ), first and fourth lumbar (L 1 and L 4 ). Results: Analysis of variance (ANOVA) showed significant differences for E (p = 0.001), for UCS (p = 0.0001) and BQI. Spearman’s rank correlation coefficient (rho) between BQI and E (r = 0.499) and BQI and UCS (r = 0.508) were moderate.

Análise comparativa das alterações nos fluxos de tensão do joelho nas próteses totais e unicompartimentais cimentadas: estudo experimental em dez cadáveres humanos

Load transfer changes on cemented total and unicompartmental knee prosthesis. Experimental study on ten human cadavers. The authors compare the load transfer changes on the distal femur and proximal tibia due to cemented total and unicompartmental knee prosthesis under compressive load-bearing on ten human cadavers employing strain gauges and a Kratos 5002 stress-testing system. The conclusions were: 1) The Total knee prosthesis does not alter the load transfer on the distal femur; 2) The unicompartmental knee prosthesis increases the compression load on the femoral medial cortex and increases the strain tension loads on the femoral lateral cortex; 3) The tibial components (partial medial and total) increase the compression strain tension on the postero-medial cortex of the tibia.