José Ricardo Lenzi Mariolani

Impact Project: Searching for Solution to the Underride Problem

Rear underride crashes kill thousands of people yearly worldwide. Underride guards did not follow the progress achieved by the automotive safety technology. Searching for solutions to this problem, two new guards have been designed and three crash tests carried out. A new articulated, an energy absorbing conceptual guard and a guard constructed according to the European (ECE-R58) regulation were tested. Both the new guards could avoid underride, the ECE-R58 one could not. The tests showed that the new articulated guard could be used after a few modifications and the conceptual one needs further optimization to become commercially feasible. (A) For the covering abstract of the conference see ITRD E203705.

QUANTITATIVE EVALUATION OF EXPERIMENTAL BONE REGENERATION USING INDENTATION TESTS

ABSTRACT Objectives: To determine whether the macroindentation test can be applied to quantitatively assess bone regeneration. Methods: A 3.2 mm diameter transverse monocortical defect was created on the medial aspect of both proximal metaphyses of the tibia of male Unib-WH rats. For the macroindentation tests, we used 5.00 mm diameter indenters with a 3.2 mm tip. Defect testing was performed 1 to 12 weeks following the surgical procedures to compare the hardness of the newly developed tissue over the 12-week study period. Additional histological, morphological and physical/chemical data were obtained by optical and electronic microscopy, Raman, and energy dispersive x-ray spectrometry (EDS). Results: The mean indentation forces increased in a time-dependent manner from 4 to 12 weeks (p<0.001). Tests performed with the 5.0 mm diameter tip were not able to measure the indentation forces in the first week after the procedure. Moreover, in the second postoperative week indentation forces and the newly formed tissue within the spinal canal were greater than those measured in the fourth and eighth weeks. Conclusions: The macroindentation test can be used to quantitatively assess bone regeneration in experimental studies. The choice of indenter tip diameter should consider the study design. Level of Evidence II, Diagnostic Studies.

Treatment of Humeral Shaft Fractures: a prospective, observational study

Despite Humeral Shaft Fractures represent a serious cause of mortality and morbidity, there are few data describing the most common treatment practices and their outcomes in Latin America. A prospective, observational multicenter study has been created to address this critical knowledge gap. This study, focused on the treatment options for humeral shaft fracture, presents the preliminary results from a single center ́s perspective.

Comparing the In Vitro Stiffness of Straight-DCP, Wave-DCP, and LCP Bone Plates for Femoral Osteosynthesis

The objective of this study was to compare the Locking Compression Plate (LCP) with the more cost-effective straight-dynamic compression plate (DCP) and wave-DCPs by testing in vitro the effects of plate stiffness on different types of diaphyseal femur fractures (A, B, and C, according to AO classification). The bending structural stiffness of each plate was obtained from four-point bending tests according to ASTM F382-99(2008). The plate systems were tested by applying compression/bending in different osteosynthesis simulation models using wooden rods to simulate the fractured bone fragments. Kruskal-Wallis test showed no significant difference in the bending structural stiffness between the three plate models. Rank-transformed two-way ANOVA showed significant influence of plate type, fracture type, and interaction plate versus fracture on the stiffness of the montages. The straight-DCP produced the most stable model for types B and C fractures, which makes its use advantageous for complex nonosteoporotic fractures that require minimizing focal mobility, whereas no difference was found for type A fracture. Our results indicated that DCPs, in straight or wave form, can provide adequate biomechanical properties for fixing diaphyseal femoral fractures in cases where more modern osteosynthesis systems are cost restrictive.

Mechanotransduction and Osteogenesis

It is well known that mechanical stimulation induces osteogenesis. Consciously or not, everyday we use mechanical loading to incite osteogenesis: normal daily activities like walking, or physical activities like gymnastics. It is easy to comprehend how biochemical factors (for example, hormones) activate biological reactions (for example, bone formation). In opposite, it is not simple to understand how mechanical forces cause biological reactions. The aim of this chapter is to describe the current knowledge about how bone cells react to mechanical stimuli, and what bone cells have to sense mechanical forces. According to Wolff’s Law, mechanical loads determine changes in bone structure (Duncan & Turner). In 1964, Frost proposed the mechanostat model, which is an upgrade of Wolff’s Law. Within this model, relative deformations of bone are sensed by bone cells, which, in turn, produce or resorb bone tissue. The relative deformation, or strain, represents the ratio between the lengthening or shortening of a body and its original length. Strain is dimensionless and can be expressed as decimal fraction, percentage or μstrain. For example, the strain of an 1 mm long body that – under action of an external load – lengthens or shortens 0.001 mm, is equal to 0.001 or 0.1% or 1000 μstrain. Deformations below 50-100 μstrain are in the disuse range, and result in bone resorption. Deformations between the ranges of 50-100 to 1000-1500 μstrain are in the physiological range. Physiological deformation can produce microfractures that are repaired; however, bone mass does not alter although the activation of osteogenesis. Deformations between the ranges of 1000-1500 to 3000 μstrain are in the overuse range, and produce microfractures, which are also repaired. Interestingly, in this case bone mass increases. There is no knowledge on how bone cells distinguish physiological and overuse deformations. Deformations above 3000 μstrain are in the pathological overuse range, and produce a number of microfractures that exceed bone repair capacity. As a result, microfractures accumulate, coalesce and weaken bone, ending in stress fractures (or fatigue fractures). Macroscopic fractures occur when relative deformation is over 25000 μstrain (Fig. 1) (Burr et al., 1998; Carter & Hayes, 1977; Frost, 2000, 2003; O’brien et al., 2005). In conclusion, the role of mechanostat is to avoid mechanical deformations above 3000 μstrain, which may cause bone fracture. Further, in addition to Frost’s mechanostat model, it was realized that mechanostat can sense other physical parameters not only relative deformation: frequency, number of cycles resting periods, relative deformation distribution and local gradients of relative deformation (Torcasio et al., 2008). Relative deformation, frequency, number of cycles and resting periods