Miroslav Sochor

Gradient of contact stress in normal and dysplastic human hips

The stress gradient index (G(p)) is introduced for the assessment of dysplasia in human hip joint. The absolute value of G(p) is equal to the magnitude of the gradient of the contact stress at the lateral acetabular rim. The parameter G(p) normalized with respect to the body weight (W(B)) is determined from the standard anteroposterior radiographs of adult human hips and pelvises using the mathematical model. The average value of G(p)/W(B) was determined for the group of dysplastic hips and for the group of normal hips. In the group of normal hips the average value of G(p)/W(B) is smaller (-0.445x10(5) m(-3)) than in the group of dysplastic hips (+1.481x10(5) m(-3)). The difference is statistically significant P<0.001. The average value of G(p)/W(B) changes its sign at the value of the centre-edge angle theta(CE) approximately 20( composite function ) which is usually considered as the boundary value of theta(CE) (lower limit) for the normal hips. Accordingly we suggest a new definition for the hip dysplasia with respect to the size and sign of the normalized stress gradient index G(p)/W(B). The hips with positive G(p)/W(B) are considered to be dysplastic while the hips with negative G(p)/W(B) are considered to be normal. The statistically significant correlation between the value of the Harris hip score, used in the clinical assessment of the hip dysplasia, and the normalized stress gradient index was found.

Contact stress in hips with osteonecrosis of the femoral head

Contact stress distribution in the articular surface of the hip is considered a factor in the development of osteoarthritis, a common complication in hips with aseptic necrosis of the femoral head. We present evidence supporting the hypothesis that osteoarthritis in hips with aseptic necrosis of the femoral head can be caused by elevated contact stress related to the reduced load-bearing ability of the necrotic bone. By using a previously validated mathematical model, we observed that hip contact stress may increase considerably if the load-bearing capacity of the necrotic lesion is decreased, if the size of the necrotic segment is increased, and if the necrotic segment is located more laterally. These effects are affected by the intrinsic shape of the hip. As the estimated values of stress in hips with osteonecrosis are in the range obtained by the same method in dysplastic hips, osteoarthritis in hips with osteonecrosis can be caused by elevated contact stress.

Hypothesis of regulation of hip joint cartilage activity by mechanical loading.

Hypothesis of regulation of proteosynthetic activity of chondrocytes is suggested. A deformation of the cartilage caused by contact hip joint stress and consequent deformation of the chondrocytes are considered as main factors that could influence the metabolism of the cartilage.

Optimizing and evaluating the biocompatibility of fiber composites with calcium phosphate additives.

SummaryComposite materials based on a polyamide fabric (aramid) and a polydymethylsiloxane (PDMS) matrix were designed for application in bone surgery. In order to increase the bioactivity, 2, 5, 10, 15, 20, and 25 vol.% of nano/micro hydroxyapatite (HA) and tricalcium phosphate (TCP) were added. We studied the effect of the additives on the biocompatibility of the composite. It appears that nano additives have a more favorable effect on mechanical properties than microparticles. 15 vol.% of nano hydroxyapatite additive is an optimum amount for final application of the composites as substitutes for bone tissue: in this case both the mechanical properties and the biological properties are optimized without distinct changes in the inner structure of the composite.

Characterization of the Interphase in Carbon Fiber Reinforced Polymeric Composite by a Modulus Mapping Test

The effect of sterilization on the structural integrity of the polydimethylsiloxane (PDMS) matrix composite reinforced with carbon fibers (CF) is investigated by nanoindentation test. We present the investigation of the influence of sterilization processes on fiber/matrix interphase properties. The effect of multiple widely-used steam sterilization processes on fibers/matrix interphase region properties was studied by modulus mapping test.

Effect of Sterilization Processes on the Fiber/Matrix Interphase Properties of CF/PDMS Composite to be Used in Orthopaedics

In this study we present the investigation of the influence of multiple sterilization processes on micromechanical properties carried out on a composite based on carbon fibers (CF) and polymer matrix composite polydimethylsiloxane (PDMS). The effect of widely-used steam sterilization process on fibers/matrix interphase region properties was studied by nanoindentation.

The influence of sterilisation processes on the micromechanical properties of polyamide fibre-reinforced PDMS composites for orthopaedic applications

fibre-reinforced PDMS composites for orthopaedic applications R. Sedláček*, T. Suchý, Z. Sucharda, K. Balı́k, M. Sochor, J. Šepitka and J. Lukeš Department of Mechanics, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Czech Technical University in Prague, Technická 4, 166 07 Prague 6, Czech Republic; Department of Composite and Carbon Materials, Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, v.v.i, V Holešovickách 41, Prague 8, Czech Republic

Comparison of Nanofiber and Particle Form of GELATINE/HA Biocomposites

This report is about composites used for bone grafting. Targets the composites compact of organic chemical compounds (biopolymers) and anorganic chemical compounds (nanoparticles). These composites must be, among others, biocompatible, nontoxic for organism and their mechanical properties must be near to mechanical properties of bone. This report focused on biodegradable composites based on gelatine and nanopowder of hydroxyapatite in nanofiber and particle form.