The Morse taper junction in modular revision hip replacement--a biomechanical and retrieval analysis.

All biomaterials used for total joint surgery are subjected to wear mechanisms. Morse taper junctions of modular hip revision implants are predilection sites for both fretting and crevice corrosion, dissociation and breakage of the components. The aim of this study is to quantify wear and study metallurgical changes of Morse taper junctions of in-vitro and in-vivo loaded modular revision stems. Three modular revision stems (MRP-Titan, Peter Brehm GmbH, Germany) were loaded by a servohydraulic testing machine. The loads and conditions used exceeded by far the values required by ISO-standard 7206. The tests were performed with maximum axial loads of 3,500 N to 4,000 N over 10-12 x 10(6) cycles at 2 Hz. Additionally, the female part of the taper junctions were coated with blood and bone debris. The free length of the implant was set to 200 mm. One other MRP stem was investigated after retrieval following 5.5 years of in-vivo use. All contact surfaces of the modular elements were assessed by visual inspection, optical microscopy and scanning electron microscopy (SEM). The degree of plastic deformation of the male part of the morse taper junction was determined by contouroscopy. None of the morse taper junctions broke or failed mechanically. Corrosion and wear affected all tapers, especially at the medial side. The retrieved implant showed no cracks and the amount of debris measured only one third of that for the stems tested in-vitro. The present retrieval and laboratory investigations have proven, that the morse taper junctions of the MRP-titanium stem are stable and resistant to relevant wear mechanisms. The longevity of the junctions for clinical use is given. If an optimal taper design is selected, the advantages of modular femoral components in total hip revision arthroplasty will outweigh the possible risks.     

The bending rod prosthesis: an experimental approach to metaphyseal hip arthroplasty]

The aim of our study was to develop a femoral component for total hip arthroplasty that would exclusively anchor in the metaphysis of the femoral neck. To forego trochanteric fixation, the load needs to be transferred to the metaphysis at as many points as possible. A computer simulation model suggested that an implant with a central cylinder and 16 rods aligned along a thread would be the preferable solution. To evaluate primary implantation stability, 14 fresh frozen cadaver femora were used. A special instrument set was developed to allow for centered implantation of the prosthesis without the need to dissect the greater trochanter. For our tests, we used two prototype implants: one made from titanium and the other from a CoCrMo alloy. For the measurement of micromotions at the medial proximal femur, sinusoid dynamic loading with a force between 300 N and 1700 N and a frequency of 1 Hz was employed. In a neutral position of 16 degrees adduction and 9 degrees antetorsion, the average micromotions measured were 119 microm. Despite these convincing in vitro results with regards to primary stability, circular cut-out of the implant, followed by aseptic osteonecrosis, loosening might still occur in a clinical situation. Animal experiments are therefore required to further evaluate this new implant design.     

A comparison of forefoot stiffness in running and running shoe bending stiffness

This study characterizes the stiffness of the human forefoot during running. The forefoot stiffness, defined as the ratio of ground reaction moment to angular deflection of the metatarsophalangeal joint, is measured for subjects running barefoot. The joint deflection is obtained from video data, while the ground reaction moment is obtained from force plate and video data. The experiments show that during push-off, the forefoot stiffness rises sharply and then decreases steadily, showing that the forefoot behaves not as a simple spring, but rather as an active mechanism that exhibits a highly time-dependent stiffness. The forefoot stiffness is compared with the bending stiffness of running shoes. For each of four shoes tested, the shoe stiffness is relatively constant and generally much lower than the mean human forefoot stiffness. Since forefoot stiffness and shoe bending stiffness act in parallel (i.e., are additive), the total forefoot stiffness of the shod foot is dominated by that of the human foot.     

Possibilities of avoiding an intra-femoral increase in pressure during hip revision surgery]

An earlier experimental study carried out by us revealed an increase in intrafemoral pressure during removal of cement in hip revision arthroplasty. This increase is greater while removing cement from the distal femoral shaft. Maximum pressure increases occurred while removing the medullary plug (cement stopper), and the measured pressure of more than 150 mmHg is associated with an increased risk of fat embolism. The present study shows that this phenomenon can be avoided through the use of cannulated instruments.     

A comparative study of the characteristics of femoral hip prosthesis heads--study and results ceramic-coated hip joint heads of titanium]

Today, only hard/soft cup and femoral head combinations are employed for hip joint prostheses. Highly polished ceramic is a material with very good tribological properties for femoral heads, being highly resistant to mechanical wear and tear, and highly resistant to chemical reactions in the biological environment. The advantage of metal heads, in contrast, undoubtedly lies in their resistance to breakage and the ease with which their geometry can be modified with respect, for example, to antirotation angle and neck length. The ideal material for femoral heads is a combination of the two materials. The new multi-layer combination of titanium-niobium oxide/nitride ceramic coating applied to a prehardened titanium head combines the positive material properties in an ideal manner. Femoral heads made of CoCrMo, oxide-hardened titanium, aluminium oxide or multilayer titanium-niobium ceramic were compared by means of friction an wear and tear tests. The TiNb-ceramic-metal heads showed similar abrasion at the surface as the ceramic heads. At the high loads of more than 400 kp, which may also be reached under physiological conditions, the specially coated titanium-ceramic heads proved to be superior in terms of resistance to fracture and tribological properties.     

Binding of tropomyosin-troponin to actin increases filament bending stiffness

Rheologic measurements show that the association of tropomyosin-troponin with actin filaments is responsible for the reduction of the internal chain dynamic and increase in the mechanical rigidity of actin filaments. Basing calculations on the linear relation between the plateau modulus, G(N)('), and bending modulus, kappa, I find that tropomyosin-troponin at r(AT) = 7 increases actin filament stiffness by approximately 50%. This is confirmed by dynamic light scattering. Further increases are observed at rising F-actin and constant tropomyosin-troponin concentrations. Tropomyosin-troponin also delays actin assembly and subsequent network formation and increases filament stiffness over time.     

In vivo measurement of bending stiffness in fracture healing

Background  

Measurement of the bending stiffness a healing fracture represents a valid variable in the assessment of fracture healing. However, currently available methods typically have high measurement errors, even for mild pin loosening. Furthermore, these methods cannot provide actual values of bending stiffness, which precludes comparisons among individual fractures. Thus, even today, little information is available with regards to the fracture healing pattern with respect to actual values of bending stiffness. Our goals were, therefore: to develop a measurement device that would allow accurate and sensitive measurement of bending stiffness, even in the presence of mild pin loosening; to describe the course of healing in individual fractures; and help to evaluate whether the individual pattern of bending stiffness can be predicted at an early stage of healing.     

Investigation of explanted hip and acetabulum hip prostheses]

Retrieved ceramic femoral heads and acetabular cups were investigated. On the basis of the case studies, the reasons for revision are discussed. Wear patterns and wear rates were found to differ from those observed in hip simulating testing. Monolithic ceramic cups showed a high wear rate. Owing to their limited range of motion, ceramic "mushroom heads" are associated with impingement that leads to a high risk of cup loosening, high wear rates and in vivo fractures. The combination of ceramic "mushroom heads" and cups is not recommended. An evaluation of complications shows that some can be explained by patient behaviour--e.g. Japanese sitting position, horse riding. Designers need to develop new concepts offering a larger range of motion, for example, with head diameters of 32 and 36 mm that reduce the risk of impingement, subluxation and dislocation, while increasing the range of motion. The potential of ceramic/ceramic coupling has been known since the 70s, and ceramic concepts for total hip replacement are currently experiencing a renaissance, although further developments are still possible.     

The diagnostic value of digital subtraction arthrography and radionuclide arthrography in revision total hip arthroplasty.

An analysis of plain radiographs, digital subtraction arthrography, and radionuclide arthrography was performed in 25 revision hip arthroplasties to evaluate the efficacy and usefulness of these methods in the diagnosis of loosening. The findings by each method were compared with intraoperative assessment of the status of components and expressed in terms of sensitivity, specificity, and predictive accuracy. Overall accuracy for the acetabular component by plain radiographs was 80%; by digital subtraction arthrography, 88%; by radionuclide arthrography, 68%. Overall accuracy for the femoral component by plain radiographs was 92%; by digital subtraction arthrography, 84%; radionuclide arthrography, 76%. We consider subtraction arthrography and radionuclide arthrography to be adjuvant diagnostic tools which may be indicated in individual cases of suspected implant loosening of total hip arthroplasty. The routine use of these two methods is not warranted when compared to plain radiographs.     

The effect of matrix stiffness on the chondrogenic differentiation of mesenchymal stem cells

Journal of Molecular Histology - Articular cartilage is one of the most important weight-bearing components in human body, thus the chondrogenesis of stem cells is reactive to many intracellular...     

Effect of salicylate on the elasticity, bending stiffness, and strength of SOPC membranes

Salicylate is a small amphiphilic molecule which has diverse effects on membranes and membrane-mediated processes. We have utilized micropipette aspiration of giant unilamellar vesicles to determine salicylate's effects on lecithin membrane elasticity, bending rigidity, and strength. Salicylate effectively reduces the apparent area compressibility modulus and bending modulus of membranes in a dose-dependent manner at concentrations above 1 mM, but does not greatly alter the actual elastic compressibility modulus at the maximal tested concentration of 10 mM. The effect of salicylate on membrane strength was investigated using dynamic tension spectroscopy, which revealed that salicylate increases the frequency of spontaneous defect formation and lowers the energy barrier for unstable hole formation. The mechanical and dynamic tension experiments are consistent and support a picture in which salicylate disrupts membrane stability by decreasing membrane stiffness and membrane thickness. The tension-dependent partitioning of salicylate was utilized to calculate the molecular volume of salicylate in the membrane. The free energy of transfer for salicylate insertion into the membrane and the corresponding partition coefficient were also estimated, and indicated favorable salicylate-membrane interactions. The mechanical changes induced by salicylate may affect several biological processes, especially those associated with membrane curvature and permeability.     

Complementary patterns of stiffness in stem and leaf sheaths of Triticale

The variation in the stiffness of stem and leaf sheaths along the shoot axis of Triticale (Triticosecale W., cv. Jago) was examined, using an ultrasonic method, at two stages of development, (i) at the stage of high stem mechanical instability when upper internodes are forming (heading), and (ii) at milk maturity when development of strengthening tissues is completed (three weeks after anthesis). The squared velocity of low-frequency longitudinal pulse waves was used as a measure of the specific modulus of elasticity, averaged over the whole cross section of the structures and related to the unit density of the material. Structural material of varying effective stiffness was found to be utilized along leaf sheaths with a pattern complementary to that in growing stems. The stiffness increased basipetally along leaf sheaths in the direction of increasing flexibility of internodes. Maximum values of the specific modulus of elasticity in particular leaf sheaths were enhanced acropetally, ensuring the stronger mechanical protection of those meristematic zones which were actively elongating and were located at the upper internodes. The stiffest material present in leaf sheaths covered only those stem sections which could be the most critical for plant safety during stem elongation. This characteristic and very regular pattern of stiffness alteration along the shoot axis was structurally determined as it remained similar after air drying the specimens. It is concluded that adaptation of cereals to withstand environmental loads is realized not only on morphological and anatomical levels but is also reflected in a specific heterogeneity in the material properties of the cell walls which support the plant.This research was supported by the Ministry of Agriculture, Poland (Project CPBR 10.1 C 29).     

Analysis of the bending behaviour of porcine xenograft leaflets and of neutral aortic valve material: bending stiffness, neutral axis and shear measurements

Flexibility of the materials used in the construction of bioprosthetic heart valves is essential for proper valve operation. We therefore examined the bending behaviour of glutaraldehyde treated porcine aortic valve cusps in comparison with fresh aortic valve tissue. We repeatedly bent a total of 35 strips of fresh and treated tissue to curvatures ranging from 0.2 to 2.2 mm-1. We compared the stiffness of the two materials between circumferential and radial bending, natural and reverse curvatures and constant or variable tensile stress (0.8-40 kPa). Our results showed a weak positive relationship between bending stiffness and applied tensile stress and a strong positive dependance of stiffness on tissue thickness (t). For the fresh tissue, the bending stiffness increased in proportion to t1.14 while for the glutaraldehyde treated tissue it increased with t2.18. Fourteen strips of fresh and treated tissue were also histologically processed, sectioned and examined with polarized light microscopy. Collagen fiber wavelengths and shear deformations were measured utilizing the tissue banding patterns produced by polarized light microscopy. The neutral axis of bending was found to lie very close to the outer surface of the tissue, suggesting that aortic leaflets have a very low compressive elastic modulus. The shear strains measured in fresh tissue were 10 +/- 2.7% vs 3 +/- 4.4% for the treated, indicating a stiffening of the tissue following glutaraldehyde fixation. We conclude that both natural and bioprosthetic valve cusps have a complex flexural behaviour that cannot be modeled using simple bending principles, although the bioprosthetic material more closely approximates the simple beam than does the fresh. The non-linear elastic modulus, high compressibility and shearing between fiber layers are likely responsible for the observed behaviour of the fresh tissue, while the cross-linking and dehydrating effects of glutaraldehyde are believed to be responsible for the alteration in bending properties observed in the treated tissue. Our study suggests that bioprosthetic valve material does not adequately mimic the mechanics of the natural valve tissue, and that the current glutaraldehyde fixation process eliminates many of the beneficial, stress-reducing properties of the aortic leaflet.     

Prediction of bending stiffness and deformed shape of non-axially compressed microtubule by a semi-analytical approach

The bending stiffness of a microtubule is one of the most important parameters needed in the analysis of microtubule deformation. In this study, a semi-analytical approach is developed to predict the bending stiffness and deformed shape of a non-axially compressed microtubule in an explicit closed form. By using the solution presented in this paper and the experimentally observed values given in the literature, both the deformed configuration and bending stiffness of a single microtubule are determined. The proposed method is validated by comparing the obtained results with available data in the literature. The comparison shows that the present semi-analytical formulation provides the same accuracy with reduced numerical effort.     

The stem cells of animal tissues]

A brief historical review of concepts on stem cells is given with a stress made on the role of Russian scientists A. A. Maksimov and A. A. Zavarzin who have formulated key problems in biology of stem cells and cell renewal. Principal stages in current studies of stem cells are considered. An outline is given of traditional and recent trends in the investigations: comparative studies of tissue systems with stem cells; molecular genetic mechanisms of the self-maintainance and the differentiation of stem cells; stem cells as a subject of gene engineering.     

Effects of long-term nutrient optimisation on stem wood chemistry in Picea abies

The aim of the present study was to determine how long-term nutrient optimisation of Norway spruce stands affects the chemical composition of stem wood. Material for the study was collected from Flakaliden (Sweden) where Norway spruce [Picea abies (L.) Karst.] stands have been grown either without fertilisation or under nutrient optimisation treatment, by supplying a complete nutrient mix in the irrigation water every 2nd day during the growing season. The experiment was established in 1987 and in the autumn of 1998, 12 trees were harvested both in control (no fertilisation) and irrigated-fertilised (IL) stands. The increased growth rate caused by the IL treatment affected the chemical composition of the stem wood. The most pronounced effect was a 7% increase in lignin concentration caused by the IL treatment. Increases in concentrations of acid-soluble lignin (1.1-fold), extractives (1.2-fold), soluble sugars (1.3-fold), sterols (1.3-fold) and dehydroabietic acid (1.6-fold) as well as a decrease in the proportional quantity of terpinolene were also found. These results demonstrate that nutrient optimisation affected the chemical composition of Norway spruce wood, which may influence the suitability of such wood for specific end-use purposes.     

Reducing stem bending increases the height growth of tall pines

The hypothesis was tested that upper limits to height growth in trees are the result of the increasing bending moment of trees as they grow in height. The increasing bending moment of tall trees demands increased radial growth at the expense of height growth to maintain mechanical stability. In this study, the bending moment of large lodgepole pine (Pinus contorta Dougl. Ex Loud. var. latifolia Engelm.) was reduced by tethering trees at 10 m height to counter the wind load. Average bending moment of tethered trees was reduced to 38% of control trees. Six years of tethering resulted in a 40% increase in height growth relative to the period before tethering. By contrast, control trees showed decreased height growth in the period after tethering treatment. Average radial growth along the bole, relative to height growth, was reduced in tethered trees. This strongly suggests that mechanical constraints play a crucial role in limiting the height growth of tall trees. Analysis of bending moment and basal area increment at both 10 m and 1.3 m showed that the amount of wood added to the stem was closely related to the bending moment produced at these heights, in both control and tethered trees. The tethering treatment also resulted in an increase in the proportion of latewood at the tethering height, relative to 1.3 m height. For untethered control trees, the ratio of bending stresses at 10 m versus 1.3 m height was close to 1 in both 1998 and 2003, suggesting a uniform stress distribution along the outer surface of the bole.     

Comparison of contamination of femoral heads and pre-processed bone chips during hip revision arthroplasty

With bone impaction grafting, cancellous bone chips made from allograft femoral heads are impacted in a bone defect, which introduces an additional source of infection. The potential benefit of the use of pre-processed bone chips was investigated by comparing the bacterial contamination of bone chips prepared intraoperatively with the bacterial contamination of pre-processed bone chips at different stages in the surgical procedure. To investigate baseline contamination of the bone grafts, specimens were collected during 88 procedures before actual use or preparation of the bone chips: in 44 procedures intraoperatively prepared chips were used (Group A) and in the other 44 procedures pre-processed bone chips were used (Group B). In 64 of these procedures (32 using locally prepared bone chips and 32 using pre-processed bone chips) specimens were also collected later in the procedure to investigate contamination after use and preparation of the bone chips. In total, 8 procedures had one or more positive specimen(s) (12.5 %). Contamination rates were not significantly different between bone chips prepared at the operating theatre and pre-processed bone chips. In conclusion, there was no difference in bacterial contamination between bone chips prepared from whole femoral heads in the operating room and pre-processed bone chips, and therefore, both types of bone allografts are comparable with respect to risk of infection.     

Relationships between stem structure and bending strength in Pinus radiata seedlings

Summary Seedlings from nine families of Pinus radiata were grown in a glasshouse under conditions of high and low nitrate nitrogen availability to investigate effects on anatomical and strength characteristics of stems. Families were classified into groups dependent upon their previously determined susceptibility to stem deformation prevalent in plantations established on fertile ex-pasture. Nitrogen treatments significantly affected seedling form in terms of both branch production and stem slenderness. The high N treatment resulted in shorter seedlings, a proportion of which were obviously stunted. Stem strength of seedlings, physically supported throughout the experiment, was assessed as stem lean at harvest as well as the bending strength of the fresh stem at 50% stem height. These two variables were found not to be correlated. Stem lean at harvest was greatest in families known to be susceptible to stem deformation. These families produced stems that were also more slender than families of low susceptibility. Increased stem lean was associated mostly with increased stem slenderness while elasticity was more influenced by pith diameter, stem density and wood radius.     

Accuracy and reproducibility of bending stiffness measurements by mechanical response tissue analysis in artificial human ulnas

Osteoporosis is characterized by reduced bone strength, but no FDA-approved medical device measures bone strength. Bone strength is strongly associated with bone stiffness, but no FDA-approved medical device measures bone stiffness either. Mechanical Response Tissue Analysis (MRTA) is a non-significant risk, non-invasive, radiation-free, vibration analysis technique for making immediate, direct functional measurements of the bending stiffness of long bones in humans in vivo. MRTA has been used for research purposes for more than 20 years, but little has been published about its accuracy. To begin to investigate its accuracy, we compared MRTA measurements of bending stiffness in 39 artificial human ulna bones to measurements made by Quasistatic Mechanical Testing (QMT). In the process, we also quantified the reproducibility (i.e., precision and repeatability) of both methods. MRTA precision (1.0±1.0%) and repeatability (3.1±3.1%) were not as high as those of QMT (0.2±0.2% and 1.3+1.7%, respectively; both p<10⁻⁴). The relationship between MRTA and QMT measurements of ulna bending stiffness was indistinguishable from the identity line (p=0.44) and paired measurements by the two methods agreed within a 95% confidence interval of ±5%. If such accuracy can be achieved on real human ulnas in situ, and if the ulna is representative of the appendicular skeleton, MRTA may prove clinically useful.