Analysis of the kinematics of different hip simulators used to study wear of candidate materials for the articulation of total hip arthroplasties

We developed an analytical technique to determine the paths traced by specific points on the femoral head against the acetabulum in the human hip joint during gait. The purpose of the study was to apply this technique to the mechanical hip simulators chosen to conduct wear tests on polymeric acetabular liners used in total hip replacements. These simulators differ from one another in the type of motion produced, apart from other variables such as type of lubricant and head position. Due to the variation in the kinematics between the machines, the paths traced by the points on the femoral head against the acetabular liner ranged from simple linear traces to figure-8 loops and quasi-elliptical paths during a single simulator cycle. The distances traveled by these points during the same period also varied appreciably among the different hip simulator designs. These results are important when combined with other studies that have shown that kinematics can play an important role in the outcome of in vitro wear experiments. The kinematic differences quantified in this study can partially explain the substantial differences in wear data reported from different simulator designs and also underscore the usefulness of the technique described in this study in judging the results from different hip simulator experiments.     

Amoebiasis and the entamoeba histolytica

Summary Amoebic infection of man is one of the most frequently occurring parasitic diseases in the tropics and is nearly exclusively acquired in the tropical and subtropical zones of the earth. Recently, however, amoebiasis is found to occur increasingly in Europe and physicians should therefore become acquainted with the disease.

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Amöbiasis und die Entamoeba histolytica

Zusammenfassung Die Amöbiasis zählt zu den häufigsten Erkrankungen der Tropen. Sie wird fast ausschließlich in den Tropen und Subtropen erworben. Die weltweite Fluktuation der Bevölkerung führte im letzten Jahrzehnt zu einem immer häufigeren Vorkommen auch in Europa. Daher müssen Diagnose und Therapie der Amöbiasis auch bei uns jedem Arzt bekannt sein.

     

Introduction

The demographic transitions that took place in the developed countries during years gone by have now shifted scene to the developing countries—with the difference that, in the latter case, similar processes are being compacted in a shorter time frame. By 2020, 700 million of the world’s population will be 65 and over. Two-thirds of these elderly will be in the developing countries. The elderly segment in the world is the fastest growing group. Moreover, the ageing of the world will be predominantly a female issue. For some developing countries the problem of ageing is imminent, for others it would be after several decades.     

Differences in stiffness of the interface between a cementless porous implant and cancellous bone in vivo in dogs due to varying amounts of implant motion

To determine the mechanical properties of the interface between the tissue ingrowth into porous coatings and the implant, porous-coated cylindrical implants were inserted into the distal femur in 20 mature dogs and oscillated in vivo 8 hours per day for 6 weeks at fixed amounts of micromotion (0, 20, 40, and 150 μm). Applied torques and resulting displacements were recorded. The torsional resistance per unit angular displacement (TR/AD), reflecting the stiffness of the bone—porous coating interface, was 0.88 ± 0.25 N-M/deg immediately after implantation in the 20-μm displacement group. It increased with time after surgery, reaching a maximum of 1.25 ± 0.60 N-M/deg at 6 weeks. The TR/AD was lower initially (0.77 ± 0.43 N-M/deg) in the 40-μm group and gradually decreased with time after surgery, reaching a maximum of 0.54 ± 0.13 N-M/deg at 6 weeks. The TR/AD was even lower (0.24 ± 0.10 N-M/deg) in the 150-μm group initially and remained the same (0.16 ± 0.09 N-M/deg) with time after surgery. Histologic evaluation showed bone ingrowth in continuity with the surrounding bone in the 20-μm group consistent with the high stiffness values at sacrifice. In contrast, a mixture of fibrocallus and bone were found at the bone-porous coating interface in the 40-μm group, consistent with the intermediate stiffness values. In contrast, despite the fact that bone was found in the depth of the porous coating in the dogs in the 150-μm group, the low stiffness values were a reflection of fibrous tissue formation at the interface in that group, because of the large motion disrupting bony ingrowth at the bone—porous coating interface. By monitoring the torsional resistance per unit of angular displacement dynamically in vivo, it was possible to evaluate the mechanical properties of the bone—porous coating interface as tissue ingrowth proceeded. Twenty microns of oscillating displacement was compatible with stable bone ingrowth with high interface stiffness, whereas 40 and 150 μm of motion was not.     

Nodular hidradenoma of the breast: A case report with literature review

Nodular hidradenoma or clear cell hidradenoma is a rare skin adenexal tumor which arises from eccrine sweat glands. Skin adenexal tumors situated in the breast parenchyma are still very rare and is one of the differential diagnoses of breast tumors. Failure to identify its morphologic features may lead to a mistaken diagnosis and over treatment. We report a case of breast lump, in a 40-year-old lady, which was diagnosed clinically as a malignant breast lump. Final diagnosis of nodular hidradenoma was made only after excision biopsy as fi ne needle aspiration cytology was inconclusive.