Load transfer and periprosthetic fractures after total hip arthoplasty: Comparison of periprosthetic fractures of femora implanted with cementless distal-load or proximal-load femoral components and measurement of the femoral strain at the time of implantation.

BACKGROUND: Little is known about the causes and mechanisms underlying periprosthetic fractures around femoral components particularly in relation to the stem design. In an in vitro study 20 pairs of fresh cadaveric femora were loaded to fracture axially and transversally. FINDINGS: When proximal femoral strain was measured at the time of impaction of cementless stems the load transfer was determined by the underlying anatomy rather than by the shape of the stem, so that the so-called "load transfer" properties - proximal or distal - ascribed to stem designs are a myth. The axial-load and the transverse-load model were then exposed to loads to failure (fracture) and showed a biphasic pattern throughout independent of the impact direction. In the second phase, the fracture phase proper, the bone behaved like a brittle solid. Failure occurred very rapidly within less than 5 milliseconds. The forces to failure were between 2 and 11 kN. Most of the fractures (82.5%) occurred above the stem tip. INTERPRETATION: Note that the study was confined to early preosteointegration fractures. Neither the stem design nor the impact direction, i.e. on the knee or on the side of the hip, was related to the fracture morphology.

[Low-Carbon Metal-on-Metal Articulations for Hip Arthroplasties--Evaluation of Wear and Histology after 11 to 17 Years]. / Verschleißtechnische Analysen und histologische Befunde bei Low-Carbon-Metall-Metall-Artikulationen des Hüftgelenks nach 11 bis 17 Jahren.

BACKGROUND: High-carbon (HC) alloys for hip arthroplasties were preferred to low-carbon (LC) alloys for a long time because of their structurally hard carbide content. We opted for an LC alloy in 1994, because we expected it to be subject to less wear on account of its more homogeneous structure. Prompted by early complications not seen with ceramic-on-polyethylene mating surfaces, LC metal-on-metal articulations were, however, given up by us in early 1999. A series of implants retrieved after 11 to 17 years was now studied to establish the actual amount of wear. Potential tissue reactions associated with hypersensitivity were also evaluated histologically and correlated with the measured wear and the amount of metal particles in capsular tissue. PATIENTS AND METHODS: Ten patients with LC metal-on-metal hip implants were the subjects of analyses after a mean follow-up time of 13.9 years. They underwent revision surgery because of osteolysis, cup loosening without dislocation, late infection in 1 patient and pain. The implant positions at the time of retrieval were the same as on the postoperative radiographs. Wear was determined in keeping with ISO 14242-2 and by SEM. In addition, periprosthetic tissue including the joint capsule and interface membranes were obtained for histological analysis. The amount of metal particles and the extent of lymphocyte infiltration were determined with the method described by Willert et al. Tissue alterations were evaluated histologically for signs of ALVAL using the method of Campbell et al. and correlated with the amount of wear and metal particles. RESULTS: The mean maximum linear wear rate was found to be 1.6 (1.0-2.1) µm/year. Our data also showed a mean rate of 0.32 mm³/year (range, 0.22-0.47 mm³/year). This is equivalent to an annual metal release of 2.7 (1.9-3.9) mg/year. No corrosion or corrosion products were present on the ball heads and their taper. All mating surfaces studied by SEM showed signs of abrasion. Sporadically, additional abrasions in the submicrometer range were detected on the ball head surfaces. These were caused by corundum particles detached from the blasted implant surfaces and interpreted as third-body wear below the level of quantification. Signs of impingement were absent. Histologically, metal wear particles of variable amount were detected in all cases. In 4 of them solid corrosion products were present in the tissue. The ALVAL scores were 5 to 10 (moderate to high), but did not correlate with the measured wear and the amount of metal particles. CONCLUSION: The wear of LC articulations found after years of implant survival was very low. In fact, it was lower than the data reported for HC articulations and would permit implants to function for decades in engineering terms. However, their survival is limited by tissue alterations associated with hypersensitivity. These tissue alterations may contribute to implant loosening as also reported for HC articulations. They are apparently not related to the actual amount of wear and may reflect adaptive immunological processes.

Methyldichloroborane evidenced as an intermediate in the chemical vapour deposition synthesis of boron carbide.

The most recent ceramic-matrix composites (CMC) considered for long-life applications as thermostructural parts in aerospace propulsion contain, among others, boron-rich phases like boron carbide. This compound is prepared by thermal Chemical Vapour Infiltration (CVI), starting from precursors like boron halides and hydrocarbons. We present a study aiming at a precise knowledge of the gas-phase composition in a hot-zone LPCVD reactor fed with BCl3, CH4 and H2, which combines experimental and theoretical approaches. This work has brought strong evidences of the presence of Methydichloroborane (MDB, BCl2CH3) in the process. It is demonstrated that this intermediate, the presence of which had never been formally proved before, appears for processing temperatures slightly lower than the deposition temperature of boron carbide. The study features quantum chemical computations, which provide several pieces of information like thermochemical and kinetic data, as well as vibration and rotation frequencies, reaction kinetics computations, and experimental gas-phase characterization of several species by FTIR, for several processing parameter sets. The main results are presented, and the place of MDB in the reaction scheme is discussed.

Lung disease 35 years after aspiration of activated charcoal in combination with pulmonary lymphangioleiomyomatosis. A histological and clinicopathological study with scanning electron microscopic evaluation and element analysis.

Activated charcoal provides effective treatment for most toxic ingestions. Accidental aspiration of activated charcoal is rare. Previously, there have been a few single cases reported on charcoal-related pulmonary complications. We describe an unusual case of pulmonary lesions 35 years after accidental aspiration of activated charcoal. The 38-year-old female patient presented with recurrent pneumothorax. A routinely performed chest roentgenogram revealed pulmonary lesions, highly suggestive to lymphangioleiomyomatosis (LAM). Histopathological investigation of the lung tissue demonstrated some features of LAM but showed prominent pneumoconiotic lesions with cystic tissue destruction. The pneumoconiotic reaction was characterized by prominent black deposits accompanied by foreign-body granuloma formation and minimal fibrosis. Scanning electron microscopic investigation of these deposits showed particles measuring up to 300 microm in greatest diameter. Energy-dispersive X-ray spectra of these particles revealed carbon-rich material, presumably charcoal. The aspiration event was confirmed by the clinical history. To our knowledge, this is the first report not only on a long-term follow-up after aspiration of activated charcoal but also on charcoal-related pulmonary lesions in combination with LAM.

[A new ISO/FDIS 14242-1 compatible hip prosthesis simulator: E-SIM]. / Ein neuer, der ISO/FDIS 14242-1 entsprechender Hüftsimulator: E-SIM.

The continuing development of new, highly sophisticated materials for the articulating surfaces of total hip endoprostheses involves the need for testing, not only of biocompatibility and dynamic loadability, but also of tribological properties (friction, wear, lubrication). For decades, the wear resistance of these materials has been tested in wear simulators. In consequence of the currently often widely differing test methods, the technical committee (TC 150) of the ISO (International Organization for Standardization) has been concerned to develop an International Standard (ISO/FDIS 14242 1 and 2: Implants for Surgery--wear of total hip joint prostheses--on the basis of kinetic and kinematic data from gait analysis. This new standard will be the basis for ensuring the comparability of scientific data obtained from tribological testing of total hip endoprothesis. The new hip simulator, E-SIM, presented in this paper, complies with the currently published FDIS (Final Draft International Standard), and enables testing in accordance with these specifications.