The increasing demand for total hip arthroplasty (THA) in relatively young, high-demand patients has led to the use of hard-on-hard bearing surfaces. Adverse local tissue reaction/pseudotumor and elevated serum metal ion levels are commonly reported complications encountered in metal-on-metal THA, while audible articulation and rim fracture are reported in ceramic-on-ceramic THA. For this reason, ceramic-on-metal THA was implemented as an ideal hard-on-hard bearing combination. In this report, we describe a case of bilateral simultaneous ceramic-on-metal THA in a 69-year-old woman who presented 7 years postoperatively with unilateral hip pain associated with underlying pseudotumor and elevated serum cobalt and chromium ion levels. Pre-revision workup, intraoperative findings, and postoperative evaluation are included and suggest acetabular malposition as a potential source for complication.

Although H/D exchange is indispensable to the study of reaction mechanisms in solution, they have been underexploited in studies of heterogeneous catalysis. Spectroscopic studies of H/D exchange at low temperatures and long reaction times on solid catalysts have been reported, [1,2] and more realistic temperatures have been used for studies of equivalent exchange sites as in methane.[3] We were drawn to the possibilities of studying mechanisms by observing exchange into structurally distinct sites within the constraints of high temperatures and several-second reaction times used for these reactions in actual practice. [4] We have found that by careful experimental design of H/ D exchange reactions, including appropriate reagent compositions or concentrations, and quantitative fitting of the ion mass distributions of product species, [5] we can sometimes reveal a surprising level of complexity in reactions that at first glance would appear to be simple or even elementary. We have carried out experiments pulsing controlled amounts of protonated reactants onto deuterated catalysts (as shown here) as well as equimolar mixtures of fully protonated and fully deuterated reagents onto half-deuterated catalysts in either pulse or continuous flow mode. As the first contribution from these studies, we report on H/D exchange for propene on three microcrystalline solid acids: the aluminosilicate zeolite DZSM-5, its boron analogue D[B]ZSM-5, and the silico-aluminophosphate DSAPO-34. In every case herein the inventory of exchangeable deuterium atoms in the catalyst beds vastly exceeded that of the hydrogen atoms in the propene reagent pulses by a factor of at least 300 in all cases but one, and in that instance there was still more than a 13-fold excess. Whereas an oversimplified view of olefin H/ D exchange would predict that we would observe [D 6 ]propene as the exclusive equilibrium product of this reaction, our observations of incomplete deuteration and

Although H/D exchange is indispensable to the study of reaction mechanisms in solution, they have been underexploited in studies of heterogeneous catalysis. Spectroscopic studies of H/D exchange at low temperatures and long reaction times on solid catalysts have been reported, [1,2] and more realistic temperatures have been used for studies of equivalent exchange sites as in methane.[3] We were drawn to the possibilities of studying mechanisms by observing exchange into structurally distinct sites within the constraints of high temperatures and several-second reaction times used for these reactions in actual practice. [4] We have found that by careful experimental design of H/ D exchange reactions, including appropriate reagent compositions or concentrations, and quantitative fitting of the ion mass distributions of product species, [5] we can sometimes reveal a surprising level of complexity in reactions that at first glance would appear to be simple or even elementary. We have carried out experiments pulsing controlled amounts of protonated reactants onto deuterated catalysts (as shown here) as well as equimolar mixtures of fully protonated and fully deuterated reagents onto half-deuterated catalysts in either pulse or continuous flow mode. As the first contribution from these studies, we report on H/D exchange for propene on three microcrystalline solid acids: the aluminosilicate zeolite DZSM-5, its boron analogue D[B]ZSM-5, and the silico-aluminophosphate DSAPO-34. In every case herein the inventory of exchangeable deuterium atoms in the catalyst beds vastly exceeded that of the hydrogen atoms in the propene reagent pulses by a factor of at least 300 in all cases but one, and in that instance there was still more than a 13-fold excess. Whereas an oversimplified view of olefin H/ D exchange would predict that we would observe [D 6 ]propene as the exclusive equilibrium product of this reaction, our observations of incomplete deuteration and