Two Distinct Thermodynamic Gradients for Cellular Metalation of Vitamin B12

The acquisition of Co^II by the corrin component of vitamin B₁₂ follows one of two distinct pathways, referred to as early or late Co^II insertion. The late insertion pathway exploits a Co^II metallochaperone (CobW) from the COG0523 family of G3E GTPases, while the early insertion pathway does not. This provides an opportunity to contrast the thermodynamics of metalation in a metallochaperone-requiring and a metallochaperone-independent pathway. In the metallochaperone-independent route, sirohydrochlorin (SHC) associates with the CbiK chelatase to form Co^II-SHC. Co^II-buffered enzymatic assays indicate that SHC binding enhances the thermodynamic gradient for Co^II transfer from the cytosol to CbiK. In the metallochaperone-dependent pathway, hydrogenobyrinic acid a,c-diamide (HBAD) associates with the CobNST chelatase to form Co^II-HBAD. Here, Co^II-buffered enzymatic assays indicate that Co^II transfer from the cytosol to HBAD-CobNST must somehow traverse a highly unfavorable thermodynamic gradient for Co^II binding. Notably, there is a favorable gradient for Co^II transfer from the cytosol to the Mg^IIGTP-CobW metallochaperone, but further transfer of Co^II from the GTP-bound metallochaperone to the HBAD-CobNST chelatase complex is thermodynamically unfavorable. However, after nucleotide hydrolysis, Co^II transfer from the chaperone to the chelatase complex is calculated to become favorable. These data reveal that the CobW metallochaperone can overcome an unfavorable thermodynamic gradient for Co^II transfer from the cytosol to the chelatase by coupling this process to GTP hydrolysis.

Metalation calculators for E. coli strain JM109 (DE3): Aerobic, anaerobic and hydrogen peroxide exposed cells cultured in LB media

Three web-based calculators, and three analogous spreadsheets, have been generated that predict in vivo metal occupancies of proteins based on known metal affinities. The calculations exploit estimates of the availabilities of the labile buffered pools of different metals inside a cell. Here, metal availabilities have been estimated for a strain of E. coli that is commonly used in molecular biology and biochemistry research, for example in the production of recombinant proteins. Metal availabilities have been examined for cells grown in LB medium aerobically, anaerobically and in response to H2O2 by monitoring the abundance of a selected set of metal-responsive transcripts by qPCR. The selected genes are regulated by DNA-binding metal sensors that have been thermodynamically characterised in related bacterial cells enabling gene expression to be read-out as a function of intracellular metal availabilities expressed as free energies for forming metal complexes. The calculators compare these values with the free energies for forming complexes with the protein of interest, derived from metal affinities, to estimate how effectively the protein can compete with exchangeable binding sites in the intracellular milieu. The calculators then inter-compete the different metals, limiting total occupancy of the site to a maximum stoichiometry of 1, to output percentage occupancies with each metal. In addition to making these new and conditional calculators available, an original purpose of this article was to provide a tutorial which discusses constraints of this approach and presents ways in which such calculators might be exploited in basic and applied research, and in next-generation manufacturing.

Protein metalation in biology

Inorganic metals supplement the chemical repertoire of organic molecules, especially proteins. This requires the correct metals to associate with proteins at metalation. Protein mismetalation typically occurs when excesses of unbound metals compete for a binding site ex vivo. However, in biology, excesses of metal-binding sites typically compete for limiting amounts of exchangeable metals. Here, we summarise mechanisms of metal homeostasis that sustain optimal metal availabilities in biology. We describe recent progress to understand metalation by comparing the strength of metal binding to a protein versus the strength of binding to competing sites inside cells.

The requirement for cobalt in vitamin B12: A paradigm for protein metalation

Vitamin B12, cobalamin, is a cobalt-containing ring-contracted modified tetrapyrrole that represents one of the most complex small molecules made by nature. In prokaryotes it is utilised as a cofactor, coenzyme, light sensor and gene regulator yet has a restricted role in assisting only two enzymes within specific eukaryotes including mammals. This deployment disparity is reflected in another unique attribute of vitamin B12 in that its biosynthesis is limited to only certain prokaryotes, with synthesisers pivotal in establishing mutualistic microbial communities. The core component of cobalamin is the corrin macrocycle that acts as the main ligand for the cobalt. Within this review we investigate why cobalt is paired specifically with the corrin ring, how cobalt is inserted during the biosynthetic process, how cobalt is made available within the cell and explore the cellular control of cobalt and cobalamin levels. The partitioning of cobalt for cobalamin biosynthesis exemplifies how cells assist metalation.

Evaluation of Cu(i) binding to the E2 domain of the amyloid precursor protein - a lesson in quantification of metal binding to proteins via ligand competition

The extracellular domain E2 of the amyloid precursor protein (APP) features a His-rich metal-binding site (denoted as the M1 site). In conjunction with surrounding basic residues, the site participates in interactions with components of the extracellular matrix including heparins, a class of negatively charged polysaccharide molecules of varying length. This work studied the chemistry of Cu(i) binding to APP E2 with the probe ligands Bcs, Bca, Fz and Fs. APP E2 forms a stable Cu(i)-mediated ternary complex with each of these anionic ligands. The complex with Bca was selected for isolation and characterization and was demonstrated, by native ESI-MS analysis, to have the stoichiometry E2 : Cu(i) : Bca = 1 : 1 : 1. Formation of these ternary complexes is specific for the APP E2 domain and requires Cu(i) coordination to the M1 site. Mutation of the M1 site was consistent with the His ligands being part of the E2 ligand set. It is likely that interactions between the negatively charged probe ligands and a positively charged patch on the surface of APP E2 are one aspect of the generation of the stable ternary complexes. Their formation prevented meaningful quantification of the affinity of Cu(i) binding to the M1 site with these probe ligands. However, the ternary complexes are disrupted by heparin, allowing reliable determination of a picomolar Cu(i) affinity for the E2/heparin complex with the Fz or Bca probe ligands. This is the first documented example of the formation of stable ternary complexes between a Cu(i) binding protein and a probe ligand. The ready disruption of the complexes by heparin identified clear 'tell-tale' signs for diagnosis of ternary complex formation and allowed a systematic review of conditions and criteria for reliable determination of affinities for metal binding via ligand competition. This study also provides new insights into a potential correlation of APP functions regulated by copper binding and heparin interaction.

Copper binding and redox chemistry of the Aβ16 peptide and its variants: insights into determinants of copper-dependent reactivity

The metal-binding sites of Aβ peptides are dictated primarily by the coordination preferences of the metal ion. Consequently, Cu(i) is typically bound with two His ligands in a linear mode while Cu(ii) forms a pseudo-square planar stereochemistry with the N-terminal amine nitrogen acting as an anchoring ligand. Several distinct combinations of other groups can act as co-ligands for Cu(ii). A population of multiple binding modes is possible with the equilibrium position shifting sensitively with solution pH and the nature of the residues in the N-terminal region. This work examined the Cu(ii) chemistry of the Aβ16 peptide and several variants that targeted these binding modes. The results are consistent with: (i) at pH < 7.8, the square planar site in Cu^II-Aβ16 consists primarily of a bidentate ligand provided by the carboxylate sidechain of Asp1 and the N-terminal amine supported by the imidazole sidechains of two His residues (designated here as component IA); it is in equilibrium with a less stable component IB in which the carboxylate ligand is substituted by the Asp1-Ala2 carbonyl oxygen. (ii) Both IA and IB convert to a common component II (apparent transition pK_a ∼7.8 for IA and ∼6.5 for IB, respectively) featuring a tridentate ligand consisting of the N-terminal amine, the Asp1-Ala2 amide and the Ala2-Pro3 carbonyl; this stereochemistry is stabilized by two five-membered chelate rings. (iii) Component IA is stabilized for variant Aβ16-D1H, components I (both IA and IB) are imposed on Aβ16-A2P while the less stable IB is enforced on Aβ16-D1A (which is converted to component II at pH ∼6.5); (iv) components IA and IB share two His ligands with Cu(i) and are more reactive in redox catalysis than component II that features a highly covalent and less reactive amide N^- ligand. The redox activity of IA is further enhanced for peptides with a His1 N-terminus that may act as a ligand for either Cu(i) or Cu(ii) with lower re-organization energy required for redox-shuttling. This study provided insights into the determinants that regulate the reactivity of Cu-Aβ complexes.

Dehydrated citrus pulp alters feedlot performance of crossbred heifers during the receiving period and modulates serum metabolite concentrations before and after an endotoxin challenge

English × Continental heifers ( = 180) were sourced in 2 loads (219.3 ± 16.0 and 221.4 ± 16.4 kg, respectively) from commercial auction barns to study the effects of feeding dehydrated citrus pulp (DCP) on feedlot performance of newly received heifers. A completely randomized block design was used with BW nested within arrival load and blocked by BW into 3 dietary treatments (36 pens, 5 heifers/pen, 12 blocks, 3 pens/block, and 12 pens/treatment). Treatment diets contained 1) 0% DCP (control diet [CON]), 2) 10% DCP, or 3) 20% DCP on a DM basis. Diets containing DCP were exchanged with steam-flaked corn on a 1:1 basis. Cattle were fed a 63, 73, and 83% concentrate diet from d 0 to 28, d 28 to 42, and d 42 to 56, respectively. Over the 56-d trial period, as the amount of dietary DCP increased, DMI decreased ( = 0.01), ADG decreased ( < 0.01), and G:F decreased ( = 0.02). From d 0 to 28, there was no difference in the observed minus the predicted NEg of the diet ( = 0.73); from d 28 to 42, there was a linear increase in NEg favoring DCP treatments ( < 0.01); and from d 42 to 56, there was a linear decrease in NEg against the DCP treatments ( < 0.01). At the conclusion of the trial, a subset of heifers ( = 22; 307.89 ± 3.32 kg on d 63) were used to evaluate blood metabolite concentrations before and after a lipopolysaccharide (LPS) challenge. On d 63, heifers were fitted with jugular catheters and moved into individual stalls. On d 64, heifers were intravenously challenged with LPS (0.5 μg/kg BW), and blood samples were collected every 0.5 h from -2 to 8 h and at 24 h relative to the LPS challenge (0 h). Serum glucose, serum urea nitrogen (SUN), and NEFA concentrations were determined. Cattle lost less weight at both 24 and 72 h after the LPS challenge with increasing DCP percentage ( < 0.01). Glucose ( = 0.12) and NEFA ( = 0.13) concentrations did not differ before the LPS challenge; however, there was a treatment effect for SUN, with elevated concentrations of SUN in CON cattle ( < 0.01). After the LPS challenge, DCP-fed cattle had reduced glucose, elevated NEFA, and reduced SUN concentrations ( ≤ 0.01). Results indicate that dietary DCP modulated metabolite concentrations in heifers following an endotoxin challenge and affected feedlot performance when incorporated in receiving diets in replacement of corn. Future studies will need to address strategies to increase DMI or explore levels of DCP less than 10% in the diet of newly received heifer calves.

A set of robust fluorescent peptide probes for quantification of Cu(ii) binding affinities in the micromolar to femtomolar range

A set of four fluorescent probes were developed and demonstrated to be capable of quantifying Cu(ii) binding affinities in the micromolar to femtomolar range and exploring Cu(ii) binding ligands in peptides and proteins.

An integrated study of the affinities of the Aβ16 peptide for Cu(i) and Cu(ii): implications for the catalytic production of reactive oxygen species

Affinities of Aβ16 peptide and several selected variants for Cu(i) and Cu(ii) were determined with new probes and correlated to their binding modes and abilities in promoting ROS generation.

Complications in total knee arthroplasty with and without surgical drainage

The standard practice in total joint arthroplasty has included the use of postsurgical drains to minimize perioperative wound complications, particularly infection. This practice is not without cost and potential morbidity. Our recent cemented and cementless total knee arthroplasties (TKAs) have been done without the use of postoperative surgical drains and without any appreciable increase in wound complications. To confirm this, we retrospectively reviewed 227 consecutive TKAs, specifically evaluating perioperative wound complications. No statistical increase in perioperative complications in TKAs without drains was found. A lower percentage of complications was seen in the cementless population when compared with cemented or drained knees. We suggest that surgical drainage is not required in TKA, even when cementless fixation is used.

Cementless S-ROM femoral component: effect of stem length on stability after extended proximal femoral osteotomy

The extended proximal femoral osteotomy is becoming increasingly popular in revision total hip replacement. Our study was done to determine the femoral stem length required for stable fixation of a cementless femoral component after an extended proximal femoral osteotomy. Three lengths of the S-ROM femoral stem were implanted in paired cadaver femora and tested under torsional and axial loads. The results indicate that the standard (160 mm) and long (215 mm) stems do not provide adequate torsional stability after a 160 mm extended proximal femoral osteotomy. The extra-long (255 to 315 mm) stems provided significantly greater stability, suggesting that the extended proximal femoral osteotomy may need to be bypassed by more than 2 cortical diameters, especially when a flexible stem such as the S-ROM is used.

Prevention of venous thromboembolic disease following primary total knee arthroplasty. A randomized, multicenter, open-label, parallel-group comparison of enoxaparin and warfarin

BACKGROUND

Patients treated with total knee arthroplasty are at high risk for the development of venous thromboembolism postoperatively. This study compared the efficacy and safety of two common thromboprophylactic agents, enoxaparin (a low-molecular-weight heparin) and warfarin.

METHODS

Three hundred and forty-nine patients were included in a prospective, randomized, multicenter, open-label, parallel-group clinical trial. Treatment with enoxaparin (30 mg, administered subcutaneously twice daily) or warfarin (adjusted to an international normalized ratio of 2 to 3) was initiated during the immediate postoperative period, within eight hours after the surgery, and was continued for four to fourteen days. Venous thromboembolism was defined as deep-vein thrombosis documented by contrast venography, symptomatic deep-vein thrombosis documented by lower-extremity ultrasonography, or symptomatic pulmonary embolism confirmed by a positive lung scan or pulmonary angiography.

RESULTS

In the all-treated-patients group, eighty (45%) of the 176 warfarin-treated patients had venous thromboembolism: fifty-nine (34%) had distal deep-vein thrombosis; twenty (11%), proximal deep-vein thrombosis; and one (0.6%), pulmonary embolism. Venous thromboembolism developed in significantly fewer (p = 0.0001) enoxaparin-treated patients (forty-four of 173; 25%): forty-one (24%) had distal deep-vein thrombosis, three (2%) had proximal deep-vein thrombosis, and none had pulmonary embolism. The enoxaparin-treated patients also had a significantly lower prevalence of proximal deep-vein thrombosis (p = 0.002). The estimated odds for the development of venous thromboembolism were 2.52 times greater (95% confidence interval, 2.00 to 3.19) with warfarin than they were with enoxaparin. Major hemorrhage occurred in four warfarin-treated patients and nine enoxaparin-treated patients; with the numbers available, this difference was not significant (p = 0.17). Clinically important operative-site hemorrhage occurred in six (3%) of the warfarin-treated patients and twelve (7%) of the enoxaparin-treated patients (p = 0.15).

CONCLUSIONS

A fixed 30-mg subcutaneous dose of enoxaparin, administered twice daily, with the first dose administered within eight hours after the completion of surgery, was significantly more effective than adjusted-dose warfarin in reducing the occurrence of asymptomatic venous thromboembolism, including proximal deep-vein thrombosis, in patients undergoing total knee arthroplasty. With the numbers available, there was no significant difference between groups with regard to the occurrence of major hemorrhagic complications; however, the rate of overall hemorrhagic complications was higher in the enoxaparin group.

Light microscopic and scanning electron microscopic retrieval analyses of implanted biomaterials retrieved from humans and experimental animals

This paper reports analysis obtained from 200 implant cases retrieved from humans and submitted to the American Academy of Implant Dentistry Research Foundation, Medical College of Georgia implant retrieval center. The samples that were not decalcified were embedded in polymethylmethacrylate and examined with scanning electron microscopy and routine light, polarized, or Nomarski microscopy. Cases included both orthopedic and dental implants, as well as entire mandibles and portions of maxillae obtained at autopsy. A significant number of submitted implants had substantial amounts of adhered bone, which permitted evaluation of human bone remodeling to osseointegrated implants. These implants failed because of implant fracture. As was observed with animal studies, healthy bone supported these implants, with the bone containing an interdigitating canaliculi network that provided communication between interfacial osteocytes and osteocytes deeper within the remodeled osteonal and trabecular bone. Early dental implants containing a coating of beads showed a connective tissue interface, which corresponded to the bead surface of specific orthopedic implants that underwent some degree of micromovement. This is in contrast with the excellent response reported for successful contemporary beaded implants. Significant numbers of osseointegrated fractured hydroxyapatite (HA)-coated dental implants demonstrated the adequate serviceability of these implants before biomaterial fracture. In contrast, the HA coating was dissociated from retrieved orthopedic implants, leading to extensive cup loosening and case failure. This study, therefore, underscores the need for evaluation of failed human dental and orthopedic implants. Correlations can be drawn between human retrieval and experimental animal studies.

Correlative experimental animal and human clinical retrieval evaluations of hydroxyapatite (HA)-coated and non-coated implants in orthopaedics and dentistry

Retrieval analyses disclosed in vivo dissociation of HA in orthopaedic acetabular components, but excellent bone ingrowth into intact HA coatings on dental retrievals. Initial healing and the bone interface between HA-coated and non-coated implants in the posterior maxilla (Mx) and mandible (Md) was assessed in an animal model using light microscopy (LM), including confocal (CM) and Nomarski (NM) microscopy. Seventy-two implants (36 HA-coated; 36 non-coated) were placed into jaws of six dogs; half after extraction, half after 3 months healing. Animals were euthanized 3 months postimplantation. All implants osseointegrated; however, preliminary morphometry showed higher BCL for HA-coated (51%) than non-coated implants (44%) in the Mx (p < 0.05). BCL for HA-coated Md implants was not significantly higher (64%) than non-coated implants (62%). Bone closely apposed both implant types; however, LM suggested a more intimate association with HA coatings. Serial sections disclosed a reddish coating on the HA, possibly analogous to oral tissue proteoglycans, which was not visible with non-coated implants. This material was continuous with similar material coating endosteum, osteoid regions, and osteocyte (Os) lacunae close to the implant. An interdigitating canaliculi network allowed communication between interfacial Os and Os deeper within the bone. Data suggest HA offers enhanced initial bone fixation in the Mx, and that adequate bone exists for non-coated implant stability in the Md. No HA dissociation was seen with implants in the animal study, which was consistent with retrieved human HA dental implants.

The Properties of Supernova 1997cy Associated with GRB 970514

The extraordinary SN 1997cy associated with GRB 970514 has been observed photometrically and spectroscopically for nearly 2 yr. At the time of discovery, SN 1997cy was the brightest supernova (SN) ever observed (MV</=-20.1, vhel=19,140 km s-1, H0=65 km s-1 Mpc-1). Up to the last available observations (600 days after the gamma-ray burst), the total time-integrated flux was equal to or larger than that expected from the complete thermalization of the gamma-rays produced by 2.3 M middle dot in circle of 56Co. However, starting already on day 60 the luminosity decline is slower than the 56Co decay rate, indicating that the SN ejecta was interacting with circumstellar material (CSM). The interaction appeared to weaken around day 550. The spectra of SN 1997cy are dominated at all epochs by Halpha emission, which shows at least three components of different widths, as in SN 1988Z. Several other lines with different widths are also visible, especially at early epochs. The entire light curve of SN 1997cy is reproduced by a model of the interaction of the very energetic (E=3x1052 ergs) ejecta of a massive star (25 M middle dot in circle) with the CSM, with some contribution from radioactive decays. The CSM could have been ejected with a mass-loss rate of M&d2; approximately 4x10-4 M middle dot in circle yr-1 as the progenitor star evolved from a blue to a red supergiant about 104 yr before the explosion. The lack of oxygen and magnesium lines in the spectra at nebular phases poses a problem for models requiring high-mass progenitors. The possibility that most of the core material of the progenitor has fallen onto a massive black hole so that the reverse shock dies at the inner edge of the H/He envelope is discussed.

Retrieval analyses of implanted biomaterials: light microscopic and scanning electron microscopic analyses of implants retrieved from humans

We report analyses obtained from 135 implant cases retrieved from humans and submitted to the American Academy of Implant Dentistry Research Foundation--Medical College of Georgia Implant Retrieval Center. The undecalcified samples were embedded in polymethyl-methacrylate and examined with scanning electron microscopy and with routine light via polarized or Nomarski microscopy. Cases included both orthopedic and dental implants as well as entire mandibles obtained at autopsy. Significant numbers of submitted implants had substantial amounts of adhered bone, which permitted evaluation of human bone remodeling to osseointegrated implants. These implants failed because of implant fracture. As has been observed in animal studies, an interdigitating canaliculi network provided communication between interfacial osteocytes and osteocytes deeper within the remodeled osteonal and trabecular bone. Significant numbers of osseointegrated fractured hydroxyapatite-coated dental implants demonstrated the adequate serviceability of these implants prior to biomaterial fracture. In contrast, the hydroxyapatite coating was dissociated from retrieved orthopedic implants, leading to extensive cup loosening and case failure. Caution is advised for the use of hydroxyapatite-coated acetabular implants. This study therefore underscores the need for evaluation of failed human dental and orthopedic implants. Correlations can be drawn between human retrieval and experimental animal studies.

The biologic tissue responses to uncoated and coated implanted biomaterials

Ultrastructural examination of the morphology and morphometry of the bone supporting uncoated titanium and ceramic implants was assessed in an experimental animal model involving 120 implants placed into the mandibles of 30 adult mongrel dogs. Further, preliminary morphologic and morphometric observations of the bone supporting uncoated and hydroxylapatite-coated endosteal titanium implants was evaluated in a second investigation involving 72 implants placed into the mandibles and maxillae of 6 additional dogs. A densely mineralized collagen fiber matrix was observed directly interfacing with uncoated implants. The only material interposed between the implant and bone matrix was a 20- to 50-nm electron-dense material suggestive of a proteoglycan. Also seen in these same osseointegrated implants were narrow unmineralized zones interposed between the implant and bone matrix. In these zones of remodeling bone, numerous osteoblasts were observed interacting with the collagen fiber matrix. It was shown that a normal homeostasis of anabolic osteoblastic activity and catabolic osteoclastic activity resulted in bone remodeling and the resultant osseointegration of the implants. Hydroxylapatite-coated implants intimately interfaced with healthy bone. The mineralized matrix extended into the microporosity of the HA coating. This matrix contained viable osteocytes.

In vivo evaluation of the biocompatibility of implanted biomaterials: morphology of the implant-tissue interactions

Electron microscopic observations were made from tissues apposing titanium and ceramic root form and blade implants. The tissue was serially sectioned from the most coronal epithelium, through the gingival connective tissue, to the osseous support tissues, and directly to the most apical tissue support. Of the thousands of sections analyzed for each implant, 500 micrographs were routinely viewed for each of the implants analyzed by this study. Of the 120 total implants placed in 30 adult dogs, 60 were used for electron microscopy. Osseointegrated implants were often apposed by a mineralized matrix of collagenous fibers. The dense mineralized collagen matrix was often separated from the implant by only a ruthenium positive electron dense deposit 20 to 50 nanometers thick. Areas of the same implant were also apposed by an unmineralized collagen fiber stroma, which ranged in thickness, that contained osteoblasts. Interaction of the osteoblasts and the unmineralized collagen fibers resulted in the mineralization events of osteogenesis. Also apposing other areas of the same integrated implants were lacunar areas containing osteoclasts and vessels. These zones were similar to Howship's Lacunae. These results demonstrated that a normal homeostasis of catabolic osteoclastic activity and metabolic osteoblastic activity resulted in a dynamic implant-tissue interface. This biocompatible and dynamic support complex provides a construct for the long-term clinical serviceability of osseointegrated implants.

Ultrastructural analyses of the attachment (bonding) zone between bone and implanted biomaterials

This report presents transmission electron and high voltage transmission electron microscopic observations of bone and associated remodeling tissues directly interfacing with endosteal dental implants. Undecalcified interfacial tissues were serially sectioned from mandibular samples encasing 60 implants placed into 30 dogs. Two-dimensional ultrastructural analyses and three-dimensional stereology showed that osteogenesis adjacent to dental implants is a dynamic interaction of osseous cells and a collagenous fiber matrix. This study showed that the interfacial bone consists of a mineralized collagen fiber matrix associated with an inorganic (hydroxylapatite) matrix. This study suggested that an unmineralized collagen fiber matrix initially is laid down directly at the implant surface, and that this matrix then is mineralized. Osteoblasts interacted with this matrix, eventually becoming encased within developing lacunae during the remodeling process. This process formed the cellular (osteocyte) aspects of the developed bone. Osteocyte processes extended through canaliculi directly to the implant surface. Apparently, these processes also were entrapped within canaliculi during the mineralization events. At times, these processes paralleled the implant surface. The bone-implant interfacial zone was primarily fibrillar (both mineralized and unmineralized) in morphology, with an electron-dense, ruthenium positive deposition. This electron-dense material was approximately 20 to 50 nanometers in thickness, and only this thin layer separated the remodeled mineralized bone from the implant.

Determination of accuracy of preoperative templating of noncemented femoral prostheses

The purpose of this study was to determine the accuracy of preoperative templating of primary, noncemented femoral components. A retrospective review of charts and radiographs was performed on 74 hips in 64 patients who had undergone either noncemented total hip arthroplasty (THA) or placement of an endoprosthesis (including bipolar). Preoperative radiographs were templated by a total joint arthroplasty attending surgeon, a senior orthopaedic resident, and a junior resident. The templated size corresponded to the actual femoral implant used in approximately 50% of cases. When femoral prostheses within one size above or below the templated size were included, the accuracy of preoperative templating rose to 88-95%. When implants within two sizes of the templated size were included, the accuracy approached 100%. Factors associated with discrepancies in the size of femoral stem used included placement of an undersized implant, presence of metal hardware that obscured the ability to template accurately, proximal bone deformity, sclerotic bone, acute femoral neck fracture, and inadequate preoperative radiographs. The accuracy of templating increased gradually with the level of training. The most experienced investigator was able to template within one size of the actual implant used in 95% of cases, compared with 88% and 82% for the less experienced investigators. Acute femoral neck fractures and proximal bone deformity were associated with the largest discrepancies in templated sizes.

Avascular necrosis of the medial femoral condyle in HIV-infected patients

Avascular necrosis (AVN) of the femoral head has been described in the literature in patients infected with the human immunodeficiency virus. It has been associated with either a hypertriglyceridemic state or the presence of antiphospholipid antibodies. We describe a case of AVN of the medial femoral condyle in an HIV-infected patient associated with a hypertriglyceridemic state.

Intraoperative arterial occlusion in total joint arthroplasty

Major arterial occlusion during surgery is an uncommon complication. The authors report on two patients who developed intraoperative arterial occlusion during total joint arthroplasty. Both of the patients were smokers and had significant peripheral vascular disease.

Ipsilateral fractures of the femoral neck and shaft

The management of ipsilateral fractures of the femoral neck and shaft has proved to be a challenge to the orthopaedist. Most major institutions have treatment protocols that emphasize early rigid stabilization of the femoral-neck fracture to minimize the incidence of avascular necrosis of the femoral head. Since 1985, the authors' protocol has been to reduce and stabilize the femoral-neck fracture anatomically, followed by treatment of the femoral-shaft fracture. In 1990, we began treating this segmental fracture pattern with reconstruction nails. This study reviews the cases of 11 patients treated at the Medical College of Georgia Hospital from November 1985 to March 1992. Nine of the 11 underwent surgery within 12 hours of injury; 4 of these patients were treated with reconstruction nails. The mean follow-up was 2 years. Seven of the 11 had a good functional outcome, whereas 4 had a fair outcome. The results indicate that patients with ipsilateral fractures of the femoral neck and shaft can obtain good results when early (< 12 hours) rigid anatomic stabilization of the femoral neck is performed. The authors recommend utilizing a reconstruction nail for stabilizing this dual fracture whenever possible.

Temporal stability of paraspinal electromyographic recordings in low back pain and non-pain subjects

This paper presents the results of two studies in which bilateral surface EMG recordings of paraspinal muscle tension were measured in 29 lower back pain and 20 normal subjects in 6 different positions (standing, bending from the waist, rising, sitting with back supported, sitting unsupported, prone) on two occasions, and a comparison of the data from both studies. Measures were highly reliable when examined using analysis of variance procedures. Statistically significant reliability coefficients were obtained when the absolute values of the measures were examined, although in some instances less than 20% of the variance was explained. When examined as relative [percent change from baseline (prone) condition] values, differences between the two groups were observed: the normals were statistically more reliable than lower back pain subjects during every condition. Implications for clinical work and both basic and applied research are discussed.

Assessment of cefazolin and cefuroxime tissue penetration by using a continuous intravenous infusion

A continuous intravenous infusion was used to assess the tissue penetration of cefazolin (14 subjects) and cefuroxime (15 subjects) in orthopedic surgery patients. Subjects were randomly assigned to receive a continuous intravenous infusion of cefazolin (mean, 178.6 mg/h) or cefuroxime (mean, 330.0 mg/h) at a rate estimated to achieve a target steady-state total concentration of 50 micrograms/ml in serum. The infusion was initiated 12 to 14 h before surgery, and blood and muscle tissue samples were collected intraoperatively at the times of incision and wound closure. Although there was a significant difference between the free concentrations of cefazolin (at incision, 9.3 micrograms/ml; at closure, 9.2 micrograms/ml) and cefuroxime in serum (at incision, 26.9 micrograms/ml; at closure, 31.8 micrograms/ml), there was no difference in the total concentrations in muscle at either surgical incision (cefazolin, 6.1 micrograms/g; cefuroxime, 5.6 micrograms/g) or wound closure (cefazolin, 7.7 micrograms/g; cefuroxime, 7.4 micrograms/g). There was a significant correlation between the pooled free serum and total muscle concentrations for cefazolin (P = 0.001); however, there was no correlation between these variables with the pooled cefuroxime data (P = 0.403). These findings indicate that the free drug concentration in serum alone is not consistently predictive of the total concentration of cephalosporin in muscle.

Chronic beta-carotene supplementation does not alter the gastric mucosal response to acute aspirin ingestion

Carotenoids and retinoids have been reported to reduce gastrointestinal mucosa damage from a variety of irritants. We performed double-blind, placebo-controlled endoscopic trial to evaluate the effect of chronic beta-carotene supplementation upon the gastric mucosal response to acute aspirin injury. Six subjects taking chronic beta-carotene and six taking placebo each ingested 650 mg of aspirin after an endoscopy confirmed normal gastric mucosa. Three hours later, mucosal lesions were counted at repeat endoscopy. beta-Carotene did not prevent acute mucosal injury better than placebo.

Theory of Frustrated Total Reflection Involving Metallic Surfaces

The theory for frustrated total reflection has been developed for the case where the third medium is metallic of complex index. Using parallel polarized light a unique minimum in reflectance occurs at a definite film thickness. Experimental verification of the theory is made and indicates the theory applicable to the precise measurement of thin contact films existing between metallic and dielectric surfaces.