Exponent

About: Exponent is a company organization based out in Menlo Park, California, United States. It is known for research contribution in the topics: Population & Risk assessment. The organization has 1589 authors who have published 2680 publications receiving 88140 citations.

Patient function after a posterior stabilizing total knee arthroplasty: cam-post engagement and knee kinematics.

Abstract: Even though posterior substituting total knee arthroplasty has been widely used in surgery, how the cam–post mechanism (posterior substituting mechanism) affects knee joint kinematics and function in patients is not known. The objective of the present study was to investigate posterior femoral translation, internal tibial rotation, tibiofemoral contact, and cam–post engagement of total knee arthroplasty patients during in vivo weight-bearing flexion. Twenty-four knees with a PS TKA were investigated while performing a single leg weight-bearing lunge from full extension to maximum flexion as images were recorded using a dual fluoroscopic system. The in vivo knee position at each targeted flexion angle was reproduced using 3D TKA models and the fluoroscopic images. The kinematics of the knee was measured from the series of the total knee arthroplasty models. The cam–post engagement was determined when the surface model of the femoral cam overlapped with that of the tibial post. The mean maximum flexion angle for all the subjects was 112.5 ± 13.1°. The mean flexion angle where cam–post engagement was observed was 91.1 ± 10.9°. The femur moved anteriorly from 0° to 30° and posteriorly through the rest of the flexion range. The internal tibial rotation increased approximately 6° from full extension to 90° of flexion and decreased slightly with further flexion. Both the medial and lateral contact point moved posteriorly from 0° to 30°, remained relatively constant from 30° to 90°, and then moved further posterior from 90° to maximum flexion. The in vivo cam–post engagement corresponded to increased posterior translation and reduced internal tibial rotation at high flexion of the posterior substituting total knee arthroplasty. The initial cam–post engagement was also mildly correlated with the maximum flexion angle of the knee (R = 0.51, p = 0.019). A later cam–post engagement might indicate an environment conducive to greater flexion. If the factors that affect cam–post engagement timing can be established, proper manipulation of those factors may improve the function of the knee after posterior substituting total knee arthroplasty.

A phased approach for assessing combined effects from multiple stressors.

Abstract: We present a phased approach for evaluating the effects of physical, biological, chemical, and psychosocial stressors that may act in combination. Although a phased concept is common to many risk-based approaches, it has not been explicitly outlined for the assessment of combined effects of multiple stressors. The approach begins with the development of appropriate conceptual models and assessment end points. The approach then proceeds through a screening stage wherein stressors are evaluated with respect to their potential importance as contributors to risk. Stressors are considered individually or as a combination of independent factors with respect to one or more common assessment end points. As necessary, the approach then proceeds to consider interactions among stressors. We make a distinction between applications that begin with effects of concern (effects based) or with specific stressors (stressor based). We describe a number of tools for use within the phased approach. The methods profiled are ones that have been applied to yield results that can be communicated to a wide audience. The latter characteristic is considered especially important because multiple stressor problems usually involve exposures to communities or to ecologic regions with many stakeholders.

Synthetic scaffold coating with adeno-associated virus encoding BMP2 to promote endogenous bone repair

Abstract: Biomaterial scaffolds functionalized to stimulate endogenous repair mechanisms via the incorporation of osteogenic cues offer a potential alternative to bone grafting for the treatment of large bone defects. We first quantified the ability of a self-complementary adeno-associated viral vector encoding bone morphogenetic protein 2 (scAAV2.5-BMP2) to enhance human stem cell osteogenic differentiation in vitro. In two-dimensional culture, scAAV2.5-BMP2-transduced human mesenchymal stem cells (hMSCs) displayed significant increases in BMP2 production and alkaline phosphatase activity compared with controls. hMSCs and human amniotic-fluid-derived stem cells (hAFS cells) seeded on scAAV2.5-BMP2-coated three-dimensional porous polymer Poly(e-caprolactone) (PCL) scaffolds also displayed significant increases in BMP2 production compared with controls during 12 weeks of culture, although only hMSC-seeded scaffolds displayed significantly increased mineral formation. PCL scaffolds coated with scAAV2.5-BMP2 were implanted into critically sized immunocompromised rat femoral defects, both with or without pre-seeding of hMSCs, representing ex vivo and in vivo gene therapy treatments, respectively. After 12 weeks, defects treated with acellular scAAV2.5-BMP2-coated scaffolds displayed increased bony bridging and had significantly higher bone ingrowth and mechanical properties compared with controls, whereas defects treated with scAAV2.5-BMP2 scaffolds pre-seeded with hMSCs failed to display significant differences relative to controls. When pooled, defect treatment with scAAV2.5-BMP2-coated scaffolds, both with or without inclusion of pre-seeded hMSCs, led to significant increases in defect mineral formation at all time points and increased mechanical properties compared with controls. This study thus presents a novel acellular bone-graft-free endogenous repair therapy for orthotopic tissue-engineered bone regeneration.

Dose-response for assessing the cancer risk of inorganic arsenic in drinking water: the scientific basis for use of a threshold approach

Abstract: The biologic effects of inorganic arsenic predominantly involve reaction of the trivalent forms with sulfhydryl groups in critical proteins in target cells, potentially leading to various toxicolog...

Polycyclic aromatic hydrocarbon levels in mussels from prince william sound, ALASKA, USA, document the return to baseline conditions

Abstract: Bioavailable hydrocarbons in the Exxon Valdez oil spill zone in Prince William Sound (PWS; AK, USA) shorelines were at or near background levels in 2002, as indicated by low concentrations of polycyclic aromatic hydrocarbons (PAHs) in mussels (Mytilus trossulus) collected from sites throughout PWS. Total PAH (TPAH) minus parent naphthalene concentrations in mussels collected in 1998 to 2002 from sites oiled in 1989 were at or near reference-site values. Both oiled and reference sites included locations associated with past human and industrial activity (HA). Inclusion of the unoiled HA sites in the range of reference sites that define prespill conditions is consistent with federal regulations. For the period from 1998 to 2002, the geometric mean of TPAH concentrations for 218 mussel samples collected from 72 sites, including four HA sites that had been heavily oiled in 1989, is 54 ng/g dry weight (range, 2–1,190 ng/g). The maximum mussel TPAH concentrations are equivalent to a weathered-oil exposure dose to intertidal foragers that is one to three orders of magnitude less than the doses shown to cause sublethal effects in surrogate species. The geometric mean of TPAH concentrations for mussel samples from 28 locations not oiled in 1989 and unaffected by human use (NHA sites) is 28 ng/g (range, 3–355 ng/g), whereas the geometric mean of TPAH concentrations for mussel samples from 14 locations not oiled in 1989 and affected by human use (HA sites) is 106 ng/g (range, 2–12,056 ng/g). The range of data for the unoiled HA and NHA sites defines the background of bioavailable PAHs to mussels on western PWS shorelines that would have prevailed if the oil spill had not occurred. The low PAH concentrations in mussels from sites known to have subsurface oil residues demonstrates the low bioavailability of these spill remnants and, thus, are a low additional risk to foraging wildlife. The present study shows continuous exposure from four- to six-ring PAHs originating at HA sites in western PWS. At low concentrations, these PAHs are known to cause adverse biological effects. However, in the context of PWS, oiled and HA sites represent a small percentage (∼0.1–0.2%) of the total PWS shoreline.