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1.
Knee Surg Relat Res ; 34(1): 12, 2022 Mar 10.
Article in English | MEDLINE | ID: mdl-35272710

ABSTRACT

INTRODUCTION: Revision knee arthroplasty presents a number of challenges, including management of bone loss. The goal in managing moderate to large bone defects is fixation that is sufficient enough to allow early weight-bearing. The purpose of this study was to describe the surgical technique and clinical and radiographic outcomes of patients treated with porous tantalum metaphyseal cones in combination with long uncemented diaphyseal-engaging stems to manage tibial bone loss in revision total knee arthroplasty (TKA). MATERIALS AND METHODS: Thirty-six aseptic revision TKAs were performed at our institution between 2016 and 2019 by two senior authors. A single trabecular metal tantalum cone combined with a long (100 or 155 mm) press fit, diaphyseal-engaging stem was used in all cases to reconstruct metaphyseal bone defects and to augment tibial fixation. Cemented stems were excluded. The tibiofemoral angle was measured along the tibial and femoral shaft axes on the weight-bearing anteroposterior radiograph at final follow-up (range 15-56 months). All clinical and surgical complications, reoperations, and revisions of any component were recorded. Survivorship free of revision was evaluated at the time of the latest follow-up. RESULTS: The mean Knee Society Score (KSS) and Knee Society Function Score (KSS-F) improved significantly from 29.7 points preoperatively (range 11-54 points) to 86 points (range 43-99 points) and from 20.4 points preoperatively (range 0-55 points) to 72.3 points (range 30-90 points) (p < 0.05), respectively. Eleven tibial constructs (30.5%) had incomplete, nonprogressive radiolucent lines (≤ 2 mm). All tibial cones demonstrated osteointegration. One patient underwent a full revision for periprosthetic joint infection, and survivorship free of any component revision was 91.7% at final follow-up. CONCLUSIONS: Hybrid fixation with uncemented diaphyseal-engaging stems and porous tantalum metaphyseal cones resulted in radiographic lack of osteolysis, good clinical outcomes, and survivorship of 91.7% at a median follow-up of 33 months when considering all-cause revision as the endpoint.

2.
J Thromb Haemost ; 10(3): 382-9, 2012 Mar.
Article in English | MEDLINE | ID: mdl-22212890

ABSTRACT

BACKGROUND: A key feature of factor IXa is its allosteric transformation from an enzymatically latent form into a potent procoagulant. Although several small molecules have been found to be capable of partially affecting FIXa function (i.e. ethylene glycol, Ca(2+), and low molecular weight heparin [LMWH]), the resulting modest changes in peptidolytic activity have made the study of their mechanisms of action challenging. As these effects provide hints about potential regulatory forces that may be operational in the full expression of FIXa coagulant activity, their description remains of great interest. Studies of crystal structures have yielded insights into the structural changes induced by these effectors, but there remains a paucity of information to correlate any given structural change with specific consequences for FIXa function. OBJECTIVES: To correlate structural changes induced by these modulators with defined consequences for FIXa substrate discrimination and function. METHODS: A peptidomics-based mass spectrometry (MS) approach was used to examine the patterns of hydrolysis of four combinatorial chemistry-derived pentapeptide libraries by FIXa under various conditions in a soluble, active enzyme system. RESULTS: Ethylene glycol specifically altered the S3 subsite of FIXa to render it more tolerant to side chains at the P3 substrate position, whereas Ca(2+) enhanced tolerance at the S2 subsite. In contrast, LMWH altered both the S2 and S1' subsites. CONCLUSIONS: These results demonstrate the role of plasticity in regulating FIXa function with respect to discrimination of extended substrate sequences, as well as providing crucial insights into active site modulations that may be capitalized on by various physiologic cofactors of FIXa and in future drug design.


Subject(s)
Factor IXa/metabolism , Binding Sites , Calcium/metabolism , Catalytic Domain , Chromogenic Compounds/metabolism , Combinatorial Chemistry Techniques , Ethylene Glycol/metabolism , Factor IXa/chemistry , Heparin, Low-Molecular-Weight/metabolism , Humans , Hydrolysis , Kinetics , Models, Molecular , Oligopeptides/metabolism , Peptide Library , Peptidomimetics/metabolism , Protein Conformation , Proteomics/methods , Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization , Structure-Activity Relationship , Substrate Specificity
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