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State v. McAfee.

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Civil Rights↗

Revisability of the CHARITE artificial disc replacement: analysis of 688 patients enrolled in the U.S. IDE study of the CHARITE Artificial Disc.

STUDY DESIGN: A prospective, randomized, multicenter, FDA-regulated Investigational Device Exemption clinical trial. OBJECTIVES: To analyze the incidence of, and reasons for, reoperation in all patients (treatment and control) enrolled in the IDE study. SUMMARY OF BACKGROUND DATA: This is the first report of the incidence and nature of reoperations following lumbar TDR as part of a controlled, prospective, multicenter trial. METHODS: A total of 688 patients meeting the inclusion and exclusion criteria were enrolled in one of three arms of the study at 14 centers across the United States. This cohort includes 71 nonrandomized cases, 205 randomized cases, and 313 continued access cases, all receiving the CHARITE Artificial Disc, as well as 99 randomized cases in the control group (ALIF with threaded fusion cages and autograft). A detailed analysis was performed of clinical chart notes, operative notes, and adverse event reports for all patients requiring reoperation following their index surgery. RESULTS: Of the 589 patients with TDR, 52 (8.8%) required reoperation. Of the 99 patients with lumbar fusion, 10 (10.1%) required reoperation, and an additional 2 required surgery for adjacent level disease (P = 0.7401). There were 24 TDR patients who underwent a repeated anterior retroperitoneal approach, with 22 (91.7%) having had a successful removal of the prosthesis. Seven of the 24 TDR prostheses requiring removal were revised to another CHARITE Artificial Disc. The mean time to reoperation in all patients was 9.7 months. A total of 29 patients (4.9%) in the TDR group required posterior instrumentation and fusion as did 10 (10.1%) in the control group (P = 0.0562). At 2 years or more follow-up, 93.9%(553/589 = 93.9%) of patients receiving TDR with the CHARITE Artificial Disc had a successfully functioning prosthesis with a mean of over 7 degrees of flexion-extension mobility. CONCLUSIONS: Lumbar TDR with the CHARITE Artificial Disc did not preclude any further procedures at the index level during primary insertion, with nearly one third being revisable to a new motion-preserving prosthesis and just over two thirds being successfully converted to ALIF and/ or posterior pedicle screw arthrodesis, the original alternative procedure.

Adult↗

Identification and determination of material properties for porohyperelastic analysis of large arteries.

A "porohyperelastic" (PHE) material model is described and the theoretical framework presented that allows identification of the necessary material properties functions for soft arterial tissues. A generalized Fung form is proposed for the PHE constitutive law in which the two fundamental Lagrangian material properties are the effective strain energy density function, W(e), and the hydraulic permeability, kij. The PHE model is based on isotropic forms using W(e) = Ue (phi) = 1/2C0(e phi - 1) and the radial component of permeability, kRR = kRR(phi), with phi = C1'(I1 - 3) + C2'(I2 - 3) + K'(J - 1)2. The methods for determination of these material properties are illustrated using experimental data from in situ rabbit aortas. Three experiments are described to determine parameters in Ue and kRR for the intima and media of the aortas, i.e., (1) undrained tests to determine C0, C1', and C2'; (2) drained tests to determine K'; and (3) steady-state pressurization tests of intact and de-endothelialized vessels to determine intimal and medial permeability (adventitia removed in these models). Data-reduction procedures are presented that allow determination of kRR for the intima and media and Ue for the media using experimental data. The effectiveness and accuracy of these procedures are studied using input "data" from finite element models generated with the ABAQUS program. The isotropic theory and data-reduction methods give good approximations for the PHE properties of in situ aortas. These methods can be extended to include arterial tissue remodeling and anisotropic behavior when appropriate experimental data are available.

Animals↗

Finite element models for arterial wall mechanics.

Arterial wall mechanics has been studied for nearly 200 years. This subject is of importance if we are to gain a fundamental understanding of this complex biological structure, as well as information needed to design prosthetics. Biomechanical arterial models continue to play an important role in the study of atherosclerosis, a disease of the arterial wall that is the chief cause of mortality and morbidity in the United States and the Western World. Over the past 20 years, the finite element model (FEM) has been used in a variety of ways to simulate the structural response of large arteries. Our purpose is to summarize the uses of FEMs in arterial mechanics. We will also indicate directions for future research in this area. A specialized FEM was described in the literature for the study of transport in the arterial wall, however the convection was not directly linked to arterial wall mechanics. In this paper special attention will be given to the development of FEMs based on the poroelastic view of arterial tissues which couple wall deformation, free tissue fluid motion, and associated transport phenomena in the arterial wall. In the future such models should provide fundamental quantitative information relating arterial wall mechanics and transport which may lead to a better understanding of both normal arterial physiology and atherogenesis.

Arteries↗