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2003 Summer Bioengineering Conference, June 25-29, Sonesta Beach Resort in Key Biscayne, Florida INTRODUCTION Wear of ultra-high molecular weight polyethylene (UHMWPE) in total knee replacements remains a major limitation to the longevity of these clinically successful devices [1]. Improvements in sterilization techniques over the past decade have reduced oxidative degradation of the UHMWPE bearing, with potentially dramatic long-term reductions in fatigue-related pitting and delamination wear. However, abrasive- adhesive or “mild” wear mechanisms remain, with the potential to generate large numbers of submicron debris particles of osteolytic potential [2]. Figure 1. Four-step process used to develop and evaluate in vivo computational wear predictions. This study presents a novel computational approach for predicting patient-specific mild wear from in vivo knee kinematics (Fig. 1a), dynamic contact simulations (Fig 1b), and tribological modeling (Fig 1c). The effort was guided by the concept that no tuning of model parameters would be done, and only previously published values for material properties and other input parameters would be used. The approach was evaluated by predicting wear in a knee for which an autopsy-retrieved tibial insert was available (Fig. 1d). METHODS Fluoroscopic kinematic data previously collected from one total knee arthroplasty patient (female, age 65 at surgery, height 170 cm, mass 70 kg) were used in this study [3]. The patient received a cemented posterior cruciate ligament retaining prosthesis (Series 7000, Stryker Howmedica Osteonics, Allendale, NJ) with a 6.8 mm thick tibial insert. The patient gave written informed consent to participate as described previously [3]. The patient performed treadmill gait and stair rise/descent activities during fluoroscopic motion analysis [4] 21 months after surgery (Fig. 1a). Kinematic data from one representative cycle of each activity were averaged in 5° increments of knee flexion for stair and 1% increments for gait including stance and swing phases. Cycle duration was 1.22 sec for gait and 4.6 sec for stair. Dynamic simulations to predict in vivo tibial insert contact pressures and slip velocities were created by incorporating an elastic contact model into the commercial multibody dynamics code Pro/MECHANICA MOTION (Parametric Technology, Waltham, MA). The contact model treats the tibial insert as an elastic foundation
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This note was uploaded on 08/22/2011 for the course EGM 4313 taught by Professor Mei during the Spring '08 term at University of Florida.

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