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Unformatted text preview: 2003 Summer Bioengineering Conference, June 25-29, Sonesta Beach Resort in Key Biscayne, Florida INTRODUCTION Debris particle generation of ultra-high-molecular-weight polyethylene (UHMWPE) remains a clinical issue in total joint replacements such as knees and hips. Significant advances in modeling and understanding the origin of wear debris liberation in total hip replacements have been made over the past decade. One recently- discovered aspect is the importance of sliding direction on wear in UHMWPE [1,2]. Orders of magnitude changes in wear rate with increasing degree of crossing motion have been reported. In contrast to the hip, which is axi-symmetric and conformal, the knee produces complex motions that have prevented detailed study of tibial insert crossing patterns. Locus plots (Fig. 1a), which seek to represent the kinematics by following the most probable trajectory of contact on the surface, do not capture the relative motions experienced by particular surface locations (Fig. 1a). While slip velocity vectors can be plotted for individual surface locations (Fig. 1b) , they cannot be plotted for all locations simultaneously to visualize crossing on the entire surface. Thus, a new approach is needed to visualize the extent of crossing experienced by all locations on the surface simultaneously over an entire activity cycle. This study presents such an approach and evaluates it using in vivo patient-specific kinematics. Figure 1. (a) Locus plot and (b) slip velocity representations of crossing motions on the tibial insert contact surfaces based on in vivo stair kinematic data. METHODS 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 . 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 performed treadmill gait and stair rise/descent activities during fluoroscopic motion analysis  and gave written informed consent to participate . 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 normalized to 1 sec for both activities....
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- Spring '08
- Aerospace Engineering, Knee replacement, tibial insert, tibial insert contact