Evaluation of model-based RSA for in vivo measurement of polyethylene wear in a total knee replacement
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There is a need for a repeatable method of measuring polyethylene wear in total knee re-placement (TKA). Model-based radiostereometric analysis (MBRSA) is a high accuracy diagnostic tool with the potential to meet this need; however, a number of unknowns must be examined. This research examines optimized patient positioning for MBRSA imaging as well as in vitro validation of a wear measurement technique using a loaded TKA phantom to mimic patient physiology. Imaging along the antero-posterior and medio-lateral axes of the patient achieved op-timal MBRSA accuracy of better than 0.035 mm (in-plane) and 0.12° (in-plane). The de-veloped MBRSA technique underestimated TKA wear on previously-worn polyethylene bearings; however, a number of factors can be corrected to improve this discrepancy. This research provides an overall methodology for measuring TKA wear, but additional experimentation and an improved physiological phantom are needed to obtain accurate wear measurement.