Activities of Daily Living and Their Impact on Total Knee Replacement Wear

There are multiple factors affecting the wear performance of total knee replacement (TKR) polyethylene tibial components. The prosthesis (materials and design), the patient (joint loading during daily activities and their frequency) and the surgeon (implant alignment and soft tissue balancing) all influence the wear performance. While many of these factors have been investigated, the contributions of patient factors, such as daily physical activities and activity level, are not fully understood. This thesis investigated the effect of various daily physical activities on the wear of TKR tibial components. A sample TKR population was followed throughout the day to gain more knowledge about frequencies and durations of daily physical activities and their transitions. External knee moments and internal knee motions were obtained for the most frequent physical activities. The knee moments and motions were used to calculate knee contact forces using a parametric modeling approach. Two analytical wear models based on sliding distance and cross-shear motion were used to assess the wear impact of different physical activities. An in vitro methodology to accelerate the creation and assessment of wear scars generated by different physical activities was also developed. Chair and stair were the most frequent activities performed throughout the day and were therefore further investigated. In comparison to ISO walking, the loads and motions generated during chair and stair maneuvers were larger and comprised longer period of time. Results from the sliding distance and cross-shear wear models indicated that standardized preclinical wear evaluation may only account for about 70% of the wear generated in vivo. The wear scar features produced by chair and stair activities shared more similarities with in vivo worn components than with those components tested according to ISO. In conclusion, the results of this thesis suggest that daily physical activities, such as chair and stair, should be included in standardized wear testing protocols for the pre-clinical wear evaluation of TKR prosthesis. Such a multi-activity wear testing protocol may generate wear conditions that better recreate those occurring in vivo.