OBJECTIVES: While a variety of knee-specific instruments currently exist, no patient-reported outcome (PRO) measures correlate function with improved stability, motion, satisfaction, and confidence. The objective of our study was to address the identified gap in available PROs assessing this phenomenon of a “normal” knee following primary TKA. METHODS: A conceptual model linking the impact of clinical mechanics to hypothesized functional outcomes was generated following a literature review of available assessment tools.  Participants aged 18 to 80 who had undergone TKA within the past 10 to 18 months were identified through clinical sites to participate in Phase 1) focus groups, or Phase 2) in-depth interviews. Participants were asked to describe experiences with their knee replacement and general questions about how their knee feels now, since they had the surgery, followed by cognitive debriefing of the draft items.  Specific inclusion and exclusion criteria were developed in addition to a semi-structured interview guide. Constant comparative analysis was employed to identify key points and compared across all results to observe themes in participant experiences. RESULTS: Results from the first phase of the project indicated that the concepts of confidence, stability, and satisfaction in their replacement knee when performing activities requiring certain motions were felt to be distinct from each other and important in the patients’ assessment of their TKA. Phase 2 efforts yielded a final version of the PKIP scale containing 9 items assessing the broader concepts of stability, confidence and satisfaction in association with activities. Both a pre and post-surgical version of the measure were created. CONCLUSIONS: Results of this qualitative study support the use of the PKIP to assess performance following primary TKA. Psychometric evaluation of the PKIP is planned.