Background Medicare is rapidly moving toward using patient-reported outcome measures (PROMs) for outcomes assessment and justification of orthopaedic and other procedures. Numerous measures have been developed to study knee osteoarthritis (OA); however, many of these surveys are long, disruptive to clinic flow, and result in incomplete data capture and/or low followup rates. The Knee injury and Osteoarthritis Outcome (KOOS) physical function short-form (KOOS-PS), while shorter, ignores pain, which is a primary concern of patients with advanced knee OA. Questions/purposes Our objective was to derive and validate a short-form survey focused on the patient with end-stage knee OA undergoing TKA.Methods Using our hospital's knee replacement registry, we retrospectively identified 2291 patients with knee OA who underwent primary unilateral TKA and had completed preoperative and 2-year postoperative PROMs. We assessed 30 items from the 42-item KOOS that were quantitatively most difficult for patients to perform before TKA and qualitatively most relevant to patients with endstage knee OA. Rasch analysis identified the KOOS, JR, a seven-item instrument, representing a single dimension, which we define as ''knee health'' because it reflects aspects of pain, symptom severity, and activities of daily living (ADL) including movements or activities that are directly relevant and difficult for patients with advanced knee OA. We assessed the internal consistency, external One or more of the authors (SL, PDF) has received funding from the Agency for Healthcare Research and Quality (Rockville, MD, USA). One of the authors certifies that he (MBC), or a member of his or her immediate family, has or may receive payments or benefits, during the study period, an amount of USD 10,000 to USD 100,00 from Intellijoint (Waterloo, ON, Canada), an amount of USD 10,000 to USD 100,000 from Smith & Nephew (London, UK), an amount of USD 10,000 to USD 100,00 from Exactech (Gainesville, FL, USA), an amount of USD 10,000 to USD 100,00 from Link (Hamburg, Germany), and an amount of USD 10,000 to USD 100,000 from Acelity (San Antonio, TX, USA). One of the authors certifies that he (DEP) or a member of his or her immediate family, has or may receive payments or benefits, during the study period, an amount of more than USD 1,000,001 from Stryker-Mako (Fort Lauderdale, FL, USA). All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research 1 editors and board members are on file with the publication and can be viewed on request. Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.