The KOOS, JR. is a short, patient-reported measure of knee health designed for use around knee replacement. This page explains what the KOOS, JR. is, what it measures, the questions it contains, how it is scored, and how it is used.
What is the KOOS, JR.?
The KOOS, JR. (Knee Injury and Osteoarthritis Outcome Score for Joint Replacement) is a seven-item, patient-reported outcome measure of knee health. It was developed from the longer KOOS using Rasch analysis by Stephen Lyman and colleagues at the Hospital for Special Surgery, and it is designed specifically for evaluating outcomes of total knee arthroplasty. It is recommended by the American Academy of Orthopaedic Surgeons for patients with knee osteoarthritis and requires only about a fifth-grade reading level.
What does the KOOS, JR. measure?
The KOOS, JR. captures a single dimension of overall knee health that combines pain, stiffness, and function in daily living. It is intended for pre- and postoperative assessment of patients undergoing knee replacement.
What questions are included in the KOOS, JR.?
The seven items are drawn from the original KOOS and address knee stiffness, pain during specific activities such as twisting or pivoting and straightening the knee, and difficulty with daily tasks such as rising from sitting, standing, and getting in or out of a car or bath.
How is the KOOS, JR. scored?
Each item is answered on a five-point scale coded 0 (none) to 4 (extreme). The seven raw item scores are summed (raw range 0 to 28) and converted to an interval score from 0 to 100 using a published conversion table, where 0 represents total knee disability and 100 represents perfect knee health.
How is the KOOS, JR. used in clinical practice?
The KOOS, JR. is used to establish a preoperative baseline and to monitor recovery after knee replacement. Its brevity makes it suitable for frequent administration, and clinical research supports its use at more frequent intervals than longer instruments. For example, a patient might start with a preoperative score around 40 and improve to roughly 75 by twelve weeks after surgery, reflecting reduced symptoms and greater independence.
Strengths and limitations
Strengths include brevity, easy readability, structural validity, and suitability for high-volume outcome programs. Limitations include a narrower scope than the full KOOS, since it does not separately report sport or quality-of-life subscales, and it is designed for the joint-replacement population rather than every knee condition.
Frequently asked questions
How many questions are on the KOOS, JR.? Seven items drawn from the original KOOS.
What does a KOOS, JR. score of 100 mean? It represents perfect knee health; 0 represents total knee disability.
How is KOOS, JR. different from the full KOOS? The full KOOS has 42 items across five subscales, while the KOOS, JR. is a seven-item single-dimension short form.
References
- Lyman S, Lee YY, Franklin PD, Li W, Cross MB, Padgett DE. Validation of the KOOS, JR: a short-form knee arthroplasty outcomes survey. Clinical Orthopaedics and Related Research. 2016;474(6):1461-1471.
- Roos EM, Roos HP, Lohmander LS, Ekdahl C, Beynnon BD. Knee Injury and Osteoarthritis Outcome Score (KOOS): development of a self-administered outcome measure. Journal of Orthopaedic & Sports Physical Therapy. 1998;28(2):88-96.
- Hospital for Special Surgery. KOOS, JR. scoring instructions and interval score table.
