The Knee injury and Osteoarthritis Outcome Score (KOOS) is a widely used patient-outcome reporting (PRO) tool for research purposes in experimental studies and large-scale databases. One of the strongest points of KOOS is that it can be used in both short-term and long-term patient outcome monitoring, which makes this a very unique feature.

The development of KOOS was based on the idea that traumatic knee injuries often cause simultaneous damage to multiple structures (ligaments, menisci, cartilage, etc.), which frequently leads to the development of osteoarthritis in later life.

In order to follow patients after a trauma and gain insight into their changing symptoms and function over time, a tool was needed to help capture patient outcomes at different intervals, not just in the short or long term. Thus, KOOS was born.

Prior instruments, such as the Lysholm knee scoring scale, are focused on the short-term outcomes [1]. Meanwhile, instruments such as the WOMAC focus on long-term results [2]. The KOOS helps to bridge this gap and it can be used for follow-up of both sets of patients: those that require monitoring for acute injury and those that require it for chronic ongoing conditions.

Scoring of the KOOS is straightforward. The questionnaire holds five separately scored subscales: Pain, function in daily living (ADL), Function in Sport and Recreation, Other symptoms, and knee-related Quality of Life (QOL). Each question is assigned a score (0-4) and a normalized score is calculated for each subscale (100 indicates no symptoms and 0 indicates extreme symptoms). The KOOS may be scored manually or via a KOOS Excel scoring file.

The KOOS has been validated for several orthopedic interventions such as anterior cruciate ligament reconstruction, meniscectomy and total knee replacement [3].

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The main advantage of the KOOS is its widespread use in both research and clinical settings. Additionally, because this tool was predicated on the WOMAC survey and contains many of the same questions, a WOMAC score can be calculated from the KOOS questionnaire.

A key advantage of this PRO tool is the ability to use KOOS for both short and long-term outcome reporting. This means it can be used to assess changes from week to week that are induced by treatments (ie. medication, operation, physical therapy etc.), or over years following a primary injury or osteoarthritis.



From a practical standpoint, the KOOS survey presents some challenges. It’s much longer than other questionnaires, and takes patients a considerable amount of time to fill out. In addition, compared to other tools the scoring system is quite complicated and can be very labor and time consuming. If this can be overlooked, the KOOS questionnaire is an excellent tool that’s quickly becoming the instrument of choice for the total knee replacement patient population.

In addition to gaining popularity in the orthopedic surgery community, KOOS is now being recognized by insurance companies as a way to evaluate indications for joint replacement candidates, and to quantify the success of total knee replacement outcomes.



Permission is not required to use the KOOS tool and no license is needed. The official version of KOOS can be obtained free of charge from



  1. Roos, E. M., & Lohmander, L. S. (2003). The Knee injury and Osteoarthritis Outcome Score (KOOS): from joint injury to osteoarthritis. Health and quality of life outcomes, 1(1), 64.
  2. Roos, E. M., & Lohmander, L. S. (2003). The Knee injury and Osteoarthritis Outcome Score (KOOS): from joint injury to osteoarthritis. Health and Quality of Life Outcomes, 1, 64.