Classification Criteria for EsSKOA

EsSKOA logo rev

Symptomatic Knee Osteoarthritis at an Early Structural Stage

In 2021, OARSI launched an initiative to develop classification criteria for Early-stage Symptomatic Knee Osteoarthritis (EsSKOA). This initiative aims to provide a standardized method for identifying and enrolling individuals with symptomatic knee osteoarthritis (OA) but without established OA, i.e. EsSKOA, into clinical studies (people who are currently ineligible for OA clinical trials). The eventual classification criteria must accomplish two tasks: accurately discriminate individuals with EsSKOA from those with other causes for their knee symptoms, and from individuals with established knee OA.

This multi-phase initiative follows methodology established by the American College of Rheumatology (ACR) and European League Against Rheumatism (EULAR) for developing classification criteria, which incorporates: 1) generation of a list of candidate items that should be considered in development of the criteria; 2) data acquisition and analysis to examine the ability of the candidate items, individually and in combination, to discriminate people with EsSKOA from other causes of knee symptoms (mimic conditions) and from individuals with established knee OA; 3) establish the criteria, weights and provisional classification threshold through an evidence-informed consensus approach, including multi-criteria decision analysis; and finally, 4) Assessment of the criteria’s performance characteristics in an independent sample. Ultimately, we want to find the most concise combination of factors that, when applied to individuals with undifferentiated knee symptoms, accurately identifies those with high probability of having EsSKOA.

EsSKOA Phases

As of January 2026, Phase II is underway – determining the usefulness of the candidate items, alone or in combination, to discriminate individuals with EsSKOA from those with a mimic condition or with established radiographic knee OA. Phase II requires data on the candidate items from participants with possible EsSKOA and mimic conditions. We are obtaining this information through two concurrent processes: a) primary data collection; and b) secondary data analysis of existing cohorts. An environmental scan identified 19 existing datasets that might contribute to candidate item analysis. However, most lacked candidate item information and the prevalence of participants with Kellgren-Lawrence (KL) grade 0-1 and possible EsSKOA or a mimic condition was unclear. A pilot study is underway to determine whether to proceed with secondary data abstraction.

As a result, primary data collection is necessary. A protocol has been developed, and funding is being sought to recruit ~200 participants with EsSKOA, ~200 with a mimic condition, and ~200 with established radiographic knee OA (~600 participants total). Eligible participants must have recent knee symptoms, no recent surgery or injury, and no prior joint replacement. Data on candidate items will be collected using standardized questionnaires and physical examination, and laboratory and imaging tests. Presence of established radiographic knee OA will be determined by weight-bearing radiographs of the tibiofemoral and patellofemoral knee compartments. MRI will be performed in those without established radiographic knee OA. A blinded adjudication process will be used to assign ‘gold standard case status’ (EsSKOA or a mimic condition).

A detailed overview of the EsSKOA initiative, our work to date, and future phases is provided in the accompanying slide deck found HERE:

Member Updates:

OCTOBER 2025

September 2024

September 2023

Contact

For further information on the EsSKOA initiative or if you are interested in participating (provide cohort dataset for analysis, collect candidate items, participate in adjudication or expert panel), please contact us at arin.deveci@unityhealth.to.

Acknowledgements and Thanks

Thank you to the industry supporters of this initiative, Grünenthal and Viatris Inc., and the fundraising efforts by Stefan Lohmander, Ali Mobasheri, and Francis Berenbaum, on behalf of OARSI. We also would like to acknowledge support from the OARSI Board of Directors.

View the list of EsSKOA Committee Members here.

Publications

Manuscripts

  1. Mahmoudian A, King LK, Liew JW, Wang Q, Berenbaum F, Das S, Ding C, Emery CA, Filbay SR, Hochberg MC, Ishijima M, Kloppenburg M, Lane NE, Losina E, Mobasheri A, Appleton CT, Englund M, Lohmander LS, Runhaar J, Turkiewicz A, Hawker GA, Neogi T, Haugen IK; OARSI Early-stage Symptomatic Knee Osteoarthritis Initiative. Reframing Early-stage Symptomatic Knee Osteoarthritis (EsSKOA): A Strategic Lens for Trial Design. Osteoarthritis Cartilage. 2025 Dec 20:S1063-4584(25)01279-8. doi: 10.1016/j.joca.2025.12.016.

  2. King LK, Mahmoudian A, Liew JW, Wang Q, Stanaitis I, Schiphof D, Callahan LF, Hunter DJ, Appleton CT, Turkiewicz A, Englund M, Lohmander LS, Haugen IK, Hawker GA, Neogi T, Runhaar J; OARSI Early-stage Symptomatic Knee Osteoarthritis Initiative. Elucidating the initial symptoms and experiences of knee osteoarthritis: An international patient survey. Osteoarthritis Cartilage. 2025;33(9):1147-1152. doi: 10.1016/j.joca.2025.05.008.
  3. Hawker GA, King LK, Liew JW, Wang Q, Mahmoudian A, Jansen NEJ, Stanaitis I, Berenbaum F, Das S, Ding C, Emery CA, Filbay SR, Hochberg MC, Ishijima M, Kloppenburg M, Lane NE, Losina E, Mobasheri A, Runhaar J, Appleton CT, Turkiewicz A, Englund M, Lohmander LS, Haugen IK, Neogi T; OARSI Early-stage Symptomatic Knee Osteoarthritis Initiative. OARSI initiative to develop classification criteria for early-stage symptomatic knee OA (EsSKOA): What conditions should be considered in the differential diagnosis of EsSKOA? Osteoarthritis Cartilage. 2025;33(9):1141-1146. doi: 10.1016/j.joca.2025.05.005.

  4. King LK, Liew JW, Mahmoudian A, Wang Q, Jansen NEJ, Stanaitis I, Hung V, Berenbaum F, Das S, Ding C, Emery CA, Filbay SR, Hochberg MC, Ishijima M, Kloppenburg M, Lane NE, Losina E, Mobasheri A, Turkiewicz A, Runhaar J, Haugen IK, Appleton CT, Lohmander LS, Englund M, Neogi T, Hawker GA; OARSI Early-stage Symptomatic Knee Osteoarthritis Initiative. Multi-centre modified Delphi exercise to identify candidate items for classifying early-stage symptomatic knee osteoarthritis. Osteoarthritis Cartilage. 2025;33(1):155-165. doi: 10.1016/j.joca.2024.10.016.

    ​​​​​Corrigendum to "Multi-centre modified Delphi exercise to identify candidate items for classifying early-stage symptomatic knee osteoarthritis”. Osteoarthritis Cartilage. 33(4):530-533. doi: 10.1016/j.joca.2025.01.002. Erratum for: Osteoarthritis Cartilage. 2025;33(1):155-165. doi: 10.1016/j.joca.2024.10.016.

  5. Mahmoudian A, King LK, Liew JW, Wang Q, Appleton CT, Englund M, Haugen IK, Lohmander LS, Runhaar J, Turkiewicz A, Neogi T, Hawker GA; OARSI Early-stage Symptomatic Knee Osteoarthritis Initiative. Timing is everything: Towards classification criteria for early-stage symptomatic knee osteoarthritis. Osteoarthritis Cartilage. 2024;32(6):649-653. doi: 10.1016/j.joca.2024.02.888.

  6. King LK, Mahmoudian A, Waugh EJ, Stanaitis I, Gomes M, Hung V, MacKay C, Liew JW, Wang Q, Turkiewicz A, Haugen IK, Appleton CT, Lohmander S, Englund M, Runhaar J, Neogi T, Hawker GA; OARSI Early-stage Symptomatic Knee Osteoarthritis Initiative. "You don't put it down to arthritis": A qualitative study of the first symptoms recalled by individuals with knee osteoarthritis. Osteoarthr Cartil Open. 2023;6(1):100428. doi: 10.1016/j.ocarto.2023.100428.

  7. Liew JW, King LK, Mahmoudian A, Wang Q, Atkinson HF, Flynn DB, Appleton CT, Englund M, Haugen IK, Lohmander LS, Runhaar J, Neogi T, Hawker G; OARSI Early Osteoarthritis Classification Criteria Task Force. A scoping review of how early-stage knee osteoarthritis has been defined. Osteoarthritis Cartilage. 2023;31(9):1234-1241. doi: 10.1016/j.joca.2023.04.015.

  8. Hawker GA, Lohmander LS. What an earlier recognition of osteoarthritis can do for OA prevention. Osteoarthritis Cartilage 2021;29:1632-1634. doi: 10.1016/j.joca.2021.08.007.

Abstracts

  1. Hawker G, King L, Liew J, Wang Q, Mahmoudian A, Jansen N, Stanaitis I, Runhaar J, Appleton T, Turkiewicz A, Englund M, Lohmander S, Haugen I, Neogi T. OARSI Initiative to Develop Classification Criteria for Early-Stage Symptomatic Knee OA (EsSKOA): What Should Be Considered in the Differential Diagnosis of EsSKOA? [abstract]. Arthritis Rheumatol. 2024;76(suppl 9). https://acrabstracts.org/abstract/oarsi-initiative-to-develop-classification-criteria-for-early-stage-symptomatic-knee-oa-esskoa-what-should-be-considered-in-the-differential-diagnosis-of-esskoa/.

  2. King L, Mahmoudian A, Liew J, Wang Q, Stanaitis I, Schiphof D, Callahan L, Hunter D, Appleton T, Turkiewicz A, Englund M, Lohmander S, Haugen I, Neogi T, Hawker G, Runhaar J. An International Patient Survey to Identify Candidate Items for Classifying Early-Stage Symptomatic Knee Osteoarthritis [abstract]. Arthritis Rheumatol. 2024;76(suppl 9). https://acrabstracts.org/abstract/an-international-patient-survey-to-identify-candidate-items-for-classifying-early-stage-symptomatic-knee-osteoarthritis/

  3. King L, Liew J, Wang Q, Mahmoudian A, Stanaitis I, Runhaar J, Appleton CT, Turkiewicz A, Englund M, Lohmander S, Haugen IK, Neogi T, Hawker GA. Multi-centre Modified Delphi Exercise to Identify Important Candidate Items for Classifying Early-stage Symptomatic Knee Osteoarthritis. Osteoarthritis Cartilage. 2024;32(suppl 1):S260. doi: 10.1016/j.joca.2024.02.374.

  4. King L, Mahmoudian A, Liew J, Wang Q, Stanaitis I, Schiphof D, Callahan LF, Hunter D, Appleton CT, Turkiewicz A, Englund M, Lohmander S, Haugen IK, Neogi T, Hawker GA, Runhaar J. An International Patient Survey to Identify Candidate Items for Classifying Early-stage Symptomatic Knee Osteoarthritis. Osteoarthritis Cartilage. 2024;32(suppl 1):S257-8. doi: 10.1016/j.joca.2024.02.371.

  5. Liew J, King LK, Mahmoudian A, Wang Q, Flynn DB, Appleton T, Englund M, Haugen IK, Lohmander L, Runhaar J, Neogi T, Hawker G. Defining Early-Stage Knee Osteoarthritis: A Scoping Review. Osteoarthritis Cartilage. 2023;31(suppl 1):S201-S202. doi: 10.1016/j.joca.2023.01.177.

  6. King L, Mahmoudian A, Waugh E, MacKay C, Stanaitis I, Liew JW, Wang Q, Turkiewicz A, Haugen I, Appleton CT, Lohmander S, Englund M, Runhaar J, Neogi T, Hawker GA. “You Don’t Put It Down To Arthritis”: Qualitative Analysis Of The First Symptoms Recalled By Individuals With Knee Osteoarthritis. Osteoarthritis Cartilage. 2023;31 (suppl 1):S208-S209. doi: 10.1016/j.joca.2023.01.186.

  7. Mahmoudian A, King LK, Liew JW, Wang Q, Appleton CT, Englund M, Haugen IK, Lohmander LS, Runhaar J, Turkiewicz A, Neogi T, Hawker G. Candidate Items For Classifying Early-Stage Knee Osteoarthritis: Results From An International Expert Survey. Osteoarthritis Cartilage. 2023;31 (suppl 1):S215. doi: 10.1016/j.joca.2023.01.195.

  8. Liew J, King L, Mahmoudian A, Wang Q, Neogi T, Hawker G. Defining Early-stage Knee Osteoarthritis: A Scoping Review. Arthritis Rheumatol. 2022; 74 (suppl 9). https://acrabstracts.org/abstract/defining-early-stage-knee-osteoarthritis-a-scoping-review/