Validity and sensitivity to change of three scales for the radiographic assessment of knee osteoarthritis using images from the Multicenter Osteoarthritis Study (MOST)

Abstract

Objectives: The purpose of this study was to assess the concurrent validity and sensitivity to change of three knee osteoarthritis (OA) grading scales. The Kellgren-Lawrence (KL) and the Osteoarthritis Research Society International (OARSI) joint space narrowing (JSN) grading scales are well-established. The third scale, the compartmental grading scale for OA (CG) is a novel scale which grades JSN, femoral osteophytes, tibial erosion and subluxation to create a total score.

Methods: One sample of 72 posteroanterior (PA) fixed-flexion radiographs displaying mild to moderate knee OA was selected from the Multicenter Osteoarthritis Study (MOST) to study validity. A second sample of 75 radiograph pairs, which showed an increase in OA severity over 30 months, was selected to study sensitivity to change. The three radiographic grading scales were applied to each radiograph in both samples. Spearman's rank correlation coefficients were used to correlate the radiographic grades and the change in grades over 30 months with a Whole-organ Magnetic Resonance Imaging Score (WORMS)-based composite score which included five articular features of knee OA.

Results: Correlations between the KL, OARSI JSN and CG grading scales and the magnetic resonance image (MRI)-based score were 0.836, 0.840 and 0.773 (P < 0.0001) respectively while correlations between change in the radiographic grading scales and change in the MRI-based score were 0.501, 0.525 and 0.492 (P < 0.0001).

Conclusions: All three radiographic grading scales showed high validity and are suitable to assess knee OA severity. They showed moderate sensitivity to change; therefore caution should be taken when using ordinal radiographic grading scales to monitor knee OA over time.

Keywords: Grading; Knee osteoarthritis; Knee radiographs; Sensitivity to change; Validity.

Conflict of interest statement

Conflict of interest: Co-author T.D.V. Cooke is the president of Orthopedic Alignment and Imaging Services, Inc. which provided the Surveyor™ image analysis program 3.1 free-of-charge. He has shares in OAISYS Inc. and has submitted a patent for a Joint Surgery Triage Tool which uses the compartmental grading scale for knee OA described in this paper.

Co-author N. Segal is an OA CME publication editor for Vindico and editor of a book on musculoskeletal care during pregnancy and current PM&R Journal for Springer SBM, LLC. He has an R42 application in for NIBIB.

Co-author J.A. Singh is a member of the executive of OMERACT, an organization that develops outcome measures in rheumatology and receives arms-length funding from 36 companies; a member of the American College of Rheumatology's Guidelines Subcommittee of the Quality of Care Committee; and a member of the Veterans Affairs Rheumatology Field Advisory Committee. He is a consultant for Savient, Takeda, Allergan and Regeneron and has grants from Takeda and Savient.

Copyright © 2015 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

Figures

Figure 1

Radiographic grade plotted against the WORMS composite score for 72 knees with a range of osteoarthritis severity. KL – Kellgren-Lawrence grading scale OARSI JSN – Osteoarthritis Research Society International joint space narrowing grading scale CG – Compartmental osteoarthritis grading scale WORMS – Whole organ magnetic resonance imaging score