Evolution of semi-quantitative whole joint assessment of knee OA: MOAKS (MRI Osteoarthritis Knee Score)

Abstract

Objective: In an effort to evolve semi-quantitative scoring methods based upon limitations identified in existing tools, integrating expert readers' experience with all available scoring tools and the published data comparing the different scoring systems, we iteratively developed the magnetic resonance imaging (MRI) Osteoarthritis Knee Score (MOAKS). The purpose of this report is to describe the instrument and its reliability.

Methods: The MOAKS instrument refines the scoring of bone marrow lesions (BMLs) (providing regional delineation and scoring across regions), cartilage (sub-regional assessment), and refines the elements of meniscal morphology (adding meniscal hypertrophy, partial maceration and progressive partial maceration) scoring. After a training and calibration session two expert readers read MRIs of 20 knees separately. In addition, one reader re-read the same 20 MRIs 4 weeks later presented in random order to assess intra-rater reliability. The analyses presented here are for both intra- and inter-rater reliability (calculated using the linear weighted kappa and overall percent agreement).

Results: With the exception of inter-rater reliability for tibial cartilage area (kappa=0.36) and tibial osteophytes (kappa=0.49); and intra-rater reliability for tibial BML number of lesions (kappa=0.54), Hoffa-synovitis (kappa=0.42) all measures of reliability using kappa statistics were very good (0.61-0.8) or reached near-perfect agreement (0.81-1.0). Only intra-rater reliability for Hoffa-synovitis, and inter-rater reliability for tibial and patellar osteophytes showed overall percent agreement <75%.

Conclusion: MOAKS scoring shows very good to excellent reliability for the large majority of features assessed. Further iterative development and research will include assessment of its validation and responsiveness.

Conflict of interest statement

Conflict of interest statement

The corresponding author had full access to all the data in the study and had final responsibility for the decision to submit for publication.

Other authors declared no conflict of interest.

Copyright © 2011 Osteoarthritis Research Society International. All rights reserved.

Figures

Figure 1

Subregional division of the patella in the axial plane. Axial T2w image shows the medial (M) and lateral (L) portions of the patella as divided in MOAKS. Note that the patellar apex is part of the medial subregion (arrow).

Figure 2

Anatomical delineation of femur into trochlea (T), central (C) and posterior (P) regions on sagittal projection. Sagittal projection depicts delineation of the tibia into anterior, central and posterior subregions, which is divided into equal thirds.

Figure 3

Coronal IW image shows anatomical delineation of the tibia into medial, subspinous (SS) and lateral subregions. The femur is divided into the medial and lateral femoral condyle. The intercondylar notch is considered to be part of the medial femur.

Figure 4

BML grading. Grade 0= none, grade 1 66% of subregional volume. A. Coronal T2 w image shows small grade 1 BML in central subregion of medial tibia. B. A grade 2 BML is depicted in central subregion of medial femur. C. Grade 3 BMLs in the central subregions of the medial femur (arrows) and central medial tibia (arrowheads). D. Coronal image shows BML consisting of non-cystic/ill-defined portion (arrowheads) and cystic (arrow) part.

Figure 5

Grade for size of any cartilage loss as a % of surface area as related to the size of each individual region. Grade 0= none, grade 1 75% of region of cartilage surface area. (Drawing courtesy of Daichi Hayashi, MD)

Figure 6

Locations for osteophytes scoring. A. Coronal plane. Osteophytes are scored at the marginal locations of the medial and lateral femur and tibia, respectivel (arrowheads). B. Sagittal plane. Osteophytes are scored at the superior and inferior patellar pole (arrowheads). C. Axial plane. Osteophytes are scored at yhe medial and lateral patella poles (arrowheads), at the anterior medial and lateral femur (black arrows) and the posterior femur medial and lateral (white arrows). Note that there are two locations medially and laterally for osteophytes scoring at the posterior femur, the central and peripheral location. Only the larger osteophyte for either the central or peripheral location will be scored.

Figure 7

Scoring of osteophytes. Grade 0= none, grade 1=small, grade 2= medium and grade 3= large. A. Grade 1 osteophyte medial femur. B. Grade 2 osteophyte lateral femur. C. Grade 3 osteophyte lateral femur. Size of osteophyte should reflect protuberance (how far the osteophyte extends from the joint) rather than total volume of osteophyte

Figure 8

Hoffa-synovitis. Sagittal T2w image shows grade 2 hyperintense signal changes in Hoffa’s fat pad consistent with Hoffa-synovitis.

Figure 9

Effusion-synovitis. Hyperintensity within the articular cavity represents a composite of effusion and synovial thickening that cannot be distinguished from each other in the absence of contrast. Grade 0= none, grade 1=small, grade 2= medium and grade 3= large. A. Grade 0 effusion-synovitis. Normal intraarticular hyperintensity is depicted. B. Grade 1 effusion-synovitis. C. Grade 2 effusion synovitis. D. Grade 3 effusion-synovitis.