Impact of Sustained Synovitis on Knee Joint Structural Degeneration: 4-Year MRI Data from the Osteoarthritis Initiative

Abstract

Background: Synovial inflammation is a risk factor for osteoarthritis (OA). But to date, there is limited information on how inflammation impacts progression of knee OA.

Purpose: To investigate how sustained synovitis, assessed with semi-quantitative magnetic resonance imaging (MRI) scores, impacts progression of knee degenerative changes over 4 years.

Study type: Retrospective cohort study.

Subjects: In 249 participants (N = 132 women [53%]), from the Osteoarthritis Initiative (OAI) two definitions for synovitis were used resulting in two groups of participants with sustained synovitis at baseline, 2-year, and 4-year follow-up (N = 80 and N = 132), and two groups without synovitis at all three time points (N = 81 and N = 47).

Field strength/sequence: 3 T intermediate-weighted (IW) turbo spin-echo (TSE) sequence and three-dimensional (3D) dual-echo steady-state (DESS) sequence.

Assessment: Synovitis was scored semi-quantitatively using the Anterior Cruciate Ligament Osteoarthritis Score (ACLOAS), MRI Osteoarthritis Knee Score (MOAKS), and synovial proliferation score (SPS). Two MRI-based definitions of synovitis were used: (i) score ≥2 based on cumulative score of MOAKS and ACLOAS, and (ii) score ≥3 based on the cumulative score of ACLOAS, MOAKS, and SPS. Changes in structural abnormalities from baseline to year 4 measured using the whole-organ MRI score (WORMS) were defined as outcomes.

Statistical tests: Linear regression models were used to compare the differences in longitudinal changes in WORMS scores between participants with and without sustained synovitis for each definition of sustained synovitis. A P-value of <0.05 was considered statistically significant.

Results: Significantly higher rates of progression were found in participants with synovitis for patellar (Beta coeff. = 0.29) and medial tibial cartilage abnormalities (Beta coeff. = 0.29) for definition (i). For definition (ii), patellar (Beta coeff. = 0.36) and medial femoral cartilage (Beta coeff. = 0.30) abnormalities demonstrated significant differences.

Data conclusion: Greater progression of structural degenerative disease was observed in individuals with sustained synovitis compared to those without sustained synovitis, suggesting that sustained synovitis is associated with progressive OA.

Level of evidence: 3 TECHNICAL EFFICACY: Stage 2.

Keywords: osteoarthritis; osteoarthritis progression; semi-quantitative scores; synovial inflammation; synovitis.

Figure 1:

Subject selection from the OAI database. ACLOAS (Anterior Cruciate Ligament OsteoArthritis Score); BMI (body mass index); KL (Kellgren-Lawrence); MOAKS (MRI Osteoarthritis Knee Score); SD (standard deviation); SPS knee (synovial proliferation score in knee).

Figure 2:

A) Mid-sagittal intermediate-weighted fat-suppressed TSE image of a 47-year-old man with effusion-synovitis in the suprapatellar recess (arrow) consistent with grade 2 according to the ACLOAS grading. B) Axial reformatted 3D DESS image of the same individual with mild irregularity of the synovium consistent with grade 2 synovial proliferation score (arrows) and grade 3 effusion-synovitis according to MOAKS. ACLOAS (Anterior Cruciate Ligament OsteoArthritis Score); MOAKS (MRI Osteoarthritis Knee Score).

Figure 3:

Mid-sagittal intermediate-weighted fat-suppressed TSE images of a 56-year-old participant with sustained effusion-synovitis in the suprapatellar recess (arrow) at baseline (A) and 4-year follow-up (B). Note, progressive cartilage loss at the patella in (B) (Asterix).

Figure 4:

MRI images demonstrating different synovitis classifications. A) Mid-sagittal fat-saturated intermediate weighted TSE image of a knee with ACLOAS 2 (largest suprapatellar recess AP diameter between 5–10 mm). B) Axial fat-saturated DESS reconstruction of a knee with MOAKS score of 1 (small amount of fluid continuously extending into retropatellar space. C) Mid-sagittal fat-saturated intermediate weighted TSE images of knees with SPS score of 3 (extensive synovial thickening with irregular villonodular proliferation) and D) SPS 2 (mildly irregular synovium with presence of synovial bands). Corresponding abnormalities are highlighted with arrows.