Abstract| Volume 28, SUPPLEMENT 1, S26, April 2020

Comparison of radiographic and MRI osteoarthritis definitions and their combination for prediction of tibial cartilage loss, knee symptoms and total knee replacement - a longitudinal study

      Purpose: In the absence of a clear definition of osteoarthritis (OA) using magnetic resonance imaging (MRI) features, the Osteoarthritis Research Society International (OARSI) OA Imaging Working Group developed a definition of MRI-defined structural OA (MRI-OA) by incorporating MRI changes using a Delphi approach, but this needs validation. This study aimed to assess whether MRI-OA is superior to the radiographic definition of OA (ROA) by describing their value for predicting tibial cartilage loss, knee pain and disability and total knee replacement (TKR) in a population-based cohort.
      Methods: In a prospective, population-based older adult cohort, 574 participants (mean 62 years, 49% female) with baseline data on both MRI and x-ray scans of the right knee were included in this study. ROA and MRI-OA at baseline were defined according to the OARSI atlas and a published Delphi exercise, respectively. A 1.5T MRI of the right knee was also performed at 2.6 and 10.7 years. Tibial cartilage volume was measured over 2.6 and 10.7 years. Knee pain and disability were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) at baseline, 2.6, 5.1 and 10.7 years. TKR of the right knee over 13.5 years was identified with linkage to the Australian Orthopaedic Association National Joint Replacement Registry. The value of ROA (vs. no ROA), MRI-OA (vs. no MRI-OA) and the combination of them (vs. those with neither) for predicting tibial cartilage loss, the onset and progression of knee symptoms and risk of TKR was evaluated using multivariable linear regression or log-binomial regression models.
      Results: Of participants included, 8% had ROA alone, 15% had MRI-OA alone, 13% had both ROA and MRI-OA. Having ROA (vs. no ROA) and MRI-OA (vs. no MRI-OA) predicted greater tibial cartilage loss over 2.6 years (-75.9 and -86.4 mm3/year, respectively) and higher risk of TKR over 13.5 years (Risk Ratio [RR]: 15.0 and 10.9, respectively). However, only MRI-OA predicted tibial cartilage loss over 10.7 years (-7.1 mm3/year) and only ROA predicted the onset and progression of knee symptoms (RR: 1.32-1.88). Compared to participants with neither MRI-OA nor ROA, those with ROA alone showed an increased risk of knee symptom progression over 10.7 but not 2.6 or 5.1 years (RR: 1.32-1.88) and those with MRI-OA alone had greater loss of tibial cartilage volume over 2.6 but not 10.7 years (-81.7 mm3). Participants with either ROA or MRI-OA alone had an increased risk of TKR (6.4% and 3.6%, respectively; RR: 11.5 and 6.8, respectively) compared to those with neither (0.5%). In contrast, participants with both MRI-OA and ROA had the greatest loss of tibial cartilage volume (over 2.6 years: -116.1 mm3/year; over 10.7 years: -11.2 mm3/year) and the highest onset and progression of knee symptoms (RR: 1.75-2.89) and risk of TKR (25%, RR: 50.9).
      Conclusions: The findings of this study suggest that the present MRI-defined OA using Delphi exercise is not superior to ROA for predicting structural or symptomatic OA progression but, its combination with ROA has much stronger predictive validity.