Background Total knee joint replacement (TKR) is a cost-effective procedure with good long-term outcomes. However, at present there is no clear consensus on indications for TKR. Imaging biomarkers capable of predicting TKR therefore are urgently needed and may be helpful in clinical studies and trials which utilize TKR as an outcome. Hoffa-synovitis and effusion-synovitis, which may be assessed on non-contrast enhanced MRI, have been identified as important disease features relevant for clinical disease manifestations such as pain but may also be relevant for structural progression. Furthermore, worsening or improvement in these inflammatory imaging markers is associated with worsening or improvement in pain. For these reasons Hoffa- and effusion-synovitis are promising candidate imaging biomarkers for TKR.

Objectives Aim of the study was to assess if presence or worsening of Hoffa- and effusion-synovitis prior to TKR increases risk for TKR and if change in these two measures prior to TKR further affects the risk for TKR.

Methods We studied 121 knees from OAI participants (age 45-78 years) that underwent TKR before the 48 month visit using the time point prior to TKR, (e.g. for a TKR reported at the 48 month (M) visit, T0 =36M and T-1 =24M) and 121 control knees that did not undergo TKR that were matched for radiographic disease stage, gender, and age and were assessed at the same T0 and T-1 follow-up visit. Images were acquired at four OAI clinical centers using dedicated 3 T scanners. MRIs were read for Hoffa- and effusion-synovitis using the semiquantitative MOAKS system, which scores both features from 0-3 with 0 being normal and 3 coding severe structural changes. Conditional logistic regression comparing matched knees was applied to assess the risk of TKR at T0. In addition change in Hoffa- and effusion-synovitis from the time point prior (T-1) to T0 was analyzed in regard to risk for TKR following T0.

Results Subjects were on average 65.5 years old (SD ± 8.6), predominantly female (58.1%) and overweight (mean BMI 29.5 SD ± 4.88). In the comparison of the T0 time point, the odds for TKR were significantly increased for the group exhibiting any effusion-synovitis at T0 when compared to the knees without effusion-synovitis at T0 as the reference (OR 2.45 95% confidence interval [CI] 1.22-4.95). No significant associations were found for presence of Hoffa-synovitis at T0 (OR 1.11, 95% CI 0.58-2.15).

Worsening of either Hoffa- and effusion-synovitis from T-1 to T0 was associated with increased odds for TKR (OR 7.0, 95% CI 1.59,30.80 and 2.27, 95% CI 1.11,4.62 respectively).

Conclusions Presence of effusion-synovitis at the time point prior to TKR (T0) increases risk of TKR, while presence of Hoffa-synovitis does not. The latter finding is likely explained by the non-specific character of this imaging marker. Worsening of Hoffa- and effusion-synovitis from T-1 to T0 both increase risk for TKR. Presence and change of these imaging markers are important prognostic markers in regard to the structural progression of knee OA using TKR as the outcome measure.

Disclosure of Interest A. Guermazi Shareholder of: Boston Imaging Core Lab (BICL),LLC., Consultant for: Facet Solutions, Genzyme, Novartis, Stryker,Merck Serono, F. Roemer Shareholder of: Boston Imaging Core Lab (BICL), LLC., Consultant for: Merck Serono, NIH, M. Hannon: None Declared, R. Boudreau: None Declared, D. Hunter Grant/Research support from: Australia Research Council Future Fellowship, Consultant for: DonJoy, NIH, Stryker, F. Eckstein Shareholder of: Chondrometrics, D. Hayashi: None Declared, Z. Wang: None Declared, C. K. Kwoh Consultant for: Novartis