SIZE OF KNEE OSTEOPHYTES is under‐estimated as Assessed by MRI USING CT AS A REFERENCE STANDARD

Abstract

The radiographic diagnosis of knee osteoarthritis (OA) is based on the presence of a definite osteophyte (OP). Epidemiologic studies and clinical trials commonly employ MRI using standard clinical sequences and OP assessment is one of the features included. Commonly used sequence protocols in such studies are based on triplanar fat suppressed T2- or proton density-weighted sequences with bony features as well as fibrous and lipomatous tissues appearing hypointense. This may potentially result in underestimation of such features including osteophyte assessment. Computed tomography (CT) is considered as the modality of choice for the analysis of OPs and may therefore be considered a reference standard. To explore the diagnostic performance of routine MRI as used in observational studies and clinical trials of knee OA for the assessment of OPs in all three knee compartments and the femoral notch using CT as a reference standard. The Strontium Ranelate Efficacy in Knee Osteoarthritis Trial (SEKOIA) clinical trial explored the effect of 3 years of treatment with strontium ranelate in patients with primary knee OA. All patients included in the current study participated in the CT sub-study of SEKOIA. In the current investigation, baseline data from three different centers were used. OPs were scored using a modified MOAKS scoring system in the patellofemoral (PFJ), the medial tibio-femoral (TFJ) and the lateral TFJ. Size was assessed from 0 to 3 in 18 locations. Descriptive statistics were used to describe differences in ordinal grading between CT and MRI. In addition, weighted-kappa statistics were employed to assess agreement between scoring using the two methods. Finally, sensitivity, specificity, positive predictive value and negative predictive value as well as AUC measures of diagnostic performance were employed using CT as the reference standard. Mean age of the randomized patients was 62.9 ±7.5 years with a majority of women (70%). Body mass index was 29.9±5.0 kg/m 2 . The target knee JSW was 3.50±0.84 mm at baseline, patients were Kellgren and Lawrence grade 2 (62%) or 3 (38%). Included were 74 patients with available MRI and CT data. Altogether 1332 locations were evaluated. For the PFJ MRI detected 141 (72%) of 197 CT-defined OPs with a w-kappa of 0.58 (95% CI [0.52-0.65]). In the medial TFJ, MRI detected 178 (81%) of 219 CT-OPs with a w-kappa of 0.58 (95% CI [0.51-0.64]). For the lateral compartment these numbers were 84 (70%) of 120 CT-OPs with a w-kappa of 0.58 (95% CI [0.50-0.66]). Regarding disagreement, for the PFJ MRI underestimated OP size in 94 cases (21%) and over-estimated in 27 cases (6%). For the medial TFJ these numbers were 90 (20%) and 29 (7%), and for the lateral TFJ 67 (15%) and 15 (3%). Details of the diagnostic performance analysis are presented in Table 1 . MRI underestimates presence and size of osteophytes in all 3 knee compartments. However, the sensitivity of >0.9 for OP detection in the medial compartment, which is commonly the compartment of relevance in clinical DMOAD trials, reflects that MRI is adequately able to detect osteophytes that commonly define structural disease. CT may be helpful particularly reading assessment of small osteophytes particularly in early disease. No funding was received for this sub-analysis of the SEKOIA Study AG has received consultancies, speaking fees, and/or honoraria from Pfizer, Novartis, AstraZeneca, Merck Serono, and TissueGene and is President and shareholder of Boston Imaging Core Lab (BICL), LLC a company providing image assessment services. FWR is Chief Medical Officer and shareholder of BICL, LLC. and has received consultancies, speaking fees, and/or honoraria from Calibr –California Institute of Biomedical Research and Grünenthal, GmbH CORRESPONDENCE ADDRESS: frank.roemer@uk-erlangen.de .