OP0055 A novel method for assessing proximal tibiofibular joint on mr images in patients with knee osteoarthritis

Background Proximal tibiofibular joint (ProxTibFibJ) is a synovial sliding joint that has been estimated to transmit one-sixth of the leg’s static load. One study has reported that proximal fibular osteotomy could significantly improve the clinical outcomes in patients with medial compartment OA. However, no study has delineated the measurement of ProxTibFibJ morphological parameters (ProxTibFibJ contacting area, load-bearing area, lateral stress-bolstering area and posterior stress-bolstering area) on magnetic resonance imaging (MRI) and investigated their correlations with knee OA structural abnormalities. Objectives To validate a pragmatic method to measure the morphological parameters of the ProxTibFibJ and to describe their associations with knee structural abnormalities in patients with knee osteoarthritis (OA). Methods A total of 408 participants with knee OA were selected. The morphological status of ProxTibFibJ were measured on coronal and sagittal magnetic resonance images (MRI). We calculated the contacting area of ProxTibFibJ (S), and its projection areas onto the horizontal (load-bearing area, Sτ), sagittal (lateral stress-bolstering area, Sφ) and coronal plane (posterior stress-bolstering area, Sυ), respectively. Knee structural abnormalities including cartilage defects, bone marrow lesions (BMLs) and cartilage volume were evaluated. Clinical construct validity was examined through describing the associations between the morphological parameters of ProxTibFibJ and knee structural abnormalities. The reliabilities were examined by calculating the intra- and inter-observer correlation coefficients. Results The average ProxTibFibJ fibular contacting area was 2.4±0.7 cm 2 . The intra- and inter-observer correlation coefficients for all measures were excellent (all ≥0.90). In cross-sectional analyses, the ProxTibFibJ morphological parameters (S, Sτ, Sυ and Sφ) were significantly associated with radiographic medial JSN (OR 1.72 for S; 2.20 for Sτ; 1.65 for Sυ), radiographic medial osteophyte (OR 0.51 for Sφ) and MRI-assessed knee joint structural abnormalities including cartilage volume (β −0.07 for S; −0.09 for Sτ), cartilage defects (OR 1.63 for S; 1.95 for Sτ) and BMLs (OR 1.54 for S; 1.74 for Sτ) at medial tibiofemoral compartment. In longitudinal analyses, S (RR, 1.45) and Sτ (RR, 1.55) of ProxTibFibJ were significantly and positively associated with an increase in medial tibial cartilage defects over 2 years, after adjustment for age, gender, height, weight, ROA, tibial plateau bone area and intervention. Sτ (β, −0.07), Sυ (β, −0.07) and S (β, −0.06) of ProxTibFibJ were significantly and negatively associated with change in medial tibial cartilage volume, after adjusted for above covariates. Sτ (RR, 1.55) of ProxTibFibJ was positively associated with an increase in medial tibial BML, and Sφ (RR, 0.35) was negatively associated with an increase in medial femoral BMLs. Conclusions This novel method to assess the morphological parameters of ProxTibFibJ using MRI is reproducible, and has clinical construct validity. The longitudinal associations with osteoarthritic changes suggest that higher load-bearing area of ProxTibFibJ is a potential risk factor for medial compartment OA. Disclosure of Interest None declared