Background Earlier studies showed that several MRI features in osteoarthritis (OA) are associated with cartilage damage progression. Which factors are involved in progression is however difficult to understand, since they are all highly correlated.

Objectives To investigate patterns of MRI abnormalities in the patellofemoral (PFJ) and tibiofemoral joint (TFJ) and their association with radiological progression over 6 years' time.

Methods Patients from the Genetics, Osteoarthritis, and Progression (GARP) study, including sib-pairs with symptomatic OA at multiple sites (mean age (SD) 60 (7) years, 80% woman, median BMI (range) 26 (20-40)), were investigated. MRI (1.5T) of one knee, median (range) Kellgren-Lawrence (KL) score 1 (0-3), was made. Cartilage damage, osteophytes (OP), cysts, bone marrow lesions (BMLs) and effusion were scored according to the Knee Osteoarthritis Scoring System (KOSS). Baseline and 6-year semi-flexed posterior-anterior and lateral knee radiographs were scored (0-3) for joint space narrowing (JSN) at both FTJ and PFJ according to the OARSI atlas and Burnett atlas. Radiographic progression was defined as an increase of 1 point in JSN. Associations between MRI features were investigated in the whole joint, using principal component analysis (PCA). Subsequently, the association of components of MRI features with radiological progression adjusted for age, gender, BMI and baseline JSN was investigated, using generalized estimation equation models to correct for family effects.

Results Of 205 patients,68% had a KL score ≥1 at baseline;55% had an JSN score ≥1. Progression was evaluated in 133 patients with radiological follow-up and was seen in TFJ in 29% and in TFJ in 9% of patients. PCA resulted in extraction of 6 components, explaining 69% of variance. Component 1 consisted of medial and lateral cartilage damage, OP of the PFJ and OP of the TFJ and associated with progression in the TFJ (OR (95%CI) 1.8 (1.1-3.1). Component 2 included lateral cartilage damage, cysts and BMLs of the PFJ and associated with progression of the PFJ (OR (95%CI) 8.7 (1.8-41.6). Component 3 consisted of medial cartilage damage, cysts and BMLs of the TFJ and was associated with progression in the PFJ (OR (95%CI) 12.3 (3.3-46.7)).Component 4 included medial cartilage damage, cysts and BMLs of the PFJ, component 5 included the lateral cysts and BMLs and component 6 included cartilage damage and OP of the TFJ, and were not associated with progression. Effusion was not included in any of the components. In patients with KL grade ≥1 at baseline, similar associations of component 1,2 and 3 with progression were seen

Conclusions Hypothesis free association between MRI features reveal several patterns including cysts, BML and cartilage damage and OP and cartilage damage. Especially those including BMLs in the medial TFJ and lateral TFJ were associate with progression in the PFJ, whereas those including OP and cartilage damage were associated with progression in the TFJ. Our results indicate that underlying processes resulting in structural progression is related in PFJ and TFJ.

Disclosure of Interest : None declared

DOI 10.1136/annrheumdis-2014-eular.4786