The patellofemoral and femorotibial joints are related based on patterns of MRI features and their association with radiologic progression

Purpose: Several MRI features in osteoarthritis (OA) have been found to associate with radiological progression. As these MRI features are known to be highly correlated with each other, we investigated the presence of patterns of MRI features by principle component analysis (PCA) and their association with radiological progression over 6 years’ time. Methods: 205 patients (mean age (SD) 60 (7) years, 79.5% woman, median BMI (range) 26 (20–40), were investigated. These patients were part of the Genetics, Osteoarthritis, and Progression (GARP) study, that includes probands and their siblings with symptomatic OA at multiple sites; patients were followed for 6 years. MRI of one knee, median (range) Kellgren-Lawrence (KL) score 1 (0–3), was made in every patient and included in the present study. At baseline coronal, axial and sagittal proton density and T2-weighted images as well as sagittal 3D T1-weighted spoiled gradient echo frequency-selective fat-suppressed images were made at 1.5T MRI. Cartilage damage (thinning and focal lesions), osteophytes (central and marginal), cysts, bone marrow lesions (BMLs) and effusion/synovitis were scored according the Knee Osteoarthritis Scoring System (KOSS) score for presence or absence in 9 compartments, including the patellofemoral joint (PFJ) and tibiofemoral joint (TFJ). Baseline and 6-year semi-flexed posterior-anterior and lateral knee radiographs were scored (0–3) for both osteophytes and joint space narrowing (JSN) at both FTJ and PFJ according to the Osteoarthritis Research Society International (OARSI) atlas and Burnett atlas, respectively. Radiographic progression was defined as an increase of 1 point in JSN. Patterns of MRI features were investigated in the whole joint, using principal component analysis (PCA). A factor was considered to load significantly on a component when loading exceeded 0.4. Subsequently, the association of patterns of MRI features with radiological progression adjusted for age, gender, BMI and baseline JSN was investigated, using generalized estimation equation (GEE) models to correct for possible family effects. Results: Of 205 patients 139 (68%) had KL score ≥ 1 at baseline. 55% had an JSN score ≥ 1 and 50 % osteophyte score ≥ 1 in PFJ or TFJ. Radiological follow-up was available in 133 patients. In TFJ progression of JSN was seen in 28.6% of patients and progression of osteophytes in 293% of patients. In PFJ progression of JSN was seen in 9.2% of patients and progression of osteophytes in 15.4% of patients. PCA of MRI features of the whole joint of all patients resulted in extraction of 6 components (Eigen value > 1), explaining 69% of variance. Component 1 was characterized by medial and lateral cartilage damage and osteophytes of the PFJ and medial and lateral osteophytes of the TFJ and was associated with JSN progression in the TFJ (OR(95%CI)1.8(1.1–3.1), whereas a trend was observed with progression of JSN in the PFJ (OR(95%CI) 4.9(1.0–25.4)). Component 2 included lateral cartilage damage, cysts and BMLs of the PFJ and was significantly associated with JSN progression of the PFJ (OR(95%CI) 8.7(1.8–41.6), not with JSN progression of the TFJ. Component 3 consisted of medial cartilage damage, cysts and BMLs of the TFJ and was associated with JSN progression in the PFJ (OR(95%CI) 12.3(3.3–46.7)), whereas a trend was observed with JSN progression in the TFJ (OR(95%CI) 1.5 (1.0–2.5)). Component 4 was characterized by medial cartilage damage, cysts and BMLs of the PFJ, in component 5 the lateral MRI features cysts and BML were incorporated and component 6 included cartilage damage and osteophytes on both sides of the TFJ. Component 4, 5 and 6 did not associate with JSN progression. Interestingly effusion/synovitis was not incorporated in any of the components. When analysing only patients with KL grade ≥ 1 at baseline comparable associations of component 1,2 and 3 with JSN progression were seen. Conclusions: Investigation of patterns of MRI features show that cysts and BMLs are related with cartilage damage in all compartments except in the lateral TFJ. Components including medial TFJ BMLs and lateral PFJ BMLs are associated with JSN progression. Furthermore, also components characterized by medial and lateral cartilage damage and osteophytes of both PFJ and TFJ are associated with JSN progression. These results suggest that JSN progression in PFJ and TFJ is related.