Objective-The Osteoarthritis Initiative (OAI) is a multicentre study targeted at identifying biomarkers for evaluating the progression and risk factors of symptomatic knee OA. Here cartilage loss using 3 Tesla (3 T) MRI is analysed over 1 year in a subset of the OAI, together with its association with various risk factors.Methods-An age-and gender-stratified subsample of the OAI progression subcohort (79 women and 77 men, mean (SD) age 60.9 (9.9) years, body mass index (BMI) 30.3 (4.7)) with both frequent symptoms and radiographic OA in at least one knee was studied. Coronal FLASHwe (fast low angle shot with water excitation) MRIs of the right knee were acquired at 3 T. Seven readers segmented tibial and femoral cartilages blinded to order of acquisition. Segmentations were quality controlled by one expert.Results-The reduction in mean cartilage thickness (ThC) was greater (p = 0.004) in the medial than in the lateral compartment, greater (p = 0.001) in the medial femur (−1.9%) than in the medial tibia (−0.5%) and greater (p = 0.011) in the lateral tibia (−0.7%) than in the lateral femur (0.1%). Multifactorial analysis of variance did not reveal significant differences in the rate of change in ThC by sex, BMI, symptoms and radiographic knee OA status. Knees with Kellgren-Lawrence grade 2 or 3 and with a BMI >30 tended to display greater changes. Conclusions-In this sample of the OAI progression subcohort, the greatest, but overall very modest, rate of cartilage loss was observed in the weight-bearing medial femoral condyle. Knees with radiographic OA in obese participants showed trends towards higher rates of change than those of other participants, but these trends did not reach statistical significance.MRI at 1.5 Tesla (T) can provide valuable information on articular cartilage loss and other structural changes in knee osteoarthritis (OA). The rate and SD of change over time reported, however, has varied substantially between studies. 1-12 These variations may be partly due to differences in study populations, with different profiles of risk factors for progression. The rate and SD of change to be expected for a certain cohort has, however, major implications for powering epidemiological, clinical and pharmacological studies in OA. It is therefore important to identify the factors that drive cartilage loss in OA.Methodologically, it has been shown that 3 T MRI provides a higher signal-and contrast-tonoise ratio 13 and higher test-retest precision of cartilage morphology measurements than 1.5 T MRI. 14 Previous longitudinal studies, have, however, relied on 1.5 T MRI. [1][2][3][4][5][6][7][8][9][10][11][12] There is thus the hope that 3 T MRI may provide a higher sensitivity to change of cartilage morphometry than 1.5 T MRI.The Osteoarthritis Initiative (OAI) is targeted at identifying sensitive biomarkers of symptomatic knee OA, and at characterising risk factors associated with its onset and progression. A total of 4796 participants were recruited between 2004 and 2006: 1389 participants had frequent ...

Objective The Osteoarthritis Initiative (OAI) is aimed at validating (imaging) biomarkers for monitoring progression of knee OA. Here we analyze regional femorotibial cartilage thickness changes over one year using 3 Tesla MRI. Specifically, we tested whether changes in central subregions exceed those in the total cartilage plates. Methods The right knees of a subsample of the OAI progression subcohort (n=156 age 60.9±9.9 y) were studied. 54 participants had definite radiographic OA (KLG 2 or 3) and a BMI>30. Mean and minimal cartilage thickness was determined in subregions of the medial/lateral tibia (MT/LT), and of the medial/lateral weight-bearing femoral condyle (cMF/cLF), after paired (baseline, follow-up) segmentation of coronal FLASHwe images with blinding to the order of acquisition. Results The central aspect of cMF displayed a 5.8%/2.8% change in mean thickness in the group of 54/156 participants, respectively, with a standardized response mean (SRM) of -0.47/-0.31, whereas cartilage loss in the total cMF was 4.1%/1.9% (SRM -0.49/-0.30). In the central MT, the rate of change was -1.6% /-0.9% and the SRM -0.29/-0.20, whereas for the entire MT the rate was -1.0%/-0.5% and the SRM -0.21/-0.12. Minimal thickness displayed greater rates of change, but lower SRMs than mean thickness. Conclusions This study shows that the rate of cartilage loss is greater in central subregions than in entire femorotibial cartilage plates. The sensitivity to change in central subregions was higher than for the total cartilage plate in the medial tibia and was similar to the total plate in the medial weight-bearing femur.

Objective To study the longitudinal rate of (and sensitivity to) change of knee cartilage thickness across defined stages of radiographic osteoarthritis (ROA), specifically healthy knees and knees with end-stage ROA. Methods One knee of 831 Osteoarthritis Initiative (OAI) participants was examined: 112 healthy, without ROA or risk factors for knee OA, and 719 ROA knees: 310 calculated Kellgren Lawrence [cKLG] grade 2, 300 cKLG3, and 109 cKLG4. Subregional change in thickness was assessed after segmentation of weight-bearing femorotibial cartilage at baseline and at one year from coronal MRI. Regional and ordered values (OV) of change were compared by baseline ROA status. Results Healthy knees displayed small changes in plates and subregions (±0.7%; standardized response mean [SRM] ±0.15), with OVs being symmetrically distributed around zero. In cKLG2 knees, changes in cartilage thickness were small (≤1%; minimal SRM -0.22) and not significantly different from healthy knees. Knees with cKLG3 showed substantial loss of cartilage thickness (up to -2.5%; minimal SRM -0.35), with OV changes being significantly (p<0.05) greater than those in healthy knees. cKLG4 knees displayed the largest rate of loss across ROA grades (up to -3.9%; minimal SRM -0.51), with OV changes also significantly (p<0.05) greater than in healthy knees. Conclusion MRI-based cartilage thickness showed high rates of loss in knees with moderate and end-stage ROA, and small rates (indistinguishable from healthy knees) in mild ROA. From the perspective of sensitivity to change, end-stage ROA knees need not be excluded from longitudinal studies using MRI cartilage morphology as an endpoint.

Objective The Osteoarthritis Initiative (OAI) is targeted at identifying sensitive biomarkers and risk factors of symptomatic knee OA onset and progression. Quantitative cartilage imaging in the OAI relies on validated FLASH sequences that suffer from relatively long acquisition times, and on a near-isotropic double echo steady state (DESS) sequence. We therefore directly compared the sensitivity to cartilage thickness changes and the correlation of these protocols longitudinally. Methods Baseline and 12 month followup data of 80 knees were acquired using 1.5mm coronal FLASH and 0.7mm sagittal DESS sequences. In these and in 1.5mm coronal multiplanar reconstructions (MPR) of the DESS the medial femorotibial cartilage was segmented with blinding to acquisition order. In the weight-bearing femoral condyle, a 60% (distance trochlear notch to posterior femur) and 75% region of interest (ROI) were studied. Results The standardized response mean (SRM=mean change /standard deviation of change) in central medial femorotibial (cMFTC) cartilage thickness was −0.34 for coronal FLASH, −0.37 for coronal MPR DESS, −0.36 for sagittal DESS with the 60% ROI, and −0.38 for the 75% ROI. Using every 2nd 0.7mm sagittal slice (DESS) yielded similar SRMs in cMFTC for the 60% and 75% ROI from odd (−0.35/−0.36) and even slice numbers (−0.36/−0.39), respectively. Baseline cartilage thickness displayed high correlations (r≥0.94) between the three protocols; the correlations of longitudinal changes were ≥0.79 (Pearson) and ≥0.45 (Spearman). Conclusions Cartilage morphometry with FLASH and DESS display similar longitudinal sensitivity to change. Analysis of every second slice of the 0.7mm DESS provides adequate sensitivity to change.

Objective. To determine by magnetic resonance imaging (MRI), whether knees with advanced radiographic disease (medial joint space narrowing [mJSN]) encounter greater longitudinal cartilage loss than contralateral knees with earlier disease (no or less mJSN). Methods. Participants were selected from 2,678 cases in the Osteoarthritis Initiative, based on exhibition of bilateral pain, body mass index >25 (kg/m 2 ), mJSN in 1 knee, no or less mJSN in the contralateral knee, and no lateral JSN in both knees. Eighty participants (mean ؎ SD age 60.6 ؎ 9.1 years) fulfilled these criteria. Medial tibial and femoral cartilage morphology was analyzed from the baseline and the 1-year followup MRI (sagittal double echo at steady state by 3.0T) of both knees by experienced readers blinded to the time point and mJSN status. Results. Knees with more radiographic mJSN displayed greater medial cartilage loss (؊80 m) assessed by MRI than contralateral knees with less mJSN (؊57 m). The difference reached statistical significance in participants with an mJSN grade of 2 or 3 (P ‫؍‬ 0.005-0.08), but not in participants with an mJSN grade of 1 (P ‫؍‬ 0.28 -0.98). In knees with more mJSN, cartilage loss increased with higher grades of mJSN (P ‫؍‬ 0.003 in the medial femur). Knees with an mJSN grade of 2 or 3 displayed greater cartilage loss in the weight-bearing medial femur than in the posterior femur or in the medial tibia (P ‫؍‬ 0.048). Conclusion. Knees with advanced mJSN displayed greater cartilage loss than contralateral knees with less mJSN. These data suggest that radiography can be used to stratify fast structural progressors, and that MRI cartilage thickness loss is more pronounced at advanced radiographic disease stage.