Quantitative MR Imaging of Cartilage and Trabecular Bone in Osteoarthritis

Gender differences in patterns of cartilage loss: Data from the Osteoarthritis Initiative

OBJECTIVE

Understanding gender-specific differences in patterns of cartilage loss can improve our knowledge of the pathogenesis of knee osteoarthritis (KOA) development and progression and may inform clinical trials of treatments for KOA. The goal of our observational study was to examine gender differences in patterns of cartilage loss in the central weight-bearing regions of the femur.

METHODS

We measured cartilage volume change in the indexed knee of 700 subjects with Kellgren-Lawrence 1, 2, or 3 from the Osteoarthritis Initiative for four follow-up periods (baseline [BL] to 24 mo, BL to 48 mo, BL to 72 mo, and BL to 96 mo) using the local area cartilage segmentation (LACS) method. Briefly, the LACS method uses robust coordinate systems fixed to anatomical landmarks to measure patterns of change in cartilage volume in sub-regions using responsiveness heat maps.

RESULTS

We observed a statistically significant gender difference in cartilage change in the medial femur (MF), lateral femur (LF), and medial tibia. The heat maps showed loss was primarily in the posterior central weight-bearing portion of the LF and more general in the LT and MF. Similar patterns were observed for each of the four follow-up periods.

CONCLUSIONS

The LACS method was capable of illustrating gender-specific differences in patterns of cartilage loss that may offer insight into the variation of gender differences in the natural history of KOA and may be useful in evaluating the benefit of interventions for KOA.

Emerging role of integrated PET-MRI in osteoarthritis

Osteoarthritis (OA) is a common degenerative disorder of the articular cartilage, which is associated with hypertrophic changes in the bone, synovial inflammation, subchondral sclerosis, and joint space narrowing (JSN). Radiography remains the first line of imaging till now. Due to the lack of soft-tissue depiction in radiography, researchers are exploring various imaging techniques to detect OA at an early stage and understand its pathophysiology to restrict its progression and discover disease-modifying agents in OA. As the OA relates to the degradation of articular cartilage and remodeling of the underlying bone, an optimal imaging tool must be sensitive to the bone and soft tissue health. In that line, many non-invasive imaging and minimally invasive techniques have been explored. Out of these, the non-invasive compositional magnetic resonance imaging (MRI) for evaluation of the integrity of articular cartilage and positron emission tomography (PET) scan with fluorodeoxyglucose (FDG) and more specific bone-seeking tracer like sodium fluoride (18F-NaF) for bone cartilage interface are some of the leading areas of ongoing work. Integrated PET-MRI system, a new hybrid modality that combines the virtues of the above two individual modalities, allows detailed imaging of the entire joint, including soft tissue cartilage and bone, and holds great potential to research complex disease processes of OA. This narrative review attempts to signify individual characteristics of MRI, PET, the fusion of these characteristics in PET-MRI, and the ongoing research on PET-MRI as a potential tool to understand the pathophysiology of OA.

How to effectively utilize imaging in disease-modifying treatments for osteoarthritis clinical trials: the radiologist's perspective

Introduction: One of the reasons for failures of disease-modifying osteoarthritis drug clinical trials has been the radiography-based definition of structural eligibility criteria. Imaging, particularly MRI, has a critical role in planning and conducting clinical trials of osteoarthritis.Areas covered: A literature search was performed using keywords including 'osteoarthritis,' 'knee,' 'MRI,' 'intra-articular injection,' 'semiquantitative scoring,' 'clinical trial,' and other specific terms where relevant. The core concepts of using MRI in osteoarthritis clinical trials are explained focusing on knee osteoarthritis, including its role in determining patient eligibility and inclusion/exclusion criteria as well as outcome measures from the expert musculoskeletal radiologist's perspective. A brief overview of statistical analyses that should be deployed in clinical trials utilizing semiquantitative MRI analyses is discussed.Expert opinion: In order to increase chances to detect measurable efficacy effects, investigators should consider utilizing MRI from screening to outcome assessment. Recognition of several phenotypes of osteoarthritis helps in participant stratification and will lead to more targeted clinical trials. Inclusion and exclusion criteria need to be defined using not only radiography but also MRI. Correct intra-articular injection of investigational compounds is critically important if intra-articular drug delivery is required, and such procedure should be performed and documented using appropriate imaging guidance.

Age-related histological changes in calcified cartilage and subchondral bone in femoral heads from healthy humans

OBJECTIVE

Age is the most important risk factor for osteoarthritis (OA). It is suggested that changes in subchondral bone and calcified cartilage may occur in early OA. Therefore, the aim was to investigate age-related changes in the femoral head composition. We hypothesise that the thickness of the subchondral bone plate decreases with age, while the thickness of the calcified cartilage increases with age as seen in early-stage OA.

METHODS

Femoral heads from 29 women (20-74 years) and 32 men (23-78 years), who had died suddenly and unexpectedly, were obtained at autopsy. Individuals with bone or joint diseases or macroscopic abnormal cartilage were excluded. Using design-based stereology, femoral head volume as well as thickness and volume of the calcified cartilage and subchondral bone plate were estimated and correlated to sex and age.

RESULTS

The thickness and volume of the subchondral bone plate were not correlated with age. Calcified cartilage thickness and volume correlated positively with age in women, while the femoral head volume was correlated positively with age in men.

CONCLUSION

In human femoral heads obtained from a cross-sectional population without macroscopic OA changes, the thickness of the subchondral bone plate did not change with age, which differs from the thinning seen in early OA. Surprisingly, the age-related changes of the volume and thickness of the calcified cartilage and of the volume of the femoral head were different for women and men. This indicate that cartilage and bone metabolism is sex-specific, which may influence ageing of the hip joint.

Anatomically Standardized Maps Reveal Distinct Patterns of Cartilage Thickness With Increasing Severity of Medial Compartment Knee Osteoarthritis

While cartilage thickness alterations are a central element of knee osteoarthritis (OA), differences among disease stages are still incompletely understood. This study aimed to quantify the spatial-variations in cartilage thickness using anatomically standardized thickness maps and test if there are characteristic patterns in patients with different stages of medial compartment knee OA. Magnetic resonance images were acquired for 75 non-OA and 100 OA knees of varying severities (Kellgren and Lawrence (KL) scores 1-4). Three-dimensional cartilage models were reconstructed and a shape matching technique was applied to convert the models into two-dimensional anatomically standardized thickness maps. Difference thickness maps and statistical parametric mapping were used to compare the four OA and the non-OA subgroups. This analysis showed distinct thickness patterns for each clinical stage that formed a coherent succession from the non-OA to the KL 4 subgroups. Interestingly, the only significant difference for early stage (KL 1) was thicker femoral cartilage. With increase in disease severity, typical patterns developed, including thinner cartilage in the anterior area of the medial condyle (significant for KL 3 and 4) and thicker cartilage in the posterior area of the medial and lateral condyles (significant for all OA subgroups). The tibial patterns mainly consisted of thinner cartilage for both medial and lateral compartments (significant for KL 2-4). Comparing anatomically standardized maps allowed identifying patterns of thickening and thinning over the entire cartilage surface, consequently improving the characterization of thickness differences associated with OA. The results also highlighted the value of anatomically standardized maps to analyze spatial variations in cartilage thickness. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2442-2451, 2017.

A robust diffusion tensor model for clinical applications of MRI to cartilage

PURPOSE

Diffusion tensor imaging (DTI) of articular cartilage is a promising technique for the early diagnosis of osteoarthritis (OA). However, in vivo diffusion tensor (DT) measurements suffer from low signal-to-noise ratio (SNR) that can result in bias when estimating the six parameters of the full DT, thus reducing sensitivity. This study seeks to validate a simplified four-parameter DT model (zeppelin) for obtaining more robust and sensitive in vivo DTI biomarkers of cartilage.

METHODS

We use simulations in a substrate to mimic changes during OA; and analytic simulations of the DT drawn from a range of fractional anisotropies (FA) measured with high-quality DT data from ex vivo human cartilage. We also use in vivo data from the knees of a healthy subject and two OA patients with Kellgren-Lawrence (KL) grades 1 and 2.

RESULTS

For simulated in vivo cartilage SNR (∼25) and anisotropy levels, the estimated mean values of MD from the DT and zeppelin models were identical to the ground truth values. However, zeppelin's FA is more accurate in measuring water restriction. More specifically, the FA estimations of the DT model were additionally biased by between +2% and +48% with respect to zeppelin values. Additionally, both mean diffusivity (MD) and FA of the zeppelin had lower parameter variance compared to the full DT (F-test, P < 0.05). We observe the same trends from in vivo values of patient data.

CONCLUSION

The zeppelin is more robust than the full DT for cartilage diffusion anisotropy and SNR at levels typically encountered in clinical applications of articular cartilage. Magn Reson Med 79:1157-1164, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Preliminary validation of the Knee Inflammation MRI Scoring System (KIMRISS) for grading bone marrow lesions in osteoarthritis of the knee: data from the Osteoarthritis Initiative

Objective

Bone marrow lesions (BML) are an MRI feature of osteoarthritis (OA) offering a potential target for therapy. We developed the Knee Inflammation MRI Scoring System (KIMRISS) to semiquantitatively score BML with high sensitivity to small changes, and compared feasibility, reliability and responsiveness versus the established MRI Osteoarthritis Knee Score (MOAKS).

Methods

KIMRISS incorporates a web-based graphic overlay to facilitate detailed regional BML scoring. Observers scored BML by MOAKS and KIMRISS on sagittal fluid-sensitive sequences. Exercise 1 focused on interobserver reliability in Osteoarthritis Initiative observational data, with 4 readers (two experienced/two new to KIMRISS) scoring BML in 80 patients (baseline/1 year). Exercise 2 focused on responsiveness in an open-label trial of adalimumab, with 2 experienced readers scoring BML in 16 patients (baseline/12 weeks).

Results

Scoring time was similar for KIMRISS and MOAKS. Interobserver reliability of KIMRISS was equivalent to MOAKS for BML status (ICC=0.84 vs 0.79), but consistently better than MOAKS for change in BML: Exercise 1 (ICC 0.82 vs 0.53), Exercise 2 (ICC 0.90 vs 0.32), and in new readers (0.87–0.92 vs 0.32–0.51). KIMRISS BML was more responsive than MOAKS BML: post-treatment BML improvement in Exercise 2 reached statistical significance for KIMRISS (SRM −0.69, p=0.015), but not MOAKS (SRM −0.12, p=0.625). KIMRISS BML also more strongly correlated to WOMAC scores than MOAKS BML (r=0.80 vs 0.58, p<0.05).

Conclusions

KIMRISS BML scoring was highly feasible, and was more reliable for assessment of change and more responsive to change than MOAKS BML for expert and new readers.

Clinical utility of quantitative imaging

Quantitative imaging (QI) is increasingly applied in modern radiology practice, assisting in the clinical assessment of many patients and providing a source of biomarkers for a spectrum of diseases. QI is commonly used to inform patient diagnosis or prognosis, determine the choice of therapy, or monitor therapy response. Because most radiologists will likely implement some QI tools to meet the patient care needs of their referring clinicians, it is important for all radiologists to become familiar with the strengths and limitations of QI. The Association of University Radiologists Radiology Research Alliance Quantitative Imaging Task Force has explored the clinical application of QI and summarizes its work in this review. We provide an overview of the clinical use of QI by discussing QI tools that are currently used in clinical practice, clinical applications of these tools, approaches to reporting of QI, and challenges to implementing QI. It is hoped that these insights will help radiologists recognize the tangible benefits of QI to their patients, their referring clinicians, and their own radiology practice.

Is loss in femorotibial cartilage thickness related to severity of contra-lateral radiographic knee osteoarthritis?--longitudinal data from the Osteoarthritis Initiative

OBJECTIVE

Anti-catabolic disease modifying drugs (DMOADs) aim to reduce cartilage loss in knee osteoarthritis (KOA). Testing such drugs in clinical trials requires sufficient rates of loss in the study participants to occur, preferably at a mild disease stage where cartilage can be preserved. Here we analyze a "progression" model in mild radiographic KOA (RKOA), based on contra-lateral radiographic status.

METHODS

We studied 837 participants (62.4 ± 9 yrs; 30 ± 4.9 kg/m²; 61.8% women) from the Osteoarthritis Initiative (OAI) with mild to moderate RKOA (Kellgren Lawrence grade [KLG] 2-3) and with/without Osteoarthritis Research Society International (OARSI) atlas radiographic joint space narrowing (JSN). These had quantitative measurements of subregional femorotibial cartilage thickness from magnetic resonance imaging (MRI) at baseline and 1-year follow-up. They were stratified by contra-lateral knee status: no (KLG 0/1), definite (KLG2) and moderate RKOA (KLG 3/4).

RESULTS

KLG2 knees with JSN and moderate contra-lateral RKOA had (P = 0.008) greater maximum subregional cartilage loss -220 μm [95% confidence interval (CI) -255, -184 μm] than those without contra-lateral RKOA -164 μm [-187, -140 μm]. Their rate of subregional cartilage loss was similar and not significantly different (P = 0.61) to that in KLG 3 knees without contra-lateral RKOA (-232 μm; [-266; -198 μm]). The effect of contra-lateral RKOA status was less in KLG2 knees without JSN, and in KLG3 knees.

CONCLUSION

KLG2 knees with JSN and moderate contra-lateral RKOA, display relatively high rates of subregional femorotibial cartilage loss, despite being at a relatively mild stage of RKOA. They may therefore provide a unique opportunity for recruitment in clinical trials that explore the efficacy of anti-catabolic DMOADs on structural progression.

Rapid, automated imaging of mouse articular cartilage by microCT for early detection of osteoarthritis and finite element modelling of joint mechanics

OBJECTIVE

Mouse articular cartilage (AC) is mostly assessed by histopathology and its mechanics is poorly characterised. In this study: (1) we developed non-destructive imaging for quantitative assessment of AC morphology and (2) evaluated the mechanical implications of AC structural changes.

METHODS

Knee joints obtained from naïve mice and from mice with osteoarthritis (OA) induced by destabilization of medial meniscus (DMM) for 4 and 12 weeks, were imaged by phosphotungstic acid (PTA) contrast enhanced micro-computed tomography (PTA-CT) and scored by conventional histopathology. Our software (Matlab) automatically segmented tibial AC, drew two regions centred on each tibial condyle and evaluated the volumes included. A finite element (FE) model of the whole mouse joint was implemented to evaluate AC mechanics.

RESULTS

Our method achieved rapid, automated analysis of mouse AC (structural parameters in <10 h from knee dissection) and was able to localise AC loss in the central region of the medial tibial condyle. AC thickness decreased by 15% at 4 weeks and 25% at 12 weeks post DMM surgery, whereas histopathology scores were significantly increased only at 12 weeks. FE simulations estimated that AC thinning at early-stages in the DMM model (4 weeks) increases contact pressures (+39%) and Tresca stresses (+43%) in AC.

CONCLUSION

PTA-CT imaging is a fast and simple method to assess OA in murine models. Once applied more extensively to confirm its robustness, our approach will be useful for rapidly phenotyping genetically modified mice used for OA research and to improve the current understanding of mouse cartilage mechanics.

2D and 3D MOCART scoring systems assessed by 9.4 T high-field MRI correlate with elementary and complex histological scoring systems in a translational model of osteochondral repair

OBJECTIVE

To compare the 2D and 3D MOCART system obtained with 9.4 T high-field magnetic resonance imaging (MRI) for the ex vivo analysis of osteochondral repair in a translational model and to correlate the data with semiquantitative histological analysis.

METHODS

Osteochondral samples representing all levels of repair (sheep medial femoral condyles; n = 38) were scanned in a 9.4 T high-field MRI. The 2D and adapted 3D MOCART systems were used for grading after point allocation to each category. Each score was correlated with corresponding reconstructions between both MOCART systems. Data were next correlated with corresponding categories of an elementary (Wakitani) and a complex (Sellers) histological scoring system as gold standards.

RESULTS

Correlations between most 2D and 3D MOCART score categories were high, while mean total point values of 3D MOCART scores tended to be 15.8-16.1 points higher compared to the 2D MOCART scores based on a Bland-Altman analysis. "Defect fill" and "total points" of both MOCART scores correlated with corresponding categories of Wakitani and Sellers scores (all P ≤ 0.05). "Subchondral bone plate" also correlated between 3D MOCART and Sellers scores (P < 0.001).

CONCLUSIONS

Most categories of the 2D and 3D MOCART systems correlate, while total scores were generally higher using the 3D MOCART system. Structural categories "total points" and "defect fill" can reliably be assessed by 9.4 T MRI evaluation using either system, "subchondral bone plate" using the 3D MOCART score. High-field MRI is valuable to objectively evaluate osteochondral repair in translational settings.

Non-invasive and in vivo assessment of osteoarthritic articular cartilage: a review on MRI investigations

Early detection of knee osteoarthritis (OA) is of great interest to orthopaedic surgeons, rheumatologists, radiologists, and researchers because it would allow physicians to provide patients with treatments and advice to slow the onset or progression of the disease. Early detection can be achieved by identifying early changes in selected features of degenerative articular cartilage (AC) using non-invasive imaging modalities. Magnetic resonance imaging (MRI) is becoming the standard for assessment of OA. The aim of this paper was to review the influence of MRI on the selection, detection, and measurement of AC features associated with early OA. Our review of the literature indicates that the changes associated with early OA are in cartilage thickness, cartilage volume, cartilage water content, and proteoglycan content that can be accurately, consistently, and non-invasively measured using MRI. Choosing an MR pulse sequence that provides the capability to assess cartilage physiology and morphology in a single acquisition and advanced multi-nuclei MRI is desirable. The results of the review indicate that using an ultra-high magnetic strength, MR imager does not affect early OA detection. In conclusion, MRI is currently the most suitable modality for early detection of knee OA, and future research should focus on the quantitative evaluation of early OA features using advances in MR hardware, software, and data processing with sophisticated image/pattern recognition techniques.

Feasibility of in vivo diffusion tensor imaging of articular cartilage with coverage of all cartilage regions

OBJECTIVES

To investigate the value of diffusion tensor imaging (DTI) of articular cartilage to differentiate healthy from osteoarthritis (OA) subjects in all cartilage regions.

METHODS

DTI was acquired sagittally at 7 T in ten healthy and five OA (Kellgren-Lawrence grade 2) subjects with a line scan diffusion tensor sequence (LSDTI). Three healthy volunteers and two OA subjects were examined twice to assess the test-retest reproducibility. Averaged mean diffusivity (MD) and fractional anisotropy (FA) were calculated in each cartilage region (femoral trochlea, lateral and medial femoral condyles, patella, and lateral and medial tibia).

RESULTS

The test-retest reproducibility was 2.9% for MD and 5.6% for FA. Averaged MD was significantly increased (+20%, p < 0.05) in the OA subjects in the lateral femoral condyle, lateral tibia and the femoral trochlea compartments. Averaged FA presented a trend of lower values in the OA subjects (-12%), which was only significant for the lateral tibia.

CONCLUSIONS

In vivo DTI of articular cartilage with coverage of all cartilage regions using an LSDTI sequence is feasible, shows excellent reproducibility for MD and FA, and holds potential for the diagnosis of OA.

KEY POINTS

• DTI of articular cartilage is feasible at 7 T in all cartilage regions • DTI of articular cartilage can potentially differentiate healthy and OA subjects.

Cartilage thickening in early radiographic knee osteoarthritis: a within-person, between-knee comparison

OBJECTIVE

To determine whether the presence of definite osteophytes (in the absence of joint space narrowing [JSN]) on radiographs is associated with (subregional) increases in cartilage thickness in a within-person, between-knee cross-sectional comparison of participants in the Osteoarthritis Initiative. Based on previous results, the external weight-bearing medial femoral condyle (ecMF) and external weight-bearing lateral femoral condyle (ecLF) subregions were selected as primary end points.

METHODS

Both knees of 61 Osteoarthritis Initiative participants (n = 4,796) displayed definite tibial or femoral marginal osteophytes and no JSN in 1 knee, and no signs of radiographic osteoarthritis (OA) in the contralateral knee; this was confirmed by an expert central reader. In these participants, cartilage thickness was measured in 16 femorotibial subregions of each knee, based on sagittal double-echo steady-state with water excitation magnetic resonance images. Location-specific joint space width from fixed-flexion radiographs was determined using dedicated software. Location-specific associations of osteophytes with cartilage thickness were evaluated using paired t-tests and mixed-effects models.

RESULTS

Of the 61 participants, 48% had only medial osteophytes, 36% only lateral osteophytes, and 16% bicompartmental osteophytes. The knees with osteophytes had significantly thicker cartilage than contralateral knees without osteophytes in the ecMF (mean ± SD +71 ± 223 μmoles, equivalent to an increase of +5.5%; P = 0.015) and ecLF (mean ± SD +64 ± 195 μmoles, +4.1%; P = 0.013). No significant differences between knees were noted in other subregions or in joint space width. Cartilage thickness in the ecMF and ecLF was significantly associated with tibial osteophytes in the same (medial or lateral) compartment (P = 0.003).

CONCLUSION

The knees with early radiographic OA display thicker cartilage than (contralateral) knees without radiographic findings of OA, specifically in the external femoral subregions of compartments with marginal osteophytes.

How do short-term rates of femorotibial cartilage change compare to long-term changes? Four year follow-up data from the osteoarthritis initiative

OBJECTIVE

To compare unbiased estimates of short- vs long-term cartilage loss in osteoarthritic knees.

METHOD

441 knees [216 Kellgren Lawrence (KL) grade 2, 225 KL grade 3] from participants of the Osteoarthritis Initiative were studied over a 4-year period. Femorotibial cartilage thickness was determined using 3 T double echo steady state magnetic resonance imaging, the readers being blinded to time points. Because common measurement time points bias correlations, short-term change (year-1 to year-2: Y1 → Y2) was compared with long-term change (baseline to year-4: BL → Y4), and initial (BL → Y1) with subsequent (Y2 → Y4) observation periods.

RESULTS

The mean femorotibial cartilage thickness change (standardized response mean) was -1.2%/-0.8% (-0.42/-0.28) over 1 (BL → Y1/Y1 → Y2), -2.1%/-2.5% (-0.56/-0.55) over 2 (BL → Y2/Y2 → Y4), -3.3% (-0.63) over 3 (Y1 → Y4), and -4.5% (-0.78) over 4 years. Spearman correlations were 0.33 for Y1 → Y2 vs BL → Y4, and 0.17 for BL → Y1 vs Y2 → Y4 change. Percent agreement between knees showing progression during Y1 → Y2 vs BL → Y4 was 59%, and 64% for BL → Y1 vs Y2 → Y4. The area under the receiver operating characteristic curve was 0.66 for using Y1 → Y2 to predict BL → Y4, and 0.59 for using BL → Y1 to predict Y2 → Y4 change.

CONCLUSION

Weak to moderate correlations and agreement were observed between individual short- vs long-term cartilage loss, and between initial and subsequent observation periods. Hence, longer observation periods are recommended to achieve robust results on cartilage loss in individual knees. At cohort and subcohort level (e.g., KLG3 vs KLG2 knees), the mean cartilage loss increased almost linearly with the length of the observation period and was constant throughout the study.

Femorotibial Cartilage Thickness Change Distributions for Subjects without Signs, Symptoms, or Risk Factors of Knee Osteoarthritis

OBJECTIVE

To describe the distribution of longitudinal femorotibial cartilage thickness annualized rate of change (ΔThCtAB) from quasi-population-based studies, and to construct a reference distribution for men and women without signs, symptoms, or risk factors of knee osteoarthritis (OA).

METHODS

Segmented baseline and 1-year follow-up MRI from 43 men and 69 women of the Osteoarthritis Initiative (OAI) asymptomatic control cohort without risk factors and also baseline and 2-year follow-up data from 77 asymptomatic women of the Pfizer A9001140 study were included. The mean, standard deviation (SD), and correlation of ΔThCtAB in medial and lateral femorotibial subregions were estimated; distributions were tested for normality and for differences between cohorts and gender.

RESULTS

Distributions of femorotibial ΔThCtAB rates were consistent between cohorts and were normally distributed, with rates <0.7%/y. Subregion ΔThCtAB SDs were correlated with mean baseline cartilage thickness (ratio = 3%-5%). However, ΔThCtAB SD did not increase with baseline thickness when estimated for different tertiles of any given subregion, indicating the relationship may rather be due to spatial location than to baseline thickness.

CONCLUSIONS

Distributions of (subregional) longitudinal cartilage thickness rates of change appear to be normally distributed, not significantly different from zero, and similar for different cohorts of asymptomatic subjects. Given the spatial heterogeneity of subregional cartilage change observed in OA knees, the proposed reference distribution of subregional, ΔThCtAB may be used to describe and identify structural progression (i.e., cartilage loss) in individual OA knees with greater accuracy and sensitivity than conventional approaches, such as minimal detectable difference.

Equivalence and precision of knee cartilage morphometry between different segmentation teams, cartilage regions, and MR acquisitions

OBJECTIVE

To compare precision and evaluate equivalence of femorotibial cartilage volume (VC) and mean cartilage thickness over total area of bone (ThCtAB.Me) from independent segmentation teams using identical Magnetic Resonance (MR) images from three series: sagittal 3D Dual Echo in the Steady State (DESS), coronal multi-planar reformat (DESS-MPR) of DESS and coronal 3D Fast Low Angle SHot (FLASH).

DESIGN

Nineteen subjects underwent test-retest MR imaging at 3 T. Four teams segmented the cartilage using prospectively defined plate regions and rules. Mixed models analysis of the pooled data were used to evaluate the effect of acquisition, team and plate on precision and Pearson correlations and mixed models were used to evaluate equivalence.

RESULTS

Segmentation team differences dominated measurement variability in most cartilage regions for all image series. Precision of VC and ThCtAB.Me differed significantly by team and cartilage plate, but not between FLASH and DESS. Mean values of VC and ThCtAB.Me differed by team (P < 0.05) for DESS, FLASH and DESS-MPR. FLASH VC was 4-6% larger than DESS in the medial tibia and lateral central femur, and FLASH ThCtAB.Me was 5-6% larger in the medial tibia, but 4-8% smaller in the medial central femur. Correlations between DESS and FLASH for VC and ThCtAB.Me were high (r = 0.90-0.97), except for DESS vs FLASH medial central femur ThCtAB.Me (r = 0.81-0.83).

CONCLUSIONS

Cartilage morphology metrics from different image contrasts had similar precision, were generally equivalent, and may be combined for cross-sectional analyses if potential systematic offsets are accounted for. Data from different teams should not be pooled unless equivalence is demonstrated for cartilage metrics of interest.

Greater rates of cartilage loss in painful knees than in pain-free knees after adjustment for radiographic disease stage: data from the osteoarthritis initiative

OBJECTIVE

To investigate whether rates of cartilage loss differ in knees with frequent baseline pain versus those without pain, after adjustment for radiographic osteoarthritis (OA) stage.

METHODS

One knee in each of 718 Osteoarthritis Initiative participants was examined: 310 with calculated Kellgren/Lawrence (K/L) grade 2, 299 with calculated K/L grade 3, and 109 with calculated K/L grade 4. Twelve-month change in (subregional) cartilage thickness was assessed by magnetic resonance imaging. Change in cartilage thickness in the central subregion of the weight-bearing medial femoral condyle and ordered value 1 (OV1) were selected as primary end points. Frequent knee symptoms were defined as pain, aching, or stiffness on most days of at least 1 month during the previous year.

RESULTS

The mean 12-month rate of change in cartilage thickness in the central subregion of the medial femoral condyle was -12 μm (standardized response mean [SRM] -0.15) in knees without pain (n = 146), -27 μm (SRM -0.25) in those with infrequent pain (n = 255), and -54 μm (SRM -0.32) in those with frequent pain (n = 317). Rates differed significantly between frequently painful knees and pain-free knees after adjustment for age, sex, body mass index, and calculated K/L grade (P = 0.011, R(2) = 2.6%, partial R(2) for frequent pain = 1.4%). Similar results were found in stratified samples of calculated K/L grade 2/calculated K/L grade 3 knees, and in analyses restricted to knees with consistent pain frequency between baseline and followup. OV1 results showed similar trends but were not significant.

CONCLUSION

Knees with frequent pain display greater rates of medial cartilage loss longitudinally than knees without pain, with or without adjustment or stratification for radiographic disease stage. Enrollment of participants with frequent knee pain in clinical trials can increase the observed rate of structural progression (i.e., cartilage loss) and sensitivity to change.

Advances in imaging of osteoarthritis and cartilage

Osteoarthritis (OA) is the most frequent form of arthritis, with major implications for individual and public health care without effective treatment available. The field of joint imaging, and particularly magnetic resonance (MR) imaging, has evolved rapidly owing to technical advances and the application of these to the field of clinical research. Cartilage imaging certainly is at the forefront of these developments. In this review, the different aspects of OA imaging and cartilage assessment, with an emphasis on recent advances, will be presented. The current role of radiography, including advances in the technology for joint space width assessment, will be discussed. The development of various MR imaging techniques capable of facilitating assessment of cartilage morphology and the methods for evaluating the biochemical composition of cartilage will be presented. Advances in quantitative morphologic cartilage assessment and semiquantitative whole-organ assessment will be reviewed. Although MR imaging is the most important modality in imaging of OA and cartilage, others such as ultrasonography play a complementary role that will be discussed briefly.

MRI-based extended ordered values more efficiently differentiate cartilage loss in knees with and without joint space narrowing than region-specific approaches using MRI or radiography--data from the OA initiative

OBJECTIVE

The sensitivity to change of quantitative analysis of cartilage in knee osteoarthritis using magnetic resonance imaging (MRI) is compromised by the spatial heterogeneity of cartilage loss. We explore whether extended (medial-lateral) "ordered values" (OVs) are superior to conventional approaches of analyzing subregional cartilage thickness loss and to radiography, in differentiating rates of progression in knees with and without joint space narrowing (JSN).

METHODS

607 Osteoarthritis Initiative (OAI) participants (308 without and 299 with baseline JSN at baseline) were studied over 12 months. Subregional femorotibial cartilage loss was determined in all knees, and changes in minimum joint space width (mJSW) in a subset of 290 knees. Subregional thickness changes in medial and lateral tibial and femoral cartilages were sorted in ascending order (OV1-16). A Wilcoxon rank-sum test was used to compare rates of change in knees with and without JSN.

RESULTS

JSN-knees displayed greater cartilage loss than those without JSN, with minimal P-values of 0.008 for femorotibial subregions, 3.3×10(-4) for medial OV1, and 5.4×10(-7) for extended (medial and lateral) OV1. mJSW measurements (n=290) did not discriminate between longitudinal rates of change in JSN vs no-JSN knees (P=0.386), whereas medial OV1 (P=5.1×10(-4)) and extended OV1 did (P=2.1×10(-5)).

CONCLUSION

Extended OVs showed higher sensitivity to detecting differences in longitudinal rates of cartilage loss in knees with and without baseline JSN than anatomical (sub)regions and radiography. The OV technique also circumvents challenges of selecting particular regions "a priori" in clinical trials and may thus provide a powerful tool in studying risk factors or treatment efficacy in osteoarthritis.

Articular cartilage in the knee: current MR imaging techniques and applications in clinical practice and research

Magnetic resonance (MR) imaging is the most important imaging modality for the evaluation of traumatic or degenerative cartilaginous lesions in the knee. It is a powerful noninvasive tool for detecting such lesions and monitoring the effects of pharmacologic and surgical therapy. The specific MR imaging techniques used for these purposes can be divided into two broad categories according to their usefulness for morphologic or compositional evaluation. To assess the structure of knee cartilage, standard spin-echo (SE) and gradient-recalled echo (GRE) sequences, fast SE sequences, and three-dimensional SE and GRE sequences are available. These techniques allow the detection of morphologic defects in the articular cartilage of the knee and are commonly used in research for semiquantitative and quantitative assessments of cartilage. To evaluate the collagen network and proteoglycan content in the knee cartilage matrix, compositional assessment techniques such as T2 mapping, delayed gadolinium-enhanced MR imaging of cartilage (or dGEMRIC), T1ρ imaging, sodium imaging, and diffusion-weighted imaging are available. These techniques may be used in various combinations and at various magnetic field strengths in clinical and research settings to improve the characterization of changes in cartilage.

In vivo measures of cartilage deformation: patterns in healthy and osteoarthritic female knees using 3T MR imaging

Objective

To explore and to compare the magnitude and spatial pattern of in vivo femorotibial cartilage deformation in healthy and in osteoarthritic (OA) knees.

Methods

One knee each in 30 women (age: 55 ± 6 years; BMI: 28 ± 2.4 kg/m²; 11 healthy and 19 with radiographic femorotibial OA) was examined at 3Tesla using a coronal fat-suppressed gradient echo SPGR sequence. Regional and subregional femorotibial cartilage thickness was determined under unloaded and loaded conditions, with 50% body weight being applied to the knee in 20° knee flexion during imaging.

Results

Cartilage became significantly (p < 0.05) thinner during loading in the medial tibia (−2.7%), the weight-bearing medial femur (−4.1%) and in the lateral tibia (−1.8%), but not in the lateral femur (+0.1%). The magnitude of deformation in the medial tibia and femur tended to be greater in osteoarthritic knees than in healthy knees. The subregional pattern of cartilage deformation was similar for the different stages of radiographic OA.

Conclusion

Osteoarthritic cartilage tended to display greater deformation upon loading than healthy cartilage, suggesting that knee OA affects the mechanical properties of cartilage. The pattern of in vivo deformation indicated that cartilage loss in OA progression is mechanically driven.

Using ordered values of subregional cartilage thickness change increases sensitivity in detecting risk factors for osteoarthritis progression

OBJECTIVE

To examine whether ordered values of (sub)regional femorotibial cartilage thickness change are superior to region-based approaches in detecting risk factors for cartilage loss in osteoarthritis (OA).

METHODS

58 women with knee OA had 3 Tesla MR images acquired at baseline and 24 months. Changes in cartilage thickness (∆ThCtAB) were determined in eight medial femorotibial subregions. An ascending sort of individual ∆ThCtAB measurements was done to create "ordered values". Risk factors for cartilage loss considered were: age, BMI, anatomical knee axis (AAA), minimal (medial) joint space width (mJSW), and percent of medial tibial plateau covered by the meniscus (percent cover). All change metrics were tested for association with the risk factors using Kendall's τ and relative sensitivity of multiple tests of subregions and ordered values were compared with single metrics of change from plate and compartment summaries and the first ordered value.

RESULTS

The associations between subregion ∆ThCtAB and AAA (P=0.0002), mJSW (P=0.016), and age (P=0.011) were significant, but only AAA (at α=0.05) and age (at α=0.1) remained significant after adjusting for multiple subregions. In contrast, cMFTC had P-values<0.05 for AAA (P=0.0001), mJSW (P=0.016), and meniscus subluxation (0.04). The first ordered value had significant associations with AAA (P=0.0004), mJSW (P=0.003), meniscus subluxation (P=0.02) and percent cover (P=0.031) all of which were significant at α=0.05 after adjusting for tests on multiple risk factors.

CONCLUSION

Ordered values of ∆ThCtAB were more sensitive in detecting risk factors of cartilage loss than subregional ∆ThCtAB. Sensitivity was further enhanced by considering the minimum ordered value as a single test, thus not requiring adjustment for multiple tests. Using ordered values there was a significant association between ∆ThCtAB and baseline AAA, mJSW, meniscus subluxation and meniscus percent cover. This study provides an important step in validating ordered values of cartilage change.

Knee articular cartilage damage in osteoarthritis: analysis of MR image biomarker reproducibility in ACRIN-PA 4001 multicenter trial

PURPOSE

To prospectively determine the reproducibility of quantitative magnetic resonance (MR) imaging biomarkers of the morphology and composition (spin lattice relaxation time in rotating frame [T1-ρ], T2) of knee cartilage in a multicenter multivendor trial involving patients with osteoarthritis (OA) and asymptomatic control subjects.

MATERIALS AND METHODS

This study was HIPAA compliant and approved by the institutional review committees of the participating sites, with written informed consent obtained from all participants. Fifty subjects from five sites who were deemed to have normal knee joints (n = 18), mild OA (n = 16), or moderate OA (n = 16) on the basis of Kellgren-Lawrence scores were enrolled. Each participant underwent four sequential 3-T knee MR imaging examinations with use of the same imager and with 2-63 days (median, 18 days) separating the first and last examinations. Water-excited three-dimensional T1-weighted gradient-echo imaging, T1-ρ imaging, and T2 mapping of cartilage in the axial and coronal planes were performed. Biomarker reproducibility was determined by using intraclass correlation coefficients (ICCs) and root-mean-square coefficients of variation (RMS CVs, expressed as percentages).

RESULTS

Morphometric biomarkers had high reproducibility, with ICCs of 0.989 or greater and RMS CVs lower than 4%. The largest differences between the healthy subjects and the patients with radiographically detected knee OA were those in T1-ρ values, but precision errors were relatively large. Reproducibility of T1-ρ values was higher in the thicker patellar cartilage (ICC range, 0.86-0.93; RMS CV range, 14%-18%) than in the femorotibial joints (ICC range, 0.20-0.84; RMS CV range, 7%-19%). Good to high reproducibility of T2 was observed, with ICCs ranging from 0.61 to 0.98 and RMS CVs ranging from 4% to 14%.

CONCLUSION

MR imaging measurements of cartilage morphology, T2, and patellar T1-ρ demonstrated moderate to excellent reproducibility in a clinical trial network.

Comparison of 1-year vs 2-year change in regional cartilage thickness in osteoarthritis results from 346 participants from the Osteoarthritis Initiative

OBJECTIVE

To compare femorotibial cartilage thickness changes over a 2- vs a 1-year observation period in knees with radiographic knee osteoarthritis (OA).

METHODS

One knee of 346 Osteoarthritis Initiative (OAI) participants was studied at three time points [baseline (BL), year-1 (Y1), year-2 (Y2) follow-up]: 239 using coronal fast low angle shot (FLASH) and 107 using sagittal double echo at steady state (DESS) MR imaging. Changes in cartilage thickness were assessed in femorotibial cartilage plates and subregions, after manual segmentation with blinding to time-point.

RESULTS

The standardized response mean (SRM) of total joint cartilage thickness over 2 years was modestly higher than over 1 year (FLASH: -0.44 vs -0.32/-0.28 [first/second year]; DESS: -0.42 vs -0.39/-0.18). For the subregion showing the largest change per knee (OV1), the 2-year SRM was similar or lower (FLASH: -1.20 vs -1.22/-1.61; DESS: -1.38 vs -1.64/-1.51) than the 1-year SRM. The changes in total joint cartilage thickness were not significantly different in the first and second year (FLASH: -0.8% vs -0.7%; DESS: -1.3% vs -0.8%) and were negatively correlated. Analysis of smallest detectable changes (SDCs) revealed that only few participants displayed significant progression in both consecutive periods. The location of the subregion contributing to OV1 in each knee was highly inconsistent between the first and second year observation period.

CONCLUSIONS

The SRM of region-based cartilage thickness change in OA is modestly larger following a 2-year vs a 1-year observation period, while it is relatively similar when an OV-approach is chosen. Structural progression displays strong temporal and spatial heterogeneity at an individual knee level that should be considered when planning clinical trials.

Quantitative cartilage imaging in knee osteoarthritis

Quantitative measures of cartilage morphology (i.e., thickness) represent potentially powerful surrogate endpoints in osteoarthritis (OA). These can be used to identify risk factors of structural disease progression and can facilitate the clinical efficacy testing of structure modifying drugs in OA. This paper focuses on quantitative imaging of articular cartilage morphology in the knee, and will specifically deal with different cartilage morphology outcome variables and regions of interest, the relative performance and relationship between cartilage morphology measures, reference values for MRI-based knee cartilage morphometry, imaging protocols for measurement of cartilage morphology (including those used in the Osteoarthritis Initiative), sensitivity to change observed in knee OA, spatial patterns of cartilage loss as derived by subregional analysis, comparison of MRI changes with radiographic changes, risk factors of MRI-based cartilage loss in knee OA, the correlation of MRI-based cartilage loss with clinical outcomes, treatment response in knee OA, and future directions of the field.

Early osteoarthritis and microdialysis: a novel in vivo approach for measurements of biochemical markers in the perisynovium and intraarticularly

The microdialysis technique was evaluated as a possible method to obtain local measurements of biochemical markers from knee joints with degenerative changes. Seven patients scheduled for arthroscopy of the knee due to minor to moderate degenerative changes had microdialysis catheters inserted under ultrasonographic guidance, intraarticularly and in the synovium-close tissue. Catheters were perfused at a rate of 2 μl/min for approximately 100 min with a Ringer solution containing radioactively labeled glucose, and the positions of the catheters were later visualized during arthroscopy. All intraarticular catheters and 6/7 subsynovial catheters were positioned correctly. Relative recovery (RR) was intraarticularly 0.64 ± 0.02 (mean ± SEM) and synovium-close 0.54 ± 0.06. Mean values of cartilage oligomeric matrix protein (COMP), aggrecan and glucosyl-galactosyl-pyridinoline in the intraarticular dialysates were 18.1 ± 7.0 U/l, 243.6 ± 108.6 ng/ml and 108.0 ± 29.0 pmol/ml, respectively. COMP and glucosyl-galactosyl-pyridinoline concentrations were significantly higher intraarticularly compared to perisynovial tissue (P < 0.05), whereas for aggrecan, no significant difference was found (P = 0.06). The microdialysis method can be used for intraarticular and subsynovial determination of metabolites in human knees at these sites. The present methodology displays a potential for future studies of simultaneous biochemical changes within and around joints.

Reference values and Z-scores for subregional femorotibial cartilage thickness--results from a large population-based sample (Framingham) and comparison with the non-exposed Osteoarthritis Initiative reference cohort

OBJECTIVE

To establish sex-specific (subregional) reference values of cartilage thickness and potential maximal Z-scores in the femorotibial joint.

METHODS

The mean cartilage thickness (ThCtAB.Me) in femorotibial compartments, plates and subregions was determined on coronal magnetic resonance imaging (MRI) from a population-based sample (Framingham) and from a healthy reference sample of the Osteoarthritis Initiative (OAI).

RESULTS

686 Framingham participants (309 men, 377 women, age 62 ± 8 years) had no radiographic femorotibial osteoarthritis (OA) ("normals") and 376 (156 men, 220 women) additionally had no MRI features of cartilage lesions ("supernormals"). The Framingham "normals" had thinner cartilage in the medial (3.59 mm) than in the lateral femorotibial compartment (3.86 mm). Medially, the femur displayed thicker cartilage (1.86 mm) than the tibia (1.73 mm), and laterally the tibia thicker cartilage (2.09 mm) than the femur (1.77 mm). The thickest cartilage was observed in central, and the thinnest in external femorotibial subregions. Potential maximal Z-scores ranged from 5.6 to 9.8 throughout the subregions; men displayed thicker cartilage but similar potential maximal Z-scores as women. Mean values and potential maximal Z-scores in Framingham "supernormals" and non-exposed OAI reference participants (112 participants without symptoms or risk factors of knee OA) were similar to Framingham "normals".

CONCLUSIONS

We provide reference values and potential maximal Z-scores of cartilage thickness in middle aged to elderly non-diseased populations without radiographic OA. Results were similar for "supernormal" participants without MRI features of cartilage lesions, and in a cohort without OA symptoms or risk factors. A cartilage thickness loss of around 27% is required for attaining a Z-score of -2.

Magnitude and regional distribution of cartilage loss associated with grades of joint space narrowing in radiographic osteoarthritis--data from the Osteoarthritis Initiative (OAI)

OBJECTIVE

Clinically, radiographic joint space narrowing (JSN) is regarded a surrogate of cartilage loss in osteoarthritis (OA). Using magnetic resonance imaging (MRI), we explored the magnitude and regional distribution of differences in cartilage thickness and subchondral bone area associated with specific Osteoarthritis Research Society International (OARSI) JSN grades.

METHOD

Seventy-three participants with unilateral medial JSN were selected from the first half (2678 cases) of the OA Initiative cohort (45, 21, and 7 with OARSI JSN grades 1, 2, and 3, respectively, no medial JSN in the contra-lateral knee). Bilateral sagittal baseline DESSwe MRIs were segmented by experienced operators. Intra-person between-knee differences in cartilage thickness and subchondral bone areas were determined in medial femorotibial subregions.

RESULTS

Knees with medial OARSI JSN grades 1, 2, and 3 displayed a 190 microm (5.2%), 630 microm (18%), and 1560 microm (44%) smaller cartilage thickness in weight-bearing medial femorotibial compartments compared to knees without JSN, respectively. The weight-bearing femoral condyle displayed relatively greater differences than the posterior femoral condyle or the medial tibia (MT). The central subregion within the weight-bearing medial femur (cMF) of the femoral condyle (30-75 degrees ), and the external and central subregions within the tibia displayed relatively greater JSN-associated differences compared to other medial femorotibial subregions. Knees with higher JSN grades also displayed larger than contra-lateral femorotibial subchondral bone areas.

CONCLUSIONS

This study provides quantitative estimates of JSN-related cartilage loss, with the central part of the weight-bearing femoral condyle being most strongly affected. Knees with higher JSN grades displayed larger subchondral bone areas, suggesting that an increase in subchondral bone area occurs in advanced OA.

Femorotibial subchondral bone area and regional cartilage thickness: a cross-sectional description in healthy reference cases and various radiographic stages of osteoarthritis in 1,003 knees from the Osteoarthritis Initiative

OBJECTIVE

To identify structural differences in total subchondral bone area (tAB) and cartilage thickness between healthy reference knees and knees with radiographic osteoarthritis (OA).

METHODS

Baseline magnetic resonance images from 1 knee of 1,003 Osteoarthritis Initiative participants were studied: 112 healthy reference knees without radiographic OA, symptoms, or risk factors; 70 preradiographic OA knees (calculated Kellgren/Lawrence [K/L] grade 0/1); and 821 radiographic OA knees (calculated K/L grade ≥2). Means and standard (Z) scores (SD unit differences compared with normal subjects) of the tAB and regional cartilage thickness were assessed in the weight-bearing femorotibial joint and compared between groups.

RESULTS

In men, tAB was 8.2% larger in preradiographic OA knees and 6.6%, 8.1%, and 8.5% larger in calculated K/L grade 2, 3, and 4 radiographic OA knees, respectively, than in reference knees. In women, the differences were +6.8%, +7.3%, +9.9%, and +8.1%, respectively. The external medial tibia showed the greatest reduction in cartilage thickness (Z scores -5.1/-5.6 in men/women) with Osteoarthritis Research Society International medial joint space narrowing (JSN) grade 3, and the external lateral tibia (Z scores -6.0 for both sexes) showed the greatest reduction with lateral JSN grade 3. In all subregions of end-stage radiographic OA knees, ≥25% of the average normal cartilage thickness was maintained. An overall trend toward thicker cartilage was found in preradiographic OA and calculated K/L grade 2 knees, especially in the external central medial femur.

CONCLUSION

tABs were larger in preradiographic OA and radiographic OA knees than in healthy reference knees, and the difference did not become larger with higher calculated K/L grades. Specific subregions with substantial cartilage thickening or thinning were identified in pre-, early, and late radiographic OA.

Magnetic resonance imaging-based semiquantitative and quantitative assessment in osteoarthritis

Whole organ magnetic resonance imaging (MRI)-based semiquantitative (SQ) assessment of knee osteoarthritis (OA), based on reliable scoring methods and expert reading, has become a powerful research tool in OA. SQ morphologic scoring has been applied to large observational cross-sectional and longitudinal epidemiologic studies as well as interventional clinical trials. SQ whole organ scoring analyzes all joint structures that are potentially relevant as surrogate outcome measures of OA and potential disease modification, including cartilage, subchondral bone, osteophytes, intra- and periarticular ligaments, menisci, synovial lining, cysts, and bursae. Resources needed for SQ scoring rely on the MRI protocol, image quality, experience of the expert readers, method of documentation, and the individual scoring system that will be applied. The first part of this article discusses the different available OA whole organ scoring systems, focusing on MRI of the knee, and also reviews alternative approaches. Rheumatologists are made aware of artifacts and differential diagnoses when applying any of the SQ scoring systems. The second part focuses on quantitative approaches in OA, particularly measurement of (subregional) cartilage loss. This approach allows one to determine minute changes that occur relatively homogeneously across cartilage structures and that are not apparent to the naked eye. To this end, the cartilage surfaces need to be segmented by trained users using specialized software. Measurements of knee cartilage loss based on water-excitation spoiled gradient recalled echo acquisition in the steady state, fast low-angle shot, or double-echo steady-state imaging sequences reported a 1% to 2% decrease in cartilage thickness annually, and a high degree of spatial heterogeneity of cartilage thickness changes in femorotibial subregions between subjects. Risk factors identified by quantitative measurement technology included a high body mass index, meniscal extrusion and meniscal tears, knee malalignment, advanced radiographic OA grade, bone marrow alterations, and focal cartilage lesions.