The osteoarthritis initiative: report on the design rationale for the magnetic resonance imaging protocol for the knee

Interobserver reproducibility of quantitative meniscus analysis using coronal multiplanar DESS and IWTSE MR imaging

The objective of this study was to determine the interobserver reproducibility of quantitative measures of meniscus size and position, and to compare the interobserver reproducibility and agreement between a double echo steady state water excitation and an intermediately-weighted turbo spin-echo sequence. Eight knees (four healthy, four with radiographic knee osteoarthritis) from the Osteoarthritis Initiative cohort were studied. Manual segmentation of the menisci was performed by three observers and quantitative measures of meniscus size and position (i.e., extrusion) computed using image analysis software. The root mean square interobserver reproducibility error (e.g., 5.4% for medial meniscus volume with double echo steady state and 8.4% with intermediately-weighted turbo spin-echo) was found considerably smaller than the intersubject variability (average ratio ~1:3). The lowest interobserver reproducibility error for meniscus extrusion was obtained for the central five coronal slices across the tibial surface. Quantitative meniscus measures from double echo steady state and intermediately-weighted turbo spin-echo were highly correlated (r = 0.71 to 0.99 for the medial meniscus).

Relationship of 3D meniscal morphology and position with knee pain in subjects with knee osteoarthritis: a pilot study

OBJECTIVES

To explore whether quantitative, three-dimensional measurements of meniscal position and size are associated with knee pain using a within-person, between-knee study design.

METHODS

We studied 53 subjects (19 men, 34 women) from the Osteoarthritis Initiative, with identical radiographic OA grades in both knees, but frequent pain in one and no pain in the other knee. The tibial plateau and menisci were analyzed using coronally reconstructed double echo steady-state sequence with water excitation (DESSwe) MRI.

RESULTS

The medial meniscus covered a smaller proportion of the tibial plateau (-5%) and displayed greater extrusion of the body (+15%) in painful than in painless knees (paired t-test; p < 0.05). The external margin of the lateral meniscus showed greater extrusion of the body in painful knees (+22%; p = 0.03), but no significant difference in the position of its internal margin or tibial coverage. Medial or lateral extrusion ≥3 mm was more frequent in painful (n = 23) than in painless knees (n = 12; McNemar's test; p = 0.02). No significant association was observed between meniscal size and knee pain.

CONCLUSIONS

These data suggest a relationship between extrusion of the meniscal body, as measured with quantitative MRI, and knee pain in subjects with knee OA. Further studies need to confirm these findings and their clinical relevance.

Routine 3D magnetic resonance imaging of joints

Due to its high spatial resolution and excellent tissue contrast, magnetic resonance imaging (MRI) has become the most commonly used imaging method to evaluate joints. Most musculoskeletal MRI is performed using 2D fast spin-echo sequences. However, 3D sequences have also been used for joint imaging and have the advantage of acquiring thin continuous slices through joints, which reduces the effects of partial volume averaging. With recent advances in MR technology, 3D sequences with isotropic resolution have been developed. These sequences allow high-quality multiplanar reformat images to be obtained following a single acquisition, thereby eliminating the need to repeat sequences with identical tissue contrast in different planes. Preliminary results on the diagnostic performance of 3D isotropic resolution sequences are encouraging. However, additional studies are needed to determine whether these sequences can replace currently used 2D fast spin-echo sequences for providing comprehensive joint assessment in clinical practice.

A novel fast knee cartilage segmentation technique for T2 measurements at MR imaging--data from the Osteoarthritis Initiative

Magnetic resonance imaging (MRI) T(2) relaxation time assesses non-invasively cartilage composition and can be used as early biomarker for knee osteoarthritis. Most knee cartilage segmentation techniques were primarily developed for volume measurements in DESS or SPGR sequences. For T(2) quantifications, these segmentations need to be superimposed on T(2) maps. However, given that these procedures are time consuming and require manual alignment, using them for analysis of T(2) maps in large clinical trials like the Osteoarthritis Initiative (OAI) is challenging. A novel direct segmentation technique (DST) for T(2) maps was therefore developed. Using the DST, T(2) measurements were performed and compared with those determined with an established segmentation superimposition technique (SST). MR images of five OAI participants were analysed with both techniques three times by one reader and five different images sets additionally with DST three times by two readers. Segmentations and T(2) measurements of one knee required on average 63±3min with DST (vs 302±13min for volume and T(2) measurements with SST). Bland-Altman plots indicated good agreement between the two segmentation techniques, respectively the two readers. Reproducibility errors of both techniques (DST vs SST) were similar (P>0.05) for whole knee cartilage mean T(2) (1.46% vs 2.18%), laminar (up to 2.53% vs 3.19%) and texture analysis (up to 8.34% vs 9.45%). Inter-reader reproducibility errors of DST were higher for texture analysis (up to 15.59%) than for mean T(2) (1.57%) and laminar analysis (up to 2.17%). Due to these results, the novel DST can be recommended for T(2) measurements in large clinical trials like the OAI.

Evolution of semi-quantitative whole joint assessment of knee OA: MOAKS (MRI Osteoarthritis Knee Score)

OBJECTIVE

In an effort to evolve semi-quantitative scoring methods based upon limitations identified in existing tools, integrating expert readers' experience with all available scoring tools and the published data comparing the different scoring systems, we iteratively developed the magnetic resonance imaging (MRI) Osteoarthritis Knee Score (MOAKS). The purpose of this report is to describe the instrument and its reliability.

METHODS

The MOAKS instrument refines the scoring of bone marrow lesions (BMLs) (providing regional delineation and scoring across regions), cartilage (sub-regional assessment), and refines the elements of meniscal morphology (adding meniscal hypertrophy, partial maceration and progressive partial maceration) scoring. After a training and calibration session two expert readers read MRIs of 20 knees separately. In addition, one reader re-read the same 20 MRIs 4 weeks later presented in random order to assess intra-rater reliability. The analyses presented here are for both intra- and inter-rater reliability (calculated using the linear weighted kappa and overall percent agreement).

RESULTS

With the exception of inter-rater reliability for tibial cartilage area (kappa=0.36) and tibial osteophytes (kappa=0.49); and intra-rater reliability for tibial BML number of lesions (kappa=0.54), Hoffa-synovitis (kappa=0.42) all measures of reliability using kappa statistics were very good (0.61-0.8) or reached near-perfect agreement (0.81-1.0). Only intra-rater reliability for Hoffa-synovitis, and inter-rater reliability for tibial and patellar osteophytes showed overall percent agreement <75%.

CONCLUSION

MOAKS scoring shows very good to excellent reliability for the large majority of features assessed. Further iterative development and research will include assessment of its validation and responsiveness.

Morphometric differences between the medial and lateral meniscus in healthy men - a three-dimensional analysis using magnetic resonance imaging

The objective of this work was to characterize tibial plateau coverage and morphometric differences of the medial (MM) and lateral meniscus (LM) in a male reference cohort using three-dimensional imaging. Coronal multiplanar reconstructions of a sagittal double-echo steady state with water excitation magnetic resonance sequence (slice thickness: 1.5 mm, and in-plane resolution: 0.37 × 0.70 mm) were analyzed in 47 male participants without symptoms, signs or risk factors of knee osteoarthritis of the reference cohort of the Osteoarthritis Initiative. The medial and lateral tibial (LT) plateau cartilage area and the tibial, femoral and external surfaces of the MM and LM were manually segmented throughout the entire knee. This process was assisted by parallel inspection of a coronal intermediately weighted turbo spin echo sequence. Measures of tibial coverage, meniscus size, and meniscus position were computed three-dimensionally for the total menisci, the body, and the anterior and the posterior horn. The LM was found to cover a significantly greater (p < 0.001) proportion of the LT plateau (59 ± 6.8%) than the MM of the medial plateau (50 ± 5.5%). Whereas the volume of both menisci was similar (2.444 vs. 2.438 ml; p = 0.92), the LM displayed larger tibial and femoral surface areas (p < 0.05) and a smaller maximal (7.2 ± 1.0 vs. 7.7 ± 1.1 mm; p < 0.01) and mean thickness (2.7 ± 0.3 vs. 2.8 ± 0.3 mm; p < 0.001) than the medial one. Also, the LM displayed less (physiological) extrusion than the medial one. These data may guide strategies for meniscal tissue engineering and transplantation aiming to restore normal joint conditions.

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.

Rates of change and sensitivity to change in cartilage morphology in healthy knees and in knees with mild, moderate, and end-stage radiographic osteoarthritis: results from 831 participants from the Osteoarthritis Initiative

OBJECTIVE

To study the longitudinal rate of (and sensitivity to) change of knee cartilage thickness across defined stages of radiographic osteoarthritis (OA), specifically healthy knees and knees with end-stage radiographic OA.

METHODS

One knee of 831 Osteoarthritis Initiative participants was examined: 112 healthy knees, without radiographic OA or risk factors for knee OA, and 719 radiographic OA knees (310 calculated Kellgren/Lawrence [K/L] grade 2, 300 calculated K/L grade 3, and 109 calculated K/L grade 4). Subregional change in thickness was assessed after segmentation of weight-bearing femorotibial cartilage at baseline and 1 year from coronal magnetic resonance imaging (MRI). Regional and ordered values (OVs) of change were compared by baseline radiographic OA status.

RESULTS

Healthy knees displayed small changes in plates and subregions (±0.7%; standardized response mean [SRM] ±0.15), with OVs being symmetrically distributed close to zero. In calculated K/L grade 2 knees, changes in cartilage thickness were small (<1%; minimal SRM -0.22) and not significantly different from healthy knees. Knees with calculated K/L grade 3 showed substantial loss of cartilage thickness (up to -2.5%; minimal SRM -0.35), with OV1 changes being significantly (P < 0.05) greater than those in healthy knees. Calculated K/L grade 4 knees displayed the largest rate of loss across radiographic OA grades (up to -3.9%; minimal SRM -0.51), with OV1 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 radiographic OA, and small rates (indistinguishable from healthy knees) in mild radiographic OA. From the perspective of sensitivity to change, end-stage radiographic OA knees need not be excluded from longitudinal studies using MRI cartilage morphology as an end point.

Automatic graph-cut based segmentation of bones from knee magnetic resonance images for osteoarthritis research

In this paper, a new, fully automated, content-based system is proposed for knee bone segmentation from magnetic resonance images (MRI). The purpose of the bone segmentation is to support the discovery and characterization of imaging biomarkers for the incidence and progression of osteoarthritis, a debilitating joint disease, which affects a large portion of the aging population. The segmentation algorithm includes a novel content-based, two-pass disjoint block discovery mechanism, which is designed to support automation, segmentation initialization, and post-processing. The block discovery is achieved by classifying the image content to bone and background blocks according to their similarity to the categories in the training data collected from typical bone structures. The classified blocks are then used to design an efficient graph-cut based segmentation algorithm. This algorithm requires constructing a graph using image pixel data followed by applying a maximum-flow algorithm which generates a minimum graph-cut that corresponds to an initial image segmentation. Content-based refinements and morphological operations are then applied to obtain the final segmentation. The proposed segmentation technique does not require any user interaction and can distinguish between bone and highly similar adjacent structures, such as fat tissues with high accuracy. The performance of the proposed system is evaluated by testing it on 376 MR images from the Osteoarthritis Initiative (OAI) database. This database included a selection of single images containing the femur and tibia from 200 subjects with varying levels of osteoarthritis severity. Additionally, a full three-dimensional segmentation of the bones from ten subjects with 14 slices each, and synthetic images with background having intensity and spatial characteristics similar to those of bone are used to assess the robustness and consistency of the developed algorithm. The results show an automatic bone detection rate of 0.99 and an average segmentation accuracy of 0.95 using the Dice similarity index.

Atlas-based knee cartilage assessment

Magnetic resonance imaging analysis of knee cartilage properties at corresponding anatomic locations could be a valuable tool in studies of knee osteoarthritis by enabling accurate comparisons at practically any region. A technique of this kind is presented in this study. The proposed technique is based on gray-level bone matching using affine transformations and free-form deformations thus eliminating the need of bone segmentations and landmark matching. Sixteen subjects of the osteoarthritis initiative with knee osteoarthritis (10 from baseline; 6 from 24-month follow-up) were included in this study. Baseline subjects were used to create a gray-level atlas of the patella with its corresponding mean cartilage thickness and T2 maps. Follow-up subjects were used to validate atlas-based point-to-point cartilage comparisons. All registrations were qualitatively evaluated with fused gray-level images of registered patellas. Quantitative evaluation was performed based on mean values of minimum Euclidean distances between matched bone-cartilage interfaces. A mean distance of 0.554 mm was obtained between the subjects used to build the atlas, and a mean distance of 0.633 mm was found between the atlas and validation subjects. The technique can be applied to other anatomical regions and with other cartilage measures. Qualitative and quantitative results demonstrate the accuracy of the technique and warrant its application in larger cross-sectional and longitudinal studies of osteoarthritis.

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.

Magnetic resonance imaging evaluation of weight-bearing subchondral trabecular bone in the knee

OBJECTIVE

Changes in weight-bearing subchondral bone are central to osteoarthritis (OA) pathophysiology. Using MR, knee trabecular bone is typically assessed in the axial plane, however partial volume artifacts limit the utility of MR methods for femorotibial compartment subchondral bone analysis. Oblique-coronal acquisitions may enable direct visualization and quantification of the expected increases in femorotibial subchondral trabecular bone.

METHODS

MR acquisition parameters were first optimized at 3 Tesla. Thereafter, five volunteers underwent axial and coronal exams of their right knee. Each image series was evaluated visually and quantitatively. An anatomically standardized region-of-interest was placed on both the medial and lateral tibial plateaus of all coronal slices containing subchondral bone. Mean and maximum marrow signal was measured, and "bone signal" was calculated.

RESULTS

The MR acquisition had spatial resolution 0.2 × 0.2 × 1.0 mm and acquisition time 10.5 min. The two asymptomatic knees exhibited prominent horizontal trabeculae in the tibial subchondral bone, while the one confirmed OA knee had disorganized subchondral bone and absent horizontal trabeculae. The subchondral bone signal was 8-14% higher in both compartments of the OA knee than the asymptomatic knees.

CONCLUSION

The weight-bearing femorotibial subchondral trabecular bone can be directly visualized and changes quantified in the coronal-oblique plane. Qualitative and quantitative assessments can be performed using the resultant images and may provide a method to discriminate between the healthy and OA knees. These methods should enable a quantitative evaluation of the role of weight-bearing subchondral bone in the natural history of knee OA to be undertaken.

Vastus lateralis/vastus medialis cross-sectional area ratio impacts presence and degree of knee joint abnormalities and cartilage T2 determined with 3T MRI - an analysis from the incidence cohort of the Osteoarthritis Initiative

OBJECTIVE

To study the role of vastus lateralis/vastus medialis cross-sectional area CSA ratio (VL/VM CSA ratio) in preclinical knee osteoarthritis (OA) using magnetic resonance imaging (MRI)-based cartilage T2 mapping technique and morphological analysis at 3.0T in non-symptomatic, middle-aged subjects.

MATERIAL AND METHODS

174 non-symptomatic individuals aged 45-55 years with OA risk factors were selected from the Osteoarthritis Initiative (OAI) incidence cohort. OA-related knee abnormalities were analyzed using the whole-organ magnetic resonance imaging score (WORMS). Knee cartilage T2 maps were generated using sagittal 2D multi-echo spin-echo images of the right knee. CSA of thigh muscles was measured using axial T1W images of the right mid thigh. Spline-based segmentation of cartilage and muscles was performed on a SUN/SPARC workstation. Muscle measurements were normalized to body size using body surface area (BSA). Statistical significance was determined using Student's t-test, Pearson correlation test, and multiple regression models. To correct for multiple testing, Bonferroni adjustments were applied across all tests within each of the primary results tables (Tables III-VII).

RESULTS

Higher T2 values were associated with increased prevalence and severity of cartilage degeneration. In our study, male and female subjects with higher VL/VM CSA ratio demonstrated significantly lower mean cartilage T2 values (all compartments combined) (mean 44.10 vs 45.17, P=0.0017), and significantly lower WORMS scores (mean 14.12 vs 18.68, P=0.0316). Regression analyses of combined mean cartilage T2 using VL/VM CSA ratio as a continuous predictor showed a significant curvilinear relationship between these two variables (P=0.0082).

CONCLUSION

Our results suggested that higher VL/VM CSA ratio is associated with lower T2 values and decreased presence and severity of OA-related morphological changes. Additional studies will be needed to determine causality.

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.

Clinical application of SPHARM-PDM to quantify temporomandibular joint osteoarthritis

The severe bone destruction and resorption that can occur in osteoarthritis of the temporomandibular joint (TMJ) is associated with significant pain and limited joint mobility. However, there is no validated method for the quantification of discrete changes in joint morphology in early diagnosis or assessment of disease progression or treatment effects. To achieve this, the objective of this cross-sectional study was to use simulated bone resorption on cone-beam CT (CBCT) to study condylar morphological variation in subjects with temporomandibular joint (TMJ) osteoarthritis (OA). The first part of this study assessed the hypothesis that the agreement between the simulated defects and the shape analysis measurements made of these defects would be within 0.5mm (the image's spatial resolution). One hundred seventy-nine discrete bony defects measuring 3mm and 6mm were simulated on the surfaces of 3D models derived from CBCT images of asymptomatic patients using ITK-Snap software. SPHARM shape correspondence was used to localize and quantify morphological differences of each resorption model with the original asymptomatic control. The size of each simulated defect was analyzed and the values obtained compared to the true defect size. The statistical analysis revealed very high probabilities that mean shape correspondence measured defects within 0.5mm of the true defect size. 95% confidence intervals (CI) were (2.67, 2.92) and (5.99, 6.36) and 95% prediction intervals (PI) were (2.22, 3.37) and (5.54, 6.82), respectively for 3mm and 6mm simulated defects. The second part of this study applied shape correspondence methods to a longitudinal sample of TMJ OA patients. The mapped longitudinal stages of TMJ OA progression identified morphological variants or subtypes, which may explain the heterogeneity of the clinical presentation. This study validated shape correspondence as a method to precisely and predictably quantify 3D condylar resorption.

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.

Longitudinal analysis of MRI T2 knee cartilage laminar organization in a subset of patients from the osteoarthritis initiative: a texture approach

Cartilage magnetic resonance imaging T(2) relaxation time is sensitive to hydration, collagen content, and tissue anisotropy, and a potential imaging-based biomarker for knee osteoarthritis. This longitudinal pilot study presents an improved cartilage flattening technique that facilitates texture analysis using gray-level co-occurrence matrices parallel and perpendicular to the cartilage layers, and the application of this technique to the knee cartilage of 13 subjects of the osteoarthritis initiative at baseline, 1-year follow-up, and 2-year follow-up. Cartilage flattening showed minimum distortion (∼ 0.5 ms) of mean T(2) values between nonflattened and flattened T(2) maps. Gray-level co-occurrence matrices texture analysis of flattened T(2) maps detected a cartilage laminar organization at baseline, 1-year follow-up, and 2-year follow-up by yielding significant (P < 0.05) differences between texture parameters perpendicular and parallel to the cartilage layers. Tendencies showed higher contrast, dissimilarity, angular second moment, and energy perpendicular to the cartilage layers; and higher homogeneity, entropy, variance, and correlation parallel to them. Significant (P < 0.05) longitudinal texture changes were also detected reflecting subtle signs of a laminar disruption. Tendencies showed decreasing contrast, dissimilarity, and entropy; and increasing homogeneity, energy, and correlation. Results of this study warrant further investigation to complete the assessment of the usefulness of the presented methodology in the study of knee osteoarthritis.

Pharmacologic therapy for osteoarthritis--the era of disease modification

Osteoarthritis (OA) is a prevalent and disabling condition for which few safe and effective therapeutic options are available. Current approaches are largely palliative and in an effort to mitigate the rising tide of increasing OA prevalence and disease impact, modifying the structural progression of OA has become a focus of drug development. This Review describes disease modification and discusses some of the challenges involved in the discovery and development of disease-modifying OA drugs (DMOADs). A variety of targeted agents are in mature phases of development; specific agents that are beyond preclinical development in phase II and III trials and show promise as potential DMOADs are discussed. A research agenda with respect to disease modification in OA is also provided, and some of the future challenges we face in this field are discussed.

Comparison of BLOKS and WORMS scoring systems part I. Cross sectional comparison of methods to assess cartilage morphology, meniscal damage and bone marrow lesions on knee MRI: data from the osteoarthritis initiative

OBJECTIVE

To compare two semiquantitative scoring systems for assessing the prevalence and severity of morphologic cartilage lesions, meniscal damage and bone marrow lesions (BMLs) from Magnetic Resonance Imagings (MRIs) of knees with osteoarthritis (OA).

METHODS

From participants in the OA Initiative (OAI), a sample of 115 knees with radiographic OA at high risk of cartilage loss, were selected based on risk factors for progression. Knee MRIs were read separately using both Whole Organ MR Scoring (WORMS) and Boston-Leeds OA Knee Scoring (BLOKS), and a subset was fed back to readers for reliability. Baseline readings were used for comparison of the two methods for inter-reader reliability as well as agreement on presence/absence and severity of MRI features at both the compartment level and finer anatomical subregion levels.

RESULTS

Both methods had high inter-reader agreement for all features studied (kappa for WORMS 0.69-1.0 and for BLOKS 0.65-1.0). Although the methods agreed well on presence and severity of morphological cartilage lesions (inter-method kappas from 0.66 to 0.95), BLOKS was more sensitive for full thickness defects. The two methods gave equivalent results for extent (kappa 0.74-0.80) and number (Spearman's Rho=0.85) of BMLs, and little extra information was obtained using the more complex BLOKS BML scoring. Similar results were also obtained for the common types of meniscal damage and extrusion (inter-method kappa 0.85-0.94), but the inclusion in BLOKS of meniscal signal abnormality and uncommon types of tear may be an advantage if these prove clinically meaningful.

CONCLUSION

Both WORMS and BLOKS had high reliability. The two methods gave similar results in this sample for prevalence and severity of cartilage loss, BMLs and meniscal damage. Selecting between, or combining, the two methods should be based on factors such as reader effort, appropriateness for the goals of a study, and longitudinal performance.

Cartilage morphology at 3.0T: assessment of three-dimensional magnetic resonance imaging techniques

PURPOSE

To compare six new three-dimensional (3D) magnetic resonance (MR) methods for evaluating knee cartilage at 3.0T.

MATERIALS AND METHODS

We compared: fast-spin-echo cube (FSE-Cube), vastly undersampled isotropic projection reconstruction balanced steady-state free precession (VIPR-bSSFP), iterative decomposition of water and fat with echo asymmetry and least-squares estimation combined with spoiled gradient echo (IDEAL-SPGR) and gradient echo (IDEAL-GRASS), multiecho in steady-state acquisition (MENSA), and coherent oscillatory state acquisition for manipulation of image contrast (COSMIC). Five-minute sequences were performed twice on 10 healthy volunteers and once on five osteoarthritis (OA) patients. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured from the volunteers. Images of the five volunteers and the five OA patients were ranked on tissue contrast, articular surface clarity, reformat quality, and lesion conspicuity. FSE-Cube and VIPR-bSSFP were compared to IDEAL-SPGR for cartilage volume measurements.

RESULTS

FSE-Cube had top rankings for lesion conspicuity, overall SNR, and CNR (P < 0.02). VIPR-bSSFP had top rankings in tissue contrast and articular surface clarity. VIPR and FSE-Cube tied for best in reformatting ability. FSE-Cube and VIPR-bSSFP compared favorably to IDEAL-SPGR in accuracy and precision of cartilage volume measurements.

CONCLUSION

FSE-Cube and VIPR-bSSFP produce high image quality with accurate volume measurement of knee cartilage.

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.

Three-dimensional magnetic resonance imaging of joints

Magnetic resonance (MR) imaging is one of the most commonly used imaging modality for evaluating patients with joint pain. Musculoskeletal MR protocols at most institutions consist of 2-dimensional fast spin echo (FSE) sequences repeated in multiple planes. Three-dimensional sequences have also been used to evaluate the musculoskeletal system and have many potential advantages over 2-dimensional FSE sequences. Three-dimensional sequences acquire thin continuous slices through joints with high in-plane spatial resolution, which minimize the effects of partial volume averaging. Newly developed 3-dimensional isotropic resolution sequences can also be used to create high-quality multiplanar reformat images that allow joints to be evaluated in any orientation after a single acquisition. Preliminary results on the use of 3-dimensional isotropic resolution sequences for evaluating the musculoskeletal system are encouraging. However, additional studies are needed to document the advantages of 3-dimensional sequences before they can replace currently used 2-dimensional FSE sequences for evaluating the musculoskeletal system in clinical practice.

Longitudinal assessment of cyst-like lesions of the knee and their relation to radiographic osteoarthritis and MRI-detected effusion and synovitis in patients with knee pain

Introduction

The purpose of the present study was to determine the prevalence of cystic lesions and cyst-like bursitides in subjects with frequent knee pain and to assess their relation to radiographic osteoarthritis (OA) severity; to describe bilaterality and size fluctuation of the lesions over 6 months; and to assess relations between the prevalence of synovium-lined lesions communicating with the joint capsule and severity of magnetic resonance imaging (MRI)-detected effusion and synovitis.

Methods

One hundred and sixty-three subjects (total 319 knees) aged 35 to 65 with chronic, frequent knee pain were included. Imaging with 3 Tesla MRI was performed at baseline and 6-month follow-up with the same protocols as those used in the Osteoarthritis Initiative. Severity of radiographic OA was assessed using the Kellgren-Lawrence grade (0 to 4). Severity of effusion and synovitis was graded 0 to 3 based on the Whole Organ Magnetic Resonance Imaging Score system. The associations of cysts and cyst-like bursitides and severity of radiographic OA, MRI-detected effusion and synovitis were analyzed using logistic regression controlling for clustering by person. The Wilcoxon signed-rank test was used to determine whether there was a significant change in the size of lesions between baseline and follow-up.

Results

At least one lesion (any type) was present in 222 (70%) knees. The most prevalent lesions were popliteal cysts (40%, 128/319), followed by subgastrocnemius bursitis (15%, 49/319) and proximal tibiofibular joint cysts (8%, 26/319). Bilateral lesions were seen in 49% of the subjects. Only popliteal cysts and subgastrocnemius bursitis showed a significant change in size (P < 0.001). No trend was observed between prevalence of any of the cyst-like lesions analyzed and the increasing radiographic OA severity. Increasing prevalence of subgastrocnemius bursitis was associated with increasing severity of effusion (P = 0.0072) and synovitis (P = 0.0033).

Conclusions

None of the cyst-like lesions analyzed seems to be a marker of radiographic OA severity in knees with chronic frequent pain. Subgastrocnemius bursitis may be used as a marker of effusion/synovitis severity. Bilateral cyst-like lesions are relatively commonly observed in people with chronic knee pain.

Spatial patterns of cartilage loss in the medial femoral condyle in osteoarthritic knees: data from the Osteoarthritis Initiative

The objective of this study was to develop a technique for analyzing spatial patterns of cartilage loss in the medial femoral condyle (MF), and to study MF cartilage loss in participants of the Osteoarthritis Initiative. Using a 0.7 mm sagittal double echo at steady state (DESS) sequence, 160 osteoarthritic knees from 80 participants with varying degrees of medial joint space narrowing were imaged at baseline and 1-year follow-up. MF cartilage was segmented and cartilage loss determined. Rate of change varied significantly (P = 0.0067) along the anterior-posterior extension of the MF, with the greatest changes (-45 microm, -2.7%) observed 30-60 degrees posterior to the trochlear notch. The rate was greater in the central MF after excluding peripheral aspects of the MF from analysis. Sensitivity to change was greatest at 45-75 degrees (standardized response mean = -0.32) but was minimally affected by medial-lateral trimming. In conclusion, the greatest sensitivity to change was achieved when analyzing the posterior aspect of the central, weight-bearing MF.

Subjects with higher physical activity levels have more severe focal knee lesions diagnosed with 3T MRI: analysis of a non-symptomatic cohort of the osteoarthritis initiative

PURPOSE

To study the prevalence of focal knee abnormalities using 3 Tesla (T) magnetic resonance (MR) studies in relation to physical activity levels in asymptomatic, middle-aged subjects from the osteoarthritis initiative (OAI).

MATERIAL AND METHODS

We analyzed baseline data from 236, 45-55 years old individuals (136 women, 100 men) without knee pain (based on Western Ontario and McMaster University scores) and a body mass index (BMI) of 19-27 kg/m(2). Physical activity levels were determined in all subjects using the Physical Activity Scale for the Elderly (PASE). MR imaging (MRI) at 3T was performed using coronal intermediate-weighted (IW) 2D fast spin-echo (FSE), sagittal 3D dual-echo in steady state (DESS) and 2D IW fat-suppressed (fs) FSE sequences of the right knee. All images were analyzed by two musculoskeletal radiologists identifying and grading cartilage, meniscal, ligamentous and other knee abnormalities using the whole-organ MR imaging score (WORMS) MRI OA scoring method. Statistical significances between subjects with different activity levels were determined using one-way analysis of variance (ANOVA), chi-square tests and a multi-variate regression model adjusted for gender, age, BMI, Kellgren-Lawrence (KL) score and osteoarthritis (OA) risk factors.

RESULTS

Meniscal lesions were found in 47% of the 236 subjects, cartilage lesions in 74.6%, bone marrow edema pattern (BMEP) in 40.3% and ligament lesions in 17%. Stratification of subjects by physical activity resulted in an increasing incidence of cartilage, meniscus and ligament abnormalities, BMEP and joint effusion according to activity levels (PASE). The severity grade of cartilage lesions was also associated with PASE levels and presence of other knee abnormalities was also significantly associated with cartilage defects.

CONCLUSION

Asymptomatic middle-aged individuals from the OAI incidence cohort had a high prevalence of knee abnormalities; more physically active individuals had significantly more and more severe knee abnormalities independently of gender, age, BMI, KL score and OA risk factors. These data therefore also suggest that subjects with higher physical activity levels may be at greater risk for cartilage, meniscus and ligament abnormalities, but the analysis of the longitudinal data will show whether these subjects will demonstrate accelerated progress.

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.

Presence, location, type and size of denuded areas of subchondral bone in the knee as a function of radiographic stage of OA - data from the OA initiative

OBJECTIVE

To assess the presence, location, type and size of denuded areas of subchondral bone (dAB) in the femorotibial joint, measured quantitatively with 3T MRI, in a large subset of OAI participants.

METHODS

One knee of 633 subjects (250 men, 383 women, aged 61.7+/-9.6 y) were studied, spanning all radiographic osteoarthritis (OA) stages. dABs were determined quantitatively using segmentations of coronal FLASHwe images, representing areas where the subchondral bone was not covered by cartilage. Post hoc visual examination of segmented images determined whether dABs represented full thickness cartilage loss or internal osteophyte.

RESULTS

7% Of the knees were Kellgren & Lawrence (KL) grade 0, 6% grade 1, 41% grade 2, 41% grade 3, and 5% grade 4. 39% Of the participants (48% of the men and 33% of the women) displayed dABs; 61% of the dABs represented internal osteophytes. 1/47 Participants with KL grade 0 displayed 'any' dAB whereas 29/32 of the KL grade 4 knees were affected. Even as early as KL grade 1, 29% of the participants showed dABs. There were significant relationships of dAB with increasing KL grades (P<0.001) and with ipsi-compartimental JSN (P< or =0.001). Internal osteophytes were more frequent laterally (mainly posterior tibia and internal femur) whereas full thickness cartilage loss was more frequent medially (mainly external tibia and femur).

CONCLUSIONS

dABs occur already at earliest stages of radiographic OA (KL grades 1 and 2) and become more common (and larger) with increasing disease severity. Almost all KL grade 4 knees exhibited dABs, with cartilage loss being more frequent than internal osteophytes.

Can cartilage loss be detected in knee osteoarthritis (OA) patients with 3-6 months' observation using advanced image analysis of 3T MRI?

PURPOSE

Prior investigations of magnetic resonance imaging (MRI) biomarkers of cartilage loss in knee osteoarthritis (OA) suggest that trials of interventions which affect this biomarker with adequate statistical power would require large clinical studies of 1-2 years duration. We hypothesized that smaller, shorter duration, "Proof of Concept" (PoC) studies might be achievable by: (1) selecting a population at high risk of rapid medial tibio-femoral (TF) progression, in conjunction with; (2) high-field MRI (3T), and; (3) using advanced image analysis. The primary outcome was the cartilage thickness in the central medial femur.

METHODS

Multi-centre, non-randomized, observational cohort study at four sites in the US. Eligible participants were females with knee pain, a body mass index (BMI)> or =25 kg/m(2), symptomatic radiographic evidence of medial TF OA, and varus mal-alignment. The 29 participants had a mean age of 62 years, mean BMI of 36 kg/m(2), with eight index knees graded as Kellgren-Lawrence (K&L)=2 and 21 as K&L=3. Eligible participants had four MRI scans of one knee: two MRIs (1 week apart) were acquired as a baseline with follow-up MRI at 3 and 6 months. A trained operator, blind to time-point but not subject, manually segmented the cartilage from the Dual Echo Steady State water excitation MR images. Anatomically corresponding regions of interest were identified on each image by using a three-dimensional statistical shape model of the endosteal bone surface, and the cartilage thickness (with areas denuded of cartilage included as having zero thickness - ThCtAB) within each region was calculated. The percentage change from baseline at 3 and 6 months was assessed using a log-scale analysis of variance (ANOVA) model including baseline as a covariate. The primary outcome was the change in cartilage thickness within the aspect of central medial femoral condyle exposed within the meniscal window (w) during articulation, neglecting cartilage edges [nuclear (n)] (nwcMF x ThCtAB), with changes in other regions considered as secondary endpoints.

RESULTS

Anatomical mal-alignment ranged from -1.9 degrees to 6.3 degrees , with mean 0.9 degrees . With one exception, no changes in ThCtAB were detected at the 5% level for any of the regions of interest on the TF joint at 3 or 6 months of follow-up. The change in the primary variable (nwcMF x ThCtAB) from (mean) baseline at 3 months from the log-scale ANOVA model was -2.1% [95% confidence interval (CI) (-4.4%, +0.2%)]. The change over 6 months was 0.0% [95% CI (-2.7%, +2.8%)]. The 95% CI for the change from baseline did not include zero for the cartilage thickness within the meniscal window of the lateral tibia (wLT x ThCtAB) at 6 month follow-up (-1.5%, 95% CI [-2.9, -0.2]), but was not significant at the 5% level after correction for multiple comparisons.

CONCLUSIONS

The small inconsistent compartment changes, and the relatively high variabilities in cartilage thickness changes seen over time in this study, provide no additional confidence for a 3- or 6-month PoC study using a patient population selected on the basis of risk for rapid progression with the MRI acquisition and analyses employed.

Sensitivity to change of cartilage morphometry using coronal FLASH, sagittal DESS, and coronal MPR DESS protocols--comparative data from the Osteoarthritis Initiative (OAI)

OBJECTIVE

The Osteoarthritis Initiative (OAI) is targeted at identifying sensitive biomarkers and risk factors of symptomatic knee osteoarthritis (OA) onset and progression. Quantitative cartilage imaging in the OAI relies on validated fast low angle shot (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 (BL) and 12 month follow-up data of 80 knees were acquired using 1.5 mm coronal FLASH and 0.7 mm sagittal DESS (sagDESS) sequences. In these and in 1.5 mm coronal multi-planar 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 between the trochlear notch and the posterior femur) and a 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 sagDESS with the 60% ROI, and -0.38 for the 75% ROI. Using every second 0.7 mm 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. BL cartilage thickness displayed high correlations (r > or = 0.94) between the three protocols; the correlations of longitudinal changes were > or = 0.79 (Pearson) and > or = 0.45 (Spearman).

CONCLUSIONS

Cartilage morphometry with FLASH and DESS displays similar longitudinal sensitivity to change. Analysis of every second slice of the 0.7 mm DESS provides adequate sensitivity to change.

Semi-automated segmentation to assess the lateral meniscus in normal and osteoarthritic knees

OBJECTIVE

The goal of this study was to develop an algorithm to semi-automatically segment the meniscus in a series of magnetic resonance (MR) images to use for normal knees and those with moderate osteoarthritis (OA).

METHOD

The segmentation method was developed then evaluated on 10 baseline MR images obtained from subjects with no evidence, symptoms, or risk factors of knee (OA), and 14 from subjects with established knee OA enrolled in the Osteoarthritis Initiative (OAI). After manually choosing a seed point within the meniscus, a threshold level was calculated through a Gaussian fit model. Under anatomical, intensity, and range constraints, a threshold operation was completed followed by conditional dilation and post-processing. The post-processing operation reevaluates the pixels included and excluded in the area surrounding the meniscus to improve accuracy. The developed method was evaluated for both normal and degenerative menisci by comparing the segmentation algorithm results with manual segmentations from five human readers.

RESULTS

The semi-automated segmentation method produces results similar to those of trained observers, with an average similarity index over 0.80 for normal participants and 0.75, 0.67, and 0.64 for participants with established knee OA with Osteoarthritis Research Society International (OARSI) joint space narrowing (JSN) scores of 0, one, and two respectively.

CONCLUSION

The semi-automatic segmentation method produced accurate and consistent segmentations of the meniscus when compared to manual segmentations in the assessment of normal menisci in mild to moderate OA. Future studies will examine the change in volume, thickness, and intensity characteristics at different stages of 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.

Longitudinal analysis of MRI T(2) knee cartilage laminar organization in a subset of patients from the osteoarthritis initiative

The purpose of this pilot study was to longitudinally quantify the T(2) laminar integrity of knee cartilage in a subset of subjects with osteoarthritis from the Osteoarthritis Initiative at baseline, 1-year follow-up, and 2-year follow-up. Cartilage from 13 subjects was divided into six compartments and subdivided into deep and superficial layers. At each time point, mean T(2) values in superficial and deep layers were compared. Longitudinal analysis included full-thickness mean T(2), mean deep T(2), mean superficial T(2), mean T(2) laminar difference, mean percentage T(2) laminar difference, and two-dimensional measures of cartilage thickness. More compartments showed significantly higher superficial T(2) than deep T(2) values at baseline and 1-year follow-up compared to 2-year follow-up. No significant longitudinal changes of full-thickness mean T(2) and superficial T(2) values were observed. Significant longitudinal changes were observed in the deep T(2) values, T(2) laminar difference, and percentage T(2) laminar difference. Cartilage thickness had no influence on T(2) analysis. Results of this study suggest that laminar analysis may improve the sensitivity to detect longitudinal T(2) changes and that disruption of the T(2) laminar organization of knee cartilage may be present in knee osteoarthritis progressors. Further investigation is warranted to evaluate the potential of the presented methodology to better characterize evolution and pathophysiology of osteoarthritis.

Patellar cartilage: T2 values and morphologic abnormalities at 3.0-T MR imaging in relation to physical activity in asymptomatic subjects from the osteoarthritis initiative

PURPOSE

To study the interrelationship between patella cartilage T2 relaxation time, other knee abnormalities, and physical activity levels in asymptomatic subjects from the Osteoarthritis Initiative (OAI) incidence cohort.

MATERIALS AND METHODS

The study had institutional review board approval and was HIPAA compliant. One hundred twenty subjects from the OAI without knee pain (age, 45-55 years) and with risk factors for knee osteoarthritis (OA) were studied by using knee radiographs, 3.0-T knee magnetic resonance (MR) images (including intermediate-weighted fast spin-echo and T2 mapping sequences), and the Physical Activity Scale for the Elderly. MR images of the right knee were assessed by two musculoskeletal radiologists for the presence and grade of abnormalities. Segmentation of the patella cartilage was performed, and T2 maps were generated. Statistical significance was determined by using analysis of variance, chi(2) analysis, correlation coefficient tests, the Cohen kappa, and a multiple linear regression model.

RESULTS

Cartilage lesions were found in 95 (79.0%) of 120 knees, and meniscal lesions were found in 54 (45%) of 120 knees. A significant correlation between patella cartilage T2 values and the severity and grade of cartilage (P = .0025) and meniscus (P = .0067) lesions was demonstrated. Subjects with high activity levels had significantly higher prevalence and grade of abnormalities and higher T2 values (48.7 msec +/-4.35 vs 45.8 msec +/-3.93; P < .001) than did subjects with low activity levels.

CONCLUSION

Middle-aged asymptomatic individuals with risk factors for knee OA had a high prevalence of cartilage and meniscus knee lesions. Physically active individuals had more knee abnormalities and higher patellar T2 values. Additional studies will be needed to determine causality.

Magnetic resonance imaging-based cartilage loss in painful contralateral knees with and without radiographic joint space narrowing: Data from the Osteoarthritis Initiative

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 mum) assessed by MRI than contralateral knees with less mJSN (-57 mum). 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.

MR imaging-based semiquantitative assessment in osteoarthritis

Whole-organ semiquantitative (SQ) assessment by expert readers has become a powerful research tool in understanding the natural history of osteoarthritis (OA). SQ morphologic scoring has been applied to observational large cross-sectional and longitudinal epidemiologic studies in addition to interventional clinical trials. In comparison to quantitative and biochemical assessment of cartilage, SQ whole-organ scoring also analyzes additional joint structures that are potentially relevant as surrogate outcome measures for interventional approaches. Resources needed for SQ scoring rely on the MR imaging protocol, image quality, experience of the expert readers, method of documentation, and individual scoring system that is applied. This article discusses the different available OA whole-organ scoring systems, focusing on MR imaging of the knee, and also reviews alternative approaches.

MR imaging in osteoarthritis: hardware, coils, and sequences

Whole-organ assessment of a joint with osteoarthritis (OA) requires tailored MR imaging hardware and imaging protocols to diagnose and monitor degenerative disease of the cartilage, menisci, bone marrow, ligaments, and tendons. Image quality benefits from increased field strength, and 3.0-T MR imaging is used increasingly for assessing joints with OA. Dedicated surface coils are required for best visualization of joints affected by OA, and the use of multichannel phased-array coils with parallel imaging improves image quality and/or shortens acquisition times. Sequences that best show morphologic abnormalities of the whole joint include intermediate-weighted fast-spin echo sequences. Also quantitative sequences have been developed to assess cartilage volume and thickness and to analyze cartilage biochemical composition.

Relationship of compartment-specific structural knee status at baseline with change in cartilage morphology: a prospective observational study using data from the osteoarthritis initiative

INTRODUCTION

The aim was to investigate the relationship of cartilage loss (change in medial femorotibial cartilage thickness measured with magnetic resonance imaging (MRI)) with compartment-specific baseline radiographic findings and MRI cartilage morphometry features, and to identify which baseline features can be used for stratification of fast progressors.

METHODS

An age and gender stratified subsample of the osteoarthritis (OA) initiative progression subcohort (79 women; 77 men; age 60.9 +/- 9.9 years; body mass index (BMI) 30.3 +/- 4.7) with symptomatic, radiographic OA in at least one knee was studied. Baseline fixed flexion radiographs were read centrally and adjudicated, and cartilage morphometry was performed at baseline and at one year follow-up from coronal FLASH 3 Tesla MR images of the right knee.

RESULTS

Osteophyte status at baseline was not associated with medial cartilage loss. Knees with medial joint space narrowing tended to show higher rates of change than those without, but the relationship was not statistically significant. Knees with medial femoral subchondral bone sclerosis (radiography), medial denuded subchondral bone areas (MRI), and low cartilage thickness (MRI) at baseline displayed significantly higher cartilage loss than those without, both with and without adjusting for age, sex, and BMI. Participants with denuded subchondral bone showed a standardized response mean of up to -0.64 versus -0.33 for the entire subcohort.

CONCLUSIONS

The results indicate that radiographic and MRI cartilage morphometry features suggestive of advanced disease appear to be associated with greater cartilage loss. These features may be suited for selecting patients with a higher likelihood of fast progression in studies that attempt to demonstrate the cartilage-preserving effect of disease-modifying osteoarthritis drugs.

Multiecho IDEAL gradient-echo water-fat separation for rapid assessment of cartilage volume at 1.5 T: initial experience

Institutional review board approval and informed consent were obtained for this HIPAA-compliant study. The purpose was to prospectively compare multiecho iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) gradient-echo (GRE) magnetic resonance (MR) imaging with three-dimensional fat-suppressed (FS) spoiled GRE (SPGR) MR imaging to evaluate the articular cartilage of the knee. Six healthy volunteer and 10 cadaver knees were imaged at 1.5 T. Signal-to-noise ratio (SNR), SNR efficiency, and cartilage volume were measured. SNR and SNR efficiency were significantly higher with multiecho IDEAL GRE than with FS SPGR imaging (P < .031). Both methods produced equivalent cartilage volumes (overall concordance correlation coefficient, 0.998) with high precision and accuracy. The use of a cartilage phantom confirmed high accuracy in volume measurements and high reproducibility for both methods. Multiecho IDEAL GRE provides high signal intensity in cartilage and synovial fluid and is a promising technique for imaging articular cartilage of the knee.