Michel D. Crema

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.

Presence of MRI-detected joint effusion and synovitis increases the risk of cartilage loss in knees without osteoarthritis at 30-month follow-up: the MOST study

Objective To evaluate if two different measures of synovial activation, baseline Hoffa synovitis and effusion synovitis, assessed by MRI, predict cartilage loss in the tibiofemoral joint at 30 months follow-up in subjects with neither cartilage damage nor tibiofemoral radiographic osteoarthritis of the knee. Methods Non-contrast-enhanced MRI was performed using proton density-weighted fat-suppressed sequences in the axial and sagittal planes and a short tau inversion recovery sequence in the coronal plane. Hoffa synovitis, effusion synovitis and cartilage status were assessed semiquantitatively according to the WORMS scoring system. Included were knees that had neither radiographic osteoarthritis nor MRI-detected tibiofemoral cartilage damage at the baseline visit. The presence of Hoffa synovitis was defined as any grade ≥2 (range 0–3) and effusion synovitis as any grade ≥2 (range 0–3). Logistic regression was performed to examine the relation of the presence of either measure to the risk of cartilage loss at 30 months adjusting for other potential confounders. Results Of 514 knees included in the analysis, the prevalence of Hoffa synovitis and effusion synovitis at the baseline visit was 8.4% and 10.3%, respectively. In the multivariable analysis, baseline effusion synovitis was associated with an increased risk of cartilage loss. No such association was observed for baseline Hoffa synovitis. Conclusions Baseline effusion synovitis, but not Hoffa synovitis, predicted cartilage loss. The findings suggest that effusion synovitis, a reflection of inflammatory activity including joint effusion and synovitic thickening, may play a role in the future development of cartilage lesions in knees without osteoarthritis.

Meniscus pathology, osteoarthritis and the treatment controversy.

The menisci are internal structures that are of central importance for a healthy knee joint; they have a key role in the structural progression of knee osteoarthritis (OA), and the risk of the disease dramatically increases if they are damaged by injury or degenerative processes. Meniscus damage might be considered a signifying feature of incipient OA in middle-aged and elderly people. As approximately every third knee of people in these groups has a damaged meniscus, tears are common incidental findings of knee MRI. However, as most tears do not cause symptoms, careful clinical evaluation is required to determine if a damaged meniscus is likely to directly impact a patients symptoms. Conservative management of patients with knee pain and a degenerative meniscal tear should be considered as a first-line therapy before surgical treatment is contemplated. Patients with mechanical interference of joint movements, such as painful catching or locking, might need surgical treatment with meniscal repair if possible. In a subset of patients, meniscal resection might relieve pain and other symptoms that potentially originate directly from the torn meniscus. However, the possibility of an increased risk of OA if functional meniscal tissue is removed cannot be overlooked.

Tibiofemoral Joint Osteoarthritis: Risk Factors for MR-depicted Fast Cartilage Loss over a 30-month Period in the Multicenter Osteoarthritis Study

PURPOSE To assess baseline factors that may predict fast tibiofemoral cartilage loss over a 30-month period. MATERIALS AND METHODS The Multicenter Osteoarthritis (MOST) study is a longitudinal study of individuals who have or who are at high risk for knee osteoarthritis. The HIPAA-compliant protocol was approved by the institutional review boards of all participating centers, and written informed consent was obtained from all participants. Magnetic resonance (MR) images were read according to the Whole-Organ Magnetic Resonance Imaging Score (WORMS) system. Only knees with minimal baseline cartilage damage (WORMS < or = 2.5) were included. Fast cartilage loss was defined as a WORMS of at least 5 (large full-thickness loss, less than 75% of the subregion) in any subregion at 30-month follow-up. The relationships of age, sex, body mass index (BMI), ethnicity, knee alignment, and several MR features (eg, bone marrow lesions, meniscal damage and extrusion, and synovitis or effusion) to the risk of fast cartilage loss were assessed by using a multivariable logistic regression model. RESULTS Of 347 knees, 90 (25.9%) exhibited cartilage loss, and only 20 (5.8%) showed fast cartilage loss. Strong predictors of fast cartilage loss were high BMI (adjusted odds ratio [OR], 1.11; 95% confidence interval [CI]: 1.01, 1.23), the presence of meniscal tears (adjusted OR, 3.19; 95% CI: 1.13, 9.03), meniscal extrusion (adjusted OR, 3.62; 95% CI: 1.34, 9.82), synovitis or effusion (adjusted OR, 3.36; 95% CI: 0.91, 12.4), and any high-grade MR-depicted feature (adjusted OR, 8.99; 95% CI: 3.23, 25.1). CONCLUSION In participants with minimal baseline cartilage damage, the presence of high BMI, meniscal damage, synovitis or effusion, or any severe baseline MR-depicted lesions was strongly associated with an increased risk of fast cartilage loss. Patients with these risk factors may be ideal subjects for preventative or treatment trials.

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.

Assessment of synovitis with contrast-enhanced MRI using a whole-joint semiquantitative scoring system in people with, or at high risk of, knee osteoarthritis: the MOST study.

Objectives To introduce a comprehensive and reliable scoring system for the assessment of whole-knee joint synovitis based on contrast-enhanced (CE) MRI. Methods Multicenter Osteoarthritis Study (MOST) is a cohort study of people with, or at high risk of, knee osteoarthritis (OA). Subjects are an unselected subset of MOST who volunteered for CE-MRI. Synovitis was assessed at 11 sites of the joint. Synovial thickness was scored semiquantitatively: grade 0 (<2 mm), grade 1 (2–4 mm) and grade 2 (>4 mm) at each site. Two musculoskeletal radiologists performed the readings and inter- and intrareader reliability was evaluated. Whole-knee synovitis was assessed by summing the scores from all sites. The association of Western Ontario and McMaster Osteoarthritis Index pain score with this summed score and with the maximum synovitis grade for each site was assessed. Results 400 subjects were included (mean age 58.8±7.0 years, body mass index 29.5±4.9 kg/m2, 46% women). For individual sites, intrareader reliability (weighted κ) was 0.67–1.00 for reader 1 and 0.60–1.00 for reader 2. Inter-reader agreement (κ) was 0.67–0.92. For the summed synovitis scores, intrareader reliability (intraclass correlation coefficient ( ICC)) was 0.98 and 0.96 for each reader and inter-reader agreement (ICC) was 0.94. Moderate to severe synovitis in the parapatellar subregion was associated with the higher maximum pain score (adjusted OR (95% CI), 2.8 (1.4 to 5.4) and 3.1 (1.2 to 7.9), respectively). Conclusions A comprehensive semiquantitative scoring system for the assessment of whole-knee synovitis is proposed. It is reliable and identifies knees with pain, and thus is a potentially powerful tool for synovitis assessment in epidemiological OA studies.

MRI-based semiquantitative scoring of joint pathology in osteoarthritis

The use of MRI techniques to investigate tissue pathology has become increasingly widespread in osteoarthritis (OA) research. Semiquantitative assessment of the joints by expert interpreters of MRI data is a powerful tool that can increase our understanding of the natural history of this complex disease. Several reliable and validated semiquantitative scoring systems now exist and have been applied to large-scale, multicentre, cross-sectional and longitudinal observational epidemiological studies. Such approaches have advanced our understanding of the associations of different tissue pathologies with pain and improved the definition of joint alterations that lead to disease progression. Semiquantitative MRI outcome measures have also been applied in several clinical trials in OA. Indeed, interest in MRI-based semiquantitative scoring systems has led to the development of several novel scoring systems that can be applied to different joints: a knee synovitis scoring system based on contrast-enhanced MRI; the MRI Osteoarthritis Knee Score (MOAKS); the Hip Osteoarthritis MRI Score (HOAMS); and the Oslo Hand Osteoarthritis MRI score (OHOA-MRI). Although these new scoring systems offer theoretical advantages over pre-existing systems, whether they offer actual superiority with regard to reliability, responsiveness and validity remains to be seen.

Hoffa's Fat Pad: Evaluation on Unenhanced MR Images as a Measure of Patellofemoral Synovitis in Osteoarthritis

OBJECTIVE The purpose of this study was to compare synovitis-like signal changes in Hoffas fat pad on unenhanced proton density-weighted fat-suppressed sequences with signal alterations in Hoffas fat pad and peripatellar synovial thickening on T1-weighted fat-suppressed contrast-enhanced sequences in patients with osteoarthritis. SUBJECTS AND METHODS Fifty patients with osteoarthritis of the knee participated in the study. MRI was performed with triplanar proton density-weighted fat-suppressed sequences and a sagittal T1-weighted fat-suppressed contrast-enhanced sequence. Signal intensity alterations in Hoffas fat pad were scored semiquantitatively on unenhanced and contrast-enhanced images by two radiologists in consensus. Peripatellar synovial thickness was measured on the T1-weighted fat-suppressed contrast-enhanced images in six locations. Agreement between scoring of signal changes on unenhanced and contrast-enhanced sequences was assessed with kappa statistics. The sensitivity, specificity, and accuracy of scoring of signal-intensity changes on unenhanced images were calculated with T1-weighted contrast-enhanced MRI as the reference standard. In addition, we also examined the relation between signal changes and summed synovial thickness using Spearmans rank correlation coefficient. RESULTS Agreement between unenhanced and contrast-enhanced MRI was fair to moderate (weighted kappa = 0.35 and 0.45). The sensitivity of signal intensity changes in Hoffas fat pad on proton density-weighted fat-suppressed images was high, but specificity was low. Correlations of signal intensity changes in Hoffas fat pad with synovial thickness were lower for unenhanced scans but all were statistically significant. CONCLUSION Signal intensity alterations in Hoffas fat pad on unenhanced images do not always represent synovitis but are a nonspecific albeit sensitive finding. Semiquantitative scoring of synovitis of the patellofemoral region in osteoarthritis ideally should be performed with T1-weighted contrast-enhanced sequences and should include scoring of synovial thickness.

Compositional MRI techniques for evaluation of cartilage degeneration in osteoarthritis.

Osteoarthritis (OA), a leading cause of disability, affects 27 million people in the United States and its prevalence is rising along with the rise in obesity. So far, biomechanical or behavioral interventions as well as attempts to develop disease-modifying OA drugs have been unsuccessful. This may be partly due to antiquated imaging outcome measures such as radiography, which are still endorsed by regulatory agencies such as the United States Food and Drug Administration (FDA) for use in clinical trials. Morphological magnetic resonance imaging (MRI) allows unparalleled multi-feature assessment of the OA joint. Furthermore, advanced MRI techniques also enable evaluation of the biochemical or ultrastructural composition of articular cartilage relevant to OA research. These compositional MRI techniques have the potential to supplement clinical MRI sequences in identifying cartilage degeneration at an earlier stage than is possible today using morphologic sequences only. The purpose of this narrative review is to describe compositional MRI techniques for cartilage evaluation, which include T2 mapping, T2* Mapping, T1 rho, dGEMRIC, gagCEST, sodium imaging and diffusion weighted imaging (DWI). We also reviewed relevant clinical studies that have utilized these techniques for the study of OA. The different techniques are complementary. Some focus on isotropy or the collagen network (e.g., T2 mapping) and others are more specific in regard to tissue composition, e.g., gagCEST or dGEMRIC that convey information on the GAG concentration. The application and feasibility of these techniques is also discussed, as they will play an important role in implementation in larger clinical trials and eventually clinical practice.

Risk factors for medial meniscal pathology on knee MRI in older US adults: a multicentre prospective cohort study

Objectives Meniscal pathology in which the aetiology is often unclear is a frequent finding on knee MRI. This study investigates potential risk factors for medial meniscal lesions or extrusion in middle-aged and elderly persons. Methods Prospective cohort study using population-based subjects from Birmingham, Alabama and Iowa City, Iowa, USA (the Multicenter Osteoarthritis Study). 644 men and women aged 50–79 years with or at high risk of knee osteoarthritis (Kellgren and Lawrence grade 0–2) but with normal medial meniscal status at baseline were studied. Paired baseline and 30-month 1.0 T knee MRI were scored for meniscal lesions and extrusion (pathology) and the following systemic, knee-specific and compartment-specific potential risk factors were evaluated: age, sex, body mass index, bony enlargement of finger joints, knee trauma, leg-length inequality and knee alignment. Results Of 791 knees, 77 (9.7%) had medial meniscal pathology at 30 months follow-up. 61 of the 77 (81%) had no report of trauma during follow-up. Including all potential risk factors in the multivariable model, the adjusted OR for medial meniscal pathology was 4.14 (95% CI 2.06 to 8.31) for knee trauma during follow-up, 1.64 (1.00 to 2.70) for five or more bony enlargements of finger joints (vs ≤4) and 2.00 (1.18 to 3.40) for varus alignment (vs not varus) at baseline examination. Obesity was a risk factor for the development of meniscal extrusion, OR 3.04 (1.04 to 8.93) but not for meniscal lesions, OR 1.15 (0.52 to 2.54). Conclusions Apart from knee trauma, possible generalised osteoarthritis, expressed as multiple bony enlargements of finger joints, varus alignment and obesity are risk factors for medial meniscal pathology.