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

The design of a sample rapid magnetic resonance imaging (MRI) acquisition protocol supporting assessment of multiple articular tissues and pathologies in knee osteoarthritis

Objective

This expert opinion paper proposes a design for a state-of-the-art magnetic resonance image (MRI) acquisition protocol for knee osteoarthritis clinical trials in early and advanced disease. Semi-quantitative and quantitative imaging endpoints are supported, partly amendable to automated analysis. Several (peri-) articular tissues and pathologies are covered, including synovitis.

Method

A PubMed literature search was conducted, with focus on the past 5 years. Further, osteoarthritis imaging experts provided input. Specific MRI sequences, orientations, spatial resolutions and parameter settings were identified to align with study goals. We strived for implementation on standard clinical scanner hardware, with a net acquisition time ≤30 ​min.

Results

Short- and long-term longitudinal MRIs should be obtained at ≥1.5T, if possible without hardware changes during the study. We suggest a series of gradient- and spin-echo-sequences, supporting MOAKS, quantitative analysis of cartilage morphology and T2, and non-contrast-enhanced depiction of synovitis. These sequences should be properly aligned and positioned using localizer images. One of the sequences may be repeated in each participant (re-test), optimally at baseline and follow-up, to estimate within-study precision. All images should be checked for quality and protocol-adherence as soon as possible after acquisition. Alternative approaches are suggested that expand on the structural endpoints presented.

Conclusions

We aim to bridge the gap between technical MRI acquisition guides and the wealth of imaging literature, proposing a balance between image acquisition efficiency (time), safety, and technical/methodological diversity. This approach may entertain scientific innovation on tissue structure and composition assessment in clinical trials on disease modification of knee osteoarthritis.

Quantitative bone marrow lesion, meniscus, and synovitis measurement: current status

Imaging plays a pivotal role in osteoarthritis research, particularly in epidemiological and clinical trials of knee osteoarthritis (KOA), with the ultimate goal being the development of an effective drug treatment for future prevention or cessation of disease. Imaging assessment methods can be semi-quantitative, quantitative, or a combination, with quantitative methods usually relying on software to assist. The software generally attempts image segmentation (outlining of relevant structures). New techniques using artificial intelligence (AI) or deep learning (DL) are currently a frequent topic of research. This review article provides an overview of the literature to date, focusing primarily on the current status of quantitative software-based assessment techniques of KOA using magnetic resonance (MR) imaging. We will concentrate on the imaging evaluation of three specific structural imaging biomarkers: bone marrow lesions (BMLs), meniscus, and synovitis consisting of effusion synovitis (ES) and Hoffa's synovitis (HS). A brief clinical and imaging background review of osteoarthritis evaluation, particularly relating to these three structural markers, is provided as well as a general summary of the software methods. A summary of the literature with respect to each KOA assessment method will be presented overall as well as with respect to each specific biomarker individually. Novel techniques, as well as future goals and directions using quantitative imaging assessment, will be discussed.

Association of quantitative measures of medial meniscal extrusion with structural and symptomatic knee osteoarthritis progression - Data from the OAI FNIH biomarker study

OBJECTIVE

To study the association of quantitative medial meniscal position measures with radiographic and symptomatic knee osteoarthritis (OA) progression over 2-4 years.

METHODS

The FNIH OAI Biomarkers study comprised 600 participants in four subgroups: 194 case knees with combined structural (medial minimum joint space width (minJSW) loss ≥0.7 mm) and symptomatic (persistent Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain subscale increase ≥9 [0-100 scale]) progression; 200 knees with neither structural nor symptomatic progression; 103 knees with isolated structural and 103 with isolated symptomatic progression. Coronal double echo at steady state (DESS) MRIs were used for segmenting five central slices of the medial meniscus. Associations with progression were examined using logistic regression (adjusted for demographic and clinical data).

RESULTS

Greater baseline medial meniscal extrusion was associated with combined structural/symptomatic progression (OR 1.59; 95%CI: [1.25,2.04]). No relationship was observed for tibial plateau coverage or meniscal overlap distance. The two-year increase in meniscal extrusion (OR 1.48 [1.21, 1.83]), and reduction in tibial plateau coverage (OR 0.70 [0.58,0.86]) and overlap distance (OR 0.73 [0.60,0.89]) were associated with combined progression. Greater baseline extrusion was associated with isolated structural and less extrusion with isolated symptomatic progression. The longitudinal increase in meniscal extrusion, and reduction in tibial plateau coverage and overlap distance were associated with structural, but not with symptomatic progression.

CONCLUSION

Baseline measures of medial meniscal extrusion were consistently positively associated with combined radiographic/symptomatic progression and with isolated structural, but not with isolated symptomatic progression. These measures may therefore allow one to assess the risk of structural knee OA progression and to monitor interventions restoring meniscal position and function.

Correction of B0 and linear eddy currents: Impact on morphological and quantitative ultrashort echo time double echo steady state (UTE-DESS) imaging

The purpose of the current study was to investigate the effects of B0 and linear eddy currents on ultrashort echo time double echo steady state (UTE-DESS) imaging and to determine whether eddy current correction (ECC) effectively resolves imaging artifacts caused by eddy currents. 3D UTE-DESS sequences based on either projection radial or spiral cones trajectories were implemented on a 3-T clinical MR scanner. An off-isocentered thin-slice excitation approach was used to measure eddy currents. The measurements were repeated four times using two sets of tested gradient waveforms with opposite polarities and two different slice locations to measure B0 and linear eddy currents simultaneously. Computer simulation was performed to investigate the eddy current effect. Finally, a phantom experiment, an ex vivo experiment with human synovium and ankle samples, and an in vivo experiment with human knee joints, were performed to demonstrate the effects of eddy currents and ECC in UTE-DESS imaging. In a computer simulation, the two echoes (S+ and S-) in UTE-DESS imaging exhibited strong distortion at different orientations in the presence of B0 and linear eddy currents, resulting in both image degradation as well as misalignment of pixel location between the two echoes. The same phenomenon was observed in the phantom, ex vivo, and in vivo experiments, where the presence of eddy currents degraded S+, S-, echo subtraction images, and T2 maps. The implementation of ECC dramatically improved both the image quality and image registration between the S+ and S- echoes. It was concluded that ECC is crucial for reliable morphological and quantitative UTE-DESS imaging.

Meniscus position and size in knees with versus without structural knee osteoarthritis progression: data from the osteoarthritis initiative

OBJECTIVE

To explore whether and which quantitative 3D measures of medial and/or lateral meniscus position and size are associated with subsequent medial femorotibial structural progression of knee osteoarthritis and to determine the correlation between central slice and total meniscus measures.

MATERIALS AND METHODS

Knees with radiographic osteoarthritis from Osteoarthritis Initiative participants with longitudinal medial MRI-based cartilage thickness and radiographic joint space width (JSW) loss over 12 months were selected. These 37 structural progressor knees (64.7 ± 8.0y, 30.2 ± 4.6 kg/m², 35% men) were matched 1:1 to 37 non-progressor knees (64.6 ± 9.8y, 30.2 ± 4.4 kg/m², 35% men) without cartilage thickness or JSW loss. Quantitative measures of meniscus position and size were computed from manual segmentations of coronal baseline MRIs. Cohen's D was used as measure of effect size.

RESULTS

Maximum extrusion distance of the total medial meniscus and mean extrusion in the central 5 and in the central slice were greater for progressor than non-progressor knees (Cohen's D 0.58-0.66). No significant differences were observed for medial tibial coverage or mean extrusion (entire meniscus). Among medial meniscus morphology measures, only mean height differed between progressor vs non-progressor knees (Cohen's D 0.40). Among lateral meniscus measures, height and volume were greater in progressor vs. non-progressor knees (Cohen's D 0.46-0.83). Mean extrusion measures were highly correlated between the entire meniscus and the central (r = 0.88) or the central 5 (r = 0.93) slices.

CONCLUSIONS

3D maximum and central medial meniscus extrusion may serve as predictors for subsequent structural progression. Central meniscus extrusion measures could substitute 3D extrusion measurement across the entire meniscus.

Association between meniscal volume and development of knee osteoarthritis

OBJECTIVE

To assess the association between meniscal volume, its change over time and the development of knee OA after 30 months in overweight/obese women.

METHODS

Data from the PRevention of knee Osteoarthritis in Overweight Females study were used. This cohort included 407 women with a BMI ≥ 27 kg/m2, free of OA-related symptoms. The primary outcome measure was incident OA after 30 months, defined by one out of the following criteria: medial or lateral joint space narrowing (JSN)  ≥ 1.0 mm, incident radiographic OA [Kellgren and Lawrence (K&L)  ≥ 2], or incident clinical OA. The secondary outcomes were either of these items separately. Menisci at both baseline and follow-up were automatically segmented to obtain meniscal volume and delta-volumes. Generalized estimating equations were used to evaluate associations between the volume measures and the outcomes.

RESULTS

Medial and lateral baseline and delta-volumes were not significantly associated to the primary outcome. Lateral meniscal baseline volume was significantly associated to lateral JSN [odds ratio (OR) = 0.87; 95% CI: 0.75, 0.99], while other measures were not. Medial and lateral baseline volume were positively associated to K&L incidence (OR = 1.32 and 1.22; 95% CI: 1.15, 1.50 and 1.03, 1.45, respectively), while medial and lateral delta-volume were negatively associated to K&L incidence (OR = 0.998 and 0.997; 95% CI: 0.997, 1.000 and 0.996, 0.999, respectively). None of the meniscal measures were significantly associated to incident clinical OA.

CONCLUSION

Larger baseline meniscal volume and the decrease of meniscal volume over time were associated to the development of structural OA after 30 months in overweight and obese women.

Ultrashort echo time Cones double echo steady state (UTE-Cones-DESS) for rapid morphological imaging of short T2 tissues

PURPOSE

In this study, we aimed to develop a new technique, ultrashort echo time Cones double echo steady state (UTE-Cones-DESS), for highly efficient morphological imaging of musculoskeletal tissues with short T₂ s. We also proposed a novel, single-point Dixon (spDixon)-based approach for fat suppression.

METHODS

The UTE-Cones-DESS sequence was implemented on a 3T MR system. It uses a short radiofrequency (RF) pulse followed by a pair of balanced spiral-out and spiral-in readout gradients separated by an unbalanced spoiling gradient in-between. The readout gradients are applied immediately before or after the RF pulses to achieve a UTE image (S₊ ) and a spin/stimulated echo image (S_- ). Weighted echo subtraction between S₊ and S_- was performed to achieve high contrast specific to short T₂ tissues, and spDixon was applied to suppress fat by using the intrinsic complex signal of S₊ and S_- . Six healthy volunteers and five patients with osteoarthritis were recruited for whole-knee imaging. Additionally, two healthy volunteers were recruited for lower leg imaging.

RESULTS

The UTE-Cones-DESS sequence allows fast volumetric imaging of musculoskeletal tissues with excellent image contrast for the osteochondral junction, tendons, menisci, and ligaments in the knee joint as well as cortical bone and aponeurosis in the lower leg within 5 min. spDixon yields efficient fat suppression in both S₊ and S_- images without requiring any additional acquisitions or preparation pulses.

CONCLUSION

The rapid UTE-Cones-DESS sequence can be used for high contrast morphological imaging of short T₂ tissues, providing a new tool to assess their association with musculoskeletal disorders.

Volumetric assessment of extrusion in medial meniscus posterior root tears through semi-automatic segmentation on 3-tesla magnetic resonance images

BACKGROUND

Many reports have described the relationship between medial meniscus posterior root tears (MMPRTs) and meniscal extrusion on coronal magnetic resonance (MR) images. However, volumetric assessment of meniscal extrusion has not been performed, and the correlation between extrusion length and volume remains unclear.

HYPOTHESIS

Extrusion in both length and volume would be greater in MMPRTs than that in the normal medial meniscus, and the extrusion length measured on coronal MR images would be correlated with the extrusion volume.

PATIENTS AND METHODS

A total of 20 knees who underwent isolated MMPRTs without trauma history were included in the MMPRT group, and another 20 knees with normal medial meniscus were selected as the control group. All 40 knees underwent 3-tesla MR imaging. The extrusion length of the medial meniscus was measured using coronal MR images only. Volumetric assessments of the meniscus were performed and analyzed via a semi-automatic segmentation. Group-wise comparisons of the extrusion length and volumetric values were conducted, and the correlation between the two measures in both groups was evaluated.

RESULTS

The mean extrusion length of the medial meniscus in the MMPRT group was significantly longer (2.60 vs. 0.63mm; p<0.001) than that in the control group. The mean extrusion volume was also significantly higher in the MMPRT than that in the control group (770.93 vs. 193.80 mm³; p<0.001). The extrusion length was significantly and positively correlated with the extrusion volume in both groups (R=0.64; p=0.002 in MMPRT, R=0.73; p<0.001 in the control group).

DISCUSSION

Semi-automatic segmentation was used to measure the volume of meniscal extrusion, which had previously only been estimated indirectly with the extrusion length on coronal MR images. MMPRTs significantly increased the extrusion in both measures. The extrusion length measured on coronal MR images was positively correlated with the extrusion volume in both groups.

LEVEL OF EVIDENCE

III, Case-control study.

Quantifying dog meniscal volume at 1.5T and 3.0T MRI

The dog has been used extensively as an experimental model to study meniscal treatments such as meniscectomy, meniscal repair and regeneration. Accurate quantification of meniscal size and morphology are a crucial step for developing models of the meniscus. 3.0T magnetic resonance imaging (MRI) has been found to be highly accurate in analyzing the meniscus in both clinical and research fields. However, 3.0T MRI systems are still uncommonly used in veterinary medicine. The goal of the study was to compare meniscal volume measurements from 1.5T MRI system with 3.0T MRI system using proton density sequence, a clinically relevant protocol. The MR images were segmented to reconstruct 3D surface representations of both medial and lateral menisci to compare the meniscal volumes measurements. Average volume differences were 8.8% (P=0.42) and 8.9% (P=0.535) for medial and lateral meniscus, respectively. No significant volume differences were found between 1.5T and 3.0T magnetic resonance (MR) measurements, with high Pearson's correlation coefficient of r > 0.8 and the intraclass correlation coefficient (ICC) of 0.899. For inter- and intra-observer reproducibility, high correlation (ICC = 0.942 and 0.814) was observed, but with high variability for intra-observer reproducibility (lower bound 0.478, upper bound 0.949). We have shown that common clinical MR scanners and pulse sequences can be used to quantify dogs' meniscal volumes with good reproducibility. We believe that repeatable measurements of meniscal volumes using MR may provide a useful capability for assessment of postoperative results following meniscal treatments such as meniscectomy and meniscal regeneration.

Where does meniscal damage progress most rapidly? An analysis using three-dimensional shape models on data from the Osteoarthritis Initiative

OBJECTIVES

Meniscal pathology is integral to knee osteoarthritis (OA) and its progression; it provides a progression biomarker and a potential treatment target. Magnetic resonance imaging (MRI) demonstrates large heterogeneity in meniscal damage; this structural complexity means measurement is difficult. The aim of this study was to apply novel 3D image analysis to determine which meniscal pathologies demonstrated most change during OA progression.

METHODS

Knee images were selected from the progression cohort of the Osteoarthritis Initiative choosing participants with risk factors for medial OA progression. Medial and lateral menisci were manually segmented then analysed using a statistical shape model of the tibia as a reference surface. Responsiveness was assessed at 1 year using standardised response means (SRMs) for four constructs: meniscal volume, extrusion volume, thickness and tibial coverage; anatomical sub-regions of these constructs were also explored.

RESULTS

Paired images from 86 participants (median age 61.5, 49% female, 56% obese) were included. Reliability of the novel meniscal measurements was very good intraclass correlation coefficients (ICCs all > 0.98). Meniscal volume and extrusion demonstrated no significant change. Moderate responsiveness was observed for medial meniscus thickness (SRM -0.35) and medial tibial coverage (SRM -0.36). No substantial change was seen for the lateral meniscus measures. Sub-region analysis did not improve responsiveness; while greater change was seen in the posterior medial compartment, it was associated with increased variance of the change.

CONCLUSIONS

The location of meniscal damage was consistently in the posterior medial region, and two measurements (thickness and tibial coverage) were most responsive. Meniscal measures should add to discriminatory power in OA progression assessment.

Sensitivity to change and association of three-dimensional meniscal measures with radiographic joint space width loss in rapid clinical progression of knee osteoarthritis

Objective

To determine whether 3D meniscal measures had similar sensitivity to longitudinal change as cartilage thickness; to what extent these measures are associated with longitudinal joint space width (JSW) change; and whether the latter associations differ between minimum (mJSW) and fixed-location JSW.

Methods

Two-year changes in medial meniscal position and morphology, cartilage thickness (MRI) and minimum and fixed-location JSW (radiography) were determined in 35 Osteoarthritis Initiative knees [12 men, age: 67 (51-77) years; 23 women, age: 65 (54-78) years], progressing from baseline Kellgren-Lawrence grade ≤2 to knee replacement within 3-5 years. Multiple linear regression assessed the features contributing to JSW change.

Results

Meniscal measures, cartilage thickness and JSW displayed similar sensitivity to change (standardised response mean≤|0.76|). Meniscal changes were strongly associated with JSW change (r≤|0.66|), adding ≤20% to its variance in addition to cartilage thickness change. Fixed-location JSW change (multiple r²=72%) was more strongly related to cartilage and meniscal change than mJSW (61%). Meniscal morphology explained more of fixed-location JSW and meniscal position more of mJSW.

Conclusion

Meniscal measures provide independent information in explaining the variance of radiographic JSW change. Fixed-location JSW appears to be more reflective of structural change than mJSW and, hence, a potentially superior measure of structural progression.

Key Points

• 3D positional/morphological meniscal measures change in rapidly progressing knees.

• Similar sensitivity to 2-year change of quantitative meniscal/cartilage measures in rapid progression.

• Changes in meniscal measures are strongly associated with radiographic JSW change.

• Meniscal change provides information to explain JSW variance independent of cartilage.

• Fixed-location JSW reflects structural disease stage more closely than minimum JSW.

Automated T2-mapping of the Menisci From Magnetic Resonance Images in Patients with Acute Knee Injury

RATIONALE AND OBJECTIVES

This study aimed to evaluate the accuracy of an automated method for segmentation and T2 mapping of the medial meniscus (MM) and lateral meniscus (LM) in clinical magnetic resonance images from patients with acute knee injury.

MATERIALS AND METHODS

Eighty patients scheduled for surgery of an anterior cruciate ligament or meniscal injury underwent magnetic resonance imaging of the knee (multiplanar two-dimensional [2D] turbo spin echo [TSE] or three-dimensional [3D]-TSE examinations, T2 mapping). Each meniscus was automatically segmented from the 2D-TSE (composite volume) or 3D-TSE images, auto-partitioned into anterior, mid, and posterior regions, and co-registered onto the T2 maps. The Dice similarity index (spatial overlap) was calculated between automated and manual segmentations of 2D-TSE (15 patients), 3D-TSE (16 patients), and corresponding T2 maps (31 patients). Pearson and intraclass correlation coefficients (ICC) were calculated between automated and manual T2 values. T2 values were compared (Wilcoxon rank sum tests) between torn and non-torn menisci for the subset of patients with both manual and automated segmentations to compare statistical outcomes of both methods.

RESULTS

The Dice similarity index values for the 2D-TSE, 3D-TSE, and T2 map volumes, respectively, were 76.4%, 84.3%, and 75.2% for the MM and 76.4%, 85.1%, and 76.1% for the LM. There were strong correlations between automated and manual T2 values (r_MM = 0.95, ICC_MM = 0.94; r_LM = 0.97, ICC_LM = 0.97). For both the manual and the automated methods, T2 values were significantly higher in torn than in non-torn MM for the full meniscus and its subregions (P < .05). Non-torn LM had higher T2 values than non-torn MM (P < .05).

CONCLUSIONS

The present automated method offers a promising alternative to manual T2 mapping analyses of the menisci and a considerable advance for integration into clinical workflows.

Relationship Between Medial Meniscal Extrusion and Cartilage Loss in Specific Femorotibial Subregions: Data From the Osteoarthritis Initiative

OBJECTIVE

Medial meniscal extrusion is known to be related to structural progression of knee osteoarthritis. However, it is unclear whether medial meniscal extrusion is more strongly associated with cartilage loss in certain medial femorotibial subregions than in others.

METHODS

Segmentation of the medial tibial and femoral cartilage (baseline; 1-year followup) and the medial meniscus (baseline) was performed in 60 participants with frequent knee pain (mean ± SD ages 61.3 ± 9.2 years, body mass index 31.3 ± 3.9 kg/m(2) ) and with unilateral medial radiographic joint space narrowing (JSN) grades 1-3, using double-echo steady-state magnetic resonance images. Medial meniscal extrusion distance and extrusion area (percentage) between the external meniscal and tibial margin at baseline, and longitudinal medial cartilage loss in 8 anatomic subregions were determined.

RESULTS

A significant association (Pearson's correlation coefficient) was seen between medial meniscal extrusion area in JSN knees and cartilage loss over 1 year throughout the entire medial femorotibial compartment. The strongest correlation was with cartilage loss in the external medial tibia (r =-0.34, P < 0.01 in JSN; r =-0.30, P = 0.02 in knees without JSN).

CONCLUSION

Medial meniscal extrusion was associated with subsequent medial cartilage loss. The external medial tibial cartilage may be particularly vulnerable to thinning once the meniscus extrudes and its surface is exposed to direct, nonphysiological, cartilage-to-cartilage contact.

Quantitative measures of meniscus extrusion predict incident radiographic knee osteoarthritis--data from the Osteoarthritis Initiative

OBJECTIVE

To test the hypothesis that quantitative measures of meniscus extrusion predict incident radiographic knee osteoarthritis (KOA), prior to the advent of radiographic disease.

METHODS

206 knees with incident radiographic KOA (Kellgren Lawrence Grade (KLG) 0 or 1 at baseline, developing KLG 2 or greater with a definite osteophyte and joint space narrowing (JSN) grade ≥1 by year 4) were matched to 232 control knees not developing incident KOA. Manual segmentation of the central five slices of the medial and lateral meniscus was performed on coronal 3T DESS MRI and quantitative meniscus position was determined. Cases and controls were compared using conditional logistic regression adjusting for age, sex, BMI, race and clinical site. Sensitivity analyses of early (year [Y] 1/2) and late (Y3/4) incidence was performed.

RESULTS

Mean medial extrusion distance was significantly greater for incident compared to non-incident knees (1.56 mean ± 1.12 mm SD vs 1.29 ± 0.99 mm; +21%, P < 0.01), so was the percent extrusion area of the medial meniscus (25.8 ± 15.8% vs 22.0 ± 13.5%; +17%, P < 0.05). This finding was consistent for knees restricted to medial incidence. No significant differences were observed for the lateral meniscus in incident medial KOA, or for the tibial plateau coverage between incident and non-incident knees. Restricting the analysis to medial incident KOA at Y1/2 differences were attenuated, but reached significance for extrusion distance, whereas no significant differences were observed at incident KOA in Y3/4.

CONCLUSION

Greater medial meniscus extrusion predicts incident radiographic KOA. Early onset KOA showed greater differences for meniscus position between incident and non-incident knees than late onset KOA.

Intra- and inter-observer reliability of quantitative analysis of the infra-patellar fat pad and comparison between fat- and non-fat-suppressed imaging--Data from the osteoarthritis initiative

The infra-patellar fat pad (IPFP), as intra-articular adipose tissue represents a potential source of pro-inflammatory cytokines and its size has been suggested to be associated with osteoarthritis (OA) of the knee. This study examines inter- and intra-observer reliability of fat-suppressed (fs) and non-fat-suppressed (nfs) MR imaging for determination of IPFP morphological measurements as novel biomarkers. The IPFP of nine right knees of healthy Osteoarthritis Initiative participants was segmented by five readers, using fs and nfs baseline sagittal MRIs. The intra-observer reliability was determined from baseline and 1-year follow-up images. All segmentations were quality controlled (QC) by an expert reader. Reliability was expressed as root mean square coefficient of variation (RMS CV%). After QC, the inter-observer reliability for fs (nfs) imaging was 2.0% (1.1%) for IPFP volume, 2.1%/2.5% (1.6%/1.8%) for anterior/posterior surface areas, 1.8% (1.8%) for depth, and 2.1% (2.4%) for maximum sagittal area. The intra-observer reliability was 3.1% (5.0%) for volume, 2.3%/2.8% (2.5%/2.9%) for anterior/posterior surfaces, 1.9% (3.5%) for depth, and 3.3% (4.5%) for maximum sagittal area. IPFP volume from nfs images was systematically greater (+7.3%) than from fs images, but highly correlated (r=0.98). The results suggest that quantitative measurements of IPFP morphology can be performed with satisfactory reliability when expert QC is implemented. The IPFP is more clearly depicted in nfs images, and there is a small systematic off-set versus analysis from fs images. However, the high linear relationship between fs and nfs imaging suggests that fs images can be used to analyze IPFP morphology, when nfs images are not available.

Longitudinal change in quantitative meniscus measurements in knee osteoarthritis--data from the Osteoarthritis Initiative

OBJECTIVE

We aimed to apply 3D MRI-based measurement technology to studying 2-year change in quantitative measurements of meniscus size and position.

METHODS

Forty-seven knees from the Osteoarthritis Initiative with medial radiographic joint space narrowing had baseline and 2-year follow-up MRIs. Quantitative measures were obtained from manual segmentation of the menisci and tibia using coronal DESSwe images. The standardized response mean (SRM = mean/SD change) was used as measure of sensitivity to longitudinal change.

RESULTS

Medial tibial plateau coverage decreased from 34.8% to 29.9% (SRM -0.82; p < 0.001). Change in medial meniscus extrusion in a central image (SRM 0.18) and in the central five slices (SRM 0.22) did not reach significance, but change in extrusion across the entire meniscus (SRM 0.32; p = 0.03) and in the relative area of meniscus extrusion (SRM 0.56; p < 0.001) did. There was a reduction in medial meniscus volume (10%; p < 0.001), width (7%; p < 0.001), and height (2%; p = 0.08); meniscus substance loss was strongest in the posterior (SRM -0.51; p = 0.001) and weakest in the anterior horn (SRM -0.15; p = 0.31).

CONCLUSION

This pilot study reports, for the first time, longitudinal change in quantitative 3D meniscus measurements in knee osteoarthritis. It provides evidence of improved sensitivity to change of 3D measurements compared with single slice analysis.

KEY POINTS

• First longitudinal MRI-based measurements of change of meniscus position and size. • Quantitative longitudinal evaluation of meniscus change in knee osteoarthritis. • Improved sensitivity to change of 3D measurements compared with single slice analysis.

Automated segmentation and analysis of normal and osteoarthritic knee menisci from magnetic resonance images--data from the Osteoarthritis Initiative

OBJECTIVE

To validate an automatic scheme for the segmentation and quantitative analysis of the medial meniscus (MM) and lateral meniscus (LM) in magnetic resonance (MR) images of the knee.

METHOD

We analysed sagittal water-excited double-echo steady-state MR images of the knee from a subset of the Osteoarthritis Initiative (OAI) cohort. The MM and LM were automatically segmented in the MR images based on a deformable model approach. Quantitative parameters including volume, subluxation and tibial-coverage were automatically calculated for comparison (Wilcoxon tests) between knees with variable radiographic osteoarthritis (rOA), medial and lateral joint space narrowing (mJSN, lJSN) and pain. Automatic segmentations and estimated parameters were evaluated for accuracy using manual delineations of the menisci in 88 pathological knee MR examinations at baseline and 12 months time-points.

RESULTS

The median (95% confidence-interval (CI)) Dice similarity index (DSI) (2 ∗|Auto ∩ Manual|/(|Auto|+|Manual|)∗ 100) between manual and automated segmentations for the MM and LM volumes were 78.3% (75.0-78.7), 83.9% (82.1-83.9) at baseline and 75.3% (72.8-76.9), 83.0% (81.6-83.5) at 12 months. Pearson coefficients between automatic and manual segmentation parameters ranged from r = 0.70 to r = 0.92. MM in rOA/mJSN knees had significantly greater subluxation and smaller tibial-coverage than no-rOA/no-mJSN knees. LM in rOA knees had significantly greater volumes and tibial-coverage than no-rOA knees.

CONCLUSION

Our automated method successfully segmented the menisci in normal and osteoarthritic knee MR images and detected meaningful morphological differences with respect to rOA and joint space narrowing (JSN). Our approach will facilitate analyses of the menisci in prospective MR cohorts such as the OAI for investigations into pathophysiological changes occurring in early osteoarthritis (OA) development.

Imaging research results from the osteoarthritis initiative (OAI): a review and lessons learned 10 years after start of enrolment

The Osteoarthritis Initiative (OAI) is a multicentre, prospective, observational, cohort study of knee osteoarthritis (OA) that began recruitment in 2004. The OAI provides public access to clinical and image data, enabling researchers to examine risk factors/predictors and the natural history of knee OA incidence and progression, and the qualification of imaging and other biomarkers. In this narrative review, we report imaging findings and lessons learned 10 years after enrolment has started. A literature search for full text articles published from the OAI was performed up to 31 December 2013 using Pubmed and the OAI web page. We summarise the rationale, design and imaging protocol of the OAI, and the history of OAI publications. We review studies from early partial, and later full OAI public data releases. The latter are structured by imaging method and tissue, reviewing radiography and then MRI findings on cartilage morphology, cartilage lesions and composition (T2), bone, meniscus, muscle and adipose tissue. Finally, analyses directly comparing findings from MRI and radiography are summarised. Ten years after the first participants were enrolled and first papers published, the OAI has become an invaluable resource to the OA research community. It has fuelled novel methodological approaches of analysing images, and has provided a wealth of information on OA pathophysiology. Continued collection and public release of long-term observations will help imaging measures to gain scientific and regulatory acceptance as 'prognostic' or 'efficacy of intervention' biomarkers, potentially enabling shorter and more efficient clinical trials that can test structure-modifying therapeutic interventions (NCT00080171).

Medial meniscal displacement and strain in three dimensions under compressive loads: MR assessment

PURPOSE

To investigate the 3D displacement and the local strain of the medial meniscus and its attachments under compressive loading.

MATERIALS AND METHODS

Magnetic resonance imaging (MRI) scans of six porcine knee joints were performed under unloaded and loaded conditions (100% and 200% body weight [BW]). Volumes were registered to obtain a 3D displacement field of the medial meniscus and its attachments, which were divided into five anatomic compartments. Finally, displacements of the center of mass of each compartment and the local strain were analyzed.

RESULTS

The meniscus and its attachments significantly displaced by up to 2.6 ± 1.2 mm (P < 0.01) under knee joint loads of 200% BW. An increase of 0.9 mm in the distance between posterior and anterior horn (P < 0.001) was observed. The meniscus and its attachment showed an average radial stretch of 0.6%, an average circumferential stretch of 0.9%, and an average axial compression of 11.6% at 200% BW.

CONCLUSION

High-resolution MRI was successfully combined with image registration to investigate the displacement and strain of the meniscus and its attachments under compression. The results of this study contribute to the basic understanding of meniscal movement which may impact the design of meniscal implants and the validation of finite element models in the future.

Contribution of regional 3D meniscus and cartilage morphometry by MRI to joint space width in fixed flexion knee radiography--a between-knee comparison in subjects with unilateral joint space narrowing

BACKGROUND

Radiographic joint space width (JSW) is considered the reference standard for demonstrating structural therapeutic benefits in knee osteoarthritis. Our objective was to determine the proportion by which 3D (regional) meniscus and cartilage measures explain between-knee differences of JSW in the fixed flexion radiographs.

METHODS

Segmentation of the medial meniscus and tibial and femoral cartilage was performed in double echo steady state (DESS) images. Quantitative measures of meniscus size and position, femorotibial cartilage thickness, and radiographic JSW (minimum, and fixed locations) were compared between both knees of 60 participants of the Osteoarthritis Initiative, with strictly unilateral medial joint space narrowing (JSN). Statistical analyses (between-knee, within-person comparison) were performed using regression analysis.

RESULTS

A strong relationship with side-differences in minimum and a central fixed location JSW was observed for percent tibial plateau coverage by the meniscus (r = .59 and .47; p<.01) and central femoral cartilage thickness (r = .69 and .75; p<.01); other meniscus and cartilage measures displayed lower coefficients. The correlation of central femoral cartilage thickness with JSW (but not that of meniscus measures) was greater (r = .78 and .85; p<.01) when excluding knees with non-optimal alignment between the tibia and X-ray beam.

CONCLUSION

3D measures of meniscus and cartilage provide significant, independent information in explaining side-differences in radiographic JSW in fixed flexion radiographs. Tibial coverage by the meniscus and central femoral cartilage explained two thirds of the variability in minimum and fixed location JSW. JSW provides a better representation of (central) femorotibial cartilage thickness, when optimal positioning of the fixed flexion radiographs is achieved.

Meniscus body position, size, and shape in persons with and persons without radiographic knee osteoarthritis: quantitative analyses of knee magnetic resonance images from the osteoarthritis initiative

OBJECTIVE

To quantitatively evaluate the position, size, and shape of the menisci in subjects with radiographic knee osteoarthritis (OA) compared to subjects without OA, using magnetic resonance imaging (MRI).

METHODS

We studied the right knees of 39 Osteoarthritis Initiative participants (24 women and 15 men with a mean age of 59.6 ± 8.7 years) with medial compartment radiographic tibiofemoral OA (Kellgren/Lawrence grade of 2 or 3). Subjects were matched individually for age, sex, and height to controls without knee OA and without risk factors for knee OA. The right knees of the controls were used as references. One observer performed manual segmentation of the tibial plateau and the medial and lateral meniscus based on a coronally reconstructed double-echo steady-state sequence with water excitation, focusing on 5 central 3T MRIs.

RESULTS

In OA knees, there was less meniscal coverage of the medial tibial plateau (435 mm(2) versus 515 mm(2) ; P = 0.0004), the medial meniscus body showed more extrusion (2.64 mm versus 0.53 mm; P < 0.0001), and the peripheral margin had a more convex shape, i.e., bulged more (mean 0.61 mm versus 0.27 mm; P < 0.0001). The thickness or volume of the medial meniscus body of OA knees did not differ substantially from reference knees. In contrast, in OA knees the lateral meniscus body had a larger volume (mean 266 mm(3) versus 224 mm(3) ; P = 0.0005) and extruded more (mean 1.16 mm versus -1.01 mm; P < 0.0001), and the external margin bulged more (mean 0.53 mm versus 0.35 mm; P < 0.0001), than in reference knees.

CONCLUSION

Our findings indicate altered meniscal position and shape (i.e., more bulging) in both compartments in medial compartment knee OA. These changes may be important features of OA pathogenesis and/or disease consequences.

Tibial coverage, meniscus position, size and damage in knees discordant for joint space narrowing - data from the Osteoarthritis Initiative

INTRODUCTION

Meniscal extrusion is thought to be associated with less meniscus coverage of the tibial surface, but the association of radiographic disease stage with quantitative measures of tibial plateau coverage is unknown. We therefore compared quantitative and semi-quantitative measures of meniscus position and morphology in individuals with bilateral painful knees discordant on medial joint space narrowing (mJSN).

METHODS

A sample of 60 participants from the first half (2,678 cases) of the Osteoarthritis Initiative cohort fulfilled the inclusion criteria: bilateral frequent pain, Osteoarthritis Research Society International (OARSI) mJSN grades 1-3 in one, no-JSN in the contra-lateral (CL), and no lateral JSN in either knee (43 unilateral mJSN1; 17 mJSN2/3; 22 men, 38 women, body mass index (BMI) 31.3 ± 3.9 kg/m(2)). Segmentation and three-dimensional quantitative analysis of the tibial plateau and meniscus, and semi-quantitative evaluation of meniscus damage (magnetic resonance imaging (MRI) osteoarthritis knee score = MOAKS) was performed using coronal 3T MR images (MPR DESSwe and intermediate-weighted turbo spin echo (IW-TSE) images). CL knees were compared using paired t-tests (between-knee, within-person design).

RESULTS

Medial tibial plateau coverage was 36 ± 9% in mJSN1 vs 45 ± 8% in CL no-JSN knees, and was 31 ± 9% in mJSN2/3 vs 46 ± 6% in no-JSN knees (both P < 0.001). mJSN knees showed greater meniscus extrusion and damage (MOAKS), but no significant difference in meniscus volume. No significant differences in lateral tibial coverage, lateral meniscus morphology or position were observed.

CONCLUSIONS

Knees with medial JSN showed substantially less medial tibial plateau coverage by the meniscus. We suggest that the less meniscal coverage, i.e., less mechanical protection may be a reason for greater rates of cartilage loss observed in JSN knees.

Osteoarthritis: a review of strengths and weaknesses of different imaging options

Slowing of radiographic joint space narrowing represents the only recommended imaging-based outcome measure to assess structural disease progression in osteoarthritis (OA) clinical trials. There are no effective disease-modifying OA drugs. The ability of magnetic resonance (MR) to image structures within the knee and to visualize cartilage morphology and composition gives MR imaging a critical role in understanding the natural history of the disease and in the search for therapies. In this article, the roles and limitations of conventional radiography and MR imaging, focusing on knee OA, and the use of other modalities in clinical practice and OA research are described.

Revision 1 size and position of the healthy meniscus, and its correlation with sex, height, weight, and bone area- a cross-sectional study

Background

Meniscus extrusion or hypertrophy may occur in knee osteoarthritis (OA). However, currently no data are available on the position and size of the meniscus in asymptomatic men and women with normal meniscus integrity.

Methods

Three-dimensional coronal DESSwe MRIs were used to segment and quantitatively measure the size and position of the medial and lateral menisci, and their correlation with sex, height, weight, and tibial plateau area. 102 knees (40 male and 62 female) were drawn from the Osteoarthritis Initiative "non-exposed" reference cohort, including subjects without symptoms, radiographic signs, or risk factors for knee OA. Knees with MRI signs of meniscus lesions were excluded.

Results

The tibial plateau area was significantly larger (p < 0.001) in male knees than in female ones (+23% medially; +28% laterally), as was total meniscus surface area (p < 0.001, +20% medially; +26% laterally). Ipsi-compartimental tibial plateau area was more strongly correlated with total meniscus surface area in men (r = .72 medially; r = .62 laterally) and women (r = .67; r = .75) than contra-compartimental or total tibial plateau area, body height or weight. The ratio of meniscus versus tibial plateau area was similar between men and women (p = 0.22 medially; p = 0.72 laterally). Tibial coverage by the meniscus was similar between men and women (50% medially; 58% laterally), but "physiological" medial meniscal extrusion was greater in women (1.83 ± 1.06mm) than in men (1.24mm ± 1.18mm; p = 0.011).

Conclusions

These data suggest that meniscus surface area strongly scales with (ipsilateral) tibial plateau area across both sexes, and that tibial coverage by the meniscus is similar between men and women.