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

Conventional radiography is still the first and most important imaging examination in a clinical setting when evaluating a patient with a known or suspected diagnosis of osteoarthritis (OA). In research and clinical trials, it still is a valuable tool for stratifying patients who have OA into different categories for inclusion criteria and eligibility. MRI has become crucial in understanding the natural history of the disease and in guiding future therapies because of its ability to image the knee as a whole organ and to assess cartilage morphology and composition directly and in a three-dimensional manner. The other modalities discussed in this article are valuable additional techniques indicated on a case-by-case basis.

Objective: To validate quantitative magnetic resonance imaging (qMRI) for the assessment of cartilage volume and thickness in thin and curved cartilage layers, such as the shoulder.Methods: Eight shoulder specimens from healthy individuals (aged 31–69 years) were investigated using a 3D gradient echo sequence with selective water excitation. After segmentation with a B-spline Snake algorithm, the cartilage volume and thickness were determined three dimensionally. The cartilage volume data were compared with water displacement of surgically removed tissue, and the thickness with A-mode ultrasound.Results: The glenoid and humeral head cartilage volume from qMRI agreed highly with that from water displacement (systematic difference, ±1 to ±3%; absolute difference, 4 to 7%). For the cartilage thickness, the mean systematic difference ranged from −17% (mean cartilage thickness of the glenoid) to +7% (maximal cartilage thickness of the glenoid); the standard error of the estimate was 3.7% for the humeral head, and 6.4% for the glenoid.Conclusions: The applied technique can be used for accurate determination of cartilage volume and thickness in human joints with highly curved and thin cartilage layers, such as the shoulder. In vivo application of this method will depend on the development of efficient surface coils that allow high resolution imaging under in situ conditions.

Die Magnetresonanztomographie (MRT) stellt für Diagnostik und Verlaufsbeurteilung der Osteoarthrose (OA) ein geeignetes Verfahren dar. Zusammen mit dreidimensionalen Bildverarbeitungsmethoden eignet sie sich für eine genaue Quantifizierung struktureller Veränderungen des Gelenkknorpels. Bei fortgeschrittener OA muss der geschädigte Knorpel nicht immer zusammenhängend sein. Eine quantitative Beschreibung auch einzelner Knorpelfragmente erscheint in diesem Zusammenhang sinnvoll. Unser System erlaubt — neben der Segmentierung —eine automatische Rekonstruktion, Analyse und Darstellung auch stark fragmentierter Gelenkknorpel.

The purpose of this study was to develop an MR‐based technique for quantitative analysis of joint surface size, surface curvature, and joint incongruity and to assess its reproducibility under in vivo imaging conditions. The surface areas were determined after 3D reconstruction of the joint by triangulation and the incongruity by Gaussian curvature analysis. The precision was tested by analyzing four replicated MRI datasets of human knees in 14 individuals. The algorithms were shown to produce accurate data in geometric test objects. The interscan precision was <4% (CV%) for surface area, 2.9–5.7 m−1 (SD) for the mean principal curvature, and 4.1–7.4 m−1 for congruence indices. Incongruity was highest in the femoropatellar joint (79.7 m−1) and lowest in the medial femorotibial joint (28.6 m−1). This technique will permit identification of the specific role of surface size, curvature, and incongruity as potential risk factors for osteoarthritis. Magn Reson Med 47:554–561, 2002. © 2002 Wiley‐Liss, Inc.

Objective To test the hypotheses that absolute side differences in knee joint cartilage morphlogy are substantially smaller than intersubject variability, and that systematic side differences are determined by (force) dominance of the lower limbs.Methods Fifteen healthy volunteers with definite dominance of one lower limb were studied. Knees were imaged sagittally with a validated, high-resolution MR sequence. Transverse MR images of the thigh and calf were acquired with a spin echo sequence. Knee joint cartilage volume, thickness and joint surface areas, as well as muscle cross sectional areas were determined with in house post-processing software.ResultsAbsolute side differences amounted to 5.0±3.7% for the knee cartilage volume, 3.8±3.1% for cartilage thickness, and 3.4±1.7% for joint surface areas. The intersubject variability was 24.8%, 14.4%, and 14.1%, respectively. Volunteers with dominance of one of both lower limbs did not display significant side differences in cartilage morphology, but the side differences of the thigh musculature correlated positively with side differences of knee joint cartilage volume (r=+0.68; P< 0.01).Conclusions The results advocate the use of cartilage parameters from the contra-lateral limb for retrospectively estimating cartilage loss in patients with unilateral osteoarthritis (OA), and for determining local risk factors of OA in cross-sectional epidemiological studies, which are specific to pre-morbid cartilage morphology. Functional (force) dominance of one of both lower limbs does not explain side differences of articular cartilage morphology, but side differences are postively associated with side differences in muscle cross sectional areas. Copyright 2002 OsteoArthritis Research Society International. Published by Elsevier Science Ltd. All rights reserved.

Die Verbesserung der Diagnose, Therapie und Prognose der Osteoarthrose erfordert eine exakte In-vivo-Analyse morphometrischer und struktureller Knorpeleigenschaften. Neben morphologischen Eigenschaften, dem Knorpelvolumen, der Knorpeldicke und der Gelenkflächengröße stellt auch die Gelenkflächenkrümmung einen wichtigen Parameter dar. Es wurden zwei Techniken zur Berechnung globaler und lokaler Krümmungseigenschaften des Gelenkknorpels entwickelt. Bei der Gaußschen Krümmungsanalyse wird eine B-Spline Fläche durch die Stützpunkte der Knorpelfläche gelegt und deren Krümmung berechnet. Bei der Krümmungsbestimmung durch Oberflächenexpansion wird aus dem Maß der Flächenzunahme bei Expansion auf die Krümmung geschlossen. Beide Verfahren wurden auf Testkörper und die MRT Datensätze 28 gesunder Probanden angewendet. Erste Ergebnisse deuten darauf hin, dass es beim Patellaknorpel eine relativ konstante mittlere Krümmung gibt, die unabhängig von der Gelenkflächengröße ist.

Mit der Magnetresonanztomografie (MRT) steht ein nicht invasives, untersucherunabhängiges Verfahren der direkten, kontrastreichen Darstellung des Gelenkknorpels zu Verfügung. In Verbindung mit computergestützter, halbautomatischer 3D-Nachverarbeitung ermöglicht sie die quantitative Analyse der lokalen und globalen Knorpelmorphologie, insbesondere von Knorpeldicke und -volumen unabhängig von der primären Schichtführung. Damit wird die Basis für objektive, vergleichende Untersuchungen der quantifizierten Parameter geschaffen. Relevanz erhält dieses Verfahren besonders im Hinblick auf die Verlaufsbeobachtung der Osteoarthrose, die Evaluation verschiedener (sich durchaus erst seit kurzem entwickelnder) Therapieverfahren, aber auch im Hinblick auf die Gelenkmechanik in vivo.

The objective of this work was to develop and validate a computational method for the registration (matching) of 3D cartilage plates from MR image data sets. The technique tracks local cartilage thickness changes over time. A 3D elastic registration technique was applied that identifies corresponding points of the bone‐cartilage interface in MR data sets of 3D‐reconstructed cartilage plates. In a first rigid preregistration step, the surfaces are aligned, using the principal axes decomposition to correct for different joint positions and orientations in the MR scanner. In a second step, the surfaces are deformed elastically, based on geometric surface features, until they are sufficiently similar to identify corresponding surface points. The method was validated against artificially corrupted cartilage surfaces and MR data obtained from in vivo and in vitro compression experiments. The in vivo reproducibility was tested on patellar data sets of volunteers, with repositioning of the joint in between replicate acquisitions. Magn Reson Med 44:592–601, 2000. © 2000 Wiley‐Liss, Inc.

OBJECTIVETo employ a magnetic resonance (MR) imaging technique for quantitative assessment of thin cartilage layers, and to validate the cartilage volume and thickness measurements.METHODSWe investigated 10 normal elbow joints (age 20 to 69 years) with a 3D gradient echo sequence with selective water excitation (TR 18 ms; TE 9 ms; FA 25 degrees, resolution 1x0.25x0.25 mm2, imaging time 19 min). After interpolating the image data to a 0.125x0.125 mm2 in-plane resolution, the cartilage plates were segmented, reconstructed in 3D, and the cartilage volume and thickness determined with a 3D Euclidean distance transformation algorithm, independent of the original section plane. The cartilage volume and thickness values were compared with CT arthrography and A-mode ultrasound.RESULTSThe mean systematic difference between the elbow cartilage volume obtained from MR imaging and CT arthrography was -0.11% (-6.0 mm3) and the mean random difference 5.7% (314 mm3). Except for the fovea capitis radii, the deviations were not statistically significant (range -7.6 to +11.7%). In the humerus, the mean cartilage thickness (average = 1.35 mm) was overestimated relative to CT arthrography (+20.7%/+0.23 mm), and slightly underestimated relative to A-mode ultrasound (-6.0%/-0.05 mm). With few exceptions, there were no significant differences between MRI, CT arthrography and ultrasound in the other joint surfaces of the elbow (random deviations between 0.08 and 0.39 mm).CONCLUSIONSThe technique presented can be applied for determining the cartilage volume and 3D thickness in joints with thin cartilage layers with a reasonable degree of accuracy.

The aim of this study was to analyse the precision of three-dimensional joint surface and cartilage thickness measurements in the knee, using a fast, high-resolution water-excitation sequence and a semiautomated segmentation algorithm. The knee joint of 8 healthy volunteers, aged 22 to 29 years, were examined at a resolution of 1.5 mm x 0.31 mm x 0.31 mm, with four sagittal data sets being acquired after repositioning the joint. After semiautomated segmentation with a B-spline Snake algorithm and 3D reconstruction of the patellar, femoral and tibial cartilages, the joint surface areas (triangulation), cartilage volume, and mean and maximum thickness (Euclidean distance transformation) were analysed, independently of the orientation of the sections. The precision (CV%) for the surface areas was 2.1 to 6.6%. The mean cartilage thickness and cartilage volume showed coefficients of 1.9 to 3.5% (except for the femoral condyles), the value for the medial femoral condyle being 9.1%, and for the lateral condyle 6.5%. For maximum thickness, coefficients of between 2.6 and 5.9% were found. In the present study we investigate for the first time the precision of MRI-based joint surface area measurements in the knee, and of cartilage thickness analyses in the femur. Using a selective water-excitation sequence, the acquisition time can be reduced by more than 50%. The poorer precision in the femoral condyles can be attributed to partial Volume effects that occur at the edges of the joint surfaces with a sagittal image protocol. Since MRI is non-invasive, it is highly suitable for examination of healthy subjects (generation of individual finite element models, analysis of functional adaptation to mechanical stimulation, measurement of cartilage deformation in vivo) and as a diagnostic tool for follow-up, indication for therapy, and objective evaluation of new therapeutic agents in osteoarthritis.

Data on articular cartilage thickness in the living are important for the design for computer models, aimed at preoperatively assessing the effect of surgical procedures on joint contact and load transmission, and for the calculation of cartilage material properties from its deformational behavior as determined during arthroscopy. A non-invasive method for measuring cartilage thickness in living subjects is, however, not available. A technique based on magnetic resonance imaging has therefore been tested for assessing articular cartilage thickness throughout joint surfaces. The accuracy is determined by comparing cartilage thickness maps obtained from three patellar specimens with a fat-suppressed three-dimensional gradient-echo sequence (resolution 2 x 0.31 x 0.31 mm) to those obtained with CT arthrography, A-mode ultrasound and anatomical sections. The distribution patterns are quantitatively compared using image analysis. The highest agreement was obtained for MRI and the sections (50% identical pixels), but all techniques yielded very similar results. On average, MR slightly underestimated the cartilage thickness compared with CT and the sections, and overestimated it compared with ultrasound. No evidence of differences in the degree of similarity could be detected in areas of thin and thick cartilage. We conclude that, if the resolution and accuracy of the method presented are considered acceptable, MRI is available for repeatable determination of topographical maps of articular cartilage thickness in living subjects. These data can be used to determine joint contact and stress in computer models and to calculate cartilage material properties in vivo.

The purpose of this study was to develop an MR-based tech- nique for quantitative analysis of joint surface size, surface curvature, and joint incongruity and to assess its reproducibility under in vivo imaging conditions. The surface areas were de- termined after 3D reconstruction of the joint by triangulation and the incongruity by Gaussian curvature analysis. The preci- sion was tested by analyzing four replicated MRI datasets of human knees in 14 individuals. The algorithms were shown to produce accurate data in geometric test objects. The interscan precision was <4% (CV%) for surface area, 2.9 -5.7 m -1 (SD) for the mean principal curvature, and 4.1-7.4 m -1 for congruence indices. Incongruity was highest in the femoropatellar joint (79.7 m -1 ) and lowest in the medial femorotibial joint (28.6 m -1 ). This technique will permit identification of the specific role of surface size, curvature, and incongruity as potential risk factors for osteoarthritis. Magn Reson Med 47:554 -561, 2002. Osteoarthritis (OA) affects more than half of the popula- tion above the age of 65 (1,2), with substantial effects on the quality of life of elderly individuals (3). The direct and indirect costs involved have been estimated to currently amount to 1% of the gross national product of the United States (4). However, it remains unknown why some indi- viduals develop OA early in life, whereas others maintain normal cartilage morphology and function up to advanced age (5). Animal models (e.g., 6,7) and epidemiological studies (e.g., 8,9) have established that mechanical factors play an important role in the initiation and progression of OA. Clinical experience suggests that high degrees of joint in- congruity leads to high peak stress, and thus to early cartilage degeneration (10 -14). Theoretical computations have demonstrated that joint incongruity does not only involve higher peak stresses at the articular surface (due to smaller contact areas), but also negatively affects the mechanism of hydrostatic pressurization of the interstitial cartilage fluid (15). A lack of hydrostatic pressurization increases the shear stress encountered by the proteogly- can- collagen network at the site of articular contact and has been suggested to promote matrix failure (15). Yet there exists no method for noninvasive assessment of the size of the joint surfaces and joint incongruity in vivo, as a surrogate of the peak pressure encountered by articular cartilage. Effective postprocessing tools have recently been devel- oped for determining cartilage volume and thickness from high-resolution fat-suppressed gradient-echo MRI (16 -20). In the present work we will 1) implement a technique for quantitative determination of the size, curvature, and incongruity of articular surfaces from MRIs; 2) determine the interscan precision (reproducibility) of these parame- ters in the human knee under in vivo imaging conditions (four replicated acquisitions); and 3) assess differences in these parameters between different compartments of the human knee as well as between different individuals. Analysis of joint surface size, curvature, and incongruity should be particularly useful in epidemiological studies on OA. By measuring the surface size and incongruity in individuals before the onset of cartilage degeneration (e.g., in the contralateral knee of patients with unilateral joint disease), these studies will make it possible to determine whether individuals with small joint surfaces (in relation to body weight and height) and with high degrees of joint incongruity have a higher risk/susceptibility of OA. A noninvasive in vivo method is therefore required for reli- ably measuring these parameters in cross-sectional and longitudinal population-based studies.