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Objectiur: To analyze menisco-tibia1 and femoro-tibia1 translation patterns in healthy and ACL-deficient knees in different knee flexion angles under muscle activity.Methods: The ACL-deficient and contralateral healthy knees of 10 patients were examined with an open MR system at 30" and 90" of knee flexion, under isometric contraction of the extensors or flexor muscle groups. Translations between the tibia, the femoral condyles and the menisci were analyzed by three-dimensional image postprocessing.Results: Posterior translation of the femur and menisci relative to the tibia occurred during knee flexion (30-90") in all knees. In ACL-deficient knees, posterior translation of the medial femoral condyle (+I .3 * 3.8 mm) was significantly larger than in healthy knee (-0.9 k 2.9 mm; p < 0.05), while the translation pattern of the menisci was similar (med. meniscus 0.6 f 2.3 mm vs. 0.6 2 2.7 mm). Under isometric contraction of the extensors (relative to the flexor muscle group), an increased posterior position of the femur and menisci was observed at 30" knee flexion, but not at 90". This applied to ACL-deficient and healthy knees.Conclusions: This study shows a significant increase of translation of the medial femoral condyle in ACL-deficient knees, whereas menisco-tibia1 translation remains almost unchanged. This difference in translation patterns indicates that the posterior horn of the medial meniscus might encounter shear, potentially explaining the high rate of secondary medial meniscal tears in patients with ACL-deficiency.

We developed 3D MR based image processing methods for biomechanical analysis of joints. These methods provide quantitative data on the morphological distribution of the joint cartilage as well as biomechanical analysis of relative translation and rotation of joints. After image data acquisition in an open MR system, the segmentation of the different joint structures was performed by a semi automatic technique based on a gray value oriented region growing algorithm. After segmentation 3D reconstructions of cartilage and bone surfaces were performed. Principal axis decomposition is used to calculate a reproducible tibia plateau based coordinate system that allows the determination of relative rotation and translation of the condyles and menisci in relation to the tibia plateau. The analysis of the femoral movement is based on a reproducible, semi automatic calculated epicondylar axis. The analysis showed a posterior translation of the meniscus and even more of the femur condyles in healthy knees and in knees with an insufficiency of the anterior cruciate ligament (ACL).

Ziel dieser Studie war die Entwicklung einer MR-basierten 3-D-Technik zur Analyse der Meniskus-und Femurtranslation während der Knieflexion und unter dem Einfluß antagonistischerMuskelkräfte bei gesunden Probanden. Î n einem offenen MRT-System wurden fünf gesunde Kniegelenke in 30° und 90° Flexion mit einer Tl-gewichteten 3-D-Gradienten-Echosequenz untersucht. Es wurde eine Kraft von 30 N am distalen Unterschenkel mit extendierender und anschließend mit flektierender Zugrichtung angebracht. Nach dreidimensionaler Rekonstruktion erfolgte die Bestimmung der minimalen rä-umlichen Distanz zwischen dem Schwerpunkt des Tibiaplateaus und der Hinterkante der Menisken sowie der Femurkondylen., _ · * -' "V. Die Minimaldistanz war bei 30° sowohl für den Meniskus mit (23,2 ± l,8} mm versus (16,2 ± 3,3) mm als auch für den Kondylus mit (25,1 ± 1,5) mm versus (19,0 ± 3,0) mm medial größer als lateral. Unter Flexion auf 90° kam es zur posterioren Translation des Außenmeniskus (0,5 mm ± 0,2 mm) und des Innenmeniskus (3,4 mm ± 1,2 mm). Die Kondylen zeigten eine davon abweichende postenore Translation: lateral (2,2 ± 0,6) mm; medial (1,8 ± 1,9) mm. In keiner Stellung fand sich ein wesentlicher Unterschied zwischen extendierender und flektierender Muskelaktivitat. In dieser Studie wird eine neue In-vivo-3-D-Technik zur Untersuchung der femoralen und der meniskalen Translation in verschiedenen Knieflexionsstellungen und unter dem Einfluß von Muskelaktivität vorgestellt. Die Befunde weisen darauf hin, daß die Menisken ein anderes Translationsverhalten während der Flexion aufweisen als die Femurkondylen.-_ ~* Key words: Knee -translation -magnetic resonance imaging -muscle activity -meniscus . "-· *-. 'The aim of our study was to develop a 3-D MR-based technique for the analysis of meniscal and femoral translations during flexion of the knee, and under the influence of antagonistic muscle forces in healthy subjects. , ., \ In an open MR system, 5 knees were examined at 30° and 90° flexion using a Tl-weighted 3-D gradient echo sequence. A force of 30 Newtons, first in the extending and then in the flexing di-< rection, was applied to the distal lower leg. After three-dimensional reconstruction, the minimal, distances between the centre of the tibial plateau and the posterior edge of the menisci and fe-m oral condyles were determined. , .-Â t 30° flexion, the minimum distance for the meniscus was larger medially than laterally (23.2 ±" 1.8 mm vs. 16.2 ± 3.3 mm), and this also applied to the condyles (25.1 ± 1.5 vs. 19.0 ± 3.0 mm). Du-, nng flexion to 90°, a posterior translation of 0.5 ± 0.2 mm was observed for the lateral, and of 3.4' ±12 mm for the medial, meniscus. The condyles demonstrated a different posterior translation (lateral 2.2 ± 0.56 mm; medial 1.8 ± 1.9 mm). No obvious differences were found between extension and flexion muscle activity for the different positions of the knee.

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