Quadriceps muscle contraction causes medial patellofemoral ligament elongation by intermeshed fibers of vastus medialis oblique muscle.

The first aim of this study was to compare the medial patellofemoral length between contracted and relaxed quadriceps muscle and second to assess the importance of the intermeshed vastus medialis oblique fibers. After a priori power analysis (α = 0.05, power [1-ß] = 0.95), 35 healthy males aged 18-30 were prospectively examined with a 3.0-T magnetic resonance imaging (MRI) scanner in 10-15° of knee flexion. Two axial MRI sequences (25 s each) were made with relaxed and contracted quadriceps. Two blinded, independent raters measured twice medial patellofemoral ligament length (curved line) and attachment-to-attachment length (straight line). Mean medial patellofemoral ligament length and attachment-to-attachment length with relaxed quadriceps was: 65.5 mm (SD = 3.7), 59.7 mm (SD = 3.6), and after contraction, it increased to 68.7 mm (SD = 5.3), 61.2 mm (SD = 4.7); p < 0.01 and <0.001, respectively. Intraclass correlation coefficients for intra- and inter-rater reliabilities ranged from 0.55 (moderate) to 0.97 (excellent). Mean medial patellofemoral ligament length elongation after quadriceps contraction was significantly greater (3.2 mm, SD = 3.9) than mean attachment-to-attachment length elongation (1.6 mm, SD = 2.8); p < 0.001. Contraction of quadriceps muscle causes elongation of the medial patellofemoral ligament to the extent greater than the elongation of distance between its attachments. This confirms that medial patellofemoral ligament elongation after quadriceps contraction results not only from movement of its patellar attachment but also directly from intermeshed vastus medialis oblique fibers pulling medial patellofemoral ligament in a different direction creating a bow-like construct in agreement with the "pull-and-guide mechanism" proposed in the literature.

Reconstruction of Grains in Polycrystalline Materials From Incomplete Data Using Laguerre Tessellations.

Far-field three-dimensional X-ray diffraction microscopy allows for quick measurement of the centers of mass and volumes of a large number of grains in a polycrystalline material, along with their crystal lattice orientations and internal stresses. However, the grain boundaries-and, therefore, individual grain shapes-are not observed directly. The present paper aims to overcome this shortcoming by reconstructing grain shapes based only on the incomplete morphological data described above. To this end, cross-entropy (CE) optimization is employed to find a Laguerre tessellation that minimizes the discrepancy between its centers of mass and cell sizes and those of the measured grain data. The proposed algorithm is highly parallel and is thus capable of handling many grains (>8,000). The validity and stability of the CE approach are verified on simulated and experimental datasets.