In previous reports we and others have examined the relative movement of the tibia and femur in the living unloaded knee during flexion to 90° and 120° using MRI.1,2 We have now extended this investigation to the limits of active flexion (133°) and of passive flexion (162°). This study has been based on the knee in Japanese subjects since a position of full passive flexion is used in everyday life in Japan. Subjects and MethodsThe subjects were 20 adult male volunteers without symptoms in their knees and with normal MR images. Their mean age was 29.7 years (26 to 40). The left knee was scanned in an open MR imaging unit (Airis; Hitachi, Tokyo, Japan). The knees were imaged in neutral rotation at 90°, in active maximum flexion and in passive maximum flexion. Measurements were made as described elsewhere.3 At 90° flexion and active maximum flexion, the subject was scanned while lying on his side with the knee to be imaged in contact with the table. The position of maximum passive flexion was maintained by the body-weight (Fig. 1). At this position little tibial rotation was possible, i.e. the knee was rotationally locked. ResultsFrom 90° to full active flexion (133 ± 9°, mean ± SD) the mean posterior translation of the lateral femoral condyle was 13 ± 6 mm whereas for the medial femoral condyle it was 2 ± 2 mm. Therefore, over this arc of flexion, a mean tibial internal rotation of 15 ± 9° occurred around an axis passing through the medial tibial condyle. Passively forcing the knee from active to full passive flexion (i.e., from 133° to 162 ± 4°, mean ± SD) moved the medial femoral condyle back a further 4.5 ± 2 mm and the lateral femoral condyle 15 ± 4 mm. Thus there was a further 13 ± 6° of internal tibial rotation combined with about 4.0 mm of femoral posterior translation. At full passive flexion, the centre of the posterior circular portion of the lateral femoral condyle was 7 ± 5 mm posterior to the posterior tibial cortex and the lateral femoral condyle was only just in contact with the lateral tibial condyle. The medial femoral condyle had lifted away from the tibia.Representative MRIs, confirmatory cryosections of the medial and lateral compartments in Caucasian knees in full flexion, and the displacements of the condyles with flexion from their position at 90° are shown in Figures 2, 3 and 4. ConclusionsPrevious studies 1,2,3 have shown that as the unloaded knee is flexed to 120° in neutral rotation, the lateral femoral Scanning position at passive maximum flexion.

Geometric constraint in pregel solution enables construction of a highly ordered three-dimensional polymer network.

The crystallization behavior and crystal orientation of poly(ε-caprolactone) (PCL) homopolymers and PCL blocks spatially confined in identical nanocylinders have been investigated using differential scanning calorimetry (DSC) and two-dimensional wide-angle X-ray diffraction (WAXD) as a function of cylinder diameter D. The PCL homopolymers confined in nanocylinders were prepared using microphase separation of PCL-block-polystyrene (PCL-b-PS) copolymers with a photocleavable o-nitrobenzyl group (ONB) between PCL and PS blocks and the subsequent cleavage of ONB by irradiating UV light. The time evolution of PCL crystallinity χ PCL showed a first-order kinetics for both PCL blocks and PCL homopolymers confined in all the nanocylinders investigated. However, the D dependence of crystallization rates for PCL blocks was more drastic than that for PCL homopolymers, and consequently various Ddependent interrelations were observed between crystallization rates of PCL blocks and PCL homopolymers. The crystal orientation was also dependent on D; the b-axis of PCL crystals oriented parallel to the cylinder axis both for PCL blocks and PCL homopolymers confined in the nanocylinder with D = 13.0 nm, whereas the (110) plane of PCL crystals was normal to the cylinder axis in the nanocylinders with D ≥ 14.9 nm. The difference in the degree of crystal orientation was not detected between PCL blocks and PCL homopolymers confined in nanocylinders with D ≥ 14.9 nm.

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Polymer networks usually contain numerous inhomogeneities that deteriorate their physical properties and should be eliminated to create reliable, high‐performance materials. A simple method is introduced for the production of nearly ideal networks from various vinyl polymers through controlled polymerization and subsequent crosslinking. Monodisperse star polymers with bromide end groups were synthesized by atom‐transfer radical polymerization and end‐linked with dithiol linkers using thiol–bromide chemistry. This simple procedure formed nearly ideal polymer networks, as revealed from elasticity of the formed gel and model conjugation reactions involving linear polymers. The versatility of this method was demonstrated by preparing networks of common vinyl polymers, including polyacrylates, polymethacrylate, and polystyrene. This method can be used to prepare multiple functional nearly ideal gels and elastomers and to explore fundamental aspects of polymer networks.