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Varus and valgus joint laxity of the normal living knee in flexion was assessed using MRI. Twenty knees were flexed to 90 degrees and were imaged in neutral and under a varus-valgus stress in an open MRI system. The configuration of the tibiofemoral joint gap was studied in slices which crossed the epicondyles of the femur. When a varus stress was applied, the lateral joint gap opened by 6.7 +/- 1.9 mm (mean +/- SD; 2.1 to 9.2) whereas the medial joint gap opened by only by a mean of 2.1 +/- 1.1 mm (0.2 to 4.2). These discrepancies indicate that the tibiofemoral flexion gap in the normal knee is not rectangular and that the lateral joint gap is significantly lax. These results may be useful for adequate soft-tissue balancing and bone resection in total knee arthroplasty and reconstruction surgery on ligaments.

The study of carrier multiplication has become an essential part of many-body physics and materials science as this multiplication directly affects nonlinear transport phenomena, and has a key role in designing efficient solar cells and electroluminescent emitters and highly sensitive photon detectors. Here we show that a 1-MVcm−1 electric field of a terahertz pulse, unlike a DC bias, can generate a substantial number of electron–hole pairs, forming excitons that emit near-infrared luminescence. The bright luminescence associated with carrier multiplication suggests that carriers coherently driven by a strong electric field can efficiently gain enough kinetic energy to induce a series of impact ionizations that can increase the number of carriers by about three orders of magnitude on the picosecond time scale.

To elucidate the reactions of bone around aseptically loosened total joint arthroplasties, 24 interface tissues with adjacent bone were obtained in 17 revision operations (11 hips and six knees). The morphology of the bone surface next to the interface membrane was investigated with histochemical and immunohistochemical techniques and then histomorphometrically analysed. One-third of the total bone surface. 32.69 +/- 5.16% (mean +/- SE) (n = 24), showed positive alkaline phosphatase activity. The bone surface in contact with the cells positive for CD11b (a macrophage marker) amounted to 19.33 +/- 5.16% (n = 24). The proportion of the osteoclastic bone resorption estimated by vitronectin receptor expression was 7.67 +/- 1.82% (n = 21). Tissues retrieved from the sites where radiographic evidence of osteolysis was present (n = 12) had a significantly larger extent of the bone surface in contact with CD11b-positive cells than did the tissues from areas without osteolysis (n = 12, p = 0.0067, Mann-Whitney U test), whereas no significant difference was observed in the extent of osteoclastic bone resorption. These data demonstrate that active bone formation, regarded as a repair process, is the most common feature even in revised cases. They also highlight the role played by macrophages, not as cells producing inflammatory mediators that could activate osteoclasts, but as cells primarily responsible for the bone loss in osteolytic lesions.

This presentation summarizes the results of our recent studies on the pathogenesis of osteolysis around total joint arthroplasties. First, interface tissues with adjacent bone were retrieved and histopathologically investigated with reference to the cells on the bone surface. Secondly, polyethylene particles were extracted with the tissue digestion method and characterized with scanning electron microscopy. Finally, an animal model for osteolysis was created and various interface conditions were compared concerning their resistance to particle migration.Histopathological examinations demonstrated that active bone formation, regarded as a repair process, was the commonest feature, even in revised cases. They also highlighted the role played by macrophages, not as cells producing inflammatory mediators which could activate osteoclasts, but as cells primarily responsible for the bone loss in osteolytic lesions. Among the particle species present, only polyethylene particles were shown to play a significant role in macrophage recruitment and subsequent osteolysis.A quantitative extraction of polyethylene particles showed a significant difference in the "number" of particles between osteolysis positive and negative cases whereas the "sizes" of particles were similar in these two groups. The critical number of particles for osteolysis was around lxl0 10 particles I g tissue and the cellular reaction against phagocytosable particles accumulated over this concentration may be the prerequisite for progression of osteolysis.The animal model for osteolysis indicated that the progression of osteolysis depends on the integrity of the bone-implant interface. We suggest that the solid fixation of the prosthesis performed by current techniques (e.g., improved cementing technique, hydroxyapatite coating) is beneficial for preventing particle migration and subsequent osteolysis. Clinical relevanceOsteolysis induced by particulate wear debris from implant materials has been recognized as the major cause of long-term failure in total joint replacements. However, the development of preventive measures for this phenomenon has not been successful because the mechanism in which wear particles cause osteolysis is not quite clear.On the basis of results obtained in this study, we believe that the basic strategy for addressing the problem of osteolysis is to reduce the "number" of accumulated wear particles in the interface tissues. This could be achieved either by improving the materials or the geometry of the articulating counterface. Another possibility is to increase the integrity of the bone-implant interface to prevent particle migration. It is important to note that pre-clinical testing of materials and prosthetic designs should include an analysis of the characteristics of the particle generated (e.g., size and number).The widespread bone formation, even in revised cases, is encouraging in view of "conservative treatment" of aseptic loosening. Assuming that bone loss in aseptic loosening is not a remorseless process, some ...

We investigate the possibility of directing optical emissions using a Yagi-Uda antenna composed of a finite linear array of nanoparticles. The relevant parameters characterizing the plasma resonances of the nanoparticles are identified and the interaction between the array elements is formulated accordingly. It is shown that the directionality of the optical emission can be observed even in the presence of non-negligible absorption losses in the nanoparticles. We conclude that a finite array of gold nanorods may be sufficient for the realization of a working nano-optical Yagi-Uda antenna. PACS numbers: 78.67.-n 42.82.-m 84.40.Ba

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.