Osteoporotic fractures are caused by both cortical thinning and trabecular bone loss. Both are seen to be important for bone fragility. The relative contributions of cortical versus trabecular bone have not been established. The aim of this study was to test the contribution of cortical versus trabecular bone to femoral neck stability in bone strength. In one femur from each pair of 18 human cadaver femurs (5 female; 4 male), trabecular bone was completely removed from the femoral neck, providing one bone with intact and the other without any trabecular structure in the femoral neck. Geometrical, X-ray, and DXA measurements were carried out before biomechanical testing (forces to fracture). Femoral necks were osteotomized, slices were analyzed for cross-sectional area (CSA) and cross-sectional moment of inertia (CSMI), and results were compared with biomechanical testing data. Differences between forces needed to fracture excavated and intact femurs (DF/F mean) was 7.0% on the average (range, 4.6-17.3%). CSA of removed spongiosa did not correlate with difference of fracture load (DF/F mean), nor did BMD. The relative contribution of trabecular versus cortical bone in respect to bone strength in the femoral neck seems to be marginal and seems to explain the subordinate role of trabecular bone and its changes in fracture risk and the effects of treatment options in preventing fractures.

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Purpose The purpose of this study was to evaluate in a sheep model the biomechanical performance of augmented and nonaugmented primary repair of the anterior cruciate ligament (ACL) following transection at the femoral end during a 12-month postoperative observation. Methods Forty sheep were randomly assigned to nonaugmented or augmented primary ACL repair using a polyethylene terephthalate (PET) band. At two, six, 16, 26 and 52 weeks postoperatively four sheep in each group were sacrificed and biomechanical testing performed. Results Compared with nonaugmented primary ACL repair, the PET-augmented repair demonstrated superior biomechanical results from 16 weeks postoperatively onwards in terms of anterioposterior (AP) laxity, tensile strength and ligament stiffness. The augmentation device works as a stress shield during the ligament healing process. The nonaugmented ACL repair also resulted in ligament healing, but the biomechanical properties were at a significantly lower level. Conclusion These results support the previously reported histological findings following augmented primary ACL repair. This animal study on the healing capacity of the ACL may provide some important contributions to how primary healing in certain types of ruptures can be achieved.

A model is presented for stabilization of cracks in an atomistic solid by "bond trapping". In contrast to the normal "lattice trapping" which results from the periodicity of the atomic lattice, "bond trapping" depends on special features of the interatomic potentials and will lead to energy dissipation by phonons. It is expected to occur mainly in structures with open lattices with covalent binding, in glass, or in amorphous materials where lattice trapping is not to be expected.Ein Model1 wird vorgestellt fur die Stabilisierung von Rissen in atomaren Festkorpern durch ,,bond trapping". Im Gegensatz zum normalen ,,lattice trapping" das auf der Periodizitlt des Atomgitters beruht, hangt ,,bond trapping" von den speziellen Eigenschaften des interatomaren Potentials ab und gibt AnlaD zu Energiedissipation durch Phononen. Es tritt hauptsachlich in offenen Gittern mit homoopolarer Bindung, in Glas oder in amorphen Materialien auf, in denen ,,lattice trapping" nicht erwartet wird.

Among the b.c.c. alkali metals there are striking differences in the deformation behaviour between potassium on the one hand, which retains the b.c.c. structure down to the lowest temperatures investigated, and lithium and sodium, on the other hand, which undergo martensitic transformations to close‐packed structures at low temperatures. The deformation behaviour of potassium is very similar to that of the b.c.c. refractory metals. Recent measurements show that in potassium there exist three different temperature and stress regimes within the flow‐stress‐versus‐temperature curves, too. Hence this appears to be an intrinsic property of all b.c.c. metals. The deformation behaviour of lithium and sodium is characterized by a very strong orientation dependence and asymmetry of the flow stress with respect to the deformation direction in a temperature range which is by far too high for an intrinsic lattice mechanism to be the rate‐controlling process. A model is presented which ascribes this behaviour to precursor phenomena of the martensitic transformation.