**5. Mechanical characteristics**

In addition to the biological characteristics, the mechanical aspects are very relevant and can be decisive in the choice and obtained results using a due graft. Itoman and Nakamura, in

Fig. 2b. Biopsy of frozen human bone graft. 36 months of evolution. White arrow = graft;

cortical, but especially, most recently the spongy morcelised and impacted.

Although the freeze-dried grafts, whether human or bovine, are available in many medical centres worldwide, most work on RTHAs refers to the use of frozen bone grafts in blocks or

Tagil, in his PhD thesis published in 2000, attempted to explain the reasons for succeeding using the technique of frozen morcelised and impacted bone, once theoretically, the large volume of necrotic bone exposed to great mechanical stress tend to collapse, as in the vascular necrosis of the femoral head or knee. After detailed study, Tagil found out the following possibilities: (a) morcelised bone, as in a comminuted fracture, would produce extensive surface contact allowing access and release of biologically active substances; (b) impaction may improve osteoconductive properties of the graft leading to the release of BMPs and this way favouring osteointegration and; (c) the high elasticity may allow small deformations that would stimulate new bone formation. The importance of this study lays in the fact that it is essential, from a scientific standpoint, to know the pros and cons of a due technique and why results may be good or bad, to better use and indicate such a procedure

In addition to the biological characteristics, the mechanical aspects are very relevant and can be decisive in the choice and obtained results using a due graft. Itoman and Nakamura, in

black arrow = new bone.

more securely and confidentially.

**5. Mechanical characteristics** 

1991, studied the histological and biomechanical properties of different ways of bone graft processing in rats and noted that an increased stiffness of the bone after freezing at -80°C and lyophilising it. The freeze-dried demineralised bone has initially decreased its mechanical strength. However, after 16 weeks, a progressive increase in resistance of the grafts was observed and was likely related to its biological interaction, which might be an indicator of the osteoinductive properties of the graft. They also concluded that on the features of integration, as expected, the autologous bone showed the best results.

The physical properties of human and bovine trabecular bone are documented and their results are available, however, the range of dispersion is very wide. The Young's module, for example, in one study ranged from 70 to 673 MPa and compressive strength varied between 2.44 and 6.24 MPa. This dispersion occurred for both human and bovine bone and may be related to several factors such as donor age, bone density and methodology used in the study.

Cornu et al. in 2001, has demonstrated in vitro that the lyophilised morcelised and impacted bone is mechanically superior to the morcelised and impacted deep-frozen bone since, at least, has the same resistance after impaction, that is achieved however, more quickly and with fewer impacts, and the authors assumed as to the fact that lyophilised material was devoid of fat and bone marrow. Moreover, Macedo et al. in 1999, using an automated compression machine compared in vitro, the compressive strength of frozen and freezedried bovine bone rehydrated for an hour and found out that deep-frozen bovine bone grafts after defrosting, has similar compressive loads and deformation rate of the rehydrated lyophilised bovine bone.
