**4. Mechanical aspects**

the amount of new bone formation and the smaller the residual bone graft, though Tiango et al. in 2015 [44] in a case series resulted from his PhD thesis was notable to reconfirm these findings,

**Figure 2.** Another patient with a severe bone loss before a primary total hip arthroplasty was submitted to a revision total hip arthroplasty with acetabular bone reconstruction with bovine lyophilized xenograft. This patient was affected by recurrent dislocation of the revised arthroplasty. An inadequate positioning of the acetabular component was the aetiology. A biopsy of the acetabular bone graft reconstruction was done in the second revision surgery. In this case, the time elapsed from the first revision with the bone grafting and the second revision made to reposition the acetabulum

**Figure 1.** A representative case with a severe bone loss before a primary total hip arthroplasty was submitted to a revision total hip arthroplasty with acetabular bone reconstruction with bovine lyophilized xenograft. This patient was affected by recurrent dislocation of the revised arthroplasty. An inadequate positioning of the acetabular component was the aetiology. A biopsy of the acetabular bone graft reconstruction was done in the second revision surgery. In this case, the time elapsed from the first revision with the bone grafting and the second revision made to reposition the acetabulum

was nine months. a: new bone formed; b: lyophilised bovine xenograft; c: fibrous tissue.

60 Bone Grafting - Recent Advances with Special References to Cranio-Maxillofacial Surgery

probably due to the small number of cases with biopsies in the study [5, 17, 18, 58].

was 43 months. a: new bone formed; b: lyophilised bovine xenograft; c: fibrous tissue.

The different mechanical aspects of the various types of graft play a key role when a graft is to be chosen. These differences can lead to distinct end-results and therefore acquaintance with these mechanical aspects is of a paramount prominence.

Several physical properties of human and bovine trabecular bone have been reported [26, 54]. The compressive strength to mechanical forces varied between 2.44 and 6.24 MPa in both, human and bovine bones. In Young's module analyses the results of both bones varied between 70 and 673 MPa [42]. Galia et al [15]. in 2011 obtained a similar result between lyophilised bovine and lyophilised human bones for the scanning electron microscope analyses on the pore sizes of the trabecular bone. The mean pore size was 316 μm, ranging from 91.2 to 497.8 μm to bovine lyophilised bone and 333.5 μm, ranging from 87.2 to 963.9 μm to human lyophilised bone. Macedo et al [36]. in 1999 in an *in vitro* study demonstrated that frozen lyophilised bovine bone defrosted or rehydrated for an hour have similar compressive load and deformation rates. Cornu et al [6] in 2001 showed that lyophilized morcelised and impacted human bones were mechanically superior to morcelised and impacted deep-frozen ones. However, the resistance of both bones was similar after impaction [36].
