**3. Biological aspects**

the importance of processing, controlling and storing of this type of material becoming one of

Bone tissue can be processed in many ways. It can be stored longer and has been implanted till recently without prior testing compatibility as opposed to transplant of other organs and the vast majority of soft tissues. Nevertheless, the bone tissue can be obtained from patient's own body called autograft, from another donor of the same species (living or cadaver donors) called homograft, from donors of another species xenograft and from non-organic biomaterials [2]. Despite the success of these implants, patients who require transplant may wait quite a few years on transplant lists. These lists have grown considerably in recent years, either from

Deep-frozen homologous graft is the most common used bone graft, but its use is limited due to shortage and although small, the risks of transmitting contagious diseases and even cancers should not be overlooked [11, 44]. On the other hand, though homologous lyophilised (freeze-dried) grafts have virtually eliminated the risk of transmissible diseases is still lacking availability and therefore, alternative biomaterials from synthetic or natural source have been considered and carefully studied. Among these materials, the use of bovine lyophilised grafts is a suitable alternative with many advantages over autologous or homologous lyophilised graft ones due to the great physicochemical and structural resemblance to human bone and their practically endless availability [13, 15, 16, 45]. As a xenograft however, it may possibly present adverse immunological and inflammatory reactions [16]. Nevertheless, our physicochemical processing protocols have been developed in order to significantly reduce these problems, decreasing antigenicity and thus, turning the bovine freeze-dried bone an impor-

The bone tissue transplanting is far from being a novel issue, but it is necessary an increased knowledge about some kinds of grafts, their mechanical and biological aspects, sources and a careful analysis of outcomes. Bone transplant is responsible for an improvement in patient's quality of life; in some cases, return to daily life activities and promotion of patient social reinsertion. This chapter is intended to present a brief review of the history of bone grafts, indications for use, storage details and differences of processing techniques as well as to present the experience of our hip orthopaedic surgery group with the use of lyophilised bovine

In the first centuries of the Christian era, the idea of tissue transplantation between individuals of the same species and even of different species arose. Cosmas and Damian, considered the pioneers of bone transplantation, in the second century of Christian era removed a tumour-affected leg and soon implanted a leg taken from a recently killed Moro. But success in bone transplantation only came in 1880 with Sir William MacEwan who reconstructs a patient humerus with bone graft from another patient's leg. But Job van Meekren in 1668 was the first who realise a xenograft bone transplant. Meekren transplanted part of the skull of a

tant biomaterial for large scale use in reconstructive surgery [14, 63].

xenograft in almost two thousand orthopaedic procedures.

**2. History of bone transplantation**

the major transplanted tissues [44, 59].

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

public hospitals or from private ones [3].

The bone tissue is composed of 10% water, an inorganic part (mineral, mainly hydroxyapatite) corresponding to 65%, and an organic part corresponding to 25%, being this latter part consisting of a collagen type I matrix with low molecular weight proteoglycans and noncollagen proteins [21].

When affected by severe bone loss or osteolysis, a condition founded in several cases of total hip arthroplasty revision, the bone tissue cannot be repaired, even though it is a tissue with high recovery power. In these cases, it is necessary to use bone grafts or bone substitutes (biomaterials) that fill this gap and restore patient's bone stock [21].

Bone grafts can be of three types, depending on the location of its origin: cortical, cancellous or cortical-cancellous. These grafts can be used in three modes: blocks, segments or morselised. These different types of bone grafts will provide distinct mechanical and biological responses. The cortical bone is less osteogenic than the spongy one, showing however, a higher structural quality, for long periods and even in the absence of adequate integration. In revision arthroplasty surgeries cancellous bone graft remains the choice due to its greater osteogenic features [11, 18, 27, 34, 49, 50, 61].

A sequence of events begins after transplantation of a spongy bone, starting by an inflammatory response. This is followed by macrophage invasion, neovascularization and differentiation of mesenchymal cells into osteoblasts that place an osteoid layer on a remaining necrotic trabecular bone. Viable nuclei are reabsorbed by osteoblasts and the matrix is eventually replaced by necrotic trabeculae in the newly formed bone [57]. Urist and Hernandez in their classical study demonstrated ectopic bone formation after implantation of demineralised bovine bone matrix in rabbit's muscular tissue. This discovery showed that certain substances present in bone matrix induce cell differentiation. All these events are probably mediated by inducing protein factors, called bone morphogenetic proteins (BMPs) that have great osteogenic activity [39, 43]. These BMPs belong to a superfamily of proteins called transforming growth factors beta (TGFß) responsible for inducing growth. The TGF-ß is responsible for cell growth, differentiation and embryo formation. BMPs have been shown to be important regulators in the development and regeneration of skeletal tissue [43]. Buma and colaborators detailed Galia [14] in their PhD thesis, in 2000 and 2004 (**Figures 1** and **2**), respectively, demonstrated the relationship between time elapsed from grafting till to biopsies for histological analysis. The wider the interval, the larger

Out come in bone transplantation also depends on antigenic reaction factors. Some grafts have proved to be extremely antigenic, depending on the antigens present in these grafts. The antigenic reactions are mediated by bone marrow cells and not by T or B lymphocytes. Indeed, *in vitro* studies demonstrated that lineages of bone marrow granulocytes appear to be responsible for this immune response [7]. Moreover, *in vivo* studies in rabbits also showed that fresh grafts, frozen grafts and lyophilised bovine xenograft express distinct immune responses. Fresh and frozen grafts led to systemic response in rabbits as opposed to lyophilised bovine xenograft where rabbits were not able to develop such systemic immune response, demonstrating that the lyophilisation process clears up immunologically the graft by removing all the fat and bone marrow cells [13].

Biology of Bone Graft and the Use of Bovine Bone for Revision of Total Hip Arthroplasty…

http://dx.doi.org/10.5772/intechopen.79485

61

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

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].

**5. Sterilisation, transmission of infectious diseases and biological** 

The sterilisation is a crucial issue involving grafts and it can change their mechanical properties, as well as may affect transmission of diseases or even tumours [60, 64]. Radiation as Cobalt 60 can significantly reduce bone mechanical properties and even in low doses can destroy morphogenetic properties, in a progressive dose-dependent manner over the bone biomechanics [10]. Several authors studied gamma radiation and other sterilisation methods (ethanol and ethylene oxide at 55°C) and their effect on graft osteoinduction. Gamma radiation with 25 kGy inactivate HIV virus but reduces osteoinduction capacity of grafts in nearly 40%; ethylene oxide at 55°C provides an almost complete loss of this important potential. On the other hand, ethanol has not affected osteoinduction [10, 64]. However, toxic factors should be observed. Ethylene

**4. Mechanical aspects**

**safety**

these mechanical aspects is of a paramount prominence.

**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.

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

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

Out come in bone transplantation also depends on antigenic reaction factors. Some grafts have proved to be extremely antigenic, depending on the antigens present in these grafts. The antigenic reactions are mediated by bone marrow cells and not by T or B lymphocytes. Indeed, *in vitro* studies demonstrated that lineages of bone marrow granulocytes appear to be responsible for this immune response [7]. Moreover, *in vivo* studies in rabbits also showed that fresh grafts, frozen grafts and lyophilised bovine xenograft express distinct immune responses. Fresh and frozen grafts led to systemic response in rabbits as opposed to lyophilised bovine xenograft where rabbits were not able to develop such systemic immune response, demonstrating that the lyophilisation process clears up immunologically the graft by removing all the fat and bone marrow cells [13].
