Screening protocol for musculoskeletal tissue donors.
The use of bone graft in orthopaedic surgeries has become essential in many situations in which there is a bone defect. This includes bone tumour procedures, fracture operations where there was a loss of bone tissue and revision arthroplasty surgeries. In this chapter, we will introduce aspects related to history of bone transplantation, the biological and mechanical aspects, as well sterilization, transmission of infectious diseases and biological safety, and concluding, the functioning of tissue banks and screening of musculoskeletal tissue donors.
- bone graft
- revision of total hip arthroplasty
- acetabular reconstruction
- biological and mechanical aspects of bone tissue
- tissue banks
The use of transplants in orthopaedic surgeries has become essential in many situations in which there is a bone defect. This includes bone tumour procedures, fracture operations where there was a loss of bone tissue and revision arthroplasty surgeries [11, 44, 53]. The latter, revision arthroplasty, has considerably increased since the rate of primary arthroplasties has grown substantially in recent years. Some kind of musculoskeletal tissue is transplanted into 10 to 15% of orthopaedic surgeries performed in the United States. Annually, about 650,000 bone-based grafts are distributed by the American Tissue Banks, clearly highlighting the importance of processing, controlling and storing of this type of material becoming one of the major transplanted tissues [44, 59].
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 . 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 public hospitals or from private ones .
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 . 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 important biomaterial for large scale use in reconstructive surgery [14, 63].
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 xenograft in almost two thousand orthopaedic procedures.
2. History of bone transplantation
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 dog in a traumatic defect of the skull of a soldier, who was excommunicated by the church. The soldier asked the surgeon to remove the graft, but due to time elapsed, this could not be completely removed since it was already fully integrated. Ollier and Barth in nineteenth century concluded, though not fully correct, that bone and periosteum remained viable when transplanted, contributing to new bone formation; arising the primary concept that cells survive in the graft even when removed from donor [3, 52]. In an important and considered a classical work, Albee concluded that the most suitable tissues for transplant are those originated from connective tissue such as bone, fat and fascia [12, 19, 30].
3. Biological aspects
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 non-collagen proteins .
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 .
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 . 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 (TGF-ß) 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 . Buma and colaborators detailed Galia  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 the amount of new bone formation and the smaller the residual bone graft, though Tiango et al. in 2015  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 . 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 .
4. Mechanical aspects
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 . Galia et al . 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 . 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  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 .
5. Sterilisation, transmission of infectious diseases and biological safety
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 . 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 oxide may be maintained in the graft and may interact or be released when in contact with any liquid, including blood. Gamma radiation may be toxic when in direct contact with fat that is present in the grafts [27, 37]. Autoclaving is another way to sterilise grafts. However, xenografts must be sterilised at a temperature of 132°C to inactivate infectious proteins, i.e., prions, though this method reduces the mechanical resistance of xenografts in approximately 70% .
Frozen grafts from tissue banks undergo several protocols for donor selection before being used for transplantation. Graft rejects are reported to reach 20 to 30% [4, 51]. But even with these severe protocols for selection, transmission of an infectious disease may occur [25, 53, 55, 59. Sugihara et al  in 1999 reported the presence of tumour cells in frozen femoral heads and suggested inclusion of histopathological examinations as part of the screening protocol for donor tissues [41, 53].
The lyophilisation process until now has not been linked with infection as confirmed by Shibuya et al. , Ledford et al.  and Ribeiro et al.  who also reported no clinical signs of infections in patients submitted to revision of total hip arthroplasty with acetabular reconstruction, as well as no case of bovine spongiform encephalopathy disease (BSE) and its new variant the Creutzfeldt-Jakob disease (CJD). It is believed that lyophilisation process chemically inactivates most of the bacterial agents, viral and prion agents to a safe and acceptable level to be used in humans as reported by Wenz et al.  and among us, by Galia et al.  and Rosito et al. .
Several bone grafts storage ways are used all over the world. The two most widely accepted and used are the deep-frozen (−80°C) and lyophilisation ones.
Extremely low temperatures (<−80°C) are achieved by using temperature-controlled freezers equipped with power generators, just in case of lack of electric power cut, and alarms triggered by the system when the temperature increases. In these special freezers, a bone tissue can be maintained for up to 5 years. It should be noted that very low temperatures do not have a role in the sterilization of bone tissue.
Proposed and diffused by the Tissue Bank of USA Navy in 1951, the lyophilisation process became the technique in which bone is washed, centrifuged, decellularised, chemically degreased and subjected to physical processes of cleaning and sterilisation, and this way, only the protein-mineral matrix still remains in the graft, which is later frozen and then dehydrated. All these processes decrease antigenicity, tumour cell transmissions and inactivate prions [28, 35]. The lyophilisation is an important method of processing and storage for musculoskeletal tissues that allows not only the use of human bones, tendons and fascia (allogeneic) but also and mainly the bovine (xenogenic) [27, 31, 33, 39]. Currently, in major health centres, different types of bone grafts are available for reconstructive orthopaedic surgery: frozen and lyophilised autologous, (allogeneic) and lyophilised bovine grafts (xenogeneic) .
The frozen human graft (allogeneic) was the most used and widely accepted but the number of Tissue Banks in our country and in other developing countries is not enough to overcome the huge demand as well as the number of donors . In the same way, as mentioned, there is a risk of transmission of diseases and tumour cells [32, 34, 41, 53]. The vast majority of USA Tissue Banks produce lyophilised human grafts (allogeneic); however, there are few studies on its use or production. Therefore, lyophilised human grafts are still not widespread used among us [8, 56].
The bovine bone has a chemical composition, porosity, size, shape and biological behaviour similar to its human counterpart, although controversial bovine grafts is commonly used in dentistry surgeries and reconstructions . It provides structural support, osteoconduction and a high content of calcium and phosphorus; essential factors for the newly formed bone tissue . For these reasons, its use is growing in orthopaedic surgeries as reported by Prof. Galia  and by his co-workers in his research group, Rosito et al. [45, 46], Henning et al.  and Diesel et al. .
The most important issue is whether the graft has been processed and stored according to the standards of Associations of Tissue Banks and by national and international health authorities.
7. Tissue banks
Musculoskeletal tissue banks such as in the USA, there is an institution – the American Association of Tissue Banks (AATB) – to regulate and supervise the functioning of all in-country tissue banks since 1976 . In Brazil, however, is the Ministry of Health, under the regulation order No. 55 (Dec. 2015)  that provides the technical regulations for the functioning of musculoskeletal and skin tissue banks of human origin, determining guidance from the facility characteristics, screening of living donors or cadavers up to equipment and human resources . These regulations, though quite strict, have greatly improved the quality of tissue processing and safe use. For accrual, the decision to accept or reject a donor is carried out by the chairman of the Bank of Musculoskeletal Tissues (BMST) after rigorous tests and following an established protocol . As the protocols used by the Tissue Banks, one must consider the history, physical examination and laboratory tests of the donor (Table 1).
There are many differences when comparing distinct types of graft. Thus, it is essential the implementation of protocols for processing and quality control of all types of bone grafts. This measure will facilitate the monitoring and analysis of the results and shall provide grafting material of better quality, thoroughly tested and readily available.
There is no doubt on the importance of bone transplants in orthopaedic surgery, especially in hip procedures. Their results are well known and, to some extent, predictable when used by experienced surgeons. It is undeniable, however, that we still know little about several issues regarding host-graft interaction. Therefore, further studies have yet to be carried out to attempt to address concerns on this matter that sometimes are overlooked or underestimated in order to achieve best clinical responses, increased biosafety and lower complication rates, i.e., better surgical outcomes [20, 22].