CLINICS 2008;64:509-14 Acetabular reconstruction with human and bovine freeze- dried bone grafts and a reinforcement device Rosito R et al. use freeze-dried grafts may also be related to the number of available grafts with different steps in the production process for distinct purposes and indications as well. As a result, different mechanical and biological responses may be obtained, leading to an unjustified concern when using this type of graft.18 Levai and Boisgard (1996) reported 30 revision cases performed on loose total hip replacements with a specific technique for acetabular reconstruction combining the use of a bovine bone substitute and a support ring. No migration of the acetabular implant or osteolysis of the heterograft was seen in 27 (90%) cases within three years after the procedure was performed. Radiologically, the heterograft gradually condensed, and its appearance was similar to that observed with allografts. In that series, two failures with implant migration and heterograft osteolysis were considered to be a result of technical bias related to the use of the Muller ring, and in both cases, the Muller ring was supported by the cancellous heterograft and not by the host bone.16 De Roeck and Drabu (2001) reported on 32 patients who underwent RTHA using cemented components and allograft impaction of processed freeze- dried bones. The overall endurance with this type of graft at a mean follow-up of four years was 91%. There were no femoral component failures, although revision was required in three patients due to failure of the acetabulum. Freeze- dried grafts may require a longer period of rehydration for adequate impaction. The results of impaction bone grafting with freeze-dried bone alone have been satisfactory, although we do not feel entirely secure with its use alone in cases of hostile acetabulum.19 Thien et al. (2001) reported an overall survival rate for acetabular reconstructions of 86% in seven cases using impacted freeze-dried cancellous bone chips and a cemented cup, with an average follow- up of seven years (range: five-nine years). At this median follow-up period, no aseptic loosening was observed and the results for freeze-dried allograft bone chips were acceptable.20 Recently, Charalambides et al., 2005, published a paper addressing their poor results in 27 RTHA cases, followed up for an average of 2.5 years, after the use of combined autograft and xenograft (Surgibone) bones. Seventeen (62%) out of the 27 patients showed apparent bone incorporation within three months. However, in three (11%) patients, there was no bone incorporation. Three other cases (11%) appeared to have what they considered a pseudoinfection (with no agent identified), and one patient, who had the revision procedure revised again suffered from a deep MRSA infection.21 Disregarding the case of unequivocal infection that was unrelated to the graft, and even considering the three cases of pseudoinfection that may not be related to the grafts, this leaves a figure of 77% success, which is similar to those figures obtained using other methods, and therefore, these results may be more acceptable than previously argued. Moreover, the authors of this paper also provided a histological sample from that patient who required revision of the replacement due to acetabular loosening, despite apparent radiographic incorporation. New bone formation from the grafted area and residual necrotic bony spicules from the graft material were observed, clearly demonstrating graft incorporation.22 Considering the radiographic criteria, and despite biases, the results obtained with human and bovine freeze-dried bone grafts from TBHCPA in this series were comparable to each other and to those previously reported in the literature, including those reports describing the use of deep-frozen allografts. Using a similar technique of impacting deep- frozen graft and cement, and with a similar follow-up, Kerboull et al. reported a similar rate of 92% of graft incorporation.4 Therefore, the success of RTHA seems to be related more to the surgeon’s skills, the inherent limitations of the techniques and the severity of the individual case, rather than to the type of graft used. The use of freeze-dried bone grafts provides a decrease in the risk of transmission of infectious diseases and tumors, since chemical reagents including sodium hypochloride are used during processing to inactivate bacteria, viruses and probably prions.23 After processing, the bone is also sterilized,24,25 which in our tissue bank, is virtually 100% effective. Therefore, concerns related to prion transmission (EEB) with the use of freeze-dried bovine bone grafts appear to be unfounded. Also, careful selection and the country of origin of the herd (particularly Brazil, which has been always a risk-free country for EEB) should be considered.26 From a mechanical point of view, some studies of the use of non-decalcified freeze-dried bone concluded that there is no mechanical difference between freeze-dried and deep- frozen bone, and if there is one, the freeze-dried bones are favored, since they lack fat, blood and marrow cells.17,25 Although there is a shortage of data regarding xenograft use in RTHA, clinical complications have not been observed, except for those complications that are generally expected with the use of allografts or xenografts, since physical and chemical analyses have shown they are very similar. The results obtained here have shown that freeze-dried bovine bone grafts do not cause any types of adverse reactions, and therefore confirm their safety. We conclude that processing of bones from bovine or human sources via lyophilization in our tissue bank yields bones of a suitable quality to be used in RTHA, and that the use of freeze-dried bovine bone grafts provides similar clinical and radiographic results to human freeze-dried bone grafts. 513