The osteoinductive capacity of differently HCl-decalcified bone alloimplants

Decalcified allograft in repair of lytic lesions of bone: A study to evolve bone bank in developing countries

BACKGROUND

The quest for ideal bone graft substitutes still haunts orthopedic researchers. The impetus for this search of newer bone substitutes is provided by mismatch between the demand and supply of autogenous bone grafts. Bone banking facilities such as deep frozen and freeze-dried allografts are not so widely available in most of the developing countries. To overcome the problem, we have used partially decalcified, ethanol preserved, and domestic refrigerator stored allografts which are economical and needs simple technology for procurement, preparation, and preservation. The aim of the study was to assess the radiological and functional outcome of the partially decalcified allograft (by weak hydrochloric acid) in patients of benign lytic lesions of bone. Through this study, we have also tried to evolve, establish, and disseminate the concept of the bone bank.

MATERIALS AND METHODS

42 cases of lytic lesions of bone who were treated by decalcified (by weak hydrochloric acid), ethanol preserved, allografts were included in this prospective study. The allograft was obtained from freshly amputated limbs or excised femoral heads during hip arthroplasties under strict aseptic conditions. The causes of lytic lesions were unicameral bone cyst (n = 3), aneurysmal bone cyst (n = 3), giant cell tumor (n = 9), fibrous dysplasia (n = 12), chondromyxoid fibroma, chondroma, nonossifying fibroma (n = 1 each), tubercular osteomyelitis (n = 7), and chronic pyogenic osteomyelitis (n = 5). The cavity of the lesion was thoroughly curetted and compactly filled with matchstick sized allografts.

RESULTS

Quantitative assessment based on the criteria of Sethi et al. (1993) was done. There was complete assimilation in 27 cases, partial healing in 12 cases, and failure in 3 cases. Functional assessment was also done according to which there were 29 excellent results, 6 good, and 7 cases of failure (infection, recurrence, and nonunion of pathological fracture). We observed that after biological incorporation, the graft participates in bone physiology and morphology. We did not observe any adverse host graft antigenic reaction.

CONCLUSIONS

We conclude that decalcified allograft is suitable alloimplant for use in benign lesions of bone, is easy to prepare and store, and is thus well suited for use in developing countries.

Synthetic bone grafting in foot and ankle surgery

Synthetic bone graft materials have an established role as osteoconductive materials. The basic function is providing a matrix to support the attachment of bone-forming cells for subsequent bone formation, but these materials in various forms can be used for other functions. They can be used as a vehicle for local antibiotic delivery and in injectable form they can be used in a minimally invasive fashion to fill voids and strengthen purchase of screws in osteoporotic bones. They can provide prolonged structural support, which is important for early weight bearing in the lower extremity. These are some of the qualities that may not be obtained from autograft bone, the traditional gold standard for bone grafting. Therefore, these synthetic bone graft substitutes have earned a unique place in the armamentarium when issues such as bone defect, bone quality, and bone infection challenge bone healing and repair. This article reviews the basic science and use of such materials in foot and ankle surgery for conditions related to trauma, tumors, and infection.

Modern issues in bone graft substitutes and advances in bone tissue technology

Autogenous bone grafting is the gold standard in repair of bony defects, fracture nonunion, and promoting arthrodesis. The complications related to obtaining autogenous grafts can be significant, and numerous materials are now available for augmentation or substitution. Allograft materials are highly effective for most applications; however, the surgeon needs to be acutely aware of the source of the tissue, for some tissue banks still use unacceptable processing techniques that destroy the structural and osteoinductive capacities of the graft. DBM products are unregulated and serious concerns exist as to the distribution of inactive products as commercially available to the practicing surgeon. Pressure from the orthopedic community has caused some manufacturers to test their products for activity before distribution. Calcium-based ceramic materials are effective as osteoconductive agents and work well alone as bone void fillers; however, augmentation of these implants with osteoinductive materials should be considered for use in nonunions and arthrodesis. Composite materials that incorporate osteoinductive materials in osteoconductive scaffolds are promising. New technology in isolation and creation of recombinant human bone morphogenic proteins and growth factors, and in the application of autogenous stem cells are emerging as the future of bone grafting procedures.

Allograft bone. The influence of processing on safety and performance

Advances in tissue processing technology have been important for the successful use of bone allografts. The challenge is to prepare allografts that are well cleaned, sterile, and free of viruses while still preserving the natural biologic and biomechanical properties of the tissue. This article discusses how processing techniques aimed at achieving safety and sterility can affect the properties vital for graft incorporation and healing.

Ethylene oxide does not extinguish the osteoinductive capacity of demineralized bone. A reappraisal in rats

We examined the influence of ethylene oxide (EO) and gamma irradiation on the osteoinductive capacity of demineralized bone. Demineralized bone powder prepared from Wistar rats was exposed to EO (55 degrees C or 40 degrees C) or gamma irradiation (25 KGy) or was preserved in ethanol. Sterilely-prepared bones served as controls. The powder was packed in a gelatin capsule and implanted for 6 weeks in muscles of 6-week-old female rats. Exposure of demineralized bone particles to EO 55 degrees C resulted in an almost complete loss of osteoinductivity. Irradiated bones lost about 40% of their osteoinductive capacity, while sterilization with EO at 40 degrees C resulted in only a slight alteration of the osteoinductivity, as assessed by the recovered weight ratio, calcium content, alkaline phosphatase activity measurements and histomorphometry. Ethanol treatment had no influence on the new bone yield when compared to controls. As EO exposure at 40 degrees C is a true sterilization procedure, it can be recommended in a clinical setting for its small effect on osteoinductive capacity as assessed experimentally in rats.

[Osteoinduction and -reparation]

Traumata, diseases, developmental deformities, and tumor resections frequently cause bone defects and atrophies. In general, three different mechanisms exist by which bone restoration can be achieved: (1) osteogenesis initiated by vital, osteoblastic cells of autografts; (2) osteoconduction (or creeping substitution); and (3) osteoinduction. The latter mechanism means the differentiation of pluripotent, mesenchymal-type cells (located in a recipient bed with strong regenerative capacity) into cartilage- and bone-forming progenitor cells under the influence of inductive bone morphogenetic proteins (BMPs). Some BMPs are physiologically included in low concentrations as organic components in bone tissue. They can diffuse from demineralized bone implants into the recipient bed and induce a differentiation into new bone tissue. Nine different BMPs have been isolated, characterized, and cloned. Some of these possess inductive properties and can initiate new bone formation in muscle tissue or in bone defects. In the future recombinant BMPs will be available in unlimited quantities. This will lead to completely new therapeutic concepts in reconstructive bone surgery.

Repair of human skull defects using osteoinductive bone alloimplants

To estimate the efficacy of cranioplasty in clinical practice, autolyzed, antigen-extracted, allogenic (AAA) bone was prepared from cortical bones of human organ donors. AAA bone implants consisted of completely demineralized bone powder, completely demineralized pliable bone chips, surface-demineralized bone chips with pliable crevices, surface-demineralized rigid bone chips, or combinations thereof. 21 patients received AAA bone cranioplasties and were followed-up for between 12 and 58 months (average: 29 months). No infection or rejection of any of the AAA bone implants occurred. X-ray assessments as well as bone scintigraphies revealed osseous integration and remodelling of the AAA bone implants with minimal resorption, with the exception of completely demineralized AAA bone chips which showed partial resorption (2 cases). However, the partial resorption of completely demineralized AAA bone chips ceased after the implants had been remodelled. In 4 cases, the osteosynthesis material was removed between 10 and 18 months after the cranioplasty. In another case, a re-entry was necessary because of recurrence of an intracranial tumor. All of these five AAA bone reconstructions showed bleeding surfaces and osseous consolidations at the time of re-entry. A bone biopsy taken from one of these cranioplasties showed osteoinduction on the surface of the AAA bone implants. This first clinical review of cranial reconstructions using osteoinductive AAA bone implants emphasizes the therapeutical application of AAA bone for cranioplasty. Large AAA bone chips from human skull bones facilitate the reproduction of the skull's convexity especially when combined with preoperative stereolithography-based planning.

Osteoinductive, morphologic, and biomechanical properties of autolyzed, antigen-extracted, allogeneic human bone

Autolyzed, antigen-extracted, allogeneic (AAA) bone was prepared from human cortical bone and its morphologic, biomechanical, and osteoinductive properties were compared with untreated (frozen) as well as lyophilized human bone. Scanning electron microscopy revealed removal of inorganic calcium phosphates and persistence of shrunken collagen fibrils on the surface of AAA bone matrix. Biomechanical testing of differently prepared bone samples showed that lyophilization increased both the modulus of elasticity (P < .00001) and the compressive strength (P < .00001). Depending on the depth of decalcification in the preparation of AAA bone, both measured values decreased in rehydrated AAA bone compared with untreated bone (P < .00001). Completely demineralized and rehydrated AAA bone was soft, flexible, and showed very little compressive strength. Differences in biomechanical behavior between samples drilled longitudinally or perpendicularly to the diaphyseal bone axis were observed. Xenogeneic human bone samples were implanted in muscle pouches of Sprague-Dawley rats for 6 weeks. AAA bone implants showed chondrogenesis and osteogenesis in 50% of the cases, while untreated or lyophilized bone implants induced no new cartilage or bone formation. As decalcification exposed xenogeneic organic matrix components, AAA bone implants provoked the highest inflammatory reaction. When AAA bone samples were implanted in immunosuppressed rats, the inflammatory reaction was suppressed and 94% of the implants showed endochondral bone formation. The chondroinductivity of the bone samples also was tested in vitro using neonatal rat muscle tissue to avoid interference with inflammatory cells and secreted cytokines. In this assay, 68% of AAA bone samples induced chondroneogenesis, while untreated as well as lyophilized bone samples failed to induce any cartilage formation. The results clearly demonstrate that AAA bone has osteoinductive properties. Biomechanical stability of AAA bone implants depends on the degree of demineralization. Thus, they can be prepared in an appropriate manner for different indications in oral and maxillofacial surgery.

Comparison of histomorphometry and 85Sr uptake in induced heterotopic bone in rats

Heterotopic bone formation in the abdominal muscle of 45 male 8-week-old Wistar rats induced by implantation of 5, 10, or 15 mg demineralized bone (DBM) powder was evaluated at 4 weeks by 85Sr uptake of the implants and area histomorphometry of the induced bone. Two indices of 85Sr uptake were calculated: the osteogenic index [(counts/min/mg implant)/(counts/min/mg os ilium)] and an index that we have called the osteoquantum index in which the weight of the implant is disregarded [(counts/min implant)/(counts/min/mg os ilium)]. The osteoquantum index showed a linear relationship to the area of the induced bone with a correlation coefficient (r) of 0.90. Only weak linear relationships were found between the osteogenic index and the area of the bone (r = 0.32) and between the osteogenic index and the osteoquantum index (r = 0.33). The osteoquantum index and the area of the induced bone both increased with increasing mass of implanted DBM, whereas the osteogenic index did not change.

Graft perforations favor osteoinduction. Studies of rabbit cortical grafts sterilized with ethylene oxide

The healing of freeze-dried, ethylene oxide sterilized, segmental, allogenic cortical bone grafts was investigated in 15 rabbits using a 2-cm ulnar diaphyseal defect. Five different groups of bone grafts were evaluated: 1) unperforated undemineralized, 2) perforated undemineralized, 3) unperforated demineralized, 4) perforated demineralized, and 5) perforated demineralized grafts enclosed by silicone rubber (Silastic) sheets. There were 3 animals in each group. At 18 days, the study was terminated, and the implants were examined using radiographs and qualitative histologic preparations. We observed that healing of perforated demineralized bone was superior to unperforated demineralized bone, that undemineralized bone was partially sequestered in reactive lacunae, and that perforations in demineralized bone became centers of osteoinduction. Demineralized bone sterilized with ethylene oxide by this method vigorously formed new bone.

Fresh, frozen, or decalcified bone grafts: a study of early vascularisation and mineralisation of allogeneic and syngeneic bone grafts in rats

The incorporation of syngeneic and allogeneic bone grafts pretreated by freezing or demineralisation was studied in 10 rats. Fresh, decalcified, or frozen cancellous bone of syngeneic or allogeneic origin was transplanted to intramuscular pouches. Revascularisation was evaluated with radioactive microspheres; formation of new bone was assessed by incorporation of strontium, and resorption was assessed by measuring the reduction of graft weight. Three weeks after grafting, fresh syngeneic and allogeneic bone differed significantly in all three variables. Frozen syngeneic bone was revascularised significantly better than frozen allogeneic bone, but there was no difference in formation of new bone or resorption. There were no significant differences between syngeneic and allogeneic decalcified bone in any of the variables studied. We conclude that differences in incorporation between syngeneic and allogeneic bone grafts are reduced by pretreatment with deep-freezing or demineralisation. Both forms of pretreatment affect the incorporation of the grafts.

Effect of platelet derived growth factor on heterotopic bone formation in rats

Platelet derived growth factor (PDGF) and induction of newly woven bone growth were studied in rats. PDGF (20 ng/mL) was administered continuously for 2 weeks via micro-osmotic pumps to 6-mm-long pieces of demineralized rat femur inserted into muscle pouches. Each rat had a control piece of demineralized bone inserted into the contralateral gluteal muscle. The samples were collected after 4 weeks, and wet and ash weight were recorded. Fourteen rats were evaluated. There were no differences as regards wet weights. PDGF increased the ash weights.