Demineralized bone matrix (DBM) is a natural, collagen-based, well-established osteoinductive biomaterial. Nevertheless, there are conflicting reports on the efficacy of this product. The purpose of this study was to evaluate whether DBM collagen structure is affected by particle size and can influence DBM osteoinductivity.

Sheep cortical bone was ground and particles were divided in three fractions with different sizes, defined as large (L, 1–2 mm), medium (M, 0.5–1 mm), and small (S, < 0.5 mm). After demineralization, the three DBM samples were characterized by DTA analysis, XRD, ICP-OES, and FTIR. Data clearly showed a particle size-dependent alteration in collagen structure, with DBM-M being altered but not as much as DBM-S. The in vivo study showed that only DBM-M was able to induce new bone formation in a subcutaneous ectopic mouse model. When sheep MSC were seeded onto DBM particles before implantation, all DBM particles were able to induce new bone formation with the best incidence for DBM-M and DBM-S. Gene expression analysis performed on recovered implants supports the histological results and underlines the supportive role of MSC in DBM osteoinduction through the regulation of host cells. In conclusion, our results show a relation between DBM particle size, structural modification of the collagen and in vivo osteoinductivity. The medium particles represent a good compromise between no modification (largest particles) and excessive modification (smallest particles) of collagen structure, yielding highest osteoinduction. We believe that these results can guide researchers to use DBM particles of 0.5–1 mm size range in applications aimed at inducing new bone formation, obtaining results more comparable and reliable among different research groups. Furthermore, we suggest to carefully analyze the structure of the collagen when a collagen-based biomaterial is used alone or in association with cells to induce new bone formation.

Summary

The BMP-2 content and bone forming potential of 2 leading allograft products (OsteoAMP® and Osteocel® Plus) was tested across 3 commercially available lots. Surprisingly, there was no BMP-2 content associated with the cells contained within Osteocel® Plus. OsteoAMP® contained greater than 1000 times the overall BMP-2 content than Osteocel® Plus. Correspondingly, Osteocel® Plus did not form new bone at any timepoint in the 12 week in vivo study while OsteoAMP® had increasing new bone formation at each sequential timepoint. Interestingly, the highest cellularity of Osteocel® Plus was just prior to implant at t₀, decreasing at each timepoint, decreasing further at the terminal endpoint of the study at 12 weeks (82% of cells had died or migrated). Conversely, the cellularity of OsteoAMP® increased at each timepoint.

The osteoinductive properties of demineralised bone matrix have been demonstrated in animal studies. However, its therapeutic efficacy has yet to be proven in humans. The clinical properties of AlloMatrix, an injectable calcium-based demineralised bone matrix allograft, were studied in a prospective randomised study of 50 patients with an isolated unstable distal radial fracture treated by reduction and Kirschner (K-) wire fixation. A total of 24 patients were randomised to the graft group (13 men and 11 women, mean age 42.3 years (20 to 62)) and 26 to the no graft group (8 men and 18 women, mean age 45.0 years (17 to 69)).

At one, three, six and nine weeks, and six and 12 months post-operatively, patients underwent radiological evaluation, assessments for range of movement, grip and pinch strength, and also completed the Disabilities of Arm, Shoulder and Hand questionnaire. At one and six weeks and one year post-operatively, bone mineral density evaluations of both wrists were performed.

No significant difference in wrist function and speed of recovery, rate of union, complications or bone mineral density was found between the two groups. The operating time was significantly higher in the graft group (p = 0.004). Radiologically, the reduction parameters remained similar in the two groups and all AlloMatrix extraosseous leakages disappeared after nine weeks.

This prospective randomised controlled trial did not demonstrate a beneficial effect of AlloMatrix demineralised bone matrix in the treatment of this category of distal radial fractures treated by K-wire fixation.

Cite this article: Bone Joint J 2013;95-B:1514–20.

Introduction

The concept of “bone graft expanders” has been popularised to increase the volume and biological activity of the implanted Material.

The purpose of this study was to understand the effects of terminal sterilisation and residual calcium on human demineralised bone matrix (DBM) in ectopic bone formation in nude rat.

The intramuscular implantation of human DBM prepared by the Queensland Bone Bank (QBB) from four donors into eight male athymic rats was used to assess osteoinductivity. The DBM contained different levels of residual calcium and treated with or without gamma-irradiation at 11kGy. At 6 weeks post-implantation, calcium deposition was assessed by manual palpitation and radiological imaging. Tissue morphology and cellular interactions was analysed using various histological staining methods whilst protein expression of anabolic and catabolic biomarkers were examined through immunohistochemistry. All results were then analysed in qualitative, semi-quantitative and quantitative manners and tested for statistical significance.

Bone formation was observed in all specimens at the gross level. This was confirmed by histology which revealed bony capsules surrounded by soft tissue in the muscle pockets and differences in tissue components. On a cellular level, variations in osteoclast expression were found between the two groups as well as amongst individual donors through statistical analysis which resulted in an imbalance of the expression of anabolic and catabolic markers. Furthermore, a positive relationship between residual calcium and new bone formation in gamma irradiated DBM samples was found. To date, no studies have compared the effect of calcium in gamma irradiated DBM.

Our results suggest that gamma irradiation even at low doses and residual calcium may affect new bone formation. Taken together, this study stresses the importance of selecting ideal conditions for graft processing and the need to identify an optimal level of irradiation and remaining calcium levels that confers a balance between osteoinductivity and sterility.

Introduction: Different grafting materials for the filling of large bony defects are used in clinic. Aim of the present study was the comparative analyses of different bony grafting materials concerning their growth factor composition and osteoinductivity in vitro. Materials & Methods: Different allograft preparations from the tissue bank of the Charité and two commercial demineralized bone matrices (DBM; DBX putty and Allomatrix) were analyzed. Using ELISA-kits following growth factors were quantified: VEGF, IGF-I, FGFa/b, TGF-β1, BMP-2/4, PDGF. Osteoinductivity was investigated by the induction of alkaline phosphatase activity in C2C12-cells. Results: BMP-2 had the highest quantity within the different materials without differences between the materials. Differences in the quantity of the other growth factors were found between the investigated materials but also a high variability between the different batches was observable. The investigated materials showed individual differences which are donor related concerning their osteoinductive potential. A significant enhancement of osteogenic differentiation (AP) was seen for the two commercial DBM-products. For PES processed spongiosa from the tissue bank, 2 of the 5 materials had a negative effect on the AP-activity in the first incubation period but no effect in the second incubation period. Discussion: The results of the present study revealed, that the different investigated grafting materials contain growth factors important for bone regeneration and an osteoinductive potential of the DBMs. A high batch/donor related variability, however, was detectable in both analysis. Important for the use in vivo is beside the osteoinductivity also the osteoconductivity and further comparative studies are necessary

Bone allografts can be used in any kind of surgery involving bone from minor defects to major bone loss after tumour resection. This review describes the various types of bone grafts and the current knowledge on bone allografts, from procurement and preparation to implantation. The surgical conditions for optimising the incorporation of bone are outlined, and surgeon expectations from a bone allograft discussed.