Else Marie Pinholt

Bone induction by composite of bioerodible polyorthoester and demineralized bone matrix in rats

A composite of a local, sustained, drug-release system, Alzamer bioerodible polyorthoester, and demineralized bone-matrix (DBM) particles implanted in the abdominal muscle of 89 Wistar rats induced cartilage and bone formation at the same rate as DBM when evaluated histologically and by 85Sr uptake. The composite implant was technically easier to use than DBM alone.

Inhibition of heterotopic osteogenesis in rats by a new bioerodible system for local delivery of indomethacin

A study was done to evaluate the effect of a system for the local delivery of indomethacin on demineralized bone-induced formation of heterotopic bone in the abdominal muscles of rats. Two separate investigations were conducted on a total of forty-eight Wistar rats. In both series, two types of implants were used: polyorthoester and demineralized bone (Group A, the control group) and polyorthoester with 5 per cent indomethacin and demineralized bone (Group B, the experimental group). In the first series, host-tissue responses and osteoinduction were evaluated histologically at two, three, and four weeks after the implantation. In the second series, the formation of bone was quantified on the basis of uptake of 85Sr at four weeks after the implantation. The polyorthoester system for the local delivery of indomethacin significantly inhibited demineralized bone-induced heterotopic formation of bone, as demonstrated by light microscopy and by uptake of 85Sr. The polyorthoester, with or without the drug, caused little tissue reaction and was resorbed almost completely at four weeks.

The effect of a composite of polyorthoester and demineralized bone on the healing of large segmental defects of the radius in rats.

The effect of a composite of demineralized bone mixed with polyorthoester on the healing of large segmental defects in the rat radius was studied. Sixty male Wistar rats were divided into four groups, A through D, and an osteoperiosteal diaphyseal defect of 50 per cent of the length of the bone was made in the right radius of each rat. In Group A, the defect was filled with polyorthoester and demineralized bone; in Group B, demineralized bone; and in Group C, polyorthoester. No material was implanted in the defects in the Group-D rats. The rats were killed fifty days postoperatively. The formation of bone in the defects was quantified with computer-assisted measurements of the area on radiographs. The host-tissue response was evaluated with light microscopy. Defects that had been filled with the composite of polyorthoester and demineralized bone or with demineralized bone alone showed regeneration of bone corresponding to 93.6 and 77.6 per cent of the area of the defect, respectively. Defects that had no implant or that had been filled with polyorthoester alone showed significantly less formation of bone. No inflammation was seen with light microscopy, and only traces of the polyorthoester could be detected in the defects that had been filled with the composite or with polyorthoester alone.

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 pretrea...

The Relationship between Revascularisation and Osteogenesis in Fresh or Demineralised Bone Grafts

Bone formation generally depends on adequate blood flow. Failure of bone grafts has been attributed to delayed revascularisation of the graft. We compared the relationship between revascularisation and osteogenesis, evaluated as entrapment of 141Ce-labelled microspheres and uptake of 85Sr, respectively, in fresh or demineralised syngeneic bone grafts 3 weeks after heterotopic implantation in rats. Whereas a moderately high linear correlation between 85Sr and 141Ce radioactivity was found both in the (intact) host iliac bone (r = 0.75, p = 0.0001) and implanted fresh syngeneic grafts (r = 0.50, p = 0.001), no correlation could be demonstrated in demineralised grafts (r = 0.09, p = 0.6). The results may indicate differences in the mechanisms of vascularisation and osteogenesis in the grafts used fresh or after demineralization but are, at present, difficult to fully explain.