The Journal of Bone and Joint Surgery, Vol 73, Issue 5 692-703, Copyright © 1991 by Journal of Bone and Joint Surgery, Inc
The morphogenesis of bone in replicas of porous hydroxyapatite obtained from conversion of calcium carbonate exoskeletons of coral
U Ripamonti
South African Medical Research Council, Johannesburg.
The morphogenesis of bone in a porous hydroxyapatite substratum was studied
after intramuscular implantation in adult primates. Replicas of porous
hydroxyapatite that had been obtained after hydrothermal conversion of the
calcium carbonate exoskeleton of coral (genus Goniopora) were implanted
intramuscularly in twenty-four adult male baboons (Papio ursinus). Serial
sections from specimens that had been harvested at three, six, and nine
months showed that initially the formation of fibrous connective tissue was
characterized by a prominent vascular component and by condensations of
collagen fibers assembled at the interface of the hydroxyapatite. The
morphogenesis of bone was intimately associated with the differentiation of
the connective-tissue condensations. Bone formed without an intervening
endochondral phase. Although the amount of bone varied considerably, in
several specimens extensive bone developed, filling large portions of the
porous spaces and culminating in total penetration by bone within the
implants. The mean volume fraction composition of the specimens was 20.8
+/- 1.0 per cent (mean and standard error) for bone, 17.3 +/- 1.7 per cent
for connective-tissue condensation, 31.9 +/- 1.0 per cent for fibrovascular
tissue, 6.4 +/- 0.6 per cent for bone marrow, and 34.6 +/- 0.5 per cent for
the hydroxyapatite framework. The amount of bone and marrow increased at
each time-period, and the hydroxyapatite framework was significantly
reduced between six and nine months. This indicated a moderate
biodegradation over time, which was possibly a result of incomplete
conversion of carbonate to hydroxyapatite. Linear regression analysis
showed a negative correlation between the hydroxyapatite framework and the
magnitude of bone formation within the porosities of the hydroxyapatite (p
= 0.0001). Biochemical coating of the hydroxyapatite substratum with an
allogeneic fibrin-fibronectin protein concentrate prepared from baboon
plasma did not significantly increase the amount of bone formation within
the porous spaces. The hydroxyapatite substratum may have functioned as a
solid-phase domain for anchorage of bone morphogenetic proteins.
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