Kinetic study of bone ingrowth and ceramic resorption associated with the implantation of different injectable calcium-phosphate bone substitutes

This study investigated the in vivo performance of two composite injectable bone substitutes (IBS), each with different calcium-phosphate particles gr anulometries [40-80 (IBS 40-80) and 200-500 mu m (IBS 200-500)]. These biom aterials were obtained by associating a biphasic calcium-phosphate (BCP) ce ramic mineral phase with a 3% aqueous solution of a cellulosic polymer (hyd roxy-propyl-methylcellulose). Both materials were injected for periods of 2 , 3, 8, or 12 weeks into bone defects at the distal end of rabbit femurs. Q uantitative results on new bone formation, BCP resorption, and staining for tartrate-resistant acid phosphatase (TRAP) activity were studied for stati stical purposes. Measurements with scanning electron microscopy and image a nalysis showed that the final rates of newly formed bone were similar for b oth tested IBS after 12 weeks of implantation. Bone colonization occurred m ore extensively during early implantation times for IBS 40-80 than for IBS 200-500. For the latter, BCP degradation occurred regularly throughout the implantation period, whereas it was very intensive during the first 2 weeks for IBS 40-80. Positive TRAP-stained degradation cells were significantly more numerous for IBS 40-80 than for IBS 200-500 regardless of implantation time. With the granulometry of either mineral phase, both tested IBS suppo rted extensive bone colonization, which was greater than that previously re ported for an equivalent block of macroporous DCP. The resorption-bone subs titution process seemed to occur earlier and faster for IBS 40-80 than for IBS 200-500. Both tested IBS expressed similar biological efficiency, with conserved ill vivo bioactivity and bone-filling ability. (C) 1999 John Wile y & Sons, Inc.