Sunday, November 3, 2002
372

A One-Year Study of Hydroxyapatite Derivatives in Reconstruction of Cranial Defects: Can the Ideal Implant be Bioengineered?

Arun K. Gosain, MD, Lianshen Song, DDS, Paul A. Riordan, Marco T. Amarante, MD, Behrooz Kalantarian, MD, Paul G. Nagy, PhD, Charles R. Wilson, PhD, Jeffrey M. Toth, PhD, and Brian McIntyre, PhD.

HYPOTHESIS: Introducing macropores within hydroxyapatite cement paste will optimize bone replacement. METHODS: Hydroxyapatite cement paste was combined with beta-tricalcium phosphate (TCP), a compound which rapidly resorbs to leave macropores in the HA cement paste. Five calvarial defects 16.8 mm in diameter were made in each of 10 adult sheep. Three defects were filled with cement paste (CP) composites of HA and TCP as follows: 1) 100% HA-CP, 2) 60% HA-CP, 3) 20% HA-CP. One defect was filled with a ceramic (CER) composite containing 60% HA-CER, and the fifth defect remained unfilled. One-year post-implantation the volume of all biomaterials was determined from CT scan, and porosity and bone ingrowth were determined using backscatter electron microscopy. RESULTS: There was no significant change in volume of the pure HA cement paste and the 20% HA-CP implants one year post-implantation, whereas the volumes of both 60% HA composites increased significantly one year post-implantation (p<.02). Mean bone replacement in the 20% HA-CP implants was 28.5%, which was significantly greater than that in all remaining implants (p<.01). There was no significant difference in bone replacement between CP and CER implants containing 60% HA, with mean bone replacement of 11.2% and 13.6%, respectively. Mean bone replacement in the pure HA-CP implants was 4.8%, which was significantly less than that in all remaining biomaterials (p<.05). There was an inverse correlation between the concentration of HA and the amount of bone replacement for each cement paste implant tested (p<.01). CONCLUSIONS: Implants which contain macropores (i.e., ceramic derivatives of HA) demonstrate consistent bone replacement, whereas those which contain micropores (i.e., cement paste derivatives of HA) demonstrate minimal bone replacement. The present study demonstrates that cement paste derivatives of HA can be bioengineered to maximize bone replacement by titrating the composition of a rapidly resorbing component such as TCP.
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