Hydroxyapatite-ceramic for juxta-articular implantation

Abstract

The histocompatibility of hydroxyapatite-ceramic (HAC) has been proven extensively. For the reconstruction of juxta-articular cancellous bone defects with this synthetic material, the mechanical properties of the HAC-bone regeneration complex needed to be investigated. In order not to alter the specific ability of the articular structures to distribute and absorb loading stress, the physiological force-transmitting performance of the subchondral zone must be achieved by filling the defect within HAC. This study deals with the influence of a physiological load on the remodelling within HAC-filled subchondral bone defects. As orientation is the important factor affecting the physical properties of hard tissue, we show the morphological aspect of functional adaptation of the hydroxyapatite-bone compound determined by the orientation of the bone collagen fibres. By biomechanical methods, the elastic properties of the resulting ceramo-osseous regeneration complex were tested. Reproducible subchondral bone defects were prepared in medial femoral condyles of rabbits, leaving a 0.5 mm coplanar layer of bone and cartilage. The defects were filled with granules of HAC. Polarizing microscopy revealed the dynamical aspect of the bony integration of the material and the remodelling process under physiological locomotion. It showed a rapid ongrowth of collagen fibres on the ceramic surface. By its increasing orientation to domains from woven texture to economical trabecular architecture, the load-bearing facility is documented. Indenting the articular surface on an impressive force testing machine 18 months after HAC implantation proved the equal elastic response of the ceramo-osseous regeneration complex with the overlying structures in comparison with the integrity of not-operated femoral condyles. When integrated by bone, HAC fulfils in our dynamic animal model physiological demands even in large bone defects close to articular surfaces.