An animal study was performed to assess whether hydroxyapatite could induce bone ingrowth to close gaps at the bone – implant junction in a weight-bearing model. 14 titanium alloy plates, 2 x 0,5 X 0,1 cm, sprayed on one flat side with HA and left as bare metal on the other, concave surface, were inserted into the distal metaphysis of the femur of 14New Zealand adult rabbits, perpen-diculary to the diaphyseal long axis . The sections of the femur were performed through the plate and were observed by S.E.M. During the first week, we found medullary hyper-plasia and differentiation of osteogenic cells producing osteoid. By the 2nd-3rd week, immature bone formed from the endosteum towards the plate, leading to the filling of the gap with the HA – coated surface of the plate. Between the 4th and the 8th week the remodeling process occurred with formation of lamellar bone. At 12 weeks bone – ingrowth appeared to be greater in areas of proximity to the endosteal wall, especially when the plate was oriented in such a way that acute angles with the endosteum were present. Ha –coatings were degraded by a process of creeping substitution. The gap between bone and non-coated surface was not filled at the end of the experiment. At six months the crystalline part of the coating appeared as separated grains (for dissolution of the amorphous phase). This degradation is responsible for the release of calcium-phosphate debris. The present study shows great evidence of HA osteo-conductivity. The physico-chemical similarity between artificial HA and mineralized bone probably explains that the mechanism of HA resorption is similar to that of bone resorption. The remodeling cycles of resorption and new formation give as a final result the deposition of bone tissue onto the metallic alloy.
It is well known that articular cartilage in adults has a limited capacity for self-repair. Numerous methods have been devised to augument its natural healing response, but these methods generally lead to filling of the defect with fibrous tissue or fibrocartilage, which lacks the mechanical characteristics of articular cartilage and fails with time. Tissue engineering combines aspects of cell biology, engineering, material science and surgery to generate new functional tissue and provides an important approach to the repair of articular cartilage lesions and, ultimately, functional success. The purpose of our study was to perform experimental resurfacing of articular cartilage in 18 sheep using different techniques: before implantation in all sheep a full-thickness chondral lesion of medial femoral condyle was created; subsequently, autologous chondrocytes seeded into the matrix were implantd into five sheep; a periosteum flap was implanted in five sheep; and, as source of growth factors, adipocytes by vascular peduncle of Hoffa tissue were implanted in five sheep. The reparative tissue of the chondral lesion was compared with uninjured contralateral knee. The results present the bonding between implantation tissue and host tissue, preservation of phenotypic stability of chondrocytes culture, standard dosage of growth factor secreted by adipocytes and characterisation of the histological properties of reparative tissue, comparing different surgical techniques.
