The objective of this study was to evaluate the effects of a complex of beta-tricalcium phosphate (beta-TCP) granules and 3.5% hyaluronate (beta-TCP granules-HY complex) compared with a beta-TCP block, in terms of osteoconductivity and biodegradability, to determine whether this complex would be a good candidate for bone void filler. Both materials were implanted into cavities drilled in rabbit femoral condyles. New bone formation and mineral apposition rate were evaluated to analyze osteoconductivity, whereas residual beta-TCP within the defects and tartrate-resistant acid phosphatase (TRAP) cellular activity were studied for beta-TCP resorption. The results show that both the beta-TCP block and the beta-TCP granules-HY complex support bone ingrowth; however, bioresorption was rapid for beta-TCP granules-HY but weak for beta-TCP block. This biodegradation mechanism was considered to be a cell-mediated disintegration by numerous TRAP-positive giant cells. The time lag between the peak value of TRAP-positive giant cell population and that of new bone formation rate suggests that a coupling-like phenomenon could be occurring in the beta-TCP-filled bone defects. In addition, beta-TCP granules-HY complex, which is an injectable, pastelike material, has similar osteoconductive properties to beta-TCP block. Thus, this complex may be useful as a bone filler in clinical application.
To evaluate the ability of a biphasic construct to repair osteochondral defects in articular cartilage, plugs made of chondrocytes in collagen gel overlying a resorbable porous beta-tricalcium phosphate (TCP) block were implanted into defects in rabbit knees. The repair tissue was evaluated at 8, 12, and 30 weeks. Eight weeks after implantation of the biphasic construct, histologic examination showed hyaline-like cartilage formation that was positive for safranin O and type II collagen. At 12 weeks, most of the beta-TCP was replaced by bone, with a small amount remaining in the underlying cartilage. In the cell-seeded layer, the newly formed middle and deep cartilage adjacent to the subchondral bone stained with safranin O, but no staining was observed in the superficial layer. In addition, cell morphology was distinctly different from the deep levels of the reparative cartilage, with hypertrophic cells at the bottom of the cartilaginous layer. At 30 weeks, beta-TCP had completely resorbed and a tidemark was observed in some areas. In contrast, controls (defects filled with a beta-TCP block alone) showed no cartilage formation but instead had subchondral bone formation. These findings indicate that beta-TCP-supported chondrocytes in collagen gel can partially repair isolated articular cartilage osteochondral defects.
Most of the implanted porous beta-tricalcium phosphate (beta-TCP) can be resorbed. However, beta-TCP block with 75% porosity is inadequate for weight-bearing sites until bone incorporation occurs. Thus, the authors have recently developed beta-TCP block with 60% porosity, which is approximately sevenfold greater in terms of compressive strength than that of beta-TCP with 75% porosity. The authors investigated bone formation and resorption of beta-TCP after implantation in patients of beta-TCP blocks with two different porosities. From May 2003 to November 2004, medial opening high tibial osteotomy was performed in 25 patients with a mean age of 66 years. The opened defect was fixed with a Puddu plate. Then 6-8 cm(3) of beta-TCP block with 75% porosity was used to fill the cancellous bone defect, except on the medial side where 2.83-3.18 cm(3) of wedge-shaped beta-TCP block with 60% porosity was implanted. At least 2 years after surgery, the 25 patients had no correction loss, and bone formation was noted in all cases. Complete or nearly complete resorption of beta-TCP with 60 and 75% porosity was obtained within 3.5 years. Thirteen biopsy samples obtained from the 60% porosity implantation sites showed good lamellar bone formation, and the percentage of beta-TCP remaining relative to the newly formed bone plus beta-TCP ranged from 0.3 to 14.5%, with a mean of 6.7%. The authors suspect that mechanical stress loading to the medial side of the tibia facilitated bone formation and resorption of beta-TCP with 60% porosity.
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