Enhancement of tendon-bone interface healing and graft maturation with cylindrical titanium-web (TW) in a miniature swine anterior cruciate ligament reconstruction model: histological and collagen-based analysis.

BACKGROUND: Tendon-bone interface healing and ligamentization of the graft in anterior cruciate ligament (ACL) reconstruction with autografts are important factors affecting treatment outcome. This study aimed to investigate the effectiveness of a cylindrical titanium-web (TW) in tendon-bone interface healing and graft maturation in ACL reconstruction. METHODS: Fourteen mature female CLAWN miniature swine underwent bilateral ACL reconstructions with patellar tendon (PT) autografts. In one limb, the TW/tendon complex was placed into the proximal side of the tibial tunnel. Only the graft was transplanted into the tunnel in the control limb. The proximal side of the graft was sutured into the stump of the native ACL and the distal end was stapled to the tibia. The animals were euthanized at 4 and 15 weeks postoperatively, for histological and biochemical analyses. RESULTS: Microscopic images in TW limbs showed that ingrowth of tendon-like tissue and mineralized bone tissue into the TW connected the bone and the tendon directly. In contrast, fibrous tissue intervened between the bone and tendon in the control limbs. The total amount of collagen cross-links (which defines the strength of collagen fibers) and the maturation of collagen cross-links in TW tendons were significantly higher (p < 0.05) than those of control limbs. There was no significant difference in the ratio of dihydroxy-lysinonorleucine to hydroxy-lysinonorleucine (an indicator of tissue specific collagen maturation) between TW tendons and that of the native PT. CONCLUSIONS: TW promoted the maturation and formation of collagen cross-links in the grafted tendon while maintaining the cross-links pattern of native tendon collagen, and enabled direct binding of tendon to bone.

Local application of alendronate controls bone formation and ß-tricalcium phosphate resorption induced by recombinant human bone morphogenetic protein-2.

This study examined the ability of local alendronate (ALN) administration to control ß-tricalcium phosphate (ß-TCP) resorption as well as the induction of bone formation by recombinant human bone morphogenetic protein-2 (rhBMP-2). A 15-mm critical-sized bone defect was created in the diaphysis of rabbit ulnae. Nine female rabbits (4 to 5 months-old) were divided into 3 groups. Group 1 (n = 6 ulnae) animals received implants consisting of ß-TCP granules and 25 µg of rhBMP-2 in 6.5% collagen gel. Group 2 (6 ulnae) and Group 3 (6 ulnae) animals received the same implants, but with 10-6 M and 10-3 M ALN-treated TCP granules, respectively. Two weeks postsurgery, tartrate-resistant acid phosphatase-positive cell counts, new bone formation, and residual ß-TCP were evaluated. This study showed that a high dose of ALN strongly reduced osteoclastic resorption of ß-TCP induced by rhBMP-2, resulting in decreased bone formation. In contrast, a low dose of ALN slightly reduced the bone resorptive effect but increased bone formation. These results suggest that osteoclast-mediated resorption plays an important role in bone formation and a coupling-like phenomenon could occur in the ß-TCP-implanted area, and that administration of a low dose of ALN may solve clinical bone resorptive problems induced by rhBMP-2.

Effects of micro-porosity and local BMP-2 administration on bioresorption of ß-TCP and new bone formation.

BACKGROUND: It has been reported that the microporous structure of calcium phosphate (CaP) ceramics is important to osteoconduction. Bone morphogenetic protein-2 (BMP-2) has been shown to be a promising alternative to bone grafting and a therapeutic agent promoting bone regeneration when delivered locally. The aim of this study was to evaluate the effects of micro-porosity within beta-tricalcium phosphate (ß-TCP) cylinders and local BMP-2 administration on ß-TCP resorption and new bone formation. METHODS: Bilateral cylindrical bone defects were created in rabbit distal femora, and the defects were filled with ß-TCP. Rabbits were divided into 3 groups; defects were filled with a ß-TCP cylinder with a total of approximately 60% porosity (Group A: 13.4% micro- and 46.9% macropore, Group B: 38.5% micro- and 20.3% macropore, Group C: the same micro- and macro-porosity as in group B supplemented with BMP-2). Rabbits were sacrificed 4, 8, 12, and 24 weeks postoperatively. RESULTS: The number of TRAP-positive cells and new bone formation in group B were significantly greater than those in group A at every period. The amount of residual ß-TCP in group C was less than that in group B at all time periods, resulting in significantly more new bone formation in group C at 8 and 12 weeks. The number of TRAP-positive cells in group C was maximum at 4 weeks. CONCLUSIONS: These results suggest that the amount of submicron microporous structure and local BMP-2 administration accelerated both osteoclastic resorption of ß-TCP and new bone formation, probably through a coupling-like phenomenon between resorption and new bone formation.

Effects of alendronate on bone formation and osteoclastic resorption after implantation of beta-tricalcium phosphate.

The aim of this study was to determine the effects of alendronate (ALN) on osteoclastic resorption of beta-tricalcium phosphate (beta-TCP) and bone formation. beta-TCP blocks of 75% porosity, with or without ALN treatment, were implanted into cavities drilled in rabbit femoral condyles. New bone formation, residual amount of beta-TCP, and the number of tartrate-resistant acid phosphatase-positive cells were evaluated 2 weeks after surgery. The results show that local application of ALN at a concentration of 10(-2) to 10(-6)M reduced the number of osteoclasts on the surface of beta-TCP. New bone formation was also inhibited by ALN in a dose-dependent manner. Thus, inhibition of osteoclast formation resulted in reduced beta-TCP resorption and bone formation. These results suggest that osteoclast-mediated resorption plays an important role in bone formation and a coupling-like phenomenon could occur in beta-TCP-filled bone defects.

Electron microscopic study on bone formation and bioresorption after implantation of beta-tricalcium phosphate in rabbit models.

BACKGROUND: The role of bone formation and bioresorption in an early stage after implantation of beta-tricalcium phosphate (beta-TCP) was investigated using scanning and transmission electron microscopy (SEM, TEM). METHODS: The ceramic beta-TCP cylinders were implanted into cavities drilled in the femoral condyles of eight NZW rabbits. Four of the rabbits were sacrificed at 2 weeks and four at 4 weeks after implantation, respectively. The femoral condyles were excised to prepare the specimens for SEM and TEM. RESULTS: SEM showed giant cells of more than 20 mum in diameter were observed on the surface of beta-TCP at 2 weeks after implantation. TEM demonstrated that collagen fibrils secreted from the monocytic cells invaded beta-TCP micropores at 2 weeks. Multinucleated giant cells (MNGCs) were in contact with the surface of beta-TCP at 2 weeks. Some of them had a ruffled border (RB) at the cell-substrate interface, characteristic of osteoclasts. CONCLUSIONS: These findings suggest that cell-mediated disintegration by osteoclasts played a role in the bioresorption of beta-TCP at an early stage after implantation. In addition, the micropores of beta-TCP ceramic may provide an environment for collagen formation, leading to the deposition of apatite crystals. Therefore, the micropores facilitate bone ingrowth as well as ceramic resorption.

Bone formation and resorption in patients after implantation of beta-tricalcium phosphate blocks with 60% and 75% porosity in opening-wedge high tibial osteotomy.

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.