Response of articular cartilage and subchondral bone to internal fixation devices made of poly-L-lactide: a histomorphometric and microradiographic study on rabbits

To study the tissue response of articular cartilage and subchondral bone to biodegradable fixation devices, pins and rods made of poly-L-lactide with a fibers-in-matrix texture were implanted through the articular surface of the intercondylar portion of the distal rabbit femur. The initial raw material viscosity average molecular weight of the polymer was 660,000. One pin or screw was implanted per animal. The pins were cylindrical and measured 4.5 mm in transverse diameter. The screws had a core diameter of 3.2 mm and an outer diameter of 4.5 mm. At insertion, the implants were cut flush with the articular surface. After follow-up times of 36 and 48 weeks, the specimens were examined histomorphometrically and microradiographically. The intact contralateral femur served as a control for comparison. No signs of erosion or degradation of the polymer could be seen in the specimens. A brim of reparative tissue was formed at the entrance of the implant channel. The width of the reparative tissue from the tissue-implant boundary towards the center of the entrance hole varied greatly between the specimens, from 30 to 950 microm. In most specimens this bridging tissue consisted of undifferentiated mesenchymal tissue. Only two out of 24 specimens showed a near-normal metachromatic toluidine-blue staining of the matrix. Degenerative chondrocyte clustering occurred in the pre-existing cartilage within a 400 microm wide zone from the tissue-implant interface into the recipient tissues. Some new-bone formation was seen to envelop the implant in all specimens, but the fractional osteoid formation surface of the trabeculae showed a value significantly higher than that of the intact control side only in the screw-implanted 36-week specimens. Because of the long degradation time of poly-L-lactide, the restoration process of the articular cartilage was slow, and with regard to the quality and quantity of the reparative tissue, very variable. Large implants made of poly-L-lactide may not be suitable for insertion through intra-articular surfaces.     

Composite poly(lactide)/hydroxylapatite screws for fixation of osteochondral osteotomies. A morphometric,histologic and radiographic study in sheep

The aim of this study was to evaluate the healing of an osteochondral fragment created in the distal sheep femur in response to fixation with a biodegradable polylactide/hydroxylapatite composite screw. Poly(L-lactide) screws were used for comparison. At follow-up times of 4 and 8 weeks, the specimens were examined with standard radiography and computed tomography, as well as with macro- and micro-histomorphometry. The intact contralateral femur served as a control. Only minimal signs of degradation of the polymer could be seen in the histologic specimens. At 8 weeks, nearly all osteotomies had healed completely and an association between implant type and delayed osteotomy healing was found. The width of the repair tissue at the tissue-implant interface was 250 +/- 48 microm, representing a clear transition zone of newly formed trabecular bone separating the implant from the surrounding plexiform bone. This study showed that large polylactide implants which are buffered with hydroxylapatite show benign tissue responses and good implant osteointegration. The osteotomy healing in a weight-bearing osteochondral fragment model in sheep utilizing a composite polylactide/hydroxylapatite screw was equivalent to a similar polylactide screw implant, indicating that hydroxylapatite-buffered screw implants could be used for similar indications in current clinical use.     

Composite resorbable polymer/hydroxylapatite composite screws for fixation of osteochondral osteotomies

The aim of this study was to evaluate biomechanically the healing of an osteochondral fragment created in the distal sheep femur in response to fixation with a resorbable composite screw made of polylactide and hydroxylapatite. Pure poly(L-lactide) screws were used for comparison. At follow-up times of 4 or 8 weeks, specimens were examined with standard radiography, biomechanics, and histology. The intact contralateral femur served as a control. Only minimal signs of polymer degradation were seen in the histologic specimens. At 8 weeks, most osteotomies had healed completely and there was no difference in compressive strength and elastic modulus of cylindrical cores between the two types of biodegradable implants used. The width of the repair tissue at the tissue-implant interface was 250+/-50 micro m representing a clear transition zone of newly formed trabecular bone separating the implant from the surrounding plexiform bone. We conclude that relatively large polylactide implants, blended with hydroxyapatite, are capable of fixing an osteochondral fragment in an animal model. Biomechanical data assessing the quality of the bone formed at the osteotomy sites were found to be equivalent when compared to the control poly(L-lactide) implants of similar design and size. In addition, hydroxylapatite composite implants showed benign tissue responses and good implant osteointegration. Results suggest that hydroxylapatite composite screw implants can be used for similar indications as pure poly(L-lactide) implants in current clinical use.     

Response of articular cartilage and subchondral bone to internal fixation devices made of poly- -lactide: a histomorphometric and microradiographic study on rabbits

To study the tissue response of articular cartilage and subchondral bone to biodegradable fixation devices, pins and rods made of poly- -lactide with a fibers-in-matrix texture were implanted through the articular surface of the intercondylar portion of the distal rabbit femur. The initial raw material viscosity average molecular weight of the polymer was 660,000. One pin or screw was implanted per animal. The pins were cylindrical and measured 4.5 mm in transverse diameter. The screws had a core diameter of 3.2 mm and an outer diameter of 4.5 mm. At insertion, the implants were cut flush with the articular surface. After follow-up times of 36 and 48 weeks, the specimens were examined histomorphometrically and microradiographically. The intact contralateral femur served as a control for comparison. No signs of erosion or degradation of the polymer could be seen in the specimens. A brim of reparative tissue was formed at the entrance of the implant channel. The width of the reparative tissue from the tissue–implant boundary towards the center of the entrance hole varied greatly between the specimens, from 30 to 950 μm. In most specimens this bridging tissue consisted of undifferentiated mesenchymal tissue. Only two out of 24 specimens showed a near-normal metachromatic toluidine-blue staining of the matrix. Degenerative chondrocyte clustering occurred in the pre-existing cartilage within a 400 μm wide zone from the tissue–implant interface into the recipient tissues. Some new-bone formation was seen to envelop the implant in all specimens, but the fractional osteoid formation surface of the trabeculae showed a value significantly higher than that of the intact control side only in the screw-implanted 36-week specimens. Because of the long degradation time of poly- -lactide, the restoration process of the articular cartilage was slow, and with regard to the quality and quantity of the reparative tissue, very variable. Large implants made of poly- -lactide may not be suitable for insertion through intra-articular surfaces.     

Composite poly(lactide)/hydroxylapatite screws for fixation of osteochondral osteotomies. A morphometric,histologic and radiographic study in sheep

The aim of this study was to evaluate the healing of an osteochondral fragment created in the distal sheep femur in response to fixation with a biodegradable polylactide/hydroxylapatite composite screw. Poly(L-lactide) screws were used for comparison. At follow-up times of 4 and 8 weeks, the specimens were examined with standard radiography and computed tomography, as well as with macro- and micro-histomorphometry. The intact contralateral femur served as a control. Only minimal signs of degradation of the polymer could be seen in the histologic specimens. At 8 weeks, nearly all osteotomies had healed completely and an association between implant type and delayed osteotomy healing was found. The width of the repair tissue at the tissue–implant interface was 250 ± 48 μm, representing a clear transition zone of newly formed trabecular bone separating the implant from the surrounding plexiform bone. This study showed that large polylactide implants which are buffered with hydroxylapatite show benign tissue responses and good implant osteointegration. The osteotomy healing in a weight-bearing osteochondral fragment model in sheep utilizing a composite polylactide/hydroxylapatite screw was equivalent to a similar polylactide screw implant, indicating that hydroxylapatite-buffered screw implants could be used for similar indications in current clinical use.     

The restoration of the articular surfaces overlying Replamineform porous biomaterials.

Replamineform porous implants (4 mm X 4 mm diameter) were placed into full-thickness cartilage and bone defects of the weight-bearing surface of the lateral femoral condyles of adult male white rabbits. These were analyzed at 1 day, 1 week, 6 weeks, 3 months, and 6 months for 1) ingrowth of tissue within the implants and 2) restoration of the articular surface overlying them. Appropriate unfilled, but similar, control defects were also studied. Mineralized bone was seen within the substance of both the TiO2 and hydroxyapatite implants at 1 week; this extremely rapid response was present in every specimen studied and was not seen with alphaAl2O3 or control animals. With the passage of time, maturation of this bone ingrowth occurred so that by 3 months, they were all incorporated into the surrounding bone. Only the hydroxyapatite implants showed consistent regenerative healing of hyaline articular cartilage from the margins of the defects with the passage of time; this occurred whenever the subchondral bone adjacent to the defect proliferated in a "creeping" fashion over the articular aspect of the implant, and the undamaged cartilage then followed it. Fibrocartilage, and not hyaline cartilage, formed the articular surface over the TiO2 and alphaAl2O3 implants and in the controls.     

Articular cartilage repair in rabbits by using suspensions of allogenic chondrocytes in alginate

The feasibility of allogenic implants of chondrocytes in alginate gels was tested for the reconstruction in vivo of artificially full-thickness-damaged articular rabbit cartilage. The suspensions of chondrocytes in alginate were gelled by the addition of calcium chloride solution directly into the defects giving in situ a construct perfectly inserted and adherent to the subchondral bone and to the walls of intact cartilage. The tissue repair was controlled at 1, 2, 4 and 6 months after the implant by NMR microscopy, synchrotron radiation induced X-ray emission to map the sulfur of glycosaminoglycans and by histochemistry. Practically a complete repair of the defect was observed 4-6 months from the implant of the chondrocytes with the recovery of a normal tissue structure. Controls in which Ca-alginate alone was implanted developed only a fibrous cartilage.     

Integration of metallic endoprotheses in dog femur studied by near-infrared Fourier-transform Raman microscopy.

The integration of hydroxyapatite-coated implants in dog femur was studied by near-infrared Fourier-transform Raman microscopy. Raman spectra were taken in lateral scans in step widths of 10-40 microm from the implant surface up to a distance of 320 microm into the bone tissue. The spectra were subjected to a component analysis for the quantitative determination of the protein and the inorganic components. This quantitative analysis is shown to be more reliable than conventional band fitting procedures and allows, for the first time, the quantitative distinction between the hydroxyapatite form of mature bone tissue and synthetic hydroxyapatite introduced by the implant coating. It is demonstrated that full mineralization of the ongrowing bone is not achieved after 6 months. In contrast, after a residence time of 18 months in the body, the Raman spectra reveal a complete calcification of the new bone tissue as indicated by content of biological hydroxyapatite that is the same as in mature bone tissue throughout the whole implant/bone interface. On the other hand, the content of synthetic hydroxyapatite is strongly reduced in the sample prepared after eighteen months implantation whereas for the shorter implantation time. substantial contributions of synthetic hydroxyapatite are found even at positions beyond the thickness of the implant coating. These results indicate that the coating material is actively involved in the mineralization of ongrowing bone. Possible mechanisms for the underlying transport processes in the implant/bone interface are discussed.     

多孔羟基磷灰石陶瓷诱导成骨的作用

多孔羟基磷灰石陶瓷种植体埋植于狗背部肌肉内,分别于植入后1、2、4和8月处死动物,取出种植体,将其固定,脱钙,切片、HE染色,在光镜下作组织形态学观察发现:一月的种植体孔隙内充满了血管丰富的结缔组织;二、四和八月的种植体孔隙内有较多量的新骨组织形成,种植体固有完整的纤维结缔组织包膜。本研究从组织形态学说明了多孔羟基磷灰石陶瓷具有诱导骨形成的能力。     

Mechanical and histological response of carbon fibre pads implanted in the rabbit patella

Small carbon fibre pads (3 mm in diameter) were implanted into rabbit patellae to ascertain the relationship between their mechanical and histological responses. After 3 months a highly vascularized collagenous matrix is formed within and around the implant securely anchored to the bone and providing a continuous layer to the articular surface. Mechanically, the resulting repair is much more compliant than the original articular cartilage/bone structure since the subchondral bone plate is not present within the implant; it also provides a functioning congruent surface with no evidence of fragmentation. This may be attractive in the long term by decreasing friction and the subsequent degeneration and wear commonly seen in fibrillated, disrupted articular cartilage.     

Transmission electron microscopic visualization of the degradation and phagocytosis of a poly-L-lactide screw in cancellous bone: a long-term experimental study

The increasing clinical use of biodegradable implants in orthopedic surgery makes it necessary to determine their long-term behavior in tissues. In this study, a biodegradable screw made of poly-L-lactide (PLLA) was inserted axially into the right distal femur in 18 rabbits. The degradation and phagocytosis process of PLLA was assessed histologically and by transmission electron microscopy (TEM). The follow-up times were 3 and 4.5 years for groups of nine and eight animals, respectively. Abundant birefringent polymeric material was still present in the center of the implant channel in all specimens in both follow-up groups. The PLLA material studied appeared to be a biologically relatively inert material, with only sparse reactive cellular activity at the tissue-implant boundary. In the TEM specimens, polymeric particles of an average area of 2 microm2 were seen to be located intracellularly within phagocytic cells. The spheric and polygonal particles were membrane-bound and to a great extent filled up each phagocyte. In the 4.5-year specimens, the size of the polymeric particles, measured as area and perimeter, was significantly smaller (p < 0.02) than that of the 3-year specimens. The findings indicate that the ultimate degradation process of PLLA is much longer than it previously was thought to be. Complete degradation probably still would have taken years after the 4.5-year span of this study.     

Reaction of bone to HA, carbonate-HA, hydroxyapatite + calcium orthophosphate and to hydroxyapatite + calcium ortho- and pyrophosphate.

Slip cast conical implants of HA, carbonate-HA, calcium orthophosphate/hydroxyapatite and hydroxyapatite/calcium pyrophosphate/calcium orthophosphate with weight ratios 75/25 and 50/30/20 were implanted in rabbit tibia. The bone-implant interfaces were evaluated histologically, by means of SEM/EDX analysis and by push-out test. Thirty-six implanted samples were investigated after 2, 8, and 24 weeks. The triphasic calcium phosphate showed a moderate disintegration. This material showed 2 weeks after implantation a bonding between new bone and implant could be seen in parts of the operation site by SEM. Eight weeks after implantation an intimate relationship between the bone tissue and all specimens of each material was found. After 24 weeks the Ca/P ratio in the bone had reached the Ca/P ratio of mature bone determined by SEM/EDX analysis.     

Nondegradable hydrogels for the treatment of focal cartilage defects

Nondegradable materials have long been suggested for the treatment of articular cartilage defects; however, the mechanics of the implant/tissue system necessary to ensure long-term function are unknown. The objective of this study was to explore the performance of nondegradable hydrogel implants in cartilage defects. Our hypothesis was that the structural integrity of the implant and surrounding tissue would be influenced by the compressive modulus of the material used, and that superior results would be obtained with the implantation of a more compliant material. Poly(vinyl alcohol)-poly(vinyl pyrrolidone) hydrogel implants of two different moduli were implanted into osteochondral defects in a rabbit model. Six-month postoperative histological and mechanical data were used to assess the wear and fixation of the implants. The compliant implants remained well fixed and a thin layer of soft tissue grew over the surface of the implants. However, gross deformation of the compliant implants occurred and debris was evident in surrounding bone. The stiffer implants were dislocated from their implantation site, but with no accompanying evidence of debris or implant deformation. Our hypothesis that superior results would be obtained with implantation of a more compliant material was rejected; a compromise between the wear and fixation properties dependent on modulus was found.     

Subchondral nacre implant in the articular zone of the sheep's knee: a pilot study

The present study was designed to analyze the intra-articular behaviour of nacre, when implanted in the subchondral bone area in the sheep knee. We implanted nacre blocks in sheep's trochlea by replacing the half of the femoral trochlea (nacre group). For comparison we used complete cartilage resection (resection group) down to the subchondral bone. In the "nacre group", implants were well tolerated without any synovial inflammation. In addition, we observed centripetal regrowth of new cartilage after 3 months. In the "resection group", no chondral regrowth was observed, but, in contrast, a thin layer of fibrous tissue was formed. After 6 months, a new tissue covered the nacre implant formed by an osteochondral regrowth. Nacre, as a subchondral implant, exerts benefic potential for osteochondral repair.     

Effect of nitinol implant porosity on cranial bone ingrowth and apposition after 6 weeks.

The present study addresses two aspects of the use of nitinol in cranial bone defect repair. The first is to verify that there is substantial bone ingrowth into the implant after 6 weeks; the second is to determine the effect of pore size on the ability of bone to grow into the implant during the early (6-week) postoperative period. Porous equiatomic (equal atomic masses of titanium and nickel) nickel-titanium (nitinol) implants with three different morphologies (differing in pore size and percent porosity) were implanted for 6 weeks in the parietal bones of New Zealand White rabbits. Ingrowth of bone into the implants and apposition of bone along the exterior and interior implant surfaces were calculated. The mean pore size (MPS) of implant type #1 (353 +/- 74 microm) differed considerably from implant types #2 (218 +/- 28 microm) and #3 (178 +/- 31 microm). There was no significant difference among implant types in the percentages of bone and void/soft tissue composition of the aggregate implants. The amount of bone ingrowth also was not significantly different among the implant types. Implant #1 was significantly higher in pore volume and thus had a significantly higher volume of ingrown bone (2.59 +/- 0.60 mm3) than implant #3 (1. 52 +/- 0.66 mm3) and a greater amount, but not significantly greater, than implant #2 (1.76 +/- 0.47 mm3). Pore size does not appear to affect bone ingrowth during the cartilaginous period of bone growth in the implant. This implies that within the commonly accepted range of implant porosities (150-400 microm), at 6 weeks bone ingrowth near the interface of nitinol implants is similar.     

Micro-observation and characterization of bonding between bone and HA-glass-titanium functionally gradient composite

Bioactive composite implants consisting of hydroxyapatite (HA)-glass (G) ceramic layer and Ti-6AI-4V alloy, so-called HA-G-Ti functionally gradient implant, were provided for investigating the bonding behaviour of bone to the implant in vivo. The HA-G-Ti composites were implanted in femur and tibia of dog for various periods (1-12 month). Microstructural appearance of the interface between bone and the HA-G coating layer as well as the transverse sections of the HA-G coating layer and further apposition of bone to the implant have been studied in detail with SEM. The ingress of collagen fibres into the HA-G coating layer and the deposit of apatite on the collagen fibres and HA crystal grains being containing within the HA-G coating layer have been observed. Radiographical experiments indicate that the reparative process in the bone tissue surrounding the implants is markedly ahead even at one month after implantation. FT-IR measurement and X-ray diffraction were carried out for studying the characterization of the calcified bone matrix around the implants and the new bone proliferated along the HA-G-coated face (surface).     

丝素蛋白/羟基磷灰石材料复合骨髓间充质干细胞构建组织工程化软骨

背景：随着组织工程的兴起,软骨损伤的修复可能性显著地提高,但单一的支架材料均不能符合理想支架,有一定的局限性。 目的：观察骨髓间充质干细胞复合丝素蛋白/羟基磷灰石构建组织工程化软骨的可行性。 方法：体外分离培养骨髓间充质干细胞,并定向诱导成软骨细胞,与丝素蛋白/羟基磷灰石复合培养,构建膝关节胫骨平台全层关节软骨缺损。54只大白兔单侧膝关节全层软骨缺损模型后随机抽签法分为3组,复合组植入细胞-丝素蛋白/羟基磷灰石复合物;材料组植入单纯丝素蛋白/羟基磷灰石,对照组不行任何植入。植入后8,12周CT检查及组织学检查观察软骨缺损修复情况。 结果与结论：植入后8周,复合组关节面不平整,关节间隙增大,形成新生类软骨细胞,基质丰富。材料组关节面塌陷,软骨细胞少量增殖。植入后12周,复合组关节面平整,关节间隙如常。大量软骨细胞出现,与周边软骨色泽一样,支架材料完全降解。材料组关节面不平整,软骨细胞不完全充填,支架材料部分降解。对照组未见修复。提示用骨髓间充质干细胞复合丝素蛋白/羟基磷灰石可形成透明软骨修复动物膝关节全层软骨缺损,显示了丝素蛋白/羟基磷灰石材料作为关节软骨组织工程支架材料的良好生物相容性。     

An experimental intraarticular implantation of woven carbon fiber pad into osteochondral defect of the femoral condyle in rabbit

The defects of the articular cartilage structure are not replaced unless the subchondral plate has been breached. However, following the creation of a defect in the subchondral plate, the area is filled in with a fibrous tissue which gradually transforms to hyaline cartilage. The porous nontoxic materials of both biologic and synthetic origin have reportedly been used as matrices for repairing bone and cartilage. Following implantation, carbon fibre, chemically inert and well-tolerated by the body, induces a proliferation of ordered fibrous tissue. We implanted carbon fiber pads in osteochondral defects in rabbits. Those repairs were compared to control holes with no implants. The pads appeared to induce the gross appearance of a restored joint surface, mechanically strong to loading for periods from 2 to 6 weeks. Also, carbon fiber pads promoted the healing of the osteochondral defects in the rabbit femoral condyle, supplying well-organized cartilagenous tissue over repaired subchondral bone. The use of carbon fiber pads as implant material is suggested for the restoration of articular surface in osteoarthritis and osteochondritis dissecans.     

Bone bonding in sintered hydroxyapatite combined with a new synthesized agent, TAK-778.

We studied the stimulatory effects of TAK-778, a new synthetic 3-benzothiepin derivative that promotes osteoblast differentiation, in bone bonding to sintered hydroxyapatite implants in rabbit tibiae. Smooth-surfaced rectangular plates (15 x 10 x 2 mm) made of sintered hydroxyapatite were implanted into the proximal metaphyses of bilateral rabbit tibiae, with TAK-778-containing sustained-release microcapsules packed into the medullary cavity in one limb and untreated microcapsules packed in the contralateral limb to serve as a paired control. At 4, 8, and 16 weeks after implantation, bone bonding at the bone-implant interfaces was evaluated by a detaching test and undecalcified histological examination. The tensile failure load increased from 4 to 16 weeks for both groups; however, the tensile failure load of the TAK-778-treated group was significantly greater than that of the control group at each interval after implantation. Histologically, the TAK-778-treated specimens showed greater active new bone formation mainly in the medullary cavity and more extensive bonding between the implant and bone than the untreated specimens. The results of this study suggest that adding osteoinductive TAK-778 to hydroxyapatite implants may significantly accelerate bone apposition to the implants and improve the bonding process at the interface. This would help to establish an earlier and stronger bonding of orthopedic ceramic implants between the surrounding bone tissue.     

Osteochondritis dissecans of the elbow: histopathological assessment of the articular cartilage and subchondral bone with emphasis on their damage and repair

Osteochondritis dissecans (OCD) of the elbow is a localized injury of the articular cartilage and subchondral bone that is commonly seen in the young athlete. In the present study, the extent of damage and repair on the articular cartilage and subchondral bone was examined histologically using specimens of 25 osteochondral cylinders and seven loose bodies obtained from 25 young athletes who had undergone osteochondral autograft surgery. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) assays for detecting apoptotic cells and immunohistochemistry of matrix metalloproteinases (MMP) were performed on the osteochondral cylinder specimens. The histological findings of the OCD of the elbow showed that the articular cartilage exhibited degenerative change, mimicking osteoarthritis, and was markedly damaged as the lesion progressed. TUNEL-positive cells and MMP-3- and -13-expressing cells were distributed in the degenerative articular cartilage and reparative fibrocartilage tissue. Separation occurred at either the deep articular cartilage or the subchondral bone, with the former being dominant in the early OCD lesions. The present results suggest that the primary pathological changes in OCD of the elbow were due to damage of articular cartilage induced by repeated stress following degenerative and reparative process of articular cartilage and subchondral fracturing, and separation subsequently occurred on the cartilage and developed onto the subchondral bone in its advanced stages.