Histopathological abnormalities in painful bipartite patellae in adolescents

The purpose of this study was to clarify the etiology of painful bipartite patella in adolescents by histopathological examination of excised specimens. We performed excision of a fragment of painful bipartite or tripartite patella from six patients (six knees). The articular cartilage, interposed tissue, bone, and bone marrow of the excised specimens were histologically examined. The articular cartilage was intact in all but two patellae. The predominant composition of the interposed tissue was fibrous tissue in one patient; fibrous tissue and fibrocartilage in four patients; and fibrous tissue, fibrocartilage, and hyaline cartilage in one patient. In the interposed tissue, diffuse degenerative and necrotic fibrocartilage was observed in four patients and focal necrotic fibrocartilage was seen in two patients. In all patients, the central region of the interposed tissue almost completely lacked blood vessels. Other histological features of the interposed tissue included necrosis of the trabecular bone in three patients, irregularly shaped spicules of immature bone in three patients, and fragments of hyaline cartilage in two patients. In all patients the bone marrow adjacent to the interposed tissue showed numerous small blood vessels, and trabecular bone surfaces and the fibrocartilage surface adjacent to this bone marrow was scalloped and lined with numerous osteoclasts. The striking histopathological features of the interposed tissue were fibrous tissue and necrosis of the fibrocartilage. These abnormalities may ultimately lead to the failure of an accessory ossification center to unite with the main portion of the patella.     

The role of implant alignment on stability and particles on periprosthetic osteolysis--A rabbit model of implant failure

The study objective was to determine the tissue response to polyethylene and/or titanium particles and the role that these play in peri-prosthetic osteolysis in a rabbit model of implant failure. Twenty-two mature rabbits were used. Unilateral tibial arthroplasty was performed on all of them. The test animals received implants that were intentionally rotationally unstable with reference to the host tibia in order to create a model of failure. The test rabbits were divided into three groups. Group 1 consisted of seven rabbits in which only the carrier was implanted. Group 2 consisted of seven rabbits that received only polyethylene particles suspended in the carrier. Group 3 consisted of eight rabbits that received a mixture of polyethylene and titanium alloy particles suspended in the carrier. The rabbits were sacrificed at 6 months post surgery. The entire knee, together with the immediately surrounding soft tissue, was retrieved. The position of the implant in each rabbit was assessed with reference to its alignment to the tibia. The number of inflammatory, foreign-body reactive cells, the presence of neovascularization, edema, and necrosis in the periprosthetic zones were recorded and assessed in a qualitative and semiquantitative manner. Quantitative histomorphometry was used to determine the proportion of implant surface that interfaced with osseous or fibrous tissue. Also assessed was the thickness and maturity of the fibrous tissue and the endosteal remodeling activity in the peri-implant bone counting both osteoclastic and osteoblastic activity. The results showed that implanted particles and misalignment of the implants combined to produce peri-prosthetic bone resorption. Bone resorption was found to be proportional to the degree of misalignment. The animals that received combined polyethylene/titanium particles had a greater degree of foreign-body and inflammatory response with osteolysis than the other groups. The combination of bio-material particles (polyethylene and titanium alloy) produced a greater degree of bone resorption than the single biomaterial particles (polyethylene). The amount of bone resorption surrounding the implant was directly proportional to the degree of misalignment of the implant.     

Histomorphometric analysis of the intramedullary bone response to titanium particles in wild-type and IL-1R1 knock-out mice: a preliminary study

Aseptic loosening of implants following total joint arthroplasty remains a major cause of implant failure. Particulate debris generated primarily from wear results in inflammatory mediated periprosthetic osteolysis. Titanium is a commonly utilized metal in joint arthroplasty and titanium debris induces the production of the pro-inflammatory cytokine IL-1. To further elucidate the role of IL-1, this study examined the response of murine femora to the presence of titanium particles following implantation of an intramedullary rod in mice lacking the receptor for IL-1. We hypothesized that the inflammatory effects of wear debris on bone would be mitigated in IL-1R1 deficient mice with a resultant decrease in resorption. Femora receiving titanium particles demonstrated a marked inflammatory response in wild-type mice with increased endocortical resorption, periprosthetic membrane formation, and significant histomorphometric changes. Femora exposed to titanium particles in the knockout mice also demonstrated osteolysis with irregular deposition of trabecular bone and increased cortical porosity. The persistence of inflammation and osteolysis, despite the lack of functional IL-1R1, suggests a multi-factorial role for IL-1 in the proinflammatory cascade resulting from wear debris. This intramedullary murine model provides the ability to evaluate and quantify the proinflammatory cascade in an in vivo model approximating prosthesis failure.     

Effect of implant material properties on the performance of a hip joint replacement

A composite material implant prosthesis for hip replacement has been developed. The design of the prosthesis substructure was based on investigation of the stress and strain fields that were developed in the human femur at the proximal end when a prosthesis stem had been inserted into it. The prosthesis stem structure was of unidirectional fibrous composite material core (graphite fibres in polysulfone matrix), wrapped with four layers of the same material but orientated at different angles. The orthotropic moduli of the outer layer are very close to the moduli of a human cortical bone in the vertical and circumferential directions. The moduli increased gradually from the outer layer to the inner core. A three-dimensional finite element model of the prosthesis and the bone has been constructed and loaded with the range of forces that might appear upon operation. The behaviour of the composite prosthesis and the femur was then compared with the intact femur and three other types of prosthesis materials, namely stainless steel, titanium, an isoelastic material and a hypothetical one with moduli identical to the cortical bone. The titanium has modulus of elasticity that is only half of the stainless steel. It was found that the composite prosthesis gave the best performance for most of the categories that were examined.     

人工髋关节置换术假体固定与骨溶解的研究

目的探讨人工髋关节置换术后假体的固定与骨溶解之间的关系,以减少术后假体无菌性松动.方法选取我院2005年3月~2011年11月人工关节无菌性松动行髋关节翻修术者28例30髋.首次行全髋关节置换术10髋,年龄38~80岁,平均66岁.分别将金属头与金属臼组合、金属头与高分子聚乙烯臼组合、陶瓷头与高分子聚乙烯臼组合、首次行全髋关节置换术者,设为A、B、C、D四组,每组10髋.手术中取假体周围磨损颗粒及周围各组织,组织学观察成骨情况,颗粒分布及其周围的组织细胞学反应.采用计算机图像分析在OLYMPUS-BX51镜下将组织切片分成若干个视野,测量每个视野中小梁骨面积﹙bone area, BA﹚和该视野组织总面积﹙total tissue area , TTA﹚,并计算BA/TTA比值.所得数据在各处理组间进行比较,以方差分析法作显著性检验﹙a=0.05﹚.结果A、B、C组与D组之间有显著性差异﹙P<0.05﹚,说明A、B、C组均明显抑制周围网织骨形成,并有以巨噬细胞为主的炎症反应及纤维组织大量增生.结论人工髋关节置换后无菌性松动及假体周围磨损颗粒除可激活巨噬细胞为主的炎症产生骨溶解外,还可抑制网织骨形成.其造成的人工髋关节假体—骨界面骨重建障碍可能是骨吸收增加和骨形成减少协同作用的结果.这可能是磨损颗粒刺激下细胞因子介导的骨—假体界面骨代谢异常在人工髋关节无菌性松动中发挥重要作用的关键所在.     

Distribution of matrix metalloproteinases and their inhibitor, TIMP-1, in developing human osteophytic bone

Connective tissues synthesise and secrete a family of matrix metalloproteinases (MMPs) which are capable of degrading most components of the extracellular matrix. Animal studies suggest that the MMPs play a role in bone turnover. Using specific polyclonal antisera, immunohistochemistry was used to determine the patterns of synthesis and distribution of collagenase (MMP-1), stromelysin (MMP-3), gelatinase A (MMP-2) and gelatinase B (MMP-9) and of the tissue inhibitor of metalloproteinases-1 (TIMP-1) within developing human osteophytic bone. The different MMPs and TIMP showed distinct patterns of localisation. Collagenase expression was seen at sites of vascular invasion, in osteoblasts synthesising new matrix and in some osteoclasts at sites of resorption. Chondrocytes demonstrated variable levels of collagenase and stromelysin expression throughout the proliferative and hypertrophic regions, stromelysin showing both cell-associated and strong matrix staining. Intense gelatinase B expression was observed at sites of bone resorption in osteoclasts and mononuclear cells. Gelatinase A was only weakly expressed in the fibrocartilage adjacent to areas of endochondral ossification. There was widespread but variable expression of TIMP-1 throughout the fibrous tissue, cartilage and bone. These results indicate that MMPs play a role in the development of human bone from cartilage and fibrous tissue and are likely to have multiple functions.     

The histological spectrum of subperiosteal fibrocartilaginous pseudotumor of long bone (focal fibrocartilaginous dysplasia)

Clinicopathological features in six cases of focal fibrocartilaginous dysplasia (FFCD) which involved either the tibia (n = 4) or the femur (n = 2) were reviewed. All cases presented clinical and radiological characteristic features, and histopathological findings were analyzed in five of the six cases. The subject group comprised three boys and three girls, ages ranged from 12 to 18 months. Histologically, the individual lesions showed regional variation in cellularity, amount of fibrous and cartilaginous components. Paucicellular areas were mainly composed of dense fibrous tissue while more cellular areas contained foci of fibrocartilaginous element. The chondrocytes and stellate cells around cartilaginous area were positive for S-100 protein. One case contained both hyaline and fibrocartilage, and architecturally mimicked normal tendinous insertion. One case, which involved proximal tibia, was purely composed of fibrous tissue without fibrocartilage. All cases formed undulating and irregular borders against underlying cortical bone. Histopathologically variable spectrum suggests a strong possibility of undergoing transition from initial cellular and cartilagnous to late paucicellular, fibrous phase. Although any evidence that can explain basic pathogenesis or prognostic histological parameter is lacking, we believe that the term FFCD is not relevant because the presence of fibrocartilage is not an essential feature, and it can cause confusion with other pathological processes. We propose the term 'subperiosteal fibrocartilaginous pseudotumor of long bone' for this unique clinicopathological entity with which heterologous cartilaginous element can be associated.     

Cranial defect repair using e-PTFE: part I. Evaluation of bone stiffness

Autologous bone grafts are the preferred material for craniofacial reconstruction, but such procedures lead to increased operative time and bleeding, donor site morbidity, and graft resorption. The efficacy of expanded-polytetrafluoroethylene (e-PTFE) sheets to increase bone regeneration and remodeling in cranial defects using a rabbit model was evaluated by mechanical testing. New Zealand white rabbits were divided into 3 groups and sacrificed 6 months after surgery. In the Split Table group, (n = 16), a bilateral bone defect was created on the outer table of the parietal bones. In the Full Table group, (n = 16), a bilateral defect was created through both the inner and outer table of the cranium. The control group, (n = 10) was subjected to a sham operation. Indentation testing was performed to determine the stiffness of newly formed bone in and around the defect. Near the center of the defect, Split Table defects repaired with e-PTFE resulted in significantly stiffer bone than regenerated control bone. The Full Table defects repaired with e-PTFE also resulted in bone significantly stiffer than control regenerated bone around the central region of the defect. The data supports the hypothesis that e-PTFE improves the repair of cranial defects in a rabbit model. It is surmised that the porosity of the e-PTFE provides a stable scaffold for migration of tissue regenerating cells, which may be preferentially localized near the cranial suture lines. This porosity may also provide a barrier to fibrous tissue regenerating cells.     

Titania and titania-silica coatings for titanium: comparison of ectopic bone formation within cell-seeded scaffolds

The aim of this study was to compare titania (TiO(2))-coated, titania-silica (TiSi)-coated, and uncoated (cpTi) titanium fiber meshes as scaffolds for bone engineering. The scaffolds were loaded with bone marrow stromal cells and implanted subcutaneously in rats. Ectopic bone formation after 1, 4, and 12 weeks of implantation was evaluated using histology and histomorphometry. After 1 week of implantation, multiple patches of unorganized mineralizing tissue were seen in all implants. The amount of this bone-like tissue clearly increased from 1 to 4 weeks. Bone apposition occurred in direct contact with coated meshes, while a thin layer of unmineralized fibrous tissue was often observed surrounding cpTi mesh fibers. After 12 weeks, the structure of bone, with bone marrow-like tissue, was further matured and mesh fibers were embedded in lamellar bone. No statistical differences in the amount of mineralized bone were observed between scaffold types at any point of time. Only TiSi scaffolds showed further increase in bone area from 4 to 12 weeks (p < 0.01). A notable difference was that the sol-gel coatings resulted in enhanced initial bone contact and distribution of bone tissue, whereas uncoated implants showed bone formation mainly in the center of the scaffolds. In conclusion, TiO(2)-based sol-gel coatings may be used in tissue engineering to gain more uniform distribution of bone throughout titanium fiber mesh scaffolds.     

Fibrocartilage in tendons and ligaments — an adaptation to compressive load

Where tendons and ligaments are subject to compression, they are frequently fibrocartilaginous. This occurs at 2 principal sites: where tendons (and sometimes ligaments) wrap around bony or fibrous pulleys, and in the region where they attach to bone, i.e. at their entheses. Wrap-around tendons are most characteristic of the limbs and are commonly wider at their point of bony contact so that the pressure is reduced. The most fibrocartilaginous tendons are heavily loaded and permanently bent around their pulleys. There is often pronounced interweaving of collagen fibres that prevents the tendons from splaying apart under compression. The fibrocartilage can be located within fascicles, or in endo- or epitenon (where it may protect blood vessels from compression or allow fascicles to slide). Fibrocartilage cells are commonly packed with intermediate filaments which could be involved in transducing mechanical load. The ECM often contains aggrecan which allows the tendon to imbibe water and withstand compression. Type II collagen may also be present, particularly in tendons that are heavily loaded. Fibrocartilage is a dynamic tissue that disappears when the tendons are rerouted surgically and can be maintained in vitro when discs of tendon are compressed. Finite element analyses provide a good correlation between its distribution and levels of compressive stress, but at some locations fibrocartilage is a sign of pathology. Enthesis fibrocartilage is most typical of tendons or ligaments that attach to the epiphyses of long bones where it may also be accompanied by sesamoid and periosteal fibrocartilages. It is characteristic of sites where the angle of attachment changes throughout the range of joint movement and it reduces wear and tear by dissipating stress concentration at the bony interface. There is a good correlation between the distribution of fibrocartilage within an enthesis and the levels of compressive stress. The complex interlocking between calcified fibrocartilage and bone contributes to the mechanical strength of the enthesis and cartilage-like molecules (e.g. aggrecan and type II collagen) in the ECM contribute to its ability to withstand compression. Pathological changes are common and are known as enthesopathies.     

The interface zone of inorganic implantsIn vivo: Titanium implants in bone

The interface zone between titanium implants and bone is considered at the macroscopic, microscopic, and molecular levels. A high rate of successful dental implants of pure titanium is associated with a very close apposition of the bone to the titanium surface, called osseointegration. At the macroscopic level, osseointegration allows efficient stress transfer from the implant to the bone without abrasion or progressive movement that can take place if a fibrous layer intervenes. At the microscopic level, surface roughness and porosity provide interlocking of the implant and bone tissue which grows into direct contact with titanium. Sections studied in the electron microscope show that calcified tissue can be identified within 50 Å of the implant surface. The interface zone includes a tightly adherent titanium oxide layer on the surface of the implant which may be similar to a ceramic material in relation to tissue response. The five year success rate of 90% in 2895 implants in clinical trials since 1965 is associated with the favorable behavior of bone tissue at the interface zone with pure titanium.     

髋假体置入后假体周围松动骨质的病理学变化

背景：磨损颗粒是导致假体周围骨质溶解的重要潜在性因素之一,但引起假体周围骨溶解的原因及其发展过程尚未完全清楚。 目的：复习人工关节置换后翻修病例的病理切片,分析病理检查在人工关节置换后感染诊断中的价值。 方法：由第一作者检索1990/2008 PubMed数据及万方数据库有关髋假体置入后假体周围松动以及假体松动周围骨质的病理学变化方面的文献。 结果与结论：人工假体与骨空隙的产生导致界膜充填,磨损微粒刺激界膜释放炎性细胞因子导致骨溶解而出现假体松动,如果尽可能地减少活动中产生的磨损碎屑可减少炎性递质的释放;减少由充填性界膜向溶骨性界膜的转变,就可从生物学角度降低人工髋关节置换后假体松动的发生率。     

Histological analysis of bone/heteroplastic implant interfaces in dog tibia.

This work presents histological analysis of interfaces between bone and heteroplastic implants in dog tibias. The study was performed in four tibias (of four mongrel dogs) into which cylindrical implants were inserted. One ceramic (titania) implant and three grit-blasted titanium implants (with sandblasted and acid-corroded surfaces) were chosen for histological analysis of the implant surface/bone tissue interface. The implants remained in the tibias for eight months and none were loaded during this period. The animals were subsequently sacrificed and the samples were processed for analysis. Light microscope analysis revealed a large amount of osteoid tissue and proximity of osteoblasts and osteocytes to the implant surfaces. In addition, little or no fibrous tissue was observed between the bone and implant surfaces. The titanium implants presented better osseointegration than did the ceramic implant.     

Stimulative and regulative functions of osteoblasts loaded under the titanium particles on osteoclasts

Our previous studies on the function of the osteoblasts (OBs) have shown that worn titanium particles decrease osteoblast function and promot secretion of bone resorption cytokines of OBs surrounding the synovium-like interface membrane of loosening implants. The current study was aimed to test the hypothesis that osteoclasts (OCs) bone absorption function is induced by conditioned media (CM) prepared from OBs loaded in the presence or absence of titanium particles (with three mean diameters 6.9 microm, 2.7 microm, and 0.9 microm, respectively). The effects of CM on OCs function were examined using a combination of the morphological characteristics tests, i.e., TRAP dyeing, scanning electron microscopy, F-actin immunofluorescence protocol for confocal microscopy, bone resorption lacunae assay, osteoclastic calcium tracking, with biochemical evaluation, i.e., C-terminal cross-linked telopeptides of type I collagen evaluated with ABC-ELISA method. The results showed that CM from 0.9 microm titanium particles could induce osteoclastic differentiation and formation, could partially influence the survival of the OCs; while CM of 2.7 microm and 6.9 microm titanium particles, especially the latter, could obviously augmented osteoclastic activity, survival, or differentiation. The stimulation of osteoclast function may be due to a parallel increase in the intracellular free calcium concentration. The present study provides strong support for the hypothesis that osteoclastic activity, survival, or differentiation are very important in the development of aseptic loosening. The development of therapeutic interventions to reduce osteoclastic function and optimization of biomaterials may be useful approaches for improving the performance of orthopaedic implants.     

Stem cell based tissue engineering for meniscus repair

Defects of the meniscus greatly alter knee function and predispose the joint to degenerative changes. The purpose of this study was to test a recently developed cell-scaffold combination for the repair of a critical-size defect of the rabbit medial meniscus. A bilateral, complete resection of the pars intermedia of the medial meniscus was performed in 18 New Zealand White rabbits. A hyaluronan/gelatin composite scaffold was implanted into the defect of one knee of 6 rabbits and the contralateral defect was left untreated. Scaffolds loaded with autologous marrow-derived mesenchymal stem cells and cultured in a chondrogenic medium for 14 days were implanted in a second series of 12 rabbits. Empty scaffolds were implanted in the contralateral knees. Meniscii were harvested at 12 weeks. Untreated defects had a muted fibrous healing response. Defects treated with cell-free implants showed also predominantly fibrous tissue whereas fibrocartilage was present in some scaffolds. The cross-sectional width of the repair tissue after treatment with cell-free scaffolds was significantly greater than controls (p < 0.05). Pre-cultured implants integrated with the host tissue and 8 of 11 contained meniscus-like fibrocartilage, compared with 2 of 11 controls (p < 0.03). The mean cross-sectional width of the pre-cultured implant repair tissue was greater than controls (p < 0.004). This study demonstrates the repair of a critical size meniscal defect with a stem cell and scaffold based tissue engineering approach.     

The effects of titanium and polymethylmethacrylate particles on osteoblast phenotypic stability

Wear particles generated following total joint arthroplasty interact with cells at the periprosthetic margin and induce an inflammatory response that contributes to osteolysis, aseptic loosening, and implant failure. This study examined the long-term effects of particles from two commonly implanted materials, titanium (Ti) and polymethylmethacrylate (PMMA), on cell viability and metabolism over a 21-day time course, using the human osteoblast-like cell line MG-63. Addition of particles was not associated with increased cell death or nitric oxide production at the particle concentration chosen. Collagen production was increased with exposure to titanium particles, whereas alkaline phosphatase and osteocalcin expression remained unchanged following exposure to both types of particles. The data show that titanium but not PMMA particles shifts bone cell metabolism to preferentially produce fibrous tissue rather than bone.     

局部运用阿仑磷酸钠对兔人工假体无菌性松动抑制作用的研究

目的 探讨局部运用阿仑磷酸钠对抑制破骨细胞性骨吸收的影响,为临床上人工关节的松动提供预防和治疗的方法。方法 用20只大耳白兔建立骨质疏松模型后,在模型兔右侧股骨中上段截骨,用仿锤形不锈钢假体连接断端,一组用阿仑磷酸钠加骨水泥(PMMA)固定假体,对照组为单用PMMA固定。8周后处死全部实验兔,取出实验股骨,作生物力学实验和病理形态学检查,进行图像分析和统计学处理。结果 在拔出实验和扭转实验,阿仑磷酸钠组均显著优于对照组(P<0.01)。病理组织形态学检查阿仑磷酸钠组骨小梁体积比、厚度和数目高于对照组(P<0.01或P<0.05)。结论局部运用阿仑磷酸钠对人工假体无菌性松动有明显抑制作用,增加了人工假体的稳定性。     

Ex Vivo bone formation in bovine trabecular bone cultured in a dynamic 3D bioreactor is enhanced by compressive mechanical strain

Our aim was to test cell and trabecular responses to mechanical loading in vitro in a tissue bone explant culture model. We used a new three-dimensional culture model, the ZetOS system, which provides the ability to exert cyclic compression on cancellous bone cylinders (bovine sternum) cultured in forced flow circumfusion chambers, and allows to assess mechanical parameters of the cultivated samples. We evaluated bone cellular parameters through osteocyte viability test, gene and protein expression, and histomorphometric bone formation rate, in nonloaded versus loaded samples. The microarchitecture of bone cores was appraised by in vivo micro-CT imaging. After 3 weeks, the samples receiving daily cyclic compression exhibited increased osteoblast differentiation and activity associated with thicker, more plate-like-shaped trabeculae and higher Young's modulus and ultimate force as compared to unloaded samples. Osteoclast activity was not affected by mechanical strain, although it was responsive to drug treatments (retinoic acid and bisphosphonate) during the first 2 weeks of culture. Thus, in the ZetOS apparatus, we reproduce in vitro the osteogenic effects of mechanical strain known in vivo, making this system a unique and an essential laboratory aid for ex vivo testing of lamellar bone remodeling.     

Interface analysis of titanium and zirconium bone implants

A thin layer of titanium or zirconium was evaporated onto the surface of a plastic implant which was then inserted in the rabbit tibial metaphysis for six months. The implants and surrounding bone were cut out en bloc and sectioned for phase contrast microscopy, scanning- and transmission-electron microscopy. The intact bone-to-metal interface in the case of titanium revealed a fibrous tissue-free boundary zone with a 200-400 A thick proteoglycan coat immediately adjacent to the titanium oxide. Thereafter collagen filaments were seen and, at approximately 1000 A from the interface, collagen bundles. The tissues surrounding the zirconium-coated implant consisted of a 300-500 A thick proteoglycan layer, followed by a zone with collagen filaments and collagen bundles, not closer to the zirconium oxide than a few thousand A.     

Ultrastructural comparisons of ceramic and titanium dental implants in vivo: a scanning electron microscopic study

Identically prepared, screw-type ceramic and titanium endosteal dental implants were inserted in the jaws of adult mongrel dogs for periods of up to 6 months. Sixteen of the 32 total implants supported fixed bridgework. The interface of bone and soft connective tissues with the dental implants was examined by routine and innovative scanning electron microscopic (SEM) techniques using both secondary and backscattered electron imaging. Results demonstrated excellent bone adaptation to both titanium and ceramic implants. Direct adaptation of bone to the upper third of both type implants was observed with only minimal amounts of any intervening fibrous connective tissue. A composite of trabecular bone and fibrous connective tissue was observed in the lower two-thirds of the implants examined. Areas of bone alteration suggestive of osteoid were observed at the thread apicis of some loaded implants. From this investigation we concluded that similar longitudinal tissue responses were generated to one-piece, cylindrical screw-type titanium and alpha alumina oxide ceramic dental implants. Possible bone remodeling was observed at the thread apicis of the loaded implants, an area where occlusal forces may be distributed. We further suggest that one-stage endosteal implants are capable of maintaining a proportional bone-to-implant interface at the apical support region, similar to that suggested to two-stage implant systems.