Comparison of hydroxyapatite and hydroxyapatite tricalcium-phosphate coatings

This study compared the effects of hydroxyapatite (HA) coating and biphasic HA/tricalcium-phosphate (HA/TCP) coating on the osseointegration of grit-blasted titanium-alloy implants. Each coated implant was compared with uncoated grit-blasted implants as well. The implants were press-fit into the medullary canal of rabbit femora, and their osseointegration was evaluated 3 to 24 weeks after surgery. The coated implants had significantly (P<.05) greater new bone ongrowth than the uncoated implants (HA, 56.1 +/- 3.1%; HA/TCP, 53.8 +/- 2.6%; uncoated, 32.2 +/- 1.4% of the implant perimeter, 12 weeks). Unmineralized tissue (cartilage and osteoid) was seen on the uncoated implants but never on the coated implants. The coated implants had significantly (P<.05) greater interfacial shear strength than the uncoated implants (HA, 4.1 +/- 0.4 MPa; HA/TCP, 4.8 +/- 0.5 MPa; uncoated, 2.6 +/- 0.2 MPa, 12 weeks). There was no difference between HA and HA/TCP coating in regard to new bone growth or interfacial shear strength. These data show a comparable enhancement effect of HA and HA/TCP coatings on the osseointegration of titanium-alloy implants.     

Comparative study of porous hydroxyapatite and tricalcium phosphate as bone substitute

This study was performed to quantitate the bone ingrowth and biodegradability of porous calcium phosphate. Two kinds of coralline hydroxyapatite (CHA), along with sintered tricalcium phosphate (TCP), were evaluated. All implants had totally interconnecting pores. These pores measured 260-600 mu for CHA-Goniopora (CHAG), 190-230 microns for CHA-Porites (CHAP), and 100-300 microns for TCP. Cylindrical implants (3 mm in diameter by 8 mm in length) were implanted into the diaphyses of rabbit tibias for 3 to 24 weeks. The quantity of regenerated bone, remaining implant, nonmineralized space, and the middle two quarters of the cortical area were measured by a computerized operator-assisted analysis for bone histomorphometry. At 3 weeks after implantation, 17.3% of CHAG, 11.3% of CHAP, and 7.0% of TCP were infiltrated by regenerated bone. At 24 weeks, 56.1% of CHAG, 52.7% of CHAP, and 44.7% of TCP were occupied by lamellar-type bone. Implant degradation was noted to be 46.4% for TCP and 27.5% for CHAP. In contrast, CHAG did not show appreciable degradation until 24 weeks.     

The effect of hydroxyapatite coating on bone growth into porous titanium alloy implants

In rabbits and goats, test implants with a porous surface of two layers of Tl-6A;-4V beads were examined at intervals for bond strength with bone. Half of the implants were coated with hydroxyapatite by plasma spray. The bonding strength with bone in the coated specimens was about four times greater than that of the uncoated specimens at two weeks, and twice as strong at six weeks. Twelve weeks after implantation, the strengths were similar. The hydroxyapatite coating of the beads provided earlier and stronger fixation.     

Mechanical failure of hydroxyapatite- and polysulfone-coated titanium rods in a weight-bearing canine model.

Three types of material that have shown potential as coatings for orthopaedic implants were studied. Using a weight-bearing canine model, Ti-6A1-4V femoral intramedullary rods coated with (1) sintered titanium beads, (2) plasma-sprayed hydroxyapatite, and (3) silyl coupled polysulfone beads were evaluated for mechanical strength and bone ingrowth. The model was designed to secure optimal prosthetic stability by obtaining maximal bony ingrowth during an initial non-weight-bearing phase, then stressing the implant during a full-weight-bearing phase. None of the rods coated with titanium beads failed. All 17 polysulfone-coated rods failed, 13 of them at the interface between the polysulfone coating and the titanium core. Of 18 rods coated with hydroxyapatite, 15 suffered implant breakdown at the interface between the hydroxyapatite coating and the titanium core. This may be due to dissolution of the plasma-sprayed hydroxyapatite in vivo. Testing of retrieved specimens from both hydroxyapatite- and polysulfone-coated implants showed that the shear strength at the coating-rod interface had decreased to less than 40% of the shear strength at manufacture. Despite mechanical failure, histologic study showed extensive bone ingrowth or apposition onto both the polysulfone and hydroxyapatite coatings.     

Interfacial shear strength of bioactive‐coated carbon fiber reinforced polyetheretherketone after in vivo implantation

Despite the excellent osseointegration of carbon‐fiber‐reinforced polyetheretherketone (CFR/PEEK) with a surface hydroxyapatite (HA) coating, the bone‐implant interfacial shear strength of HA‐coated CFR/PEEK after osseointegration is unclear. We examined the interfacial shear strength of HA‐coated CFR/PEEK implants after in vivo implantation in a rabbit femur‐implant pull‐out test model. HA coating was performed by a newly developed method. Uncoated CFR/PEEK, HA‐coated blasted titanium alloy, and uncoated blasted titanium alloy were used as control implants. The implants were inserted into drilled femoral cortex, and pull‐out tests were conducted after 6 and 12 weeks of implantation to determine maximum interfacial shear strength. The HA‐coated CFR/PEEK (15.7 ± 4.5 MPa) and HA‐coated titanium alloy (14.1 ± 6.0 MPa) exhibited significantly larger interfacial shear strengths than the uncoated CFR/PEEK (7.7 ± 1.8 MPa) and the uncoated titanium alloy (7.8 ± 2.1 MPa) at 6 weeks. At 12 weeks, only the uncoated CFR/PEEK (8.3 ± 3.0 MPa) exhibited a significantly smaller interfacial shear strength, as compared to the HA‐coated CFR/PEEK (17.4 ± 3.6 MPa), HA‐coated titanium alloy (14.2 ± 4.8 MPa), and uncoated titanium alloy (15.0 ± 2.6 MPa). Surface analysis of the removed implants revealed detachment of the HA layer in both the HA‐coated CFR/PEEK and titanium alloy implants. The proposed novel HA coating method of CFR/PEEK significantly increased interfacial shear strength between bone and CFR/PEEK. The achieved interfacial shear strength of the HA‐coated CFR/PEEK implant is of the same level as that of grit‐blasted titanium alloy with HA. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1618–1625, 2012     

Porous-coated uncemented components in experimental total hip arthroplasty in dogs. Effect of plasma-sprayed calcium phosphate coatings on bone ingrowth.

The effect of a thin plasma-sprayed, calcium phosphate ceramic coating on bone ingrowth into titanium fiber mesh porous-surfaced prostheses was examined in a controlled canine cementless total hip arthroplasty model. Bone ingrowth was quantified using backscattered scanning electron microscopy of undemineralized sections. When good contact between the bone and porous coating was present, the calcium phosphate-coated prostheses contained significantly higher amounts of bone ingrowth at three weeks postimplantation than the uncoated control prostheses. At six weeks, however, there was no significant difference in the amount of bone ingrowth between the coated prostheses and uncoated prostheses. The ingrown bone seemed to be more intimately associated with the calcium phosphate-coated porous surfaces than the uncoated porous surfaces. When gaps at the bone-porous coating interface occurred, the calcium phosphate coating did not enhance bone ingrowth across those gaps. Plasma-sprayed calcium phosphate coatings may be useful in enhancing the early ingrowth of bone into porous-surfaced joint replacement prostheses, but they may lack long-term effectiveness. The coatings were not effective in enhancing bone ingrowth across gaps between the porous surface and the bone bed prepared at surgery.     

羟基磷灰石涂层钢板螺钉改善骨折稳定性的实验研究

目的　比较国产羟基磷灰石 (hydroxyapatite ,HA)涂层钢板螺钉与非涂层钢板螺钉在体负重情况下对骨折的内固定效果。方法　四孔钢板螺钉 2 4套 ,附加螺钉 60枚 ,对其中 12套钢板、30枚螺钉行HA等离子喷涂 ,其余的钢板、螺钉不喷。 12只成年杂种犬 ,每只犬的两侧肱骨线型骨折后分别以HA涂层钢板、螺钉或非涂层钢板、螺钉内固定 ,每只犬的右胫骨间隔 2cm交递置入HA涂层钉和非涂层钉共 5枚。按术后即刻、3、6周将犬分成 3组。处死后行组织学观察和生物力学测试。结果　组织学观察 :术后 3、6周组HA涂层均无明显降解 ,其与不锈钢基底结合良好 ,与骨组织结合紧密 ,3、6周组HA涂层钢板下都有不同程度的皮质骨上新生骨形成 ,该处未见明显的骨质疏松。相反非涂层钢板、螺钉与骨接触不紧密 ,其间有薄层纤维组织生长 ,钢板下可见不同程度的骨质疏松。力学测试 :3、6周组犬中HA涂层组的三点折弯强度及螺钉拔出强度均比非涂层组大。结论　国产HA涂层的钢板螺钉可增加骨折内固定的稳定性。     

Clinical and roentgenographic evaluation of hydroxyapatite-coated and uncoated porous total hip arthroplasty: a preliminary report

Sixty osteoarthritic patients undergoing primary uncemented total hip arthroplasty were matched for age and weight and randomized into one of four groups with respect to implant coating and postoperative protected weight-bearing status: group 1, hydroxyapatite, 12 weeks; group 2, uncoated, 12 weeks; group 3, hydroxyapatite, 6 weeks; group 4, uncoated, 6 weeks. Tantalum spheres were implanted periprosthetically into the femur at the time of arthroplasty, thus providing constant references for stereoscopic radiographs. Patients were then evaluated over a 1-year period with clinical examination, plain radiography, and roentgen stereophotogrammetric analysis (RSA). Clinical evaluation using Charnley scoring showed no significant preoperative or postoperative intergroup differences, whereas visual analog testing noted less thigh pain with hydroxyapatite-coated stems at 12 weeks and 6 months follow-up. Plain radiographic analysis produced no significant differences, with no instability detected and bony ingrowth noted uniformly in all groups. The preliminary stereographic evaluation showed migration in all groups, but there were no significant differences between coated and uncoated stems or 6-week and 12-week partial weightbearing protocols. The Charnley, plain radiographic, and preliminary stereogrammetric evaluations all suggest that migration is unaltered by enhanced surfaces and that early unprotected weightbearing does not jeopardize implant fixation regardless of coating design. The lower incidence of visual analog thigh pain with the hydroxyapatite-coated stems, however, may be a reflection of bony ingrowth and as such add some validity to the theoretical advantages of enhanced surface prostheses.     

Hydroxyapatite-coated porous titanium for use as an orthopedic biologic attachment system

The biologic attachment characteristics of hydroxyapatite (HA)-coated porous titanium and uncoated porous titanium implants were investigated. The implants were placed transcortically in the femora of adult mongrel dogs and evaluated after periods of three, six, and 12 weeks. The HA coating was applied using a modified plasma spray process to samples with pore volume and pore size of the porous coating expanded to equal the pore morphology of uncoated porous specimens. Mechanical push-out testing revealed that the bone-porous material interface shear strength increased with time in situ for both the uncoated and HA-coated implants. The use of the HA coating on porous titanium, however, did not significantly increase attachment strength. Histologic and microradiographic sections yielded similar qualitative results in the amount of bone grown into each system. After three weeks, both systems displayed primarily woven bone occupying approximately 50% of the available porous structure. Six and 12 weeks postimplantation, each system displayed more extensive bone ingrowth, organization, and mineralization, with only limited areas of immature bone. Histologically, differences were noted at the ingrown bone-porous material interface between the two implant types. The HA coating supported mineralization directly onto its surface, and a thin osseous layer was found lining all HA-coated surfaces. An extremely thin fibrous layer was observed separating the uncoated titanium particle surface from ingrown bone. There was no extensive direct apposition or lining of the ingrown bone to the uncoated porous titanium particle surfaces.     

A long-term study on defect filling and bone ingrowth using a canine fiber metal total hip model.

When performing primary and revision total hip arthroplasty (THA), bone defects are often encountered. At present, grafting osseous defects with autogeneic bone is a common means of treatment. In this study, defects in bone were created in the femora and acetabula of dogs being treated with cementless THA with a fiber metal implant (Group A) or a hydroxyapatite tricalcium phosphate (HA/TCP) sprayed implant (Group B). The following methods of defect filling were compared: (1) leaving defects unfilled, (2) filling with autogeneic bone graft, (3) filling with a 50:50 mixture of autograft and a biphasic ceramic composed of HA/TCP, and (4) filling with a collagen-HA/TCP-bone marrow mixture. Analysis of defect healing and the extent of ingrowth into the overlying fiber metal, at defect sites and sites distant from defects, was made at six, 12, and 24 weeks postimplantation. Defect healing was enhanced at six and 12 weeks in all grafted groups when compared with ungrafted controls. Bone ingrowth into the porous fiber metal overlying the defects was not significantly affected by grafting the defects, compared with the ungrafted defects. The extent of bone ingrowth into the fiber metal acetabular implant at sites away from the defects increased during the entire study. In contrast, the extent of bone ingrowth on the femoral side was maximal at 12 weeks. The HA/TCP coating enhanced ingrowth into the acetabular component at 12 weeks, compared with the uncoated prosthesis, but did not enhance ingrowth on the femoral side. The data from this study demonstrate that defect healing is enhanced with graft materials. However, this does not necessarily result in increased ingrowth into porous surfaces overlying osseous defects. General bone ingrowth and ingrowth at defect sites at 12 weeks postimplantation can be enhanced on the acetabular side with the use of HA/TCP-sprayed implants. However, no positive effect is seen with the use of an HA/TCP-sprayed femoral implant.     

Bonding of bone to apatite-coated implants

Implants of solid sintered hydroxyapatite form very tight bonds with living bone, but are susceptible to fatigue failure. This problem can be overcome by using plasma-sprayed apatite coatings on titanium implants. A very strong bond is formed between bone and this composite material; this was studied in canine bone with plug implants, avoiding any mechanical retention. Mechanical testing showed an interface shear strength at six weeks of 49 MPa with a maximum of 64 MPa after six months. There was histological evidence of direct bonding between the apatite coating and living bone while uncoated control plugs were easily extracted. The results indicate that apatite-coated implants can form a chemical fixation with a strength comparable to that of cortical bone itself. This fixation is far stronger than that provided by current cemented or uncemented fixation techniques.     

A back-scattered electron microscopy (BSEM) study of the tight apposition between bone and hydroxyapatite coating

We performed a back-scattered electron microscopy analysis of the interface between newly formed bone and hydroxyapatite coating, in an experimental rabbit model. Twenty cylinders made of Ti6A14V and coated with hydroxyapatite at different crystallinity were implanted in the distal femural canal and retrieved at 4, 8, 26 an 34 weeks. Crystallinity of the coating varied from 90% to 60% and thickness varied between 50 and 100 μm. Osteocytes were detectable a few micrometers in proximity of the coating. They produced new bone which was so tightly apposed to the coating that high magnification BSEM did not resolve any discontinuity at the interface. This was not observed in uncoated implants. Degradation of the hydroxyapatite coating is not a simple hydrolytic process because newly formed bone is remodelled in areas were a tight apposition with hydroxyapatite is present. The coatint itself is likely to be attacked by the resorptive action of multinucleated giant cells and osteoclasts. In conclusion, response to coated samples is morphologically characterized by tight apposition with bone. The substitution of areas of the coating by newly formed bone is possible. Received: 28 April 2000/Accepted: 2 June 2000     

Controlled‐release of bone morphogenetic protein‐2 from a microsphere coating applied to acid‐etched Ti6AL4V implants increases biological bone growth in vivo

A central clinical challenge regarding the surgical treatment of bone and joint conditions is the eventual loosening of an orthopedic implant as a result of insufficient bone ingrowth at the bone–implant interface. We investigated the in vivo effectiveness of a coating containing recombinant human bone morphogenetic protein‐2 (rhBMP‐2)‐loaded microspheres applied to acid‐etched Ti6Al4V cylinders for implantation. Three groups of rabbits (24 per group) were used for implantation: (1) acid‐etched Ti6Al4V implants coated with a mixture of rhBMP‐2‐loaded microspheres (125 ng rhBMP‐2/mg microspheres) and α‐butyl cyanoacrylate; (2) acid‐etched, uncoated implants; and (3) bare, smooth uncoated implants. After implantation, 12 rabbits from each group were used for bone ingrowth determination at 4, 5, 6, 7, 8, and 12 weeks (2 rabbits per time point), while the remainder were used for histological analysis and push‐out testing at 12 weeks. Scanning electron microscopy showed significant improvement in bone growth of the rhBMP‐2 microspheres/α‐butyl cyanoacrylate group compared with the other groups (p < 0.01). Histological analysis and push‐out testing also demonstrated enhanced bone growth of the rhBMP‐2 group over that in the other two groups (p < 0.01). The rhBMP‐2 group showed the most significant bone growth, suggesting that coating acid‐etched implants with a mixture of rhBMP‐2‐loaded microspheres and α‐butyl cyanoacrylate may be an effective method to improve the osseointegration of orthopedic implants. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:744–751, 2014.     

Biological fixation of hydroxyapatite-coated versus grit-blasted titanium hip stems: a canine study

BACKGROUND: The purpose of the study was to evaluate the influence of a proximal hydroxyapatite (HA) coating in comparison with a grit-blasted titanium surface of an anatomic hip stem in an animal model over a maximum duration of 2 years. METHODS: Thirty adult dogs underwent implantation of either a proximally HA-coated or a grit-blasted anatomic titanium stem. The animals were clinically evaluated for their walking ability, and serial radiographs were taken. The femora were assessed histomorphologically at set time points from 6 weeks to 2 years postoperatively. Undecalcified thin section specimens through the proximal and distal portion of the coating or grit blasting were prepared. The percentage of implant surface with direct bone contact without connective tissue involvement was determined. RESULTS: Radiographically, animals with uncoated prostheses showed characteristic signs of loosening more frequently. Histomorphometrically, an average of 65% of the surface of HA-coated implants had bone contact, but only 14.7% of the surface of grit-blasted prostheses ( p=0.0001). There was no relationship between bone contact and the duration of implantation of the prosthesis, either for the coated or for the uncoated prostheses. HA coating enhances osseointegration of an anatomic hip stem. CONCLUSION: Anatomic stems with rounded design require a surface coating or surface structure, since the mere grit-blasting of the titanium surface does not ensure osseointegration in this animal model.     

Macroscopic and microscopic evidence of prosthetic fixation with porous-coated materials

The host response to porous-coated prostheses appears favorable; there is little evidence of any adverse tissue response or significant osteoclastic activity except in grossly loose specimens. While the nature of retrieval specimens makes any statistical correlation problematic, some generalizations can be made. Femoral hip prostheses are most likely to present bone ingrowth along the lateral quadrant of their porous coating. The frequency of bone ingrowth of femoral components was nearly twice that of acetabular devices. Pore size, geometry, and porous-coating composition did not appear to influence the appearance of bone and fibrous tissue ingrowth. Direct bonding of bone to the uncoated portion of the prosthesis was rarely seen and occurred only in closest proximity to the porous-coated regions. Indications of pain and looseness are evidence that fibrous tissue ingrowth alone is not always sufficient to ensure stability. Additionally, some bone-ingrown prostheses were retrieved because of pain, which leads to the conclusion that local bone ingrowth cannot ensure a general freedom from pain, especially with partially coated prostheses. Bone and fibrous tissue response to the porous coatings generally consists of interdigitation, while the response to uncoated regions is fibrous tissue encapsulation. Burnishing the distal tips of many of the partially coated femoral prostheses is an indication of relative motion in that region, which may be a potential source of pain.     

A comparison of bone remodelling around hydroxyapatite-coated, porous-coated and grit-blasted hip replacements retrieved at post-mortem

We investigated the implant-bone interface around one design of femoral stem, proximally coated with either a plasma-sprayed porous coating (plain porous) or a hydroxyapatite porous coating (porous HA), or which had been grit-blasted (Interlok). Of 165 patients implanted with a Bimetric hip hemiarthroplasty (Biomet, Bridgend, UK) specimens were retrieved from 58 at post-mortem. We estimated ingrowth and attachment of bone to the surface of the implant in 21 of these, eight plain porous, seven porous HA and six Interlok, using image analysis and light morphometric techniques. The amount of HA coating was also quantified. There was significantly more ingrowth (p = 0.012) and attachment of bone (p < 0.05) to the porous HA surface (mean bone ingrowth 29.093 +/- 2.019%; mean bone attachment 37.287 +/- 2.489%) than to the plain porous surface (mean bone ingrowth 21.762 +/- 2.068%; mean bone attachment 18.9411 +/- 1.971%). There was no significant difference in attachment between the plain porous and Interlok surfaces. Bone grew more evenly over the surface of the HA coating whereas on the porous surface, bone ingrowth and attachment occurred more on the distal and medial parts of the coated surface. No significant differences in the volume of HA were found with the passage of time. This study shows that HA coating increases the amount of ingrowth and attachment of bone and leads to a more even distribution of bone over the surface of the implant. This may have implications in reducing stress shielding and limiting osteolysis induced by wear particles.     

Functional osseointegration of hydroxyapatite-coated implants in a weight-bearing canine model

That hydroxyapatite (HA) can form a strong chemical bond with bone has been confirmed by several precedent workers using unloaded implants. The relation-ship between the histomorphometric measurements of the interface of the cementless femoral stems with and without HA coating and their mechanical properties in a weight-bearing canine model was evaluated in this study. Seven HA-coated and seven uncoated titanium (Ti6Al4V) hemiarthroplasties were implanted in the right hip of 14 dogs for a 5-month period. The specimens were taken to conduct mechanical testing andmorphometric measuring. The average interface shear strength of 2.13 MPa for the HA-coated specimens was significantly higher than 0.93 MPa for the uncoated specimens (P<.05). There was greater bone apposition with the HA coating (72.39%) than without the coating (15.96%). Bone interfaces were divided into tow types histomorphometrically: type A, simple bony shell without supporting trabeculae and type B, buttressed bony shell with supporting trabeculae. A positive correlation between the type B HA-bone interface and interface shear strength was found (r=.81)     

Osseointegration of hydroxyapatite porous-coated femoral implants in a canine model.

This study evaluated the quality and quantity of osseointegration of two thicknesses of hydroxyapatite coating on press-fit, porous-coated titanium implants in a canine hip model. In 12 dogs, titanium press-fit porous-coated prostheses were implanted. The stems had a 50-microm thickness hydroxyapatite coating, 100-microm thickness hydroxyapatite coating, or no hydroxyapatite coating. The animals were randomized into one of three groups and received one of the three implants. The implants were retrieved and examined 4 months after implantation. Direct juxtaposition of bone to the surface of the hydroxyapatite-coated implants with no intervening fibrous tissue layer was observed. There was no histologic evidence that hydroxyapatite initiated any foreign body reaction, nor was there any irregularity or resorption of the hydroxyapatite coating. There was a statistically significant greater degree of total bone apposition and bone ingrowth in the implants coated with hydroxyapatite at the level of the isthmus and the calcar. No statistical difference was found between the two groups with hydroxyapatite coatings in the degree of bone ingrowth or bone apposition.     

Improved bone-screw interface with hydroxyapatite coating: an in vivo study of loaded pedicle screws in sheep

STUDY DESIGN: An in vivo sheep model with loaded pedicle screws was used, wherein each animal served as its own control. OBJECTIVES: To examine the effects of hydroxyapatite (HA) coating on the bone-to-implant interface in loaded spinal instrumentations. SUMMARY OF BACKGROUND DATA: Spinal instrumentation improves the healing rate in spinal fusion, but screw loosening constitutes a problem. HA coating of other implants has resulted in favorable effects on the bone-to-implant interface. METHODS: Nine sheep were operated on with destabilizing laminectomies at two levels: L2-L3 and L4-L5. Each level was stabilized separately with a four-screw instrumentation. Uncoated screws (stainless steel) or the same type of screws coated with plasma-sprayed HA were used in either the upper or the lower instrumentation in a randomized fashion. The animals were killed at 6 or 12 weeks after surgery. The specimens were embedded in resin, ground to approximately 10 microm, and stained with toluidine blue. Histomorphometric evaluation was carried out in a Leitz Aristoplan (Wetzlar, Germany) light microscope equipped with a Leitz Microvid unit. RESULTS: The average percentage of bone-to-implant contact after 6 weeks was 69 +/- 10 for the HA-coated screws and 18 +/- 11 for the uncoated screws (P < 0.03), and after 12 weeks 64 +/- 31 (HA-coated) and 9 +/- 13 (uncoated, P < 0.02). The average bone volume in the area close to the screw was significantly higher for the HA-coated screws at both 6 and 12 weeks. CONCLUSIONS: HA coating improved the bone-to-implant interface significantly, indicating that HA coating can become useful for improving the purchase of pedicle screws.     

Experimental study on the stability of cementless porous coated endoprosthesis]

This study investigated cementless fixation of titanium porous coated endoprosthesis using canine weight-bearing model. Though immature and thin, ingrown trabeculae reached the deepest region of porous coating four weeks after implantation, and gradually matured and thickened thereafter. Pull-out tests of the porous stem at eight weeks showed excellent fixation with average ultimate pull-out force of 142 kgf and average ultimate shear strength of 2.6 GPa. Bone ingrowth rate gradually increased at the proximal and distal region of the stem and, conversely, it gradually decreased at the middle level, suggesting the dependence of bone ingrowth upon the distribution of the amount of stress transferred from implant to the femur. Severe bone remodeling was found on some specimens in which stress transfer was not physiological. Porous coated femoral stems achieve excellent fixation by bone ingrowth, but require physiological stress transfer in order to avoid significant bone remodeling after implantation.