HA particles can be released from well-fixed HA-coated stems

20 hip arthroplasties with a Landos Corail Ti6Al4V stem entirely plasma-sprayed with a 155 ±35 μm thick HA coating were reoperated on after median 6 (2-8) years because of polyethylene wear (10), acetabular loosening (7), instability (2), or infection (1). We took biopsies from the proximal femurs adjacent to the well-fixed stems. Undecalcified sections were prepared and examined with a light microscope. The biopsies contained median 5 (1.3-16 ) mm metal interface with 54% HA, 32% bone, and 14% soft tissue. The median thickness of the remaining HA coating was 137 (6-380) μm, and the HA-tissue interface included 89% bone and 11% soft tissue. All HA coatings showed partial degradation and replacement by soft tissue, osteoid-like tissue, or bone. 6 hips had tissue ingrowth between HA and metal consistent with delamination. 14 hips showed bone resorptive areas containing some HA particles and large amounts of polyethylene and metal particles, partly internalized in multinucleated giant cells and macrophages. Bone resorption was associated with metal and polyethylene particles, but not with HA particles. The HA coatings were undermined, resulting in release of large flakes of HA with free access to the articulation. We believe this mechanism may be responsible for third-body wear.     

Sealing effect of hydroxyapatite coating on peri-implant migration of particles. An experimental study in dogs

We have studied the beneficial effects of a hydroxyapatite (HA) coating on the prevention of the migration of wear debris along the implant-bone interface. We implanted a loaded HA-coated implant and a non-coated grit-blasted titanium alloy (Ti) implant in each distal femoral condyle of eight Labrador dogs. The test implant was surrounded by a gap communicating with the joint space and allowing access of joint fluid to the implant-bone interface. We injected polyethylene (PE) particles into the right knee three weeks after surgery and repeated this weekly for the following five weeks. The left knee received sham injections. The animals were killed eight weeks after surgery. Specimens from the implant-bone interface were examined under plain and polarised light. Only a few particles were found around HA-coated implants, but around Ti implants there was a large amount of particles. HA-coated implants had approximately 35% bone ingrowth, whereas Ti implants had virtually no bone ingrowth and were surrounded by a fibrous membrane. Our findings suggest that HA coating of implants is able to inhibit peri-implant migration of PE particles by creating a seal of tightly-bonded bone on the surface of the implant.     

Degradation of hydroxyapatite coating on a well-functioning femoral component

We carried out a histological study of a proximally hydroxyapatite (HA)-coated femoral component, retrieved after 9.5 years of good function. The HA coating had completely degraded. Bone was in direct contact with the titanium surface in all the areas which had been coated, with no interposing fibrous tissue. There were no signs of particles, third-body wear, adverse tissue reactions or osteolysis. Bone remodelling was evident by the presence of resorption lacunae; tetracycline labelling showed bone laid down six years after implantation. The loss of the HA-coating had no negative effect on the osseo-integration of the stem. We conclude that the HA coating contributes to the fixation of the implant and that its degradation does not adversely affect the long-term fixation.     

Hydroxyapatite-coated titanium for orthopedic implant applications

The interface mechanical characteristics and histology of commercially pure (CP) titanium- and hydroxyapatite- (HA) coated Ti-6Al-4V alloy were investigated. Interface shear strength was determined using a transcortical push-out model in dogs after periods of three, five, six, ten, and 32 weeks. Undecalcified histologic techniques with implants in situ were used to interpret differences in mechanical response. The HA-coated titanium alloy implants developed five to seven times the mean interface strength of the uncoated, beadblasted CP titanium implants. The mean values for interface shear strength increased up to 7.27 megaPascals (MPa) for the HA-coated implants after ten weeks of implantation, and the maximum mean value of interface shear strength for the uncoated CP titanium implants was 1.54 MPa. For both implant types there was a slight decrease in mean shear strength from the maximum value to that obtained after the longest implantation period (32 weeks). Histologic evaluations in all cases revealed mineralization of interface bone directly onto the HA-coated implant surface, with no fibrous tissue layer interposed between the bone and HA visible at the light microscopic level. The uncoated titanium implants had projections of bone to the implant surface with apparent direct bone-implant apposition observed in some locations. Measurements of the HA coating material made from histologic sections showed no evidence of significant HA resorption in vivo after periods of up to 32 weeks.     

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.     

HA particles can be released from well-fixed HA-coated stems: histopathology of biopsies from 20 hips 2-8 years after implantation

20 hip arthroplasties with a Landos Corail Ti6Al4V stem entirely plasma-sprayed with a 155+/-35 microm thick HA coating were reoperated on after median 6 (2-8) years because of polyethylene wear (10), acetabular loosening (7), instability (2), or infection (1). We took biopsies from the proximal femurs adjacent to the well-fixed stems. Undecalcifled sections were prepared and examined with a light microscope. The biopsies contained median 5 (1.3-16 ) mm metal interface with 54% HA, 32% bone, and 14% soft tissue. The median thickness of the remaining HA coating was 137 (6-380) microm, and the HA-tissue interface included 89% bone and 11% soft tissue. All HA coatings showed partial degradation and replacement by soft tissue, osteoid-like tissue, or bone. 6 hips had tissue ingrowth between HA and metal consistent with delamination. 14 hips showed bone resorptive areas containing some HA particles and large amounts of polyethylene and metal particles, partly internalized in multinucleated giant cells and macrophages. Bone resorption was associated with metal and polyethylene particles, but not with HA particles. The HA coatings were undermined, resulting in release of large flakes of HA with free access to the articulation. We believe this mechanism may be responsible for third-body wear.     

Sealing effect of hydroxyapatite coating: a 12-month study in canines

This study addresses the clinical problems regarding access of wear debris to the bone-implant interface and the possible dissemination of polyethylene (PE) particles to distant organs. We inserted two implants into each knee of 7 dogs allowing access of joint fluid to the bone-implant interface with a 0.75 mm initial gap around the implant. Hydroxyapatite (HA)-coated and non-coated (Ti) titanium alloy implants were randomly allocated to each distal femoral condyle. PE particles were repeatedly injected into the right knee joint 3 weeks after surgery for a period of 49 weeks, while only vehicle was injected into the left knee joint. We found huge amounts of PE particles mainly in the bone-implant interface around Ti implants. Infiltration of mononuclear inflammatory cells was present around 3 of 7 Ti implants in relation to PE particles. HA implants had approximately 70% bone ongrowth. In contrast, no bone ongrowth was seen on any Ti implants, all being surrounded by a fibrous membrane. The number of PE particles was evaluated semi-quantitatively. More PE particles were found around Ti implants than with HA implants (p < 0.002). Specimens from iliac lymph nodes, liver, spleen and lung were examined and showed dissemination of PE particles only in regional lymph nodes.     

Bone graft incorporation around titanium-alloy- and hydroxyapatite-coated implants in dogs.

To evaluate cancellous allogenic bone graft incorporation into porous-coated implants, the fixation of titanium alloy-(Ti) and hydroxyapatite-(HA) coated implants with and without bone graft was compared. An unloaded model with unilateral carragheenin-induced osteopenia of the knee was used in 12 mature dogs. Ti- and HA-coated cylinders were implanted in the distal femoral condyles and centralized in 2-mm overreamed drill holes. Allogenic, fresh-frozen (-80 degrees) cancellous bone graft was packed around the implants in six dogs. In a matched group of six other dogs, the implants were left in overreamed canals without bone graft. After six weeks the interface shear strength of grafted Ti-coated implants had significantly increased compared to the nongrafted Ti implants. However, HA coating used without bone graft was capable of enhancing the bone-implant interface shear strength to nearly the same degree. The fixation of grafted Ti- and HA-coated implants was equal. No significant difference in implant fixation was found between osteopenic and control bone. Histomorphometric evaluation of mineralizing surfaces in direct contact with the implant confirmed the results from the push-out test. Bone-implant fixation when using allogeneic fresh-frozen cancellous bone graft in osteopenic and control bone was enhanced by hydroxyapatite coating but the HA coating alone appeared to offer almost the same improvement in anchorage in 2-mm defects. Loss of bone stock around loose prosthetic implants often requires bone grafting. However, because of anatomic constraints in joint prosthetic surgery, a complete filling of defects with bone graft is difficult, and areas of gaps between bone and implant will remain. Provided mechanical stability of the prosthesis, the results reported here suggest that these areas will probably be filled early with new mineralizing bone if the prosthesis is coated with a thin layer of hydroxyapatite.     

Superior sealing effect of hydroxyapatite in porous-coated implants: experimental studies on the migration of polyethylene particles around stable and unstable implants in dogs

Background Migration of wear debris to the periprosthetic bone is a major cause of osteolysis and implant failure. Both closed-pore porous coatings and hydroxyapatite (HA) coatings have been claimed to prevent the migration of wear debris. We investigated whether HA could augment the sealing effect of a porous coating under both stable and unstable conditions.

Methods We inserted porous-surfaced knee implants, with and without HA coating, in 16 dogs, according to a paired, randomized study design. 8 dogs had 2 implants inserted into each knee using a stable implant device and 8 dogs received 1 implant in each knee using a micro-motion (500 μm) implant device. Implants had a periimplant gap of 0.75 mm. We then injected polyethylene (PE) particles or a control solution into the knee joints on a weekly basis.

Results After 16 weeks, the rating of particles around stable implants was reduced by the HA coating from a median value of 2 (1-4) to 1 (0-1) (p = 0.01) and during micromotion from 3 (2-4) to 1 (0-3) (p = 0.002). HA-coated implants had superior bone ongrowth during stable and unstable conditions. We found no difference in bone ongrowth between PE-exposed and vehicle-exposed implants.

Interpretation Compared to a pure plasma-sprayed porous coating, a layer of HA coating provides better bone ongrowth and protects the bone-implant interface against the migration of wear debris under both stable and unstable conditions.     

Effect of low‐dose X‐ray irradiation and Ti particles on the osseointegration of prosthetic

Low‐dose irradiation (LDI) exhibits a positive effect on osteoblasts and inhibitory effect of inflammation. Here, we test the hypothesis that LDI can promote osseointegration and inhibit the inflammatory membrane formation in the presence of titanium (Ti) particles. Endotoxin‐free titanium particles were injected into rabbit, prior to the insertion of a Ti6‐Al‐4‐V sticks pre‐coated with hydroxyapatite. Two days after operation, both distal femurs of the animal were exposed to 0.5 Gy X‐ray irradiation. All ani­mals were euthanized 8 weeks after the operation. The PINP concentration was determined at day 0, 2, 4, and 8 weeks after operation. Trabecular morphology around the implants 8 weeks after operation was assessed using micro‐CT, then the maximum push out force of simples was assessed using biomechanics test. Five samples in each group were chosen for bone histomorphology study without decalcification 8 weeks after operation. The results confirmed that the LDI can significantly improve ingrowth of bone into the prosthetic interface and stability of the prosthesis when there was no wear particles. Although promotion effects for bone formation induced by LDI can be counteracted by wear particles, LDI can significantly inhibit the interface membrane formation around the implant induced by wear particles. Based on these results, we conclude that LDI may be useful for enhancing the stability of prosthesis when there are no wear particles and for inhibiting the interface membrane formation during the early stage of aseptic loosening in the presence of wear particles. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1688–1696, 2016.     

Eight-year results of hydroxyapatite-coated hip arthroplasty

Ninety hips in 82 patients using Omnifit hydroxyapatite (HA)-coated prosthesis were followed for at least 7 years. All stems were stable at the final follow-up. However, aseptic loosening was found in 8 cups and 6 of them were revised. Two polyethylene wear were treated with inserts exchanged. The mechanical failure rate was 11.4% and the combined failure rate was 14.3% for HA-coated cup. Four other cups with wear and osteolysis without loosening or pain and 2 cups with polyethylene wear without osteolysis were still under observation. Our findings suggest that hip arthroplasties with HA coating on the smooth surface of a titanium cup is not reliable. The mid-term result of HA-coated stem is as good as that of porous-coated stem.     

Porous cups with and without hydroxylapatite-tricalcium phosphate coating: 23 matched pairs evaluated with radiostereometry

Migration, wear, and presence of radiolucencies were studied in 23 matched pairs of patients operated with porous-coated acetabular cups with additional screw fixation. All implants had the same type of titanium fiber mesh. In each pair, one of the cups was plasma-sprayed with a coating consisting of 70% hydroxylapatite (HA) and 30% tricalcium phosphate (TCP). Radiostereometric analysis up to 2 years after the operation revealed smaller rotations around the horizontal axis in cups with HA/TCP coating. The migration of the cup center was not significantly influenced. Evaluation of femoral head penetration in 12 of the matched pairs did not reveal any significant difference. Immediately after operation, implants with HA/TCP coating had more central radiolucencies, which, despite minimal migration, disappeared during the follow-up. The clinical results did not differ between the 2 groups. The findings of less tilting and diminishing radiolucencies in the cups with HA/TCP coating suggest a more complete ingrowth of bone and a better sealing of the interface.     

Superior sealing effect of hydroxyapatite in porous-coated implants

Background Migration of wear debris to the periprosthetic bone is a major cause of osteolysis and implant failure. Both closed-pore porous coatings and hydroxyapatite (HA) coatings have been claimed to prevent the migration of wear debris. We investigated whether HA could augment the sealing effect of a porous coating under both stable and unstable conditions.

Methods We inserted porous-surfaced knee implants, with and without HA coating, in 16 dogs, according to a paired, randomized study design. 8 dogs had 2 implants inserted into each knee using a stable implant device and 8 dogs received 1 implant in each knee using a micro-motion (500 μm) implant device. Implants had a periimplant gap of 0.75 mm. We then injected polyethylene (PE) particles or a control solution into the knee joints on a weekly basis.

Results After 16 weeks, the rating of particles around stable implants was reduced by the HA coating from a median value of 2 (1–4) to 1 (0–1) (p = 0.01) and during micromotion from 3 (2–4) to 1 (0–3) (p = 0.002). HA-coated implants had superior bone ongrowth during stable and unstable conditions. We found no difference in bone ongrowth between PE-exposed and vehicle-exposed implants.

Interpretation Compared to a pure plasma-sprayed porous coating, a layer of HA coating provides better bone ongrowth and protects the bone-implant interface against the migration of wear debris under both stable and unstable conditions.     

Sealing effect of hydroxyapatite coating: A 12-month study in canines

This study addresses the clinical problems regarding access of wear debris to the bone-implant interface and the possible dissemination of polyethylene (PE) particles to distant organs. We inserted two implants into each knee of 7 dogs allowing access of joint fluid to the bone-implant interface with a 0.75 mm initial gap around the implant. Hydroxyapatite (HA)-coated and non-coated (Ti) titanium alloy implants were randomly allocated to each distal femoral condyle. PE particles were repeatedly injected into the right knee joint 3 weeks after surgery for a period of 49 weeks, while only vehicle was injected into the left knee joint. We found huge amounts of PE particles mainly in the bone-implant interface around Ti implants. Infiltration of mononuclear inflammatory cells was present around 3 of 7 Ti implants in relation to PE particles. HA implants had approximately 70% bone ongrowth. In contrast, no bone ongrowth was seen on any Ti implants, all being surrounded by a fibrous membrane. The number of PE particles was evaluated semi-quantitatively. More PE particles were found around Ti implants than with HA implants (p < 0.002). Specimens from iliac lymph nodes, liver, spleen and lung were examined and showed dissemination of PE particles only in regional lymph nodes.     

比格犬体内涂层螺钉-骨组织界面的组织学观察

目的了解钛涂层、羟基磷灰石(hydroxyapatite,HA)涂层及钛+HA复合涂层螺钉置入体内后,螺钉-骨界面在术后早期的骨整合情况。方法选取成年比格犬16只平均分为普通螺钉组、HA涂层螺钉组、钛涂层螺钉组及钛+HA复合涂层螺钉组(每组4只,雌雄各2只)。螺钉置入比格犬颈椎椎体3个月,之后取出椎体,进行脱水、包埋处理,进行硬组织切片染色,观察涂层-骨界面的骨整合情况。结果 HA涂层螺钉和钛+HA复合涂层螺钉与周围骨组织结合紧密,骨组织的接触率明显高于普通螺钉和钛涂层螺钉,其中HA涂层螺钉与周围骨组织的接触率最高。结论HA涂层螺钉与周围骨组织的接触率最高,这可以作为生物力学测试中HA涂层螺钉具有较高生物力学稳定性的界面组织学基础。     

Ceramic coating improves tibial component fixation in total knee arthroplasty

Forty uncemented total knee arthroplasties (36 patients) were randomly allocated to a Miller-Galante II prosthesis with or without hydroxyapatite/tricalcium phosphate (HA/TCP) coating on the titanium fiber mesh on the undersurface of the tibial component. The patients were followed for 2 years with repeated radiostereometric examinations. After 2 years, the HA/TCP tibial components displayed smaller anterior-posterior tilt and less subsidence. The mean value of maximal total point motion was small: 0.5 mm in both groups. At 24 months, there were more radiolucent lines under the tibial tray and around the stem in the uncoated group, but the clinical results did not differ. HA/TCP coating on the undersurface of the tibial component improved the stability and seemed to improve the quality of the interface between the tibial component and the bone.     

Osteolysis from a press-fit hydroxyapatite-coated implant: A case study

The clinical and histological results of hydroxyapatite (HA) coating separation from a press-fit total hip arthroplasty 3.3 years after surgery are documented. Semiquantitative histological analysis showed grade 3+ mononuclear histiocytes and giant cells present in the retrieved capsule and periprosthetic tissues. Grad 3+ (titanium alloy, HA, and polyethylene) particles could be seen throughout the tissues. Backscattered electron and correlated elemental analysis confirmed that the HA coating had migrated to the articulating surface of the polyethylene insert causing third-body wear. The authors suggest that the orthopedic surgeon be cautioned in the routine use of HA-coated implants if osteolysis associated with HA separation and migration is to be avoided.     

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.     

磨屑在人工关节无菌性松动中作用的实验研究

目的：观察磨屑在动物体内引起的组织学反应，比较了不同磨屑所致反应差别，比较磨屑在羟基磷灰石涂层钛合金棒－骨界面和光滑钛合金棒－骨界面间移动差别，探讨人工关节无菌性松动机制。方法：６４只家兔分为８组（ｎ＝８），分别将羟基磷灰石涂层钛合金棒和光滑钛合金棒经膝关节置入股骨远端，定期膝关节注入聚乙烯，钛合金及两者的混合磨屑。光镜、偏振光显微镜和电镜观察关节滑膜、两种钛合金棒－骨界面的组织学和超微结构。结果     

Tissue reactions adjacent to well-fixed hydroxyapatite-coated acetabular cups. Histopathology of ten specimens retrieved at reoperation after 0.3 to 5.8 years

Ten acetabular cups coated with hydroxyapatite (HA) had originally been inserted in five primary and five revision total hip replacements. The thickness of the HA was 155 +/- 35 microm. The cups, which were well-fixed, were retrieved, with their adherent tissue, at reoperation after 0.3 to 5.8 years because of infection (five hips), wear of polyethylene (three hips), and instability (two hips). Undecalcified sections showed a direct contact between bone and osteoid-like tissue which had formed directly onto the HA coating. The area within the threads and their mirror images, as well as the implant-tissue interfaces consisted of similar amounts of bone and soft tissue. Degradation of HA was seen in all hips. The mean thickness of the remaining HA coating was 97 microm (95% CI 94 to 101). The metal interface comprised 66% HA. The HA-tissue interface contained more bone than soft tissue (p = 0.001), whereas the metal-tissue interface included more soft tissue than bone (p = 0.019). Soft tissue at the implant interface and poor replacement of HA by bone may interfere with long-term fixation.