The effect of surface immobilized bisphosphonates on the fixation of hydroxyapatite-coated titanium implants in ovariectomized rats

Immobilized bisphosphonates (BPs) have been introduced to improve implant fixation, however, no information could be found about the efficiency of this approach in osteoporotic bone. This study was designed to evaluate the bone response to surface immobilized BPs on implants inserted in tibiae of ovariectomized (OVX) rats. Three months after bilateral ovariectomy, 40 rats were randomly assigned into four groups for implantation of hydroxyapatite-coated titanium implants with or without immobilized BPs: (1) control group (without BP treatments); (2) pamidronate (PAM) group (1 mg/ml of PAM immersing); (3) ibandronate group (1 mg/ml of ibandronate immersing); and (4) zoledronic acid (ZOL) group (1 mg/ml of ZOL immersing). After implantation periods of 3 months, the peri-implant–bone density, trabecular microstructure, bone–implant interface and mechanical fixation of implants were evaluated by dual energy X-ray absorptiometry, micro-computed tomography, histology and push-out test. We found that three BPs triggered pronounced bone–implant integration and early bone formation around implants in OVX rats, with a rank order of ZOL > ibandronate > PAM. These results provide new evidence that immobilized BPs have positive effects on implant fixation in osteoporotic bone, in addition to their well-documented potency to inhibit implant loosening in normal bone.     

Screw insertion in trabecular bone causes peri-implant bone damage

Secure fracture fixation is still a major challenge in orthopedic surgery, especially in osteoporotic bone. While numerous studies have investigated the effect of implant loading on the peri-implant bone after screw insertion, less focus has been put on bone damage that may occur due to the screw insertion process itself. Therefore, the aim of this study was to localize and quantify peri-implant bone damage caused by screw insertion.We used non-invasive three-dimensional micro-computed tomography to scan twenty human femoral bone cores before and after screw insertion. After image registration of the pre- and post-insertion scans, changes in the bone micro-architecture were identified and quantified. This procedure was performed for screws with a small thread size of 0.3 mm (STS, N = 10) and large thread size of 0.6 mm (LTS, N = 10).Most bone damage occurred within a 0.3 mm radial distance of the screws. Further bone damage was observed up to 0.6 mm and 0.9 mm radial distance from the screw, for the STS and LTS groups, respectively. While a similar amount of bone damage was found within a 0.3 mm radial distance for the two screw groups, there was significantly more bone damage for the LTS group than the STS group in volumes of interest between 0.3–0.6 mm and 0.6–0.9 mm.In conclusion, this is the first study to localize and quantify peri-implant bone damage caused by screw insertion based on a non-invasive, three-dimensional, micro-CT imaging technique. We demonstrated that peri-implant bone damage already occurs during screw insertion. This should be taken into consideration to further improve primary implant stability, especially in low quality osteoporotic bone. We believe that this technique could be a promising method to assess more systematically the effect of peri-implant bone damage on primary implant stability. Furthermore, including peri-implant bone damage due to screw insertion into patient-specific in silico models of implant-bone systems could improve the accuracy of these models.     

Peri-implant bone microstructure determines dynamic implant cut-out

Dynamic implant cut-out is a frequent complication associated with surgical fracture fixation. In this in vitro study, we investigated the influence of the local trabecular bone microstructure on the rate and path of implant migration. Dynamic hip screws were implanted into six human femoral head specimens with a wide range of bone volume fractions. The specimens were subjected to image-guided failure assessment using physiological dynamic hip loading. Mechanical testing was used intermittently with high-resolution computed tomography scanning. A high correlation was found between the bone volume fraction and implant migration (R² = 0.95). Profiles of the bone-implant interface were computed based on the positions of the screw and the femoral head. With a larger interface, the implant migration rate was smaller. The bone-implant interface was significantly smaller on the approximated screw migration path than if it had been on a straight line in loading direction. We thus hypothesize that implants migrate on a path of least resistance. This would indicate a relevant mechanism for targeted surgical intervention.     

Comparison of dental implant stabilities by impact response and resonance frequencies using artificial bone

PurposeWe compared implant stability as determined by the peak frequency from the impact response with the implant stability quotient (ISQ) by resonance frequency analysis (RFA) in various artificial bone conditions. The clinical bone conditions were simulated using an artificial bone material with different cortical thicknesses and trabecular densities.Materials and methodsThe artificial bone material was solid, rigid polyurethane. The polyurethane foam of 0.8 g/cm³ density was used for the cortical bone layer, and that of 0.08, 0.16, 0.24, 0.32, and 0.48 g/cm³ densities for the trabecular bone layer. The cortical bone material of 4 different thicknesses (1.4, 1.6, 1.8, and 2.0 mm) was attached to the trabecular bone with varying density. Two types of dental implants (10 and 13 mm lengths of 4.0 mm diameter) were placed into the artificial bone blocks. An inductive sensor was used to measure the vibration caused by tapping the adapter–implant assembly. The peak frequency of the power spectrum of the impact response was used as the criterion for implant stability. The ISQ value was also measured for the same conditions.ResultsThe stability, as measured by peak frequency (SPF) and ISQ value, increased as the trabecular density and the cortical density increased in linear regression analysis. The SPF and ISQ values were highly correlated with each other when the trabecular bone density and cortical bone thickness changed (Pearson correlation = 0.90, p < 0.01). The linear regression of the SPF with the cortical bone thickness showed higher goodness of fit (R² measure) than the ISQ value with the cortical bone thickness. The SPF could differentiate implantation conditions as many as the ISQ value when the trabecular bone density and the cortical density changed. However, the ISQ value was not consistent with the general stability tendency in some conditions.ConclusionThe SPF showed better consistency and differentiability with implant stability than the ISQ value by resonance frequency analysis in the various implantation conditions.     

Local application of fluvastatin improves peri-implant bone quantity and mechanical properties: A rodent study

Statins are known to stimulate osteoblast activity and bone formation. This study examines whether local application of fluvastatin enhances osteogenesis around titanium implants in vivo. Ten-week-old rats received a vehicle gel (propylene glycol alginate (PGA)) or PGA containing fluvastatin (3, 15, 75 or 300 μg) in their tibiae just before insertion of the implants. For both histological and histomorphometric evaluations undecalcified ground sections were obtained and the bone–implant contact (BIC), peri-implant osteoid volume and mineralized bone volume (MBV) were calculated after 1, 2 and 4 weeks. Using the same models mechanical push-in tests were also performed to evaluate the implant fixation strength. After 1 week the MBV and push-in strength were significantly lower in the 300 μg fluvastatin-treated group than in the other groups (P < 0.01). At 2 weeks, however, the BIC and MBV were both significantly higher in the 75 μg fluvastatin-treated group than in the non-fluvastatin-treated groups (P < 0.01). Similar tendencies were observed at week 4. Furthermore, the data showed a good correlation between the MBV and the push-in strength. These results demonstrate positive effects of locally applied fluvastatin on the bone around titanium implants and suggest that this improvement in osseointegration may be attributed to calcification of the peri-implant bone.     

Peri-implant reactivity and osteoinductive potential of immobilized rhBMP-2 on titanium carriers

Recombinant human BMP-2 (rhBMP-2) was immobilized non-covalently and covalently as a monolayer on plasma vapour deposited (PVD) porous commercially pure titanium surfaces in amounts of 5–8 μg cm^?2, providing a ca. 10-fold increase vs. previously reported values [37]. Dissociation of the immobilized [¹²⁵I]rhBMP-2 from the surface occurred in a two-phase exponential decay: a first rapid phase (ca. 15% of immobilized BMP-2) with a half-life of 1–2 days and a second slow sustained release phase (ca. 85% of immobilized BMP-2) with a half-life of 40–60 days. Dissociation rate constants of sustained release of k_?1 = 1.3–1.9 × 10^?7 s^?1 were determined, allowing an estimation of the binding constants (K_A) for the adsorbed rhBMP-2 monolayer, to be around 10¹² M^?1. The rhBMP-2-coated surfaces showed a high level of biological activity, as demonstrated by in vitro epifluorescence tests for alkaline phosphatase with MC3T3-E1 cells and in vivo experiments. In vivo osteoinductivity of rhBMP-2-coated implants was investigated in a gap-healing model in the trabecular bone of the distal femur condylus of sheep. Healing occurred without inflammation or capsule formation. The calculated concentration of released rhBMP-2 in the 1 mm gap ranged from 20 to 98 nM – well above the half-maximal response concentration (K_0.5) for inducing alkaline phosphatase in MC3T3-E1 cells. After 4, 9 and 12 weeks the bone density (BD) and bone-to-implant contact (BIC) of the explanted implants were assessed histomorphometrically. Implants with immobilized rhBMP-2 displayed a significant (2- to 4-fold) increase in BD and BIC values vs. negative controls after 4–9 weeks. Integration of implants by trabecular bone was achieved after 4 weeks, indicating a mean “gap-filling rate” of ～250 μm week^?1. Integration of implants by cortical bone was observed after 9 weeks. Control implants without rhBMP-2 were not osseointegrated. This study demonstrates the feasibility of enhancing peri-implant osseointegration and gap bridging by immobilized rhBMP-2 on implant surfaces which may serve as a model for future clinical applications.     

The quantitative assessment of peri-implant bone responses using histomorphometry and micro-computed tomography

In the present study, the effects of implant design and surface properties on peri-implant bone response were evaluated with both conventional histomorphometry and micro-computed tomography (micro-CT), using two geometrically different dental implants (Screw type, St; Push-in, Pi) either or not surface-modified (non-coated, CaP-coated, or CaP-coated + TGF-β1). After 12 weeks of implantation in a goat femoral condyle model, peri-implant bone response was evaluated in three different zones (inner: 0–500 μm; middle: 500–1000 μm; and outer: 1000–1500 μm) around the implant. Results indicated superiority of conventional histomorphometry over micro-CT, as the latter is hampered by deficits in the discrimination at the implant/tissue interface. Beyond this interface, both analysis techniques can be regarded as complementary. Histomorphometrical analysis showed an overall higher bone volume around St compared to Pi implants, but no effects of surface modification were observed. St implants showed lowest bone volumes in the outer zone, whereas inner zones were lowest for Pi implants. These results implicate that for Pi implants bone formation started from two different directions (contact- and distance osteogenesis). For St implants it was concluded that undersized implantation technique and loosening of bone fragments compress the zones for contact and distant osteogenesis, thereby improving bone volume at the interface significantly.     

Hydroxyapatite coating affects the Wnt signaling pathway during peri-implant healing in vivo

Owing to its bio- and osteoconductivity, hydroxyapatite (HA) is a widely used implant material, but its osteogenic properties are only partly evaluated in vitro and in vivo. The present study focused on bone healing adjacent to HA-coated titanium (Ti) implants, with or without incorporated lithium ions (Li⁺). Special attention was given to the Wnt signaling pathway. The implants were inserted into rat tibia for 7 or 28 days and analyzed ex vivo, mainly by histomorphometry and quantitative real-time polymerase chain reaction (qPCR). HA-coated implants showed, irrespective of Li⁺ content, bone–implant contact (BIC) and removal torque values significantly higher than those of reference Ti. Further, the expression of OCN, CTSK, COL1A1, LRP5/6 and WISP1 was significantly higher in implant-adherent cells of HA-coated implants, with or without Li⁺. Significantly higher β-catenin expression and significantly lower COL2A1 expression were observed in peri-implant bone cells from HA with 14 ng cm⁻² released Li⁺. Interestingly, Ti implants showed a significantly larger bone area (BA) in the threads than HA with 39 ng cm⁻² released Li⁺, but had a lower BIC than any HA-coated implant. This study shows that HA, with or without Li⁺, is a strong activator of the Wnt signaling pathway, and may to some degree explain its high bone induction capacity.     

Anterior cruciate ligament fixation: Is radial force a predictor of the pullout strength of soft-tissue interference devices?

BackgroundIn anterior cruciate ligament (ACL) reconstruction, an interference device achieves soft-tissue graft fixation by radially compressing the graft against the bone.PurposeThe objective of this study was to measure the radial force generated by different interference devices and evaluate the effect of this radial force on the pullout strength of graft-device constructs.Study DesignControlled laboratory study.MethodsA resultant force (F_R) was used as a representative measure of the total radial force generated. Bovine tendons were fixated in either synthetic bone or porcine tibia using one of following devices: (1) RCI titanium screw, (2) PEEK screw, (3) IntraFix sheath-and-screw device, and (4) ExoShape sheath-and-insert device. F_R was measured while each device was inserted into synthetic bone mounted on a test machine (n = 5 for each device). In a subsequent test series, graft-device constructs were loaded to failure at 50 mm/min. The pullout strength was measured as the ultimate load before failure (n = 10 for each device).ResultsThe F_R values generated during insertion into synthetic bone were 777 ± 86 N, 865 ± 140 N, 1313 ±198 N, and 1780 ± 255 N for the RCI screw, PEEK screw, IntraFix, and ExoShape, respectively. The pullout strengths in synthetic bone for the RCI screw, PEEK screw, IntraFix and ExoShape were 883 ± 125 N, 716 ± 249 N, 1147 ± 142 N, and 1233 ± 190 N, respectively.ConclusionsThese results suggest that the F_R generated during interference fixation affects the pullout strength with sheath-based devices providing superior F_R compared with interference screws. The use of synthetic bone was validated by comparing the pullout strengths to those when tested in porcine tibia.Clinical relevanceThese results could be valuable to a surgeon when determining the best fixation device to use in the clinical setting.     

Numerical simulation of the effect of time-to-loading on peri-implant bone

PurposeTo evaluate the effect of time-to-loading on trabecular bone around single-tooth dental implants using numerical solutions based on computer models.Materials and methodsA global model with a coarse mesh carrying a Straumann dental implant (043.033S; Institut Straumann, Basel, Switzerland) was created. A region of interest in trabecular bone was defined to study a localized part of the global model with a refined mesh. Time-to-loading submodels to simulate 2 h, 4 days, 1, 4, 6 and 12 wks of trabecular bone-healing status were designed and created. Bone types were considered in the simulation by different elastic bone properties. A 100-N oblique static load was applied. Maximum and minimum principal stresses were calculated and visualized.ResultsBone types with higher elastic moduli experienced higher stress levels. Changes in the quality and quantity of bone at the bone-implant interface did not affect the overall stress distribution. Peri-implant bone with a higher elastic modulus preserved the stress increase at the implant–bone interface.DiscussionReduced bone contact may not have a prevailing effect over bone quality and quantity on stress generation at the peri-implant bone.ConclusionTime-to-loading of single-tooth implants may not differ in terms of load distributions in neighboring peri-implant bone.     

Effects of soluble cobalt and cobalt incorporated into calcium phosphate layers on osteoclast differentiation and activation

Metal ions originating from mechanical debris and corrosive wear of prosthetic implant alloys accumulate in peri-implant soft tissues, bone mineral, and body fluids. Eventually, metal ions such as cobalt (II) (Co²⁺), which is a major component of cobalt–chromium-based implant alloys and a known activator of osteolysis, are incorporated into the mineral phase of bone. We hypothesize that the accumulation of Co²⁺ in the mineral could directly activate osteolysis by targeting osteoclasts. To test this hypothesis, we coated tissue culture plastic with a thin layer of calcium phosphate (CaP) containing added traces of Co²⁺, thereby mimicking the bone mineral accumulation of Co²⁺. Murine bone marrow osteoclasts formed in the presence of M-CSF and RANKL were cultured on these surfaces to examine the effects of Co²⁺ on osteoclast formation and resorptive activity. Treatment conditions with Co²⁺ involved incorporation into the CaP layer, adsorption to the mineral surface, or addition to culture media. Micromolar concentrations of Co²⁺ delivered to developing osteoclast precursors by all 3 routes increased both osteoclast differentiation and resorptive function. Compared to CaP layers without Co²⁺, we observed a maximal 75% increase in osteoclast numbers and a 2.3- to 2.7-fold increase in mineral resorption from the tissue culture wells containing 0.1 μm Co²⁺ and 0.1–10 μm Co²⁺, respectively. These concentrations are well within the range found in peri-implant tissues in vivo. This direct effect of Co²⁺ on osteoclasts appears to act independently of the particulate phagocytosis/inflammation-mediated pathways, thus enhancing osteolysis and aseptic implant loosening.     

Integrating micro CT indices,CT imaging and computational modelling to assess the mechanical performance of fluoride treated bone

In this study we evaluate the influence of low-dose fluoride treatment on 23 patient biopsies. Computational finite element (FE) models of each biopsy were subjected to a range of loads including compression, shear and torsion. The modelling framework was validated against three 3D printed models with known material properties subjected to compression till failure using an Instron machine. The primary outcomes from this study were that mechanical strength was not significantly correlated to low-dose (<10 mg/day) of fluoride levels (one-way ANOVA, P-values of 0.78, 0.69 and 0.62 for compression, shear and torsion, respectively). However, when bulk bone material properties were derived from DXA bone mineral density (BMD) from each patient's proximal femur a non-significant linear decline in mechanical strength with increase in fluoride was predicted. When the same material property was used for all bones (to evaluate bone architecture influence) then mechanical strength showed a characteristic concave upwards trend, consistent with the variation of micro CT derived percentage bone volume (BV/TV). The secondary outcomes from this study were that in compression, BV/TV was observed to be a strong surrogate measure for mechanical strength (R² = 0.83), while bone surface density (R² = 0.6), trabecular thickness (R² = 0.5) and intersection surface (R² = 0.6) also explained the variation of mechanical strength well. However, trabecular separation and trabecular number were mildly correlated with mechanical strength (R² of 0.31 and 0.35, respectively). Compression was the loading mode most strongly correlated to micro CT indices. Material properties adapted from the proximal femur reduced the CT index correlations by up to 58% indicating that bulk density from a near proximity is a poor representation of specific localised density. Substituting the 3D micro CT indices with 2D histomorphometric data decreased correlations by at least 33% indicating that structural identification on a plane is not representative of the full 3D architecture necessary for a complete bone strength analysis. The presented computational framework may be used to assess the roles that bone architecture and loading modes play in bone quality, and which micro CT indices are good surrogate measures for mechanical strength.     

Predicting time-dependent remodeling of bone around immediately loaded dental implants with different designs

The purpose of this study was to predict time-dependent biomechanics of bone around cylindrical screw dental implants with different macrogeometric designs under simulated immediate loading condition. The remodeling of bone around a parallel-sided and a tapered dental implant of same length was studied under 100 N oblique load by implementing the Stanford theory into three-dimensional finite element models. The results of the analyses were examined in five time intervals consisting loading immediately after implant placement, and after 1, 2, 3 and 4 weeks following implantation. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x-(implant lateral direction with a projection of the oblique force) and y-(implant longitudinal direction) axes of the implant were evaluated. The highest value of the maximum and minimum principal stresses around both implants increased in cortical bone and decreased in trabecular bone. The maximum and minimum principal stresses in cortical bone were higher around the tapered cylindrical implant, but stresses in the trabecular bone were higher around the parallel-sided cylindrical implant. Strain energy density around both implants increased in cortical bone, slightly decreased in trabecular bone, and higher values were obtained for the parallel-sided cylindrical implant. Displacement values slightly decreased in time in x-axis, and an initial decrease followed by a slight increase was observed in the y-axis. Bone responded differently in remodeling for the two implant designs under immediate loading, where the cortical bone carried the highest load. Application of oblique loading resulted in increase of stiffness in the peri-implant bone.     

Understanding the influence of MgO and SrO binary doping on the mechanical and biological properties of β-TCP ceramics

The objective of this study was to evaluate the influence of MgO and SrO doping on the mechanical and biological properties of β-tricalcium phosphate (β-TCP). β-TCP was doped with two different binary compositions, 0.25 and 1.0 wt.% SrO along with 1.0 wt.% MgO. MgO and SrO doping increased the β phase stability at a sintering temperature of 1250 °C and marginally decreased the compressive strength of β-TCP. An in vitro cell–material interaction study, using human fetal osteoblast cells (hFOB), indicated that doped β-TCP was non-toxic, and MgO/SrO dopants improved cell attachment and growth. β-TCP implants doped with 1.0 wt.% MgO and 1.0 wt.% SrO showed good in vivo biocompatibility when tested in male Sprague–Dawley rats for 16 weeks. Histomorphology analysis indicated that MgO/SrO-doped β-TCP promoted more osteogenesis than pure β-TCP. In vivo osteocalcin and type I collagen assay also revealed faster bone formation in rats with doped β-TCP implant compared to rats with pure β-TCP implant. Low Ca²⁺ concentration in the urine of rats with doped β-TCP implant confirmed slower degradation of MgO/SrO-doped β-TCP than pure β-TCP.     

The effect of polyelectrolyte multilayer coated titanium alloy surfaces on implant anchorage in rats

Advances have been achieved in the design and biomechanical performance of orthopedic implants in the last decades. These include anatomically shaped and angle-stable implants for fracture fixation or improved biomaterials (e.g. ultra-high-molecular-weight polyethylene) in total joint arthroplasty. Future modifications need to address the biological function of implant surfaces. Functionalized surfaces can promote or reduce osseointegration, avoid implant-related infections or reduce osteoporotic bone loss. To this end, polyelectrolyte multilayer structures have been developed as functional coatings and intensively tested in vitro previously. Nevertheless, only a few studies address the effect of polyelectrolyte multilayer coatings of biomaterials in vivo. The aim of the present work is to evaluate the effect of polyelectrolyte coatings of titanium alloy implants on implant anchorage in an animal model. We test the hypotheses that (1) polyelectrolyte multilayers have an effect on osseointegration in vivo; (2) multilayers of chitosan/hyaluronic acid decrease osteoblast proliferation compared to native titanium alloy, and hence reduce osseointegration; (3) multilayers of chitosan/gelatine increase osteoblast proliferation compared to native titanium alloy, hence enhance osseointegration. Polyelectrolyte multilayers on titanium alloy implants were fabricated by a layer-by-layer self-assembly process. Titanium alloy (Ti) implants were alternately dipped into gelatine (Gel), hyaluronic acid (HA) and chitosan (Chi) solutions, thus assembling a Chi/Gel and a Chi/HA coating with a terminating layer of Gel or HA, respectively. A rat tibial model with bilateral placement of titanium alloy implants was employed to analyze the bones’ response to polyelectrolyte surfaces in vivo. 48 rats were randomly assigned to three groups of implants: (1) native titanium alloy (control), (2) Chi/Gel and (3) Chi/HA coating. Mechanical fixation, peri-implant bone area and bone contact were evaluated by pull-out tests and histology at 3 and 8 weeks. Shear strength at 8 weeks was statistically significantly increased (p < 0.05) in both Chi/Gel and Chi/HA groups compared to the titanium alloy control. No statistically significant difference (p > 0.05) in bone contact or bone area was found between all groups. No decrease of osseointegration of Chi/HA-coated implants compared to non-coated implants was found. The results of polyelectrolyte coatings in a rat model showed that the Chi/Gel and Chi/HA coatings have a positive effect on mechanical implant anchorage in normal bone.     

Variation of the impact duration during the in vitro insertion of acetabular cup implants

The acetabular cup (AC) is an implant impacted into a bone cavity and used for hip prosthesis surgery. Initial stability of the AC is an important factor for long term surgical success. The aim of this study is to determine the variations of the impact duration during AC implant insertion.Twenty-two bone samples taken from bovine femurs were prepared ex vivo for the insertion of an acetabular cup implant, following the surgical procedure used in the clinic. For each bone sample, ten impacts were applied using reproducible mass falls (3.5 kg) in order to insert the AC implant. Each impact duration was recorded using a wide bandwidth force sensor.For all bone samples, the impact duration was shown to first decrease as a function of the impact number, then reaching a stationary value equal in average to 4.2 ± 0.7 ms after an average number of 4.1 ± 1.7 impacts. The impact duration may be related to variations of the bone–implant interface contact rigidity because of an increase the amount of bone tissue in contact with the AC implant.Measurements of impact duration have a good potentiality for clinical application to assist the surgeon during the insertion of the AC implant, providing valuable information on the bone–implant interface contact properties.     

Probability of mechanical loosening of the femoral component in high flexion total knee arthroplasty can be reduced by rather simple surgical techniques

BackgroundSome follow-up studies of high flexion total knee arthoplasties report disturbingly high incidences of femoral component loosening. Femoral implant fixation is dependant on two interfaces: the cement–implant and the cement–bone interface. The present finite-element model (FEM) is the first to analyse both the cement–implant interface and cement–bone interface. The cement–bone interface is divided into cement–cancellous and cement–cortical bone interfaces, each having their own strength values. The research questions were: (1) which of the two interfaces is more prone to failure? and (2) what is the effect of different surgical preparation techniques for cortical bone on the risk of early failure.?MethodsFEM was used in which the posterior-stabilized PFC Sigma RP-F (DePuy) TKA components were incorporated. A full weight-bearing squatting cycle was simulated (ROM = 50°–155°). An interface failure index (FI) was calculated for both interfaces.ResultsThe cement-bone interface is more prone to failure than the cement implant interface. When drilling holes through the cortex behind the anterior flange instead of unprepared cortical bone, the area prone to early interface failure can be reduced from 31.3% to 2.6%.ConclusionThe results clearly demonstrate high risk of early failure at the cement–bone interface. This risk can be reduced by some simple preparation techniques of the cortex behind the anterior flange.Clinical relevanceHigh-flexion TKA is currently being introduced. Some reports show high failure rates. FEM can be helpful in understanding failure of implants.     

In vivo bone response and mechanical evaluation of electrosprayed CaP nanoparticle coatings using the iliac crest of goats as an implantation model

Recent trends in clinical implantology include the use of endosseous dental implant surfaces embellished with nano-sized modifications. The current study was initiated to evaluate the mechanical properties, as well as the potential beneficial effects, of electrosprayed CaP nanoparticle-coated (nano-CaP) implants on the in vivo osteogenic response, compared with grit-blasted, acid-etched (GAE) implant surfaces as controls. For this purpose nano-CaP coatings were deposited on cylindrical screw-type (St) implants and implanted bilaterally into the iliac crest of goats for 6 weeks. In addition to histological and histomorphometrical analyses, insertion torque and removal torque values were measured on implant placement and retrieval, respectively. The present study showed similar insertion and removal torque values for nano-CaP-coated and GAE control implants, with no statistically significant increase in torque value during the implant period for either group. With regard to bone–implant contact and peri-implant bone volume, no significant differences were found between nano-CaP-coated and GAE implants after 6 weeks implantation. In conclusion, this study has demonstrated that in situations in which implants are placed in a non-compromised situation using a standard press fit implantation strategy the performance of electrosprayed nano-CaP coatings is comparable with GAE implants, both with respect to implant fixation and bone healing response.     

Low-level laser therapy using the minimally invasive laser needle system on osteoporotic bone in ovariectomized mice

This study tested the effectiveness of low-level laser therapy (LLLT) in preventing and/or treating osteoporotic trabecular bone. Mice were ovariectomized (OVX) to induce osteoporotic bone loss. The tibiae of eight OVX mice were treated for 5 days each week for 2 weeks by LLLT (660 nm, 3 J) using a minimally invasive laser needle system (MILNS) which is designed to minimize loss of laser energy before reaching bone (LASER group). Another eight mice received a sham treatment (SHAM group). Structural parameters of trabecular bone were measured with in vivo micro-computed tomography images before and after laser treatment. After LLLT for 2 weeks, the percentage reduction (%R) was significantly lower in BV/TV (bone volume fraction) and Tb.N (trabecular number, p < 0.05 and p < 0.05) and significant higher in Tb.Sp (trabecular separation) and SMI (structure model index, p < 0.05 and p < 0.05) than in the SHAM group. The %R in BV/TV at sites directly treated by LLLT was significantly lower in the LASER group than the SHAM group (p < 0.05, p < 0.05). These results indicated that LLLT using MILNS may be effective for preventing and/or treating trabecular bone loss and the effect may be site-dependent in the same bone.