Biomechanical Pull-out Tests Research Articles

Effects of antiseptic irrigation solutions on osseointegration in a cementless tibial implantation mouse model.

Despite the success of standard antiseptic irrigation solutions in reducing periprosthetic joint infection (PJI) rates, there is still a need for more effective solutions. Synergistic use of povidone-iodine (PI) and hydrogen peroxide (H2O2) has shown promising results; however, the optimal solution concentration balancing bactericidal activity and osseointegration remains unknown. This study aims to evaluate the impact of these antiseptic irrigation solutions on osseointegration and the bone-implant interface strength in vivo. Forty C57BL/6 mice underwent bilateral tibial implantation surgery and were randomly allocated into three groups receiving 0.3% PI, 10% PI mixed with 3% H2O2, or saline as irrigation solutions intraoperatively. Assessments were performed on postoperative Days 1 and 28, including plain radiographs, microcomputed tomography (microCT) evaluation, histological analysis, immunohistochemistry, and biomechanical pull-out testing. No wound complications were observed. MicroCT scans revealed no differences in peri-implant trabecular bone parameters. Biomechanical pull-out testing showed no differences in the bone-implant interface strength across groups. Histological analysis indicated no differences in bone and bone marrow percentage areas among treatment groups. Immunohistochemical analysis demonstrated no differences among groups in peri-implant osteocalcin, osterix, or endomucin-positive cells. In conclusion, using either antiseptic irrigation solution showed no differences in osseointegration parameters compared to the control group, demonstrating safety and the absence of toxicity. CLINICAL RELEVANCE: Dilute 0.3% povidone-iodine and a 1:1 combination of 10% povidone-iodine mixed with 3% hydrogen peroxide can be safely used during primary and revision total joint arthroplasty without compromising osseointegration or causing wound complications.

An investigational time course study of titanium plasma spray on osseointegration of PEEK and titanium implants: an in vivo ovine model

Background ContextMethods to improve osseointegration of orthopedic spinal implants remains a clinical challenge. Materials composed of poly-ether-ether-ketone (PEEK) and titanium are commonly used in orthopedic applications due to their inherent properties of biocompatibility. Titanium has a clinical reputation for durability and osseous affinity, and PEEK offers advantages of a modulus that approximates osseous structures and is radiolucent. The hypothesis for the current investigation was that a titanium plasma spray (TPS) coating may increase the rate and magnitude of circumferential and appositional trabecular osseointegration of PEEK and titanium implants versus uncoated controls. PurposeUsing an in vivo ovine model, the current investigation compared titanium plasma-sprayed PEEK and titanium dowels versus nonplasma-sprayed dowels. Using a time course study of 6 and 12 weeks postoperatively, experimental assays to quantify osseointegration included micro-computed tomography (microCT), biomechanical testing, and histomorphometry. Study Design/SettingIn-vivo ovine model. MethodsTwelve skeletally mature crossbred sheep were equally randomized into postoperative periods of 6 and 12 weeks. Four types of dowel implants–PEEK, titanium plasma-sprayed PEEK (TPS PEEK), titanium, and titanium plasma-sprayed titanium (TPS titanium) were implanted into cylindrical metaphyseal defects in the distal femurs and proximal humeri (one defect per limb, n=48 sites). Sixteen nonoperative specimens (eight femurs and eight humeri) served as zero time-point controls. Half of the specimens underwent destructive biomechanical pullout testing and the remaining half quantitative microCT to quantify circumferential bone volume within 1 mm and 2 mm of the implant surface and histomorphometry to compute direct trabecular apposition. ResultsThere were no intra- or perioperative complications. The TPS-coated implants demonstrated significantly higher peak loads at dowel pullout at 6 and 12 weeks compared with uncoated controls (p<.05). No differences were observed across dowel treatments at the zero time-point (p>.05). MicroCT results exhibited no significant differences in circumferential osseointegration between implants within 1 mm or 2 mm of the dowel surface (p>.05). Direct appositional osseointegration of trabecular bone based on histomorphometry was higher for TPS-coated groups, regardless of base material, compared with uncoated treatments at both time intervals (p<.05). ConclusionsThe current in vivo study demonstrated the biological and mechanical advantages of plasma spray coatings. TPS improved histological incorporation and peak force required for implant extraction. Clinical SignificancePlasma spray coatings may offer clinical benefit by improving biological fixation and osseointegration within the first 6 to 12 weeks postoperatively- the critical healing period for implant-based arthrodesis procedures.

Simvastatin-hydroxyapatite coatings prevent biofilm formation and improve bone formation in implant-associated infections.

Implant-associated infections (IAIs) caused by biofilm formation are the most devastating complications of orthopedic surgery. Statins have been commonly and safely used drugs for hypercholesterolemia for many years. Here, we report that simvastatin-hydroxyapatite-coated titanium alloy prevents biofilm-associated infections. The antibacterial properties of simvastatin against Staphylococcus aureus and Staphylococcus epidermidis biofilms in vitro was confirmed by crystal violet staining and live-dead bacterial staining. We developed a simvastatin-and hydroxyapatite (Sim-HA)-coated titanium alloy via electrochemical deposition. Sim-HA coatings inhibited Staphylococcus aureus biofilm formation and improved the biocompatibility of the titanium alloy. Sim-HA coatings effectively prevented Staphylococcus aureus IAI in rat femurs, as confirmed by radiological assessment and histological examination. The antibacterial effects of the Sim-HA coatings were attributed to their inhibitory effects on biofilm formation, as verified by scanning electron microscopic observations and bacterial spread plate analysis. In addition, the Sim-HA coatings enhanced osteogenesis and osteointegration, as verified by micro-CT, histological evaluation, and biomechanical pull-out tests. In summary, Sim-HA coatings are promising implant materials for protection against biofilm-associated infections.

Intermittent parathyroid hormone increases stability and improves osseointegration of initially unstable implants.

AimsTo develop an early implant instability murine model and explore the use of intermittent parathyroid hormone (iPTH) treatment for initially unstable implants.Methods3D-printed titanium implants were inserted into an oversized drill-hole in the tibiae of C57Bl/6 mice (n = 54). After implantation, the mice were randomly divided into three treatment groups (phosphate buffered saline (PBS)-control, iPTH, and delayed iPTH). Radiological analysis, micro-CT (µCT), and biomechanical pull-out testing were performed to assess implant loosening, bone formation, and osseointegration. Peri-implant tissue formation and cellular composition were evaluated by histology.ResultsiPTH reduced radiological signs of loosening and led to an increase in peri-implant bone formation over the course of four weeks (timepoints: one week, two weeks, and four weeks). Observational histological analysis shows that iPTH prohibits the progression of fibrosis. Delaying iPTH treatment until after onset of peri-implant fibrosis still resulted in enhanced osseointegration and implant stability. Despite initial instability, iPTH increased the mean pull-out strength of the implant from 8.41 N (SD 8.15) in the PBS-control group to 21.49 N (SD 10.45) and 23.68 N (SD 8.99) in the immediate and delayed iPTH groups, respectively. Immediate and delayed iPTH increased mean peri-implant bone volume fraction (BV/TV) to 0.46 (SD 0.07) and 0.34 (SD 0.10), respectively, compared to PBS-control mean BV/TV of 0.23 (SD 0.03) (PBS-control vs immediate iPTH, p < 0.001; PBS-control vs delayed iPTH, p = 0.048; immediate iPTH vs delayed iPTH, p = 0.111).ConclusioniPTH treatment mediated successful osseointegration and increased bone mechanical strength, despite initial implant instability. Clinically, this suggests that initially unstable implants may be osseointegrated with iPTH treatment.Cite this article: Bone Joint Res 2022;11(5):260–269.

Parathyroid hormone enhances gap healing and osseointegration in orthopedic porous coated titanium implants: a correlative micro-computed tomographic, histomorphometric and biomechanical analysis

BackgroundParathyroid hormone, with its anabolic effect on bone formation, has shown excellent outcomes of curing postmenopausal osteoporosis as well as enhancing osseointegration around orthopaedic and stomatologic implants.The purpose of the present study is to test if low-dose intermittent PTH (1–34) treatment could achieve a satisfactory osseointegration in 2-mm peri-implant gaps, as to provide a new idea for improving the stability of such prosthesis, which will be of great clinical value.MethodsA custom-made titanium implant was implanted on the calvarium of New Zealand White rabbits. 48 male rabbits were randomly divided into control and PTH group. PTH group received subcutaneous injection of PTH (20 μg/day, 5 days/week). Animals were sacrificed at 4 and 8 weeks after surgery. Quantitative micro-computed tomography, histology and biomechanical pull-out testing were performed to evaluate the gap healing at implantation site.ResultsAnalysis of micro-computed tomography demonstrated that PTH group achieved more new bone formation in 2-mm gaps and on bone-implant interface. Quantitatively, significant differences were observed between two groups in regard to BIC and BV/TV at each time-point. Histological staining revealed that PTH group had a superiority in trabecular number, thickness, separation and better osseointegration compared to control group. As for biomechanical pull-out testing, PTH group also showed significant improvement of ultimate force than control group.ConclusionsLow-dose intermittent administration of PTH for 4 and 8 weeks enhances early osseointegration and fixation of orthopedic implants surrounded by a 2-mm gap in terms of increased bone regeneration and mechanical stability. These findings suggest PTH a potential for reducing the postoperative complications of implants by improving bone healing at peri-implant gaps.

Effects of Surface Topography and Chemistry on Polyether-Ether-Ketone (PEEK) and Titanium Osseointegration.

An in vivo study examining the functional osseointegration of smooth, rough, and porous surface topographies presenting polyether-ether-ketone (PEEK) or titanium surface chemistry. To investigate the effects of surface topography and surface chemistry on implant osseointegration. Interbody fusion devices have been used for decades to facilitate fusion across the disc space, yet debate continues over their optimal surface topography and chemistry. Though both factors influence osseointegration, the relative effects of each are not fully understood. Smooth, rough, and porous implants presenting either a PEEK or titanium surface chemistry were implanted into the proximal tibial metaphyses of 36 skeletally mature male Sprague Dawley rats. At 8 weeks, animals were euthanized and bone-implant interfaces were subjected to micro-computed tomography analysis (n = 12), histology (n = 4), and biomechanical pullout testing (n = 8) to assess functional osseointegration and implant fixation. Micro-computed tomography analysis demonstrated that bone ingrowth was 38.9 ± 2.8% for porous PEEK and 30.7 ± 3.3% for porous titanium (P = 0.07). No differences in fixation strength were detected between porous PEEK and porous titanium despite titanium surfaces exhibiting an overall increase in bone-implant contact compared with PEEK (P < 0.01). Porous surfaces exhibited increased fixation strength compared with smooth and rough surfaces regardless of surface chemistry (P < 0.05). Across all groups both surface topography and chemistry had a significant overall effect on fixation strength (P < 0.05), but topography accounted for 65.3% of the total variance (ω = 0.65), whereas surface chemistry accounted for 5.9% (ω = 0.06). The effect of surface topography (specifically porosity) dominated the effect of surface chemistry in this study and could lead to further improvements in orthopedic device design. The poor osseointegration of existing smooth PEEK implants may be linked more to their smooth surface topography rather than their material composition. N/A.

Individualized prediction of pedicle screw fixation strength with a finite element model

Pedicle screws are used for the treatment of a wide variety of spinal pathologies. A good screw holding power in bone is required for treatment success, but has so far not been predictable computationally. The goal of this study was to develop an automated tool able to predict patient-specific screw fixation strength through finite element simulation. We compared the simulation results with results from biomechanical pull-out tests performed on animal lumbar specimens. Experimental and simulation pull-out strengths were highly correlated and the mean error was 20.25%. The fixation strength was also associated to great extent with pull-out stiffness and strain energy, as well as the screw size and mean vertebral density.

Enhanced Osseointegration of Titanium Alloy Implants with Laser Microgrooved Surfaces and Graphene Oxide Coating.

Rapid and effective osseointegration, as a critical factor in affecting the success rate of titanium (Ti) implants in orthopedic applications, is significantly affected by their surface microstructure and chemical composition. In this work, surface microgrooved Ti-6Al-4V alloys with graphene oxide coating (Ti-G-GO) were fabricated by a combination of laser processing and chemical assembly techniques. The osteogenic capability in vitro and new bone formation in vivo of the implants were systematically investigated, and biomechanical pull-out tests of the screws were also performed. First, in vitro studies indicated that the optimal microgroove width of the titanium alloy surface was 45 μm (Ti-G), and the optimum GO concentration was 1 mg/mL. Furthermore, the effects of the surface microstructure and GO coating on the in vitro bioactivity were investigated through culturing bone marrow mesenchymal stem cells (BMSCs) on the surface of titanium alloy plates. The results showed that the BMSCs cultured on the Ti-G-GO group exhibited the best adhesion, proliferation, and differentiation, compared with that on the Ti-G and Ti groups. Micro-computed tomography evaluation, histological analysis, and pull-out testing demonstrated that both Ti-G and Ti-G-GO implants had the higher osseointegration than the untreated Ti implant. Moreover, the osteogenic capability of the Ti-G-GO group appeared to be superior to that of the Ti-G group, which could be attributed to the improvement of surface wettability and apatite formation by the GO coatings. These results suggest that the combination of the microgroove structure and GO coatings exhibits considerable potential for enhancing the surface bioactivation of materials, and the combination modification is expected to be used on engineered titanium alloy surfaces to enhance osseointegration for orthopedic applications.

62. Impaction grafting of the pedicle: a biomechanical analysis

BACKGROUND CONTEXT Current options for revising screw failure includes larger diameter revisions and/or injecting cement into the vertebral body for secondary screw fixation. An alternative revision method is impaction grafting (pedicoplasty) of the failed pedicle screw track. This technique utilizes impaction of allograft bone into the pedicle and vertebral body through a series of funnels in an attempt to reconstitute a new pedicle. PURPOSE Evaluate the feasibility of a new revision technique (pedicoplasty) compared to conventional clinical options. STUDY DESIGN/SETTING In vitro biomechanical pullout testing. METHODS Investigators utilized 10 vertebral bodies (L1–L5) free of metastatic disease or primary bone disease. Following primary screw insertion, each screw was subjected to a pullout force that was applied axially along the screw trajectory at 5 mm per minute until failure. Each specimen was instrumented with a pedicoplasty (P) revision utilizing the original screw size and on the contralateral side either a fenestrated screw with cement augmentation (CA) or a screw upsized by 1 mm (UP) in a semi-randomized fashion; these revisions were then pulled out using the previously mentioned methods. RESULTS There were no significant differences in initial pullout values between all groups (p 0.05). Primary pullout values for the paired CA and P were 396 ±227N and 308 ±114N, respectively (n=5). Revised pullout values for the paired CA and P were 960 ±227N and 598 ±114N, respectively (p CONCLUSIONS This biomechanical investigation demonstrated no significant differences between pedicoplasty and upsized revision screws. There was significantly higher pullout strength for cement augmented revisions compared to both pedicoplasty and upsized revisions. Consideration should be given to this novel pedicoplasty technique when maintenance of pedicle dimensions is required or further screw diameter increases are not possible. FDA DEVICE/DRUG STATUS Pedicle Screws (Approved for this indication), Bone Cement (Approved for this indication).

Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: innovation, surface technology and biomechanics: 174. Surface topography and chemistry effects on PEEK and titanium osseointegration

BACKGROUND CONTEXT Nearly 500,000 spinal fusion surgeries are performed each year in the U.S. Interbody fusion devices have been used for decades to facilitate fusion across the disc space, yet debate continues over the optimal material and structure used for these devices. Current cages are primarily made from PEEK due to its radiolucency and bone-like stiffness. However, current smooth PEEK cages are often associated with fibrous encapsulation and implant migration. This poor response is often attributed to inherent material properties of PEEK. However, the smooth surface of conventional PEEK surfaces may equally impede osseointegration, particularly when considering that rough and porous surfaces of various non-PEEK materials elicit more favorable osseointegration compared to smooth surfaces. PURPOSE The current study aimed to assess the relative influence of surface topography and chemistry on PEEK osseointegration by investigating the osseous response to smooth, rough, and porous surface topographies possessing a PEEK or titanium surface chemistry. STUDY DESIGN/SETTING Preclinical implant osseointegration model in the proximal tibial metaphysis of the rat. OUTCOME MEASURES Osseointegration was assessed by calculating bone ingrowth percentage, histological tissue evaluation, and biomechanical pullout testing. METHODS Porous PEEK implants were created as described previously. Rough surfaces were created by soda-blasting PEEK surfaces and smooth surfaces maintained an as-machined surface finish. Half of each group was coated with a ∼30nm thick layer of TiO2 using atomic layer deposition (ALD) while the other half maintained their native PEEK chemistry. Sterile implants were implanted into the proximal tibial metaphyses of skeletally mature male Sprague Dawley rats. At 8 weeks, animals were euthanized and bone-implant interfaces were subjected to µCT analysis (n=12), histology (n=4), and biomechanical pullout testing (n=8). All data were reported as mean±SE. Comparisons between groups were calculated using a 2-way ANOVA followed by a Tukey multiple comparisons test. RESULTS Quantitative µCT analysis demonstrated that mineralized tissue ingrowth was 38.9±2.8% for porous PEEK and 30.7±3.3% for porous titanium (p=0.07). µCT tomograms and matching histological sections showed bone ingrowth in porous titanium surfaces primarily consisted of thin bone shells that conformed to the pore walls, leaving the center of pores devoid of bone. In contrast, bone ingrowth within porous PEEK was greater in the center of pores with periodic contact with pore walls. Greater bone-implant contact was observed for titanium compared to PEEK surfaces. Histological and µCT observations were corroborated by biomechanics outcomes. Across all groups both surface chemistry and topography had a significant overall effect on pullout force (p CONCLUSIONS The poor osseointegration of conventional PEEK implants may be linked more to their smooth surface topography rather than their material composition. The effect of surface topography (specifically porosity) dominated the effect of surface chemistry in this study and could lead to further improvements in orthopaedic device design.

Intraosseous Injection of Simvastatin in Poloxamer 407 Hydrogel Improves Pedicle-Screw Fixation in Ovariectomized Minipigs.

Osteoporosis leads to poor osseointegration and reduces implant stability. Statins have been found to stimulate bone formation, but the bioavailability from oral administration is low. Local application may be more effective at augmenting bone formation and enhancing implant stability. This study was performed to evaluate the efficacy of an intraosseous injection of simvastatin in thermosensitive poloxamer 407 hydrogel to enhance pedicle-screw fixation in calcium-restricted ovariectomized minipigs. Nine mature female Guangxi Bama minipigs underwent bilateral ovariectomy and were fed a calcium-restricted diet for 18 months. Simvastatin (0, 0.5, or 1 mg) in thermosensitive poloxamer 407 hydrogel was injected into the lumbar vertebrae (L4-L6), and titanium alloy pedicle screws were implanted. Bone mineral density (BMD) measurements of the lumbar vertebrae were determined by dual x-ray absorptiometry (DXA) before and 3 months after treatment. The lumbar vertebrae were harvested and analyzed with use of microcomputed tomography, biomechanical pull-out testing, histological analysis, and Western blot analysis for bone morphogenetic protein (BMP)-2 and vascular endothelial growth factor (VEGF) expression. Evaluation over a 3-month study period demonstrated that the BMD of the vertebrae injected with 0.5 and 1.0 mg of simvastatin had increased by 31.25% and 31.09%, respectively, compared with vehicle-only injection (p ≤ 0.00014 for both) and increased by 32.12% and 28.16%, respectively, compared with the pre-treatment levels (p < 0.0001 for both). A single injection of simvastatin in poloxamer 407 increased trabecular volume fraction, thickness, and number and decreased trabecular separation (p ≤ 0.002). The bone formation and mineral apposition rates significantly increased (p ≤ 0.023). The percentage of osseointegration in the simvastatin 0.5 and 1-mg groups was 46.54% and 42.63% greater, respectively, than that in the vehicle-only group (p ≤ 0.006), and the maximum pull-out strength was 45.75% and 51.53% greater, respectively, than in the vehicle-only group (p ≤ 0.0005). BMP-2 and VEGF expressions were higher than for the vehicle-only injection. A single intraosseous injection of simvastatin in thermosensitive poloxamer 407 hydrogel stimulated bone formation, increased BMD, improved bone microstructure, promoted osseointegration, and significantly enhanced the stability of pedicle screws in calcium-restricted ovariectomized minipigs. These results provide rationale for evaluating intraosseous injection of simvastatin in poloxamer 407 to enhance implant fixation in patients with osteoporosis.

Direct bone-to-bone integration between recombinant human bone morphogenetic protein-2-injected tendon graft and tunnel wall in an anterior cruciate ligament reconstruction model.

This study was performed to evaluate one-stage anterior cruciate ligament (ACL) reconstruction using a semitendinosus tendon graft injected with bone morphogenetic protein 2 (BMP-2) in a rabbit model. We injected recombinant human BMP-2 (rhBMP-2) in the experimental group and phosphate-buffered saline in the control group at two sites of the semitendinosus tendon (15 μg in each site) to replace tendon with bone in the bone tunnel. Twenty minutes later, the injected tendon graft was transplanted for ACL reconstruction by passing the graft through the bone tunnel. The animals were harvested at four, eight, or 12 weeks postoperatively and examined by histological and biomechanical methods. Histological analysis revealed that the tendon graft was replaced with new bone in the tunnel of the experimental group. Characteristic features identical to the regenerated direct insertion morphology at the bone-tendon junction were acquired at eight or 12 weeks in the experimental group. Biomechanical pull-out testing revealed greater stiffness in the experimental than control group at 12 weeks, although the maximum load to failure showed no significant difference between the two groups at four, eight, or 12 weeks. These results indicate the potential for ACL reconstruction with regenerated direct insertion morphology.

A Validated Method for Titanium Implant Anchorage Analysis using MicroCT and Biomechanical Testing

We present here a protocol for the combined microstructural and biomechanical evaluation of endosseous titanium implant anchorage. The protocol is highly relevant for orthopedic and oral surgery experimentalists studying endosseous implantation, a discipline comprising ~150 publications yearly. The protocol is based on (i) insertion of titanium mini-implants horizontally into the rat proximal tibial metaphysis; (ii) quantitative microstructural evaluation by micro-computed tomography, including assessment of the bone-implant contact; (iii) correction of the bias due to implant positioning; (iv) biomechanical pullout testing using a customized jig for linear axial loading. A highlight of the protocol is image guided failure assessment consisting of time-lapsed biomechanical-microstructural analysis of the peri-implant bone deformation during implant pullout. Using this protocol we have demonstrated highly significant correlations between key microstructural and mechanical parameters. More importantly, we showed how changes to the metabolic state of the organism, like gonadectomy and bone anabolic agents, as well as implant surface properties affect the distribution and magnitude of critical strains in the peri-implant bone.

May "Dubel" be a solution for pullout problem of the pedicle screws at osteoporotic spine?

To improve the strength of stabilization systems currently used in osteoporotic spinal fractures, essentially by increasing the fixation force of pedicle screws. Six human cadaveric vertebrae were used. Bone mineral densities of the specimens were measured with Dual Energy X-ray Absorptiometry in order to assess the osteoporosis. All vertebrae were found to be severely osteoporotic. Standard pedicle screws were applied to left pedicles of vertebrae. Pedicle screws reinforced by fixing plugs "Dubel" were applied to right pedicles of vertebrae. Afterwards the vertebrae were embedded in acrylic casts to prevent possible fracture of the osteoporotic vertebrae and to obtain a correct vertical pull-out vector. The biomechanical pullout tests were performed with biomechanical testing machine. Pullout forces in each group were recorded and compared with Mann-Whitney U test. The pedicle screws strengthened by "Dubel" were found to be four times stronger than the standard pedicle screws, in the osteoporotic human cadaveric vertebrae. "Dubel"-augmented pedicle screws may contribute to developing better stabilization systems for osteoporotic thoracolumbar fractures needing surgery and in the revision of the previous fusion surgeries of the spine.

Therapeutic potentials of naringin on polymethylmethacrylate induced osteoclastogenesis and osteolysis, in vitro and in vivo assessments

Wear debris associated periprosthetic osteolysis represents a major pathological process associated with the aseptic loosening of joint prostheses. Naringin is a major flavonoid identified in grapefruit. Studies have shown that naringin possesses many pharmacological properties including effects on bone metabolism. The current study evaluated the influence of naringin on wear debris induced osteoclastic bone resorption both in vitro and in vivo. The osteoclast precursor cell line RAW 264.7 was cultured and stimulated with polymethylmethacrylate (PMMA) particles followed by treatment with naringin at several doses. Tartrate resistant acid phosphatase (TRAP), calcium release, and gene expression profiles of TRAP, cathepsin K, and receptor activator of nuclear factor-kappa B were sequentially evaluated. PMMA challenged murine air pouch and the load bearing tibia titanium pin-implantation mouse models were used to evaluate the effects of naringin in controlling PMMA induced bone resorption. Histological analyses and biomechanical pullout tests were performed following the animal experimentation. The in vitro data clearly demonstrated the inhibitory effects of naringin in PMMA induced osteoclastogenesis. The naringin dose of 10 μg/mL exhibited the most significant influence on the suppression of TRAP activities. Naringin treatment also markedly decreased calcium release in the stimulated cell culture medium. The short-term air pouch mouse study revealed that local injection of naringin ameliorated the PMMA induced inflammatory tissue response and subsequent bone resorption. The long-term tibia pin-implantation mouse model study suggested that daily oral gavage of naringin at 300 mg/kg dosage for 30 days significantly alleviated the periprosthetic bone resorption. A significant increase of periprosthetic bone volume and regaining of the pin stability were found in naringin treated mice. Overall, this study suggests that naringin may serve as a potential therapeutic agent to treat wear debris associated osteolysis.

ACL reconstruction using bone-tendon-bone graft engineered from the semitendinosus tendon by injection of recombinant BMP-2 in a rabbit model

We attempted to generate a bone-tendon-bone structure by injecting human-type recombinant human bone morphogenetic protein-2 (rhBMP-2) into the semitendinosus tendon, and an anterior cruciate ligament (ACL) defect was reconstructed by grafting the engineered bone-tendon-bone graft. Two ossicles with a separation distance of 1 cm were generated within the left semitendinosus tendon of a rabbit 6 weeks after the injection of rhBMP-2 (15 µg at each site). The engineered bone-tendon-bone graft was transplanted in order to reconstruct the ACL by passing the graft through the bone tunnels. In the control group, the ACL was reconstructed with the semitendinosus tendon without BMP-2 using the same methods as those used in the experimental group. The animals were harvested at 4 or 8 weeks after surgery and examined by radiographic, histological, and biomechanical methods. In the experimental group, ossicles in the bone-tendon-bone graft were successfully integrated into the host bone of the femur and tibia. Histological analysis revealed that characteristic features identical to the normal direct insertion morphology had been restored. Biomechanical pull-out testing showed that the ultimate failure load and stiffness of the reconstructed ACL in the experimental group were significantly higher than those in the control group at both 4 and 8 weeks (p < 0.05). These results indicate the potential of regenerative reconstruction of the ACL, and the reconstruction resulted in the restoration of morphology and function equivalent to those of the normal ACL.

Biomechanical comparison of different anchors (foundations) for the pediatric dual growing rod technique

Background context Children with early onset scoliosis benefit from early operative treatment with dual growing rods as they provide an “internal brace” for the spine and allow curve correction and sequential lengthenings to maximize thoracic cage development. The foundations that provide anchor points for the dual growing rods may incorporate hooks, screws, or a hybrid construct. It is unclear how stable different types of foundation constructs are with regard to pullout. Purpose This study was to determine the differences in stability between four foundation configurations used in the pediatric dual growing rod technique. Eight porcine spines were sectioned and randomly assigned to one of four foundation groups: 1) hook-hook with cross-link; 2) hook-screw with cross-link; 3) screw-screw with cross-link; and 4) screw-screw without cross-link. After instrumentation, biomechanical pullout tests were conducted. Ultimate failure loads, modes of failure, and level of instrumentation were analyzed. Study design/setting Controlled in vitro laboratory investigation. Results Screw-screw with cross-link constructs demonstrated the greatest failure load but this was not statistically significant compared with the screw-screw without cross-link constructs. Both screw-screw constructs were statistically stronger than either construct containing hooks. There was no difference between the hook-screw and hook-hook constructs that was statistically significant. Hook-containing constructs sustained higher failure loads in lumbar versus thoracic vertebrae. Conclusions A foundation composed of four pedicle screws implanted in two adjacent vertebral bodies provides the strongest construct in pullout testing. A cross-link does not seem to enhance fixation. Hook constructs are stronger in lumbar versus thoracic laminae.

Expansion anchors for use in anterior cruciate ligament (ACL) reconstruction: establishing proof of concept in a benchtop analysis

The current method for graft fixation in bone tendon-bone anterior cruciate ligament (ACL) reconstruction is the interference screw. Although this method of fixation provides for adequate graft fixation with respect to strength, intraoperative placement is difficult and the failure rate is high. To address these concerns, we have designed and fabricated prototype expansion anchors that could be expanded to anchor the graft in the bone tunnel. As a first step in assessing the validity of this concept, in the current work, we demonstrate that these systems are of comparable fixation strength (biomechanical pullout testing) to the standard interference screw, are smaller at the time of insertion and thus provide for increased visibility and ease of placement. The increased visibility should result in better placement and reduced failure rates. The increased ease of placement should result in significant savings in decreased OR time.

Biocompatibility and degradation of collagen bone anchors in a rabbit model.

Bone anchors are used to fasten tendons and ligaments to bone during reconstructive surgery. Although metal anchors are often used, an anchor that could resorb and permit normal bone regeneration would be advantageous. The objective of the study was to evaluate the biocompatibility and degradation of bone anchors that consist of collagen-based bodies, ceramic washers, and polyester sutures. Eighteen rabbits underwent bilateral implantations in the distal femoral condyles. Nine animals received glutaraldehyde-crosslinked fibrillar collagen bone anchors (FC) and nine received glutaraldehyde-crosslinked fibrillar collagen bone anchors containing tricalcium phosphate (FC-TCP). Three animals per group were sacrificed at postimplantation weeks 1, 6, and 12. One femur from each rabbit was evaluated histologically, and the contralateral side underwent biomechanical pull-out testing. Histological evaluation of the implant site indicated that the FC and FC-TCP bone anchors were both biocompatible. The FC-TCP formulation degraded earlier than the FC formulation, and FC-TCP showed significant degradation at 6 weeks; the FC and FC-TCP formulations both showed similar amounts of degradation at 12 weeks. The degrading anchor bodies appeared to be osteoconductive as evidenced by new bone ingrowth into the degrading collagen matrices without a fibrous interface. These results suggest that collagen-based bone anchors have potential as bioresorbable orthopedic implants.