Enhancement of bone growth into porous intramedullary implants using non-invasive low intensity ultrasound

The role of hydroxyapatite coating in joint replacement surgery - Key considerations

The use of a porous hydroxyapatite (HA) coating has definitively increased the durability and biocompatibility of joint replacement prostheses (JRP) since its introduction. This article will contextualise the properties of porous HA and relate these characteristics to its clinical function. Novel strategies to encourage osseointegration will also be explored, alongside their clinical relevance. All major literature databases were scrutinised for literature relevant to the scope of our review. The role of Hydroxyapatite was evaluated, alongside further strategies to augment bone ingrowth. HA coatings remain the most optimal coating for widespread clinical use. Advantages are conferred due to the method of application, the tribology and the biocompatibility of the material. Further strategies are available to augment bone ingrowth, pertaining to biological modifications and implantation of external factors. An evaluation of the literature has described the relative long term performance of the HA coated JRPs both in isolation and when compared with cemented prosthesis. Metanalyses have shown HA coated JRPs to perform as well as cemented prosthesis in terms of survivability over both short and long term follow ups. Concerning strategies to augment osseointegration, consideration should be given to form and function of the coating surface, as this provides the basis for cell adherence, proliferation, and differentiation.

Low-Intensity Pulsed Ultrasound Stimulation for Bone Fractures Healing: A Review

Low-intensity pulsed ultrasound (LIPUS) is a developing technology, which has been proven to improve fracture healing process with minimal thermal effects. This noninvasive treatment accelerates bone formation through various molecular, biological, and biomechanical interactions with tissues and cells. Although LIPUS treatment has shown beneficial effects on different bone fracture locations, only very few studies have examined its effects on deeper bones. This study provides an overview on therapeutic ultrasound for fractured bones, possible mechanisms of action, clinical evidences, current limitations, and its future prospects.

Ultrasonic Propagation in a Dental Implant

Ultrasound techniques can be used to characterize and stimulate dental implant osseointegration. However, the interaction between an ultrasonic wave and the implant-bone interface (IBI) remains unclear. This study-combining experimental and numerical approaches-investigates the propagation of an ultrasonic wave in a dental implant by assessing the amplitude of the displacements along the implant axis. An ultrasonic transducer was excited in a transient regime at 10 MHz. Laser interferometric techniques were employed to measure the amplitude of the displacements, which varied 3.2-8.9 nm along the implant axis. The results demonstrated the propagation of a guided wave mode along the implant axis. The velocity of the first arriving signal was equal to 2110 m.s^-1, with frequency components lower than 1 MHz, in agreement with numerical results. Investigating guided wave propagation in dental implants should contribute to improved methods for the characterization and stimulation of the IBI.

Effect of Low-Intensity Pulsed Ultrasound Stimulation, Extracorporeal Shockwaves and Radial Pressure Waves on Akt, BMP-2, ERK-2, FAK and TGF-β1 During Bone Healing in Rat Tibial Defects

An experimental study was conducted to determine whether low-intensity pulsed ultrasound stimulation (LIPUS), extracorporeal shockwave treatment (ESWT) and radial pressure wave treatment (RPWT) modulate Akt, bone morphogenetic protein-2 (BMP-2), extracellular signal-regulated kinase-2 (ERK-2), focal adhesion kinase (FAK) and transforming growth factor-β1 (TGF-β1) during bone healing in rat tibial defects. Rat tibial defects were exposed to 500 shots of ESWT delivered at 0.12 mJ/mm², 500 impulses of RPWT operated at 2.0 bar or to daily 20-min 30 mW/cm² LIPUS. Following 1, 3 and 6 wk, bones were harvested to determine the expression and activity of Akt, BMP-2, ERK-2, FAK and TGF-β1. Animals exposed to ultrasound were followed up to 3 wk. Protein expression and activity were unchanged following LIPUS treatment. ESWT increased Akt activity 2.11-fold (p = 0.043) and TGF-β1 expression 9.11-fold (p = 0.016) at 1 wk and increased FAK activity 2.16-fold (p = 0.047) at 3 wk. RPWT increased FAK activity 2.6-fold (p = 0.028) at 3 wk and decreased Akt expression 0.52-fold (p = 0.05) at 6 wk. In conclusion, the protocols employed for ESWT and RPWT modulated distinct signaling pathways during fracture healing, while LIPUS standard protocol did not change the usual signaling pathways of the proteins investigated. Future studies are required to monitor osteogenesis so that the biologic meaning of our results can be clarified.

Reflection of an ultrasonic wave on the bone-implant interface: Effect of the roughness parameters

Quantitative ultrasound can be used to characterize the evolution of the bone-implant interface (BII), which is a complex system due to the implant surface roughness and to partial contact between bone and the implant. The aim of this study is to derive the main determinants of the ultrasonic response of the BII during osseointegration phenomena. The influence of (i) the surface roughness parameters and (ii) the thickness W of a soft tissue layer on the reflection coefficient r of the BII was investigated using a two-dimensional finite element model. When W increases from 0 to 150 μm, r increases from values in the range [0.45; 0.55] to values in the range [0.75; 0.88] according to the roughness parameters. An optimization method was developed to determine the sinusoidal roughness profile leading to the most similar ultrasonic response for all values of W compared to the original profile. The results show that the difference between the ultrasonic responses of the optimal sinusoidal profile and of the original profile was lower to typical experimental errors. This approach provides a better understanding of the ultrasonic response of the BII, which may be used in future numerical simulation realized at the scale of an implant.

Reflection of an ultrasonic wave on the bone-implant interface: A numerical study of the effect of the multiscale roughness

Quantitative ultrasound is used to characterize and stimulate osseointegration processes at the bone-implant interface (BII). However, the interaction between an ultrasonic wave and the implant remains poorly understood. This study aims at investigating the sensitivity of the ultrasonic response to the microscopic and macroscopic properties of the BII and to osseointegration processes. The reflection coefficient R of the BII was modeled for different frequencies using a two-dimensional finite element model. The implant surface roughness was modeled by a sinusoidal function with varying amplitude h and spatial frequency L. A soft tissue layer of thickness W was considered between bone tissue and the implant in order to model non-mineralized fibrous tissue. For microscopic roughness, R is shown to increase from around 0.55 until 0.9 when kW increases from 0 to 1 and to be constant for kW > 1, where k is the wavenumber in the implant. These results allow us to show that R depends on the properties of bone tissue located at a distance comprised between 1 and 25 μm from the implant surface. For macroscopic roughness, R is highly dependent on h and this dependence may be explained by phase cancellation and multiple scattering effects for high roughness parameters.

Effect of low-intensity pulsed ultrasound on the biological behavior of osteoblasts on porous titanium alloy scaffolds: An in vitro and in vivo study

Low-intensity pulsed ultrasound (LIPUS) has been used in patients with fresh fractures, delayed union and non-union to enhance bone healing and improve functional outcome. However, there were few studies concerning the effects of LIPUS on the biological behavior of osteoblasts on porous scaffolds. This study aimed to evaluate the effects of LIPUS on the biological behavior of osteoblasts on porous titanium-6aluminum-4vanadium (Ti6Al4V) alloy scaffolds in vitro and in vivo. Scaffolds were randomly divided into an ultrasound group and a control group. Mouse pre-osteoblast cells were cultured with porous Ti6Al4V scaffolds in vitro. The effects of LIPUS on the biological behavior of osteoblasts were evaluated by observing the adhesion, proliferation, differentiation and ingrowth depth on porous Ti6Al4V scaffolds. In addition, scaffolds were implanted into rabbit mandibular defects in vivo. The effects of LIPUS on bone regeneration were evaluated via micro-CT, fluorescent staining and toluidine blue staining. The results revealed that osteoblast adhered well to the scaffolds, and there was no significant difference in the methyl thiazolyl tetrazolium value between the ultrasound group and the control group (p>0.05). Compared with the control group, ultrasound promoted the alkaline phosphatase activity, osteocalcin levels and ingrowth depth of the cells on the scaffolds (p<0.05). In addition, micro-CT and histomorphological analysis showed that the volume and amount of new bone formation were increased and that bone maturity was improved in the ultrasound group compared to the control group. These results indicate that LIPUS promotes osteoblast differentiation as well as enhances bone ingrowth in porous Ti6Al4V scaffolds, and promotes bone formation and maturity in porous Ti6Al4V scaffolds.

Modified porous tantalum rod technique for the treatment of femoral head osteonecrosis

AIM: To study a modified porous tantalum technique for the treatment of osteonecrosis of the femoral head.

METHODS: The porous tantalum rod was combined with endoscopy, curettage, autologous bone grafting and use of bone marrow aspirates from iliac crest aspiration in 49 patients (58 hips) with a mean age of 38 years. The majority of the patients had idiopathic osteonecrosis, followed by corticosteroid-induced osteonecrosis. Thirty-eight hips were of Steinberg stage II disease and 20 hips were of stage III disease. Patients were followed for 5 years and were evaluated clinically with the Merle D’Aubigne and Postel score and radiologically. The primary outcome of the study was survival based on the conversion to total hip arthroplasty (THA). Secondary outcomes included deterioration of the osteonecrosis to a higher disease stage at 5 years compared to the preoperative period and identification of factors that were associated with survival. The Kaplan-Meier survival analysis was performed to evaluate the survivorship of the prosthesis, and the Fisher exact test was performed to test associations between various parameters with survival.

RESULTS: No patient developed any serious intraoperative or postoperative complication including implant loosening or migration and donor site morbidity. During the 5-year follow up, 1 patient died, 7 patients had disease progression and 4 hips were converted to THA. The 5-year survival based on conversion to THA was 93.1% and the respective rate based on disease progression was 87.9%. Stage II disease was associated with statistically significant better survival rates compared to stage III disease (P = 0.04). The comparison between idiopathic and non-idiopathic osteonecrosis and between steroid-induced and non-steroid-induced osteonecrosis did not showed any statistically significant difference in survival rates. The clinical evaluation revealed statistically significantly improved Merle d’Aubigne scores at 12 mo postoperatively compared to the preoperative period (P < 0.001). The mean preoperative Merle d’Aubigne score was 13.0 (SD: 1.8). The respective score at 12 mo improved to 17.0 (SD: 2.0). The 12-mo mean score was retained at 5 years.

CONCLUSION: The modified porous tantalum rod technique presented here showed encouraging outcomes. The survival rates based on conversion to THA are the lowest reported in the published literature.

Biological strategies for improved osseointegration and osteoinduction of porous metal orthopedic implants

The biological interface between an orthopedic implant and the surrounding host tissue may have a dramatic effect upon clinical outcome. Desired effects include bony ingrowth (osseointegration), stimulation of osteogenesis (osteoinduction), increased vascularization, and improved mechanical stability. Implant loosening, fibrous encapsulation, corrosion, infection, and inflammation, as well as physical mismatch may have deleterious clinical effects. This is particularly true of implants used in the reconstruction of load-bearing synovial joints such as the knee, hip, and the shoulder. The surfaces of orthopedic implants have evolved from solid-smooth to roughened-coarse and most recently, to porous in an effort to create a three-dimensional architecture for bone apposition and osseointegration. Total joint surgeries are increasingly performed in younger individuals with a longer life expectancy, and therefore, the postimplantation lifespan of devices must increase commensurately. This review discusses advancements in biomaterials science and cell-based therapies that may further improve orthopedic success rates. We focus on material and biological properties of orthopedic implants fabricated from porous metal and highlight some relevant developments in stem-cell research. We posit that the ideal primary and revision orthopedic load-bearing metal implants are highly porous and may be chemically modified to induce stem cell growth and osteogenic differentiation, while minimizing inflammation and infection. We conclude that integration of new biological, chemical, and mechanical methods is likely to yield more effective strategies to control and modify the implant-bone interface and thereby improve long-term clinical outcomes.

Enhancement of cell ingrowth, proliferation, and early differentiation in a three-dimensional silicon carbide scaffold using low-intensity pulsed ultrasound

Concerns over the use of autografts or allografts have necessitated the development of biomaterials for bone regeneration. Various studies have been performed to optimize the cultivation of osteogenic cells using osteoconductive porous scaffolds. The aim of this study was to evaluate the osteogenic efficiency of bone cell ingrowth, proliferation, and early differentiation in a silicon carbide (SiC) porous ceramic scaffold promoted with low-intensity pulsed ultrasound. MC3T3-E1 mouse preosteoblasts were seeded onto scaffolds and cultured for 4 and 7 days with daily of 20-min ultrasound treatment. The cells were evaluated for cell attachment, morphology, viability, ingrowth depth, volumetric proliferation, and early differentiation. After 4 and 7 days of culture and ultrasound exposure, the cell density was higher in the ultrasound-treated group compared with the sham-treated group on SiC scaffolds. The cell ingrowth depths inside the SiC scaffolds were 149.2±27.3 μm at 1 day, 310.1±12.6 μm for the ultrasound-treated group and 248.0±19.7 μm for the sham control at 4 days, and 359.6±18.5 μm for the ultrasound-treated group and 280.0±17.7 μm for the sham control at 7 days. They were significantly increased, that is, 25% (p=0.0029) and 28% (p=0.0008) increase, respectively, with ultrasound radiation force as compared with those in sham control at 4 and 7 days postseeding. The dsDNA contents were 583.5±19.1 ng/scaffold at 1 day, 2749.9±99.9 ng/scaffold for the ultrasound-treated group and 2514.9±114.7 ng/scaffold for the sham control at 4 days, and 3582.3±325.3 ng/scaffold for the ultrasound-treated group and 2825.7±134.3 ng/scaffold for the sham control at 7 days. There was a significant difference in the dsDNA content between the ultrasound- and sham-treated groups at 4 and 7 days. The ultrasound-treated group with the SiC construct showed a 9% (p=0.00029) and 27% (p=0.00017) increase in the average dsDNA content at 4 and 7 days over the sham control group, respectively. Alkaline phosphatase activity was significantly increased by the treatment of ultrasound at 4 (p=0.012) and 7 days (p=0.035). These results suggested that ultrasound treatment with low-intensity acoustic energy facilitated the cellular ingrowth and enhanced the proliferation and early differentiation of osteoblasts in SiC scaffolds.

Clinical and immunohistopathological aspects of venous ulcers treatment by Low-Intensity Pulsed Ultrasound (LIPUS)

The immunological mechanisms that are triggered by Low-Intensity Pulsed Ultrasound (LIPUS) in wound healing are unknown. In the present study, experimental groups were used to assess the treatment of chronic venous ulcers with 30mW/cm(2) SATA peripheral LIPUS three times per week compared to a daily treatment of 1% silver sulfadiazine (SDZ). The ulcers of the SDZ group (n=7) (G1) and LIPUS group (n=9) (G2) were photographed five times three months, and the images were analyzed using ImageJ software to quantify the total area (S), fibrin/sphacel area (yellow) and granulation area (red). The healing process was evaluated by the wound healing rate (WHR), granulation tissue rate (GTR) and fibrin/sphacel tissue rate (FTR). The ulcers were biopsied on days 1 and 45 and stained for collagen fiber quantification (picrosirius) and CD68(+) protein and VEGF (vascular endothelial growth factor) expression using HRP-streptavidin (horseradish peroxidase-streptavidin). On day 90, G2 had a mean 41% decrease in the ulcer area, while no decrease was observed in G1 (p<0.05). An increased tendency toward positive labeling of collagen fibers and VEGF (p>0.05) was observed in G2 compared to G1, and the number of CD68(+) cells was greater in G2 than in G1 (p<0.05). LIPUS presents superior activity compared to SDZ in stimulating the inflammatory and proliferative (angiogenesis and collagenesis, respectively) phases of chronic venous wound healing.

Low-intensity pulsed ultrasound (LIPUS) may prevent polyethylene induced periprosthetic osteolysis in vivo

We investigated the effect of local low-intensity pulsed ultrasound (LIPUS) on polyethylene debris induced periprosthetic osteolysis. The periprosthetic osteolysis model was made by injecting endotoxin-free pure polyethylene particles into the distal part of the femur canal and inserting a stainless steel plug into this femur. The effects of polyethylene and LIPUS were assessed histologically and by the shear strength test and periprosthetic bone mineral density (BMD) test. Sixteen rabbits received a stainless steel plug on one side and both polyethylene and a stainless steel plug on the other side. Three months later, the side that received polyethylene showed periprosthetic osteolysis. Subsequently, another 16 rabbits received polyethylene plus local LIPUS (200 mW/cm(2) for 20 min daily) on one side and polyethylene alone on the other side. Three months later, LIPUS effectively prevented the periprosthetic osteolysis caused by polyethylene in this rabbit model.

Advances in segmental endoprosthetic reconstruction for extremity tumors: a review of contemporary designs and techniques

BACKGROUND

Improved understanding and advances in treatment regimens have led to increased longevity among patients diagnosed with extremity soft tissue sarcomas. Limb salvage techniques and implants have improved and continue to evolve to accommodate the increasing demands and survival of these patients.

METHODS

The current report is a review of the literature for recent advancements in techniques, implant design, and outcomes in the field of limb salvage therapy using segmental megaprostheses for the treatment of extremity sarcomas. We report on our experience in this field utilizing a classification system of failure mechanisms to outline to discuss current controversies in management.

RESULTS

Five mechanisms of failure have been identified: soft-tissue failure, aseptic loosening, structural failure, infection, and tumor progression. Infection was the most common mode of failure in our series, accounting for 34% of cases. Soft-tissue failure occurred most commonly in the joints that depend heavily on periarticular muscles and ligaments for stability due to their high degree of functional range of motion. We observed a 28% soft-tissue failure rate about the shoulder and hip, aseptic loosening accounted for 19% of implant failures, and structural failure was seen in 17% of cases. Seventeen percent of cases failed due to tumor progression, an etiology that is defined by biological factors, surgical technique, and adjuvant therapies.

CONCLUSIONS

Surgical techniques and megaprosthesis designs are constantly changing in order to meet the challenge of increasing functional demands and longevity in this unique patient population. A classification system defined by treatment failure etiologies provides the framework for discussion of current controversies in limb salvage therapy as well as a guide for advancement and potential solutions in this challenging arena.

Mechanical means to improve bone strength: ultrasound and vibration

Not all fractures heal well. One method that has been used to improve fracture healing is low-intensity pulsed ultrasound (LIPUS). LIPUS has been US Food and Drug Administration approved for several years, and some preclinical and clinical evidence indicates that fracture healing can be improved by this technique, which appears to be generally safe. There are several suggested mechanisms of action of LIPUS. Clinical studies generally support its usefulness in accelerating fracture healing. A less-established modality is whole body vibration (WBV), which appears to stimulate bone and muscle growth while suppressing adipogenesis in animal studies. Early studies in humans, including some in children with disabilities, suggest that WBV holds promise as a technique for reducing fracture risk. The exact place of WBV in preventing fracture remains to be established.

Ultrasound enhances recombinant human BMP-2 induced ectopic bone formation in a rat model

Two methods to improve bone repair include the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) and low-intensity pulsed ultrasound (LIPUS). The present study was designed to determine if LIPUS enhances the effect of rhBMP-2-induced bone formation in a well characterized ectopic implant model. Absorbable collagen sponges loaded with 0-, 1-, 2.5- or 5-microg doses of rhBMP-2 were implanted subcutaneously in 11-week-old, male Long Evans rats, followed by daily 20-min LIPUS or sham LIPUS treatment beginning 1 d after surgery. Explanted sponges were assessed for bone volume, mineral density and mineral content by microcomputed tomography (microCT). At two weeks, LIPUS had no effect on rhBMP-2-induced bone formation, but at four weeks, LIPUS increased bone volume in the 1-microg rhBMP-2-treated implants 117.7-fold (0.02 +/- 0.04 mm(3)vs. 2.07(S.E.M.) +/- 1.67 mm(3);p = 0.028), and 2.3-fold in the 5-microg dose implants (5.96 +/- 3.68 mm(3)vs. 13.52 +/- 6.81 mm(3);p = 0.077) compared with sham LIPUS. Bone mineral density was not affected by LIPUS treatment. Total mineral content followed the same pattern as bone volume. Histologic staining for mineralized tissue was consistent with the microCT observations. The present study is the first to demonstrate that LIPUS enhances bone formation induced by rhBMP-2.

No midterm benefit from low intensity pulsed ultrasound after chevron osteotomy for hallux valgus

Chevron osteotomy is a widely accepted method for correction of symptomatic hallux valgus deformity. Full weight bearing in regular shoes is not recommended before 6 weeks after surgery. Low intensity pulsed ultrasound is known to stimulate bone formation leading to more stable callus and faster bony fusion. We performed a randomized, placebo-controlled, double-blinded study on 44 participants (52 feet) who underwent chevron osteotomy to evaluate the influence of daily transcutaneous low intensity pulsed ultrasound (LIPUS) treatment at the site of osteotomy. Follow-up at 6 weeks and 1 year included plain dorsoplantar radiographs, hallux-metatarsophalangeal-interphalangeal scale and a questionnaire on patient satisfaction. There was no statistical difference in any pre- or postoperative clinical features, patient satisfaction or radiographic measurements (hallux valgus angle, intermetatarsal angle, sesamoid index and metatarsal index) except for the first distal metatarsal articular angle (DMAA). The DMAA showed statistically significant (p = 0.046) relapse in the placebo group upon comparison of intraoperative radiographs after correction and fixation (5.2 degrees) and at the 6-week follow-up (10.6 degrees). Despite potential impact of LIPUS on bone formation, we found no evidence of an influence on outcome 6 weeks and 1 year after chevron osteotomy for correction of hallux valgus deformity.

Metallic Scaffolds for Bone Regeneration

Bone tissue engineering is an emerging interdisciplinary field in Science, combining expertise in medicine, material science and biomechanics. Hard tissue engineering research is focused mainly in two areas, osteo and dental clinical applications. There is a lot of exciting research being performed worldwide in developing novel scaffolds for tissue engineering. Although, nowadays the majority of the research effort is in the development of scaffolds for non-load bearing applications, primarily using soft natural or synthetic polymers or natural scaffolds for soft tissue engineering; metallic scaffolds aimed for hard tissue engineering have been also the subject of in vitro and in vivo research and industrial development. In this article, descriptions of the different manufacturing technologies available to fabricate metallic scaffolds and a compilation of the reported biocompatibility of the currently developed metallic scaffolds have been performed. Finally, we highlight the positive aspects and the remaining problems that will drive future research in metallic constructs aimed for the reconstruction and repair of bone.

Biological aspects and clinical importance of ultrasound therapy in bone healing

OBJECTIVES

The purpose of this study was to review past and recent literature findings regarding the effects of ultrasound therapy on bone healing and its clinical efficacy in medical and dental interventions.

METHODS

A literature review was conducted on the effects of ultrasound therapy on bone healing. The studies regarding clinical applications in long bones and maxillofacial bones were evaluated separately from each other.

RESULTS

The effects of therapeutic ultrasound on bone healing have been studied for half a century. Numerous clinical and experimental studies have addressed this relationship, and many of them have shown positive correlations. Although several theories have been proposed to explain the mechanism of action, the exact mechanism has not been fully understood.

CONCLUSIONS

Therapeutic ultrasound therapy in clinical settings is a noninvasive application and has no serious complications or side effects. It may be an acceptable treatment of choice in many types of clinical procedures involving maxillofacial bones.

Enhanced gap filling and osteoconduction associated with alendronate-calcium phosphate-coated porous tantalum

BACKGROUND

Porous tantalum has been shown to be effective in achieving bone ingrowth. However, in some circumstances, bone quality or quantity may be insufficient to allow adequate bone ingrowth. We hypothesized that local delivery of alendronate from porous tantalum would enhance the ability of the tantalum to achieve bone ingrowth when there is a gap between the implant and bone. We evaluated the effect of alendronate-coated porous tantalum on new bone formation in an animal model incorporating a gap between the implant and bone.

METHODS

A cylindrical porous tantalum implant was implanted in the distal part of each femur in eighteen rabbits (a total of thirty-six implants) and left in situ for four weeks. Three types of porous tantalum implants were inserted: those with no coating (the control group), those with microporous calcium phosphate coating, and those coated with microporous calcium phosphate and alendronate. Subcutaneous fluorescent labeling was used to track new bone formation. Bone formation was analyzed with backscattered electron microscopy and fluorescent microscopy of undecalcified samples.

RESULTS

The relative increases in the mean volume of gap filling, bone ingrowth, and total bone formation in the group treated with the porous tantalum implants coated with calcium phosphate and alendronate were 143% (p < 0.001), 259% (p < 0.001), and 193% (p < 0.001), respectively, compared with the values in the control group treated with the uncoated porous tantalum implants. The percentage of the length of the implant that was in contact with new bone in the group treated with the calcium phosphate and alendronate coating was increased by an average of 804% compared with the percentage in the group treated with the uncoated implants.

CONCLUSIONS

The study demonstrated significantly enhanced filling of the bone-implant gap and bone ingrowth in association with the porous tantalum implants coated with calcium phosphate and alendronate.

The effect of ultrasound on bone dimensional changes following extraction: a pilot study

BACKGROUND

Because of bone resorption following tooth extraction, preservation of adequate bony dimension is performed often for subsequent treatment with dental implants. This study evaluated a novel, non-invasive treatment using ultrasound to accelerate healing following extraction to minimize alveolar bone loss. The objective of this study was to evaluate the effect of ultrasound on the dimensional healing changes of alveolar bone following tooth extraction using cone-beam volumetric tomography (CBVT).

METHODS

This randomized, split-mouth trial involved 12 subjects requiring extraction of two contralateral erupted permanent teeth. Baseline CBVT scans were captured 7 to 10 days following extraction, after which time ultrasound therapy commenced in test sites. Ultrasound therapy was delivered for 20 minutes using a piezoelectric transducer for 10 sessions over the subsequent 4 weeks. Follow-up radiographic scans were obtained at 4 weeks and 3 months postextraction. Analyses of variance and covariance were performed to assess dimensional changes over the 3-month healing period.

RESULTS

Analysis of dimensional changes in all measures of vertical height and horizontal width demonstrated no statistically significant differences between the ultrasound and control groups from baseline to 3 months postextraction. Evaluation of correlations between dimensional changes demonstrated a moderately strong correlation (r = 0.67; P = 0.023) in the ultrasound group between the change in buccal vertical height and the baseline crestal ridge width. Analysis of the change in buccal vertical height relative to baseline crestal width demonstrated a statistically significant benefit to ultrasound compared to control (P = 0.016). This benefit was more pronounced in wider sockets compared to narrow sockets.

CONCLUSIONS

In this pilot study, there was no significant benefit to ultrasound in absolute bony dimensional changes following tooth extraction. There was a significant interaction between the treatment rendered (ultrasound versus control) and the change in buccal ridge height relative to baseline ridge width at the crest and 3 mm apical to the crest. This benefit was apparent in wide sockets compared to narrow sockets; however, the clinical importance of these relative dimensional changes in the ultrasound group are difficult to determine given the inclusion of all tooth types in a pilot study with a small sample size.

Low-intensity pulsed ultrasound does not enhance distraction callus in a rabbit model

Low-intensity pulsed ultrasound has been reported to have a positive effect when applied during the consolidation phase of distraction osteogenesis and bone transportation, but the optimal application time has not been determined. We used a rabbit model to determine whether low-intensity pulsed ultrasound applied during the distraction and early consolidation phases of tibial lengthening would have a positive effect on regenerated bone formation. Radiographic analysis showed no differences in regenerated callus area or in percent of callus mineralization between treated and control tibias immediately after distraction or at 1, 2, or 3 weeks after distraction. Similarly, we observed no differences in structural stiffness or maximal torque to failure at 1.5 or 3 weeks after distraction. We detected no differences in bone mineral appositional rates or percent tissue composition measured histologically between groups. Our data do not support the application of low-intensity pulsed ultrasound to regenerated bone during distraction osteogenesis.

Low-intensity pulsed ultrasound increases bone ingrowth into porous hydroxyapatite ceramic

Synthetic porous ceramic made of hydroxyapatite (HA) has been used as a bone graft substitute. In the present study we investigated whether low-intensity pulsed ultrasound (LIPUS) accelerates bone ingrowth into the pores of HA ceramic. Application of LIPUS did not mechanically weaken porous ceramic that was immersed in water in vitro. In vivo experiments using rabbits showed that LIPUS application for 2 weeks significantly increased osteoblast number and bone area in the central part of the porous HA ceramic implanted in the femoral condyle in comparison with similarly implanted HA ceramic that was not exposed to LIPUS. LIPUS application for 3 weeks significantly increased mineralized tissue volume and mineral content in the porous HA ceramic. Wound healing assays revealed increased migration of MC3T3-E1 cells as a result of LIPUS treatment, partly accounting for the increased osteoblast number. Use of porous HA ceramic combined with LIPUS may be a promising treatment for filling large bone defects in a clinical setting.

Zoledronic acid causes enhancement of bone growth into porous implants

The effect of zoledronic acid on bone ingrowth was examined in an animal model in which porous tantalum implants were placed bilaterally within the ulnae of seven dogs. Zoledronic acid in saline was administered via a single post-operative intravenous injection at a dose of 0.1 mg/kg. The ulnae were harvested six weeks after surgery. Undecalcified transverse histological sections of the implant-bone interfaces were imaged with backscattered scanning electron microscopy and the percentage of available pore space that was filled with new bone was calculated. The mean extent of bone ingrowth was 6.6% for the control implants and 12.2% for the zoledronic acid-treated implants, an absolute difference of 5.6% (95% confidence interval, 1.2 to 10.1) and a relative difference of 85% which was statistically significant. Individual islands of new bone formation within the implant pores were similar in number in both groups but were 69% larger in the zoledronic acid-treated group. The bisphosphonate zoledronic acid should be further investigated for use in accelerating or enhancing the biological fixation of implants to bone.

Current trends in the enhancement of biomaterial osteointegration: biophysical stimulation

To enhance bone implant osteointegration, many strategies for improving biomaterial properties have been developed which include optimization of implant material, implant design, surface morphology and osteogenetic coatings. Other methods that have been attempted to enhance endogenous bone healing around biomaterials are different forms of biophysical stimulations such as pulsed electromagnetic fields (PEMFs) and low intensity pulsed ultrasounds (LIPUS), which were initially developed to accelerate fracture healing. To aid in the use of adjuvant biophysical therapies in the management of bone-implant osteointegration, the present authors reviewed experimental and clinical studies published in the literature over the last 20 years on the combined use of biomaterials and PEMFs or LIPUS, and summarized the methodology, and the possible mechanism of action and effectiveness of the different biophysical stimulations for the enhancement of bone healing processes around bone implanted biomaterials.

Extracortical bone bridging in tumor endoprostheses. Radiographic and histologic analysis

BACKGROUND

Aseptic loosening remains a major problem following prosthetic replacement after resection of periarticular tumors. Attempts to decrease the rate of loosening led to the introduction of a composite segmental prosthesis in which the shoulder of the intramedullary stem is porous-coated to allow extracortical bone bridging and bone ingrowth. The purposes of this study were to determine the extent of extracortical bone bridging around, and the amount of bone growth into, the porous-coated shoulder of endoprostheses implanted following the resection of periarticular bone tumors and to correlate the radiographic and histologic findings.

METHODS

Twenty tumor endoprostheses implanted with use of the extracortical bone-bridging technique were evaluated radiographically to determine the extent of extracortical bone and the amount of bone ingrowth. Five of these endoprostheses were retrieved and subjected to histologic analysis with backscattered electron microscopy and transmitted light microscopy to determine the extent of bone ingrowth.

RESULTS

At a mean of twenty-eight months postoperatively, varying amounts of extracortical bone formation were seen radiographically in all patients. Radiographs also appeared to show bone growth into the porous-coated segment of all implants. However, histologic analysis of the five retrieved prostheses revealed that none of the extracortical bone had actually grown into the porous-coated segment of the implant.

CONCLUSIONS

This study confirmed that autogenous bone-grafting of the bone-implant junction of a tumor endoprosthesis consistently results in the formation of extracortical bone. Although radiographs seemed to indicate that this bone grows into the porous coating, this was not confirmed histologically. Growth of extracortical bone into the extramedullary, porous-coated portion of tumor endoprostheses in humans may not be attainable with the current prosthetic design and surgical technique.

Low-intensity ultrasound stimulation in distraction osteogenesis in rabbits

Low-intensity pulsed ultrasound has been shown to accelerate fracture healing. This experiment investigated its possible role in distraction. Thirty-four New Zealand White rabbits had distraction osteogenesis, followed by low-intensity pulsed ultrasound therapy. Seventeen animals had the ultrasound transducer switched off (controls). Four and 6 weeks postoperatively, tibiae were analyzed using quantitative computed tomography and four-point mechanical testing. Two tibiae from each group had histologic analysis at 4 weeks. No significant differences were identified between regenerates of ultrasound-treated and control groups with respect to bone mineral content, cross-sectional area, and strength. No significant reductions in osteopenia proximal and distal to the regenerate were observed. Histologic observation showed no differences in bone volume fraction, but ultrasound-treated regenerates appeared to have fewer trabeculae of increased thickness, and fewer osteoclasts. The modulation by ultrasound may occur by accelerating endochondral ossification through action on chondrocytes, yet distraction osteogenesis is largely intramembranous. Although ultrasound is proven to be effective in unconstrained systems such as plaster, the current study does not support the role of low-intensity pulsed ultrasound as an adjunct for patients having distraction osteogenesis in a rigid fixator. Additional research is needed to definitively support the use of low-intensity pulsed ultrasound in such situations.

The effects of sex and estrogen therapy on bone ingrowth into porous coated implant

Amounts of bone ingrowth into porous cobalt-chromium plugs were compared between male and female dogs, and among sham-operated and ovariectomized female dogs, with or without estrogen treatment, to investigate the effect of gender and estrogen therapy on biologic fixation. Each group consisted of eight skeletally mature dogs. Plugs were implanted bilaterally in the distal femur at 6 months after ovariectomy or sham operation. Estrogen treatment group received estradiol 20 microg/kg/day subcutaneous injection. Three months after implantation, histological examination showed significantly more bone ingrowth in areas with cortical bone contact than in areas with cancellous bone contact (P<0.001 for all groups). Bone ingrowth was essentially the same in male and female control dogs. Ovariectomized dogs showed less overall bone ingrowth than male and female controls (P=0.007). Bone ingrowth in areas with cortical bone contact did not decrease significantly, whereas bone ingrowth in areas with cancellous bone contact was significantly impaired (P<0.001) in ovariectomized dogs compared with female controls. Short-term, high-dose estradiol treatment did not increase bone ingrowth volume fraction. Mechanical tests did not show any statistical differences among groups.

CONCLUSION

Type of bone contact is the key factor affecting the amount and pattern of bone ingrowth into the porous surface. Ovariectomy results in decreased bone ingrowth in areas with cancellous bone contact, but does not compromise bone ingrowth in areas with cortical bone contact. Short-term, high-dose estradiol treatment does not enhance bone ingrowth into the porous surface. Extensively coated or full-coated porous prostheses are recommended to achieve enough cortical bone contact and ingrowth for post-menopausal patients.

Osseointegration of endosseous ceramic implants after postoperative low-power laser stimulation: an in vivo comparative study

Stimulation with low-power laser (LPL) can enhance bone repair as reported in experimental studies on bone defects and fracture healing. Little data exist concerning the use of LPL postoperative stimulation to improve osseointegration of endosseous implants in orthopaedic and dental surgery. An in vivo model was used for the present study to evaluate whether Ga-Al-As (780 nm) LPL stimulation can improve biomaterial osseointegration. After drilling holes, cylindrical implants of hydroxyapatite (HA) were placed into both distal femurs of 12 rabbits. From postoperative day 1 and for 5 consecutive days, the left femurs of all rabbits were submitted to LPL treatment (LPL group) with the following parameters: 300 J/cm2, 1 W, 300 Hz, pulsating emission, 10 min. The right femurs were sham-treated (control group). Three and 6 weeks after implantation, histomorphometric and microhardness measurements were taken. A higher affinity index was observed at the HA-bone interface in the LPL group at 3 (P<0.0005) and 6 weeks (P<0.001); a significant difference in bone microhardness was seen in the LPL group vs. the control group (P<0.01). These results suggest that LPL postoperative treatment enhances the bone-implant interface.