Dental implant failures in Utah and US veteran cohorts

INTRODUCTION

Approximately, 5.5 million dental implants are estimated to be surgically placed in the United States yearly, with an anticipated long-term failure rate ranging from 3% to 10%. At the Salt Lake City Dental Clinic within the Department of Veterans Affairs (VHA), specific protocols have been established to mandate that clinicians present every dental implant case for review by a committee. To understand the effectiveness of this approach, a comparative data analysis was undertaken to compare local dental implant failure data against national VHA data.

METHODS

Leveraging electronic health records of veterans spanning from 2000 to 2021, we gathered procedural records related to dental implant placement or failure, demographic information, and medical history for individuals who received dental care at various dental clinics within the nationwide VHA network. Subsequently, statistical analyses were conducted using mixed-effects Poisson regression models with cluster-robust standard errors. Incident rate ratios (IRRs) for Utah-specific and nationwide cohorts were ascertained.

RESULTS

The Utah VHA dental clinical data showed that there was a slightly lower prevalence of implant failure at 6.7% compared to the national cohort, which had a rate of 6.9%. The implant level failure rates were also low, with 4.20 (confidence interval [CI]: 3.68, 4.81) per 1000 implant placements per year for Utah cohorts. The adjusted IRR indicated a relative 16% reduction in risk among Utah Veterans (IRR 0.84, 95% CI [0.76-0.92]; p < 0.001).

CONCLUSIONS

The stringent protocols in place at Salt Lake City, which integrate evidence-based practices and expert opinion for evaluating patient suitability for dental implant placement and subsequent care, contributed to the reduced risk among Utah Dental Clinic veterans pool compared to veterans of other states.

Association between blood markers and the progression of osseointegration in percutaneous prostheses patients-A pilot study

Patients implanted with osseointegrated (OI) prosthetic systems have reported vastly improved upper and lower extremity prosthetic function compared with their previous experience with socket-suspension systems. However, OI systems have been associated with superficial and deep-bone infections and implant loosening due, in part, to a failure of the osseointegration process. Although monitoring the osseointegration using circulating biomarkers has clinical relevance for understanding the progression of osseointegration with these devices, it has yet to be established. Ten patients were enrolled in this study. Blood samples were collected at pre-selected times, starting before implantation surgery, and continuing to 12 months after the second surgery. Bone formation markers, bone resorption markers, and circulating amino acids were measured from blood samples. A linear mixed model was generated for each marker, incorporating patient ID and age with the normalized marker value as the response variable. Post hoc comparisons were made between 1 week before Stage 1 Surgery and all subsequent time points for each marker, followed by multiple testing corrections. Serial radiographic imaging of the residual limb containing the implant was obtained during follow-up, and the cortical index (CI) was calculated for the bone at the porous region of the device. Two markers of bone formation, specifically bone-specific alkaline phosphatase (Bone-ALP) and amino-terminal propeptide of type I procollagen (PINP), exhibited significant increases when compared with the baseline levels of unloaded residual bone prior to the initial surgery, and they subsequently returned to their baseline levels by the 12-month mark. Patients who experienced clinically robust osseointegration experienced increased cortical bone thickness at the porous coated region of the device. A medium correlation was observed between Bone-ALP and the porous CI values up to PoS2-M1 (p = .056), while no correlation was observed for PINP. An increase in bone formation markers and the lack of change observed in bone resorption markers likely reflect increased cortical bone formation induced by the end-loading design of the Utah OI device used in this study. A more extensive study is required to validate the correlation observed between Bone-ALP and porous CI values.

Freeze casting of hydroxyapatite-titania composites for bone substitutes

Hydroxyapatite (HA) is commonly used as a bone substitute material, but it lacks mechanical strength when compared to native bone tissues. To improve the efficacy of HA as a bone substitute by improving the mechanical strength and cell growth attributes, porous composite scaffolds of HA and titania (HA-TiO2 ) were fabricated through a freeze-casting process. Three different compositions by weight percent, 25-75 HA-TiO2 , 50-50 HA-TiO2 , and 75-25 HA-TiO2 , were custom-made for testing. After sintering at 1250°C, these composite scaffolds exhibited improved mechanical properties compared to porous HA scaffolds. Substrate mixing was observed, which helped reduce crystal size and introduced new phases such as β-TCP and CaTiO3 , which also led to improved mechanical properties. The composition of 50-50 HA-TiO2 had the highest ultimate compressive strength of 3.12 ± 0.36 MPa and elastic modulus 63.29 ± 28.75 MPa. Human osteoblast cell proliferation assay also increased on all three different compositions when compared to porous HA at 14 days. These results highlight the potential of freeze casting composites for the fabrication of bone substitutes, which provide enhanced mechanical strength and biocompatibility while maintaining porosity.

Sintered fluorapatite scaffolds as an autograft-like engineered bone graft

Hydroxyapatite (HA)-based materials are widely used as bone substitutes due to their inherent biocompatibility, osteoconductivity, and bio-absorption properties. However, HA scaffolds lack compressive strength when compared to autograft bone. It has been shown that the fluoridated form of HA, fluorapatite (FA), can be sintered to obtain this desired strength as well as slower degradation properties. Also, FA surfaces have been previously shown to promote stem cell differentiation toward an osteogenic lineage. Thus, it was hypothesized that FA, with and without stromal vascular fraction (SVF), would guide bone healing to an equal or better extent than the clinical gold standard. The regenerative potentials of these scaffolds were tested in 32 Lewis rats in a femoral condylar defect model with untreated (negative), isograft (positive), and commercial HA as controls. Animals were survived for 12 weeks post-implantation. A semi-quantitative micro-CT analysis was developed to quantify the percent new bone formation within the defects. Our model showed significantly higher (p < .05) new bone depositions in all apatite groups compared to the autograft group. Overall, the FA group had the most significant new bone deposition, while the differences between HA, FA, and FA + SVF were insignificant (p > .05). Histological observations supported the micro-CT findings and highlighted the presence of healthy bone tissues without interposing capsules or intense immune responses for FA groups. Most importantly, the regenerating bone tissue within the FA + SVF scaffolds resembled the architecture of the surrounding trabecular bone, showing intertrabecular spaces, while the FA group presented a denser cortical bone-like architecture. Also, a lower density of cells was observed near FA granules compared to HA surfaces, suggesting a reduced immune response. This first in vivo rat study supported the tested hypothesis, illustrating the utility of FA as a bone scaffold material.

Fluorapatite-Coated Percutaneous Devices Promote Wound Healing and Limit Epithelial Downgrowth at the Skin-Device Interface

A percutaneous osseointegrated device becomes deeply ingrown by endosteal bone and traverses the overlying soft tissues of the residual limb, providing a direct link to the bone-anchored artificial limb. Continuous wound healing around these devices can result in the formation of sinus tracts as “down-growing” epithelial cells are unable to recognize and adhere to the “nonbiological” implant surface. Such sinus tracts provide paths for bacterial colonization and deep infection. In order to limit adverse outcomes and provide a robust seal, it was hypothesized that by coating the titanium surface of the percutaneous post with the mineral component of dental enamel, down-growing epidermal cells might recognize the coating as “biological” and adhere to this nonliving surface. To test this hypothesis, sintered partially and fully fluoridated hydroxyapatite (HA) was chosen as coatings. Using an established surgical protocol, fluorapatite (FA), hydroxyfluorapatite (FHA), HA-coated percutaneous posts, and titanium controls were surgically placed under the dorsal skin in 20 CD hairless rats. The animals were sacrificed at four weeks, and implants and surrounding tissues were harvested and subjected to further analyses. Downgrowth and granulation tissue area data showed statistically significant reductions around the FA-coated devices. Moreover, compared to the control group, the FA- and HA-coated groups showed downregulation of mRNA for EGFr, EGF, and FGF-10. Interestingly, the FA-coated group had upregulation of TGF-α. These data suggest that FA could become an ideal coating material for preventing downgrowth, assuming the long-term stability of these coated surfaces can be verified in a clinically relevant animal model.

Serum procalcitonin level is independently associated with mechanical ventilation and case-fatality in hospitalized COVID-19-positive US veterans-A potential marker for disease severity

The Coronavirus-19 disease (COVID-19) has claimed over 6.8 million lives since first being reported in late 2019. The virus that causes COVID-19 disease is highly contagious and spreads rapidly. To date, there are no approved prognostic tools that could predict why some patients develop severe or fatal disease outcomes. Early COVID-19 studies found an association between procalcitonin (PCT) and hospitalization or duration of mechanical ventilation and death but were limited by the cohort sizes. Therefore, this study was designed to confirm the associations of PCT with COVID-19 disease severity outcomes in a large cohort. For this retrospective data analysis study, 27,154 COVID-19-positive US veterans with post-infection PCT laboratory test data and their disease severity outcomes were accessed using the VA electronic healthcare data. Cox regression models were used to test the association between serum PCT levels and disease outcomes while controlling for demographics and relevant confounding variables. The models demonstrated increasing disease severity (ventilation and death) with increasing PCT levels. For PCT serum levels above 0.20 ng/ml, the unadjusted risk increased nearly 2.3-fold for mechanical ventilation (hazard ratio, HR, 2.26, 95%CI: 2.11-2.42) and in-hospital death (HR, 2.28, 95%CI: 2.16-2.41). Even when adjusted for demographics, diabetes, pneumonia, antibiotic use, white blood cell count, and serum C-reactive protein levels, the risks remained relatively high for mechanical ventilation (HR, 1.80, 95%CI: 1.67-1.94) and death (HR, 1.76, 95%CI: 1.66-1.87). These data suggest that higher PCT levels have independent associations with ventilation and in-hospital death in veterans with COVID-19 disease, validating previous findings. The data suggested that serum PCT level may be a promising prognostic tool for COVID-19 severity assessment and should be further evaluated in a prospective clinical trial.

1127. Effectiveness of Remdesivir as Treatment for COVID-19 Positive US Veterans

Background

The COVID 19 disease has claimed over 6.3 million lives, globally. Despite such high casualties, the treatment options are limited. Although the FDA issued emergency use authorizations for oral antivirals to treat mild-to-moderate COVID 19 disease, intravenous Remdesivir treatment remains the only fully FDA-approved antiviral. However, many early studies questioned its efficacy. Accordingly, the WHO initially recommended against its use in COVID 19 positive patients. Based on the newly emerging data, as of 22 April 2022, WHO suggests that Remdesivir can be effectively used in mild or moderate COVID 19 cases. This retrospective cohort data analysis was undertaken to evaluate and clarify the effectiveness of Remdesivir use in older US veterans.

Methods

The deidentified veterans' data were accessed from the VA COVID 19 Shared Data Resources with local ethical approvals. Propensity matched cohorts with and without Remdesivir treatment were analyzed using Cox regression models, constructed in a way to avoid immortal time and calendar time biases. Limited to hospitalized veterans, patients were followed for 60 days to the outcomes of mechanical ventilation (MV) and death in separate models. The cohort was also limited to those who received low flow without high flow oxygen and a combination of low and high flow oxygen in another set of models.

Results

A total of 3,372 veterans were included in this study who were hospitalized between 01 January to 31 December 2021 for COVID 19 disease. Of those, 1,686 received Remdesivir treatment, while their matches never received it. After propensity score matching that included demography, vaccination status, comorbidities, medication use, lab tests, Remdesivir recipients and controls were similar in age (66.8±14.1 vs. 67.0±13.8 years). Relative risk reductions (1-HR), 53% for MV, and 42% for death (Fig. 1) were observed with low flow oxygen and Remdesivir therapy. In veterans who received high and low flow oxygen, although there was a significant 18% reduction in risk for death, progression to MV was not significant (P=0.22). Figure 1

A Dentist’s Perspective on the Need for Interdisciplinary Collaboration to Reduce Medication-Related Osteonecrosis of the Jaw

Antiresorptive medications, including bisphosphonates and RANK-L inhibitors, are commonly used to treat various skeletal pathologies. One devastating complication associated with these drugs is medication-related osteonecrosis of the jaw (MRONJ). Patients who develop MRONJ suffer immensely from oral lesions that may persist, even with treatment, until their death. The jawbone is known to remodel 5 to 10 times faster than skeletal bone. Dentists are at the forefront in managing the severe maxillofacial repercussions of MRONJ. Because MRONJ risk is relatively low (reportedly 0.7% to 6.7%) it is underappreciated by many clinical specialties. The minimization of MRONJ is further compounded because it may take months or years to develop. To date, dental treatment protocols are based more on expert opinion than concrete scientific evidence. This iatrogenic, intractable illness is discouraging for both the patient and the treating dentist. To promote multidisciplinary understanding and cooperation, a single MRONJ case caused by intravenous pamidronate is presented, along with commentary from a dentist’s perspective. The intent is that these data will increase awareness of MRONJ’s stomatognathic consequences to the physician, who prescribed the causative agent, and the pharmacist, who dispensed it. Collaboration between the dentist, physician, and pharmacist has tremendous potential to improve treatment strategies and, ultimately, optimize patient care.

Hospitalization, mechanical ventilation, and case-fatality outcomes in US veterans with COVID-19 disease between years 2020-2021

PURPOSE

Although veterans represent a significant proportion (7%) of the USA population, the COVID-19 disease impact within this group has been underreported. To bridge this gap, this study was undertaken.

METHOD

A total of 419,559 veterans, who tested positive for COVID-19 disease in the Veterans Affairs hospital system from March 1st, 2020 to December 31st, 2021 with 60-days follow-up, was included in this retrospective review. Primary outcome measures included age-adjusted incidences and relative incidences of COVID-19 hospitalization, mechanical ventilation, and case-fatality outcomes.

RESULTS

Of this veteran cohort with COVID-19 disease, predominately 85.7% were male, 59.1% were White veterans, 27.5% were ages 50-64, and 40.5% were obese. Although Black veterans were at 63% higher relative risk (RR) for hospitalization incidences, they had a similar risk RR for in-hospital deaths compared to the White-veteran referent. Asian, American Indian/Alaska Native races, advanced age ≥65, and the underweight were at high RR for mechanical ventilator and/or in-hospital deaths compared to respective referent groups. Veterans who are ≥85 years old had a nearly 5-fold higher incidence of death compared respective referent group. The monthly outcomes for hospitalization, ventilation, and case-fatality data showed decreasing trends with time.

CONCLUSION

An increased incidence of death was associated with age ≥65 years and underweight veterans compared to the referent group. Age-adjusted data, however, did not show any increased incidence of death in Black veterans compared to White veterans.

RATINGS OF THE QUALITY OF THE EVIDENCE

3 (Case-control studies; retrospective cohort study).

A preliminary, observational study using whole-blood RNA sequencing reveals differential expression of inflammatory and bone markers post-implantation of percutaneous osseointegrated prostheses

AIMS

While the benefits of direct skeletal attachment of artificial limbs are well recognized, device failure due to infection and insufficient osseointegration remain obstacles to obtaining consistently successful outcomes. Currently, the potential for device failure is assessed by subjective pain, clinical function scores, radiographic evidence of bone atrophy, and the presence of radiolucent lines at the bone-implant interface, and subjective pain and function scores. Our hypothesis is that measurable biological indices might add another objective means to assess trends toward bone and stomal healing. This longitudinal cohort study was undertaken to identify potential serological biomarkers suggestive of bone remodeling and the presence of stomal tissue inflammation.

METHODS

Ten unilateral transfemoral amputee veterans, who were implanted with a percutaneous osseointegrated (OI) skeletal limb docking system, were recruited to participate in this IRB-approved study. Venous blood samples were obtained from before the Stage 1 Surgery up to 1 year following the Stage 2 Surgery. Whole-blood RNA was extracted, sequenced, mapped, and analyzed. Of the significant differentially expressed (DEGs) genes (p<0.05) identified, four genes of interest (IL12B, IL33, COL2A1, and SOST) were validated using qPCR. Enrichment analysis was performed to identify significant (p<0.01) Gene Ontology (GO) terms.

RESULTS

Most differentially expressed genes were only detected at PoS1 immediately after the first surgery. Of the significant genes identified, IL12B and IL33 were related to inflammation, and COL2A1 and SOST were associated with bone remodeling. These four genes were identified with greater than 20 log fold-change.

CONCLUSION

Whole-blood RNA-seq data from 10 patients who previously underwent percutaneous osseointegrated lower limb implantation revealed four genes of interest that are known to be involved in inflammation or bone remodeling. If verified in future studies, these genes may serve as markers for predicting optimal bone remodeling and stomal tissue healing following OI device implantation.

Fluorapatite and fluorohydroxyapatite apatite surfaces drive adipose-derived stem cells to an osteogenic lineage

PURPOSE

Hydroxyapatite (HA) scaffolds are common replacement materials used in the clinical management of critical-sized bone defects. This study was undertaken to examine the potential benefits of fluoridated derivatives of hydroxyapatite, fluorapatite (FA), and fluorohydroxyapatite (FHA) as bone scaffolds in conjunction with adipose-derived stem cells (ADSCs). If FHA and FA surfaces could drive the differentiation of stem cells to an osteogenic phenotype, the combination of these ceramic scaffolds with ADSCs could produce materials with mechanical strength and remodeling potential comparable to autologous bone. This study was designed to investigate the ability of the apatite surfaces HA, FA, and FHA produced at different sintering temperatures to drive ADSCs toward osteogenic lineages.

METHODS

HA, FHA, and FA surfaces sintered at 1150 °C and 1250 °C were seeded with ADSCs and evaluated for cell growth and gene and protein expression of osteogenic markers at 2 and 10 days post-seeding.

RESULTS

In vitro, ADSC cells were viable on all surfaces; however, differentiation of these cells into osteoblastic lineage only observed in apatite surfaces. ADSCs seeded on FA and FHA expressed genes and proteins related to osteogenic differentiation markers to a greater extent by Day 2 when compared to HA and cell culture controls. By day 10, HA, FA, and FHA all expressed more bone differentiation markers compared to cell culture controls.

CONCLUSION

FA and FHA apatite scaffolds may promote the differentiation of ADSCs at an earlier time point than HA surfaces. Combining apatite scaffolds with ADSCs has the potential to improve bone regeneration following bone injury.

Characterization of porous fluorohydroxyapatite bone-scaffolds fabricated using freeze casting

With the increasing demand for orthopedic and dental reconstruction surgeries, there comes a shortage of viable bone substitutes. This study was therefore designed to assess the efficacy of porous fluorohydroxyapatite (FHA) as a potential bone substitute. For this, porous FHA scaffolds were fabricated using the freeze casting technique. They were then sintered at 1250, 1350 and, 1450 °C, and microstructural, mechanical, and in vitro properties were analyzed. The microstructure analyses revealed the porosity remained constant within the temperature range. However, the pore size decreased with increasing sintering temperature. The greatest compressive strength and elastic modulus were obtained at 1450 °C, which were 13.5 ± 4.0 MPa and 379 ± 182 MPa, respectively. These are comparable values to human trabecular bone and other porous scaffolds made using hydroxyapatite. This analysis has thus helped to attain an understanding of the mechanical and material properties of freeze-cast FHA scaffolds that have not been presented before. In vitro studies revealed an increasing rate of human osteoblast cell proliferation on freeze-cast FHA scaffolds with increasing sintering temperature, suggesting improved osteogenic properties. Additionally, osteoblasts cells were also shown to proliferate into the interior pores of all freeze-cast FHA scaffolds. These results indicate the potential of porous FHA scaffolds fabricated using the freeze-casting technique to be utilized clinically as bone substitutes.

Evaluation of soft-tissue response around laser microgrooved titanium percutaneous devices

Percutaneous devices are prone to epidermal downgrowth and sinus tract formation, which can serve as a nidus for bacterial colonization and increase the risk of peri-prosthetic infection. A laser microgrooved topography has been shown to limit gingival epidermal downgrowth around dental implants. However, the efficacy of this laser microgrooved topography to limit epidermal downgrowth around nongingival percutaneous devices is yet to be investigated. In this study, devices with a porous-coated subdermal component and a percutaneous post were designed and manufactured. The proximal 2 mm section of the percutaneous post were left smooth, or were textured with either a porous coating, or with the laser microgrooved topography. The smooth and porous topographies served as controls. The devices were tested in a hairless guinea pig back model, where 18 animals were randomly assigned into three groups, with each group receiving one implant type (n = 6/group). Four weeks postimplantation, the devices with surrounding soft-tissues were harvested and processed for histological analyses. Results indicated that the laser microgrooved topography failed to prevent epidermal downgrowth (23 ± 4%) around percutaneous posts in this model. Furthermore, no significant differences (p = 0.70) in epidermal downgrowth were present between the three topographies, with all the groups exhibiting similar measures of downgrowth. Overall, these findings suggest that the laser microgrooved topography may not halt downgrowth around percutaneous devices for dermal applications.

Analysis of the Stomal Microbiota of a Percutaneous Osseointegrated Prosthesis: A Longitudinal Prospective Cohort Study

Percutaneous osseointegrated (OI) prostheses (POPs) are used to skeletally attach artificial limbs in amputees. While any permanent percutaneous interface is at risk of becoming infected by the resident microbiota colonizing the stoma, most of these patients remain infection-free. Avoidance of infection likely depends upon a mechanically and/or biologically stable skin-to-implant interface. The ultimate question remains, "why do some stomata become infected while others do not?" The answer might be found in the dynamic bacterial communities of the patient and within the stomal site itself. This study is an appendix to the first Food and Drug Administration approved prospective early feasibility study of OI prosthetic docking, in which, 10 transfemoral amputees were implanted with a unique POP device. In this analytical, longitudinal cohort study, each patient's skin and stomal microbiota were analyzed from the initial surgery to 1 year following the second-stage surgery. During each follow-up visit, three swab samples-stomal, device thigh skin and contralateral thigh skin-were obtained. DNA was extracted, and bacterial 16S ribosomal RNA (rRNA) genes were amplified and sequenced to profile microbial communities. The stomal microbiota were distinct from the microbiota on the adjacent thigh skin and the skin of the contralateral thigh, with a significantly increased abundance of Staphylococcus aureus within the stoma. Early on stomal microbiota were characterized by high diversity and high relative abundance of obligate anaerobes. Over time, the stomal microbiota shifted and stabilized in communities of lower diversity dominated by Streptococcus, Corynebacterium, and/or Staphylococcus spp. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2645-2654, 2019.

Variation in bone response to the placement of percutaneous osseointegrated endoprostheses: A 24-month follow-up in sheep

Percutaneous osseointegrated (OI) devices for amputees are metallic endoprostheses, that are surgically implanted into the residual stump bone and protrude through the skin, allowing attachment of an exoprosthetic limb. In contrast to standard socket suspension systems, these percutaneous OI devices provide superior attachment platforms for artificial limbs. However, bone adaptation, which includes atrophy and/or hypertrophy along the extent of the host bone-endoprosthetic interface, is seen clinically and depends upon where along the bone the device ultimately transfers loading forces to the skeletal system. The goal of this study was to determine if a percutaneous OI device, designed with a porous coated distal region and an end-loading collar, could promote and maintain stable bone attachment. A total of eight, 18 to 24-month old, mixed-breed sheep were surgically implanted with a percutaneous OI device. For 24-months, the animals were allowed to bear weight as tolerated and were monitored for signs of bone remodelling. At necropsy, the endoprosthesis and the surrounding tissues were harvested, radiographically imaged, and histomorphometrically analyzed to determine the periprosthetic bone adaptation in five animals. Bone growth into the porous coating was achieved in all five animals. Serial radiographic data showed stress-shielding related bone adaptation occurs based on the placement of the endoprosthetic stem. When collar placement and achieved end-bearing against the transected bone, distal bone conservation/hypertrophy was observed. The results supported the use of a distally loading and distally porous coated percutaneous OI device to achieve distal host bone maintenance.

Biomimetic coatings and negative pressure wound therapy independently limit epithelial downgrowth around percutaneous devices

Biomimetic material coatings and negative pressure wound therapy (NPWT) have been shown independently to limit the epithelial downgrowth rates in percutaneous devices. It was therefore hypothesized that these techniques, in combination, could further limit the clinically observed epithelial downgrowth around these devices. In this study, we evaluated the efficacy of two biomimetic coatings, collagen and hydroxyapatite (HA), to prevent downgrowth when used with continuous NPWT. Using an established single-stage surgical protocol, collagen (n = 10) and HA (n = 10) coated devices were implanted subdermally on the back of hairless guinea pigs. Five animals from each group were subjected to continuous ~90 mmHg NPWT. Four weeks post-implantation, animals were sacrificed, and the devices and surrounding tissues were harvested, processed, and downgrowth was computed and compared to historical porous titanium coated controls. Data showed a significant reduction in downgrowth in NPWT treated animals (p ≤ 0.05) when compared to the untreated porous titanium controls. HA coated devices, without the NPWT treatment, also showed significantly decreased downgrowth compared to the untreated porous titanium controls.

Epidermal growth factor receptor genes are overexpressed within the periprosthetic soft-tissue around percutaneous devices: A pilot study

Epidermal downgrowth around percutaneous devices produce sinus tracts, which then accumulate bacteria becoming foci of infection. This mode to failure is epidermal-centric, and is accelerated by changes in the chemokines and cytokines of the underlying periprosthetic granulation tissue (GT). In order to more fully comprehend the mechanism of downgrowth, in this 28-day study, percutaneous devices were placed in 10 Zucker diabetic fatty rats; 5 animals were induced with diabetes mellitus II (DM II) prior to the surgery and 5 animals served as a healthy, nondiabetic cohort. At necropsy, periprosthetic tissues were harvested, and underwent histological and polymerase chain reaction (PCR) studies. After isolating GTs from the surrounding tissue and extracting ribonucleic acids, PCR array and quantitative-PCR (qPCR) analyses were carried-out. The PCR array for 84 key wound-healing associated genes showed a five-fold or greater change in 31 genes in the GTs of healthy animals compared to uninjured healthy typical skin tissues. Eighteen genes were overexpressed and these included epidermal growth factor (EGF) and epidermal growth factor receptor (EGFR). Thirteen genes were underexpressed. When GTs of DM II animals were compared to healthy animals, there were 8 genes overexpressed and 25 genes underexpressed; under expressed genes included EGF and EGFR. The qPCR and immunohistochemistry data further validated these observations. Pathway analysis of genes up-regulated 15-fold or more indicated two, EGFR and interleukin-10, centric clustering effects. It was concluded that EGFR could be a key player in exacerbating the epidermal downgrowth, and might be an effective target for preventing downgrowth.

Influence of negative pressure wound therapy on peri-prosthetic tissue vascularization and inflammation around porous titanium percutaneous devices

Negative Pressure Wound Therapy (NPWT) has been shown to limit downgrowth around percutaneous devices in a guinea pig model. However, the influence of NPWT on peri-prosthetic tissue characteristics leading to limited downgrowth is still unclear. In order to investigate this, 12 CD hairless rats were assigned into two groups, NPWT and Untreated (n = 6/group). Each animal was implanted with a porous coated titanium percutaneous device and was dressed with a gauze and semi-occlusive base dressing. Post-surgery, animals in the NPWT Group received a regimen of NPWT treatment (-70 to -90 mmHg). After 4 weeks, tissue was collected over the device and stained with CD31 and CD68 to quantify blood vessel density and inflammation, respectively. The device with the surrounding tissue was also collected to quantify downgrowth. NPWT treatment led to a 1.6-fold increase in blood vessel densities compared to untreated tissues (p < 0.05). NPWT treatment also resulted in half the downgrowth as the Untreated Group, although not statistically significant (p = 0.19). Additionally, the results showed a trend toward increased CD68 cell densities in the NPWT Group compared to the Untreated Group (p = 0.09). These findings suggest that NPWT may influence wound healing responses in percutaneous devices by increasing blood vessel densities, limiting downgrowth and potentially increasing inflammation. Overall, NPWT may enhance tissue vascularity around percutaneous devices, especially in patients with impaired wound healing. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2091-2101, 2019.

Peri-prosthetic tissue reaction to discontinuation of negative pressure wound therapy around porous titanium percutaneous devices

Negative pressure wound therapy (NPWT) has been reported to limit epithelial downgrowth, one of the failure mechanisms of percutaneous devices. In a previous study, when NPWT was applied for 4 weeks (NPWT Group) to porous coated titanium percutaneous devices, downgrowth (5 ± 4%; mean ± one SD) was significantly reduced compared to untreated controls (Untreated Group) (16 ± 6%; p ≤ 0.01). However, it was unclear whether this beneficial effect was sustained when NPWT was discontinued. In order to test this, porous coated titanium percutaneous devices were implanted into 6 hairless guinea pigs. Post-surgery, animals received 4 weeks of NPWT treatment followed by 4 weeks of no treatment (Discontinued Group). At necropsy, the devices and surrounding tissues were harvested and processed. Quantitative downgrowth measurements and qualitative analyses of tissue characteristics were performed, and compared to historical controls (NPWT and Untreated Groups). The Discontinued Group, at 8 weeks, had significantly more downgrowth than the NPWT Group at 4 weeks (23 ± 3% vs. 5 ± 4%; p ≤ 0.01). At 8 weeks, the Discontinued Group qualitatively appeared to exhibit reduced numbers of blood vessels and increased degree of fibrosis compared to the NPWT Group at 4 weeks. This study suggests that NPWT will only be an effective treatment for limiting downgrowth if used continuously. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 564-572, 2019.

A 24-month evaluation of a percutaneous osseointegrated limb-skin interface in an ovine amputation model

Percutaneous osseointegrated (OI) prostheses directly connect an artificial limb to the residual appendicular skeleton via a permanently implanted endoprosthesis with a bridging connector that protrudes through the skin. The resulting stoma produces unique medical and biological challenges. Previously, a study using a large animal amputation model indicated that infection could be largely prevented, for at least a 12-month period, but the terminal epithelium continued to downgrow. The current study was undertaken to test the longer-term efficacy of this implant construct to maintain a stable skin-implant interface for 24 months. Using the previously successful amputation and implantation surgical procedure, a total of eight sheep were fitted with a percutaneous OI prosthesis. Two animals were removed from the study due to early complications. Of the remaining six sheep, one (16.7%) became infected at 15-months post-implantation and five remained infection-free for the intended 24 months. The histological data of the remaining animals further confirmed the grossly observable epithelial downgrowth. Albeit a receding interface, it was clear that all animals that survived to the end of the study had residual fibrous soft-tissue ingrowth into, and debris within, the exposed titanium porous-coated surface. Overall, the data demonstrated that the porous coated subdermal barrier offered initial protection against infection. However, the fibrous skin attachment was continuously lysed over time by the down-growing epithelium.

Negative pressure wound therapy limits downgrowth in percutaneous devices

Maintenance of a soft tissue seal around percutaneous devices is challenged by the downgrowth of periprosthetic tissues-a gateway to potential infection. As negative pressure wound therapy (NPWT) is used clinically to facilitate healing of complex soft tissue pathologies, it was hypothesized that NPWT could limit downgrowth of periprosthetic tissues. To test this hypothesis, 20 hairless guinea pigs were randomly assigned into four groups (n = 5/group). Using a One-Stage (Groups 1 and 3) or a Two-Stage (Groups 2 and 4) surgical procedure, each animal was implanted with a titanium-alloy subdermal device porous-coated with commercially pure, medical grade titanium. Each subdermal device had a smooth titanium-alloy percutaneous post. The One-Stage procedure encompassed insertion of a fully assembled device during a single surgery. The Two-Stage procedure involved the implantation of a subdermal device during the first surgery, and then three weeks later, insertion of a percutaneous post. Groups 1 and 2 served as untreated controls and Groups 3 and 4 received NPWT. Four weeks postimplantation of the post, the devices and surrounding tissues were harvested, and histologically evaluated for downgrowth. Within the untreated control groups, the Two-Stage surgical procedure significantly decreased downgrowth (p = 0.027) when compared with the One-Stage procedure. Independent of the surgical procedures performed, NPWT significantly limited downgrowth (p ≤ 0.05) when compared with the untreated controls.

Progression of bone ingrowth and attachment strength for stability of percutaneous osseointegrated prostheses

BACKGROUND

Percutaneous osseointegrated prosthetic (POP) devices have been used clinically in Europe for decades. Unfortunately, their introduction into the United States has been delayed, in part due to the lack of data documenting the progression of osseointegration and mechanical stability.

QUESTIONS/PURPOSES

We determined the progression of bone ingrowth into porous-coated POP devices and established the interrelationship with mechanical stability.

METHODS

After amputation, 64 skeletally mature sheep received a custom porous-coated POP device and were then randomized into five time groups, with subsequent measurement of percentage of bone ingrowth into the available pore spaces (n = 32) and the mechanical pullout force (n = 32).

RESULTS

Postimplantation, there was an accelerated progression of bone ingrowth (~48% from 0 to 3 months) producing a mean pullout force of 5066 ± 1543 N. Subsequently, there was a slower but continued progression of bone ingrowth (~23% from 3 to 12 months) culminating with a mean pullout force of 13,485 ± 1855 N at 12 months postimplantation. There was a high linear correlation (R = 0.94) between the bone ingrowth and mechanical pullout stability.

CONCLUSIONS

This weightbearing model shows an accelerated progression of bone ingrowth into the porous coating; the amount of ingrowth observed at 3 months after surgery within the porous-coated POP devices was sufficient to generate mechanical stability.

CLINICAL RELEVANCE

The data document progression of bone ingrowth into porous-coated POP devices and establish a strong interrelationship between ingrowth and pullout strength. Further human data are needed to validate these findings.

Pig dorsum model for examining impaired wound healing at the skin-implant interface of percutaneous devices

Percutaneous medical devices are indispensable in contemporary clinical practice, but the associated incidence of low to moderate mortality infections represents a significant economic and personal cost to patients and healthcare providers. Percutaneous osseointegrated prosthetics also suffer from a similar risk of infection, limiting their clinical acceptance and usage in patients with limb loss. We hypothesized that transepidermal water loss (TEWL) management at the skin-implant interface may improve and maintain a stable skin-to-implant interface. In this study, skin reactions in a 3-month, pig dorsum model were assessed using standard histology, immunohistochemistry, and quantitative image analysis. Immunohistochemical analysis of peri-implant tissue explants showed evidence of: continuous healing (cytokeratin 6+), hypergranulation tissue (procollagen+), hyper-vascularity (collagen 4+), and the presence of fibrocytes (CD45+ and procollagen type 1+). Importantly, the gross skin response was correlated to a previous load-bearing percutaneous osseointegrated prosthetic sheep study conducted in our lab. The skin responses of the two models indicated a potentially shared mechanism of wound healing behavior at the skin-implant interface. Although TEWL management did not reduce skin migration at the skin-implant interface, the correlation of qualitative and quantitative measures validated the pig dorsum model as a high-throughput platform for translational science based percutaneous interface investigations in the future.

Efficacy of a porous-structured titanium subdermal barrier for preventing infection in percutaneous osseointegrated prostheses

Infections of percutaneous osseointegrated prostheses (POP) cause prolonged morbidity and device failure because once established, they are refractory to antibiotic therapy. To date, only limited translational animal studies have investigated the efficacy of POP designs in preventing infections. We developed an animal model to evaluate the efficacy of a porous-coated titanium (Ti) subdermal barrier to achieve skin-implant integration and to prevent periprosthetic infection. In a single-stage "amputation and implantation" surgery, 14 sheep were fitted with percutaneous devices with an attached porous-coated Ti subdermal barrier. Nine sheep were implanted with a smooth Ti subdermal barrier construct and served as controls, with one control sheep removed from the study due to a fractured bone. Clinical, microbiological, and histopathological data showed that the porous Ti barrier prevented superficial and deep tissue infections in all animals (14/14, 100%) at the 9-month endpoint. In contrast, animals with the smooth Ti implant construct had a 25% (2/8) infection rate. Survival analysis indicated a significant difference between the groups (log-rank test, p = 0.018). Data also indicated that although skin marsupialization was evident in both implant types, animals in the control group had a four times greater marsupialization rate. We concluded that osseointegrated implants incorporating porous-coated Ti subdermal barriers may have the ability to prevent infection by maintaining a healthy, biologically attached epithelial barrier at the skin-implant interface in load-bearing animals up to a 9-month terminus.

Cortical bone response to the presence of load-bearing percutaneous osseointegrated prostheses

Although the current percutaneous osseointegrated (OI) prosthetic attachment systems are novel clinical treatments for patients with limb loss, there have only been limited translational studies undertaken to date. To bridge this knowledge gap, from a larger study group of 86 animals that were implanted with a novel percutaneous OI implant construct, 33 sheep were randomly selected from the 0-, 3-, 6-, 9- and 12-month groups for histomorphometric analyses of periprosthetic cortical bone tissue. At necropsy, implanted and nonimplanted limbs were harvested and processed for the evaluation of cortical bone porosity and mineral apposition rate (MAR). The data showed a maximum increase in bone porosity within the first 3 months following implantation and then a progressive reduction in porosity to the baseline steady-state ("Time 0") value by 12 months. The data further verified that the MAR increased during the first 6 months of implantation, reaching a plateau between 6 and 9 months, followed by a progressive decline to the baseline steady state. It was concluded that clinical load bearing and falls precautions, taken during the first 3-6 months following percutaneous OI device implantation surgery, could greatly limit bone fractures during this vulnerable time of increasing cortical bone porosity.