Nature's answer to breaching the skin barrier: an innovative development for amputees

The Impact of Ultrashort Pulse Laser Structuring of Metals on In-Vitro Cell Adhesion of Keratinocytes

Besides the need for biomaterial surface modification to improve cellular attachment, laser-structuring is favorable for designing a new surface topography for external bone fixator pins or implants. The principle of this study was to observe how bioinspired (deer antler) laser-induced nano-microstructures influenced the adhesion and growth of skin cells. The goal was to create pins that allow the skin to attach to the biomaterial surface in a bacteria-proof manner. Therefore, typical fixator metals, steel, and titanium alloy were structured using ultrashort laser pulses, which resulted in periodical nano- and microstructures. Surface characteristics were investigated using a laser scanning microscope and static water contact angle measurements. In vitro studies with human HaCaT keratinocytes focused on cell adhesion, morphology, actin formation, and growth within 7 days. The study showed that surface functionalization influenced cell attachment, spreading, and proliferation. Micro-dimple clusters on polished bulk metals (DC20) will not hinder viability. Still, they will not promote the initial adhesion and spreading of HaCaTs. In contrast, additional nanostructuring with laser-induced periodic surface structures (LIPSS) promotes cell behavior. DC20 + LIPSS induced enhanced cell attachment with well-spread cell morphology. Thus, the bioinspired structures exhibited a benefit in initial cell adhesion. Laser surface functionalization opens up new possibilities for structuring, and is relevant to developing bioactive implants in regenerative medicine.

Culture and characterization of various porcine integumentary-connective tissue-derived mesenchymal stromal cells to facilitate tissue adhesion to percutaneous metal implants

Background

Transdermal osseointegrated prosthesis have relatively high infection rates leading to implant revision or failure. A principle cause for this complication is the absence of a durable impervious biomechanical seal at the interface of the hard structure (implant) and adjacent soft tissues. This study explores the possibility of recapitulating an analogous cellular musculoskeletal-connective tissue interface, which is present at naturally occurring integumentary tissues where a hard structure exits the skin, such as the nail bed, hoof, and tooth.

Methods

Porcine mesenchymal stromal cells (pMSCs) were derived from nine different porcine integumentary and connective tissues: hoof-associated superficial flexor tendon, molar-associated periodontal ligament, Achilles tendon, adipose tissue and skin dermis from the hind limb and abdominal regions, bone marrow and muscle. For all nine pMSCs, the phenotype, multi-lineage differentiation potential and their adhesiveness to clinical grade titanium was characterized. Transcriptomic analysis of 11 common genes encoding cytoskeletal proteins VIM (Vimentin), cell–cell and cell–matrix adhesion genes (Vinculin, Integrin β1, Integrin β2, CD9, CD151), and for ECM genes (Collagen-1a1, Collagen-4a1, Fibronectin, Laminin-α5, Contactin-3) in early passaged cells was performed using qRT-PCR.

Results

All tissue-derived pMSCs were characterized as mesenchymal origin by adherence to plastic, expression of cell surface markers including CD29, CD44, CD90, and CD105, and lack of hematopoietic (CD11b) and endothelial (CD31) markers. All pMSCs differentiated into osteoblasts, adipocytes and chondrocytes, albeit at varying degrees, under specific culture conditions. Among the eleven adhesion genes evaluated, the cytoskeletal intermediate filament vimentin was found highly expressed in pMSC isolated from all tissues, followed by genes for the extracellular matrix proteins Fibronectin and Collagen-1a1. Expression of Vimentin was the highest in Achilles tendon, while Fibronectin and Col1agen-1a1 were highest in molar and hoof-associated superficial flexor tendon bone marrow, respectively. Achilles tendon ranked the highest in both multilineage differentiation and adhesion assessments to titanium metal.

Conclusions

These findings support further preclinical research of these tissue specific-derived MSCs in vivo in a transdermal osseointegration implant model.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02666-2.

Skin adhesion to the percutaneous component of direct bone anchored systems: systematic review on preclinical approaches and biomaterials

Nowadays, direct bone anchored systems are an increasingly adopted approach in the therapeutic landscape for amputee patients. However, the percutaneous nature of these devices poses a major challenge to obtain a stable and lasting proper adhesion between the implant surface and the skin. A systematic review was carried out in three databases (PubMed, Scopus, Web of Science) to provide an overview of the innovative strategies tested with preclinical models (in vitro and in vivo) in the last ten years to improve the skin adhesion of direct bone anchored systems. Fifty five articles were selected after screening, also employing PECO question and inclusion criteria. A modified Cochrane RoB 2.0 tool for the in vitro studies and the SYRCLE tool for in in vivo studies were used to assess the risk of bias. The evidence collected suggests that the implementation of porous percutaneous structures could be one of the most favorable approach to improve proper skin adhesion, especially in association with bioactive coatings, as hydroxyapatite, and exploiting the field of nanostructure. Some issues still remain open as (a) the identification and characterization of the best material/coating association able to limit the shear stresses at the interface and (b) the role of keratinocyte turnover on the skin/biomaterial adhesion and integration processes.

An Organ System-Based Synopsis of Pseudomonas aeruginosa Virulence

Driven in part by its metabolic versatility, high intrinsic antibiotic resistance, and a large repertoire of virulence factors, Pseudomonas aeruginosa is expertly adapted to thrive in a wide variety of environments, and in the process, making it a notorious opportunistic pathogen. Apart from the extensively studied chronic infection in the lungs of people with cystic fibrosis (CF), P. aeruginosa also causes multiple serious infections encompassing essentially all organs of the human body, among others, lung infection in patients with chronic obstructive pulmonary disease, primary ciliary dyskinesia and ventilator-associated pneumonia; bacteremia and sepsis; soft tissue infection in burns, open wounds and postsurgery patients; urinary tract infection; diabetic foot ulcers; chronic suppurative otitis media and otitis externa; and keratitis associated with extended contact lens use. Although well characterized in the context of CF, pathogenic processes mediated by various P. aeruginosa virulence factors in other organ systems remain poorly understood. In this review, we use an organ system-based approach to provide a synopsis of disease mechanisms exerted by P. aeruginosa virulence determinants that contribute to its success as a versatile pathogen.

Clinical outcomes in pediatric tibial lengthening and deformity correction: a comparison of the Taylor Spatial Frame with the Orthex Hexapod System

PURPOSE

Comparison of two hexapod frame systems in paediatric tibial deformity correction; the Taylor Spatial Frame (TSF) and Orthex Hexapod System.

METHODS

Paediatric patients with congenital and acquired tibial deformities treated with either TSF (between 2014 and 2016) or Orthex (between 2017 and 2019) frames were included in a retrospective comparative study. Outcome measures were healing index, pin infection rate, regenerate quality and density, software residual rate, deformity correction accuracy, strut exchanges and quality of life (QoL).

RESULTS

The TSF group had 17 patients (18 frames) and the Orthex group had 21 patients (25 frames). The most common indications for tibial deformity correction were fibular hemimelia (14) and septic or traumatic growth arrest (8). The median time in frame was 230 days (TSF) versus 203 days (Orthex) (p= 0.06). The mean lengthening achieved was 54 mm (TSF) and 51 mm (Orthex) (p = 0.41). The healing index was 41 days/cm (TSF) versus 43 days/cm (Orthex) (p = 0.70). Pin site infections occurred more in the TSF cohort (40%) than in the Orthex cohort (18%) (p < 0.001). The regenerate in the Orthex group showed higher density at three months (p = 0.029) and was more homogenous (p = 0.023) at six months after frame application. Strut exchanges were less frequent with the Orthex system (p < 0.0001). QoL measures were similar in both cohorts (p = 0.92).

CONCLUSIONS

This is the first study to compare two hexapod designs in paediatric orthopaedics. The Orthex system showed superiority in regenerate quality and a significant reduction in pin site infection rates. Both systems delivered predictable and accurate limb deformity correction.

LEVEL OF EVIDENCE

III.

The Micro Topology and Statistical Analysis of the Forces of Walking and Failure of an ITAP in a Femur

This paper studies the forces acting upon the Intraosseous Transcutaneous Amputation Prosthesis, ITAP, that has been designed for use in a quarter amputated femur. To design in a failure feature, utilising a safety notch, which would stop excessive stress, σ, permeating the bone causing damage to the user. To achieve this, the topology of the ITAP was studied using MATLAB and ANSYS models with a wide range of component volumes. The topology analysis identified critical materials and local maximum stresses when modelling the applied loads. This together with additive layer manufacture allows for bespoke prosthetics that can improve patient outcomes. Further research is needed to design a fully functional, failure feature that is operational when extreme loads are applied from any direction. Physical testing is needed for validation of this study. Further research is also recommended on the design so that the σ within the ITAP is less than the yield stress, σ_s, of bone when other loads are applied from running and other activities.

Osseointegration of Extremity Prostheses: A Primer for the Plastic Surgeon

Interest in amputation surgery has increased in conjunction with rising public awareness about amputee care. To date, plastic surgeons have impacted the quality of life and functional potential of amputees through novel strategies for sensory feedback and prosthesis control and various techniques for neuroma treatment and prevention. Osseointegration, which involves the direct skeletal attachment of a prosthesis to bone, has the ability to further maximize amputee function. There exists a critical role for plastic surgeons to help optimize techniques for extremity osseointegration through improved wound care and soft-tissue management. An overview of current osseointegrated prostheses and their associated limitations, and potential avenues through which plastic surgeons can help mitigate these challenges, are discussed in this article.

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.

Determining the porous structure for optimal soft-tissue ingrowth: An in vivo histological study

The success of osseointegrated transcutaneous prostheses depends on a soft-tissue seal forming at the skin-implant interface in order to prevent infection. Current designs include a flange with drilled holes or a subdermal barrier with a porous coating in an attempt to promote soft-tissue attachment. However, the soft-tissue seal is not reliably achieved despite these designs and infection remains a significant problem. This study investigated soft-tissue integration into fully porous titanium alloy structures with interconnected pores. The study aimed to determine the effect of altering pore and strut size combinations on soft-tissue ingrowth into porous titanium alloy structures in vivo. It was hypothesized that implants with a more open porous structure with larger pore sizes would increase soft-tissue ingrowth more than less open porous structures. Porous titanium alloy cylinders were inserted into sheep paparaspinal muscles (n = 6) and left in situ for four weeks. A histological assessment of soft-tissue ingrowth was performed. Percentage soft-tissue pore fill, cell nuclei density and blood vessel density were quantified. The results showed that larger pore sizes were supportive of soft-tissue ingrowth. A structure with a pore size of 700μm and a strut size of 300μm supported revascularisation to the greatest degree. A flange with this structure may be used in future studies of osseointegrated transcutaneous prostheses in order to enhance the soft-tissue seal.

Improved methods for MRI-compatible implants in nonhuman primates

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We created custom PEEK implants coated with hydroxylapatite to promote osseointegration.

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Headposts and chambers were implanted with ceramic screws and the surgical incision was closed subcutaneously.

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We prevented the animal from picking and scratching after surgery by using a head cap that protects the wound margin.

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Implants integrated with the skull and remained robust after a year with no growth of granulation tissue.

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MRI signal and contrast-to-noise ratio improved in NHPs implanted with our new methods.

Background

Neuroscientists commonly use permanently implanted headposts to stabilize the head of nonhuman primates (NHPs) during electrophysiology and functional magnetic resonance imaging (fMRI). Here, we present improved methodology for MRI-compatible implants without the use of acrylic for head stabilization in NHPs.

New method

MRI is used to obtain a 3D-reconstruction of NHP skulls, which are used to create customized implants by modeling intersections with the bone. Implants are manufactured from PEEK using computer numerical control machining and coated with hydroxyapatite to promote osseointegration. Surgically, implants are attached to the skull with ceramic screws, while the skin flap is pulled over the implant and closed subcutaneously.

Results

Quality of blood oxygen level dependent (BOLD) fMRI signal is improved in animals implanted with our method as compared to traditional acrylic implants. Additionally, implants are well-integrated with the skull, remain robust for more than a year and without granulation tissue around the skin margin.

Comparison with existing method(s)

Previous improvements on NHP implants (Chen et al., 2017; McAndrew et al., 2012; Mulliken et al., 2015; Overton et al., 2017) lacked fMRI-compatibility, as they relied on titanium headposts and/or titanium screws. Thus, most fMRI studies in NHPs today still rely on the use of acrylic-based headposts for stabilization and the use of contrast-enhanced agents to improve MRI signal.

Conclusions

Our method preserves fMRI-compatibility and results in measurable improvement in BOLD signal without the use of contrast-enhanced agents. Furthermore, the long-term stability of our implants contributes positively to the wellbeing of NHPs in neuroscience research.

Biomechanical Characterisation of Bone-anchored Implant Systems for Amputation Limb Prostheses: A Systematic Review

Bone-anchored limb prostheses allow for the direct transfer of external loads from the prosthesis to the skeleton, eliminating the need for a socket and the associated problems of poor fit, discomfort, and limited range of movement. A percutaneous implant system for direct skeletal attachment of an external limb must provide a long-term, mechanically stable interface to the bone, along with an infection barrier to the external environment. In addition, the mechanical integrity of the implant system and bone must be preserved despite constant stresses induced by the limb prosthesis. Three different percutaneous implant systems for direct skeletal attachment of external limb prostheses are currently clinically available and a few others are under investigation in human subjects. These systems employ different strategies and have undergone design changes with a view to fulfilling the aforementioned requirements. This review summarises such strategies and design changes, providing an overview of the biomechanical characteristics of current percutaneous implant systems for direct skeletal attachment of amputation limb prostheses.

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.

Strategies for Optimizing the Soft Tissue Seal around Osseointegrated Implants

Percutaneous and permucosal devices such as catheters, infusion pumps, orthopedic, and dental implants are commonly used in medical treatments. However, these useful devices breach the soft tissue barrier that protects the body from the outer environment, and thus increase bacterial infections resulting in morbidity and mortality. Such associated infections can be prevented if these devices are effectively integrated with the surrounding soft tissue, and thus creating a strong seal from the surrounding environment. However, so far, there are no percutaneous/permucosal medical devices able to prevent infection by achieving strong integration at the soft tissue-device interface. This review gives an insight into the current status of research into soft tissue-implant interface and the challenges associated with these interfaces. Biological soft/hard tissue interfaces may provide insights toward engineering better soft tissue interfaces around percutaneous devices. In this review, focus is put on the history and current findings as well as recent progress of the strategies aiming to develop a strong soft tissue seal around osseointegrated implants, such as orthopedic and dental implants.

Resveratrol-Enriched Rice Attenuates UVB-ROS-Induced Skin Aging via Downregulation of Inflammatory Cascades

The skin is the outermost protective barrier between the internal and external environments in humans. Chronic exposure to ultraviolet (UV) radiation is a major cause of skin aging. UVB radiation penetrates the skin and induces ROS production that activates three major skin aging cascades: matrix metalloproteinase- (MMP-) 1-mediated aging; MAPK-AP-1/NF-κB-TNF-α/IL-6, iNOS, and COX-2-mediated inflammation-induced aging; and p53-Bax-cleaved caspase-3-cytochrome C-mediated apoptosis-induced aging. These mechanisms are collectively responsible for the wrinkling and photoaging characteristic of UVB-induced skin aging. There is an urgent requirement for a treatment that not only controls these pathways to prevent skin aging but also avoids the adverse effects often encountered when applying bioactive compounds in concentrated doses. In this study, we investigated the efficacy of genetically modified normal edible rice (NR) that produces the antiaging compound resveratrol (R) as a treatment for skin aging. This resveratrol-enriched rice (RR) overcomes the drawbacks of R and enhances its antiaging potential by controlling the abovementioned three major pathways of skin aging. RR does not exhibit the toxicity of R alone and promisingly downregulates the pathways underlying UVB-ROS-induced skin aging. These findings advocate the use of RR as a nutraceutical for antiaging purposes.

The in vivo effect of a porous titanium alloy flange with hydroxyapatite, silver and fibronectin coatings on soft-tissue integration of intraosseous transcutaneous amputation prostheses

Aims

The Intraosseous Transcutaneous Amputation Prosthesis (ITAP) may improve quality of life for amputees by avoiding soft-tissue complications associated with socket prostheses and by improving sensory feedback and function. It relies on the formation of a seal between the soft tissues and the implant and currently has a flange with drilled holes to promote dermal attachment. Despite this, infection remains a significant risk. This study explored alternative strategies to enhance soft-tissue integration.

Materials and Methods

The effect of ITAP pins with a fully porous titanium alloy flange with interconnected pores on soft-tissue integration was investigated. The flanges were coated with fibronectin-functionalised hydroxyapatite and silver coatings, which have been shown to have an antibacterial effect, while also promoting viable fibroblast growth in vitro. The ITAP pins were implanted along the length of ovine tibias, and histological assessment was undertaken four weeks post-operatively.

Results

The porous titanium alloy flange reduced epithelial downgrowth and increased soft-tissue integration compared with the current drilled flange. The addition of coatings did not enhance these effects.

Conclusion

These results indicate that a fully porous titanium alloy flange has the potential to increase the soft-tissue seal around ITAP and reduce susceptibility to infection compared with the current design.

Cite this article: Bone Joint J 2017;99-B:393–400.

Toward a skin-material interface with vacuum-integrated capped macroporous scaffolds

Avulsion, epidermal marsupialization, and infection cause failure at the skin-material interface. A robust interface would permit implantable robotics, prosthetics, and other medical devices; reconstruction of surgical defects, and long-term access to blood vessels and body cavities. Torus-shaped cap-scaffold structures were designed to work in conjunction with negative pressure to address the three causes of failure. Six wounds were made on the backs of each of four 3-month old pigs. Four unmodified (no caps) scaffolds were implanted along with 20 cap-scaffolds. Collagen type 4 was attached to 21 implants. Negative pressure then was applied. Structures were explanted and assessed histologically at day 7 and day 28. At day 28, there was close tissue apposition to scaffolds, without detectable reactions from defensive or interfering cells. Three cap-scaffolds explanted at day 28 showed likely attachment of epidermis to the cap or cap-scaffold junction, without deeper marsupialization. The combination of toric-shaped cap-scaffolds with negative pressure appears to be an intrinsically biocompatible system, enabling a robust skin-material interface. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1307-1318, 2017.

Osseointegrated hearing implant surgery using a novel hydroxyapatite-coated concave abutment design

OBJECTIVE

Recently, a novel hydroxyapatite-coated concave bone-anchored hearing device abutment was introduced, the first designed specifically to improve outcomes in soft-tissue preservation osseointegrated hearing implant surgery. We sought to evaluate our early experience with this abutment.

STUDY DESIGN

A single-center case series with planned data collection including patient-reported outcomes.

SETTING

Tertiary referral center.

SUBJECTS AND METHODS

The first 30 consecutive patients undergoing osseointegrated hearing implant surgery using the Cochlear DermaLock (BA400) abutment at our institution (February-September 2013) were studied. Follow-up was for a minimum of 6 months. The following data were collected: operative duration; wound healing; postoperative complications, chiefly soft-tissue reactions graded by Holger's classification; and postintervention patient-perceived health-related quality of life, as assessed by the Glasgow Benefit Inventory (GBI).

RESULTS

The mean operating time was 16 minutes (range, 9-22 minutes). Favorable and rapid wound healing was observed in all cases. Three patients (10%) reported transient periabutment paraesthesia. Four patients (13.3%) suffered adverse soft-tissue reactions, all of which were successfully managed conservatively and graded as follows: Holger's grade 1 (n = 2), 2 (n = 1), and 3 (n = 1). Respective overall general health, social support, and physical health GBI mean scores were +38 (95% confidence interval [CI], 31 to 45), +51 (95% CI, 42 to 60), +19 (95% CI, 8 to 30), and +8 (95% CI, -1 to 17).

CONCLUSION

Our preliminary clinical and patient-reported outcomes support soft-tissue preservation surgery and indicate that the technology on which the Cochlear DermaLock (BA400) abutment is based may enhance soft-tissue outcomes in this context. We recommend further appraisal of this approach on a larger scale with more extensive follow-up.

An animal model to evaluate skin-implant-bone integration and gait with a prosthesis directly attached to the residual limb

BACKGROUND

Despite the number of advantages of bone-anchored prostheses, their use in patients is limited due to the lack of complete skin-implant integration. The objective of the present study was to develop an animal model that would permit both detailed investigations of gait with a bone-anchored limb prosthesis and histological analysis of the skin-implant-bone interface after physiological loading of the implant during standing and walking.

METHODS

Full-body mechanics of walking in two cats were recorded and analyzed before and after implantation of a percutaneous porous titanium pylon into the right tibia and attachment of a prosthesis. The rehabilitation procedures included initial limb casting, progressively increasing loading on the implant, and standing and locomotor training. Detailed histological analysis of bone and skin ingrowth into implant was performed at the end of the study.

FINDINGS

The two animals adopted the bone-anchored prosthesis for standing and locomotion, although loads on the prosthetic limb during walking decreased by 22% and 62%, respectively, 4months after implantation. The animals shifted body weight to the contralateral side and increased propulsion forces by the contralateral hindlimb. Histological analysis of the limb implants demonstrated bone and skin ingrowth.

INTERPRETATION

The developed animal model to study prosthetic gait and tissue integration with the implant demonstrated that porous titanium implants may permit bone and skin integration and prosthetic gait with a bone-anchored prosthesis. Future studies with this model will help optimize the implant and prosthesis properties.

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.

Effect of amputation level on the stress transferred to the femur by an artificial limb directly attached to the bone

Attachment of an artificial limb directly to the skeleton has a number of potential benefits and the technique has been implemented for several amputation sites. In this paper the transfer of stress from an external, transfemoral prosthesis to the femur during normal walking activity is investigated. The stress distribution in the femur and at the implant-bone interface is calculated using finite element analysis for the 3D geometry and inhomogeneous, anisotropic material properties obtained from a CT scan of a healthy femur. Attachment of the prosthetic leg at three different levels of amputation is considered. Stress concentrations are found at the distal end of the bone and adjacent to the implant tip and stress shielding is observed adjacent to the implant. It is found that the stress distribution in the femur distal to the epiphysis, where the femur geometry is close to cylindrical, can be predicted from a cylindrical finite element model, using the correct choice of bone diameter as measured from a radiograph. Proximal to the lesser trochanter the stress decreases as the femur geometry diverges significantly from a cylinder. The stress concentration at the distal, resected end of the bone is removed when a collared implant is employed. These findings form the basis for appropriate settings of an external fail-safe device to protect the bone from excessive stress in the event of an undue load.

Multi-body simulation of various falling scenarios for determining resulting loads at the prosthesis interface of transfemoral amputees with osseointegrated fixation

Conventionally, transfemoral amputees are treated with a shaft prosthesis fitted over the residual limb. To improve the quality of life of such patients, in particular those with complications relating to conventional attachment (e.g., skin irritation, stump ulcers, and poor motor-control with short stumps), osseointegrated prosthesis fixation implants have been developed and implanted in a limited population of patients. To assess possible damage to the implant/prosthesis during falling scenarios, the loads in high-risk situations were estimated using a multi-body simulation of motion. Five falling scenarios were identified and performed by healthy volunteer wearing safety equipment. Kinematic data and ground reaction forces were captured as input for the inverse-dynamics-based simulations, from which the forces and moments at a typical implant-prosthesis interface location were computed. The estimated peak loads in all five scenarios were of a magnitude that could lead to bone fracture. The largest peak force observed was 3274 ± 519 N, with an associated resultant moment of 176 ± 55 Nm on the prosthesis-implant interface. A typical femur is prone to fracture under this load, thus illustrating the need for a safety-release element in osseointegrated prosthesis fixation.

Trichohyalin-like 1 protein, a member of fused S100 proteins, is expressed in normal and pathologic human skin

Trichohyalin-like 1 (TCHHL1) protein is a novel member of the fused-type S100 protein gene family. The deduced amino acid sequence of TCHHL1 contains an EF-hand domain in the N-terminus, one trans-membrane domain and a nuclear localization signal. We generated specific antibodies against the C-terminus of the TCHHL1 protein and examined the expression of TCHHL1 proteins in normal and pathological human skin. An immunohistochemical study showed that TCHHL1 proteins were expressed in the basal layer of the normal epidermis. In addition, signals of TCHHL1 proteins were observed around the nuclei of cultured growing keratinocytes. Accordingly, TCHHL1 mRNA has been detected in normal skin and cultured growing keratinocytes. Furthermore, TCHHL1 proteins were strongly expressed in the peripheral areas of tumor nests in basal cell carcinomas and squamous cell carcinomas. A dramatic increase in the number of Ki67 positive cells was observed in TCHHL1-expressing areas. The expression of TCHHL1 proteins also increased in non-cancerous hyperproliferative epidermal tissues such as those of psoriasis vulgaris and lichen planus. These findings highlight the possibility that TCHHL1 proteins are expressed in growing keratinocytes of the epidermis and might be associated with the proliferation of keratinocytes.

Use of ITAP implants for prosthetic reconstruction of extra-oral craniofacial defects

We report the outcomes of a single-stage, surface-mounted implant used as a bone-anchor for prosthetic reconstruction of complex facial defects. The implant used differs from other designs of osseointegrated bone-anchor because it was designed to be implanted in one-stage with the added intention of integrating with the adjacent soft-tissue. Our aim was to extend the principles underlying the intraosseous transcutaneous amputation prosthesis (ITAP) into the design of infection-free implants suitable for direct skeletal attachment of a prosthesis to the craniofacial skeleton. The implants were manufactured incorporating a porous flange structure coated with hydroxyapatite to encourage soft-tissue integration. These were inserted into the cranial facial skeleton at a number of different sites in 6 adult patients. A total of 16 implants were inserted using a one-stage procedure and implants were followed up for periods of 18 months - 7 years. One implant loosened at 3 months. This implant experienced multiple episodes of infection and was replaced with another ITAP implant 4 years later. The replacement is now stable and has never been infected at 18 months after insertion. One other patient experienced a few minor episodes of superficial infection (not requiring antibiotics) in the first year but no episodes thereafter. One patient died during follow-up (death unrelated to implant surgery). Patients were asked for their personal opinions using a structured questionnaire. All the patients were either very satisfied, or satisfied with their ITAP implants. Two patients reported problems with skin irritation under their prosthesis. All would be happy to undergo this type of surgery again. We conclude that a single-stage, surface-mounted implant designed to incorporate the principles of ITAP can be used to produce an effective bone-anchor for an external prosthesis in the reconstruction of complex craniofacial defects.

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.

The development of fibronectin-functionalised hydroxyapatite coatings to improve dermal fibroblast attachment in vitro

The success of long-term transcutaneous implants depends on dermal attachment to prevent downgrowth of the epithelium and infection. Hydroxyapatite (HA) coatings and fibronectin (Fn) have independently been shown to regulate fibroblast activity and improve attachment. In an attempt to enhance this phenomenon we adsorbed Fn onto HA-coated substrates. Our study was designed to test the hypothesis that adsorption of Fn onto HA produces a surface that will increase the attachment of dermal fibroblasts better than HA alone or titanium alloy controls.

Iodinated Fn was used to investigate the durability of the protein coating and a bioassay using human dermal fibroblasts was performed to assess the effects of the coating on cell attachment. Cell attachment data were compared with those for HA alone and titanium alloy controls at one, four and 24 hours. Protein attachment peaked within one hour of incubation and the maximum binding efficiency was achieved with an initial droplet of 1000 ng. We showed that after 24 hours one-fifth of the initial Fn coating remained on the substrates, and this resulted in a significant, three-, four-, and sevenfold increase in dermal fibroblast attachment strength compared to uncoated controls at one, four and 24 hours, respectively.

Recording of electric signal passing through a pylon in direct skeletal attachment of leg prostheses with neuromuscular control

Direct recordings were made of electrical signals emanating from the muscles in a rabbit's residuum. The signals were transmitted via wires attached on one end to the muscles, and on the other to an external recording system. The cable was held in a titanium tube inside a pylon that had been transcutaneously implanted into the residuum's bone. The tube was surrounded by porous titanium cladding to enhance its bond with the bone and with the skin of the residuum. This study was the first known attempt to merge the technology of direct skeletal attachment of limb prostheses with the technology of neuromuscular control of prostheses, providing a safe and reliable passage of the electrical signal from the muscles inside the residuum to the outside recording system.

Shaping the military wound: issues surrounding the reconstruction of injured servicemen at the Royal Centre for Defence Medicine

The conflict in Afghanistan has produced injuries similar to those produced from military conflicts for generations. What distinguishes the modern casualty of the conflict in Afghanistan from those of other conflicts is the effectiveness of modern field medical care that has led to individuals surviving with injuries, which would have been immediately fatal even a few years ago. These patients present several challenges to the reconstructive surgeon. These injured individuals present early challenges of massive soft-tissue trauma, unstable physiology, complex bony and soft-tissue defects, unusual infections, limited reconstructive donor sites, peripheral nerve injuries and traumatic amputations. Late challenges to rehabilitation include the development of heterotopic ossification in amputation stumps. This paper outlines the approach taken by the reconstructive team at the Royal Centre for Defence Medicine in managing these most difficult of reconstructive challenges.

Osseocutaneous integration of an intraosseous transcutaneous amputation prosthesis implant used for reconstruction of a transhumeral amputee: case report

Exoprosthetic replacement with an artificial limb is the main option for reconstruction after traumatic amputation of an upper limb. Direct skeletal attachment using an osseointegrated implant improves the ease of fixation of the exoprosthesis to the amputation stump. We now report the use of an intraosseous transcutaneous amputation prosthesis that is designed to achieve osseocutaneous integration. Osseocutaneous integration differs from osseointegration because the aim is to create a stable interface among the implant, the bone, and the soft tissues. This reduces the risk of soft tissue infection and troublesome discharge, which are problems encountered with current osseointegrated implants that focus largely on the bone-implant interface. We describe our experience with an intraosseous transcutaneous amputation prosthesis in a case of transhumeral amputation with 2 years of follow-up.

Developing a quantitative measurement system for assessing heterotopic ossification and monitoring the bioelectric metrics from electrically induced osseointegration in the residual limb of service members

Poor prosthetic fit is often the result of heterotopic ossification (HO), a frequent problem following blast injuries for returning service members. Osseointegration technology offers an advantage for individuals with significant HO and poor socket tolerance by using direct skeletal attachment of a prosthesis to the distal residual limb, but remains limited due to prolonged post-operative rehabilitation regimens. Therefore, electrical stimulation has been proposed as a catalyst for expediting skeletal attachment and the bioelectric effects of HO were evaluated using finite element analysis in 11 servicemen with transfemoral amputations. Retrospective computed tomography (CT) scans provided accurate reconstructions, and volume conductor models demonstrated the variability in residual limb anatomy and necessity for patient-specific modeling to characterize electrical field variance if patients were to undergo a theoretical osseointegration of a prosthesis. In this investigation, the volume of HO was statistically significant when selecting the optimal potential difference for enhanced skeletal fixation, since higher HO volumes required increased voltages at the periprosthetic bone (p = 0.024, r = 0.670). Results from Spearman's rho correlations also indicated that the age of the subject and volume of HO were statistically significant and inversely proportional, in which younger service members had a higher frequency of HO (p = 0.041, r = -0.622). This study demonstrates that the volume of HO and age may affect the voltage threshold necessary to improve current osseointegration procedures.

Evaluating antimicrobials and implant materials for infection prevention around transcutaneous osseointegrated implants in a rabbit model

Transcutaneous osseointegrated implants can improve function for select amputee patients, but infection serves as a significant limitation of implantable transcutaneous devices. This study examined the efficacy of an antimicrobial, pexiganan acetate (SUPONEX), and a porous tantalum implant material (Trabecular Metal) in preventing pin tract infection of osseointegrated implants in a rabbit model. Thirty-seven rabbits were randomized to three groups: Ti-control group (n = 11) with titanium alloy implant and no antimicrobial, Ti-Pexiganan group (n = 8) with titanium alloy implant and topical pexiganan acetate 1% applied daily at the skin/implant interface, and Ta-control group (n = 18) with porous tantalum implant and no antimicrobial. All implants were placed transcutaneously through skin, muscle, and bone. Rabbits were monitored for infection for 24 weeks. We observed a 75% reduction in rates of pin tract infection in the Ti-Pexiganan group compared to that observed in the Ti-control group (p = 0.019). No difference in rates of infection was observed between the Ta-control group and the Ti-control group (p = 0.230). In conclusion, pexiganan acetate may be an important antimicrobial for transcutaneous osseointegrated implants. Porous tantalum will not likely prevent pin tract infection without additional methods of soft tissue immobilization around the implant site.