Catherine J. Pendegrass

Sealing the skin barrier around transcutaneous implants: IN VITRO STUDY OF KERATINOCYTE PROLIFERATION AND ADHESION IN RESPONSE TO SURFACE MODIFICATIONS OF TITANIUM ALLOY

Conventional amputation prostheses rely on the attachment of the socket to the stump, which may lead to soft-tissue complications. Intraosseous transcutaneous amputation prostheses (ITAPs) allow direct loading of the skeleton, but their success is limited by infection resulting from breaching of the skin at the interface with the implant. Keratinocytes provide the skins primary barrier function, while hemidesmosomes mediate their attachment to natural ITAP analogues. Keratinocytes must attach directly to the surface of the implant. We have assessed the proliferation, morphology and attachment of keratinocytes to four titaniumalloy surfaces in order to determine the optimal topography in vitro. We used immunolocalisation of adhesion complex components, scanning electron microscopy and transmission electron microscopy to assess cell parameters. We have shown that the proliferation, morphology and attachment of keratinocytes are affected by the surface topography of the biomaterials used to support their growth. Smoother surfaces improved adhesion. We postulate that a smooth topography at the point of epithelium-ITAP contact could increase attachment in vivo, producing an effective barrier of infection.

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.

Assessment of reproducibility and accuracy in templating hybrid total hip arthroplasty using digital radiographs

In 20 patients undergoing hybrid total hip arthroplasty, the reproducibility and accuracy of templating using digital radiographs were assessed. Digital images were manipulated using either a ten-pence coin as a marker to scale for magnification, or two digital-line methods using computer software. On-screen images were templated with standard acetate templates and compared with templating performed on hard-copy digital prints. The digital-line methods were the least reliable and accuracy of sizing compared with the inserted prostheses varied between -1.6% and +10.2%. The hard-copy radiographs showed better reproducibility than the ten-pence coin method, but were less accurate with 3.7% undersizing. The ten-pence coin method was the most accurate, with no significant differences for offset or acetabulum, and undersizing of only 0.9%. On-screen templating of digital radiographs with standard acetate templates is accurate and reproducible if a radiopaque marker such as a ten-pence coin is included when the original radiograph is taken.

Tendon bone healing can be enhanced by demineralized bone matrix: A functional and histological study

Rotator cuff repair surgery has high failure rates, with tendon reattachment to bone remaining a challenging clinical problem. Increasing the integrity of the healing tendon-bone interface has been attempted by adopting a number of different augmentation strategies. Because of chondrogenic and osteogenic properties we hypothesise that demineralized bone matrix (DBM) augmentation of a healing tendon-bone interface will result in improved function, and a morphology that more closely resembles that of a normal enthesis, compared with nonaugmented controls in an ovine patellar tendon model. The right patellar tendon was detached from its insertion and reattached to an osteotomized bone bed using suture anchors. Two groups were analyzed, the control group (without augmentation) and the DBM group (DBM interposed between the tendon and bone). Animals were sacrificed at 12 weeks. Force plate, mechanical, and histomorphometric analyses were performed. Tendon repairs failed at a rate of 33 and 0% for the control and DBM groups, respectively. DBM augmentation resulted in significantly improved functional weight bearing and increased amounts of fibrocartilage and mineralized fibrocartilage. This study shows that DBM enhances tendon-bone healing and may reduce the high failure rates associated with rotator cuff repair clinically.

Intraosseous Transcutaneous Amputation Prosthesis ( ITAP ) for Limb Salvage in 4 Dogs

OBJECTIVE To report clinical application of intraosseous transcutaneous amputation prosthesis (ITAP) for limb salvage. STUDY DESIGN Retrospective case series. SAMPLE POPULATION Client owned dogs with malignant neoplasia of the distal aspect of the limb. METHOD Distal limb amputation allowed press-fit insertion of the ITAP into the radius (n = 3) or tibia (1). Remaining soft tissues including skin were attached directly to the ITAP. Limb stump and ITAP were protected by bandaging (1) or external skeletal fixation (3) for 5-6 weeks before exoprosthesis attachment. Measures of outcome included subjective assessments of limb function by owners and veterinarians, radiographic (4) and histologic (1) examination. RESULTS Dermal integration with the ITAP was achieved by 3 weeks and dogs were walking in a pain-free manner by 8 weeks. One dog was administered adjunctive carboplatin chemotherapy. No evidence of local tumor recurrence occurred. In 1 dog, ITAP fracture occurred at 10 weeks and was successfully managed by ITAP replacement. Three dogs were euthanatized because of confirmed or assumed metastatic disease at 8, 12, and 17 months. Histologic examination of the ITAP-limb interface at 1 year documented osseous and dermal integration. CONCLUSION Implantation of ITAP to the distal limb of dogs is feasible and can result in favorable functional outcomes. Biological integration of osseous and dermal tissues with ITAP is reliable and robust.

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.

Augmentation of Rotator Cuff Repair With Soft Tissue Scaffolds

Background Tears of the rotator cuff are one of the most common tendon disorders. Treatment often includes surgical repair, but the rate of failure to gain or maintain healing has been reported to be as high as 94%. This has been substantially attributed to the inadequate capacity of tendon to heal once damaged, particularly to bone at the enthesis. A number of strategies have been developed to improve tendon-bone healing, tendon-tendon healing, and tendon regeneration. Scaffolds have received considerable attention for replacement, reconstruction, or reinforcement of tendon defects but may not possess situation-specific or durable mechanical and biological characteristics. Purpose To provide an overview of the biology of tendon-bone healing and the current scaffolds used to augment rotator cuff repairs. Study Design Systematic review; Level of evidence, 4. Methods A preliminary literature search of MEDLINE and Embase databases was performed using the terms rotator cuff scaffolds, rotator cuff augmentation, allografts for rotator cuff repair, xenografts for rotator cuff repair, and synthetic grafts for rotator cuff repair. Results The search identified 438 unique articles. Of these, 214 articles were irrelevant to the topic and were therefore excluded. This left a total of 224 studies that were suitable for analysis. Conclusion A number of novel biomaterials have been developed into biologically and mechanically favorable scaffolds. Few clinical trials have examined their effect on tendon-bone healing in well-designed, long-term follow-up studies with appropriate control groups. While there is still considerable work to be done before scaffolds are introduced into routine clinical practice, there does appear to be a clear indication for their use as an interpositional graft for large and massive retracted rotator cuff tears and when repairing a poor-quality degenerative tendon.

Modification of titanium alloy surfaces for percutaneous implants by covalently attaching laminin

Percutaneous implants require a seal at the skin interface. Laminin (L-332) is a component of the basement membrane, integral to epidermal attachment. To enhance the attachment of keratinocytes onto the surface of titanium alloy (Ti(6)Al(4)V), we attached L-332 onto the surface using silanization (L-332==Ti(6)Al(4)V). Iodinated L-332 was used to investigate protein attachment kinetics. L-332==Ti(6)Al(4)V remained attached after immersion in serum compared with adsorbed L-332. Cells from a keratinocyte line (HaCaT) grown on L-332==Ti(6)Al(4)V were significantly smaller (p < 0.05) with over a 20-fold increase in the number of adhesion plaques compared with nontreated Ti(6)Al(4)V control discs or with adsorbed L-332 surfaces. We have shown that it is possible to augment the surface of Ti(6)Al(4)V with L-332 and that this significantly increases the attachment of keratinocytes.

Enhancing the soft tissue seal around intraosseous transcutaneous amputation prostheses using silanized fibronectin titanium alloy

The success of intraosseous transcutaneous amputation prostheses (ITAP) relies on achieving a tight seal between the soft tissues and the implant in order to avoid infection. Fibronectin (Fn) may be silanized onto titanium alloy (Ti-6Al-4V) in order to promote soft-tissue attachment. The silanization process includes passivation with sulphuric acid, which alters surface characteristics. This study aimed to improve in vitro fibroblast adhesion to silanized fibronectin (SiFn) titanium alloy by omitting the passivation stage. Additionally, the study assessed the effects of SiFn on in vivo dermal attachment, comparing the results with adsorbed Fn, hydroxyapatite (HA), Fn adsorbed onto HA (HAFn) and uncoated controls. Surface topography was assessed using scanning electron microscopy, profilometry and contact angle measurement. Anti-vinculin antibodies were used to immunolocalize fibroblast adhesion sites. A histological assessment of soft-tissue attachment and cell alignment relative to implants in an in vivo ovine model was performed. Passivation resulted in rougher, more hydrophobic, microcracked surfaces and was associated with poorer fibroblast adhesion than unpassivated controls. SiFn and HAFn surfaces resulted in more favourable cell alignment in vivo, implying that dermal attachment was enhanced. These results suggest that SiFn and HAFn surfaces could be useful in optimizing the soft tissue seal around ITAP.

Measuring the strength of dermal fibroblast attachment to functionalized titanium alloys in vitro

The success of intraosseous transcutaneous amputation prostheses (ITAP) relies on soft tissue attachment to prevent infection which leads to implant failure. Fibronectin (Fn) has been shown to enhance dermal fibroblast attachment in vitro, however measurement of cell attachment strength has been indirect; using cell area and immunolocalization of focal adhesion components. In this study, we have developed a flow apparatus to assess the biophysical strength of cell attachment to biomaterials used in ITAP. We have demonstrated that dermal fibroblast attachment strength increases significantly up to 96 h and that data from direct and indirect methods of assessing cell attachment strength have a significant positive correlation. Additionally, we have used direct and indirect assessment methods to demonstrate that dermal fibroblast attachment strength is significantly greater on fibronectin-coated titanium alloy compared with uncoated controls at 1, 4, and 24 hours.