No abstract

Implant loosening in bone fixation is an unresolved complication associated with internal fixation. It is generally accepted that this problem can be overcome by modifying the implant/bone interface for improved osseointegration. This is achieved, in part, by hydroxyapatite (HA) or tricalcium phosphate coatings. Unfortunately, the benefits of these coatings are constrained by not only the generally low strength of their adhesion to the implant surface but also the limited cohesion within their layers. Anodic Plasmachemical treatment (APC) has been developed to incorporate electrolytes and produce coatings with various microtopographies and strong adhesion to implants. In this in vitro study fibroblast and osteoblast morphologies and adhesion to various substrates were evaluated using qualitative and quantitative methods. The substrates were Thermanox plastic and commercially pure titanium. The latter were surface-treated using several different methods: conventional anodisation, plasma spraying of HA and anodic plasma-chemical (APC) treatment in an electrolyte solution containing either calcium and phosphate (APCCaP) or phosphoric acid (APC-P). Both osteoblasts and fibroblasts showed extensive cell spreading, total cell area and greatest amount of adhesion, with defined adhesion patterns on the Thermanox plastic, anodised titanium, and the two APC-CaP substrates. With fibroblasts, almost no cell spreading and very low adhesion, was observed in cells cultured on the APC-P and HA surfaces. The extent of cell spreading correlated with the area of focal adhesions as assessed by the amount of vinculin labelling. The Thermanox plastic, anodised titanium, and the two APCCaP substrates were the most cytocompatible substrates with regard to this in vitro evaluation.

Objective: This study was designed to assess the benefits of a new Anodic Plasma Chemical calcium-phosphate (APC-CaP) surface treatment on reducing pin track infection and pin loosening in comparison to anodized titanium (Ti) during external fracture fixation.Methods: A tibial midshaft, transverse, 6-mm gap osteotomy was created in 17 adult female Swiss alpine sheep. The tibia was stabilized with an external fixator and 4 Schanz screws of Ti or APC-CaP-treated Ti. The sheep were examined during a 12-week observation period. Infection was assessed with weekly clinical pin track grading and microbiologic assessment at sacrifice. Pin loosening was assessed by grading for radiolucency on biweekly radiographs and by measuring extraction torque on pin removal. In vivo bending stiffness measurements were performed to determine gap healing. A qualitative histologic assessment of the tissue adjacent to pin sites was also performed.Results: A trend (P = 0.056) for less infection around APC-CaP pins was found at 6 weeks, but the strength of this difference diminished with time. Significantly more radiolucency was found around Ti pins after 8 (P = 0.011) and 12 (P , 0.001) weeks. At all pin sites, the extraction torque for APC-CaP pins was higher than for Ti pins (P = 0.007). No difference in the progression of gap healing was found. Histology showed bone growth at the implant surface in the form of distance osteogenesis for Ti and contact osteogenesis for APC-CaP. Conclusions:This study has shown that the APC-CaP surface improves the clinical performance of Ti pins with respect to pin loosening and pin track infection. P in track infection and bone resorption are common problems associated with external fixation. 1,2 A recent clinical study showed that 40% of patients treated with an external fixator and titanium (Ti) pins experienced pin loosening. Twelve percent of the pins became infected and 13% of the pins had to be removed due to infection and/or loosening. 3 Although many causes of pin loosening and infection have been identified 1,4 and strategies have been used to diminish them, 5,6 they are still a common problem, which needs to be addressed. 7 The integrity of the bone-implant interface contributes to the success of the implant. 8 Osseointegration is the direct contact at the light microscope level (mm) between living bone and implant (at steady state) 9,10 and is essential for stable implant anchorage. 8 Hydroxyapatite (HA) and calcium-phosphate (CaP) coatings have been used to improve osseointegration around stainless steel and Ti implants because of their similar chemical structure to mineralized bone. These coatings have been shown to promote osseointegration by encouraging direct bone growth onto the coating surface. 11,12 Plasma sprayed-HA-coated external fixation pins have previously been tested in a long-term, loaded, ovine model. 13 This study showed a reduction in the incidence of pin loosening by the improved osseointegration of the HA coated pins compared with uncoated pins. These findings were corrob...

Implant loosening is an unresolved complication associated with prosthetics. Previous studies report improved osseointegration with hydroxyapatite (HA) or tri-calcium phosphate coatings. Unfortunately, the brittleness and low strength of these coatings in adhesion to the implant or internal cohesion is problematic, restricting their use. Anodic plasma-chemical (APC) treatment, an advanced anodisation method, allows for porous oxide layer formation with incorporation of calcium and phosphate directly into the oxide. This produces superior adhesive strength than a conventional coating of calcium phosphate offering potential for long-term osseointegration. Although the cytocompatibility of several APC treatments have been previously shown, this study was the first to investigate the biocompatibility and osteoconductivity of APC surfaces in vivo when compared with standard HA coated and noncoated commercially pure titanium implant cortical screws. Sample screws were implanted in female Swiss alpine sheep for 12 weeks. Bone remodelling in situ, differences in bone apposition resulting in cortical thickening as well as peak removal torque measurements were assessed. We found no significant differences between the tested coatings and no delamination was observed with any of the APC-treated surfaces. The results suggest that APC-treated samples have similar biological performance to HA-coated screws. In our opinion, APC treatment, which also has superior binding strength to the base metal compared with standard HA coatings as well as similar biocompatibility as shown here, holds great potential for biomedical applications. Now that the in vivo biocompatibility has been proven, the work is being extended to more challenging in vivo models.