Anodic Plasma Chemical Treatment of Titanium Schanz Screws Reduces Pin Loosening

Abstract

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...

An in vivo evaluation of the biocompatibility of anodic plasma chemical (APC) treatment of titanium with calcium phosphate

“…There is a clear trend that the irregular microrough APC‐coated surfaces initially induced good bone forming activity observed until week 6, after which point, activity was similar to that of the HA‐coated samples. Our results are in line with another previous study33 investigating the benefit of APC treatment of titanium Schanz screws. This study was carried out as a result of the good biocompatibility shown by this initial study of APC‐treated screws.…”

“…The extraction torque for APC‐CaP pins was higher than for cpTi pins, which is in agreement with our results. The authors conclude that the APC‐CaP surface improves the clinical performance of Ti pins with respect to pin loosening and pin track infection,33 which added to the original data from our study, highlighting the promise for APC‐coated cpTi screws for biomedical applications. Previous studies in our laboratory34 have also shown the excellent cytocompatibility in vitro of APC‐CaP‐treated surfaces in terms of osteoblast and fibroblast attachment (VPS not tested).…”

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

“…The ethanol may not have penetrated the tissue causing some deterioration of the tissue resulting in unclear histology slides (Table III). It is difficult to compare our histological results to the literature since previous animal studies examining pin tract infection appear to have only used clinical signs,46–49 positive cultures,56 or both clinical signs and positive cultures57 to determine the presence of pin tract infection in animal studies. However, the potential presence of false negatives in the histological results did not appear to greatly affect the overall infection conclusion for each rabbit since cultures and/or histology results confirmed infection in 18 of 20 rabbits displaying clinical signs of infection.…”

“…The rabbit was classified as infected when at least two of the three infection criteria were present: (1) greater than Grade I clinical signs of infection, (2) positive culture for one or more of the tissue samples, and/or (3) positive histology indicative of infection for one or more of the tissue samples. Although most human and animal studies investigating pin tract infection base infection on clinical signs alone,46–54 this study required conformation through culture or histology to minimize false positive results due to clinical signs of infection being caused by the rabbit irritating the pin site (i.e., licking/chewing).…”

Advances in calcium phosphate coatings - anodic spark deposition: a review

“…Thicker oxide coatings and incorporation of Ca-P ions enhances biocompatibility properties (45). In fact, the incorporation of Ca-P into the layer has been shown to increase the adhesion to titanium, compared to plasma sprayed HA coatings using ISO test 13779-2 (58). In addition to the bone promoting Ca-P ions, roughness is also increased on the anodized titanium, which is known to increase bone formation.…”