Pin loosening is a major complication in external fixation. Biological and mechanical conditions play an important role in the maintenance and enhancement of the implant-bone interface in fracture fixation. It is thought that biodegradable coatings may be capable of preventing pin track infection and pin loosening. The goal of this study was therefore to analyze the influence of a biodegradeable coating on the osseous integration of Schanz' screws during fracture treatment. Standardized osteotomies (3-mm fracture gap) of the right tibiae were performed on 16 sheep and stabilized by an AO mono-lateral external fixator. Additional, mechanically less loaded Schanz' screws were also mounted. All screws were randomly coated with biodegradable poly(D,L-lactide). The sheep were sacrificed after 9 weeks. All screws were removed and rolled on blood agar plates for microbiological analysis. Histological sections of the pin tracks were histochemically and morphometrically analyzed. Clinically, no signs of severe infection were visible. Microbiological analysis revealed 14.8% colonization by Staphylococcus aureus in the coated and 29% in the uncoated screws. Histomorphometry of the bone surrounding the Schanz' screws revealed that significantly more osseous integration had occurred on poly(D,L-lactide)-coated screws in the absence of bacterial colonization. Significantly more bone remodeling and a higher osteoclastic activity was seen near the screw-bone interface in the uncoated screw group. Up to a threefold increase in new bone formation and more severe remodeling was observed around the screw entry compared to the pin exit in all groups. Loaded screws showed significantly more callus formation around the exit sites than their less loaded counterparts. In the present study, poly(D,L-lactide) coating of Schanz' screws was found to enhance osseous integration in the absence of bacterial colonization in sheep by causing less cortical remodeling and less osteoclastic activity in the cortices compared to uncoated screws. Additionally, the coating appeared to reduce the instances of pin track infections. Mechanical loading showed an adverse effect on bone formation and remodeling. It has been shown that both biological and mechanical factors play an important role in the maintenance of osseous integrity of the pin-bone interface. Poly(D,L-lactide) coating of Schanz' screws does not prevent osseous destruction and severe bacterial colonization along the pin tracts, but can improve osseous integration of Schanz' screws in the absence of infection.
Schraubenkanal-Infektionen und Schraubenlockerungen sind wesentliche Komplikationen bei der Fixateur externe-Osteosynthese. In dieser Studie wurde der Einfluss einer Poly(D,L-laktid)-Beschichtung auf die ossäre Integration der Schrauben wäh-rend der Frakturversorgung analysiert.An 16 Schafen wurden Osteotomien der rechten Tibia mit einem monolateralen Fixateur externe stabilisiert. Zusätzlich wurden mechanisch unbelastete Schanz' Schrauben eingebracht. Die Hälfte der implantierten Schrauben wurde mit Poly(D,L-laktid) beschichtet. Nach neun Wochen wurden die Schrauben entnommen, auf Blutagar-Platten ausgerollt und mikrobiologisch untersucht. Es erfolgte die histologische Aufarbeitung der Pintrakts und eine anschließende histochemische und histomorphometrische Analyse. Obwohl klinisch keine Anzeichen für Infektionen beobachtet wurden, zeigte die mikrobiologische Bewertung bei 15 % der beschichteten Schrauben versus 29 % der unbeschichteten Schrauben eine Kontamination durch Staphylococcus aureus. Die histologische Auswertung zeigte, dass beschichtete Schrauben eine bessere Osteointegrität (p=0,0006) als unbeschichtete Implantate aufwiesen. In der Histomorphometrie wurde in der Gruppe der unbeschichteten Schrauben ein höheres knöchernes Remodeling (p = 0,006) und eine höhere Osteoklastenaktivität (p = 0,019) festgestellt. Belastete Schrauben zeigten mehr Kallus am Schraubenaustritt (p = 0,048). Eine Poly(D,L-laktid)-Beschichtung bei Schanz' Schrauben scheint die ossäre Integration durch eine Verminderung des kortikalen Remodelings und der Osteoklastenaktivität zu verbessern.Schlüsselworte: knöcherne Integration, Schanz' Schrauben, resorbierbare Beschichtung, Osteoklasten, Knochenheilung Pin track infections and pin loosening are major complications in fracture treatment by means of external fixation. In this study, the influence of Poly(D,L-lactid)-coating on osseous integration of Schanz screws was analysed during bone healing.In sixteen sheep, osteotomies of the right tibia were stabilized by means of monolateral external fixators. In addition, mechanically unloaded Schanz' screws were inserted. One half of the implanted screws was coated with Poly(D,L-lactid). After nine weeks in vivo, the screws were extracted, rolled on blood agar plates and microbiologically analysed, followed by histological, immunhistochemical and histomorphometrical analyses of the pin tracks. Even though no clinical signs of infection were observed, micro biological evaluation indicated a contamination by Staphylococcus aureus of 15 % in the coated screws and of 29 % in the uncoated screws. The histological analyses showed an improved osseous interagtion in the coated screws (p=0,0006) compared to the uncoated implants. In histomorphometry, the group of the uncoated screws showed an increased bone remodelling (p = 0,006) and an increased osteoclast activity (p = 0,019). Mechanically loaded screws had increased callus formation at the pin exit site (p = 0,048).The poly(D,L-lactid) coating of Schanz' screws seems to enhance the osseous integ...
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