Mehanička svojstva ortopedskih čeličnih implantata u simuliranim biološkim uvjetima

May Labidi, Ivan Dobrić, Anko Antabak

Brojna su propitivanja potrebe rutinskog odstranjenja metalnog implantata nakon saniranja prijeloma kosti. Pretežita indikacija za odstranjenje jest slabljenje mehaničkih svojstava i pucanje implantata prije cijeljenja kosti. Cilj ovog istraživanja bio je ispitati mehanička svojstva osteosintetske pločice izrađene od standardnoga kirurškog čelika u simuliranim biološkim uvjetima. U istraživanju smo koristili implantate nehrđajućeg čelika 316L i pohranili ih kroz godinu dana u simuliranome biološkom mediju (engl. SBF – simulated body fluid). Analizirano je 48 pločica standardnoga kirurškog čelika podijeljeno u četiri skupine. Jedna je kontrolna. Ostale su bile uronjene u otopine različitih pH vrijednosti. Uronjene pločice testirane su nakon godinu dana, a kontrolna odmah na početku istraživanja. Tijekom godinu dana analizirala se promjena mikrostrukture uronjenih pločica skenirajući elektronskim mikroskopom (SEM) u pet navrata, a kontrolna grupa samo jednom. Na pločicama koje su bile u biološkim simuliranim uvjetima, bez obzira na pH medija, značajno je veći broj jamičastih korozija kod mjerenja nakon šest mjeseci i godinu dana. Nakon godinu dana pohrane u medijima različite pH mjerene su vrijednosti mehaničkog, statičkog i dinamičkog opterećenja pločica. Niti jedno načinjeno mehaničko testiranje nije pokazalo statistički značajnu razliku između kontrolne skupine pločica i onih koje su bile u biološki simuliranim uvjetima kroz godinu dana. Nepromijenjena mehanička svojstava istraživanih implantata, unatoč značajnim promjenama mikrostrukture nastale kao posljedica jamičaste korozije u biološki simuliranim uvjetima, otklanjaju vjerojatnost slabljenja pločice kao i indikaciju za njezino odstranjenje u tom vremenskom razdoblju.

Questioning the routine metal implant removal after bone fracture healing has increased. One of the main indications for removal is metal weakening in biological bone healing conditions, in addition to reports about its breakage even prior to bone healing. The aim of this study is to investigate the mechanical properties of osteosynthesis plates made out of standard surgical stainless steel in simulated biological conditions. Implants made out of 316L stainless steel were kept for one year in simulated body fluid (SBF). We analysed 48 plates made out of standard surgical stainless steel that were divided in four groups. One was the control group and the
remaining were immersed in solutions with various pH values according to pH changes during bone fracture healing. The immersed plates were tested mechanically through one year, and those in the control group at the beginning of the study. During one year microstructural changes of the immersed plates were examined five times using a scanning electron microscope (SEM), and only once in the control group. There were significant microstructural pitting corrosion changes after six months and after one year in all plates that were in simulated biological conditions, regardless of the group pH value. Static and dynamic mechanical plate loading tests were performed one year after storage in solutions with various pH values. Following the complete mechanical testing no statistically significant changes were found between groups kept in simulated biological conditions for one year and the control group. The study showed no changes in the mechanical properties of the investigated implants regardless of significant microstructural changes as a consequence of pitting corrosion in simulated biological conditions, which precludes the probability of implant weakening and indication for its removal one year after fracture fixation.