ÖZAmaç: Bu çalışmada yaşlılarda çift kolon kırıklarında osteosenteze (plak ve vida tespiti) kıyasla kalça artroplastisi ile desteklenen aynı yöntemin (hibrid çözüm) mekanik stabilitesi karşılaştırıldı. Hastalar ve yöntemler: Çift kolon kırıkları için geliştirilen ileri sonlu eleman pelvis modelinde mekanik araştırmalar yapıldı. İncelenen simüle edilen implant kombinasyonları şunlardı: poliaksiyel vidalı ve U plaklı, halkalı, modüler asetabüler sepet; medial horizontal (linea terminalis) ve kuadrilateral kemik yüzeylerine yerleştirilen poliaksiyel vidalı plaklar; U plaklı, modüler asetabüler kap ve çeşitli ebatlarda sonlu eleman modeline (FEM) göre optimize edilen poliaksiyel vidalar. Bu modellerde yük, gerilim ve implant deformasyonuna bağlı farklı hareket paternlerinden doğan pik yük pozisyonlarındaki muhtemel kaymalar ölçüldü. Bulgular: Hibrid sistemler, piyasada bulunan implantlarda minimum deformasyona neden oldu. Tek başına konvansiyonel osteosenteze kıyasla, asetabüler kırık bölgelerinde daha az muhtemel kayma ve daha yüksek stabilite gözlendi. Mevcut ve uygun implant ebatlarına göre optimizasyon yapıldığında, stabilitede anlamlı düzeyde ilave bir artış izlendi. Sonuç: Yaşlılarda çift kolon kırıklarının tedavisinde biyomekanik modellerde osteosentez ve protez implantasyonunu içeren hibrid yöntem daha fazla stabilite sağlamaktadır.Anahtar sözcükler: Asetabüler kırık, asetabulum, sonlu eleman modeli, pelvik travma, plak osteostentezi, total kalça replasmanı. ABSTRACTObjectives: This study aims to compare mechanical stability of osteosynthesis (plate and screw fixation) alone versus the same method supplemented with hip arthroplasty (hybrid solution) for double column fractures in elderly. Patients and methods: Mechanical investigations were performed on an advanced finite element pelvis model developed for double column fractures. The following simulated implant combinations were analyzed: modular acetabular basket with a ring with polyaxial screws and U-plate; plates with polyaxial screws placed on the medialhorizontal (linea terminalis) and quadrilateral bone surfaces; modular acetabular cup with U-plates; and polyaxial screws in sizes optimized based on a finite element model (FEM). Using the models, the possible shifts in peak load positions arising in different movement patterns caused by load and tension and implant deformation were measured. Results: Hybrid systems resulted in minimal deformation of the implants already available on the market. We observed less possible shifts and greater stability in the acetabular fracture zones, compared to conventional osteosynthesis alone. Optimization with available and compatible implant sizes led to a further significant increase in stability. Conclusion: Hybrid method combining osteosynthesis and prosthesis implantation provide more stability in biomechanical models in the treatment of double column fractures in elderly.

In double column fractures, if the reduction does not require an anterior approach, it is not necessary to fix the iliac wing fracture only to improve the stability of the fixation. If the reduction does require an anterior approach, it is worth fixing the iliac wing fracture with the technically less demanding screw fixation.

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In this paper the behavior of an O-ring made of NBR rubber was investigated under extreme conditions. The effect of the extreme initial compression, operating pressure and extreme temperature conditions were examined. The rubber material was tested in simple tension, pure shear and equibiaxial tension modes complemented with a Dynamic Mechanical Thermal Analysis (DMTA) to capture the viscoelastic behavior of the material. For the investigation, a large-strain viscoelastic material model was developed by the authors, to take into account the large deformations caused by extreme conditions. Insufficient space during installation causes extreme initial compression consequently leading the material to crack on the contacting outer surfaces. It was found that the excessive strain and friction induced shear stress contributes primarily to this phenomenon. Extreme operating pressure causes the seal to penetrate into the gap between the shaft and the housing. This behavior damages the material and cracks appear on the seal. High strain areas were found in the proximity of the gap in the material. The analysis of the extreme operating temperature showed that during cooling the O-ring can completely loose its ability to seal at −70˚C. There are three contributing factors: the speed of cooling, the temperature and the coefficient of thermal expansion.

The aim of our analyses was to model the process of the thermal micro-crack development on and under a railway wheel tread, equipped only with a disk brake during an intensive braking procedure. Considering the fact that the thermal micro-crack development is a complex problem, a multistage finite element modelling technique was developed. Using the new modelling approach, the heat and the thermal stress development can be observed between the wheel and the rail using thermal and coupled thermal-elastic-plastic FE simulations.