Experimental and Theoretical Investigation of Static and Dynamic Bending Properties of Intramedullary Nails

Abstract

The greatest expectation from intramedullary nails, which are used in the treatment of long bones by placing in the bone marrow, is that they cannot be damaged during bone healing and allow the adequate load distribution. There are many different kind of commercially available intramedullary nails and also, one of the mostly used types of this nails are hollow nails. Also, static and fatigue bending loads are taken into account in different international biomechanical test standards, which refers the worst-case working conditions. However, the intramedullary nails produced in hollow form are not known to change their properties under these loads due to the change in cross-sectional thickness. Therefore, the effects of cross-sectional thickness in intramedullary nails on their static and fatigue properties were investigated in this study. For this purpose, the hollow intramedullary nails manufactured from Grade 23 Ti6Al4V ELI with thicknesses of 6.2, 6.7 and 7.2 mm were subjected to static four-point bending and fatigue tests. After tests, it was observed that both static and fatigue strengths of nails improved with increasing cross-sectional thickness. Also, it was determined that a mathematical model to be used in the design process of nails can be established by using static four-point bending tests results and theoretical results. Additionally, it was observed that there wasn’t a direct proportion between increasing cross-sectional thickness and increase rate of fatigue strength although fatigue properties of intramedullary nails improved when its cross-sectional thickness increased.

İntramedüller Çivilerin Statik ve Dinamik Eğilme Özelliklerinin Deneysel ve Teorik Olarak İncelenmesi

Abstract

Kemik iliği içerisine yerleştirilerek uzun kemiklerin tedavisinde kullanılan intramedüller çivilerden en büyük beklenti kemik iyileşmesi süresince hasara uğramamaları ve yeterli yük dağılımına olanak sağlamalarıdır. Ticari olarak farklı pek çok türde intramedüller çivi olmakla birlikte bu çiviler içerisinde en çok kullanılan türlerden biri silindirik kesitli içi boş olan türleridir. Ayrıca, intramedüller çivilerin en kötü koşullarda çalışmasını referans alan birçok uluslararası biyomekanik test standardında statik ve dinamik eğilme yükleri dikkate alınmaktadır. Ancak, içi boş şekilde üretilen intramedüller çivilerin, kesit kalınlığının değişimi sebebi ile bu yükler altında özelliklerinin ne yönde değişeceği bilinmemektedir. Bu sebeple, bu çalışmada, intramedüller çivilerde kesit etkisinin intramedüller çivilerinin statik ve yorulma dayanımları üzerindeki etkileri incelenmiştir. Bu amaçla, Grade 23 Ti6Al4V ELI malzemeden imal edilen 6.2, 6.7 ve 7.2 mm kesit kalınlığına sahip içi boş geometrideki intramedüller çiviler statik dört noktadan eğme ve yorulma testlerine tabii tutulmuşlar. Testler sonrasında, intramedüller çivilerde kesit kalınlığı arttıkça hem statik hem de yorulma dayanımlarının arttığı belirlenmiştir. Bununla birlikte, statik dört noktadan eğilme deneyleri sonucunda elde edilen sonuçlar ile teorik olarak hesaplanan değerler kullanılarak; intramedüller çivilerin tasarımı aşamasında kullanılabilecek matematiksel bir model oluşturulabileceği belirlenmiştir. Ayrıca, intramedüller çivilerde kesit kalınlığı arttıkça yorulma dayanımının da arttığı ancak artan kesit kalınlığındaki artış oranı ile yorulma dayanımındaki artışın doğru orantılı olmadığı gözlemlenmiştir.

Keywords

• İntramedüller çivi,biyomekanik,eğilme,dört noktadan eğme,yorulma

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