Issue 35

Š. Major et alii, Frattura ed Integrità Strutturale, 35 (2016) 379-388; DOI: 10.3221/IGF-ESIS.35.43 379 Focussed on Crack Paths Fatigue life prediction of pedicle screw for spinal surgery Š. Major The Institute of Theoretical and Applied Mechanics, Academy of Science, Prosecká 809/76, 19000 Praha 9, Czech Republic V. Kocour The Institute of Theoretical and Applied Mechanics, Academy of Science, Prosecká 809/76, 19000 Praha 9, Czech Republic P.Cyrus Department of Technical Education, Faculty of Education, University Hradec Králové, Rokitanského 62,500 03 Hradec Králové, Czech Republic A BSTRACT . This paper is dedicated to fatigue estimation of implants for spinal surgery. This article deals especially with special case of hollow pedicle screw. Implant systems utilizing specially designed spinal instrumentation are often used in these surgical procedures. The most common surgical procedure is spinal fusion, also known as spondylodesis, is a surgical technique used to join two or more vertebra. Implants are subjected to many loading cycles during their life, especially in the case of other degenerative changes in the skeleton, there are often changes in loading conditions, which often cannot be accurately determined. These changes often lead to further bending load in the thread. Hollow screws studied in this work show higher fatigue resistance than other types of implants. K EYWORDS . Pedicle-screw; Titan alloy; Fatigue life; Finite element analysis. I NTRODUCTION edicle screws are used for treating several types of spinal injuries. Together with rods and plates, they are used to form intrapedicular fixation or transpedicle screw devices [1-4] for spinal fusion. Fusing of the spine is used to eliminate the pain caused by abnormal motion of the vertebrae by immobilizing the faulty vertebrae or to treat most spinal deformities, such as scoliosis. Basicaly, this method involves the insertion However, screw breakage and loosening have been reported, which may create post-surgery problems [2]. Currently various types of pedicle screw are used: cylindrical and conical, hollow and solid. In this work are considered solid and hollow cylindrical screws. Hollow screws are used for filling the wound with cement. Since the bone during drilling fulfills blood and other impurities, which could be the cause internal inflammation. Filling takes place through of a hollow screw. For filing are used various cements. In this work was used polymethyl methacrylate bone cement with multi-waled carbon nanotubes [5]. The prediction of fatigue failure is important forprevention of serious medical complications. For the fatigue life P