Design and analysis of chest stabilization system

Master's Thesis

Biomechanical orientation

Abstract

Today open heart surgery has become a very common procedure all over the world. For more than half a century, steel wires were used to close the chest. Now the fixation methods have changed dramatically. By examining the common methods of closing the sternum and taking into account the important parameters in the design of these systems, it was found that the Zipfix system is more popular among surgeons and has more benefits. The Zipfix system is exclusively made of PEEK. The cost of the Zipfix system is about 5 to 8 times the cost of ordinary wires. Considering the expensiveness of PEEK material and the fact that importing this material into the country is prohibited, in this research, an alternative and cost-effective method has been presented to close the sternum. For this purpose, by using finite element modeling, the biomechanical analysis of Zipfix method with two different materials as well as new geometry has been investigated. According to the conducted researches, one of the best materials that can replace PEAK material is UHMWPE. CT scan images were used to create a 3D model of the sternum. Two stages were considered for modeling. In the first step, how to close the Zipfix was modeled by applying displacement to the two ends of the Zipfix, and the closing force of the Zipfix was approximately equal to 200 N. In the second step, the force of coughing was modeled by applying a tensile force equal to N1400. According to the results, it was determined that UHMWPE will be a very suitable substitute for PEEK in the construction of the Zipfix system, which is much cheaper, which, due to the new geometry, has no problem in terms of size and can be easily produced in the country.

Key words:

Sternotomy, sternal fixation, ZipFix system, polyether ether ketone, poly Ethylene with very heavy molecular weight, limiting element

Introduction

Nowadays open heart surgery has become a very common procedure all over the world. In 1985, fewer than 300,000 open-heart surgeries were completed. In 2007, the American Heart Association estimated the number of open heart surgeries to be around 6,846,000. From February 1 to December 30, 2011, the American Heart Association estimated the number of American adults with one or more heart diseases to be about 8,260,000, which has increased dramatically in 20 years. Approximately 3.9 million of these surgeries were performed on men and 2.9 million on women. The direct and indirect cost of this disease has been calculated to be more than 286.6 billion dollars[1].

1.1 Sternum stabilization[1]

At the beginning of every open heart surgery, in order to access the heart, the sternum bone[2] is divided in half. This operation is known as sternotomy [3]. This technique is essential for the vast majority of intrathoracic surgeries. After the surgery, the sternum must be adjusted, fixed and secured with the help of a sternum stabilization device or system.

     In approximately 98% of cases, this method is successful, but in the remaining 2%, complications occur after the operation [2]. Usually, this is due to low bone density and integrity caused by osteoporosis, especially in the elderly. This osteoporosis causes the sternum bone to become loose and lax at the fixation points. One of the complications associated with this disease is mediastinitis [4] or sternum bone infection, which has a mortality rate of over 15% [3], which is directly related to osteoporosis. It is necessary and necessary to create an optimal system that is firm, strong and suitable for the recovery of the sternum bone that has osteoporosis.

     Separation of the two halves of the sternum along with their sutures and tearing or opening of the wound is another complication after chest surgery. Studies have shown that the sternum wound was opened in 8% of all these surgeries, which was due to the limitation of their stabilization method. The mortality rate for this disease is 10 to 40% due to wound rupture, which is mainly due to infection, inflammation of the tissue around the cut part or mediastinitis, and swelling and infection in the sternum area.. The mortality rate for this disease is 10 to 40% due to wound rupture, which is mainly due to infection, inflammation of the tissue around the cut part or mediastinitis, and swelling and infection in the sternum area. The cases of opening and infection increase in people over 75 years old due to obesity or osteoporosis [4]. As a result, effective stabilization methods are necessary to improve the health process of the sternum and reduce the risks of disease.

     The progress of various industries and the new and increasing needs of humans have led to the creation of new designs and the improvement of various systems to close and stabilize the sternum. Factors such as high cost, not having the appropriate speed to perform and the inability to accelerate the recovery of patients have led to the innovation and development of these systems. Most surgeons prefer the use of a wire fixation technique to perform sternotomy surgery. However, new methods of sternal closure are becoming increasingly popular. Wire fixation (Figure 1.1a) attaches the two halves of the sternum together by making wire loops around the sternum and twisting their ends for security. Although basim fixation is simple and cost-effective, it is weak in terms of strength and mechanical stability and causes wound rupture, mediastinitis, and non-union of the sternum [5]. rtl;">p

Figure 1.1 Sternum stabilization methods [6]

a) Stabilization with wire, b) fixation with screws and plates, c) Talen system (reference all figures.)

Stabilization using plates and screws [5] (Figure 1.1 b) Another used method is to close the sternum. This method of tight binding reduces the non-welding of the sternum and other complications that exist in basim fixation. The screws used to fix the plate to the sternum loosen over time under the dynamic loading caused by breathing. Other common methods and systems that are available for sternum fixation include the Talen Fast System [6] produced by the Kealas Martin Industrial Group [7] which, as you can see in Figure 1.1p, this system is a set of adjustable clamps attached to each half of the sternum that are pulled together. Talen system is not widely used due to the large profile, high price and difficulty in installation [7]. Although all the common methods and systems have a common goal, each of these methods and systems has its own limitations. 1.2 Research Objective The purpose of this research is to propose an alternative and cost-effective method to close the sternum after chest surgery. For this purpose, the scientific sources and activities carried out in this field were first studied and reviewed, and then things such as fatigue, fracture, failure, cutting and breaking of bones, stability or instability in fixation, effect on surgery and pain after sternotomy, infections and improvement of patients' condition, size of systems and other effective and necessary parameters in the design of these systems were determined. After identifying the problems and obstacles and specific design conditions, a more appropriate method was chosen, which is the method of using Zipfix[8]. Then, for the purpose of the research, the final system was designed and modeling was done by applying the desired changes. By examining the obtained results, it was found that polyethylene material with a very heavy molecular weight can be used as a suitable substitute for the PEAK material [9] in the production of Zip Fix. There will also be information about the anatomy of the chest and sternum. In this chapter, challenges in the design of stabilization systems have also been discussed. In the third chapter, various methods of closing and stabilizing the sternum will be examined along with the design points of each system and the advantages and disadvantages of each. In the fourth chapter, the method of simulating the closure and fixation of the sternum with the Zip Fix method is described. In the fifth chapter, the results of the modeling are given, and it is also analyzed and discussed. Summary and suggestions are given in the sixth chapter.

Abstract

Cardiac surgery is a very common operation nowadays all over the world.