Intramedullary Nail: Proposed Redesigns for Extension – Nail Connection BME 200/300 Fall 2005 Client: R.T. Dueland DVM, UW-Madison Advisor: William Murphy Ph.D. Team Members: Danielle Ebben Anna Moeller Jon Sass Tony Wampole Erik Yusko October 19, 20052 Table of Contents Abstract……………………………………………………………………..3 I. Introduction and Product Motivation………………………………..…4 II. Surgical Procedures and Materials…………………………………...4 III. Client Information………………………………………………...........6 IV. Client Design Requirements………………………………………….6 V. Design Alternatives……………………………………………….....…6 VI. Design Matrix…………………………………………………….…..10 VII. Ethics…………………………………………………………………11 VIII. Conclusion………………………………………………………..…11 Appendix A: Project Design Specifications……………………………12 Appendix B: References……………...…………………………………153Abstract: Intramedullary nails are one method of repairing long bone fractures. The nail is inserted into the intramedullary space of the two fragments, and the fracture is reduced. The nail and fragments are secured via two proximal and two distal screws or bolts. In order to drill holes for the screws or bolts that align with pre-drilled holes existing in the nail a jig which guides the drill to the correct location is attached to the nail. This project specifically discusses the intramedullary nails used in canine fracture repairs. However, the jig apparatus sometimes fails to align the drill with the holes in the nail. A study preformed by our client and others, stated that approximately 4% of the distal screws failed to properly engage the nail. When this happens the nail is improperly secured and the success of the surgery and recovery of the animal are in jeopardy. Our client, R.T. Dueland, has requested we examine methods to decrease misalignment rates. It was determined that the primary source of movement between the nail and the jig occurred at the extension and nail interface. This paper proposes several design alternatives that address this junction to decrease movement of the nail relative to the jig.4I. Introduction and Project Motivation If not properly healed a severe long bone fracture can seriously complicate or even threaten an animal’s life. If bone fragments are misaligned, the animal may need a surgical procedure for proper healing to occur. One method of repair uses an intramedullary nail (IN) to secure bone fragments in alignment. The IN is inserted into the marrow of the bone, spanning the fracture. It is then attached to a jig containing drill guides. Using the drill guide a surgeon drills into the bone such that screws or bolts can fasten the IN and bone fragments in place. This procedure realigns the bone and provides support during healing. This system is a very effective method to treat clean fractures where sufficient space is available on proximal and distal fragments to secure the nail. The effectiveness of the procedure is limited if the nail fails to fasten securely to the bone. A study that was done on this surgical procedure involving 126 dogs concluded that 86% of the surgeries had excellent results, 11% had good results, and 3% had fair or poor results. According to this same study, 4% of the screws that were inserted did not pass through the nail holes due to misalignment [1]. Another study demonstrated the overall bending strength of the nails. According to this study, the 8mm nails are significantly resistant to bending (65% bending stiffness compared to intact femur) [2]. This, along with visual observation of the device under stress, suggests that the misalignment of the jig’s drill guides with the nail holes is due to movement at connections between the nail and the extension, the extension and the jig, or a combination of both rather than bending of the nail, figure 1. This project aims at reducing misalignments in IN surgical procedures used to repair canine fractures via redesigning components of the IN components. II. Surgical Materials and Procedure As stated previously IN are used to repair canine long bone fractures. IN and their components are constructed with stainless steel and manufactured by Innovative Animal Products in Rochester, Minnesota. This system of repairing fractures was developed in 1989 by R. Tass Dueland, DVM from the University of Wisconsin-Madison. The surgical procedure requires the canine to be put under local anesthesia. Standard X-rays of the fracture site enable the surgeon to determine the appropriate length and diameter nail to use in the procedure. Nails are manufactured in 4.0, 4.7, 6.0 mm and 8.0 mm diameters [4]. After choosing the nail, the marrow of the bone can then be reamed out either through the fracture Figure 1: The nail and extension are secured to the jig. The nail can be seen deviating from the jig holes at the extension-nail joint.5point, or through the proximal or distal ends of the bone. Reaming is done by hand and makes inserting the nail easier. The IN is then inserted such that the nail head does not extend past the greater trochanter [1]. Usually the nail is inserted farther such that the head of the nail is buried within the intramedullary space. The location of the nail within the bone can be determined from markings on the extension piece that are 2mm apart, figure 2. The IN head has an “H” shape, depicted in figure 2. The head allows necessary attachments to the nail that are used to insert the nail and to attach the jig. The first attachment is an extension piece. Extension pieces come in two sizes: short for the femur and longer for the tibia to prevent interference with the femoral condyles or patella. During insertion of the nail the extension piece is connected to a handle with which the surgeon forces the nail in the intramedullary space. All connections are fastened in place with threaded male and female components. The extension piece and nail head fit together with their interlocking “H” ends, figure 2. The “H” head provides alignment of the holes relative to the position of the extension piece. It
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