healed. Fractured bone is fully healed when new bone is being formed around the edge of each fractured parts, âknittingâ back all the fractured pieces together.
An Alternative Coating Technique To Strengthen Pin-Bone Interface Stresses For External Fracture Fixation: A Preliminary Study
N.S. Nahar Sham, N.A. Abu Osman and B. Pingguan-Murphy
In managing a fractured bone, the fractured pieces have to be put back into position and have to be rigid in order to prevent them from moving out of place until they are healed. Fractured bone is fully healed when new bone is being formed around the edge of each fractured parts, “knitting” back all the fractured pieces together. To achieve adequate stability, methods including casts and internal fixation are normally used. Rigid casts can be made from plaster of Paris or fiberglass. They are used to encase a limb in order to hold broken bones in proper position until they have healed. They are known to be noninvasive and inexpensive choice to treat most mechanically stable fractures. Even so, casts do not provide sufficient immobilization for grossly unstable fractures. These can lead to nonunion, delayed union or displacement of fracture segments. Casts immobilize muscles and joints adjacent to the fracture site, which then result in weakness and fibrosis of muscles. Casts can also give problems in wound care as infections, ulcerations, rashes and itching might arise after a certain period of time. Due to these problems, surgeons usually opt for internal or external fixation for unstable fractures. Internal fixation refers to intramedullary fixation and fixation of screws and plates. These are the ideal way to stabilize fractures of major weight-bearing long bones. The advantages of implementing internal fixation are the ease to align and stabilize the bone under direct vision. There are disadvantages to internal fixation [1], which include; Surgical dissection for introduction of the fixation device
Insertion of a foreign body and the additional difficulty of eliminating bacterial contamination when treating open fractures Development of osteoporosis of the bone directly under the plate due to stress shielding The need for supplementary cast immobilization and avoidance of full function Unlike those fixation methods, external fixation (Fig. 1) is always known to be minimally invasive and it rules out many disadvantages which result from using casts and internal fixation. External fixation is normally chosen when internal fixation is contraindicated, especially when treating open fractures. The device allows free access to injury site for any ongoing procedures. It also gives higher mobility to the patient besides allowing the surgeon to adjust the alignment, length and mechanical properties of the device. Ex-ternal fixation is introduced by placing pins into the broken bone, above and below the fracture site. Then, surgeon repositions the bone fragments accordingly. The pins are connected to a metal rod or rods outside the extremity using hinged-like clamps. This device functions as a stabilizing frame that holds the bone fragments in their correct position while allowing them to reattach and heal. After a period of time, the external fixation device will be removed.
Fig. 1 Schematic representation of the pins and fixator assembly. Captured from Caja V et al.
As previously mentioned, to ensure the rigidity of the system, it has to be able to resist displacement at the fracture site. Listed below are the most significant variables that determine the mechanical properties of the fixator [11, 15]: Pin diameter [13] Number of pins The spread of pins in each main bone fragment The distance between the bone and longitudinal rods The number of longitudinal rods to the same pins Pin-bone interface In this paper, we mainly concentrate on investigating the pin-bone interface factor. By having metals protruding at the limb for a certain period of time, the patient will eventually experience discomfort. The other concerned setback that arises when using this type of fixation is pin infection. The pin site where the metal work enters the skin and goes into the bone can be a source of infection. Besides infection, the pins can loosen in time and weaken the bone-pin interface [2, 3, 4, 5, 10]. It
has been identified that the causes to these problems are due to thermal and mechanical damage of the bone during pin insertion and formation of fibrous tissue at the pin-bone interface [11, 12]. These problems can be so severe and can result in discontinuation of the treatment. In order to improve pin fixation and accordingly avoid infection at the pin sites, some authors established the idea of coating the pins with a known biomaterial called hydroxyapatite. Hydroxyapatite has been widely used as a bone substitute. It is known to be osteoconductive [16] and osteoinductive [17,18]. Thus, hydroxyapatite coating enhanced bone growth. Several studies had been done to verify that sintered hydroxyapatite is able to bind to the bone and lead to non fibrous tissue interposition [19, 20, 21, 11]. The motion-induced fibrocartilaginous membrane will then be converted into a bony anchorage [22]. Many trials had proved that the affective method to ensure stronger fixation is by applying hydroxyapatite to coat the pins. Hydroxyapatitecoated pins were shown to be better bone fixation when compared to the similar uncoated pins. The goal of this study is to develop and test on the new approach in strengthening the pin-bone attachments. If the pins are coated with hydroxyapatite, we proposed that to achieve the acquired healing stage, fewer pins are needed for the fixation. It is also predicted that by having stronger pin-bone attachment, less duration needed for the fracture to heal. Thus lead to fewer complications that might occur during the bone fracture healing process.
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