By T. Gorn. East Texas Baptist University.

MECHANICAL PROPERTIES Mechanical properties of a material can be studied by measuring the response of the material to an applied load cheap evista 60mg with mastercard menopause osteoporosis. Strength of a material is judged by its ability to resist stress cheap 60 mg evista overnight delivery breast cancer 8mm in size. Stress is a quantity that describes the intensity of the internal force per unit area acting on a specific plane (area) passing through a point order 60 mg evista fast delivery women's health clinic york region. When a body is subjected to external loads, an infinitely small point within a body under load can be subjected to two possible types of stresses: normal stress and shear stress (Fig. Normal stress is the intensity of the net forces acting normal (perpendicular) to an object per unit area. The simplest load applications are tensile and compression forces. In tensile force, the specimen is gradually elongated, and in compression force the specimen is gradually compressed under an applied stress. The stress, , is the force applied per unit area and the strain is the fractional change in the length of the specimen. It can be measured as linear strain, ε, which is the change of length per unit length. In tensile and compression tests, the specimen is subjected to a progressively increasing tensile force until it fractures. At the beginning the test material deforms elastically. The strain is directly proportional to the stress and the specimen returns to its original form immediately on the removal of the stress. Beyond the elastic limit, applied force causes plastic deformation, in which deformation is permanent. In the elastic region, the stress and strain are linearly proportional and the ratio is defined as E /ε, where E is Young’s modulus. Shear stress is the intensity of force per unit area acting tangentially to an object. In other words, it is the stress component that acts in the plane of the sectioned area. When a shear stress, which acts at an angle rather than normal to the plane, is applied, the relation between shear stress, , and shear strain, , is given as G / , where G is called the shear modulus. The amount of deformation in any direction depends on the magnitude and direction of the loading and on the composition of the material (Fig. Mechanical tests can be static tests when the load is applied slowly, cyclic tests when the load is applied partly or wholly for many repetitions, and impact tests when the load is applied Figure 11 Basic stresses acting on a material under loading. Dotted lines represent the final deformed shape of the material after loading. Recent Developments in Bone Cements 257 rapidly at once. Fractures form either under constant stress (creep) or fluctuating stress (fatigue) conditions. Creep tests are carried out under certain combinations of stress and temperature. All materials exhibit an increase of strain with time when subjected to a constant stress. High temperatures lead to a rapid creep, which is often accompanied by microstructural changes. There are three common ways in which stresses may be applied: axially, torsionally, and flexurally (bending). In each type of loading, at any point of the body, normal and shear stresses exist more or less depending on the type of loading. In axial and flexural loading, normal (pure tensile or pure compressive) stress is much more than shear stress. In torsion, shear stress is much more than normal stresses. Flexural theory states that most materials will exhibit linear-plastic behavior, i.

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Anesthesia: Local anesthesia is given with the patient lying down (Fig buy 60mg evista visa breast cancer x-ray examples. The needle should be inserted 1 to 2 cm beneath the marked skin and the anesthetic injected while withdrawing the needle 60 mg evista otc menopause 20 years after hysterectomy, into the subcutaneous level buy discount evista 60 mg pregnancy body pillow. Upon completing the injection, an 1 anesthetic button is left at the site where the Subcision needle will be placed. General anesthesia and nerve blocks are not recommended. Two percent lidocaine with epi- nephrine (1) or norepinephrine, in the ratio 1:200. Tumescent anesthesia is used when there are many depressions (7) although, as this infiltrates the fat, it may reduce the bed for the hematoma and bleeding. The recom- mended dose of 2% lidocaine with vasoconstrictor is from 7. The number of lesions treatable in a single session depends on the dose of anesthetic available, calculated according to the patient’s body weight (9,10). The total anesthetic dose described as safe for lido- caine with vasoconstrictor should not exceed 500 mg (8,11) or 7. Cutting the subcutaneous septa: Following maximum vasoconstriction, apparent as TM 3 paleness and piloerection, the procedure can begin. A BD Nokor 18G is preferred, because it has a cutting blade at the point. Other alternatives are the use of a special scalpel, with the same cutting blade at the point, or a normal or three-beveled needle, as described by Orentreich and Orentreich (1). The insertion should be made at an angle of 45 to 90 to the skin surface and then, at a depth of 1 to 2 cm from the skin surface, the needle should be positioned parallel to the epidermis, with the cutting edge to the left against 256 & HEXSEL AND MAZZUCO Figure 6 After antisepsis of the surgical area, local anesthesia is performed in the surgical room. Sterile sheets are used to protect the surgical area. The septa are cut on the backstroke of the needle, while maintaining the blade traction against the septa, thus releasing the tension exerted on the skin. This cutting technique allows a precise cut with a minimum of tissue damage, which ensures better postoperative results. A slight pinch test on the treated lesion is useful because it reveals any areas that remain retracted by septa (3,5). Compression: Following cutting the septa, vigorous compression is required in the treated area for 5 to 10 minutes, sufficient time for the process of coagulation to begin, permitting hemostasis and control of the size of the hematomas. The use of sand bags is recommended; they should weigh approximately 5 kg, be made from a washable mate- rial, and be wrapped in sterile fabric (3). Such bags produce a more uniform and efficacious compression than that achieved manually. Dressings: The treated areas are covered with sterile adhesive bandages and given addi- tional compression with dressings and compressive clothing (elastic pants or shorts) that should be worn for 30 days. The patient receives the following postoperative instructions: & Use analgesics for the first 48 hours; this period can be extended if pain persists. Acetaminophen at a dose of 750 mg every six hours is recommended. SUBCISIONâ & 257 Figure 7 A gentle pinch test is performed to find residual septa pulling the skin surface. Hematomas and hemosiderosis are expected in all patients during this period. The hematomas should follow a normal evolu- tion of spontaneous reabsorption over a period varying from 10 to 20 days. Hemosiderosis may persist for several months and is directly proportional to the absorption of iron present in the extravasated red blood cells. Other complications may arise as a result of this procedure and they are listed below.

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Quantitative measures of osteoinductivity of a porous poly(propylene fumarate) bone graft extender cheap evista 60mg visa pregnancy heartburn relief. Lewandrowski KU generic evista 60 mg on line menstrual mood swings, Hile DD purchase evista 60mg amex menopause leg cramps, Kowaleski MP, Doherty SA, Wise DL, Trantolo DJ. An injectable porous poly(propylene glycol-co-fumaric acid) cement as an adjunct for treatment of metacarpal and phalangeal injuries. Mikos AG, Sarakinos G, Leite SM, Vacanti JP, Langer R. Laminated three-dimensional biodegradable foams for use in tissue engineering. Bone compressive strength: the influence of density and strain rate. INTRODUCTION Classically, internal fixation of bones has been performed using metallic devices. However, metals are much more rigid than bone itself. Rigid fixation inhibits callus formation, leading to bone atrophy due to stress protection [2,3]. Metallic implants may also harbor infection which is difficult to eradicate without implant removal. Metals that are commonly used include stainless steel and titanium, and vitalium to a lesser extent. Stainless steel, however, has low resistance to corrosion. Titanium has also been shown to ‘‘degrade,’’ and it has been found in the soft tissues surrounding titanium plates and also in the regional lymph nodes. In craniomaxillofacial (CMF) surgery the problem of translocation of metallic implants to the inner side of the cranial table and interference with the growth of the skull in children are the main serious concerns. Metallic implants may also interfere with radioimaging. They may also be associated with cold sensitivity in the facial skeleton, which is an especially important consideration in cold climates. It is recommended that metallic implants be removed, and this entails a second surgical procedure with consequent financial and psychological consequences as well as an increased risk of complications, especially in pediatric surgery. Continuous research and development in the field of biomaterials has led to the introduction of reliable bioabsorbable internal fixation devices. At the advancing front of successful implants are the new self-rein- forced (SR) devices, which will replace metallic devices, at least in certain osteofixation indica- tions. We review here the developments that have led to the current state-of-the-art use of bioabsorbable devices in bone surgery. Pseudomigration Pseudo-migration of metals [4–10] can be a problem, especially in the growing skulls of children, because cranial growth takes place by the laying of new bone on the outer surface and resorption of old bone on the inner side of the skull. Consequently, metals that are applied on the outer surface of the skull can occasionally sink into the bone, be found on the inner side of the skull, or even against the dura. Although no neurological complications have been reported yet (follow-up of 2–6 years), there is a potential risk of damage to the brain should implant dislodgement occur in conditions such as trauma. In minipigs, total invagination of titanium plates with initial intracranial translocation occurs after 12 to 16 weeks postimplantation. Hence, it is recommended that all metals used in infant crania should be removed as early as possible (within 3 months). Currently, such devices are not removed unless they give rise to problems. Pseudomigration more often complicates the use of longer plates and application in the temporal region. Growth Disturbance In pediatric CMF surgery, metals may lead to growth disturbance of the skull bones. This can occur with the placement of rigid plates, especially across sutures (in rabbits) [11–14], but it may also occur even when sutures are not crossed (in monkeys). The more complex the fixation, the greater the magnitude of growth changes seen, and hence it is advised that the least amount of fixation needed to provide three-dimensional stability should be used. Stress Protection Because of the rigidity of metals (E 100–200 GPa), which is higher than that of bone itself (e.

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This paper reviews a series of in vitro and in vivo studies on the use of a PPF-based material as a bone graft extender for use in clinically relevant repair scenarios discount evista 60 mg amex breast cancer stage 0 dcis. AUTOGRAFT BONE Iliac crest autograft is the gold standard for bone graft material generic 60 mg evista with visa pregnancy gas. Autograft bone provides the critical elements required for bone growth generic evista 60 mg on line menstrual vacuum. The material is also able to maintain the strength and structural integrity of the defect area. Despite these advantages, the material suffers from several disadvantages. The primary disadvantage is the need for a secondary surgical site. Autografts are predominantly removed from the iliac crest of the patient. The procedure of harvesting material from the iliac crest has been shown to cause complications in 4–49% of patients. These complications can range from increased pain—observed in 25% of patients—to infection, sensory loss, and neurologi- cal and vascular injury. Further complications include increased anesthesia time and operative blood loss as well as prolonged recovery time. In addition to the procedural complications, the supply of bone available for harvest is limited. These complications, along with the risk of donor site morbidity and the limited supply of material available for harvest, have pushed the search for alternative materials. ALLOGRAFT BONE Allograft bone is the substitute most often used for autograft bone. It is typically available fresh, frozen, or freeze-dried. This material undergoes extensive processing and donor screening in an effort to reduce the risk of disease transmission. This processing decreases but does not eliminate the risk of disease transmission. In addition, the processing decreases the mechanical and biological properties of the bone, while adding to the cost of the material. In summary, although a viable alternative to autograft bone, allograft bone suffers from concerns of possible disease transmission, recipient rejection, increased cost, and limited availability. SUBSTITUE BONE GRAFT MATERIALS The problems associated with autograft and allograft materials described above, not the least of which is the increasing demand for a limited supply, have acted to fuel the development of substitute materials. Substitute materials have primarily been developed as a replacement for graft materials and currently are used in approximately 10% of the bone graft procedures per- formed worldwide. Calcium salt ceramics and glasses, such as calcium phosphates and hydroxyapatites, are widely used synthetics. Demineralized bone and collagen-based materials have also been used as substitute bone graft materials. Calcium phosphate materials such as tricalcium phosphate (TCP) and hydroxyapatite (HA) are among the most common synthetics. These materials have been successfully applied in orthopedic and dental applications for decades. Calcium salt materials have compositions similar to that of native bone and provide osteoconductive surfaces on which new bone can form. Although somewhat similar in composition, the materials elicit different biological responses. The TCP material is readily resorbed, whereas the HA is a more or less permanent material, taking several years to be removed and replaced by native bone. TCP typically is more porous than HA, helping it to be resorbed more rapidly.

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