By C. Fedor. Angelo State University.
Polarization Testing—Current/Potential Response A standard electrochemical test used to evaluate the corrosion resistance of implant alloys is the polarization test purchase kamagra super 160mg line erectile dysfunction by country. This test assesses the current/potential characteristics of the metal solution interface by varying the potential of the interface and measuring the resulting current discount kamagra super 160mg visa erectile dysfunction treatment auckland. Varying the potential across the metal–oxide–solution interface in a controlled fashion forces the oxida- tion and reduction reactions, which are at a dynamic equilibrium at the open circuit potential to deviate from equilibrium. For instance, for metals which do not form passivating films (not implant alloys), the current/potential relationship is represented with the Butler-Volmer equation: n bc n (6) icorr = io [exp − exp ba where icorr is the corrosion current at the applied potential is the overpotential (the potential difference between open circuit and the applied poten- tial) ba and bc are the Tafel constants io is the exchange current density. From these polarization tests, information characteristic of the corrosion currents and potentials can be obtained, as well as the nature of the electrochemical behavior when the potential of the interface is different from the resting OCP. The typical instrumentation used for polarization tests is a potentiostat. Polarization tests are performed by applying a potential (voltage) to a metal sample (working electrode) relative to a standardized reference electrode. A counterelectrode is used to complete the circuit and to provide a current sink so that the reference electrode is not affected by the current that flows. A typical curve for a polarization test of a passivating metal is shown schematically in Fig. There are four regions of this plot that are the result of different behavior of the electrode surface. At potentials positive of the equilibrium potential, the metal has a thermodynamic driving force for oxidation and is in the active region, i. A passive film has not formed to the extent that it can limit the rate of corrosion, although incomplete oxide film formation may be occurring. This continues until the potential is increased to a sufficiently more positive potential where the metal will spontaneously begin to form an oxide film on its surface. When this film fully covers the metal substrate, the metal is said to become passive, and the potential at which this occurs is known as the passivating potential, Epp. This kinetic barrier prevents further oxidation, and the current that flows drops dramatically. As long as the oxide layer remains intact on the surface, further increases in electrode potential will not significantly increase the current. However as the potential is increased further in the passive range there is an increase in the thickness of the oxide film. This process is known as anodization and can be used to thicken the oxide film. For titanium, the anodization rate has been reported to be in the range of 20 A/V˚. Figure 2 Schematic for a polarization test of a pure metal in water with no other electrochemical reactions taking place. The y axis represents the voltage of the metal surface relative to a standard electrode of some sort, and the x axis represents the log of the current produced by the corrosion. The areas of different corrosion behavior are indicated by the dotted lines. Below the equilibrium potential (Em) metal ions tend to come out of solution onto the metal surface. Between the equilibrium potential and the passivation potential (Epp) metal ion release from the surface is thermodynamically favorable, without inhibition by surface oxide formation. However, between the passivation potential and the breakdown potential (Eb) the surface of the metal is protected by the formation of an oxide layer (i. Above Eb the driving force for ionization overcomes the protective surface oxide, resulting in corrosion within the transpassive region. Once the potential is increased further to a value where physical limitations to oxide layer growth reduce its ability to kinetically limit the high thermodynamic driving force for oxidation, the corrosion currents can increase and the electrode is said to enter transpassive behavior. This transition potential is referred to as the breakdown potential, Eb. Changes in the barrier effect of the oxide film may be the result of changes in the oxide structure or composition, valence of the metal ions in the oxide, or fracture of the oxide layer. For titanium, the breakdown potential is in the tens of volts, generally well outside of any potential capable of being induced. However, Co–Cr and stainless steel alloys have a breakdown potential of about 550 mV due to the Cr2O3 oxide layer breakdown. If a second electrode reaction, typi- cally the reduction of oxygen, is present, the resultant polarization curve will be the sum of the two reactions. The corrosion potential (or open circuit potential) for the combined reactions will be where the O2 reduction reaction curve intersects with the oxidation reaction of the metal. This more complex graph more accurately represents what happens when performing this type of testing on implant alloys using physiologically relevant solutions where there are hundreds to thousands of reactions occurring. Electrochemical Impedance Spectroscopy This technique is based on the fact that metal–oxide interfaces have characteristics which are related to electrical circuits. For instance the transfer of metal ions across the interface can be Corrosion and Biocompatibility of Implants 71 Figure 3 Schematic showing a polarization test in which there are two electrode reactions. One is a passivating metal and the other a reduction reaction (i.
J Bone Joint Surg and femoral trochlear development generic kamagra super 160mg without a prescription erectile dysfunction exercises. Factors of joint associated with hypermobility and dislocation of patellar instability: An anatomic radiographic study cheap kamagra super 160mg with mastercard erectile dysfunction in young males. J Bone Joint Surg Knee Surg Sports Traumatol Arthrosc 1994; 2(1): 19–26. An electromyographic Patellofemoral malalignment in adolescents: investigation of subluxation of the patella. J Bone Joint Computerized tomographic assessment with or with- Surg Br 1979; 61-B(2): 169–171. Dysplasia of the quadriceps mechanism: 22(1): 55–60. Hypoplasia of the vastus medialis muscle as related to 100. Surg Clin North modified Elmslie-Trillat procedure to improve abnor- Am 1975; 55: 199–226. Familial recurrent dislocation of the 22(3): 318–323. Demonstration of lateral patellar subluxa- Reparatrice Appar Mot 1998; 84(3): 285–291. Patellofemoral instability: Evaluation and manage- 103. The eval- long-term results of nonoperative management in 100 uation of patellofemoral pain using computerized patients. Treatment of Injuries to Athletes, 1986(204): 286–293. J Bone Joint Surg [Am] incongruence in chondromalacia and instability of the 1971; 53: 386. Quadriceps dyspla- of ligaments and ligament healing. In Jackson, DW, sia and patellar tilt in objective patellar instability. Acute Anatomy and surface geometry of the patellofemoral dislocation of the patella: A prospective review of joint in the axial plane. J Bone Joint Surg Br 1999; 81(3): operative treatment. We reach a correct diagnosis and once this done, must determine if the main complaint is pain or start the most appropriate treatment. It is common to have symptoms in studies only help to confirm the diagnosis or to both knees that may change from one knee to complement the data obtained by the history the other over time. This is a tip-off of a and examination of the patient. Overuse can ing studies, and arthroscopic evaluation. In these cases, history should be the evaluation must also consider all the oriented to determine which supraphysiological different factors. History Identification and rigorous control of the activi- The first diagnostic step is a thorough history. For instance, absence of a traumatic episode For example, patients with left anterior knee pain or presence of bilateral symptoms should lead should avoid driving a car with a clutch for pro- toward patellofemoral pathology and against longed periods of time because it aggravates the meniscal derangement in the young patient; symptoms. In these cases patient education is on the contrary, the presence of effusion sug- crucial to prevent recurrence. A small effusion, however, may externally rotated tibia in a flexed and valgus be present with patellofemoral syndrome. Pain rarely is con- symptoms (pain and/or instability). The loca- stant and asymptomatic periods are frequent. It is tion of pain can indicate which structure is difficult for the patient with anterior knee pain to injured, which is extremely helpful to make the pinpoint the area of pain, placing his or her hand diagnosis and plan the treatment. Both legs over the anterior aspect of the knee when we ask should be examined. However, the pain can The lateral retinaculum ought to be felt and also be medial, lateral, or popliteal. Tenderness somewhere over patients have multiple painful sites with different the lateral retinaculum, especially where the reti- pain intensity.
The limbs and the trunk cheap 160 mg kamagra super fast delivery erectile dysfunction at age 31, including the whole spine purchase 160mg kamagra super with amex erectile dysfunction early 20s, the breastbone and adjacent ribs, and the heels, should be checked for any tenderness. The ability to bend the spine backwards and side- ways (without bending the knees), or to rotate the spine, is generally the first to be impaired. Many people with early AS can bend forward quite well, and even touch the ground with their fingertips, because they have good mobility in their hip joints. However, a careful examination of lumbar spinal motion using the Schober test (Figure 5g) will often detect a decrease in the forward bending ﬂexibility of this part of their spine. The diagnosis of AS also involves X-rays and tests to exclude other possible causes of symptoms. In very early stages the symptoms may come and go, but in most people they ultimately become more persistent. However, the lower back pain and stiffness does settle down in the end, but by that time the upper part of your back and the neck may have become painful and stiff as well. It is therefore very important to main- tain a good posture and prevent a stooped (bent) spine. Modern treatment can help, provided the diagnosis is made early and you comply with the recommended treatment. Most of the loss of func- tion occurs during the ﬁrst 10 years, and is cor- related with the occurrence of peripheral arthritis (including hip and shoulder joints) and develop- ment of bamboo spine. The disease process of AS is discussed in detail in Chapter 15. Although most of the symptoms of AS begin in the lumbar and sacroiliac areas, they may sometimes mostly involve the neck and upper back, or present thefacts 19 AS-04(19-22) 5/29/02 5:48 PM Page 20 Ankylosing spondylitis: the facts as arthritis in the shoulders, hips, and feet. A variety of other problems may precede back pain and stiffness in some patients, e. Eye specialists (oph- thalmologists) should always look for the possibility of underlying AS and related diseases in someone with this kind of inﬂammation. Restricted spinal mobility and decreased chest expansion without an obvious cause such as emphysema or scoliosis should also alert the doctor to the possibility of AS. AS in men and women Until a few years ago, AS was thought to be much more common in men than in women. We now know that women frequently develop the disease too, but some of them have a very mild form of the disease which may not be as easily detected as it is in men. For example, in Germany only 10% of the AS patients diagnosed around 1960 were women, but this percentage has progressively increased since then to reach 46% among those diagnosed since 1990. There is also a signiﬁcantly longer delay in disease diagnosis for female patients, but fortunately this delay is decreasing. For example, in Germany in the 1950s there was, on average, a 15 years delay in diagnosis for women, but by 1975–79 it was down to 71⁄ years. In some women, neck and 20 thefacts AS-04(19-22) 5/29/02 5:48 PM Page 21 The course of the disease peripheral joint involvement may be the main manifestation, and some may have symptoms that resemble ﬁbrositis (ﬁbromyalgia) or early rheuma- toid arthritis. Functional outcome, as analyzed by studying activities of daily living, is similar in men and women. However, when it comes to pain and the need for drug therapy, women with AS tend to be worse off than men. The slower and relatively incomplete progression of spinal fusion in women may mean that it takes longer for pain to decrease as a result of complete spinal ankylosis. AS in older people It is very rare for AS to begin after the age of 45. However, there are many people with AS whose disease is diagnosed in old age, perhaps because they have had minimal symptoms over the years. Some- times their back pain may be due to osteoporosis or related fractures rather than to inﬂammation. Osteoporosis and AS in older people are discussed in detail in Chapter 9. Sometimes arthritis involving the hip, ankle, or foot may be the ﬁrst symptom. Some children may have mild constitutional symptoms such as malaise, loss of appetite, or mild fever in early stage of the disease. These symptoms may be relatively more common in developing countries. Some chil- dren feel pain or tenderness at the bony prominence in front of the knee, located an inch or so below the knee cap (the tibial tubercle), or heel swelling and tenderness (due to Achilles tendonitis and plantar fasciitis) (see Figure 6). Spondyloarthropathies AS belongs to a family of diseases that may affect the spine and other joints, and also share many overlapping clinical features. This group of diseases are called spondyloarthropathies, and they are dis- cussed in more detail in Chapter 17. They help maintain or improve posture, chest expansion, and spinal mobility, they improve health status, and they prevent or minimize deformity.
Like WDM kamagra super 160mg on-line erectile dysfunction low testosterone treatment, MDM is a progres- sive autosomal myopathy with onset usually in middle age (range 40–80 years) generic kamagra super 160mg impotence causes. Tibial muscles are usually affected early, with foot drop developing only in advanced stages. MDM is usually milder than WMD, the hands are usually spared and patients remain able to walk even in late life. This autosomal recessive myopathy pre- sents in early adulthood and progresses to significant weakness of anterior tibial and then posterior compartment muscles within 10–15 years. Cardio- myopathy and conduction block may occur in some patients. This autosomal recessive myopathy be- gins in early adulthood with progressive weakness and atrophy of the posterior gastrocnemius muscles. Other leg and hand muscles may be affected but proximal weakness is uncommon. This is an autosomal dominant myopathy seen in patients aged 4–25 years. Weakness begins in the neck flexors and anterior leg muscles, followed by finger extensor weakness, and ending with severe shoulder girdle weakness. MDM is linked to 2q31 and may affect Pathogenesis the gene for titin, a striated muscle protein that appears to play an important role in sarcomere assembly. Other chromosome linkages include GLDM: 14q11, MIDM: 2p12, NDM: 9p12, and DBDM: 2q35. MIDM may be an allelic variant of LGMD2B, and both show an abnormality in the large and complex DYSF gene coding for the novel mammalian protein dysferlin. Dysferlin shows some sequence homology to fer-1 and therefore may play a role in muscle membrane fusion or trafficking. Laboratory: Diagnosis Variable, serum CK is usually normal or mildly elevated except in MIDM where it may be > 100 times normal. Electrophysiology: Nerve conductions studies are usually normal except in WDM where sensory fibers may be affected. In clinically affected subjects, EMG shows an increase in insertional activity in distal muscles, along with short duration motor unit action potentials typical of myopathy. Imaging: MRI studies help in diagnosis by showing the distribution of the atrophy and fatty changes in the muscle. Muscle biopsy: WDM shows variation in fiber size, fiber splitting, and rimmed vacuoles (Fig. In MDM, a dystrophic pattern is seen with rimmed vacuoles in 30%. Evidence of apop- tosis may be observed in some muscle fibers. Rimmed vacuoles are also very frequent in NDM, but are seldom seen in MIDM. Immunostaining for desmin should be performed on muscle biopsies because DBM mimics other distal myopathies and is associated with an increased risk of cardiomyopathy. Genetic testing: Genetic testing is not currently clinically available for most of these disorders. Differential diagnosis – HMSN (Charcot-Marie Tooth disease) – SMA – FSHMD – IBM – LGMD (with distal limb involvement) – Nemalin myopathy Therapy There is no medical treatment for any of the distal myopathies, although more severely affected patients may benefit from orthotics. Cardiac complications in DBM and NDM may require use of a pacemaker. Prognosis WDM and MBDM are slowly progressive and do not affect life expectancy. In contrast, MIDM progresses more rapidly and affected patients may be nonam- bulatory within 10 years from the onset of symptoms. DBM has a rapid progression and affects respiratory, bulbar, and proximal muscles. The disorder may be associated with cardiac arrythmias. References Ahlberg G, von Tell D, Borg K, et al (1999) Genetic linkage of Welander distal myopathy to chromosome 2p13. Ann Neurol 46: 399–404 Aoki M, Liu J, Richard I, et al (2001) Genomic organization of the dysferlin gene and novel mutations in Miyoshi myopathy. Neurology 57: 271–278 Illa I (2000) Distal myopathies. J Neurol 247: 169–174 Saperstein DS, Amato AA, Barohn RJ (2001) Clinical and genetic aspects of distal myopa- thies. Muscle Nerve 24: 1440–1450 Udd B, Griggs R (2001) Distal myopathies.
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