By I. Dan. Webb Institute.

In order to analyze the stresses in the contact region of the tibio-femoral joint generic levitra 20 mg, photoelasticity techniques have been employed in which epoxy resin was used to construct models of the femur and tibia 10 mg levitra otc. The free ends of these two crossed rods are connected by a coupler that represents the tibial plateau cheap 10mg levitra mastercard. This simple apparatus was used to demonstrate the shift of the contact points along the tibio-femoral articular surfaces that occur during knee flexion generic 20 mg levitra visa. Another model purchase levitra 20 mg otc, the Burmester curve, has been used to idealize the collateral ligaments. The construct combining the crossed four-bar linkage and the Burmester curve has been used extensively to gain an insight into knee function since the cruciate and collateral ligaments form the foundation of knee kinematics. However, this model is limited because it is two-dimensional and does not bring tibial rotations into the picture. A three-dimensional model proposed by Huson allows for this additional rotational degree-of- freedom. Three survey papers appeared in the last decade to review © 2001 by CRC Press LLC mathematical knee models which can be classified into two types: phenomenological and anatomically based models. In a sense, these models are not real knee models since a model’s effectiveness in the prediction of in vivo response depends on the proper simulation of the knee’s articulating surfaces and ligamentous structures. Phenomenological models are further classified into simple hinge models, which consider the knee a hinge joint connecting the femur and tibia, and rheological models, which consider the knee a viscoelastic joint. Simple Hinge Models This type of knee model is typically incorporated into global body models. Such whole-body models represent body segments as rigid links connected at the joints which actively control their positions. Some of these models are used to calculate the contact forces in the joints and the muscle load sharing during specific body motions such as walking,38,73,86,112,114 running,25 and lifting and lowering tasks. Equations of motion are written at the joint and an optimization technique is used to solve the system of equations for the unknown muscle and contact forces. Other simple hinge models were developed to predict impulsive reaction forces and moments in the knee joint under the impact of a kick to the leg in the sagittal plane. Rheological Models These models use linear viscoelasticity theory to model the knee joint using a Maxwell fluid approximation97 or a Kelvin body idealization. These models do not represent the behavior of the individual components of the knee; they use exper- imental data to determine the overall properties of the knee. While phenomenological models are of limited use, their dynamic nature makes them of interest. Anatomically Based Mathematical Knee Models Anatomically based models are developed to study the behaviors of the various structural components forming the knee joint. These models require accurate description of the geometry and material properties of knee components. The degree of sophistication and complexity of these models varies as rigid or deformable bodies are employed. The analysis conducted in most of the knee models employs a system of rigid bodies that provides a first order approximation of the behaviors of the contacting surfaces. Deformable bodies have been introduced to allow for a better description of this contact problem. Employing rigid or deformable bodies to describe the three-dimensional surface motions of the tibia and/or the patella with respect to the femur using a mathematical model requires the development of a three-dimensional mathematical representation of the articular surfaces. Methods include describ- ing the articular surfaces using a combination of geometric primitives such as spheres, cones, and cylinders,4-7,116,125,136,137 describing each of the articular surfaces by a separate polynomial function of the form y = y (x, z),21,23,75 and describing the articular surfaces utilizing the piecewise continuous parametric bicubic Coons patches. Kinematic models describe and establish relations between motion parameters of the knee joint. They do not, however, relate these motion parameters to the loading conditions. Since the knee is a highly compliant structure, the relations between motion parameters are heavily dependent on loading condi- tions making each of these models valid only under a specific loading condition. Kinetic models try to remedy this problem by relating the knee’s motion parameters to its loading condition. Quasi-static models determine forces and motion parameters of the knee joint through solution of the equilibrium equations, subject to appropriate constraints, at a specific knee position. This procedure is repeated at other positions to cover a range of knee motion. Quasi-static models are unable to predict the effects of dynamic inertial loads which occur in many locomotor activities; as a result, dynamic models have been developed.

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Acute lacunar infarct of the basal ganglia Key Concept/Objective: To understand the pathogenesis of acute expressive aphasia and that expressive aphasia in the absence of other neurologic findings may be mistaken for confusion This patient presents with what the family described as an acute confusional episode purchase levitra 10 mg on-line, but on examination by the medical team effective 10 mg levitra, she was noted to be able to follow commands buy levitra 20 mg low cost. Her past history is essentially unremarkable discount levitra 20 mg on line, and she is on no medications and has no con- vincing evidence of a systemic or local infectious process generic levitra 20mg on-line. The major findings on her clin- ical examination are probable atrial fibrillation and expressive aphasia in the absence of other neurologic symptoms. This patient has almost assuredly experienced a thromboem- bolism to the speech area of the left temporal lobe, caused by her atrial fibrillation. An 85-year-old man presents to the emergency department after being found with a diminished level of consciousness and dense left facial and left upper extremity paresis. Examination reveals a blood pres- sure of 162/90 mm Hg and a normal heart rate and rhythm. His physical examination confirms the 12 BOARD REVIEW above findings. Carotid Doppler examination reveals minimal atherosclerotic narrowing. An echocar- diogram reveals minimal left ventricular hypertrophy and no intra-atrial or intraventricular thrombus. Serologic studies reveal a normal sedimentation rate of 32 mm/hr, a positive rapid plasma reagin (RPR) agglutination test at a titer of 1:8, and a positive fluorescent treponemal antibody (FTA) test. What is the best step to take next in the management of this patient? Obtain cerebrospinal fluid for VDRL (Venereal Disease Research Laboratories) test C. Begin antihypertensive therapy Key Concept/Objective: To understand that an imaging study of the brain is necessary in the acute phase of a cerebrovascular accident (CVA) to differentiate an intracerebral bleed from thrombosis This patient was found to have a dense hemifacial and left upper extremity hemiparesis. His examination and ancillary studies failed to reveal an obvious arterial or cardiac source of an embolism. His elevated blood pressure is a normal finding in the acute phases of a CVA and generally should not be specifically treated unless (1) the patient is a candidate for thrombolytic therapy; (2) it is after hemorrhagic conversion of the infarct; (3) the patient has an aortic dissection; or (4) the patient has hypertensive encephalopathy. This patient had a positive RPR and FTA, which suggests a prior syphilitic infection and raises the possibility that his CVA was caused by meningovascular syphilis. However, before treatment is begun or the diagnosis is confirmed with a lumbar puncture, a head imaging study is necessary to exclude hemorrhage as the etiology of his symptoms. A 32-year-old woman presents with a sudden onset of right-sided hemiparesis and headache. She has no history of cardiovascular or neurologic disease and was well before the onset of her symptoms. Her examination reveals a normal blood pressure and pulse. Her heart and lung examinations are normal, and her neurologic exami- nation confirms the above findings. Laboratory studies reveal a sedimentation rate of 20 mm/hr, a nor- mal comprehensive profile, and a negative urinary drug screen. Antinuclear antibody test was positive at 1:40 dilution, and her anti-dsDNA (double-stranded DNA) was negative. Imaging studies of her brain reveal acute ischemic transformation of her left temporal-parietal region. What is the best step to take next in the management of this patient? Administration of high-dose intravenous corticosteroids Key Concept/Objective: To know that carotid dissection is a cause of acute CVA in young adults This is a case of a CVA occurring in a young, otherwise healthy female. In such cases, illic- it drug use should be considered as a potential contributing factor, but in this case, it is essentially ruled out by the lack of confirmatory history or urinary drug screen. A vasculi- tis, perhaps secondary to a systemic process such as SLE, should be considered. This patient’s sedimentation rate is normal, and her ANA is nonspecific and low. However, the absence of any illness preceding the onset of her symptoms decreases the probability of a systemic inflammatory process. Visual evoked potentials and CSF analysis would be rec- ommended if multiple sclerosis were a serious possibility.

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It typically presents in infancy levitra 10 mg with mastercard; patients have photosensitivity buy cheap levitra 10mg online, hypertrichosis purchase levitra 10 mg amex, hemolytic anemia cheap 10 mg levitra, and ery- throdontia proven levitra 20mg. Treatment is aimed at protection from sun damage, decreasing hemolysis, increasing red blood cell production, or curing the disorder. Avoidance of sunlight and administration of β-carotene can help prevent photosensitivity reactions. Red blood cell transfusion has been helpful transiently in decreasing hemolysis and erythropoiesis, and bone marrow transplantation is curative. Vitamin B12 supplementation has not been successful in the treatment of congenital erythropoietic porphyria. She states that her symptoms are identical to those she experiences during acute attacks of AIP. Which of the following, if found, is NOT consistent with an acute attack of AIP? Seizure Key Concept/Objective: To know the symptoms of attacks of AIP AIP is an autosomal dominant disorder caused by a deficiency in porphobilinogen deaminase. Its course tends to be marked by asymptomatic periods that are interrupt- ed by acute attacks. These attacks are marked by severe abdominal complaints, includ- ing pain, which may be localized or generalized; nausea; vomiting, and bowel distur- bances. Urinary complaints, tachycardia, hypertension, fever, and tremor are also com- mon. Neurologic symptoms can include weakness, peripheral neuropathy, and seizure, particularly in patients with coexisting hyponatremia. In severe cases, the urine may be the color of port wine because of the accumulation of porphobilin. Unlike most other porphyrias, no cutaneous manifestations are associated with this enzyme deficiency. A 26-year-old woman with known AIP is brought to the hospital with abdominal pain after using nar- cotic analgesics after a tooth extraction. On examination, she is found to have fever, tachycardia, hyper- tension, and tremor. Urinalysis shows the urine to be deep red in color; there is no evidence of red blood cells. Soon after admission to the hospital for treatment, the patient suffers a generalized tonic-clonic seizure. Intravenous hematin Key Concept/Objective: To understand the treatment of an attack of AIP This patient appears to be suffering a severe attack of AIP. Treatment of her attack is aimed at eliminating or avoiding any inciting factors; achieving appropriate volume resuscitation with attention to sodium disorders; maintaining adequate nutrition, par- ticularly carbohydrates; and temporarily blocking porphyrin synthesis. Thus, intra- venous administration of fluid with both sodium chloride and dextrose is appropriate, as is identification and treatment of infection. Hematin, an inhibitor of porphyrin syn- thesis, is also effective in stopping acute attacks. However, phenobarbital is a potent inducer of the hepatic cytochrome P-450 system, which stimulates heme synthesis; this is a precipitating factor. A 45-year-old man with a long history of heavy alcohol ingestion presents with vesicles on sun-exposed areas of his body, particularly the dorsum of his hands. Some areas have become atrophic and hyper- pigmented. Which of the following laboratory findings would be consistent with a diagnosis of porphyria cutanea tarda (PCT) for this patient? Urinary fluorescence under infrared light Key Concept/Objective: To understand the laboratory tests used to diagnose PCT PCT is probably the most common of the porphyrias. It manifests as vesicle formation in sun-exposed areas, particularly the dorsum of the hands, followed by scarring and hyperpigmentation. It is frequently associated with liver abnormalities. PCT results from an inherited or acquired deficiency in uroporphyrinogen decarboxylase; the acquired form is frequently associated with excessive alcohol ingestion and iron over- load. Therefore, the serum ferritin level is typically elevated.

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In the absence of side effects and contraindi- cations buy cheap levitra 20 mg, beta-blocker therapy should be continued indefinitely purchase 20mg levitra visa. A 56-year-old man presents to the emergency department with complaint of chest pain of 20 minutes’ duration generic levitra 20mg amex. The pain is severe buy levitra 20mg with visa, crushing discount 20 mg levitra otc, substernal, and without radiation. He has associated nausea and diaphoresis without vomiting. He has had no previous episodes of chest discomfort. He has not seen a doctor for over 20 years and takes no medications. He has smoked two packs of cigarettes a day for the past 35 years and has lived a sedentary lifestyle. His family history is remarkable for an MI in his father at 49 years of age. Physical examination reveals a thin man, sitting upright, breathing rapidly on 2 L of 22 BOARD REVIEW oxygen. His vital signs include the following: temperature, 98. Cardiac examination reveals normal rate and rhythm without murmur, and neck veins are not elevated. ECG shows normal sinus rhythm with occasional premature ventricular contractions and ST segment elevations of 0. Which of the following interventions is NOT indicated for this patient at this time? Streptokinase Key Concept/Objective: To understand the initial management of acute MI This patient meets criteria for acute MI with a characteristic history and ECG changes. Emergent therapy should include oxygen, aspirin, analgesia, nitrates, beta blockers, and early reperfusion. The prophylactic administration of antiarrhythmic agents in the absence of significant arrhythmias does not reduce mortality and may actually increase mortality through increased incidence of bradyarrhythmias and asystole. The patient in Question 38 receives thrombolytic therapy with streptokinase within 30 minutes of the onset of his chest pain. Soon after administration of streptokinase, the ECG changes revert to baseline. He is monitored on telemetry for 48 hours without any arrhythmias. He is able to walk around the ward without difficulty. Further diagnostic tests during the immediate discharge period should include which of the following? Low-level exercise treadmill test at 1 week post-MI ❏ E. Symptom-limited exercise treadmill test at 1 week post-MI Key Concept/Objective: To understand the post-MI risk-stratification strategies The utility of cardiac catheterization post-MI has not been extensively studied, and pat- terns of practice vary widely. In the setting of a patient with acute MI who has successful- ly been treated with thrombolytic agents, the utility of post-MI catheterization has been studied in two clinical trials and has been found not to reduce the risk of reinfarction or death. The recommendation of the American College of Cardiology/American Heart Association is to use a submaximal exercise test at 5 to 7 days or a symptom-limited exer- cise test at 14 to 21 days. The stress echocardiogram and nuclear imaging are to be used in patients who are unable to exercise or in those whose baseline ECG has abnormalities, such as left bundle branch block or left ventricular hypertrophy with strain, that preclude interpretation of a stress test. The symptom-limited exercise treadmill test is recommend- ed not in the immediate postdischarge period but at 3 to 6 weeks. Coronary angioplasty following positive exercise treadmill tests has been shown to improve the rates of nonfa- tal MI and unstable angina in the Danish Acute Myocardial Infarction (DANAMI) study. A 72-year-old woman is seen by her primary care physician. She reports 5 days of shortness of breath on exertion. Five days ago, she reported having several hours of chest discomfort, which she ascribed to indigestion, and did not seek medical attention.

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