This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.
Question 3541
Topic: 1. General Principles & Basic Science
Pharmacoprophylaxis should be avoided in favor of a pneumatic compression device for a patient with which of the following conditions?
Correct Answer & Explanation
. factor VIII deficiency.
Explanation
For patients with known bleeding disorders, a pneumatic compression device alone is recommended over pharmacoprophylaxis to minimize risk for excessive bleeding and wound complications. Factor VIII deficiency (hemophilia) and active liver disease are the 2 conditions for which support is strongest to withhold anticoagulation.
Question 3542
Topic: Biology, Genetics & Bone Healing
A cartilage water content increase is the hallmark of which osteoarthritis stage?
Correct Answer & Explanation
. Prearthritis
Explanation
The first stage of osteoarthritis is marked by an increase in water content secondary to disruption of the matrix framework. This is followed by an increase in chondrocyte anabolic and catabolic activity in response to tissue damage. Wnt-induced signal protein 1 increases chondrocyte protease expression. Failure to restore tissue balance ultimately leads to continued destruction and osteoarthritis. One hallmark of osteoarthritic cartilage is a reduced repair mechanism attributable to decreased chondrocyte response to growth factor stimulation (transforming growth factor-alpha and insulin-like growth factor-1). Mitochondrial dysfunction and increased production of reactive oxygen species may promote cell senescence, a progressive slowing of cellular activity. Microscopic evidence of cartilage degeneration begins with fibrillation of the superficial and transition zones, followed by disruption of the tidemark by subchondral blood vessels and eventual subchondral bone remodeling. This process ultimately leads to cartilage degradation with decreased water content in the late and terminal phases of osteoarthritis.
Question 3543
Topic: 1. General Principles & Basic Science
A patient reports a sudden recurrence of sciatica on her left side after undergoing a successful left L4-L5 diskectomy 15 months ago. Which of the following imaging modalities is most accurate in differentiating recurrence of the disk herniation from postoperative epidural scar tissue?
Correct Answer & Explanation
. Myelography
Explanation
The main complication of recurrence at the same level is the presence of scar tissue from the previous operation. In addition to a careful history and physical examination, contrast-enhanced MRI is useful for differentiating scar from reherniation. MRI has become the test of choice for assessing degenerative or herniated disks-even over that of CT. Answer #1 is incorrect because it will only provide information of cord or nerve root encroachment, not thecause of the encroachment. Answer #2 makes no sense. Answers #3 and #4 are incorrect because the MRI is now the standard imaging modality.
Question 3544
Topic: Biology, Genetics & Bone Healing
A 63-year-old man has had increasing left leg pain over the last several months. History reveals that he has had recurring cyclic pain in the leg for the past several years. Radiographs show an enlarged, sclerotic tibia, with thickened coarse trabeculae and varus bowing. What is the most appropriate management for this patient? Review Topic
Correct Answer & Explanation
. Vitamin D
Explanation
Based on the signs and symptoms, Paget's disease is the most likely diagnosis. In Paget's disease, an elevated alkaline phosphatase level and high output heart failure may be seen. Hearing loss can be seen when there is involvement of the skull, and malignant degeneration is uncommon but recognized as a risk. Patients are often treated with bisphosphonate medications during the active disease process to help control osteoclastic activity and pain. Vitamin D and calcium are more appropriate for treatment of osteoporosis. Methotrexate is not indicated for the treatment of Paget's disease. NSAIDs may be helpful to treat pain associated with Paget's disease but will not alter the clinical course.
Question 3545
Topic: 1. General Principles & Basic Science
An orthopaedic surgeon frequently uses hip and knee prostheses from a specific manufacturer. The surgeon becomes acquainted with the manufacturer’s representative who provides the support for these prostheses in the hospital. They develop a personal relationship outside of work through a common interest in sailing. Together they become interested in buying a sailboat. The manufacture’s representative suggests a partnership in a boat costing $200,000. The manufacture’s representative would purchase a 90% interest and the surgeon a 10% interest in the boat. There would be no restrictions on use of the boat by the surgeon. What should the orthopaedic surgeon do?
Correct Answer & Explanation
. Accept the offer because it would allow the physician to have a boat and enjoy a hobby of sailing with a minimal financial outlay.
Explanation
Rejecting this proposal is the only appropriate course of action. Accepting it would, in essence, be receiving a huge gift from industry in the form of a sailboat. Physicians frequently assert that they are not influenced by gifts and relationships with industry representatives, but evidence is to the contrary. Such an arrangement constitutes a tremendous incentive to use the manufacturer’s products. The fact that the boatpartnership seems completely outside of the orthopaedic business relationship does not excuse it. Conflicts of interest should always be resolved and in the best interest of patient care, and in this case the best course clearly is to avoid the conflict of interest totally. An equal interest in the boat does not eliminate the conflict of interest.
Question 3546
Topic: 1. General Principles & Basic Science
What assay most directly assesses gene expression at the posttranslational level?
Correct Answer & Explanation
. Western blot
Explanation
Gene expression at the posttranslational level refers to proteins, as opposed to DNA or RNA. The only assay above that targets protein expression directly is the Western blot. Standard PCR is amplification of targeted DNA segments, regardless of whether or not they are actively expressed. Real-time PCR, Northern blot, and microarray expression profile analysis all quantify RNA as a means to determine posttranscriptional gene expression.
Question 3547
Topic: Biomechanics & Biomaterials
In a fatigue test, the maximum stress under which the material will not fail, regardless of how many loading cycles are applied, is defined as
Correct Answer & Explanation
. Endurance limit
Explanation
Fatigue failure occurs with repetitive loading cycles at stress below the ultimate tensile strength. Fatigue failure depends on the magnitude of the stress and number of cycles. If the stress is less than a predetermined amount of stress, called the endurance limit, the material may be loaded cyclically an infinite number of times without breaking.
Question 3548
Topic: 1. General Principles & Basic Science
A 52-year-old man who weighs 325 lb is wheelchair-bound from severe degenerative arthritis of the left hip. Twenty-four hours after cementless total hip arthroplasty, he develops shortness of breath and evaluation shows a saddle pulmonary embolus. The patient is started on enoxaparin sodium at 150 mg every 12 hours. Two days later, the patient’s hematocrit is 20% despite four units of transfused packed cells, and he now has developed a complete sciatic nerve palsy. What is the best course of action?
Correct Answer & Explanation
. Placement of a vena cava filter, halt anticoagulation, blood transfusion, and exploration of the sciatic nerve
Explanation
The purpose of this question is to draw attention to the early risks of therapeutic anticoagulation that will be instituted by an intensivist or pulmonologist to treat a life-threatening pulmonary embolus. The temporary vena cava filter is a recent innovation but will effectively reduce the risk of further pulmonary emboli. This requires reversal of anticoagulation for safe insertion of the filter and creates a safe situation for additional surgical solutions. Sciatic nerve compromise was caused by the expanding hematoma in this patient, which could be mitigated by exploration both to assess the nerve and to remove a large hematoma that presents its own long-term risks.
Question 3549
Topic: 1. General Principles & Basic Science
A deficiency of which of the following is associated with an increased risk of venous thromboembolism?
Correct Answer & Explanation
. Protein S
Explanation
Protein C and Protein S are endogenous proteins whose action is to inhibit the coagulation cascade. Deficiencies in these proteins are a risk factor for the development of thrombus. Prothrombin is the precursor to thrombin, which is the final common pathway for both the intrinsic and extrinsic coagulation cascade. Thrombin acts to convert fibrinogen to fibrin and thus clot formation.
Question 3550
Topic: Biology, Genetics & Bone Healing
Bone morphogenetic proteins transduce intracellular signal through what class of cell surface receptor?
Correct Answer & Explanation
. Mitogen-activated protein kinase
Explanation
Bone morphogenetic proteins (BMPs) are extracellular proteins belonging to the TGF-beta superfamily of molecules. Members of this family include BMPs, growth and differentiation factors (GDFs), anti-mnllerian hormone (AMH), activin, Nodal, and TGF-beta. These proteins exert their action by binding to cell surface receptors of the serine-threonine kinase class to activate intracellular signaling pathways. The other kinase participate in various cell signaling functions, but are not associated with BMP.
Question 3551
Topic: Biology, Genetics & Bone Healing
Bisphosphonates are indicated in the treatment of osteoporosis in patients who have a DEXA T-score of
Correct Answer & Explanation
. less than -1.
Explanation
DISCUSSION: Bisphosphonates are indicated in the treatment of osteoporosis. They have been shown to reduce the incidence of vertebral and extremity fractures in patients with a T-score of less than -1. REFERENCE: Gass M, Dawson-Hughs B: Preventing osteoporosis-related fractures: An overview. Am J Med 2006;119:S3-S11.
Question 3552
Topic: Biology, Genetics & Bone Healing
Figures 150a through 150d are the radiographs and MR images of a 37-year-old woman who has a 3-month history of severe right hip pain. She does not recall any trauma prior to the pain onset and denies any past steroid exposure. She has 3 children and is not currently pregnant. The pain is located in her groin and the onset was sudden. The pain is refractory to anti-inflammatory medications. What is the most appropriate treatment?
Correct Answer & Explanation
. Toe-touch weight-bearing activity and supportive care
Explanation
DISCUSSIONThe patient’s MR images are consistent with transient hip osteoporosis. No signs suggest avascular necrosis. She has no joint narrowing. Transient osteoporosis of the hip is characterized by bone marrow edema in the femoral head and neck. This condition affects more men than women and is sometimes seen in the third trimester of pregnancy but can be seen in women who are not pregnant as well. This is a self-limiting condition, and the treatment is limited weight-bearing activity until the symptoms resolve. Core decompression is rarely used in these cases. There is no indication for arthroplasty or osteotomy in this scenario.
Question 3553
Topic: 1. General Principles & Basic Science
What factor is considered one of the early changes in osteoarthritic cartilage?
Correct Answer & Explanation
. Increased cartilage tissue permeability
Explanation
The normal regulation of a cartilage surface is a delicate balance of degradation and synthesis. When this normal regulation of the cartilage is disturbed, a proinflammatory state tips the cellular pathway in the direction of degradation. The proinflammatory state upregulates the production of cytokines and proteolytic enzymes, specifically matrix metalloproteinases. These enzymes attack the proteoglycan content of the cartilage, leading to an overall reduction in the proteoglycan content. This reduction in content leads to increased permeability of the cartilage substrate. With increased permeability, water is able to move into the cartilage itself, thereby increasing the overall water content within the cartilage in an arthritic state. Finally, because of the increased permeability and increased water content, the overall load or pressure placed on the underlying solid matrix is increased. Increased water content, decreased proteoglycan content, and an increased load on the solid matrix are typical of an osteoarthritic process within normal cartilage. Therefore, the only correct option is that the cartilage has an increased amount of permeability in osteoarthritis.
Question 3554
Topic: 1. General Principles & Basic Science
Staphylococcus aureus develops methicillin resistance through production of which of the following agents?
Correct Answer & Explanation
. Penicillin-binding protein 2a
Explanation
DISCUSSION: Organisms may develop resistance to antibiotics by production of specific enzymes. S. aureus develops methicillin resistance by production of penicillin-binding protein 2a (PBP2a). The strains of S. aureus that have acquired the mecA gene for PBP2a are designated as methicillin-resistant S. aureus (MRSA). The enzyme manifests resistance to covalent modification by beta-lactam antibiotics at the active-site serine residue in two ways. First, the microscopic rate constant for acylation (k2) is attenuated by three to four orders of magnitude over the corresponding determinations for penicillin-sensitive PBPs. Second, the enzyme shows elevated dissociation constants (Kd) for the noncovalent preacylation complexes with the antibiotics, the formation of which ultimately would lead to enzyme acylation. The two factors working in concert effectively prevent enzyme acylation by the antibiotics in vivo, giving rise to drug resistance. Catalase and oxidase are enzymes produced by some bacteria that confer virulence to the organism but do not make the organisms methicillin resistant. Glycocalix is the pericellular layer produced by bacteria that serves many functions including attachment to surfaces. Beta-lactam describes a class of antibiotics.
Question 3555
Topic: Physiology & Rehabilitation
The nucleus pulposus of the intervertebral disk consists of chondrocyte-like cells that have a limited vascular supply and generate energy through which of the following?
Correct Answer & Explanation
. Anaerobic glycolysis
Explanation
The intervertebral disk is an avascular structure in the adult. Nucleus pulposus cells have a critical need for glucose because they obtain their energy primarily by glycolysis, even in the absence of oxygen. Disk cells do not require oxygen to remain alive but they die at low glucose levels or acidic pH. Nutrients are supplied from the blood vessels at the margins of the disk and have to traverse the cartilaginous end plate to reach the disk cells. The loss of the nutrient supply through the vertebral body will starve the cells in the disk center and may be a major factor in disk degeneration.
Question 3556
Topic: Biology, Genetics & Bone Healing
A 3-year-old child has bilateral genu varum and short stature. Radiographs show physeal widening and generalized osteopenia. The femora and tibiae show anterolateral bowing. Laboratory studies show low normal serum calcium values, significantly decreased serum phosphate levels, and normal parathyroid hormone (PTH), alkaline phosphatase, and vitamin-D levels. These findings are consistent with
Correct Answer & Explanation
. vitamin D-resistant rickets.
Explanation
DISCUSSION: Children with vitamin D-resistant rickets are short in stature and have genu varum, physeal widening, and generalized osteopenia. The abnormality in inherited vitamin D-resistant rickets is the renal tubule’s inability to resorb phosphate leading to hypophosphatemia. Laboratory findings in the condition are normal or near normal serum calcium values, significantly decreased serum phosphate levels, elevated alkaline phosphatase levels, and normal PTH and vitamin-D levels. The most common form is inherited as an X-linked dominant trait. Nutritional rickets has a normal or low serum phosphate levels, normal or low serum calcium values, and decreased levels of 25(OH) vitamin D and 1,25-dihydroxyvitamin D. Hypophosphatasia is a rare condition characterized by a deficiency of alkaline phosphatase in the serum and tissues, leading to generalized abnormal mineralization of bone. Primary hyperparathyroidism usually is caused by a parathyroid adenoma, and the child generally has abdominal problems and hypercalcemic crisis. Laboratory findings include elevated serum calcium values, alkaline phosphatase levels, and PTH levels, and decreased serum phosphate levels. Children with renal osteodystrophy tend to have genu valgum, and laboratory findings include elevated serum phosphate, alkaline phosphatase, and PTH levels, and low serum calcium values. Findings of renal disease include elevated BUN and creatinine.
Question 3557
Topic: 1. General Principles & Basic Science
In a patient who has had low back pain for less than 2 weeks, which of the following findings is an indication for continued observation and symptomatic treatment rather than more aggressive evaluation and/or treatment?
Correct Answer & Explanation
. Inability to participate in athletics
Explanation
DISCUSSION: An inability to participate in athletics generally is considered an indication for continued symptomatic treatment only. All of the other answers suggest the possibility of more significant pathology that may require more urgent treatment. REFERENCES: Frymoyer JW: Back pain and sciatica. N Engl J Med 1988;318:291-300. McCullough JA, Transfeldt EE: Macnab’s Backache, ed 3. Baltimore, MD, Williams and Wilkins, 1997, pp 240-357.
Question 3558
Topic: Surgical Anatomy & Approaches
The sartorius muscle is innervated by which of the following nerves?
Correct Answer & Explanation
. Femoral
Explanation
The femoral nerve enters the thigh behind the inguinal ligament, lying on the surface of the iliopsoas muscle lateral to the femoral artery and vein. The nerve divides into numerous muscular and cutaneous branches in the femoral triangle. The first motor branch (sometimes two branches) is to the sartorius. There is a variable branch to the pectineus. Subsequent branches go to the rectus femoris and then the vastus muscles in variable order. The last motor branch is to the articularis genu. The muscular branches can be injured in anterior approaches to the hip, especially the middle window of the ilioinguinal approach.
Question 3559
Topic: Biology, Genetics & Bone Healing
Figure 35 is the sagittal MR image of a 56-year-old woman who has a 3-year history of severe back pain. Her pain is worse with flexion at the lumbosacral junction and is relieved with extension. She denies any pain in her lower extremities and has no symptoms of neurogenic claudication. Which mediators play roles in the pathogenesis of this condition?
The patient has degenerative disk disease with diskogenic back pain. Several studies in both humans and animals have implicated TNF-a, IL-1, and MMP in extracellular matrix degeneration and disk degradation. TGF-ß, BMP-2, latent membrane protein 1, and growth and development factor-5 are all postulated to play anabolic roles in the intervertebral disk. Biglycan is a small leucine-rich proteoglycan that regulates extracellular matrix assembly within the disk. Noggin and gremlin are biochemical factors not involved in disk degradation.
Question 3560
Topic: 1. General Principles & Basic Science
During the first stage of osteoarthritis, which of the following processes predominates?
Correct Answer & Explanation
. Loss of articular cartilage proliferative response
Explanation
Articular cartilage degeneration and ensuing osteoarthritis can be divided into three stages. In the first stage, the water content increases and proteoglycan aggregation andaggrecan concentration are both decreased. Increased water content tends to decrease the stiffness of the matrix, rendering cartilage tissue more susceptible to further mechanical damage. In the second stage, chondrocytes detect tissue damage and respond by releasing mediators to increase proliferation. Clusters or clones of proliferating chondrocytes are hallmark of the response to articular degeneration. In the third stage, both the proliferative response and anabolic activity are decreased. In this stage, the loss of articular cartilage is more evident and leads to clinical signs of degenerative joint disease.
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