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1. General Principles & Basic Science MCQs

Practice Set 52 of 789

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 1021

Topic: 1. General Principles & Basic Science

Which of the following describes the mechanism of action of baclofen:

. Baclofen mimics the effect of gamma-aminobutyric acid (GABA).
. Baclofen blocks the effect of GABA.
. Baclofen binds to actylcholine receptors.
. Baclofen potentiates the effect of actylcholine.
. Baclofen inhibits serotonin reuptake.

Correct Answer & Explanation

. Baclofen mimics the effect of gamma-aminobutyric acid (GABA).

Explanation

Baclofen mimics the effect of gamma-aminobutyric acid, an inhibitory neurotransmitter in both the peripheral and central nervous system. Baclofen reduces peripheral spasticity. A major side effect of baclofen is sedation. The ratio of sedation to spasticity reduction may be enhanced by intrathecal administration.

Question 1022

Topic: 1. General Principles & Basic Science

Using a 5° angle trunk rotation (ATR) as a positive screening threshold for detection of curves with a C obb angle over 20° is characterized by:

. A high degree of sensitivity and specificity
. A high degree of sensitivity but low specificity
. A high degree of specificity but low sensitivity
. A low degree of sensitivity and specificity
. No predictable relationship to C obb angle

Correct Answer & Explanation

. A high degree of sensitivity but low specificity

Explanation

Use of a 5° ATR threshold for detection of curves with a Cobb angle over 20° has a sensitivity of 98%, but a specificity of only 64%.

Question 1023

Topic: Infection, Pharmacology & VTE

Which of the following is the most common cause of death in children with pelvic fractures:

. Intrapelvic exsanguination
. Head injury
. Pulmonary embolism
. Multisystem organ failure
. Spinal cord injury

Correct Answer & Explanation

. Head injury

Explanation

Head injury is the cause of virtually all mortality in children with pelvic fractures. The rarity of life-threatening intrapelvic hemorrhage is in marked contrast to adults. Pulmonary embolism and multisystem organ failure are rare in children.

Question 1024

Topic: 1. General Principles & Basic Science

Which of the following statements best characterizes a Dega osteotomy as a distinct osteotomy from a Salter osteotomy:

. The Dega osteotomy is stabilized by threaded pins.
. The Dega osteotomy lengthens the ipsilateral limb.
. The Salter osteotomy hinges upon the triradiate cartilage.
. The Dega osteotomy hinges upon the medial pelvic cortex.
. The Dega osteotomy should only be done after triradiate cartilage closure.

Correct Answer & Explanation

. The Dega osteotomy hinges upon the medial pelvic cortex.

Explanation

The Dega osteotomy, originally described in Poland in 1964, is an incomplete transiliac osteotomy. The medial pelvic cortex is largely preserved, and the osteotomy hinges upon this point. Both osteotomies are best performed in young children, before triradiate cartilage closure. The Salter osteotomy is stabilized by pins, so the Dega needs no internal fixation. The Salter osteotomy lengthens the limb because it is a complete osteotomy.

Question 1025

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacological treatment for Giant Cell Tumor of bone. What is its specific mechanism of action?

. Inhibits matrix metalloproteinases in the tumor microenvironment
. Binds to RANKL, preventing it from activating the RANK receptor on osteoclast precursors
. Directly induces apoptosis of the neoplastic stromal cells
. Acts as a synthetic analog of osteoprotegerin to stimulate osteoblast activity
. Inhibits the SMAD intracellular signaling pathway

Correct Answer & Explanation

. Binds to RANKL, preventing it from activating the RANK receptor on osteoclast precursors

Explanation

Denosumab is a monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents RANKL from binding to the RANK receptor, thereby inhibiting the recruitment and activation of osteoclast-like giant cells in the tumor.

Question 1026

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic protein-2 (BMP-2) enhances spinal fusion through which of the following cellular mechanisms?

. Direct osteogenesis via transplantation of viable osteoprogenitor cells
. Osteoconduction by providing a porous structural scaffold
. Osteoinduction via activation of the intracellular SMAD signaling cascade
. Inhibition of osteoclastic bone resorption via RANKL blockade
. Stimulation of primarily endochondral ossification without an inflammatory phase

Correct Answer & Explanation

. Osteoinduction via activation of the intracellular SMAD signaling cascade

Explanation

BMP-2 is a potent osteoinductive protein that binds to cell surface serine/threonine kinase receptors on mesenchymal stem cells. This binding activates the intracellular SMAD signaling pathway, driving the differentiation of these cells into functioning osteoblasts.

Question 1027

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage is characterized by the lowest water content, the highest concentration of proteoglycans, and collagen fibers oriented perpendicular to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage has the highest proteoglycan concentration and the lowest water content, with collagen fibers running vertically to resist compressive forces. Conversely, the superficial zone has the highest water content and lowest proteoglycan concentration.

Question 1028

Topic: Biomechanics & Biomaterials

Articular cartilage is divided into distinct zones. Which of the following best describes the organization of collagen fibers in the superficial (tangential) zone?

. Oriented perpendicular to the joint surface to resist shear stress
. Oriented parallel to the joint surface to resist shear stress
. Oriented obliquely to resist compressive forces
. Randomly oriented to provide isotropic strength
. Arranged in a radial pattern to anchor cartilage to subchondral bone

Correct Answer & Explanation

. Oriented parallel to the joint surface to resist shear stress

Explanation

In the superficial zone, collagen fibers are packed tightly and oriented parallel to the articular surface. This arrangement is highly specialized to resist shear stresses and provide a low-friction gliding surface.

Question 1029

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) initiate intracellular signaling leading to osteoblast differentiation primarily through which of the following pathways?

. Wnt/beta-catenin pathway
. JAK-STAT pathway
. Smad 1/5/8 pathway
. MAPK/ERK pathway
. Notch signaling pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, which phosphorylate Smad 1, 5, and 8. These receptor-regulated Smads then form a complex with Smad 4 to enter the nucleus and regulate the transcription of osteogenic genes.

Question 1030

Topic: Surgical Anatomy & Approaches

When planning a tendon transfer procedure for a patient with radial nerve palsy, the surgeon must consider muscle mechanics. Muscle excursion is primarily determined by which of the following characteristics?

. Physiological cross-sectional area
. Muscle fiber length
. Tendon length
. Pennation angle
. Motor unit ratio

Correct Answer & Explanation

. Muscle fiber length

Explanation

Muscle excursion, which is the distance a muscle can contract, is proportional to the length of its resting muscle fibers. In contrast, a muscle's force-generating capacity is determined by its physiological cross-sectional area.

Question 1031

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft or bone graft substitute materials simultaneously possesses osteoinductive, osteoconductive, and osteogenic properties?

. Demineralized bone matrix (DBM)
. Cancellous allograft
. Autologous iliac crest bone graft
. Calcium phosphate cement
. Recombinant human BMP-2

Correct Answer & Explanation

. Autologous iliac crest bone graft

Explanation

Autologous bone graft, such as from the iliac crest, is considered the gold standard because it provides all three properties necessary for bone healing. It supplies an osteoconductive scaffold, osteoinductive growth factors, and live osteogenic progenitor cells.

Question 1032

Topic: 1. General Principles & Basic Science

The most common form of chondrodysplasia punctata is much more common in girls than in boys. Which of the following explains this:

. Autosomal dominant inheritance
. X-linked dominant inheritance
. X-linked recessive inheritance
. Autosomal recessive inheritance
. The imprinting phenomenon

Correct Answer & Explanation

. X-linked dominant inheritance

Explanation

X-linked dominant inheritance would explain the preponderance of girls with this condition, because they have twice as great a chance of having an affected x-chromosome. One affected x-chromosome is sufficient to convey the disease in a dominant condition. The imprinting phenomenon refers to a condition that varies depending upon whether the mother or the father passed it on (as in Angelman versus Prader-Willi syndromes).

Question 1033

Topic: 1. General Principles & Basic Science

The most accurate and practical means of determining pregnancy status in adolescent females undergoing surgery is:

. Self report
. Morning urine human chorionic gonadotropin (HC G)
. Serum HC G
. Serum alpha fetoprotein
. Serum estrogen levels

Correct Answer & Explanation

. Morning urine human chorionic gonadotropin (HC G)

Explanation

Anesthesia and surgery can be detrimental to a fetus, especially during the first trimester. Patient self-report is not accurate in many cases. Immunospot testing of the first morning urine for human chorionic gonadotropin is 99.4% sensitive and specific, rapid, and inexpensive. Serum HC G testing is less rapid and more expensive; therefore, not appropriate for surgical screening. The other tests are not used to ascertain pregnancy status.

Question 1034

Topic: 1. General Principles & Basic Science

Becker muscular dystrophy is due to a defect in the gene for which of the following:

. Dystrophin
. Sarcoglycan
. Myelin
. Sulfate transport
. Fibroblast growth factor receptor

Correct Answer & Explanation

. Dystrophin

Explanation

Becker muscular dystrophy has a defect in the same gene as Duchenne muscular dystrophy, namely the protein dystrophin. The mutation in Becker dystrophy results in a truncated protein that retains some function, whereas the mutation in Duchenne dystrophy is different and results in an unstable protein, which is degraded quickly.

Question 1035

Topic: 1. General Principles & Basic Science

Electrodiagnostic testing in myopathies typically shows all of the following except:

. Low amplitude electromyogram (EMG) potentials
. Polyphasic EMG potentials
. Normal nerve conduction velocity
. Decreased duration of EMG response
. Fibrillation potentials

Correct Answer & Explanation

. Polyphasic EMG potentials

Explanation

Electrodiagnostic testing in myopathy typically shows low amplitude, polyphasic EMG potentials with a decreased duration of response. Nerve conduction velocity is normal, in contrast to findings in neuropathies. Fibrillations are not typically seen; these are more characteristic of neuropathy.

Question 1036

Topic: Physiology & Rehabilitation

Which of the following skeletal dysplasias is not commonly associated with non-orthopedic complications:

. McKusick metaphyseal chondrodysplasia
. Hurler syndrome
. Morquio syndrome
. C hondroectodermal dysplasia
. Multiple epiphyseal dysplasia

Correct Answer & Explanation

. Multiple epiphyseal dysplasia

Explanation

McKusick dysplasia is commonly associated with immune and gastrointestinal disorders. Hurler syndrome is associated with progressive mental retardation, hepatosplenomegaly, and cataracts. Morquio syndrome is associated with cardiorespiratory difficulties. C hondroectodermal dysplasia, or Ellis van C reveld syndrome, is associated with congenital heart disease. Multiple epiphyseal dysplasia, however, is not associated with systemic non- orthopaedic complications.

Question 1037

Topic: Infection, Pharmacology & VTE

Which of the following by itself is not an indication for surgery in a child with acute hematogenous osteomyelitis:

. Fever higher than 38.5°
. Subperiosteal abscess
. Presence of a sequestrum
. Intramedullary abscess
. Adjacent septic arthritis

Correct Answer & Explanation

. Fever higher than 38.5°

Explanation

Surgery is indicated in situations in which antibiotics alone will not be curative, including subperiosteal abscess, sequestrum, intramedullary abscess, and adjacent septic arthritis. Fever alone is not an indication for surgery.

Question 1038

Topic: Infection, Pharmacology & VTE

Which of the following is not usually seen in chronic recurrent multifocal osteomyelitis:

. Positive cultures for Staphylococcus epidermidis
. Gradual onset of symptoms
. Involvement of the spine, long bones, and feet
. Negative cultures
. Improvement with nonsteroidal anti-inflammatory agents

Correct Answer & Explanation

. Negative cultures

Explanation

Chronic recurrent multifocal osteomyelitis is believed to be an idiopathic noninfectious inflammatory disease. It has gradual onset of symptoms, and sites most commonly involved are the spine, long bones, and feet. Nonsteroidal anti-inflammatory drugs typically improve symptoms. Cultures are negative.

Question 1039

Topic: Biology, Genetics & Bone Healing

Core binding factor alpha 1 (C bfa1) is a transcription factor having which of the following effects:

. Cbfa1 induces cells to differentiate into osteoblasts.
. Cbfa1 induces cells to differentiate into osteoclasts.
. Cbfa1 inhibits endochondral ossification.
. Cbfa1 impairs sulfation of proteoglycans.
. Cbfa1 causes premature cell death.

Correct Answer & Explanation

. Cbfa1 induces cells to differentiate into osteoblasts.

Explanation

Cbfa1 is a transcription factor that causes cells to differentiate into osteoblasts. An abnormality in its gene causes cleidocranial dysplasia.

Question 1040

Topic: Biology, Genetics & Bone Healing

Which of the following statements best describes the mechanism of primary (direct) bone healing?

. Healing occurs via a cartilaginous intermediate
. It requires an absolute gap of at least 2mm
. It is mediated by cutting cones crossing the fracture site
. It forms a robust peripheral callus
. It is enhanced by micromotion at the fracture site

Correct Answer & Explanation

. It is mediated by cutting cones crossing the fracture site

Explanation

Primary bone healing occurs under conditions of absolute stability and no fracture gap. It utilizes Haversian remodeling where osteoclasts create cutting cones followed by osteoblasts, circumventing callus formation.

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