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1. General Principles & Basic Science MCQs

Practice Set 107 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 2121

Topic: 1. General Principles & Basic Science

A 9-year-old boy with Duchenne Muscular Dystrophy requires surgical release of severe lower extremity contractures. The anesthesia team avoids the use of succinylcholine during induction. This precaution prevents which of the following life-threatening complications?

. Severe anaphylactic shock
. Hyperkalemic cardiac arrest
. Hypocalcemic tetany
. Status epilepticus
. Acute fulminant hepatic failure

Correct Answer & Explanation

. Hyperkalemic cardiac arrest

Explanation

Patients with myopathies like DMD have upregulated extrajunctional acetylcholine receptors. The use of depolarizing neuromuscular blockers like succinylcholine causes massive potassium efflux from these receptors, leading to life-threatening hyperkalemia and cardiac arrest.

Question 2122

Topic: Surgical Anatomy & Approaches

A 27-year-old triathlete undergoes an isolated deep posterior compartment release for CECS using a single medial longitudinal incision. Postoperatively, he notes a burning numbness along the medial aspect of his distal lower leg and medial foot. Which nerve was most likely injured during the surgical approach?

. Sural nerve
. Superficial peroneal nerve
. Deep peroneal nerve
. Saphenous nerve
. Medial plantar nerve

Correct Answer & Explanation

. Saphenous nerve

Explanation

The saphenous nerve travels with the greater saphenous vein along the medial aspect of the leg. It is highly susceptible to iatrogenic injury during a medial approach to the leg for releasing the deep posterior compartment.

Question 2123

Topic: 1. General Principles & Basic Science

A 4-year-old boy is brought to the clinic for frequent falls, delayed motor milestones, and pseudohypertrophy of the calves. If laboratory screening is performed, which of the following serum markers is expected to be profoundly elevated as an early hallmark of his likely underlying disease?

. Alkaline phosphatase
. Creatine phosphokinase (CPK)
. Erythrocyte sedimentation rate (ESR)
. Aldolase B
. C-reactive protein (CRP)

Correct Answer & Explanation

. Creatine phosphokinase (CPK)

Explanation

Serum creatine phosphokinase (CPK) is profoundly elevated (often 10 to 100 times normal limits) in the early stages of Duchenne Muscular Dystrophy due to ongoing muscle membrane leakage and necrosis, well before significant muscle mass is lost.

Question 2124

Topic: 1. General Principles & Basic Science

Duchenne Muscular Dystrophy is caused by an X-linked recessive mutation resulting in the absence of dystrophin. In a normal muscle cell, the dystrophin protein primarily serves to link the extracellular matrix to which of the following intracellular structures?

. Myosin heavy chains
. F-actin filaments of the cytoskeleton
. The nuclear envelope
. The sarcoplasmic reticulum
. Mitochondrial outer membranes

Correct Answer & Explanation

. F-actin filaments of the cytoskeleton

Explanation

Dystrophin is a vital structural protein that anchors the intracellular F-actin cytoskeleton to the extracellular matrix via the dystrophin-associated glycoprotein complex at the sarcolemma. Its absence makes the cell membrane highly susceptible to contraction-induced damage.

Question 2125

Topic: 1. General Principles & Basic Science

In the pathogenesis of Duchenne Muscular Dystrophy, the lack of dystrophin at the sarcolemma leads to an abnormal influx of a specific ion, ultimately driving protease activation and myofiber necrosis. Which ion is primarily responsible for this intracellular damage?

. Sodium
. Potassium
. Chloride
. Calcium
. Magnesium

Correct Answer & Explanation

. Calcium

Explanation

Without dystrophin, the sarcolemma becomes fragile and leaky during muscle contraction. This allows a massive influx of extracellular calcium, which activates intracellular proteases (like calpains) and leads to myonecrosis.

Question 2126

Topic: 1. General Principles & Basic Science

A 3-year-old boy is brought to the pediatrician due to delayed motor milestones. Duchenne Muscular Dystrophy is suspected. If this diagnosis is correct, which of the following laboratory profiles is expected prior to the onset of severe clinical weakness?

. Creatine kinase (CK) levels elevated 10 to 100 times the normal limit
. Normal creatine kinase (CK) levels with elevated aldolase
. Elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
. Severe hyperkalemia and hyponatremia
. Elevated alkaline phosphatase with normal creatine kinase (CK)

Correct Answer & Explanation

. Creatine kinase (CK) levels elevated 10 to 100 times the normal limit

Explanation

In the early stages of DMD, ongoing muscle necrosis releases massive amounts of intracellular enzymes. Creatine kinase (CK) levels are characteristically elevated to 10-100 times normal values, often peaking before profound weakness appears.

Question 2127

Topic: Physiology & Rehabilitation

Becker Muscular Dystrophy (BMD) and Duchenne Muscular Dystrophy (DMD) share the same genetic locus but differ clinically. Which of the following best explains the pathophysiological difference that results in BMD having a milder clinical course?

. BMD involves an autosomal dominant mutation sparing the X chromosome.
. BMD mutations cause a complete absence of dystrophin production.
. BMD mutations result in a truncated, partially functional dystrophin protein.
. BMD selectively affects type II muscle fibers while sparing type I.
. BMD is characterized by elevated up-regulation of utrophin that fully replaces dystrophin.

Correct Answer & Explanation

. BMD mutations result in a truncated, partially functional dystrophin protein.

Explanation

DMD is caused by out-of-frame mutations leading to an almost total absence of dystrophin. BMD is caused by in-frame mutations, resulting in a shortened but partially functional dystrophin protein, yielding a milder phenotype.

Question 2128

Topic: 1. General Principles & Basic Science

A 4-year-old boy presents with progressive proximal muscle weakness and calf pseudohypertrophy. A diagnosis of Duchenne muscular dystrophy is suspected. Which of the following best describes the underlying genetic defect?

. In-frame mutation of the dystrophin gene
. Out-of-frame mutation of the dystrophin gene
. Trinucleotide repeat expansion in the DMPK gene
. Mutation in the SMN1 gene
. Mutation in the PMP22 gene

Correct Answer & Explanation

. Out-of-frame mutation of the dystrophin gene

Explanation

DMD is caused by an out-of-frame (frameshift) mutation in the dystrophin gene, resulting in absent or non-functional dystrophin. Becker MD is typically caused by an in-frame mutation resulting in a truncated but partially functional protein.

Question 2129

Topic: 1. General Principles & Basic Science

Which of the following cardiac manifestations is the most common cause of mortality in patients with Duchenne muscular dystrophy in their late teens to twenties?

. Hypertrophic cardiomyopathy
. Dilated cardiomyopathy
. Restrictive cardiomyopathy
. Arrhythmogenic right ventricular dysplasia
. Myxomatous mitral valve disease

Correct Answer & Explanation

. Dilated cardiomyopathy

Explanation

Dilated cardiomyopathy is nearly ubiquitous in patients with DMD by age 18 and is a leading cause of mortality alongside respiratory failure.

Question 2130

Topic: 1. General Principles & Basic Science

During a single-incision lateral approach to release the anterior and lateral compartments for CECS, the intermuscular septum is identified. What is the most critical technical step regarding the septum to prevent iatrogenic injury?

. Resecting the entire septum to merge the two compartments
. Identifying and protecting the deep peroneal nerve within the septum
. Identifying and protecting the superficial peroneal nerve where it exits the crural fascia or septum
. Suturing the septum to the skin to prevent hematoma
. Performing a transverse release of the septum only

Correct Answer & Explanation

. Identifying and protecting the superficial peroneal nerve where it exits the crural fascia or septum

Explanation

The superficial peroneal nerve courses in the lateral compartment and exits the crural fascia or anterior intermuscular septum in the distal third of the leg. It must be meticulously identified and protected during the release.

Question 2131

Topic: 1. General Principles & Basic Science

The absence of functional dystrophin in Duchenne muscular dystrophy leads to muscle degeneration primarily due to the loss of connection between which two cellular components?

. Myosin heavy chains and actin filaments
. The intracellular actin cytoskeleton and the extracellular matrix
. The sarcoplasmic reticulum and the T-tubule system
. Mitochondrial membranes and the nucleus
. Z-discs and M-lines

Correct Answer & Explanation

. The intracellular actin cytoskeleton and the extracellular matrix

Explanation

Dystrophin is a vital structural protein that links the intracellular actin cytoskeleton to the transmembrane dystroglycan complex, stabilizing the sarcolemma against the extracellular matrix during repeated muscle contractions.

Question 2132

Topic: Biology, Genetics & Bone Healing

During endochondral ossification, the differentiation of mesenchymal stem cells into the osteoblast lineage is highly dependent on a specific master transcription factor. A mutation in the gene encoding this factor leads to cleidocranial dysplasia. Which of the following is the correct transcription factor?

. SOX9
. RUNX2 (CBFA1)
. Osterix
. HIF-1 alpha
. Beta-catenin

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

RUNX2 (also known as CBFA1) is the essential transcription factor for osteoblast differentiation. Genetic mutations or deficiency in RUNX2 result in cleidocranial dysplasia, characterized by absent or hypoplastic clavicles and delayed skull suture closure.

Question 2133

Topic: Biology, Genetics & Bone Healing

Primary bone healing, characterized by Haversian remodeling and cutting cone formation without intermediate callus, requires which of the following mechanical environments?

. Absolute stability without an interfragmentary gap
. Relative stability with micro-motion
. Distraction osteogenesis
. Cast immobilization
. Intramedullary nailing

Correct Answer & Explanation

. Absolute stability without an interfragmentary gap

Explanation

Primary bone healing requires a mechanical environment of absolute stability (strain < 2%) and virtually no gap between bone fragments. Under these conditions, healing occurs directly via osteoclastic cutting cones and osteoblastic bone formation without a cartilaginous intermediate.

Question 2134

Topic: Biology, Genetics & Bone Healing

Denosumab is highly effective in the medical management of surgically unsalvageable giant cell tumors of bone. What is the precise molecular target of this medication?

. Osteoprotegerin (OPG)
. Receptor activator of nuclear factor kappa-B (RANK)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Macrophage colony-stimulating factor (M-CSF)
. Vascular endothelial growth factor (VEGF)

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL. By inhibiting RANKL, it prevents the interaction with RANK receptors on osteoclast precursors, thereby halting osteoclastogenesis and giant cell tumor progression.

Question 2135

Topic: 1. General Principles & Basic Science

Normal articular hyaline cartilage is composed primarily of water, proteoglycans, and a highly organized collagen framework. Which collagen type constitutes over 90% of this collagenous framework?

. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type II

Explanation

Type II collagen forms 90-95% of the collagen network in healthy articular hyaline cartilage, providing tensile strength. Type I collagen is predominant in bone, tendon, and fibrocartilage (such as the meniscus).

Question 2136

Topic: 1. General Principles & Basic Science

Following a Zone II flexor digitorum profundus (FDP) repair, what biomechanical property is most enhanced by adding an epitendinous suture to the core suture?

. Decreased gliding resistance
. Increased gap formation
. Increased breaking strength of the repair
. Decreased tendon vascularity
. Prevention of vincula rupture

Correct Answer & Explanation

. Increased breaking strength of the repair

Explanation

The addition of a peripheral epitendinous suture significantly increases the ultimate breaking strength of the tendon repair and reduces gap formation. While it helps to smooth the repair site and minimally decreases gliding resistance, its primary mechanical advantage is a major increase in construct strength.

Question 2137

Topic: Biology, Genetics & Bone Healing

Which type of bone healing occurs primarily under conditions of absolute stability, such as following open reduction and internal fixation with a compression plate?

. Endochondral ossification
. Intramembranous ossification
. Primary (Haversian) bone healing
. Secondary bone healing with callus formation
. Chondrogenesis followed by osteogenesis

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Absolute stability with a strain of less than 2%, typically achieved with compression plating, allows for primary bone healing. This occurs via direct Haversian remodeling across the fracture site without the formation of an intermediate fracture callus.

Question 2138

Topic: Biomechanics & Biomaterials

When evaluating the mechanical properties of an orthopedic implant material, the 'yield point' on a stress-strain curve represents what phenomenon?

. The point of ultimate material failure or breakage
. The transition from elastic to plastic deformation
. The region of maximum stiffness
. The point where the material undergoes minimal strain under maximum stress
. The limit of viscoelastic creep

Correct Answer & Explanation

. The transition from elastic to plastic deformation

Explanation

The yield point on a stress-strain curve marks the end of the elastic region and the beginning of the plastic region. Beyond this point, the material will no longer return to its original shape when the load is removed, representing permanent deformation.

Question 2139

Topic: Biology, Genetics & Bone Healing

A 35-year-old woman with recurrent Giant Cell Tumor of the distal radius is treated with Denosumab. What is the precise mechanism of action of this medication?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of osteoblasts
. Binding and inhibition of RANK ligand (RANKL)
. Inhibition of the mTOR pathway
. Cross-linking of bacterial DNA

Correct Answer & Explanation

. Binding and inhibition of RANK ligand (RANKL)

Explanation

Denosumab is a monoclonal antibody that specifically binds to and inhibits RANKL. This prevents the interaction between RANKL and RANK on osteoclast precursors, thereby inhibiting osteoclast-mediated bone destruction characteristic of giant cell tumors.

Question 2140

Topic: 1. General Principles & Basic Science

Articular cartilage is composed of multiple zones. Which zone contains the highest concentration of proteoglycans and the lowest concentration of water?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans and the lowest water content. Its collagen fibers are oriented perpendicularly to the articular surface to resist compressive forces.

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