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1. General Principles & Basic Science MCQs

Practice Set 660 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 13181

Topic: Biology, Genetics & Bone Healing

A 3-year-old boy presents with severe genu varum. Laboratory tests show normal serum calcium, low serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. What is the most appropriate medical treatment?

. High-dose Vitamin D3 alone
. Calcium and Vitamin D supplementation
. Oral phosphate and calcitriol (1,25-dihydroxyvitamin D)
. Intravenous bisphosphonates
. Recombinant human PTH

Correct Answer & Explanation

. Oral phosphate and calcitriol (1,25-dihydroxyvitamin D)

Explanation

The patient has X-linked hypophosphatemic rickets, characterized by excessive FGF23 leading to severe renal phosphate wasting. Treatment requires oral phosphate repletion combined with calcitriol to prevent secondary hyperparathyroidism.

Question 13182

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in fracture healing by inducing mesenchymal stem cell differentiation. Which intracellular signaling pathway is primarily activated upon BMP receptor binding?

. Wnt/beta-catenin pathway
. JAK/STAT pathway
. Notch/Hes pathway
. Smad 1/5/8 pathway
. MAP kinase pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMPs bind to serine/threonine kinase receptors, leading to the phosphorylation of receptor-regulated Smads (Smad 1, 5, and 8). These form a complex with Co-Smad 4 and translocate to the nucleus to initiate osteogenic gene transcription.

Question 13183

Topic: Physiology & Rehabilitation

Following a traumatic nerve transection, skeletal muscle undergoes characteristic physiologic changes. Which of the following is a classic finding in denervated skeletal muscle at 3-4 weeks post-injury?

. Upregulation of extrajunctional acetylcholine receptors
. Hypertrophy of type I muscle fibers
. Increased resting membrane potential
. Conversion of type IIb to type IIa fibers
. Decreased spontaneous fibrillation potentials on EMG

Correct Answer & Explanation

. Upregulation of extrajunctional acetylcholine receptors

Explanation

Following denervation, skeletal muscle becomes hypersensitive to acetylcholine due to the massive upregulation and spread of extrajunctional acetylcholine receptors across the entire sarcolemma. This manifests as spontaneous fibrillation potentials on EMG.

Question 13184

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for venous thromboembolism prophylaxis following a total hip arthroplasty. At which point in the coagulation cascade does this medication exert its primary anticoagulant effect?
. Direct inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via antithrombin III
. Direct inhibition of Factor Xa
. Vitamin K antagonism preventing activation of Factors II, VII, IX, X
. Inhibition of ADP-induced platelet aggregation

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban is an oral anticoagulant that selectively and directly inhibits Factor Xa. It does not require antithrombin III for its effect, distinguishing its mechanism from low molecular weight heparins.

Question 13185

Topic: Surgical Anatomy & Approaches

A patient sustains a crush injury resulting in a radial nerve palsy. At 4 weeks, clinical examination shows no function, but the nerve is in continuity. Surgical exploration shows intact epineurium and perineurium, but the endoneurium is disrupted. Which of Sunderland's classifications matches this injury?

. First-degree
. Second-degree
. Third-degree
. Fourth-degree
. Fifth-degree

Correct Answer & Explanation

. Third-degree

Explanation

A Sunderland third-degree injury corresponds to a severe axonotmesis where the axon and endoneurium are disrupted, but the perineurium and epineurium remain intact. The loss of endoneurial tubes increases the risk of aberrant nerve regeneration.

Question 13186

Topic: 1. General Principles & Basic Science

The kinetic energy transferred to tissues from a projectile heavily influences the severity of a gunshot wound. According to the kinetic energy equation (KE = 1/2 mv^2), which variable has the greatest exponential impact on tissue damage?

. Mass of the projectile
. Velocity of the projectile
. Caliber of the weapon
. Yaw of the bullet
. Deformation of the bullet

Correct Answer & Explanation

. Velocity of the projectile

Explanation

Tissue damage is directly proportional to the kinetic energy transferred. Because velocity is squared in the equation (KE = 1/2 mv^2), doubling the velocity quadruples the kinetic energy, making it the most critical determinant of the cavitation injury.

Question 13187

Topic: Biology, Genetics & Bone Healing

Low-intensity pulsed ultrasound (LIPUS) is utilized to accelerate fracture healing. What is the established primary cellular mechanism by which LIPUS promotes osteogenesis?

. Thermal ablation of competing fibrous tissue
. Induction of acoustic streaming and integrin-mediated mechanotransduction
. Direct activation of voltage-gated calcium channels
. Inhibition of osteoclastogenesis via OPG upregulation
. Stimulation of angiogenesis through VEGF independent pathways

Correct Answer & Explanation

. Induction of acoustic streaming and integrin-mediated mechanotransduction

Explanation

LIPUS creates micromechanical stresses within tissue via acoustic streaming. This mechanical signal is converted into a biochemical response through integrins and mechanosensitive ion channels on osteoblasts, stimulating bone formation.

Question 13188

Topic: Physiology & Rehabilitation

During a normal human gait cycle, at what specific phase does the tibialis anterior exhibit its peak electromyographic (EMG) activity?

. Initial contact (heel strike) to loading response
. Mid-stance to terminal stance
. Pre-swing
. Initial swing
. Mid-swing

Correct Answer & Explanation

. Initial contact (heel strike) to loading response

Explanation

The tibialis anterior peaks in activity during the transition from initial contact to the loading response. It fires eccentrically during this phase to control ankle plantar flexion and prevent 'foot slap'.

Question 13189

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with an expansile, lytic, epiphyseal lesion of the distal femur. Biopsy confirms a Giant Cell Tumor of bone (GCT). She is treated with denosumab prior to surgical curettage. What is the specific molecular target of this drug?

. RANK
. RANKL
. Osteoprotegerin (OPG)
. Vascular Endothelial Growth Factor (VEGF)
. Macrophage Colony-Stimulating Factor (M-CSF)

Correct Answer & Explanation

. RANKL

Explanation

Denosumab is a monoclonal antibody that targets and neutralizes RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). In GCT, neoplastic stromal cells secrete RANKL to recruit and activate the destructive multinucleated giant cells.

Question 13190

Topic: 1. General Principles & Basic Science

As normal articular cartilage ages, distinct biochemical changes occur that differentiate it from early osteoarthritis. Which of the following findings is characteristic of normal aging articular cartilage?

. Increased total water content
. Increased chondroitin sulfate concentration
. Decreased size and aggregation of aggrecan molecules
. Decreased keratin sulfate concentration
. Increased total collagen content

Correct Answer & Explanation

. Decreased size and aggregation of aggrecan molecules

Explanation

In normal aging cartilage, aggrecan molecules become smaller, less uniform, and exhibit a decreased ability to aggregate. Unlike in early osteoarthritis where water content increases, the water content in normal aging cartilage gradually decreases.

Question 13191

Topic: Biology, Genetics & Bone Healing

According to Perrenโ€™s strain theory, what is the maximum strain environment that allows for secondary bone healing via endochondral ossification (callus formation)?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 50%
. Greater than 50%

Correct Answer & Explanation

. Between 2% and 10%

Explanation

Perren's strain theory dictates that specific tissues can only form under certain strain conditions. Primary bone healing (direct osteonal remodeling) requires absolute stability with strain less than 2%. Secondary bone healing (callus formation via endochondral ossification) requires relative stability with a strain environment between 2% and 10%. Fibrocartilage tolerates up to 10-15% strain, while granulation tissue can tolerate up to 100% strain.

Question 13192

Topic: Biomechanics & Biomaterials

On a stress-strain curve for an orthopedic biomaterial, the total area under the curve up to the point of structural failure represents which of the following mechanical properties?

. Stiffness
. Yield strength
. Ultimate tensile strength
. Toughness
. Ductility

Correct Answer & Explanation

. Toughness

Explanation

The area under the entire stress-strain curve up to the point of failure represents the material's 'toughness,' which is the total amount of energy a material can absorb before it breaks. 'Stiffness' (Young's modulus) is the slope of the linear elastic portion. 'Yield strength' is the point where plastic deformation begins. 'Ductility' is the amount of plastic strain a material can sustain before failure.

Question 13193

Topic: 1. General Principles & Basic Science

Which of the following layers of articular cartilage contains the highest concentration of water and has collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial zone

Explanation

Articular cartilage is divided into distinct zones. The superficial (tangential) zone has the highest water content (approx. 80%), the lowest proteoglycan concentration, and Type II collagen fibers that run parallel to the articular surface to resist shear forces. The deep zone has the lowest water content, the highest proteoglycan content, and collagen fibers oriented perpendicular to the joint surface to resist compressive loads.

Question 13194

Topic: Biology, Genetics & Bone Healing

A 70-year-old male presents with isolated elevation of serum alkaline phosphatase. Calcium and phosphorus levels are normal. Radiographs of the pelvis reveal coarsened trabeculae and cortical thickening. A bone biopsy would most likely show large, multinucleated osteoclasts containing viral inclusion bodies. Which virus is most commonly implicated in the pathogenesis of this disease?

. Cytomegalovirus (CMV)
. Epstein-Barr virus (EBV)
. Human papillomavirus (HPV)
. Paramyxovirus
. Parvovirus B19

Correct Answer & Explanation

. Paramyxovirus

Explanation

The clinical presentation is classic for Paget's disease of bone (osteitis deformans), characterized by normal serum calcium and phosphorus with an elevated alkaline phosphatase. The primary cellular defect is in the osteoclast. Paramyxoviruses (such as Respiratory Syncytial Virus and measles virus) have been implicated in its pathogenesis, supported by the presence of paramyxovirus-like nucleocapsid inclusion bodies within the enlarged, multinucleated osteoclasts.

Question 13195

Topic: Biology, Genetics & Bone Healing

Denosumab has revolutionized the medical management of unresectable or recurrent Giant Cell Tumor (GCT) of bone. What is the specific cellular target of denosumab in the microenvironment of a GCT?

. It binds to RANK receptor on the multinucleated giant cells
. It binds to RANKL secreted by the neoplastic mononuclear stromal cells
. It binds to osteoprotegerin (OPG) produced by osteoblasts
. It directly induces apoptosis of the multinucleated giant cells
. It inhibits the Wnt/beta-catenin signaling pathway in stromal cells

Correct Answer & Explanation

. It binds to RANKL secreted by the neoplastic mononuclear stromal cells

Explanation

Giant cell tumor of bone consists of neoplastic mononuclear stromal cells and reactive multinucleated giant cells. The true neoplastic cells are the mononuclear stromal cells, which highly express RANK Ligand (RANKL). RANKL binds to the RANK receptor on the surface of osteoclast precursors, causing them to fuse into reactive multinucleated giant cells. Denosumab is a monoclonal antibody that binds to RANKL, preventing it from interacting with RANK, thereby halting giant cell formation and bone resorption.

Question 13196

Topic: Biomechanics & Biomaterials

During fracture fixation, combining a 316L stainless steel plate with titanium screws in an electrolytic physiological environment can lead to implant failure. Which biomechanical phenomenon best describes this process?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Stress shielding
. Fatigue failure

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices (electronegativities) are placed in direct physical contact within an electrically conductive fluid (such as blood or interstitial body fluid). In the case of stainless steel and titanium, the less noble metal (stainless steel) acts as the anode and undergoes accelerated corrosion, while the titanium acts as the cathode. Fretting corrosion is caused by micromotion between components, while crevice corrosion occurs in shielded areas with oxygen depletion.

Question 13197

Topic: Infection, Pharmacology & VTE

Which of the following prophylactic systemic antibiotics exerts its bactericidal effect by binding directly to the D-alanyl-D-alanine terminus of cell wall precursor units?

. Cefazolin
. Gentamicin
. Vancomycin
. Clindamycin
. Rifampin

Correct Answer & Explanation

. Vancomycin

Explanation

Vancomycin is a glycopeptide antibiotic that inhibits cell wall synthesis by binding tightly to the D-alanyl-D-alanine terminus of peptidoglycan precursors, preventing their cross-linking. Cefazolin (a beta-lactam) inhibits cross-linking by binding to penicillin-binding proteins (PBPs). Gentamicin binds the 30S ribosomal subunit. Clindamycin binds the 50S ribosomal subunit. Rifampin inhibits DNA-dependent RNA polymerase.

Question 13198

Topic: Biomechanics & Biomaterials

In the biomechanical evaluation of tendons and ligaments, which of the following best defines the viscoelastic phenomenon of "creep"?

. A decrease in stress over time when subjected to a constant deformation
. An increase in deformation over time when subjected to a constant load
. The difference between the loading and unloading curves on a stress-strain graph
. Increased stiffness observed at higher loading rates
. Failure of a material at a stress level below its ultimate tensile strength due to cyclic loading

Correct Answer & Explanation

. An increase in deformation over time when subjected to a constant load

Explanation

Creep is a viscoelastic property defined as the progressive increase in strain (deformation) over time when a material is subjected to a constant stress (load). Option A describes stress relaxation. Option C describes hysteresis. Option D describes strain-rate dependency. Option E describes fatigue failure.

Question 13199

Topic: 1. General Principles & Basic Science
The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score is utilized to stratify the risk of necrotizing soft tissue infection. Which of the following laboratory parameters is NOT a component of the LRINEC score?
. C-reactive protein (CRP)
. Total white blood cell (WBC) count
. Serum sodium
. Serum potassium
. Serum creatinine

Correct Answer & Explanation

. Serum potassium

Explanation

The LRINEC score consists of six variables: CRP, WBC count, Hemoglobin, Serum sodium, Serum creatinine, and Serum glucose. Serum potassium is not a part of the scoring system. A score of 6 or greater is highly suspicious for necrotizing fasciitis.

Question 13200

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction during fracture healing. Following the binding of a BMP ligand to its cell surface serine/threonine kinase receptor, the intracellular signal is primarily propagated to the nucleus via which family of proteins?

. JAK/STAT
. Smad
. Wnt/beta-catenin
. MAPK
. RANKL

Correct Answer & Explanation

. Smad

Explanation

BMPs act through transmembrane serine/threonine kinase receptors. Upon activation, these receptors phosphorylate intracellular Smad proteins (specifically R-Smads 1, 5, and 8), which then complex with Co-Smad 4 and translocate to the nucleus to regulate the transcription of osteogenic genes like Runx2.

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