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1. General Principles & Basic Science MCQs

Practice Set 688 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 13741

Topic: 1. General Principles & Basic Science

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

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils oriented perpendicular to the joint surface, the highest concentration of proteoglycans, and the lowest water content.

Question 13742

Topic: Infection, Pharmacology & VTE

Rifampin is frequently utilized in the treatment of staphylococcal periprosthetic joint infections due to its ability to penetrate biofilms. What is its mechanism of action?

. Inhibits cell wall synthesis by binding to D-alanyl-D-alanine
. Inhibits bacterial DNA gyrase
. Inhibits DNA-dependent RNA polymerase
. Binds to the 50S ribosomal subunit
. Inhibits folic acid synthesis

Correct Answer & Explanation

. Inhibits DNA-dependent RNA polymerase

Explanation

Rifampin exerts its bactericidal effect by binding to the beta subunit of bacterial DNA-dependent RNA polymerase, thereby inhibiting RNA synthesis. It is highly active against stationary-phase bacteria within biofilms.

Question 13743

Topic: 1. General Principles & Basic Science

A research group investigates the association between bisphosphonate use and atypical femur fractures by identifying a group of patients with atypical femur fractures and a group of matched patients without these fractures, then looking back through their records to compare their history of bisphosphonate use. What study design is this?

. Prospective cohort study
. Retrospective cohort study
. Case-control study
. Randomized controlled trial
. Cross-sectional study

Correct Answer & Explanation

. Case-control study

Explanation

Because the researchers identified patients based on their outcome (atypical femur fracture vs. no fracture) and then looked retrospectively at their exposure status (bisphosphonate use), this is a case-control study.

Question 13744

Topic: Biology, Genetics & Bone Healing

During secondary fracture healing, endochondral ossification requires the coordinated differentiation of chondrocytes. Which transcription factor is the master regulator for chondrocyte hypertrophy and subsequent osteoblast differentiation?

. Sox9
. Runx2
. Osterix
. Sclerostin
. RANKL

Correct Answer & Explanation

. Runx2

Explanation

Runx2 (Cbfa1) is the master transcription factor necessary for chondrocyte hypertrophy and osteoblast differentiation. Sox9 is critical for early chondrogenesis but must be downregulated for chondrocytes to undergo hypertrophy.

Question 13745

Topic: 1. General Principles & Basic Science

Duchenne muscular dystrophy is inherited in which of the following genetic patterns?

. Autosomal dominant
. Autosomal recessive
. X-linked recessive
. X-linked dominant
. Mitochondrial

Correct Answer & Explanation

. X-linked recessive

Explanation

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder caused by a frameshift mutation in the dystrophin gene located on the X chromosome (Xp21).

Question 13746

Topic: 1. General Principles & Basic Science
According to the Sunderland classification of peripheral nerve injuries, a third-degree nerve injury is characterized by disruption of the axon and which other structure(s)?
. Myelin sheath only
. Endoneurium only
. Endoneurium, with intact perineurium
. Endoneurium and perineurium, with intact epineurium
. Endoneurium, perineurium, and epineurium

Correct Answer & Explanation

. Endoneurium, with intact perineurium

Explanation

A Sunderland III injury involves disruption of the axon and endoneurium, but the perineurium and epineurium remain intact. Recovery is unpredictable because internal scarring within the fascicle can obstruct axonal regeneration.

Question 13747

Topic: Infection, Pharmacology & VTE
Rivaroxaban is a widely used oral anticoagulant for venous thromboembolism prophylaxis after total joint arthroplasty. Which step in the coagulation cascade does it directly inhibit?
. Thrombin (Factor IIa)
. Factor Xa
. Antithrombin III
. Vitamin K epoxide reductase
. Plasminogen

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that work by competitively and reversibly inhibiting Factor Xa. Dabigatran is a direct thrombin (Factor IIa) inhibitor.

Question 13748

Topic: 1. General Principles & Basic Science

When attempting to maximize the pull-out strength of a cortical bone screw, which of the following geometric modifications to the screw design will have the most significant positive effect?

. Increasing the outer (thread) diameter
. Increasing the inner (core) diameter
. Decreasing the outer (thread) diameter
. Increasing the thread pitch
. Decreasing the length of engagement

Correct Answer & Explanation

. Increasing the outer (thread) diameter

Explanation

Pull-out strength of a screw is directly proportional to the outer (thread) diameter, the length of engagement in the bone, and the shear strength of the surrounding bone. Increasing the inner (core) diameter increases the screw's bending or fatigue strength but does not primarily increase pull-out strength.

Question 13749

Topic: Biomechanics & Biomaterials
The incorporation of Vitamin E (alpha-tocopherol) into highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) components in total joint arthroplasty primarily serves to:
. Increase the melting temperature of the polymer
. Promote biological fixation to the bone
. Scavenge free radicals and prevent long-term oxidation
. Increase the elastic modulus of the bearing surface
. Prevent galvanic corrosion at modular interfaces

Correct Answer & Explanation

. Scavenge free radicals and prevent long-term oxidation

Explanation

Irradiation used to cross-link UHMWPE produces free radicals, which can lead to oxidation and embrittlement over time. Vitamin E is an antioxidant added to the polyethylene to scavenge these free radicals, preventing oxidation without the mechanical property compromises associated with post-irradiation remelting.

Question 13750

Topic: Biology, Genetics & Bone Healing

Within a cortical bone osteon, adjacent osteocytes communicate with each other and share nutrients via gap junctions located within microscopic channels. What are these channels called?

. Haversian canals
. Volkmann's canals
. Canaliculi
. Howship's lacunae
. Cement lines

Correct Answer & Explanation

. Canaliculi

Explanation

Canaliculi are narrow, microscopic channels that radiate from the lacunae housing osteocytes. The dendritic processes of osteocytes extend through the canaliculi to contact adjacent cells via gap junctions, facilitating communication and nutrient exchange.

Question 13751

Topic: Biology, Genetics & Bone Healing

Paget's disease of bone occurs in three distinct phases. Which of the following best describes the primary cellular abnormality during the initial phase?

. Overactive, large multinucleated osteoclasts
. Deficient osteoblast matrix synthesis
. Malignant transformation of osteoprogenitor cells
. Impaired mineralization of normal osteoid
. Deposition of amyloid within the marrow space

Correct Answer & Explanation

. Overactive, large multinucleated osteoclasts

Explanation

Paget's disease typically begins with an intense osteolytic phase characterized by a profound increase in the number, size, and activity of osteoclasts. These osteoclasts are abnormally large and have numerous nuclei. This is followed by a mixed phase and finally a sclerotic phase.

Question 13752

Topic: Infection, Pharmacology & VTE

A 55-year-old male presents with acute severe pain in the first metatarsophalangeal joint. Aspiration yields negatively birefringent, needle-shaped crystals. For long-term management to prevent recurrent attacks, which of the following drugs acts by inhibiting xanthine oxidase?

. Colchicine
. Probenecid
. Allopurinol
. Indomethacin
. Anakinra

Correct Answer & Explanation

. Allopurinol

Explanation

Allopurinol is a xanthine oxidase inhibitor used for the chronic management of gout to decrease uric acid production. Colchicine inhibits microtubule assembly, probenecid is a uricosuric agent, and indomethacin is an NSAID used for acute attacks.

Question 13753

Topic: Biology, Genetics & Bone Healing

In a patient with X-linked hypophosphatemic rickets (XLH), which of the following laboratory profiles is typically observed?

. Low serum calcium, low serum phosphate, highly elevated PTH
. Normal serum calcium, low serum phosphate, normal or mildly elevated PTH
. High serum calcium, low serum phosphate, highly elevated PTH
. Normal serum calcium, high serum phosphate, low PTH
. Low serum calcium, high serum phosphate, highly elevated PTH

Correct Answer & Explanation

. Normal serum calcium, low serum phosphate, normal or mildly elevated PTH

Explanation

X-linked hypophosphatemic rickets is caused by a mutation in the PHEX gene, leading to elevated FGF23 and subsequent renal phosphate wasting. Typical lab values show low serum phosphate, normal serum calcium, and a normal or only mildly elevated PTH level. This contrasts with nutritional rickets, which features low calcium and significantly elevated PTH.

Question 13754

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the primary mechanism of action of osteoprotegerin (OPG) in bone metabolism?

. It binds directly to the RANK receptor on osteoclasts
. It binds to RANKL on osteoblast lineage cells
. It stimulates macrophage colony-stimulating factor (M-CSF)
. It activates the Wnt/beta-catenin pathway
. It directly inhibits the ruffled border proton pump

Correct Answer & Explanation

. It binds to RANKL on osteoblast lineage cells

Explanation

Osteoprotegerin (OPG) acts as a soluble decoy receptor that binds to RANKL. By binding RANKL, it prevents it from interacting with the RANK receptor on osteoclast precursors, thereby inhibiting osteoclast differentiation and bone resorption.

Question 13755

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum amount of interfragmentary strain that can be tolerated to achieve primary (direct) bone healing without a cartilaginous intermediate?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Greater than 30%
. Strain has no effect on primary bone healing

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires absolute stability, which corresponds to an interfragmentary strain of less than 2%. Under these conditions, cutting cones cross the fracture site directly followed by osteoblast-mediated lamellar bone deposition.

Question 13756

Topic: 1. General Principles & Basic Science

Which of the following biochemical changes is characteristic of articular cartilage in the early stages of osteoarthritis, distinguishing it from the normal aging process?

. Decreased water content
. Increased chondroitin sulfate concentration
. Increased water content
. Decreased keratin sulfate concentration
. Increased total collagen content

Correct Answer & Explanation

. Increased water content

Explanation

In early osteoarthritis, the initial degradation of the collagen matrix allows the hydrophilic proteoglycans to swell, leading to an increased water content in the cartilage. In contrast, normal aging cartilage undergoes dehydration and exhibits decreased water content.

Question 13757

Topic: Biomechanics & Biomaterials

When comparing the torsional rigidity of a solid intramedullary nail to a hollow nail of the same material, the polar moment of inertia is primarily determined by which dimensional parameter?

. The length of the nail squared
. The cross-sectional area
. The inner diameter cubed
. The radius to the fourth power
. The square of the wall thickness

Correct Answer & Explanation

. The radius to the fourth power

Explanation

Torsional rigidity is governed by the polar moment of inertia. For a solid cylinder, this value is directly proportional to the radius to the fourth power (r^4), demonstrating how small increases in nail diameter drastically increase torsional stiffness.

Question 13758

Topic: Biomechanics & Biomaterials

The combination of a 316L stainless steel screw with a titanium plate in an orthopedic fracture construct significantly increases the risk of which type of corrosion?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within a conductive fluid environment. The less noble metal acts as an anode and undergoes accelerated corrosion.

Question 13759

Topic: Physiology & Rehabilitation

A 45-year-old weightlifter experiences an acute distal biceps tendon rupture. This specific injury biomechanically occurs most frequently during which type of muscle contraction?

. Isotonic concentric
. Isometric
. Isokinetic
. Eccentric
. Plyometric

Correct Answer & Explanation

. Eccentric

Explanation

Eccentric contractions occur when a muscle generates tension while actively lengthening, yielding the highest peak force of any contraction type. This massive force generation renders the muscle-tendon unit most susceptible to mechanical failure and rupture.

Question 13760

Topic: Surgical Anatomy & Approaches

A patient sustains a closed midshaft humerus fracture with an associated radial nerve palsy. According to Sunderland's classification, a 3rd-degree nerve injury involves the disruption of the axon and myelin sheath along with which of the following connective tissue layers?

. None; all connective tissues remain intact
. The endoneurium is disrupted, but the perineurium remains intact
. The perineurium is disrupted, but the epineurium remains intact
. The epineurium is disrupted, constituting complete transection
. The epimysium and surrounding fascia are disrupted

Correct Answer & Explanation

. The endoneurium is disrupted, but the perineurium remains intact

Explanation

A Sunderland 3rd-degree injury involves damage to the axon, myelin, and the endoneurium, while the perineurium remains intact. Because the endoneurial tubes are disrupted, axonal regeneration may be misdirected, leading to incomplete or aberrant functional recovery.

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