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1. General Principles & Basic Science MCQs

Practice Set 666 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 13301

Topic: Biology, Genetics & Bone Healing

A 55-year-old postmenopausal woman is evaluated for osteoporosis. She is started on denosumab. Which of the following best describes the primary mechanism of action of this medication?

. Direct inhibition of farnesyl pyrophosphate synthase
. Binding to RANK ligand (RANKL), preventing interaction with RANK
. Activation of the osteoblast Wnt signaling pathway
. Binding to parathyroid hormone receptors to stimulate bone formation
. Direct inhibition of cathepsin K

Correct Answer & Explanation

. Binding to RANK ligand (RANKL), preventing interaction with RANK

Explanation

Denosumab is a monoclonal antibody that targets RANKL, preventing it from binding to RANK on the surface of osteoclasts and their precursors. This inhibits osteoclastogenesis and decreases bone resorption. Bisphosphonates inhibit farnesyl pyrophosphate synthase. Romosozumab activates Wnt signaling.

Question 13302

Topic: Biomechanics & Biomaterials

During the clinical examination of a knee ligament, a constant force is applied, and the ligament is observed to slowly elongate over time. Which viscoelastic property does this describe?

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Isotropic behavior

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation (elongation) of a viscoelastic material when subjected to a constant load (force) over time. Stress relaxation is the decrease in stress (force) over time when a material is held at a constant length (strain). Hysteresis is the energy lost as heat during the loading and unloading cycle.

Question 13303

Topic: Infection, Pharmacology & VTE

A 60-year-old man with poorly controlled diabetes presents with a rapidly spreading erythematous, exquisitely tender swelling of his right leg. Crepitus is palpated. Gram stain of fluid from a blister reveals a polymicrobial infection including Gram-positive cocci and Gram-negative rods. What is the most appropriate initial management?

. Intravenous vancomycin and observation
. Hyperbaric oxygen therapy
. MRI of the right lower extremity
. Immediate surgical debridement
. Local wound care with silver sulfadiazine

Correct Answer & Explanation

. Immediate surgical debridement

Explanation

The patient is presenting with signs of necrotizing fasciitis (Type I, polymicrobial, common in diabetics). The presence of crepitus, rapid spread, and severe pain demands immediate surgical debridement. Delaying surgery for imaging or relying solely on antibiotics significantly increases mortality.

Question 13304

Topic: Biology, Genetics & Bone Healing

A 72-year-old man presents with dull aching pain in his right thigh and an enlarging hat size. Radiographs of the femur show cortical thickening, coarse trabeculae, and a radiolucent V-shaped leading edge. Histologic evaluation of the affected bone would most likely demonstrate:

. A mosaic pattern of lamellar bone with prominent cement lines
. Sheets of uniform, small round blue cells
. A proliferation of woven bone lined by atypical osteoblasts
. Granulomas with caseous necrosis
. Extensive empty lacunae with necrotic marrow

Correct Answer & Explanation

. A mosaic pattern of lamellar bone with prominent cement lines

Explanation

The clinical presentation is classic for Paget's disease of bone. The V-shaped leading edge is the 'blade of grass' sign of the lytic phase. The hallmark histologic finding in the mixed phase of Paget's disease is a 'mosaic pattern' of lamellar bone with prominent, haphazard cement lines due to chaotic bone resorption and formation.

Question 13305

Topic: Biomechanics & Biomaterials

A surgeon decides to use a stainless steel screw to secure a titanium plate during open reduction and internal fixation of a femur fracture. The patient subsequently develops a localized reaction. Which of the following types of corrosion is most likely occurring at the implant interface?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are in physical contact within a conductive fluid medium (such as body fluids). This creates an electrochemical cell, leading to the accelerated corrosion of the less noble metal.

Question 13306

Topic: Biology, Genetics & Bone Healing

Articular cartilage has a highly specialized extracellular matrix. Which of the following components is primarily responsible for the tissue's ability to resist compressive forces?

. Type I collagen
. Type II collagen
. Proteoglycans (e.g., aggrecan)
. Hyaluronic acid
. Chondronectin

Correct Answer & Explanation

. Proteoglycans (e.g., aggrecan)

Explanation

The ability of articular cartilage to withstand compressive forces is primarily provided by proteoglycans (predominantly aggrecan), which are highly negatively charged and attract water, creating a swelling pressure (Donnan osmotic effect). The Type II collagen network provides tensile strength.

Question 13307

Topic: Biology, Genetics & Bone Healing

A 68-year-old man is prescribed alendronate for the prevention of osteoporotic fragility fractures. At the cellular level, this medication ultimately inhibits bone resorption by which of the following mechanisms?

. Binding to estrogen receptors on osteoclasts
. Inhibiting the ruffled border proton pump (V-ATPase)
. Disrupting the mevalonate pathway, leading to osteoclast apoptosis
. Increasing the secretion of osteoprotegerin (OPG) from osteoblasts
. Directly inhibiting matrix metalloproteinases

Correct Answer & Explanation

. Disrupting the mevalonate pathway, leading to osteoclast apoptosis

Explanation

Nitrogen-containing bisphosphonates (like alendronate) inhibit farnesyl pyrophosphate synthase, a key enzyme in the mevalonate pathway. This prevents the prenylation of small GTP-binding proteins (like Ras, Rho, and Rab) essential for osteoclast function and survival, ultimately leading to osteoclast apoptosis and decreased bone resorption.

Question 13308

Topic: 1. General Principles & Basic Science
Which of the following screw modifications will most significantly increase its theoretical pullout strength when placed into cancellous bone?
. Increasing the core diameter
. Decreasing the outer (thread) diameter
. Increasing the outer (thread) diameter
. Decreasing the pitch
. Decreasing the length of engagement

Correct Answer & Explanation

. Increasing the outer (thread) diameter

Explanation

Pullout strength of a cortical or cancellous screw is determined primarily by the formula: Pullout strength = S × L × π × D, where S is the shear strength of the surrounding bone, L is the length of engagement of the threads in the bone, and D is the outer (major or thread) diameter of the screw. Increasing the outer diameter, increasing the length of engagement, and increasing the shear strength of the bone all directly increase pullout strength.

Question 13309

Topic: 1. General Principles & Basic Science

In the structural organization of articular cartilage, which zone is characterized by the highest concentration of water, the lowest concentration of proteoglycans, and type II collagen fibers oriented parallel to the articular surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone makes up 10-20% of articular cartilage thickness. It has the highest water content (approx. 80%), the lowest proteoglycan content, and densely packed type II collagen fibers arranged parallel to the joint surface to resist shear forces.

Question 13310

Topic: Biology, Genetics & Bone Healing

A 14-year-old boy presents with multiple fractures after minor trauma, recurrent dental infections, and mild hearing loss. Radiographs show diffusely dense, 'marble-like' bones with absent medullary canals. Which of the following cellular mechanisms is primarily defective in this condition?

. Osteoblast differentiation and maturation
. Osteocyte apoptosis in cortical bone
. Osteoclast ruffled border formation
. Type I collagen triple-helix synthesis
. Extracellular mineralization of osteoid

Correct Answer & Explanation

. Osteoclast ruffled border formation

Explanation

The clinical and radiographic presentation is classic for osteopetrosis (marble bone disease). Osteopetrosis is caused by defective osteoclast function, most commonly a failure to form the ruffled border, leading to impaired bone resorption. Common genetic defects include mutations in carbonic anhydrase II (CAII) and TCIRG1.

Question 13311

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, lamellar bone can only form when the interfragmentary strain at the fracture site is below what percentage?

. 100%
. 50%
. 10%
. 2%
. 0%

Correct Answer & Explanation

. 2%

Explanation

Perren's strain theory dictates that tissues cannot form in an environment where the strain exceeds their tolerance. Granulation tissue tolerates up to 100% strain, fibrocartilage tolerates up to 10%, and true lamellar bone formation requires a stable environment with an interfragmentary strain of less than 2%.

Question 13312

Topic: Infection, Pharmacology & VTE
A 9-year-old boy from Massachusetts presents with acute right knee swelling and a large effusion. He has no fever and can bear weight. Knee aspiration yields a synovial white blood cell count of 55,000 cells/mm³ with 85% polymorphonuclear leukocytes. Enzyme-linked immunosorbent assay (ELISA) and Western blot are positive for Borrelia burgdorferi. What is the most appropriate initial management?
. Immediate arthroscopic irrigation and debridement
. Intravenous ceftriaxone for 14 days
. Oral doxycycline or amoxicillin for 28 days
. Intra-articular corticosteroid injection
. Serial daily knee aspirations

Correct Answer & Explanation

. Oral doxycycline or amoxicillin for 28 days

Explanation

Lyme arthritis frequently presents with massive joint effusions, most commonly in the knee, with synovial WBC counts that can mimic septic arthritis (often 20,000 to >60,000). The first-line treatment for Lyme arthritis without systemic neurologic involvement is a 28-day course of oral antibiotics (doxycycline in children >8, amoxicillin, or cefuroxime).

Question 13313

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy is evaluated for short stature and significant bowing of the lower extremities. Laboratory studies reveal normal serum calcium, profoundly decreased serum phosphate, normal PTH, and normal 25-hydroxyvitamin D. However, 1,25-dihydroxyvitamin D is inappropriately normal. Which of the following is the most likely genetic defect?

. Mutation in the Vitamin D receptor (VDR)
. Mutation in the PHEX gene
. Mutation in the COL1A1 gene
. Mutation in the FGFR3 gene
. Mutation in the CAII gene

Correct Answer & Explanation

. Mutation in the PHEX gene

Explanation

The clinical and laboratory profile (hypophosphatemia, normal calcium, normal PTH, and inappropriately normal 1,25-dihydroxyvitamin D despite low phosphate) is classic for X-linked hypophosphatemic rickets. This is caused by an inactivating mutation in the PHEX gene, leading to excessive levels of FGF23, which suppresses renal phosphate reabsorption and 1-alpha-hydroxylase activity.

Question 13314

Topic: 1. General Principles & Basic Science

Which of the following proprioceptive structures is located in series with extrafusal muscle fibers and is primarily responsible for monitoring muscle tension, thereby preventing excessive force during a maximal contraction?

. Muscle spindle
. Golgi tendon organ
. Pacinian corpuscle
. Ruffini ending
. Free nerve ending

Correct Answer & Explanation

. Golgi tendon organ

Explanation

The Golgi tendon organ is located at the myotendinous junction in series with extrafusal muscle fibers. It is an inhibitory receptor (via Ib afferent fibers) that monitors muscle tension and acts to reflexively relax the muscle when tension becomes dangerously high, preventing structural damage.

Question 13315

Topic: Infection, Pharmacology & VTE
Low-molecular-weight heparin (LMWH) is frequently utilized for venous thromboembolism prophylaxis following total joint arthroplasty. What is the primary mechanism of action of LMWH?
. Direct inhibition of thrombin (Factor IIa)
. Potentiation of antithrombin III with selective inhibition of Factor Xa over Factor IIa
. Vitamin K antagonism preventing synthesis of Factors II, VII, IX, and X
. Direct irreversible inhibition of the P2Y12 ADP receptor on platelets
. Activation of plasminogen to plasmin

Correct Answer & Explanation

. Potentiation of antithrombin III with selective inhibition of Factor Xa over Factor IIa

Explanation

Low-molecular-weight heparins (e.g., enoxaparin) act by binding to and potentiating antithrombin III. Unlike unfractionated heparin, which has roughly equal anti-Factor Xa and anti-Factor IIa activity, LMWH has a higher ratio of anti-Factor Xa to anti-Factor IIa activity (typically 2:1 to 4:1) because its shorter polysaccharide chains are less able to form the ternary complex required to inhibit thrombin.

Question 13316

Topic: Biomechanics & Biomaterials

In orthopedic implant constructs, combining a stainless steel plate with titanium screws is generally discouraged primarily due to the increased risk of which of the following processes?

. 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 anodic indices (electropotentials) are in direct physical contact within an electrolytic medium (such as bodily fluids). The less noble metal (stainless steel) acts as an anode and corrodes at an accelerated rate, while the more noble metal (titanium) acts as a cathode.

Question 13317

Topic: 1. General Principles & Basic Science

In Sunderland's classification of peripheral nerve injuries, a third-degree injury is defined by disruption of the axon and which of the following connective tissue layers?

. Endoneurium only
. Perineurium only
. Epineurium only
. Endoneurium and perineurium
. Endoneurium and epineurium

Correct Answer & Explanation

. Endoneurium and perineurium

Explanation

Sunderland classification: 1st degree (Neuropraxia) = local myelin damage; 2nd degree (Axonotmesis) = axon severed, all connective tissue intact; 3rd degree = axon and endoneurium disrupted (perineurium intact); 4th degree = axon, endoneurium, and perineurium disrupted (epineurium intact); 5th degree (Neurotmesis) = complete transection of the nerve.

Question 13318

Topic: Biology, Genetics & Bone Healing

In mature cortical bone, the Haversian systems (osteons) run parallel to the long axis of the bone. Which of the following structures is responsible for connecting adjacent Haversian canals to facilitate vascular communication between osteons?

. Canaliculi
. Volkmann canals
. Howship lacunae
. Sharpey's fibers
. Cement lines

Correct Answer & Explanation

. Volkmann canals

Explanation

Volkmann canals are transverse or oblique channels in cortical bone that contain blood vessels and connect adjacent longitudinally running Haversian canals to each other, as well as to the periosteal and endosteal blood supplies.

Question 13319

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with deep, aching bone pain in his right femur and an enlarging hat size. Laboratory tests show a significantly elevated serum alkaline phosphatase but normal calcium and phosphorus. A biopsy of the femur is most likely to demonstrate which of the following pathognomonic histological features?

. Irregular areas of unmineralized osteoid with an absence of calcified cartilage
. A mosaic pattern of lamellar bone with prominent, irregular cement lines
. Sheets of plasma cells with 'clock-face' nuclei
. Uniform sheets of small round blue cells with scant cytoplasm
. Non-caseating granulomas with multinucleated giant cells

Correct Answer & Explanation

. A mosaic pattern of lamellar bone with prominent, irregular cement lines

Explanation

The clinical scenario is classic for Paget's disease of bone (osteitis deformans). The pathognomonic histological finding in the mixed and late/sclerotic phases is a mosaic, 'jigsaw puzzle' pattern of lamellar bone with prominent, haphazard cement lines, reflecting the chaotic, rapid cycles of bone resorption and formation.

Question 13320

Topic: Biology, Genetics & Bone Healing
A 35-year-old man undergoes closed reduction and cast application for a closed tibial shaft fracture. Secondary bone healing is anticipated. During the cartilaginous callus phase, which collagen type is predominantly synthesized before being replaced by woven bone?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Secondary bone healing involves a soft cartilaginous callus phase characterized by the production of Type II collagen by chondrocytes. As the cartilage undergoes endochondral ossification, hypertrophic chondrocytes produce Type X collagen, followed by osteoblasts producing Type I collagen in the hard callus.

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