Menu

1. General Principles & Basic Science MCQs

Practice Set 276 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 5501

Topic: Biology, Genetics & Bone Healing

A 45-year-old patient presents with diffuse bone pain, muscle weakness, and pseudofractures (Looser zones) on radiographs. Labs demonstrate hypocalcemia and hypophosphatemia. A bone biopsy would most likely show which of the following classic histological features?

. Increased osteoclast tunneling and disorganized woven bone
. Markedly thickened unmineralized osteoid seams
. A mosaic pattern of lamellar bone with prominent cement lines
. Empty osteocyte lacunae and necrotic trabeculae
. Marrow fibrosis with an overabundance of woven bone

Correct Answer & Explanation

. Markedly thickened unmineralized osteoid seams

Explanation

The clinical scenario is consistent with osteomalacia. Histologically, osteomalacia is defined by a defect in bone mineralization, resulting in an accumulation of unmineralized matrix and markedly widened osteoid seams.

Question 5502

Topic: Biology, Genetics & Bone Healing

A 72-year-old woman is prescribed teriparatide for severe osteoporosis. Which of the following best describes the cellular mechanism by which this medication exerts its primary anabolic effect?

. Direct inhibition of RANK ligand
. Binding to the Wnt receptor to antagonize sclerostin
. Pulsatile activation of PTH receptors stimulating osteoblast differentiation
. Irreversible binding to hydroxyapatite inhibiting osteoclast ruffled border
. Downregulation of osteoprotegerin (OPG) expression

Correct Answer & Explanation

. Pulsatile activation of PTH receptors stimulating osteoblast differentiation

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered in intermittent, pulsatile doses, it has an anabolic effect on bone by stimulating osteoblast activity and differentiation over osteoclast activity.

Question 5503

Topic: 1. General Principles & Basic Science

Which of the following modifications to a cortical screw design will most significantly increase its pullout strength?

. Increasing the core diameter
. Decreasing the outer diameter
. Increasing the thread pitch
. Increasing the outer diameter
. Decreasing the length of screw engagement

Correct Answer & Explanation

. Increasing the outer diameter

Explanation

Screw pullout strength is directly proportional to the outer diameter, the length of engagement, and the shear strength of the bone. It is inversely proportional to the thread pitch, making the increase of the outer diameter the most significant positive modification.

Question 5504

Topic: Biology, Genetics & Bone Healing

A novel therapeutic agent for osteoporosis functions by inhibiting sclerostin. Which of the following pathways is directly affected by this inhibition?

. RANK/RANKL pathway
. Wnt/beta-catenin pathway
. TGF-beta/Smad pathway
. Notch signaling pathway
. BMP/Smad pathway

Correct Answer & Explanation

. Wnt/beta-catenin pathway

Explanation

Sclerostin is produced by osteocytes and inhibits bone formation by antagonizing the Wnt/beta-catenin signaling pathway. Monoclonal antibodies targeting sclerostin (e.g., romosozumab) lead to increased osteoblastic bone formation.

Question 5505

Topic: Biomechanics & Biomaterials

Tendons and ligaments exhibit viscoelastic properties. Which of the following terms describes the phenomenon where the load required to maintain a constant deformation decreases over time?

. Creep
. Hysteresis
. Stress relaxation
. Fatigue
. Strain rate dependency

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property defined as the decrease in applied stress (or load) over time when a material is held at a constant strain (deformation). Creep, conversely, is continued deformation under a constant load.

Question 5506

Topic: Biomechanics & Biomaterials

On a stress-strain curve for cortical bone, the area under the entire curve up to the point of failure represents which of the following mechanical properties?

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

Correct Answer & Explanation

. Toughness

Explanation

Toughness is defined as the total amount of energy a material can absorb before it fractures, corresponding to the entire area under the stress-strain curve. Stiffness is represented by the slope of the elastic region.

Question 5507

Topic: 1. General Principles & Basic Science

When utilizing a locking compression plate as a bridging construct for a comminuted diaphyseal fracture, what is the primary biomechanical rationale for leaving empty screw holes over the fracture site?

. To increase the torsional rigidity of the construct
. To decrease the working length of the plate
. To reduce stress concentration and increase the working length
. To allow primary bone healing through absolute stability
. To prevent galvanic corrosion at the fracture gap

Correct Answer & Explanation

. To reduce stress concentration and increase the working length

Explanation

Leaving empty screw holes over the fracture site increases the working length of the plate. This reduces construct stiffness, distributes stress over a larger area to prevent plate failure, and promotes callus formation for secondary healing.

Question 5508

Topic: 1. General Principles & Basic Science

In the biphasic model of articular cartilage, which component provides the primary resistance to initial, rapid compressive loads?

. Type I collagen network
. Type II collagen network
. Aggrecan molecules
. Interstitial fluid pressurization
. Chondrocyte deformation

Correct Answer & Explanation

. Interstitial fluid pressurization

Explanation

During initial, rapid compressive loading, the low permeability of the extracellular matrix limits fluid flow out of the cartilage. Consequently, interstitial fluid pressurization provides over 90% of the initial load support and resistance to compression.

Question 5509

Topic: Biology, Genetics & Bone Healing

During the process of secondary fracture healing, the initial soft callus is eventually replaced by hard callus. This process is most dependent on which of the following biological phenomena?

. Intramembranous ossification
. Endochondral ossification
. Osteoclastic cutting cones
. Piezoelectric effect
. Apoptosis of osteoblasts

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary fracture healing involves the formation of a cartilaginous soft callus, which is subsequently mineralized and replaced by woven bone via endochondral ossification. Primary healing, by contrast, relies on osteoclastic cutting cones.

Question 5510

Topic: Biomechanics & Biomaterials

If a stainless steel screw is used in conjunction with a titanium plate in an internal fixation construct, what type of corrosion is most likely to occur?

. Crevice corrosion
. Fretting corrosion
. Pitting corrosion
. Galvanic 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 medium, such as body fluids. This leads to accelerated corrosion of the less noble metal.

Question 5511

Topic: 1. General Principles & Basic Science

A patient with chronic kidney disease presents with renal osteodystrophy. Which of the following hormonal profiles is most characteristic of this condition?

. Low PTH, low 1,25-dihydroxyvitamin D, high calcium
. High PTH, high 1,25-dihydroxyvitamin D, high calcium
. High PTH, low 1,25-dihydroxyvitamin D, low calcium
. Low PTH, high 1,25-dihydroxyvitamin D, low calcium
. Normal PTH, normal 1,25-dihydroxyvitamin D, low calcium

Correct Answer & Explanation

. High PTH, low 1,25-dihydroxyvitamin D, low calcium

Explanation

In chronic kidney disease, impaired renal hydroxylation leads to low levels of 1,25-dihydroxyvitamin D. This decreases intestinal calcium absorption, leading to hypocalcemia, which in turn stimulates secondary hyperparathyroidism.

Question 5512

Topic: Biomechanics & Biomaterials

A surgeon plans to ream the medullary canal to accommodate a larger diameter intramedullary nail. The torsional rigidity of a hollow cylindrical nail is proportional to which of the following?

. The outer radius raised to the fourth power minus the inner radius raised to the fourth power
. The outer radius squared minus the inner radius squared
. The outer radius raised to the third power
. The difference between the outer and inner diameters
. The cross-sectional area of the nail

Correct Answer & Explanation

. The outer radius raised to the fourth power minus the inner radius raised to the fourth power

Explanation

The torsional rigidity of a hollow cylinder is determined by its polar moment of inertia, which is proportional to the difference between the outer radius to the fourth power and the inner radius to the fourth power. Increasing nail diameter vastly improves torsional stability.

Question 5513

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a bone graft substitute. Which of the following bone graft properties is preserved in DBM?

. Osteogenesis
. Osteoinduction
. Mechanical structural support
. Viable osteoblasts
. Viable osteoprogenitor cells

Correct Answer & Explanation

. Osteoinduction

Explanation

Demineralized bone matrix lacks viable cells and structural strength due to the demineralization process. However, this process exposes bone morphogenetic proteins (BMPs), conferring excellent osteoinductive properties.

Question 5514

Topic: 1. General Principles & Basic Science
Following primary repair of a flexor tendon, the healing process passes through distinct phases. During the remodeling phase, what is the primary change in the collagen matrix?
. Replacement of Type I collagen with Type III collagen
. Replacement of Type III collagen with Type I collagen
. Deposition of predominantly proteoglycans
. Proliferation of inflammatory macrophages
. Formation of a hematoma scaffold

Correct Answer & Explanation

. Replacement of Type III collagen with Type I collagen

Explanation

During the remodeling phase of tendon healing, the initial weak Type III collagen laid down during the proliferative phase is gradually replaced by stronger, highly organized Type I collagen. This transition substantially increases the tensile strength of the tendon.

Question 5515

Topic: Biomechanics & Biomaterials

Cortical bone exhibits strain rate dependency. Which of the following best describes the mechanical behavior of bone when subjected to a high rate of loading, such as high-speed trauma?

. It becomes more ductile and fails at a lower ultimate strength
. It becomes less stiff and absorbs less energy
. It becomes stiffer, sustains higher loads before failure, and absorbs more energy
. Its yield point decreases significantly
. It undergoes greater plastic deformation before failure

Correct Answer & Explanation

. It becomes stiffer, sustains higher loads before failure, and absorbs more energy

Explanation

Bone is a viscoelastic material, meaning its properties change based on the speed of loading. At high strain rates, bone becomes stiffer, can withstand a higher ultimate load, and stores more energy before failure, often resulting in comminuted fractures.

Question 5516

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates, such as alendronate, inhibit osteoclast function and induce apoptosis. What is the specific intracellular target of these medications?

. Cathepsin K
. Carbonic anhydrase II
. Farnesyl pyrophosphate (FPP) synthase
. RANK receptor
. V-ATPase proton pump

Correct Answer & Explanation

. Farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate (FPP) synthase within the mevalonate pathway. This prevents the prenylation of small GTPases essential for osteoclast cytoskeletal organization and ruffled border formation, leading to apoptosis.

Question 5517

Topic: Biology, Genetics & Bone Healing

A 14-year-old boy presents with multiple fractures and a history of delayed tooth eruption. Radiographs show diffusely dense, 'bone-within-bone' appearance. His condition is caused by a genetic mutation affecting a specific enzyme required for proper bone resorption. Which of the following is the primary function of this enzyme in the osteoclast?

. Cleavage of type I collagen
. Generation of protons for the resorption pit
. Binding of RANKL to the RANK receptor
. Secreting tartrate-resistant acid phosphatase (TRAP)
. Attachment of the osteoclast to the bone surface via integrins

Correct Answer & Explanation

. Generation of protons for the resorption pit

Explanation

The patient has osteopetrosis, likely due to Carbonic Anhydrase II deficiency. This enzyme converts CO2 and H2O into carbonic acid, providing the protons needed to acidify and dissolve bone mineral in the resorption pit.

Question 5518

Topic: Biomechanics & Biomaterials

A biomedical engineer is evaluating a new titanium alloy for intramedullary nails. During mechanical testing, the material undergoes proportional deformation up to a specific limit before permanent deformation occurs. The slope of the load-deformation curve in this linear elastic region represents which of the following mechanical properties?

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

Correct Answer & Explanation

. Stiffness

Explanation

The slope of the linear elastic region on a load-deformation curve represents the stiffness of the material. On a stress-strain curve, this slope represents Young's modulus (modulus of elasticity).

Question 5519

Topic: Biomechanics & Biomaterials

A patient undergoes correction of a severe knee flexion contracture using a hinged external fixator. Over several days, the tension in the soft tissues gradually decreases despite the fixator maintaining a constant length. Which viscoelastic property does this phenomenon best describe?

. Creep
. Stress relaxation
. Hysteresis
. Fatigue
. Isotropism

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in stress (tension) over time when a viscoelastic material is held at a constant strain (length). In contrast, creep is the progressive deformation over time under a constant load.

Question 5520

Topic: Biology, Genetics & Bone Healing

An investigational drug for the treatment of severe osteoporosis acts by inhibiting sclerostin. By neutralizing sclerostin, this medication primarily increases bone mass through which of the following mechanisms?

. Inhibition of the RANKL-RANK interaction
. Direct stimulation of osteoclast apoptosis
. Activation of the Wnt/beta-catenin signaling pathway
. Enhanced absorption of intestinal calcium
. Increased production of parathyroid hormone

Correct Answer & Explanation

. Activation of the Wnt/beta-catenin signaling pathway

Explanation

Sclerostin, produced by osteocytes, normally inhibits the Wnt/beta-catenin signaling pathway to decrease osteoblastogenesis. Inhibiting sclerostin (e.g., romosozumab) upregulates Wnt signaling, leading to increased bone formation.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page