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1. General Principles & Basic Science MCQs

Practice Set 676 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 13501

Topic: Physiology & Rehabilitation

During the early stance phase of the normal gait cycle, the quadriceps muscle contracts to control knee flexion. This type of muscle contraction is best described as:

. Concentric
. Eccentric
. Isometric
. Isokinetic
. Auxotonic

Correct Answer & Explanation

. Eccentric

Explanation

An eccentric contraction occurs when a muscle lengthens while under tension, serving to decelerate a joint. The quadriceps act eccentrically during early stance to absorb shock and prevent the knee from buckling.

Question 13502

Topic: 1. General Principles & Basic Science
During the remodeling phase of tendon healing, the biomechanical strength of the tendon improves significantly. This is primarily due to which of the following processes?
. Replacement of type I collagen with type III collagen
. Increased cellularity and angiogenesis
. Replacement of type III collagen with type I collagen
. Random orientation of collagen fibrils
. Decreased collagen cross-linking

Correct Answer & Explanation

. Replacement of type III collagen with type I collagen

Explanation

The remodeling phase is characterized by a decrease in cellularity and the progressive replacement of weaker type III collagen with stronger, longitudinally aligned type I collagen. This transition is crucial for restoring the tendon's tensile strength.

Question 13503

Topic: Biology, Genetics & Bone Healing

A surgeon utilizes a demineralized bone matrix (DBM) allograft for a spinal fusion. Which of the following biologic properties does DBM possess?

. Osteoconduction only
. Osteoinduction only
. Osteogenesis and osteoconduction
. Osteoconduction and osteoinduction
. Osteogenesis, osteoconduction, and osteoinduction

Correct Answer & Explanation

. Osteoconduction and osteoinduction

Explanation

DBM is osteoconductive due to its collagenous matrix and osteoinductive due to preserved bone morphogenetic proteins (BMPs). It lacks live osteoprogenitor cells, so it is not osteogenic.

Question 13504

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for venous thromboembolism prophylaxis following a total knee arthroplasty. What is the specific mechanism of action of this medication?
. Direct thrombin inhibitor
. Vitamin K antagonist
. Direct factor Xa inhibitor
. Indirect factor Xa inhibitor via antithrombin III
. Cyclooxygenase inhibitor

Correct Answer & Explanation

. Direct factor Xa inhibitor

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that work by selectively inhibiting Factor Xa. Unlike low-molecular-weight heparins, they directly inhibit the target without requiring antithrombin III.

Question 13505

Topic: Biology, Genetics & Bone Healing

A 4-year-old child fed exclusively boiled cow's milk presents with irritability, bleeding gums, and subperiosteal hematomas. The primary defect in bone formation is related to the impaired function of which of the following enzymes?

. Lysyl oxidase
. Prolyl hydroxylase
. Alkaline phosphatase
. Carbonic anhydrase
. Collagenase

Correct Answer & Explanation

. Prolyl hydroxylase

Explanation

The patient exhibits classic signs of scurvy (Vitamin C deficiency). Vitamin C is an essential cofactor for prolyl and lysyl hydroxylase, which are required for the intracellular hydroxylation of proline and lysine during collagen synthesis.

Question 13506

Topic: Biology, Genetics & Bone Healing

A 70-year-old man undergoes total hip arthroplasty for secondary osteoarthritis. Radiographs demonstrate cortical thickening and coarse trabeculae in the proximal femur. Preoperative labs show an isolated elevation of alkaline phosphatase. Histologic evaluation of the femoral head would most likely show:

. Woven bone lacking cement lines
. A mosaic pattern of lamellar bone with prominent cement lines
. Sheets of plasma cells with amyloid deposition
. Atypical spindle cells producing osteoid
. Extensive marrow fibrosis with cystic changes

Correct Answer & Explanation

. A mosaic pattern of lamellar bone with prominent cement lines

Explanation

The patient's presentation is indicative of Paget's disease of bone, which features hyperactive osteoclasts and chaotic osteoblastic bone formation. The classic histologic hallmark is a 'mosaic' or 'jigsaw puzzle' pattern of lamellar bone with irregular cement lines.

Question 13507

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is frequently used in joint arthroplasty. The addition of barium sulfate to PMMA serves which of the following purposes?

. Increases the porosity of the cement
. Reduces the exothermic reaction temperature
. Provides radiopacity
. Accelerates the polymerization time
. Increases the ultimate tensile strength

Correct Answer & Explanation

. Provides radiopacity

Explanation

Barium sulfate or zirconium dioxide is added to PMMA to make the cement radiopaque, allowing for postoperative radiographic evaluation of the cement mantle. These additives act as stress risers and actually decrease the ultimate tensile strength of the cement.

Question 13508

Topic: Biology, Genetics & Bone Healing

During secondary fracture healing, the biomechanical stability of the fracture determines the type of tissue that forms in the gap according to Perren's strain theory. If the strain at the fracture gap is between 2% and 10%, which tissue will primarily form?

. Lamellar bone
. Granulation tissue
. Hyaline cartilage
. Fibrocartilage
. Woven bone

Correct Answer & Explanation

. Fibrocartilage

Explanation

According to Perren's strain theory, low strain (<2%) allows primary bone healing. Intermediate strain (2-10%) promotes the formation of a fibrocartilaginous callus, while high strain (>10%) results in granulation tissue and potential nonunion.

Question 13509

Topic: 1. General Principles & Basic Science

According to the inverse square law of radiation exposure, if an orthopedic surgeon increases their distance from the fluoroscopy source from 1 meter to 3 meters, the radiation exposure is reduced to what fraction of the original dose?

. 1/3
. 1/6
. 1/9
. 1/12
. 1/27

Correct Answer & Explanation

. 1/9

Explanation

The inverse square law dictates that radiation intensity is inversely proportional to the square of the distance from the source. Tripling the distance (from 1 to 3 meters) reduces the exposure to 1/(3^2) or 1/9 of the original dose.

Question 13510

Topic: 1. General Principles & Basic Science

In the pathogenesis of osteoarthritis, matrix metalloproteinases (MMPs) play a critical role in articular cartilage degradation. Which specific MMP is primarily responsible for the cleavage of type II collagen?

. MMP-1
. MMP-3
. MMP-9
. MMP-13
. MMP-14

Correct Answer & Explanation

. MMP-13

Explanation

MMP-13 (collagenase-3) is the principal enzyme responsible for the degradation of the type II collagen network in the pathogenesis of osteoarthritis. Its expression is highly upregulated in osteoarthritic cartilage.

Question 13511

Topic: 1. General Principles & Basic Science

When inserting a cortical screw into a diaphysis, the "pull-out strength" of the screw is directly proportional to which of the following variables?

. Inner root diameter
. Pitch
. Outer thread diameter
. Thread thickness
. Insertion torque

Correct Answer & Explanation

. Outer thread diameter

Explanation

The pull-out strength of a bone screw is directly proportional to the outer thread diameter, the length of thread engagement in the bone, and the shear strength of the surrounding bone. The inner root diameter dictates the screw's resistance to fatigue bending failure.

Question 13512

Topic: Biology, Genetics & Bone Healing

A 68-year-old female with severe osteoporosis is treated with alendronate. Bisphosphonates inhibit osteoclast-mediated bone resorption by interfering with which of the following intracellular pathways?

. Wnt/beta-catenin signaling
. Mevalonate pathway
. RANK/RANKL interaction
. Transforming growth factor-beta signaling
. Cyclooxygenase pathway

Correct Answer & Explanation

. Mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates, such as alendronate, inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents the prenylation of small GTPase proteins (e.g., Ras, Rho), disrupting osteoclast function and leading to apoptosis.

Question 13513

Topic: Biomechanics & Biomaterials

A viscoelastic material subjected to a constant load will continuously deform over time. This specific biomechanical phenomenon is known as which of the following?

. Stress relaxation
. Creep
. Fatigue failure
. Hysteresis
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a viscoelastic material under a constant load over time. Stress relaxation refers to a decrease in stress over time when the material is held at a constant deformation.

Question 13514

Topic: Biology, Genetics & Bone Healing

A 70-year-old female is prescribed alendronate for osteoporosis. Which of the following best describes the cellular mechanism of action of this medication?

. Inhibition of RANKL
. Stimulation of osteoblast differentiation
. Inhibition of farnesyl pyrophosphate synthase
. Direct binding to parathyroid hormone receptors
. Inhibition of sclerostin

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates like alendronate inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents osteoclast ruffled border formation and induces osteoclast apoptosis.

Question 13515

Topic: 1. General Principles & Basic Science

When comparing articular cartilage changes in early osteoarthritis to normal aging, which of the following changes is characteristic of osteoarthritis but NOT normal aging?

. Decreased water content
. Increased water content
. Decreased chondrocyte size
. Increased total proteoglycan content
. Increased keratin sulfate concentration

Correct Answer & Explanation

. Increased water content

Explanation

In osteoarthritis, the earliest change is an increase in water content and a decrease in total proteoglycan content. In contrast, normal aging cartilage typically demonstrates a decrease in water content.

Question 13516

Topic: 1. General Principles & Basic Science

During skeletal muscle contraction, the release of calcium from the sarcoplasmic reticulum directly initiates the power stroke by binding to which of the following structures?

. Tropomyosin
. Myosin heavy chain
. Troponin C
. Troponin I
. Actin

Correct Answer & Explanation

. Troponin C

Explanation

Calcium released from the sarcoplasmic reticulum binds to Troponin C. This causes a conformational change that moves tropomyosin, exposing the myosin-binding sites on the actin filament.

Question 13517

Topic: 1. General Principles & Basic Science

A patient sustains a peripheral nerve injury characterized by loss of axonal continuity and endoneurial tube disruption, but with an intact perineurium. What is the corresponding Sunderland classification?

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

Correct Answer & Explanation

. Third-degree

Explanation

A third-degree Sunderland nerve injury involves disruption of the axon and endoneurium, while the perineurium and epineurium remain intact. This corresponds to a severe axonotmesis in Seddon's classification.

Question 13518

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is used primarily to reduce volumetric wear. Which of the following mechanical properties is typically decreased as a result of the cross-linking process?
. Yield strength
. Fatigue crack propagation resistance
. Elastic modulus
. Hardness
. Melting point

Correct Answer & Explanation

. Fatigue crack propagation resistance

Explanation

Highly cross-linking UHMWPE significantly reduces abrasive and adhesive wear but reduces its fatigue resistance and ductility. This makes the material more susceptible to fatigue crack propagation and fracture.

Question 13519

Topic: Biomechanics & Biomaterials

A 60-year-old male presents with acute knee pain and effusion. Joint aspiration yields synovial fluid with 45,000 WBCs/mcL. Polarized light microscopy reveals weakly positively birefringent rhomboid-shaped crystals. What is the most likely composition of these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Calcium hydroxyapatite
. Cholesterol
. Basic calcium phosphate

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate

Explanation

Weakly positively birefringent, rhomboid-shaped crystals are diagnostic of calcium pyrophosphate dihydrate (CPPD) deposition disease (pseudogout). Monosodium urate crystals are needle-shaped and strongly negatively birefringent.

Question 13520

Topic: Biology, Genetics & Bone Healing

During secondary fracture healing, the transition from the soft callus to the hard callus phase is primarily characterized by which of the following biological processes?

. Endochondral ossification
. Intramembranous ossification
. Hematoma organization
. Osteoclast cutting cone formation
. Fibrocartilage production

Correct Answer & Explanation

. Endochondral ossification

Explanation

The conversion of the cartilaginous soft callus into a hard bony callus occurs via endochondral ossification. Intramembranous ossification occurs directly from mesenchymal stem cells without a cartilage intermediate.

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