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1. General Principles & Basic Science MCQs

Practice Set 355 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 7081

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement provides immediate fixation of total joint arthroplasty components. By which of the following mechanisms does PMMA secure the implant to the surrounding host bone?

. Covalent chemical bonding to the bony trabeculae
. Osteointegration at the cement-bone interface
. Interlocking micro-mechanical fixation
. Galvanic adhesion
. Direct binding to type I collagen

Correct Answer & Explanation

. Covalent chemical bonding to the bony trabeculae

Explanation

PMMA is not an adhesive and does not chemically bond to bone. It functions as a grout, providing rigid fixation via interlocking micro-mechanical fixation as it permeates the cancellous bone trabeculae before polymerizing.

Question 7082

Topic: 1. General Principles & Basic Science

During the remodeling phase of tendon healing, the biochemical composition of the extracellular matrix changes to restore tensile strength. This process is characterized by a transition from which collagen type to another?

. Type I to Type II
. Type II to Type I
. Type III to Type I
. Type I to Type III
. Type II to Type III

Correct Answer & Explanation

. Type I to Type II

Explanation

During the initial reparative phase of tendon healing, fibroblasts produce large amounts of Type III collagen. As the tendon remodels and matures, this is progressively replaced by stronger, highly organized Type I collagen.

Question 7083

Topic: Biology, Genetics & Bone Healing

Osteocalcin is the most abundant non-collagenous protein found in the bone matrix and is frequently used as a serum marker. What is its primary physiological role within the matrix?

. Providing tensile strength to the osteon
. Initiating collagen fibril cross-linking
. Regulating osteoclast apoptosis
. Binding extracellular calcium to regulate mineralization
. Serving as a structural template for proteoglycans

Correct Answer & Explanation

. Providing tensile strength to the osteon

Explanation

Osteocalcin is secreted by mature osteoblasts and contains gamma-carboxyglutamic acid residues (Vitamin K dependent) that tightly bind calcium. Its primary role is regulating bone mineralization and density.

Question 7084

Topic: 1. General Principles & Basic Science

The menisci of the knee protect the articular cartilage by converting vertical compressive loads into tangential "hoop stresses". Which structural component of the meniscus is primarily responsible for resisting these hoop stresses?

. Radially oriented Type I collagen fibers
. Circumferentially oriented Type I collagen fibers
. Radially oriented Type II collagen fibers
. Circumferentially oriented Type II collagen fibers
. Randomly oriented elastin fibers

Correct Answer & Explanation

. Radially oriented Type I collagen fibers

Explanation

The outer two-thirds of the meniscus consists primarily of Type I collagen arranged in a circumferential pattern. These circumferential fibers are uniquely adapted to resist the expansile "hoop stresses" generated during axial loading.

Question 7085

Topic: 1. General Principles & Basic Science

The bending stiffness of a rectangular bone plate is determined by its geometric properties. If a surgeon switches to a plate that is double the thickness of the original plate, the bending stiffness of the construct increases by a factor of:

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 2

Explanation

The area moment of inertia for a rectangular plate is given by the formula I = (b ยท hยณ) / 12, where b is the base and h is the thickness. Doubling the thickness increases the bending stiffness by a factor of 2ยณ, or 8.

Question 7086

Topic: Biology, Genetics & Bone Healing

Intermittent administration of low-dose parathyroid hormone (e.g., Teriparatide) is used clinically for its profound anabolic effect on bone. This anabolic action is primarily mediated by:

. Inhibition of osteoclast ruffled border formation
. Direct stimulation of osteoblast survival, proliferation, and differentiation
. Upregulation of sclerostin production by osteocytes
. Increased secretion of OPG by circulating macrophages
. Downregulation of Runx2 in mesenchymal stem cells

Correct Answer & Explanation

. Inhibition of osteoclast ruffled border formation

Explanation

While continuous elevated PTH causes bone resorption, intermittent administration has an anabolic effect. It directly stimulates osteoblast proliferation and differentiation while preventing osteoblast apoptosis, leading to net bone formation.

Question 7087

Topic: Biology, Genetics & Bone Healing

A patient with osteoporosis is started on denosumab. This medication acts by binding to which of the following targets, thereby mimicking the action of what endogenous molecule?

. Binds to RANKL, mimicking osteoprotegerin (OPG)
. Binds to RANK receptor, mimicking osteoprotegerin (OPG)
. Binds to RANKL, mimicking parathyroid hormone (PTH)
. Binds to osteoblasts, mimicking bisphosphonates
. Binds to sclerostin, mimicking Wnt signaling

Correct Answer & Explanation

. Binds to RANKL, mimicking osteoprotegerin (OPG)

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from interacting with the RANK receptor on osteoclasts. This mechanism directly mimics the function of the endogenous decoy receptor osteoprotegerin (OPG).

Question 7088

Topic: Biomechanics & Biomaterials

During the physiological loading of a normal ligament, the initial non-linear "toe region" of the stress-strain curve represents which of the following microstructural events?

. Failure of the weakest collagen fibrils
. Viscoelastic stress relaxation
. Micro-tearing of cross-links
. Uncrimping of collagen fibers
. Fluid exudation from the extracellular matrix

Correct Answer & Explanation

. Failure of the weakest collagen fibrils

Explanation

The "toe region" represents the initial phase of the stress-strain curve where minimal force results in significant elongation. This corresponds microscopically to the straightening or "uncrimping" of the naturally crimped collagen fibers.

Question 7089

Topic: 1. General Principles & Basic Science

The pullout strength of a bone screw is directly proportional to which of the following geometric parameters?

. Inner root diameter
. Outer thread diameter
. Screw insertion torque
. Length of the unthreaded shaft
. Pitch of the screw

Correct Answer & Explanation

. Inner root diameter

Explanation

Screw pullout strength is directly proportional to the outer thread diameter, the length of thread engagement in the bone, and the shear strength of the bone material. Increasing the outer diameter maximizes the volume of bone captured between the threads.

Question 7090

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which zone is characterized by the highest concentration of water and collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage contains the highest water content and lowest proteoglycan concentration. Its collagen fibers are densely packed and oriented parallel to the articular surface to resist shear forces.

Question 7091

Topic: Biomechanics & Biomaterials

Mixing stainless steel and titanium implants in the same surgical field can lead to accelerated degradation of the implants. Which of the following best describes the primary mechanism of this process?

. Abrasive wear
. Fretting corrosion
. Galvanic corrosion
. Crevice corrosion
. Fatigue failure

Correct Answer & Explanation

. Abrasive wear

Explanation

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

Question 7092

Topic: Biomechanics & Biomaterials

Because bone is a viscoelastic material, its mechanical properties depend heavily on the rate of loading. When cortical bone is subjected to a high strain rate (fast loading), how do its properties change compared to low strain rate loading?

. It becomes more ductile and absorbs less energy
. It becomes stiffer and fails at a higher ultimate load
. It experiences greater stress relaxation
. Its yield point decreases significantly
. It exhibits increased plastic deformation before failure

Correct Answer & Explanation

. It becomes more ductile and absorbs less energy

Explanation

Due to its viscoelastic nature, bone loaded at high strain rates becomes stiffer, sustains higher ultimate loads before failure, and absorbs more energy (higher area under the stress-strain curve) compared to slow loading rates.

Question 7093

Topic: Biomechanics & Biomaterials

Which of the following wear mechanisms is defined as the removal of material resulting from two articulating surfaces rubbing against each other, leading to local microscopic welding and subsequent tearing off of particles?

. Abrasive wear
. Adhesive wear
. Third-body wear
. Fretting wear
. Corrosive wear

Correct Answer & Explanation

. Abrasive wear

Explanation

Adhesive wear occurs when two surfaces slide against each other, causing local asperities to bond or "weld" together. Subsequent movement tears these micro-welds apart, releasing wear debris.

Question 7094

Topic: 1. General Principles & Basic Science

What is the primary mechanical advantage of a locked plating construct over a conventional non-locked plating construct in osteoporotic bone?

. Increased frictional forces between the plate and the bone
. Reliance on the pullout strength of individual individual screws
. Prevention of sequential screw pullout through fixed-angle stability
. Promotion of primary bone healing through dynamic compression
. Decreased working length of the construct

Correct Answer & Explanation

. Increased frictional forces between the plate and the bone

Explanation

Locked plates act as single-beam constructs with fixed-angle stability, meaning failure requires simultaneous pullout of all screws. This prevents the sequential screw failure often seen with conventional non-locked plates in poor-quality bone.

Question 7095

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) regulates serum calcium levels through multiple mechanisms. Which of the following is a direct physiologic effect of continuous, high-dose PTH exposure on bone cellular activity?

. Stimulation of osteoprotegerin (OPG) release
. Direct binding to osteoclasts to increase bone resorption
. Upregulation of RANKL expression on osteoblasts
. Inhibition of 1-alpha-hydroxylase in the kidney
. Decreased calcium reabsorption in the distal tubule

Correct Answer & Explanation

. Stimulation of osteoprotegerin (OPG) release

Explanation

Continuous PTH exposure binds to receptors on osteoblasts, stimulating them to upregulate RANKL expression. RANKL then binds to RANK on osteoclast precursors, driving osteoclastogenesis and increasing bone resorption.

Question 7096

Topic: Biomechanics & Biomaterials

Which of the following common orthopaedic biomaterials possesses the highest modulus of elasticity (stiffness)?

. Polymethylmethacrylate (PMMA)
. Cortical bone
. Titanium alloy (Ti-6Al-4V)
. 316L Stainless steel
. Cobalt-chromium (Co-Cr) alloy

Correct Answer & Explanation

. Polymethylmethacrylate (PMMA)

Explanation

Cobalt-chromium has the highest modulus of elasticity (~220-240 GPa), making it the stiffest among standard implant materials. Stainless steel is ~200 GPa, Titanium alloy is ~110 GPa, and cortical bone is ~15-20 GPa.

Question 7097

Topic: 1. General Principles & Basic Science

The primary biomechanical function of the circumferentially oriented Type I collagen fibers in the menisci of the knee is to:

. Resist radial shear forces during knee flexion
. Convert compressive loads into tensile hoop stresses
. Provide boundary lubrication to the articular surfaces
. Anchor the meniscus securely to the peripheral joint capsule
. Prevent anterior translation of the tibia relative to the femur

Correct Answer & Explanation

. Resist radial shear forces during knee flexion

Explanation

The wedge shape of the meniscus and its strong circumferential collagen fibers work together to convert axial compressive loads across the joint into tensile "hoop stresses," effectively dissipating force and protecting the articular cartilage.

Question 7098

Topic: Biology, Genetics & Bone Healing

The compressive stiffness of articular cartilage is primarily provided by the interaction between interstitial fluid and which of the following extracellular matrix components?

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

Correct Answer & Explanation

. Type I collagen

Explanation

Proteoglycans, primarily aggrecan, possess highly negatively charged glycosaminoglycan (GAG) side chains that repel each other and draw in water via the Donnan osmotic effect. This creates a swelling pressure that is resisted by the collagen network, providing compressive stiffness.

Question 7099

Topic: Biology, Genetics & Bone Healing

Primary (strain-free) bone healing, such as that achieved with rigid absolute stability, is characterized microscopically by which of the following processes?

. Formation of a soft cartilaginous callus
. Endochondral ossification
. Direct osteonal remodeling via cutting cones across the fracture site
. Intramembranous ossification originating from the periosteum
. Rapid woven bone formation leading to a hard external callus

Correct Answer & Explanation

. Formation of a soft cartilaginous callus

Explanation

Primary bone healing occurs without callus formation under conditions of absolute stability. It is characterized by direct Haversian remodeling, where osteoclastic cutting cones traverse the fracture site, followed by osteoblasts laying down lamellar bone.

Question 7100

Topic: Physiology & Rehabilitation

Which type of muscle contraction generates the highest peak force and is most commonly associated with muscle strain injuries?

. Isometric contraction
. Concentric isotonic contraction
. Eccentric contraction
. Isokinetic contraction
. Tetanic contraction

Correct Answer & Explanation

. Isometric contraction

Explanation

Eccentric contractions, where the muscle lengthens while contracting against a load, generate the highest peak forces. Due to these high forces and mechanical tissue disruption, eccentric loading is the primary mechanism for muscle strains.

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