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1. General Principles & Basic Science MCQs

Practice Set 303 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 6041

Topic: 1. General Principles & Basic Science
During the remodeling phase of ligament healing, the initial disorganized collagen matrix is gradually replaced. Which of the following represents the primary transition in collagen type during this phase?
. Type I to Type II
. Type III to Type I
. Type II to Type X
. Type I to Type III
. Type III to Type II

Correct Answer & Explanation

. Type III to Type I

Explanation

In the early stages of ligament and tendon healing, fibroblasts predominantly synthesize Type III collagen. During remodeling, this is gradually replaced by stronger, more organized Type I collagen.

Question 6042

Topic: Biomechanics & Biomaterials



On a standard stress-strain curve for a ductile material, the point at which the material transitions from elastic deformation to plastic deformation is known as the:

. Ultimate tensile point
. Failure point
. Yield point
. Proportional limit
. Toughness maximum

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the end of elastic (reversible) deformation and the beginning of plastic (permanent) deformation. Any load applied beyond this point causes permanent structural change.

Question 6043

Topic: Biology, Genetics & Bone Healing

Osteoprotegerin (OPG) regulates bone resorption by which of the following mechanisms?

. Acting as a decoy receptor for RANKL
. Directly inhibiting the proton pump on osteoclasts
. Stimulating osteoblast apoptosis
. Binding to M-CSF to prevent macrophage differentiation
. Upregulating sclerostin expression

Correct Answer & Explanation

. Acting as a decoy receptor for RANKL

Explanation

OPG is secreted by osteoblasts and binds to RANKL, preventing it from interacting with the RANK receptor on osteoclast precursors. This prevents osteoclastogenesis and limits bone resorption.

Question 6044

Topic: 1. General Principles & Basic Science

In which zone of articular cartilage do collagen fibers align perpendicular to the joint surface to resist shear forces and anchor to the subchondral bone?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

In the deep (radial) zone, collagen fibers are oriented perpendicular to the articular surface. This arrangement allows them to cross the tidemark and securely anchor the cartilage to the underlying subchondral bone.

Question 6045

Topic: Biomechanics & Biomaterials

In the load-elongation curve of a healthy tendon, the initial nonlinear "toe region" represents which of the following physiologic phenomena?

. Microfailure of collagen fibrils
. Uncrimping of collagen fibers
. Elastic deformation of the whole tendon
. Plastic deformation
. Complete macroscopic failure

Correct Answer & Explanation

. Uncrimping of collagen fibers

Explanation

The initial "toe region" of a tendon's stress-strain curve represents the straightening out, or "uncrimping," of the naturally wavy collagen fibers under low loads. Linear elastic stretching occurs only after the fibers are fully straightened.

Question 6046

Topic: Biology, Genetics & Bone Healing

A 45-year-old male undergoes open reduction and internal fixation of a diaphyseal radius fracture utilizing a dynamic compression plate to achieve absolute stability. What is the primary histological mechanism by which this fracture will heal?

. Direct bone healing via cutting cones and Haversian remodeling
. Endochondral ossification via a cartilaginous intermediate
. Intramembranous ossification from the periosteal surface
. Fibrocartilage callus formation and subsequent mineralization
. Appositional bone growth via osteoblast recruitment from the bone marrow

Correct Answer & Explanation

. Direct bone healing via cutting cones and Haversian remodeling

Explanation

Absolute stability minimizes interfragmentary strain, allowing for primary bone healing. This occurs directly via cutting cones and Haversian remodeling without intermediate callus formation.

Question 6047

Topic: Biomechanics & Biomaterials

Among the following structural metallic biomaterials utilized in orthopedic implants, which possesses a modulus of elasticity (Young's modulus) closest to that of cortical bone?

. Titanium alloy (Ti-6Al-4V)
. 316L Stainless steel
. Cobalt-chromium-molybdenum alloy
. Alumina ceramic
. Zirconia ceramic

Correct Answer & Explanation

. Titanium alloy (Ti-6Al-4V)

Explanation

Titanium alloy has a modulus of elasticity (~110 GPa) that is closer to cortical bone (~15-20 GPa) compared to stainless steel (~200 GPa) and cobalt-chrome (~220 GPa). This lower modulus helps to minimize stress shielding.

Question 6048

Topic: Biology, Genetics & Bone Healing

Denosumab is an established therapeutic agent for osteoporosis and giant cell tumor of bone. Which of the following best describes its specific molecular mechanism of action?

. It acts as a decoy receptor binding directly to RANK
. It binds to RANKL, preventing its interaction with the RANK receptor
. It directly induces apoptosis of mature, multinucleated osteoclasts
. It inhibits the Wnt/beta-catenin pathway in osteoblasts
. It inhibits farnesyl pyrophosphate synthase in the mevalonate pathway

Correct Answer & Explanation

. It binds to RANKL, preventing its interaction with the RANK receptor

Explanation

Denosumab is a monoclonal antibody that selectively binds to RANKL. By blocking RANKL from binding to RANK on osteoclast precursors, it inhibits osteoclastogenesis, function, and survival.

Question 6049

Topic: 1. General Principles & Basic Science

During the insertion of a cortical screw, which of the following design parameters is directly proportional to the pullout strength of the screw?

. Inner (root) diameter
. Outer (thread) diameter
. Thread pitch
. Screw head diameter
. Core cross-sectional area

Correct Answer & Explanation

. Outer (thread) diameter

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter, the length of thread engagement, and the shear strength of the bone. It is inversely proportional to the thread pitch.

Question 6050

Topic: 1. General Principles & Basic Science

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

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone of articular cartilage contains the highest concentration of water and Type II collagen fibers aligned parallel to the joint surface. This arrangement is optimally designed to resist shear forces.

Question 6051

Topic: Biology, Genetics & Bone Healing

Mesenchymal stem cells differentiate into osteoblasts under the influence of specific gene regulators. Which of the following transcription factors is considered the essential master regulator for osteoblast differentiation?

. Sox9
. PPAR-gamma
. Runx2 (Cbfa1)
. MyoD
. NFATc1

Correct Answer & Explanation

. Runx2 (Cbfa1)

Explanation

Runx2 (also known as Cbfa1) is the core transcription factor required for osteoblast differentiation. Mice lacking Runx2 exhibit a complete absence of osteoblasts and bone formation.

Question 6052

Topic: Biomechanics & Biomaterials

In biomechanical material testing, an S-N (Stress-Number of cycles) curve is often generated to assess fatigue failure. What does the endurance limit on this curve represent?

. The point of irreversible plastic deformation
. The maximum stress a material can sustain before fracture in a single cycle
. The stress level below which the material can theoretically endure an infinite number of cycles without failing
. The total energy absorbed by the material prior to complete failure
. The intrinsic stiffness of the material in the elastic region

Correct Answer & Explanation

. The stress level below which the material can theoretically endure an infinite number of cycles without failing

Explanation

The endurance limit (or fatigue limit) is the highest stress level that a material can withstand for an infinite number of load cycles without experiencing fatigue failure.

Question 6053

Topic: Biology, Genetics & Bone Healing

Teriparatide is utilized in the management of severe osteoporosis. What is the primary cellular effect responsible for its anabolic action on bone when administered via daily intermittent subcutaneous injections?

. Decreased osteoblast apoptosis and prolonged osteoblast lifespan
. Continuous upregulation of RANKL leading to coupled bone resorption
. Direct inhibition of osteoclast ruffled border formation
. Precipitation of calcium and phosphate directly into the osteoid matrix
. Direct stimulation of osteoprotegerin (OPG) secretion by osteocytes

Correct Answer & Explanation

. Decreased osteoblast apoptosis and prolonged osteoblast lifespan

Explanation

Intermittent administration of parathyroid hormone (PTH) analogs exerts an anabolic effect primarily by inhibiting osteoblast apoptosis. This prolongs the functional lifespan of osteoblasts, leading to net bone formation.

Question 6054

Topic: Biomechanics & Biomaterials

A tendon undergoes progressive elongation when subjected to a constant, sustained tensile load over a period of time. This fundamental viscoelastic property is defined as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Strain hardening

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent deformation or elongation of a viscoelastic material when it is subjected to a constant load. In contrast, stress relaxation is the decrease in stress over time when the material is held at a constant length.

Question 6055

Topic: Biology, Genetics & Bone Healing

The compressive stiffness and resilience of articular cartilage are primarily determined by the physiochemical interaction between interstitial fluid and which of the following macromolecular components?

. Type I collagen
. Type II collagen
. Aggrecan
. Decorin
. Hyaluronic acid alone

Correct Answer & Explanation

. Aggrecan

Explanation

Aggrecan is the predominant proteoglycan in articular cartilage. Its highly negatively charged glycosaminoglycan side chains repel each other and attract water via the Donnan osmotic effect, providing the tissue's compressive stiffness.

Question 6056

Topic: 1. General Principles & Basic Science

During endochondral ossification, the initial phase of primary mineralization within the osteoid matrix is facilitated by which of the following structures?

. Matrix vesicles released by hypertrophic chondrocytes and osteoblasts
. Lysosomes secreted by multinucleated osteoclasts
. Mitochondria extruded from apoptotic mesenchymal stem cells
. Cleavage fragments of Type X collagen
. Direct precipitation of calcium from adjacent capillary networks

Correct Answer & Explanation

. Matrix vesicles released by hypertrophic chondrocytes and osteoblasts

Explanation

Matrix vesicles are membrane-bound structures that bud from hypertrophic chondrocytes and osteoblasts. They provide a protected microenvironment rich in calcium and phosphate, initiating hydroxyapatite crystal formation.

Question 6057

Topic: 1. General Principles & Basic Science

Following the implantation of a massive cortical bone allograft for tumor reconstruction, incorporation into the host skeleton occurs predominantly via which of the following biological processes?

. Rapid revascularization and complete cellular repopulation within 6 months
. Intramembranous ossification directly from the periosteal allograft surface
. Creeping substitution characterized by osteoclastic resorption followed by host osteoblastic deposition
. Endochondral ossification at the diaphyseal host-graft junction
. Direct differentiation of surviving allograft osteocytes

Correct Answer & Explanation

. Creeping substitution characterized by osteoclastic resorption followed by host osteoblastic deposition

Explanation

Massive cortical allografts incorporate extremely slowly via creeping substitution. Host cutting cones must progressively resorb the necrotic allograft bone and sequentially lay down new host bone in its place.

Question 6058

Topic: Biomechanics & Biomaterials

The torsional stiffness of a solid intramedullary nail is mathematically proportional to its radius raised to which of the following powers?

. First power
. Second power
. Third power
. Fourth power
. Fifth power

Correct Answer & Explanation

. Fourth power

Explanation

The torsional stiffness of a solid cylinder is proportional to its polar moment of inertia. For a solid cylindrical intramedullary nail, the polar moment of inertia is proportional to the radius raised to the fourth power (r^4).

Question 6059

Topic: 1. General Principles & Basic Science

Histologically, woven bone can be distinguished from mature lamellar bone by which of the following characteristic features?

. Higher mineral content per unit volume
. Lower overall osteocyte density
. Isotropic (random) orientation of collagen fibers
. Anisotropic (highly parallel) orientation of collagen fibers
. Slower rate of osteoid deposition

Correct Answer & Explanation

. Isotropic (random) orientation of collagen fibers

Explanation

Woven bone is immature, rapidly deposited bone characterized by an isotropic (random, disorganized) orientation of collagen fibers. It also features a higher density of osteocytes and a lower mineral content compared to lamellar bone.

Question 6060

Topic: 1. General Principles & Basic Science

When constructing a unilateral half-pin external fixator for tibial lengthening, which of the following structural modifications will most effectively increase the overall bending stiffness of the construct?

. Decreasing the diameter of the half-pins
. Increasing the distance between the longitudinal bar and the bone
. Increasing the distance between the pins within a single bone segment (pin spread)
. Decreasing the total number of pins per segment
. Utilizing stainless steel rather than carbon fiber for the longitudinal bar

Correct Answer & Explanation

. Increasing the distance between the pins within a single bone segment (pin spread)

Explanation

Increasing the pin spread (the distance between the two outermost pins within a single bone fragment) significantly increases the bending and torsional stiffness of an external fixator construct.

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