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1. General Principles & Basic Science MCQs

Practice Set 270 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 5381

Topic: Biomechanics & Biomaterials

In total joint arthroplasty, stress shielding of the proximal femur is primarily determined by the mismatch in which of the following material properties between the metallic implant and the host bone?

. Yield strength
. Ultimate tensile strength
. Modulus of elasticity
. Fatigue limit
. Ductility

Correct Answer & Explanation

. Modulus of elasticity

Explanation

Stress shielding occurs due to a mismatch in the modulus of elasticity (Young's modulus) between the stiffer metallic implant and the less stiff surrounding bone. This lack of physiologic loading leads to adaptive bone resorption according to Wolff's Law.

Question 5382

Topic: Biology, Genetics & Bone Healing

Sclerostin, a glycoprotein produced by mature osteocytes, regulates bone mass primarily by inhibiting which of the following molecular pathways?

. Bone morphogenetic protein (BMP) pathway
. Wnt/beta-catenin pathway
. RANK/RANKL/OPG pathway
. Notch signaling pathway
. Hedgehog signaling pathway

Correct Answer & Explanation

. Wnt/beta-catenin pathway

Explanation

Sclerostin binds to LRP5/6 receptors on osteoblasts, effectively inhibiting the canonical Wnt/beta-catenin signaling pathway. This inhibition leads to decreased osteoblastogenesis and a subsequent reduction in bone formation.

Question 5383

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain that permits the formation of lamellar bone via primary (direct) bone healing without the formation of a visible callus?

. Less than 2 percent
. Between 2 percent and 10 percent
. Between 10 percent and 30 percent
. Between 30 percent and 50 percent
. Greater than 50 percent

Correct Answer & Explanation

. Less than 2 percent

Explanation

Primary bone healing requires absolute stability with an interfragmentary strain of less than 2%, allowing osteonal cutting cones to cross the fracture gap. Strains between 2% and 10% permit secondary bone healing with endochondral callus formation.

Question 5384

Topic: Biology, Genetics & Bone Healing

Which of the following intracellular signaling molecules is directly phosphorylated upon the binding of Bone Morphogenetic Protein-2 (BMP-2) to its cell surface serine/threonine kinase receptor?

. Beta-catenin
. Smad 1/5/8
. Smad 2/3
. MAP kinase
. JAK/STAT

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMP-2 binds to specific cell surface receptors, which then directly phosphorylate Smad 1, 5, and 8. These phosphorylated molecules complex with Smad 4 to translocate to the nucleus and regulate osteogenic gene transcription.

Question 5385

Topic: Biomechanics & Biomaterials
An ultra-high-molecular-weight polyethylene (UHMWPE) acetabular liner undergoes progressive, time-dependent deformation under the constant compressive load of a patient's body weight. This specific biomechanical phenomenon is known as:
. Fatigue failure
. Stress relaxation
. Creep
. Galvanic corrosion
. Strain hardening

Correct Answer & Explanation

. Creep

Explanation

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

Question 5386

Topic: Biomechanics & Biomaterials

An orthopaedic surgeon revises a nonunion of a femur fracture by placing a titanium locking plate adjacent to a previously retained stainless steel intramedullary nail. Which of the following modes of implant failure is most likely accelerated by this specific combination of metals?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Fatigue failure
. Stress shielding

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as titanium and stainless steel) are placed in electrical contact within an electrolytic environment like body fluids. This electrochemical process leads to accelerated corrosion of the less noble metal (stainless steel).

Question 5387

Topic: 1. General Principles & Basic Science

Which of the following alterations in orthopaedic screw design most significantly increases its pullout strength when inserted into cancellous bone?

. Decreasing the thread pitch
. Increasing the inner (core) diameter
. Increasing the outer (major) diameter
. Decreasing the length of thread engagement
. Utilizing a self-tapping flute at the screw tip

Correct Answer & Explanation

. Increasing the outer (major) diameter

Explanation

Pullout strength is directly proportional to the major (outer) diameter of the screw, the length of thread engagement, and the shear strength of the host bone. Among the design variables, increasing the major diameter provides the most profound enhancement in pullout resistance.

Question 5388

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly utilized as a bone graft substitute in spinal fusions. Which of the following combinations of properties best describes its specific biological activity?

. Osteogenic and osteoinductive
. Osteoconductive and osteoinductive
. Osteogenic and osteoconductive
. Osteoinductive only
. Osteoconductive only

Correct Answer & Explanation

. Osteoconductive and osteoinductive

Explanation

Demineralized bone matrix (DBM) provides a collagen scaffold (osteoconductive) and retains bone morphogenetic proteins (BMPs) that stimulate local cells to form new bone (osteoinductive). Because it is sterilized and processed, it lacks viable donor cells and is therefore not osteogenic.

Question 5389

Topic: Biology, Genetics & Bone Healing

During the resorption phase of bone remodeling, osteoclasts must firmly adhere to the bone surface. Which specific cell-surface integrin plays a critical role in forming the sealing zone necessary for effective bone resorption?

. Alpha-5 Beta-1
. Alpha-v Beta-3
. Alpha-2 Beta-1
. Alpha-v Beta-5
. Alpha-M Beta-2

Correct Answer & Explanation

. Alpha-v Beta-3

Explanation

Osteoclasts primarily utilize the Alpha-v Beta-3 integrin to bind to bone matrix proteins containing the RGD (arginine-glycine-aspartic acid) sequence, such as osteopontin. This vital interaction allows the formation of the sealing zone and the isolated acidic microenvironment required for resorption.

Question 5390

Topic: 1. General Principles & Basic Science

Which specific alloying element is primarily responsible for the inherent corrosion resistance of 316L stainless steel utilized in orthopaedic implants?

. Carbon
. Molybdenum
. Nickel
. Chromium
. Manganese

Correct Answer & Explanation

. Chromium

Explanation

Chromium (comprising approximately 17-19% of 316L stainless steel) reacts with oxygen to form a stable, self-repairing passive oxide layer on the implant's surface. This passive layer is the primary mechanism defending against corrosion in physiologic environments.

Question 5391

Topic: Biology, Genetics & Bone Healing

During the secondary healing of a fracture, intramembranous ossification occurs predominantly in which of the following specific microenvironments?

. Within the central hypoxic fracture hematoma
. At the periphery of the fracture adjacent to the intact periosteum
. Within the medullary canal directly bridging the fracture gap
. In discrete areas of high interfragmentary strain (>10 percent)
. Through the progressive mineralization of the central cartilaginous soft callus

Correct Answer & Explanation

. At the periphery of the fracture adjacent to the intact periosteum

Explanation

Intramembranous ossification (direct bone formation without a cartilage intermediate) occurs at the periphery of the fracture site (the hard callus). This area features low interfragmentary strain and relatively high oxygen tension driven by the surrounding periosteal blood supply.

Question 5392

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what range of interfragmentary strain is required to promote secondary bone healing via callus formation?

. Less than 2%
. Between 2% and 10%
. Between 10% and 15%
. Between 15% and 30%
. Greater than 30%

Correct Answer & Explanation

. Between 2% and 10%

Explanation

Secondary bone healing (endochondral ossification with callus formation) is stimulated by moderate strain levels between 2% and 10%. Strain below 2% leads to primary bone healing, while strain above 10% typically results in a fibrous nonunion.

Question 5393

Topic: Biomechanics & Biomaterials

When evaluating the biomechanical properties of an intramedullary nail, its torsional rigidity is proportional to the radius to what power?

. Radius to the first power
. Radius squared (r^2)
. Radius cubed (r^3)
. Radius to the fourth power (r^4)
. Inversely proportional to the radius

Correct Answer & Explanation

. Radius to the fourth power (r^4)

Explanation

The torsional rigidity of a solid cylinder is governed by its polar moment of inertia, which is proportional to the radius to the fourth power (r^4). Therefore, small increases in nail diameter exponentially increase its resistance to torsional deformation.

Question 5394

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for an orthopaedic implant material, the slope of the linear (elastic) portion represents which of the following biomechanical properties?

. Yield strength
. Toughness
. Modulus of elasticity
. Ultimate tensile strength
. Ductility

Correct Answer & Explanation

. Modulus of elasticity

Explanation

The slope of the linear portion of a stress-strain curve defines the Modulus of Elasticity (Young's modulus), which indicates a material's stiffness. Toughness is the total area under the curve, and yield strength is the point at which plastic deformation begins.

Question 5395

Topic: Biomechanics & Biomaterials

According to the principles of screw biomechanics, which of the following geometric modifications most significantly increases the pullout strength of a cortical bone screw?

. Increasing the outer diameter of the screw
. Increasing the inner (core) diameter of the screw
. Increasing the thread pitch
. Decreasing the length of engagement
. Decreasing the thread depth

Correct Answer & Explanation

. Increasing the outer diameter of the screw

Explanation

Screw pullout strength is primarily determined by the outer diameter, thread length of engagement, and bone shear strength. Increasing the outer diameter directly and linearly increases the volume of bone captured between threads, maximizing pullout strength.

Question 5396

Topic: Biomechanics & Biomaterials

During biomechanical testing of a viscoelastic tissue like articular cartilage, a constant load is applied, resulting in an immediate deformation that slowly continues to increase over time. This phenomenon is termed:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a viscoelastic material over time under a constant applied load. Stress relaxation, conversely, is the decrease in stress over time when the material is held at a constant strain (deformation).

Question 5397

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs), specifically BMP-2 and BMP-7, initiate their intracellular signaling cascade primarily through which molecular pathway?

. Wnt/beta-catenin pathway
. RANK/RANKL pathway
. SMAD 1/5/8 pathway
. JAK/STAT pathway
. Notch signaling pathway

Correct Answer & Explanation

. SMAD 1/5/8 pathway

Explanation

BMPs bind to cell-surface serine/threonine kinase receptors, leading to the phosphorylation and activation of receptor-regulated SMADs (SMAD 1, 5, and 8). These form a complex with SMAD 4, which translocates to the nucleus to regulate osteogenic gene transcription.

Question 5398

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) acts as a grout rather than an adhesive in total joint arthroplasty. Biomechanically, PMMA exhibits its greatest structural strength against which type of applied load?

. Tension
. Compression
. Shear
. Torsion
. Bending

Correct Answer & Explanation

. Compression

Explanation

PMMA is highly resistant to compressive forces, making it an excellent grout for transferring physiological loads from an implant to the bone bed. It is notably weak under tensile and shear forces, which can lead to cement mantle failure.

Question 5399

Topic: Biomechanics & Biomaterials

When examining the stress-strain curve of a healthy human ligament, the initial non-linear 'toe region' is anatomically explained by which of the following?

. Micro-failure of individual collagen fibrils
. Plastic deformation of the extracellular matrix
. Uncrimping of the resting collagen fibers
. Water exudation from the proteoglycan matrix
. Maximum cross-linking of elastin molecules

Correct Answer & Explanation

. Uncrimping of the resting collagen fibers

Explanation

The toe region reflects the stretching out, or 'uncrimping,' of the naturally wavy collagen fibers with initial load application. Once straightened, the ligament enters the linear elastic phase where the collagen backbone resists further strain.

Question 5400

Topic: 1. General Principles & Basic Science

Nonsteroidal anti-inflammatory drugs (NSAIDs) are thought to negatively impact fracture healing. This delay is largely attributed to the inhibition of COX-2, which primarily impairs which stage of bone repair?

. Initial hematoma formation
. Endochondral ossification and mesenchymal stem cell differentiation
. Intramembranous ossification at the periosteal surface
. Hard callus remodeling by osteoclasts
. Primary osteonal healing via cutting cones

Correct Answer & Explanation

. Endochondral ossification and mesenchymal stem cell differentiation

Explanation

COX-2 is upregulated in the early phases of fracture healing, producing prostaglandins essential for mesenchymal stem cell differentiation into osteoblasts. NSAID-mediated COX-2 inhibition disrupts this pathway, severely impairing endochondral ossification.

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