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1. General Principles & Basic Science MCQs

Practice Set 329 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 6561

Topic: 1. General Principles & Basic Science

During the late remodeling phase of ligament and tendon healing, the tensile strength of the tissue gradually increases. This is primarily facilitated by which cellular and matrix alteration?

. Peak infiltration of polymorphonuclear leukocytes
. Synthesis of an initial type III collagen framework
. Conversion of type III collagen to type I collagen
. Formation of a highly vascularized granulation bed
. Endochondral ossification of the tendinous insertion

Correct Answer & Explanation

. Peak infiltration of polymorphonuclear leukocytes

Explanation

During the remodeling phase, the disorganized type III collagen produced during the earlier proliferative phase is gradually replaced by highly organized type I collagen. This transition significantly increases the tensile strength of the healing tendon or ligament.

Question 6562

Topic: Biology, Genetics & Bone Healing

Sclerostin is a potent inhibitor of bone formation that functions by antagonizing the Wnt/beta-catenin signaling pathway. Which cell type is the primary source of sclerostin in mature bone?

. Osteoblasts
. Osteoclasts
. Osteocytes
. Chondrocytes
. Mesenchymal stem cells

Correct Answer & Explanation

. Osteoblasts

Explanation

Osteocytes embedded in the bone matrix synthesize and secrete sclerostin, which actively inhibits osteoblastic bone formation. Monoclonal antibodies targeting sclerostin (e.g., romosozumab) are used clinically to promote bone formation in severe osteoporosis.

Question 6563

Topic: 1. General Principles & Basic Science

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown in some studies to impair fracture healing. This effect is primarily mediated by the inhibition of cyclooxygenase-2 (COX-2), which normally promotes healing by:

. Blocking local osteoclast apoptosis
. Synthesizing prostaglandins required for endochondral ossification
. Upregulating the expression of osteoprotegerin (OPG)
. Inhibiting angiogenesis during the soft callus phase
. Preventing the differentiation of fibrous tissue into cartilage

Correct Answer & Explanation

. Blocking local osteoclast apoptosis

Explanation

COX-2 is responsible for producing prostaglandins, which play a crucial role in regulating osteoblast function and promoting endochondral ossification during fracture repair. By inhibiting this pathway, NSAIDs can potentially delay or impair bone healing.

Question 6564

Topic: 1. General Principles & Basic Science

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

. Decreasing the inner (root) diameter
. Increasing the outer (thread) diameter
. Increasing the pitch (distance between threads)
. Decreasing the length of thread engagement
. Using a self-tapping rather than a non-self-tapping tip

Correct Answer & Explanation

. Decreasing the inner (root) diameter

Explanation

Screw pullout strength is directly proportional to the outer diameter of the screw, the length of thread engagement in the bone, and the shear strength of the bone. Increasing the outer diameter provides a significantly larger volume of bone captured between the threads.

Question 6565

Topic: 1. General Principles & Basic Science

Articular cartilage maintains a frictionless surface during periods of high, sudden, and short-duration compressive loading primarily through which lubrication mechanism?

. Boundary lubrication
. Elastohydrodynamic lubrication
. Squeeze-film lubrication
. Weeping lubrication
. Hydrodynamic lubrication

Correct Answer & Explanation

. Boundary lubrication

Explanation

Squeeze-film lubrication occurs under high loads over short durations. The pressure from the impending collision forces fluid out of the cartilage matrix to maintain a protective layer, preventing the opposing articular surfaces from touching.

Question 6566

Topic: Biology, Genetics & Bone Healing

Osteoclast differentiation and activation are heavily regulated by the RANK/RANKL/OPG axis. Osteoprotegerin (OPG) exerts its regulatory effect by:

. Binding to RANK on the osteoclast precursor to stimulate differentiation
. Acting as a decoy receptor binding to RANKL, preventing it from interacting with RANK
. Directly inducing apoptosis of mature multinucleated osteoclasts
. Cleaving the RANK receptor from the surface of osteoblasts
. Binding to M-CSF to inhibit the initial proliferation of macrophages

Correct Answer & Explanation

. Binding to RANK on the osteoclast precursor to stimulate differentiation

Explanation

OPG is secreted by osteoblasts and acts as a soluble decoy receptor for RANKL. By effectively binding RANKL, OPG prevents it from interacting with RANK on osteoclast precursors, thereby inhibiting osteoclastogenesis and bone resorption.

Question 6567

Topic: 1. General Principles & Basic Science

The compressive strength of mature lamellar bone is primarily derived from which of its structural components?

. Type I collagen
. Proteoglycans
. Hydroxyapatite
. Osteopontin
. Water

Correct Answer & Explanation

. Type I collagen

Explanation

Hydroxyapatite crystals [Ca10(PO4)6(OH)2] provide the inorganic mineral phase of bone, conferring its high compressive strength. Type I collagen constitutes the primary organic framework, which imparts tensile strength and flexibility to the tissue.

Question 6568

Topic: 1. General Principles & Basic Science

In which zone of articular cartilage are the collagen fibers oriented parallel to the joint surface to resist shear forces?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial tangential zone of articular cartilage has collagen fibers oriented parallel to the joint surface. This arrangement is primarily responsible for resisting shear stresses.

Question 6569

Topic: Biomechanics & Biomaterials

Which of the following orthopedic materials has a modulus of elasticity (Young's modulus) closest to that of cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Polymethylmethacrylate (PMMA)
. Ultra-high molecular weight polyethylene (UHMWPE)

Correct Answer & Explanation

. Stainless steel

Explanation

Titanium alloy has a modulus of elasticity closest to cortical bone compared to other metallic implants. This reduces the effect of stress shielding and allows more physiologic load sharing.

Question 6570

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) signals primarily through which of the following intracellular pathways to promote osteoblast differentiation?

. Wnt/beta-catenin pathway
. RANKL/NF-kappaB pathway
. Smad 1/5/8 pathway
. Notch signaling pathway
. JAK/STAT pathway

Correct Answer & Explanation

. Wnt/beta-catenin pathway

Explanation

Bone morphogenetic proteins (BMPs) bind to serine/threonine kinase receptors and primarily exert their intracellular effects via the Smad 1/5/8 signaling pathway. This upregulates osteoblast differentiation factors like Runx2.

Question 6571

Topic: Biology, Genetics & Bone Healing

Distraction osteogenesis typically relies on which of the following mechanisms for new bone formation?

. Endochondral ossification
. Intramembranous ossification
. Primary bone healing
. Appositional bone growth
. Chondrocyte hypertrophy without ossification

Correct Answer & Explanation

. Endochondral ossification

Explanation

Distraction osteogenesis predominantly proceeds via intramembranous ossification. In this process, bone forms directly from mesenchymal cells without a pre-existing cartilage intermediate.

Question 6572

Topic: Biomechanics & Biomaterials

When a constant force is applied to a ligament over time, the ligament will slowly elongate. What is this viscoelastic property called?

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Isotropic deformation

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the time-dependent deformation (elongation) of a viscoelastic material under a constant load. Stress relaxation, in contrast, is the decrease in stress over time when the material is held at a constant length.

Question 6573

Topic: Biology, Genetics & Bone Healing

Which of the following components of articular cartilage is primarily responsible for its ability to resist compressive loads?

. Type I collagen
. Type II collagen
. Aggrecan
. Elastin
. Hyaluronidase

Correct Answer & Explanation

. Type I collagen

Explanation

Aggrecan, the major proteoglycan in articular cartilage, possesses highly negatively charged glycosaminoglycan chains. These chains draw water into the tissue, creating swelling pressure that effectively resists compressive loads.

Question 6574

Topic: Biology, Genetics & Bone Healing

During fracture healing, the peak of soft callus formation typically correlates with the maximum expression of which collagen type?

. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type I

Explanation

The soft callus stage of secondary bone healing is characterized by the formation of fibrocartilage. This stage is associated with a peak expression of Type II collagen.

Question 6575

Topic: Biology, Genetics & Bone Healing

Osteoprotegerin (OPG) functions to inhibit osteoclastogenesis by binding directly to which of the following molecules?

. RANK receptor
. RANK ligand (RANKL)
. Macrophage colony-stimulating factor (M-CSF)
. Calcitonin receptor
. Sclerostin

Correct Answer & Explanation

. RANK receptor

Explanation

Osteoprotegerin acts as a decoy receptor that binds directly to RANKL. By preventing RANKL from binding to its receptor (RANK) on osteoclast precursors, OPG inhibits osteoclast differentiation and activation.

Question 6576

Topic: 1. General Principles & Basic Science

The pull-out strength of a cortical screw is most directly related to which of the following parameters?

. Inner core diameter
. Outer thread diameter
. Thread pitch
. Head size
. Screw length extending beyond the far cortex

Correct Answer & Explanation

. Inner core diameter

Explanation

Screw pull-out strength is directly proportional to the outer thread diameter and the volume of bone caught between the threads. It is also directly related to the length of screw thread engagement in the bone.

Question 6577

Topic: 1. General Principles & Basic Science

What is the primary functional significance of the tidemark in articular cartilage?

. It is the zone of highest collagen concentration
. It marks the transition between uncalcified and calcified cartilage
. It provides the major blood supply to the superficial zone
. It is the primary site of aggrecan synthesis
. It anchors the collateral ligaments to the joint capsule

Correct Answer & Explanation

. It is the zone of highest collagen concentration

Explanation

The tidemark is a histologically distinct line that separates the uncalcified deep zone from the calcified zone of articular cartilage. It acts as an anchor, tethering the uncalcified cartilage to the underlying subchondral bone.

Question 6578

Topic: Biomechanics & Biomaterials

Which of the following pairs of orthopaedic implant materials is most likely to undergo severe galvanic corrosion if placed in direct physical contact within the body?

. Titanium and Titanium alloy
. Stainless steel and Cobalt-chromium
. Stainless steel and Titanium
. Cobalt-chromium and Ultra-high molecular weight polyethylene
. Titanium and Ceramic

Correct Answer & Explanation

. Titanium and Titanium alloy

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices are in contact in an electrolytic environment. Stainless steel and titanium have significantly different electrochemical potentials and should generally not be mixed.

Question 6579

Topic: Biology, Genetics & Bone Healing

The basic structural unit of compact (cortical) bone, consisting of concentric lamellae surrounding a central canal, is known as the:

. Trabecula
. Osteon (Haversian system)
. Volkmann canal
. Canaliculus
. Howship lacuna

Correct Answer & Explanation

. Trabecula

Explanation

The osteon, or Haversian system, is the fundamental functional unit of compact bone. Volkmann canals run perpendicular to these systems, connecting adjacent central canals.

Question 6580

Topic: Biology, Genetics & Bone Healing

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

. BMP/Smad
. Wnt/beta-catenin
. RANKL/NF-kappaB
. Insulin-like growth factor
. Fibroblast growth factor

Correct Answer & Explanation

. BMP/Smad

Explanation

Sclerostin inhibits osteoblastogenesis and bone formation by binding to LRP5/6 receptors. This interaction antagonizes the canonical Wnt/beta-catenin signaling pathway.

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