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1. General Principles & Basic Science MCQs

Practice Set 712 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 14221

Topic: Biology, Genetics & Bone Healing

External beam radiation therapy is an effective prophylactic treatment for heterotopic ossification (HO) following total hip arthroplasty. What is the primary biological mechanism of action of radiation therapy in this setting?

. Inhibition of osteoclast function and survival
. Apoptosis of mature, bone-forming osteoblasts
. Inhibition of proliferation and differentiation of pluripotent mesenchymal stem cells
. Denaturation of endogenous bone morphogenetic proteins (BMPs)
. Upregulation of sclerostin production by local osteocytes

Correct Answer & Explanation

. Inhibition of proliferation and differentiation of pluripotent mesenchymal stem cells

Explanation

Heterotopic ossification prophylaxis with low-dose radiation (typically 700 cGy in a single fraction) works by inhibiting the rapid proliferation and subsequent differentiation of pluripotent mesenchymal stem cells into osteoprogenitor cells. To be effective, it must be administered within 24 hours prior to surgery or within 48 to 72 hours postoperatively before differentiation has occurred.

Question 14222

Topic: Biology, Genetics & Bone Healing

In primary hyperparathyroidism, chronically elevated levels of parathyroid hormone (PTH) lead to net bone resorption. PTH achieves this primarily by binding directly to cell surface receptors on which of the following cell types?

. Osteocytes
. Osteoclasts
. Osteoblasts
. Chondrocytes
. Macrophages

Correct Answer & Explanation

. Osteoclasts

Explanation

Osteoclasts do not possess receptors for parathyroid hormone (PTH). PTH acts primarily on osteoblasts (and osteocytes). When PTH binds to osteoblasts, it stimulates them to increase the expression of RANK Ligand (RANKL) and decrease the expression of osteoprotegerin (OPG). RANKL then binds to RANK on osteoclast precursors, stimulating their differentiation and activation.

Question 14223

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) has become standard of care in major orthopedic surgery to reduce perioperative blood loss. Which of the following best describes its pharmacological mechanism of action?

. Direct, irreversible inhibition of factor Xa in the coagulation cascade
. Competitive inhibition of plasminogen activation by binding to lysine receptor sites
. Direct activation of the intrinsic pathway to promote rapid clot formation
. Promotion of platelet aggregation via the ADP receptor pathway
. Enzymatic cross-linking of loose fibrin strands to stabilize the clot

Correct Answer & Explanation

. Competitive inhibition of plasminogen activation by binding to lysine receptor sites

Explanation

Tranexamic acid (TXA) is an antifibrinolytic agent. It is a synthetic lysine analog that competitively binds to lysine receptor sites on plasminogen. This prevents plasminogen from binding to fibrin and being converted to the active enzyme plasmin, thereby inhibiting the degradation of fibrin clots (fibrinolysis).

Question 14224

Topic: Biology, Genetics & Bone Healing

A 65-year-old postmenopausal woman undergoes dual-energy x-ray absorptiometry (DEXA) screening for osteoporosis. Her lowest T-score is -2.6. According to the World Health Organization (WHO), what is the statistical definition of a T-score of -2.6?

. Her bone mineral density is 2.6 standard deviations below the mean for age-matched and sex-matched controls
. Her bone mineral density is 2.6 standard deviations below the mean for young, healthy adults of the same sex
. Her bone mineral density is 2.6 standard errors below the mean for age-matched and sex-matched controls
. Her bone mineral density is 2.6 standard errors below the mean for young, healthy adults of the same sex
. Her fracture risk is 2.6 times higher than that of a young, healthy adult

Correct Answer & Explanation

. Her bone mineral density is 2.6 standard deviations below the mean for young, healthy adults of the same sex

Explanation

The T-score compares a patient's bone mineral density (BMD) to the optimal peak bone mass of a healthy young adult (typically 30 years old) of the same sex, expressed in standard deviations (SD). A T-score of -2.5 or lower defines osteoporosis. In contrast, the Z-score compares the patient's BMD to an age-matched and sex-matched population.

Question 14225

Topic: Biomechanics & Biomaterials

Galvanic corrosion represents a significant mechanism of implant degradation and failure in orthopedic surgery. This phenomenon is most likely to occur under which of the following clinical scenarios?

. Micro-motion and fretting of a single stainless steel plate against cortical bone
. The coupling of two dissimilar metals with significantly different anodic potentials in a conductive fluid environment
. Macrophage-mediated enzymatic degradation of ultra-high molecular weight polyethylene debris
. Cyclic fatigue loading of a titanium intramedullary nail at the site of a delayed union
. The presence of a subclinical biofilm on the surface of a highly cross-linked polyethylene liner

Correct Answer & Explanation

. The coupling of two dissimilar metals with significantly different anodic potentials in a conductive fluid environment

Explanation

Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially when it is in electrical contact with a dissimilar metal in the presence of an electrolyte (like body fluid). The metal with the lower (more active) electrode potential becomes the anode and undergoes accelerated corrosion. This is why mixing dissimilar metals (e.g., a stainless steel screw in a titanium plate) is generally avoided.

Question 14226

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Which of the following best describes the specific receptor type and intracellular signaling pathway utilized by BMP-2?

. Tyrosine kinase receptor and JAK/STAT pathway
. Serine/threonine kinase receptor and SMAD pathway
. G-protein coupled receptor and cAMP pathway
. Ion channel receptor and calcium-calmodulin pathway
. Nuclear receptor and Wnt/beta-catenin pathway

Correct Answer & Explanation

. Serine/threonine kinase receptor and SMAD pathway

Explanation

BMPs bind to cell surface serine/threonine kinase receptors. Upon binding, they induce phosphorylation of intracellular SMAD proteins (SMAD 1, 5, and 8), which then complex with SMAD 4 to translocate into the nucleus and regulate gene expression for osteoblast differentiation.

Question 14227

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked polyethylene has significantly reduced wear rates. However, compared to conventional ultra-high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene demonstrates a significant decrease in which of the following mechanical properties?
. Oxidation resistance
. Abrasive wear resistance
. Fatigue strength
. Elastic modulus
. Melting point

Correct Answer & Explanation

. Fatigue strength

Explanation

Cross-linking of polyethylene significantly improves its wear characteristics by reducing adhesive and abrasive wear. However, the process of cross-linking and subsequent thermal treatments (like remelting to eliminate free radicals) decreases several mechanical properties, most notably fatigue strength, yield strength, and ultimate tensile strength.

Question 14228

Topic: 1. General Principles & Basic Science

Articular cartilage has a highly specialized zonal architecture. In the superficial zone (lamina splendens), which of the following best describes the organization of collagen fibers and the relative concentration of water?

. Collagen fibers parallel to the joint surface; highest water content
. Collagen fibers perpendicular to the joint surface; highest water content
. Collagen fibers parallel to the joint surface; lowest water content
. Collagen fibers perpendicular to the joint surface; lowest water content
. Randomly oriented collagen fibers; uniform water content

Correct Answer & Explanation

. Collagen fibers parallel to the joint surface; highest water content

Explanation

In the superficial zone of articular cartilage, collagen fibers (primarily Type II) are arranged parallel to the articular surface to resist shear forces. This zone also contains the highest concentration of water and the lowest concentration of proteoglycans compared to the deeper zones.

Question 14229

Topic: Biology, Genetics & Bone Healing

Distraction osteogenesis (e.g., Ilizarov bone transport) primarily forms new bone via which of the following biological processes?

. Endochondral ossification
. Intramembranous ossification
. Appositional cartilaginous growth
. Physis-mediated elongation
. Creeping substitution

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Distraction osteogenesis, assuming a stable fixator and appropriate distraction rate (typically 1 mm/day), forms new bone primarily through intramembranous ossification under conditions of tension. The bone forms directly from mesenchymal cells without an intermediate cartilage phase.

Question 14230

Topic: Biomechanics & Biomaterials

A surgeon plans to revise a failed internal fixation using a combination of existing 316L stainless steel hardware and new titanium alloy implants. Which of the following mechanisms of material failure is most likely to be accelerated by placing these two dissimilar metals in direct contact in vivo?

. Crevice corrosion
. Galvanic corrosion
. Fretting corrosion
. Pitting corrosion
. Fatigue failure

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in direct contact within an electrolytic environment (such as body fluid). The less noble metal acts as an anode and undergoes accelerated oxidative corrosion.

Question 14231

Topic: 1. General Principles & Basic Science

Articular cartilage is structurally divided into four distinct zones. Which of the following statements most accurately describes the characteristics of the deep zone?

. Lowest proteoglycan content, collagen parallel to the joint surface
. Highest water content, collagen randomly oriented
. Highest proteoglycan content, collagen perpendicular to the joint surface
. Lowest water content, collagen parallel to the joint surface
. Highest cell density, collagen perpendicular to the joint surface

Correct Answer & Explanation

. Highest proteoglycan content, collagen perpendicular to the joint surface

Explanation

The deep zone of articular cartilage is characterized by the highest proteoglycan content, the lowest water content, and type II collagen fibers oriented perpendicular to the subchondral bone.

Question 14232

Topic: Biology, Genetics & Bone Healing

Denosumab is highly effective in treating advanced or unresectable Giant Cell Tumor (GCT) of bone. What is its exact target and cellular mechanism in the context of GCT?

. Inhibits farnesyl pyrophosphate synthase in reactive osteoclasts
. Binds RANK receptor on multinucleated giant cells
. Binds RANKL expressed by the mononuclear neoplastic stromal cells
. Stimulates osteoprotegerin production by osteoblasts
. Induces direct apoptosis of multinucleated giant cells

Correct Answer & Explanation

. Binds RANKL expressed by the mononuclear neoplastic stromal cells

Explanation

In Giant Cell Tumor of bone, the mononuclear stromal cells are the true neoplastic cells, and they overexpress RANKL. Denosumab is a monoclonal antibody that binds this RANKL, preventing it from recruiting and activating the reactive osteoclast-like giant cells.

Question 14233

Topic: Biology, Genetics & Bone Healing

A pediatric patient with recurrent fractures, cranial nerve palsies, and diffuse bone sclerosis on radiographs is suspected to have osteopetrosis. The most common autosomal recessive form of this disease is linked to a deficiency in which of the following?

. Cathepsin K
. Carbonic anhydrase II
. Type I collagen
. Tissue nonspecific alkaline phosphatase
. Tartrate-resistant acid phosphatase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Osteopetrosis is commonly caused by a deficiency in Carbonic Anhydrase II. This enzyme is required for osteoclasts to generate hydrogen ions, which are essential for creating the acidic environment necessary to dissolve bone mineral at the ruffled border.

Question 14234

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. Which of the following describes its primary mechanism of action?
. Inhibits factor Xa in the coagulation cascade
. Competitively inhibits plasminogen activation
. Directly inhibits thrombin
. Inhibits cyclooxygenase-1 in platelets
. Enhances antithrombin III activity

Correct Answer & Explanation

. Competitively inhibits plasminogen activation

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic by reversibly and competitively binding to the lysine receptor sites on plasminogen, preventing its activation into the fibrin-degrading enzyme plasmin.

Question 14235

Topic: Infection, Pharmacology & VTE

Biofilm formation on orthopedic implants makes periprosthetic joint infections highly resistant to host immunity and antibiotics. What represents the first distinct phase of biofilm formation?

. Irreversible attachment via exopolysaccharides
. Maturation and quorum sensing
. Reversible attachment of planktonic bacteria
. Dispersion of sessile bacteria
. Formation of the glycocalyx

Correct Answer & Explanation

. Reversible attachment of planktonic bacteria

Explanation

The first step in biofilm formation is the reversible attachment of free-floating (planktonic) bacteria to the implant surface. This is initially mediated by weak forces such as van der Waals forces and hydrophobic interactions.

Question 14236

Topic: Biology, Genetics & Bone Healing

During fracture healing, mesenchymal stem cells must commit to specific lineages. Which of the following transcription factors is considered the "master regulator" for the differentiation of mesenchymal stem cells into the osteoblast lineage?

. Sox9
. Runx2 (Cbfa1)
. HIF-1 alpha
. Beta-catenin
. MyoD

Correct Answer & Explanation

. Runx2 (Cbfa1)

Explanation

Runx2 (also known as Cbfa1) is the essential, master transcription factor for osteoblast differentiation. In contrast, Sox9 is the primary transcription factor required for chondrocyte differentiation.

Question 14237

Topic: Biology, Genetics & Bone Healing

Familial forms of Paget's disease of bone are most frequently associated with genetic mutations that lead to hyperactive osteoclasts. Which of the following genes is most commonly mutated in these familial cases?

. COL1A1
. FGFR3
. SQSTM1 (p62)
. GNAS1
. EXT1

Correct Answer & Explanation

. SQSTM1 (p62)

Explanation

Mutations in the SQSTM1 (p62) gene are the most commonly identified genetic cause of familial Paget's disease. These mutations increase RANK receptor sensitivity to RANKL, leading to massive, hyperactive osteoclasts.

Question 14238

Topic: Biomechanics & Biomaterials

When analyzing the mechanical properties of an orthopedic implant on a stress-strain curve, which of the following points indicates the transition from reversible elastic deformation to irreversible plastic deformation?

. Ultimate tensile strength
. Modulus of elasticity
. Yield point
. Failure point
. Fatigue limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point on a stress-strain curve marks the end of the elastic region and the beginning of the plastic region. Loading a material beyond this point results in permanent (irreversible) deformation.

Question 14239

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates (e.g., Alendronate) are commonly prescribed for osteoporosis. What is the precise intracellular mechanism by which these drugs impair osteoclast function?

. Inhibition of matrix metalloproteinases
. Inhibition of farnesyl pyrophosphate synthase
. Direct binding to the RANK receptor
. Inhibition of carbonic anhydrase II
. Activation of tissue nonspecific alkaline phosphatase

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents the prenylation of small GTPase proteins (like Ras and Rho) that are essential for osteoclast survival and ruffled border formation.

Question 14240

Topic: 1. General Principles & Basic Science

According to the Sunderland classification of peripheral nerve injuries, which of the following anatomical descriptions accurately defines a second-degree injury (axonotmesis)?

. Conduction block with an intact axon and intact myelin
. Disruption of the axon, but the endoneurium remains intact
. Disruption of the axon and endoneurium, but intact perineurium
. Disruption of the axon, endoneurium, and perineurium
. Complete nerve transection including the epineurium

Correct Answer & Explanation

. Disruption of the axon, but the endoneurium remains intact

Explanation

A Sunderland Grade II injury corresponds to classic axonotmesis, where the axon and myelin sheath are disrupted, but the surrounding endoneurial tube remains intact. This provides a clear pathway for predictable axonal regeneration at 1 mm/day.

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