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1. General Principles & Basic Science MCQs

Practice Set 262 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 5221

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a destructive radiolucent lesion in the distal femur. Core needle biopsy confirms Giant Cell Tumor of bone. Multidisciplinary tumor board recommends neoadjuvant treatment with Denosumab prior to intralesional curettage. Denosumab targets which of the following cellular mechanisms in this specific tumor?

. Direct induction of apoptosis in the multinucleated giant cells
. Inhibition of RANKL produced by the neoplastic mononuclear stromal cells
. Neutralization of RANK receptors on the surface of osteoclast precursors
. Inhibition of VEGF-mediated tumor angiogenesis
. Blockade of the Wnt/beta-catenin signaling pathway

Correct Answer & Explanation

. Inhibition of RANKL produced by the neoplastic mononuclear stromal cells

Explanation

Giant Cell Tumor of bone consists of neoplastic mononuclear stromal cells and reactive multinucleated giant cells (osteoclast-like cells). The neoplastic stromal cells overexpress RANKL, which recruits and activates the osteoclast-like giant cells, leading to bone destruction. Denosumab is a monoclonal antibody that binds to and inhibits RANKL produced by the stromal cells, thereby preventing the activation of the destructive giant cells.

Question 5222

Topic: Biology, Genetics & Bone Healing

During the process of secondary fracture healing (enchondral ossification), woven bone is gradually replaced by strong, organized lamellar bone. This critical transition primarily occurs during which stage of the fracture healing cascade?

. Inflammatory phase
. Soft callus formation phase
. Hard callus formation phase
. Remodeling phase
. Hematoma organization phase

Correct Answer & Explanation

. Remodeling phase

Explanation

Secondary fracture healing consists of hematoma/inflammation, soft callus (cartilage), hard callus (woven bone), and remodeling. The transition from random, disorganized woven bone (formed during the hard callus phase) to highly organized, stress-aligned lamellar bone occurs strictly during the remodeling phase, governed by osteoclast and osteoblast activity acting under Wolff's law.

Question 5223

Topic: Biomechanics & Biomaterials

An orthopedic surgeon is preparing antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for a spacer during the first stage of a two-stage exchange arthroplasty for a periprosthetic joint infection. To ensure the antibiotic remains biologically active and does not compromise the curing process, the chosen antibiotic MUST possess which of the following properties?

. High molecular weight to delay elution
. Thermostability
. A purely bacteriostatic mechanism of action
. High lipophilicity
. Susceptibility to rapid hydrolysis

Correct Answer & Explanation

. Thermostability

Explanation

The polymerization of PMMA bone cement is an exothermic reaction that can reach temperatures exceeding 80°C (176°F) in vivo. Therefore, any antibiotic incorporated into the cement must be highly thermostable to survive the curing process without degrading. Common thermostable antibiotics used include Vancomycin, Tobramycin, and Gentamicin.

Question 5224

Topic: Biomechanics & Biomaterials

During a biomechanical testing session on human tendons, a researcher applies a constant load to a tendon specimen over an extended period. Over time, the tendon demonstrates a progressive increase in length (deformation). What viscoelastic property does this describe?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the viscoelastic property where a tissue undergoes progressive deformation (lengthening) under a constant load over time. Stress relaxation, conversely, is the decrease in load/stress over time when a tissue is held at a constant length (deformation). Hysteresis refers to the energy lost as heat during the loading and unloading cycle.

Question 5225

Topic: 1. General Principles & Basic Science

Regarding the ultrastructure of articular cartilage, which zone contains the highest concentration of proteoglycans, the lowest concentration of water, and collagen fibrils aligned perpendicular to the joint surface?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

Articular cartilage is divided into four zones. The deep (radial) zone has the highest concentration of proteoglycans, the lowest water content, and the largest diameter collagen fibrils oriented vertically (perpendicular) to the articular surface, which provides the highest resistance to compressive loads. The superficial zone has the highest water and lowest proteoglycan content.

Question 5226

Topic: Biology, Genetics & Bone Healing

During bone remodeling, osteoclasts resorb bone by creating an acidic microenvironment to dissolve hydroxyapatite and by secreting enzymes to degrade the organic bone matrix. Which of the following enzymes is primarily responsible for the cleavage and degradation of Type I collagen in the osteoclast resorption pit (Howship's lacuna)?

. Alkaline phosphatase
. Matrix metalloproteinase-9
. Tartrate-resistant acid phosphatase (TRAP)
. Carbonic anhydrase II
. Cathepsin K

Correct Answer & Explanation

. Cathepsin K

Explanation

Cathepsin K is a lysosomal cysteine protease secreted by osteoclasts. It is the primary enzyme responsible for the degradation of Type I collagen and other noncollagenous proteins in the organic matrix of bone. Carbonic anhydrase II produces the protons needed to dissolve the mineral component. TRAP is a marker of osteoclast activity but does not cleave collagen. Alkaline phosphatase is produced by osteoblasts.

Question 5227

Topic: Biology, Genetics & Bone Healing

Romosozumab has been introduced for the treatment of severe osteoporosis. What is the precise cellular mechanism of action of this monoclonal antibody?

. Binds to RANKL, inhibiting osteoclast activation
. Stimulates the parathyroid hormone (PTH) receptor
. Inhibits sclerostin, leading to upregulation of the Wnt/beta-catenin signaling pathway
. Binds to Cathepsin K, preventing bone matrix degradation
. Stimulates Osteoprotegerin (OPG) production by osteoblasts

Correct Answer & Explanation

. Inhibits sclerostin, leading to upregulation of the Wnt/beta-catenin signaling pathway

Explanation

Romosozumab is a monoclonal antibody that binds to and inhibits sclerostin. Sclerostin is an endogenous inhibitor of the Wnt/beta-catenin signaling pathway produced by osteocytes. By inhibiting sclerostin, Romosozumab promotes Wnt signaling, which significantly increases bone formation (anabolic effect) and also decreases bone resorption.

Question 5228

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into four distinct structural zones. Which of the following accurately describes the properties of the superficial (tangential) zone?

. It has the highest concentration of proteoglycans and lowest water content
. Collagen fibers are oriented perpendicular to the articular surface
. It is the primary zone responsible for resisting compressive forces
. It has the highest water content and collagen fibers oriented parallel to the articular surface
. Chondrocytes are arranged in vertical columns

Correct Answer & Explanation

. It has the highest water content and collagen fibers oriented parallel to the articular surface

Explanation

The superficial (tangential) zone of articular cartilage comprises the top 10-20% of thickness. It uniquely possesses the highest water content, the lowest proteoglycan content, and type II collagen fibers that are densely packed and oriented parallel to the joint surface. This parallel alignment provides maximum tensile strength to resist shear forces.

Question 5229

Topic: Biology, Genetics & Bone Healing

A 29-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, expansile lesion in the distal femoral epiphysis extending to the subchondral bone. Biopsy confirms Giant Cell Tumor of Bone (GCT). If medical management is considered prior to surgery, what is the mechanism of action of the preferred targeted therapeutic agent (Denosumab)?

. Monoclonal antibody that binds and inhibits RANKL
. Tyrosine kinase inhibitor targeting VEGF receptors
. Monoclonal antibody targeting osteoclast integrins
. Direct inhibitor of osteoblast apoptosis
. Bisphosphonate that incorporates into the bone matrix

Correct Answer & Explanation

. Monoclonal antibody that binds and inhibits RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL), preventing RANKL from activating RANK on the surface of osteoclasts and their precursors. In Giant Cell Tumor of bone, the neoplastic mononuclear cells express RANKL, which recruits reactive osteoclast-like giant cells that cause bone destruction. Denosumab blocks this process.

Question 5230

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic behavior. Which of the following statements best defines the mechanical concept of "stress relaxation" in an orthopedic biologic tissue?

. Increasing deformation over time when subjected to a constant load
. Decreasing internal stress over time when held at a constant deformation
. Energy loss that occurs during a complete loading and unloading cycle
. Increased stiffness demonstrated when the tissue is loaded at higher strain rates
. The microfailure of collagen fibrils immediately preceding macroscopic failure

Correct Answer & Explanation

. Decreasing internal stress over time when held at a constant deformation

Explanation

Stress relaxation is a classic viscoelastic property where the stress (internal force) within a material decreases over time when it is stretched and held at a constant length (constant deformation/strain). Creep (Option A) is the gradual increase in length (deformation) when a constant load/stress is applied. Hysteresis (Option C) refers to the energy dissipated (usually as heat) during the loading and unloading cycle. Strain-rate dependency (Option D) explains why tissues become stiffer when loaded rapidly.

Question 5231

Topic: Infection, Pharmacology & VTE
A patient is admitted for an elective primary total hip arthroplasty. He is currently taking Rivaroxaban, which needs to be managed perioperatively. What is the specific mechanism of action by which Rivaroxaban exerts its anticoagulant effect?
. Direct, competitive inhibition of Factor IIa (Thrombin)
. Direct, selective inhibition of Factor Xa
. Enhancement of Antithrombin III activity
. Inhibition of Vitamin K epoxide reductase
. Direct activation of Plasminogen

Correct Answer & Explanation

. Direct, selective inhibition of Factor Xa

Explanation

Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that work by directly and reversibly inhibiting Factor Xa, preventing the conversion of prothrombin to thrombin. Dabigatran directly inhibits Factor IIa (Thrombin). Warfarin inhibits Vitamin K epoxide reductase. Heparins work by enhancing Antithrombin III.

Question 5232

Topic: Biomechanics & Biomaterials

In the field of orthopedic biomaterials, implant failure can occasionally be traced to corrosion. Galvanic corrosion is most accurately described by which of the following scenarios?

. Mechanical friction wearing away the passivation layer on a single titanium screw
. Corrosion occurring in a localized area of low oxygen tension beneath a screw head
. Electrochemical degradation occurring when two dissimilar metals are in direct contact within an electrolytic environment
. Cyclic loading causing microscopic cracking and subsequent fluid ingress
. Oxidation of a polyethylene liner after prolonged shelf storage

Correct Answer & Explanation

. Electrochemical degradation occurring when two dissimilar metals are in direct contact within an electrolytic environment

Explanation

Galvanic corrosion occurs when two different metals with differing anodic indices (e.g., stainless steel and titanium) are placed in direct electrical contact within a conductive fluid (such as serum or interstitial fluid), creating an electrochemical cell where the less noble metal corrodes rapidly. Option B describes crevice corrosion (low oxygen tension). Option A describes fretting corrosion.

Question 5233

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which zone is characterized by having the highest concentration of proteoglycans, the lowest water content, and chondrocytes that are arranged in vertical columns?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils oriented perpendicular to the joint surface. It has the highest concentration of proteoglycans, the lowest concentration of water, and its chondrocytes are classically arranged in vertical columns parallel to the collagen fibers.

Question 5234

Topic: Surgical Anatomy & Approaches

During the ilioinguinal approach for an anterior column acetabular fracture, the surgeon encounters massive hemorrhage from a vascular anastomosis crossing the superior pubic ramus. This vessel, commonly known as the 'corona mortis', connects which two vascular systems?

. External iliac and internal iliac systems
. External iliac vein and internal pudendal vein
. Femoral artery and obturator artery
. External iliac and obturator systems
. Inferior epigastric and superficial circumflex iliac systems

Correct Answer & Explanation

. External iliac and obturator systems

Explanation

The corona mortis ('crown of death') is an anatomical variant where there is an anastomotic connection between the external iliac system (specifically the inferior epigastric vessels) and the obturator system (internal iliac system) crossing the superior pubic ramus. Injury to it during pelvic/acetabular surgery can cause severe, difficult-to-control bleeding.

Question 5235

Topic: Biology, Genetics & Bone Healing

Which of the following growth factors is highly osteoinductive, signals via cell-surface serine/threonine kinase receptors to activate the SMAD intracellular pathway, and is FDA-approved for use in open tibia fractures?

. Platelet-derived growth factor (PDGF)
. Vascular endothelial growth factor (VEGF)
. Fibroblast growth factor (FGF)
. Bone morphogenetic protein-2 (BMP-2)
. Transforming growth factor-beta (TGF-b)

Correct Answer & Explanation

. Bone morphogenetic protein-2 (BMP-2)

Explanation

Bone morphogenetic proteins (specifically BMP-2 and BMP-7) are potent osteoinductive growth factors belonging to the TGF-beta superfamily. They bind to serine/threonine kinase receptors and signal intracellularly via the SMAD pathway. rhBMP-2 is FDA approved for use in open tibia fractures and anterior lumbar interbody fusions (ALIF).

Question 5236

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with a lytic, expansile lesion in the distal femur extending to the subchondral bone. A core needle biopsy confirms a Giant Cell Tumor of bone. If medical therapy is considered, it would typically involve Denosumab. What is the precise mechanism of action of this drug?

. Monoclonal antibody that binds to and inhibits RANK ligand (RANKL)
. Nitrogenous bisphosphonate that inhibits farnesyl pyrophosphate synthase
. Tyrosine kinase inhibitor targeting VEGF receptors
. Monoclonal antibody against CD20 on B-lymphocytes
. Recombinant antagonist of the parathyroid hormone (PTH) receptor

Correct Answer & Explanation

. Monoclonal antibody that binds to and inhibits RANK ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANK Ligand (RANKL), preventing it from activating RANK on the surface of osteoclasts and their precursors. In Giant Cell Tumor of bone, the neoplastic stromal cells express high levels of RANKL, which recruits the giant cell osteoclasts that cause bone destruction. Denosumab effectively halts this osteoclastic bone resorption.

Question 5237

Topic: Biomechanics & Biomaterials

In the context of orthopedic biomaterials, galvanic corrosion is most likely to occur under which of the following specific conditions?

. Fretting wear occurring between two identical metals at a modular junction
. Exposure of a single metallic implant to highly acidic synovial fluid
. Physical contact between two dissimilar metals in an electrolytic solution
. Fatigue failure of a highly polished ceramic articulating surface
. Polyethylene wear debris activating a local macrophage response

Correct Answer & Explanation

. Physical contact between two dissimilar metals in an electrolytic solution

Explanation

Galvanic corrosion is an electrochemical process that occurs when two dissimilar metals (having different anodic indices/electrochemical potentials) are placed in direct physical contact within a conductive electrolyte solution (such as human body fluid). The less noble metal acts as an anode and corrodes, while the more noble metal acts as a cathode.

Question 5238

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) signals primarily through serine/threonine kinase receptors. Which of the following intracellular signaling molecules is directly phosphorylated following rhBMP-2 receptor activation to initiate osteoblastic gene transcription?

. beta-catenin
. Smad 1/5/8
. JAK/STAT
. c-AMP
. NF-kappa B

Correct Answer & Explanation

. Smad 1/5/8

Explanation

Bone morphogenetic proteins (BMPs) belong to the TGF-beta superfamily. When rhBMP-2 binds to its dimeric serine/threonine kinase receptor, it triggers the intracellular phosphorylation of receptor-regulated Smads, specifically Smad 1, 5, and 8. These complex with Smad 4, translocate to the nucleus, and regulate the transcription of osteogenic genes like Runx2.

Question 5239

Topic: Biology, Genetics & Bone Healing

Denosumab is often utilized in the medical management of surgically unsalvageable or recurrent Giant Cell Tumors of Bone (GCTB). What is the specific mechanism of action of this medication?

. Inhibition of the mTOR pathway
. Direct apoptosis of neoplastic mononuclear stromal cells
. Binding and inhibition of the RANK Ligand (RANKL)
. Inhibition of vascular endothelial growth factor (VEGF)
. Cross-linking of DNA preventing tumor cell replication

Correct Answer & Explanation

. Binding and inhibition of the RANK Ligand (RANKL)

Explanation

Giant Cell Tumor of Bone (GCTB) contains neoplastic mononuclear stromal cells that express high levels of RANK Ligand (RANKL). RANKL normally binds to RANK on osteoclast precursors, leading to massive osteoclast-like giant cell formation and bone destruction. Denosumab is a monoclonal antibody that binds to RANKL, preventing it from activating RANK, thereby potently inhibiting osteoclast-mediated bone resorption and stabilizing the tumor.

Question 5240

Topic: 1. General Principles & Basic Science

Articular cartilage is a highly specialized tissue structured into four distinct zones. Which of the following best describes the orientation of Type II collagen fibers and the morphology of chondrocytes in the deep (radial) zone of articular cartilage?

. Fibers parallel to the joint surface; flattened chondrocytes
. Fibers arranged obliquely; spherical chondrocytes
. Fibers oriented perpendicular to the joint surface; chondrocytes arranged in columnar palisades
. Fibers arranged randomly; hyper-trophic chondrocytes
. Fibers parallel to the joint surface; chondrocytes arranged in columnar palisades

Correct Answer & Explanation

. Fibers oriented perpendicular to the joint surface; chondrocytes arranged in columnar palisades

Explanation

In the deep (radial) zone of articular cartilage, the Type II collagen fibers are oriented perpendicular to the articular surface. This arrangement provides maximal resistance to compressive forces. The chondrocytes in this zone are also distinctively arranged in vertical columns or palisades parallel to the collagen fibers. The superficial zone has parallel fibers and flattened cells; the middle zone has oblique/random fibers and spherical cells.

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