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1. General Principles & Basic Science MCQs

Practice Set 532 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 10621

Topic: 1. General Principles & Basic Science

When utilizing fresh frozen osteochondral allografts for the treatment of large focal chondral defects, the clinical success of the graft primarily depends on which of the following biological properties?

. Survival of living osteoblasts that synthesize new subchondral bone
. Preservation of a critical threshold of viable chondrocytes to maintain the extracellular matrix
. Presence of living mesenchymal stem cells to differentiate into mature cartilage
. An intact microvascular network allowing for immediate host anastomosis
. High immunogenicity of the graft to stimulate rapid host cell creeping substitution

Correct Answer & Explanation

. Preservation of a critical threshold of viable chondrocytes to maintain the extracellular matrix

Explanation

The primary advantage of fresh or fresh-stored (refrigerated, not truly 'frozen' below freezing for cartilage viability, though sometimes casually termed fresh-frozen in older literature; specifically, 'fresh' or prolonged fresh storage is used) osteochondral allografts is the preservation of viable mature chondrocytes. Chondrocytes are necessary to maintain the complex extracellular matrix of the hyaline cartilage over time. The bony portion of the allograft is dead and undergoes creeping substitution by the host.

Question 10622

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a bone graft substitute. Its osteoinductive capability is primarily mediated by the presence of which of the following components preserved during the demineralization process?

. Bone Morphogenetic Proteins (BMPs)
. Viable osteoprogenitor cells
. Living mesenchymal stem cells
. Calcium hydroxyapatite scaffolding
. Platelet-derived growth factor (PDGF)

Correct Answer & Explanation

. Bone Morphogenetic Proteins (BMPs)

Explanation

Demineralized bone matrix (DBM) is produced by acid-extracting minerals from allograft bone. This process destroys viable cells (meaning it is NOT osteogenic) and removes the mineral structure, but it exposes and preserves the non-collagenous proteins, particularly Bone Morphogenetic Proteins (BMPs). These BMPs provide DBM with its osteoinductive properties, allowing it to stimulate the differentiation of host mesenchymal cells into osteoblasts.

Question 10623

Topic: Infection, Pharmacology & VTE
An orthopaedic surgeon is evaluating a 70-year-old patient scheduled for an elective total hip arthroplasty. The patient is currently taking Rivaroxaban for non-valvular atrial fibrillation. What is the specific mechanism of action of this medication?
. Inhibits thrombin (Factor IIa) directly
. Potentiates Antithrombin III activity
. Inhibits the Vitamin K epoxide reductase complex
. Directly and reversibly inhibits Factor Xa
. Irreversibly blocks ADP (P2Y12) receptors on platelets

Correct Answer & Explanation

. Directly and reversibly inhibits Factor Xa

Explanation

Rivaroxaban (as well as Apixaban and Edoxaban) is a Direct Oral Anticoagulant (DOAC) that acts by directly and reversibly inhibiting Factor Xa, preventing the conversion of prothrombin to thrombin. Dabigatran is a direct thrombin (IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase. LMWH and unfractionated heparin potentiate Antithrombin III. Clopidogrel blocks P2Y12 ADP receptors.

Question 10624

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials possesses a Young's modulus most similar to that of human cortical bone, thereby minimizing the risk of stress shielding in arthroplasty?

. Cobalt-chromium alloy
. Titanium alloy
. Stainless steel
. Polymethylmethacrylate (PMMA)
. Alumina ceramic

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a Young's modulus (stiffness) closer to that of cortical bone compared to stainless steel or cobalt-chromium. This similarity reduces stress shielding and promotes better long-term bone mass preservation around the implant.

Question 10625

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is widely used in orthopedic surgery to reduce perioperative blood loss. What is its primary mechanism of action?

. Promotes platelet aggregation
. Competitively inhibits plasminogen activation
. Directly inhibits factor Xa
. Cross-links fibrin strands
. Inhibits cyclooxygenase-1

Correct Answer & Explanation

. Competitively inhibits plasminogen activation

Explanation

TXA is a synthetic lysine analog that competitively binds to plasminogen. This prevents plasminogen from converting to active plasmin, thereby inhibiting fibrin degradation and stabilizing blood clots.

Question 10626

Topic: Biology, Genetics & Bone Healing

During a posterolateral lumbar fusion, a surgeon utilizes recombinant human Bone Morphogenetic Protein-2 (rhBMP-2). This biologic agent promotes bone formation strictly through which of the following properties?

. Osteogenesis
. Osteoconduction
. Osteoinduction
. Creeping substitution
. Contact guidance

Correct Answer & Explanation

. Osteoinduction

Explanation

rhBMP-2 acts purely via osteoinduction, meaning it stimulates the differentiation of host mesenchymal stem cells into bone-forming osteoblasts. It does not provide a structural scaffold (osteoconduction) nor does it contain live cells (osteogenesis).

Question 10627

Topic: 1. General Principles & Basic Science

In human articular cartilage, which structural zone contains the highest concentration of collagen, with fibrils oriented parallel to the joint surface to resist high shear forces?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial zone possesses flattened chondrocytes and densely packed collagen fibrils oriented parallel to the articular surface. This specific microarchitecture provides the greatest tensile strength and resistance to shear stresses within the joint.

Question 10628

Topic: Biology, Genetics & Bone Healing

A 6-year-old child presents with bowed legs and is diagnosed with X-linked hypophosphatemic (XLH) rickets. Which of the following laboratory profiles and genetic mutations is the hallmark of this condition?

. High serum calcium; low PTH; CASR mutation
. Low serum phosphate; elevated FGF23; PHEX mutation
. Low serum calcium; high PTH; VDR mutation
. Normal phosphate; low alkaline phosphatase; ALPL mutation
. High serum phosphate; low FGF23; FGF23 mutation

Correct Answer & Explanation

. Low serum phosphate; elevated FGF23; PHEX mutation

Explanation

XLH is caused by a PHEX gene mutation that leads to the overproduction of FGF23. Elevated FGF23 causes profound renal phosphate wasting, resulting in hypophosphatemia and defective bone mineralization.

Question 10629

Topic: 1. General Principles & Basic Science

Following a primary flexor tendon repair in Zone II, at what postoperative timeframe is the repair biomechanically at its weakest due to the transition from the inflammatory to the early proliferative phase?

. 1 to 3 days
. 5 to 14 days
. 3 to 4 weeks
. 6 to 8 weeks
. 12 weeks

Correct Answer & Explanation

. 5 to 14 days

Explanation

A repaired tendon is typically weakest between 5 and 14 days postoperatively. During this window, initial inflammatory softening of the tendon ends occurs before substantial new collagen synthesis and cross-linking can generate adequate tensile strength.

Question 10630

Topic: 1. General Principles & Basic Science

According to Sunderland's classification of peripheral nerve injuries, a third-degree nerve injury describes the complete disruption of the axon and which of the following specific connective tissue layers?

. Myelin sheath only
. Epineurium only
. Endoneurium
. Perineurium
. Both perineurium and epineurium

Correct Answer & Explanation

. Perineurium

Explanation

A Sunderland third-degree injury involves disruption of the axon and the endoneurium, while the perineurium and epineurium remain intact. This intrafascicular damage leads to scarring and unpredictable, often aberrant, axonal regeneration.

Question 10631

Topic: Biology, Genetics & Bone Healing

The primary mechanism of particle-induced osteolysis in total joint arthroplasty involves macrophage phagocytosis of wear debris. Which of the following downstream mediators is most directly responsible for the subsequent terminal activation of osteoclasts?

. Interleukin-4 (IL-4)
. Interleukin-10 (IL-10)
. Transforming Growth Factor-beta (TGF-beta)
. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)
. Interferon-gamma

Correct Answer & Explanation

. Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL)

Explanation

Macrophages release pro-inflammatory cytokines (like TNF-alpha and IL-1) upon ingesting wear particles, which in turn stimulate the expression of RANKL by osteoblasts. RANKL binds to RANK on osteoclast precursors, directly driving their activation and bone resorption.

Question 10632

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with severe postmenopausal osteoporosis is treated with denosumab. Which of the following best describes the molecular mechanism of this medication?

. Binds to hydroxyapatite and disrupts the osteoclast ruffled border
. Acts as an agonist on the calcium-sensing receptor on parathyroid cells
. Competitively binds to and inhibits RANKL as a monoclonal antibody
. Stimulates bone formation as a recombinant fragment of parathyroid hormone
. Inhibits sclerostin to promote Wnt signaling and osteoblastogenesis

Correct Answer & Explanation

. Competitively binds to and inhibits RANKL as a monoclonal antibody

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to RANKL. By neutralizing RANKL, it prevents the activation, maturation, and survival of osteoclasts, leading to profoundly decreased bone resorption.

Question 10633

Topic: 1. General Principles & Basic Science

Which of the following lower extremity amputation configurations is associated with the highest increase in metabolic energy expenditure during ambulation compared to baseline normal walking?

. Unilateral Syme amputation
. Unilateral transtibial (BKA) amputation
. Bilateral transtibial (BKA) amputations
. Unilateral transfemoral (AKA) amputation
. Unilateral knee disarticulation

Correct Answer & Explanation

. Unilateral transfemoral (AKA) amputation

Explanation

A unilateral transfemoral (AKA) amputation increases baseline energy expenditure by approximately 60-65%. This metabolic demand is significantly higher than that required for bilateral transtibial amputations (which increase expenditure by roughly 40%).

Question 10634

Topic: Infection, Pharmacology & VTE

A 2-year-old child presents with an acute septic arthritis of the knee. The synovial fluid Gram stain is negative, but a targeted PCR panel is positive. Which of the following fastidious organisms is increasingly recognized as the most common cause of septic arthritis in children aged 6 months to 4 years?

. Staphylococcus aureus
. Haemophilus influenzae type B
. Kingella kingae
. Streptococcus pneumoniae
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a fastidious Gram-negative organism that has emerged as the most common cause of septic arthritis and osteomyelitis in children under 4 years old. It is difficult to isolate on traditional culture but is readily identified via nucleic acid amplification (PCR).

Question 10635

Topic: Biology, Genetics & Bone Healing

A patient with autosomal recessive malignant osteopetrosis suffers from an inability of osteoclasts to acidify the resorption pit. A deficiency in which of the following enzymes is most frequently responsible for this specific failure in hydrogen ion generation?

. Tartrate-resistant acid phosphatase (TRAP)
. Carbonic anhydrase II
. Cathepsin K
. Matrix metalloproteinase-9 (MMP-9)
. Tissue nonspecific alkaline phosphatase (TNAP)

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Carbonic anhydrase II generates the protons (H+) necessary for osteoclasts to acidify the sealed clear zone (resorption pit). Deficiency of this enzyme halts the dissolution of inorganic bone mineral, causing osteopetrosis.

Question 10636

Topic: 1. General Principles & Basic Science

Which of the following best describes the physiological process of incorporation for a structural cortical bone allograft?

. Rapid osteoblastic bone formation on the outer surface
. Initial osteoclastic resorption followed by osteoblastic formation (creeping substitution)
. Direct woven bone formation without any initial osteoclastic resorption
. Exclusively endochondral ossification
. Early robust revascularization leading to immediate strength increase

Correct Answer & Explanation

. Initial osteoclastic resorption followed by osteoblastic formation (creeping substitution)

Explanation

Structural cortical allografts incorporate via a process called creeping substitution. This involves initial osteoclastic resorption which temporarily weakens the graft, followed by osteoblastic bone formation.

Question 10637

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is commonly utilized for implant fixation in total joint arthroplasty. Which of the following best describes its fundamental mechanical properties?

. It is strongest in tension and weakest in compression
. It is strongest in shear and weakest in tension
. It functions as a true adhesive, bonding chemically to the native bone
. It is strongest in compression and weakest in tension
. It undergoes a highly endothermic reaction during polymerization

Correct Answer & Explanation

. It is strongest in compression and weakest in tension

Explanation

PMMA bone cement acts as a grout to provide mechanical interlock rather than a chemical adhesive. Mechanically, it is strongest in compression and significantly weaker in tension and shear.

Question 10638

Topic: Biology, Genetics & Bone Healing

Which of the following cellular mechanisms is most commonly defective in the pathogenesis of infantile malignant osteopetrosis?

. Failure of osteoblast differentiation from mesenchymal stem cells
. Defective RANKL expression by osteoblasts
. Inability of osteoclasts to acidify the resorption pit due to a TCIRG1 mutation
. Overproduction of osteoprotegerin (OPG) by osteocytes
. Deficiency of Vitamin D receptors on the osteoblast surface

Correct Answer & Explanation

. Inability of osteoclasts to acidify the resorption pit due to a TCIRG1 mutation

Explanation

Infantile malignant osteopetrosis is commonly caused by mutations in the TCIRG1 gene, which encodes a subunit of the osteoclast proton pump. This results in the inability of osteoclasts to secrete protons and acidify the resorption pit, leading to dense but brittle bone.

Question 10639

Topic: 1. General Principles & Basic Science

Which of the following zones of articular cartilage possesses the highest concentration of water and contains collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content and contains Type II collagen fibers that run parallel to the articular surface. This specific orientation provides the cartilage with high tensile strength to resist shear forces.

Question 10640

Topic: Biology, Genetics & Bone Healing

In distraction osteogenesis (e.g., the Ilizarov technique), bone formation within the distraction gap primarily occurs through which of the following physiologic processes?

. Primary osteonal healing
. Endochondral ossification
. Intramembranous ossification
. Creeping substitution
. Callus remodeling

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Distraction osteogenesis relies on mechanical tension applied to a healing fracture callus, which stimulates bone formation primarily via intramembranous ossification. This process bypasses the cartilaginous intermediate stage seen in endochondral ossification.

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