Menu

1. General Principles & Basic Science MCQs

Practice Set 568 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 11341

Topic: 1. General Principles & Basic Science

A researcher is evaluating the histological sections of normal adult articular cartilage. Which of the following zones is characterized by the highest concentration of proteoglycans, the lowest water content, and collagen fibers oriented perpendicular to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest concentration of proteoglycans and the lowest water content. The collagen fibers (mostly Type II) are arranged perpendicular to the articular surface to provide maximal resistance to compressive forces. The superficial zone has the highest water content and collagen fibers parallel to the joint surface to resist shear stress.

Question 11342

Topic: Biomechanics & Biomaterials

An orthopedic surgeon is revising a failed internal fixation of a distal femur fracture. The original construct utilized a 316L stainless steel plate secured with Ti-6Al-4V (titanium alloy) screws. Which type of corrosion is most likely to occur at the plate-screw interface in this scenario?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (such as stainless steel and titanium) are placed in direct physical contact within a conductive fluid medium (e.g., blood or interstitial fluid). The less noble metal (anode) undergoes accelerated corrosion. Mixing stainless steel with titanium or cobalt-chromium alloys is generally contraindicated in orthopedics due to this risk.

Question 11343

Topic: Biology, Genetics & Bone Healing

Denosumab is highly effective in the medical management of unresectable Giant Cell Tumor of Bone (GCTB). Which of the following accurately describes the molecular target of this medication?

. RANK receptor on osteoclast precursors
. RANK ligand (RANKL)
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Sclerostin

Correct Answer & Explanation

. RANK receptor on osteoclast precursors

Explanation

Denosumab is a fully human monoclonal antibody that directly targets and binds to RANK Ligand (RANKL). RANKL is produced by the neoplastic stromal cells in Giant Cell Tumor of Bone. By binding RANKL, Denosumab prevents it from interacting with the RANK receptor on osteoclasts and their precursors, thereby inhibiting osteoclast activation, differentiation, and survival.

Question 11344

Topic: Biology, Genetics & Bone Healing

A severely malnourished patient presents with bleeding gums, perifollicular hemorrhages, and impaired wound healing. Radiographs demonstrate osteopenia and an intensely radiodense line at the metaphysis. The underlying metabolic deficiency primarily impairs which of the following steps in collagen synthesis?

. Cross-linking of collagen via lysyl oxidase
. Hydroxylation of proline and lysine residues
. Cleavage of procollagen C- and N-terminals
. Intracellular assembly of the triple helix
. Glycosylation of hydroxylysine residues

Correct Answer & Explanation

. Cross-linking of collagen via lysyl oxidase

Explanation

The patient has Scurvy (Vitamin C deficiency). Ascorbic acid is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. Without Vitamin C, the hydroxylation of proline and lysine residues in the rough endoplasmic reticulum cannot occur, preventing stable triple helix formation of procollagen. Lysyl oxidase (Option A) requires copper and is defective in Menkes disease.

Question 11345

Topic: Biology, Genetics & Bone Healing

A 68-year-old male presents with increasing skull size, hearing loss, and a bowing deformity of his left tibia. Serum calcium and phosphorus are normal, but alkaline phosphatase is markedly elevated. The primary cellular defect in this disease is characterized by:

. A primary defect in osteoblast bone formation due to RUNX2 mutation
. A deficiency of tissue-nonspecific alkaline phosphatase
. A primary defect causing hyperactive, large multinucleated osteoclasts
. Autoimmune destruction of the organic bone matrix
. A mutation in the COL1A1 gene leading to brittle bone matrix

Correct Answer & Explanation

. A primary defect in osteoblast bone formation due to RUNX2 mutation

Explanation

The clinical presentation is classic for Paget's disease of bone (osteitis deformans). The primary cellular abnormality is found in the osteoclast, which is hyper-responsive to RANKL, excessively large, and highly multinucleated (up to 100 nuclei). This initiates a phase of aggressive osteolysis, followed by disorganized, woven bone formation by osteoblasts. Paget's has been linked to SQSTM1 mutations and paramyxovirus inclusions.

Question 11346

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis (DVT) prophylaxis following total hip arthroplasty. Rivaroxaban exerts its anticoagulant effect through the direct inhibition of which component of the coagulation cascade?
. Thrombin (Factor IIa)
. Factor Xa
. Antithrombin III
. Vitamin K epoxide reductase
. Plasminogen

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban and Apixaban are direct oral anticoagulants (DOACs) that specifically and reversibly inhibit free and clot-bound Factor Xa (hence the suffix '-xaban'). This interrupts both the intrinsic and extrinsic pathways of the coagulation cascade. Dabigatran (Option A) is a direct thrombin (IIa) inhibitor. Warfarin inhibits Vitamin K epoxide reductase (Option D).

Question 11347

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs), such as BMP-2 and BMP-7, are utilized clinically to enhance bone formation. They initiate osteoblastic differentiation primarily through binding cell surface receptors that subsequently activate which of the following intracellular signaling pathways?

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

Correct Answer & Explanation

. Wnt / beta-catenin pathway

Explanation

BMPs are members of the TGF-beta superfamily. They bind to serine/threonine kinase receptors on the cell surface, which phosphorylate receptor-regulated Smads (specifically Smad 1, 5, and 8). These phosphorylated Smads form a complex with the co-Smad (Smad 4), translocate to the nucleus, and induce the transcription of osteogenic genes (e.g., Runx2). The Wnt pathway (Option A) is regulated by LRP5/6 and sclerostin, independent of BMP primary signaling.

Question 11348

Topic: Biology, Genetics & Bone Healing
A patient with osteopetrosis presents with multiple fractures and a 'rugger jersey' spine appearance on radiographs. The disease is caused by an inability of osteoclasts to resorb bone. A known genetic defect underlying the most common autosomal recessive form of this condition affects which of the following?
. Type I collagen (COL1A1/COL1A2)
. Fibroblast growth factor receptor 3 (FGFR3)
. Carbonic anhydrase II (CAII)
. Tissue-nonspecific alkaline phosphatase (TNSALP)
. Fibrillin-1 (FBN1)

Correct Answer & Explanation

. Carbonic anhydrase II (CAII)

Explanation

Osteopetrosis is fundamentally a failure of osteoclast-mediated bone resorption. Osteoclasts require a highly acidic environment in the Howship lacuna to dissolve mineralized bone matrix. Mutations in Carbonic Anhydrase II (CAII), as well as the TCIRG1 gene (vacuolar proton pump), prevent the osteoclast from generating and pumping protons (H+), thereby nullifying bone resorption and resulting in abnormally dense, brittle bone.

Question 11349

Topic: Biomechanics & Biomaterials

In a standard stress-strain curve of a given orthopaedic material, what does the area under the entire curve up to the point of failure represent?

. Stiffness
. Yield strength
. Toughness
. Ductility
. Fatigue limit

Correct Answer & Explanation

. Stiffness

Explanation

The area under the stress-strain curve represents the toughness of the material, which is the total energy absorbed by the material before it fractures. Stiffness is represented by the slope of the elastic region (Young's modulus). Yield strength is the point at which plastic deformation begins. Ductility is a measure of how much plastic deformation a material can undergo before failure.

Question 11350

Topic: 1. General Principles & Basic Science

Which zone of normal articular cartilage contains the highest concentration of water and collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content (approximately 80%) and a high concentration of Type II collagen fibers that are densely packed and aligned parallel to the articular surface. This unique structural arrangement allows it to effectively resist shear stresses during joint motion.

Question 11351

Topic: Biology, Genetics & Bone Healing

A 45-year-old female presents with diffuse bone pain and muscle weakness. Laboratory studies reveal low serum calcium, low serum phosphate, elevated alkaline phosphatase, and elevated parathyroid hormone (PTH) levels. What is the most likely diagnosis?

. Osteoporosis
. Osteomalacia
. Paget disease
. Primary hyperparathyroidism
. Multiple myeloma

Correct Answer & Explanation

. Osteoporosis

Explanation

The patient's laboratory profile (low calcium, low phosphate, high alkaline phosphatase, high PTH) is characteristic of osteomalacia, most commonly caused by profound Vitamin D deficiency. This leads to impaired intestinal calcium absorption, triggering secondary hyperparathyroidism which increases phosphate excretion. Osteoporosis typically presents with normal lab values. Primary hyperparathyroidism would feature elevated serum calcium. Paget disease typically presents with an isolated elevation in alkaline phosphatase with normal calcium and phosphate.

Question 11352

Topic: 1. General Principles & Basic Science

Following a complete peripheral nerve transection and subsequent microsurgical epineurial repair, the distal nerve segment undergoes Wallerian degeneration. After a latent period, at what approximate maximal rate do the regenerating axons grow?

. 0.1 mm/day
. 1.0 mm/day
. 5.0 mm/day
. 10.0 mm/day
. 15.0 mm/day

Correct Answer & Explanation

. 0.1 mm/day

Explanation

Peripheral nerve axonal regeneration occurs at a maximal rate of approximately 1 mm/day (or about 1 inch per month) under optimal conditions, following a latent period of roughly 3 to 4 weeks during which neuronal recovery and Wallerian degeneration of the distal segment occur.

Question 11353

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is widely used in orthopaedic surgery to reduce perioperative blood loss. By which of the following mechanisms does TXA achieve its primary physiological effect?

. Inhibiting the cyclooxygenase enzyme
. Directly inhibiting Factor Xa
. Reversibly binding to plasminogen to block its conversion to plasmin
. Increasing the production of von Willebrand factor
. Activating the extrinsic coagulation cascade

Correct Answer & Explanation

. Inhibiting the cyclooxygenase enzyme

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic agent by reversibly and competitively binding to the lysine-binding sites on plasminogen molecules. This blocks the conversion of plasminogen to active plasmin, thereby preventing the degradation of fibrin clots.

Question 11354

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is commonly used to reduce wear. Which of the following is a recognized mechanical trade-off associated with increasing the cross-linking of UHMWPE?
. Increased abrasive wear
. Decreased fatigue strength and fracture toughness
. Increased oxidative degradation
. Decreased elastic modulus
. Increased adhesive wear

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

While high cross-linking of UHMWPE significantly reduces abrasive and adhesive wear rates (thereby minimizing particle-induced osteolysis), the cross-linking process alters the polymer chains, leading to a reduction in certain mechanical properties, particularly fatigue strength, tensile strength, and fracture toughness.

Question 11355

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the process of 'creeping substitution' seen during the incorporation of a cortical bone allograft?

. Simultaneous resorption of the graft by osteoclasts and formation of new bone by osteoblasts
. Induction of undifferentiated mesenchymal stem cells into osteoblasts by BMPs
. Scaffold-mediated direct primary bone healing without any intermediate callus
. Rapid revascularization followed by immediate structural strengthening of the graft
. Complete dissolution of the graft by osteoclasts before any osteoblast activity begins

Correct Answer & Explanation

. Simultaneous resorption of the graft by osteoclasts and formation of new bone by osteoblasts

Explanation

Creeping substitution is the classical histological process by which a structural bone graft (such as a cortical allograft) is incorporated. It involves the simultaneous, coupled process of graft resorption by osteoclasts and the deposition of new host bone by osteoblasts. During this slow process, cortical allografts often become temporarily weaker before full incorporation is achieved.

Question 11356

Topic: Biology, Genetics & Bone Healing

A pediatric patient presents with gingival bleeding, petechiae, and metaphyseal radiolucent bands on radiographs. This condition is caused by a nutritional deficiency that directly impairs which specific step of collagen synthesis?

. Cleavage of procollagen C-terminal propeptides
. Hydroxylation of proline and lysine residues
. Cross-linking of tropocollagen molecules by lysyl oxidase
. Transcription of the COL1A1 gene
. Intracellular assembly of the triple helix

Correct Answer & Explanation

. Cleavage of procollagen C-terminal propeptides

Explanation

The clinical presentation describes scurvy, which is caused by a deficiency of Vitamin C (ascorbic acid). Vitamin C is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. These enzymes are responsible for the hydroxylation of proline and lysine residues on the nascent procollagen chains, a step absolutely critical for the stable formation of the collagen triple helix.

Question 11357

Topic: Infection, Pharmacology & VTE

During a regional block for an orthopaedic procedure, a patient develops sudden perioral numbness, tinnitus, and subsequent cardiovascular collapse. Which of the following agents is the primary targeted rescue treatment for this acute condition?

. Flumazenil
. Naloxone
. 20% Lipid emulsion
. Intravenous calcium gluconate
. Protamine sulfate

Correct Answer & Explanation

. Flumazenil

Explanation

The patient is exhibiting signs of Local Anesthetic Systemic Toxicity (LAST), most commonly associated with highly lipid-soluble agents like bupivacaine. The primary targeted rescue therapy is the rapid intravenous administration of a 20% lipid emulsion (Intralipid), which creates a 'lipid sink' in the intravascular space, drawing the lipophilic anesthetic away from susceptible cardiac and neural tissues.

Question 11358

Topic: Infection, Pharmacology & VTE
A 65-year-old male is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the specific molecular target of this medication?
. Thrombin (Factor IIa)
. Factor Xa
. Vitamin K epoxide reductase
. Antithrombin III
. Platelet P2Y12 receptor

Correct Answer & Explanation

. Factor Xa

Explanation

Rivaroxaban is a Direct Oral Anticoagulant (DOAC) that exerts its effect by directly and reversibly inhibiting Factor Xa, halting the conversion of prothrombin to thrombin in the coagulation cascade. Dabigatran, another DOAC, acts via direct thrombin (Factor IIa) inhibition. Warfarin targets Vitamin K epoxide reductase, and clopidogrel targets the P2Y12 receptor.

Question 11359

Topic: 1. General Principles & Basic Science

A new diagnostic test for periprosthetic joint infection is evaluated in two different hospital populations. Hospital A has a 5% prevalence of PJI, while Hospital B has a 20% prevalence. If the test has a fixed sensitivity of 90% and specificity of 90%, how will the Positive Predictive Value (PPV) compare between the two hospitals?

. PPV will be higher in Hospital A
. PPV will be higher in Hospital B
. PPV will be equal in both hospitals
. PPV cannot be determined without knowing the sample size
. PPV depends only on sensitivity and specificity

Correct Answer & Explanation

. PPV will be higher in Hospital A

Explanation

The Positive Predictive Value (PPV) is heavily dependent on the baseline prevalence of the disease in the tested population. For a test with fixed sensitivity and specificity, an increase in disease prevalence results in an increased PPV. Therefore, Hospital B, having a higher prevalence (20%), will demonstrate a higher PPV for the test than Hospital A.

Question 11360

Topic: Biology, Genetics & Bone Healing

What is the primary biomechanical function of the proteoglycan aggrecan in the extracellular matrix of normal articular cartilage?

. Providing tensile strength to the tissue
. Anchoring chondrocytes to the subchondral bone
. Drawing water into the matrix to provide compressive stiffness
. Directly inhibiting osteoclast activity
. Mediating the cross-linking of Type II collagen

Correct Answer & Explanation

. Providing tensile strength to the tissue

Explanation

Aggrecan is a massive proteoglycan densely populated with negatively charged glycosaminoglycans (chondroitin sulfate and keratan sulfate). These fixed negative charges repel each other and create a strong Donnan osmotic effect, drawing water into the cartilage matrix. This swelling pressure, constrained by the Type II collagen network, provides articular cartilage with its exceptional compressive stiffness.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page