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1. General Principles & Basic Science MCQs

Practice Set 727 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 14521

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis (DVT) prophylaxis following a total knee arthroplasty. What is the exact mechanism of action of this pharmacological agent?
. Direct inhibition of thrombin (Factor IIa)
. Indirect inhibition of Factor Xa via antithrombin III
. Direct inhibition of Factor Xa
. Inhibition of Vitamin K epoxide reductase
. Irreversible inhibition of cyclooxygenase

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants that selectively and directly inhibit Factor Xa. Low molecular weight heparins inhibit Factor Xa indirectly via antithrombin III. Dabigatran directly inhibits thrombin (Factor IIa).

Question 14522

Topic: Biology, Genetics & Bone Healing

A researcher is studying the molecular mechanisms of bone remodeling. Which of the following molecules acts as a physiological decoy receptor for RANKL, thereby actively inhibiting osteoclast differentiation and activation?

. Sclerostin
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Cathepsin K
. Runx2

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Osteoprotegerin (OPG) is a glycoprotein produced by osteoblasts that serves as a soluble decoy receptor for RANKL. By binding to RANKL, OPG prevents it from activating the RANK receptor on osteoclast precursors, thereby halting osteoclastogenesis.

Question 14523

Topic: Infection, Pharmacology & VTE

In the pathogenesis of periprosthetic joint infection, Staphylococcus epidermidis relies on a specific structural matrix to adhere to metallic implants, which subsequently shields the bacteria from host immune defenses and antibiotics. What is the primary constituent of this protective biofilm?

. Peptidoglycan
. Lipopolysaccharide
. Exopolysaccharide (glycocalyx)
. Teichoic acid
. Protein A

Correct Answer & Explanation

. Exopolysaccharide (glycocalyx)

Explanation

Staphylococcus epidermidis is notorious for forming biofilms on medical implants. The biofilm matrix is primarily composed of an exopolysaccharide (also known as glycocalyx or polysaccharide intercellular adhesin, PIA), which firmly anchors the colony and resists antimicrobial penetration.

Question 14524

Topic: 1. General Principles & Basic Science

When attempting to optimize a cortical screw for maximum pullout strength in diaphyseal bone, altering which of the following geometric parameters has the greatest mathematical impact on increasing pullout resistance?

. Increasing the core diameter
. Decreasing the thread pitch
. Increasing the outer diameter
. Increasing the length of the unthreaded shaft
. Decreasing the core diameter

Correct Answer & Explanation

. Increasing the outer diameter

Explanation

Screw pullout strength is directly proportional to the outer diameter of the screw thread, the length of thread engagement, and the shear strength of the bone. Increasing the outer diameter increases the volume of bone engaged between threads, having the most significant positive impact on pullout strength.

Question 14525

Topic: 1. General Principles & Basic Science
During normal physiological wound healing, which cellular phenotype becomes the predominant cell type in the wound bed during the proliferative phase (typically days 4 to 21 post-injury)?
. Polymorphonuclear neutrophils
. Macrophages
. Fibroblasts
. Lymphocytes
. Mast cells

Correct Answer & Explanation

. Fibroblasts

Explanation

The proliferative phase of wound healing is characterized by angiogenesis, granulation tissue formation, and collagen deposition. Fibroblasts migrate into the wound and proliferate, becoming the predominant cell type responsible for producing Type III collagen during this period.

Question 14526

Topic: 1. General Principles & Basic Science

Which of the following physiologic and metabolic characteristics best describes Type I (slow-twitch) muscle fibers, such as those predominantly found in the human soleus muscle?

. High glycolytic capacity and rapid fatigue
. Low mitochondrial density and high reliance on anaerobic metabolism
. High oxidative capacity and high resistance to fatigue
. Large cross-sectional area and high force production
. Low myoglobin content and white appearance

Correct Answer & Explanation

. High oxidative capacity and high resistance to fatigue

Explanation

Type I (slow-twitch) muscle fibers are designed for endurance and postural maintenance. They feature a high oxidative capacity, rich capillary supply, high myoglobin content (giving a red appearance), high mitochondrial density, and are highly resistant to fatigue.

Question 14527

Topic: 1. General Principles & Basic Science

In musculoskeletal magnetic resonance imaging (MRI), the 'magic angle' artifact can cause a false positive appearance of tendinosis or a tendon tear. At what specific angle to the main magnetic field (B0) does this artifact occur, and on what type of sequence is it most prominent?

. 55 degrees; T1-weighted and proton density sequences
. 55 degrees; T2-weighted sequences with long TE
. 45 degrees; Short tau inversion recovery (STIR) sequences
. 90 degrees; Gradient-echo sequences
. 30 degrees; T2-weighted fast spin-echo sequences

Correct Answer & Explanation

. 55 degrees; T1-weighted and proton density sequences

Explanation

The magic angle artifact occurs when highly organized collagen fibers (like those in a tendon) are oriented at exactly 55 degrees (54.7 degrees) to the main magnetic field. It causes artificially increased signal intensity on sequences with a short echo time (TE), such as T1-weighted and proton density images. It resolves on long TE sequences (T2-weighted).

Question 14528

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory regarding fracture healing, what is the maximum permissible interfragmentary strain that will still allow for primary (contact) bone healing to occur via direct Haversian remodeling?

. Less than 2%
. Between 2% and 10%
. Between 10% and 30%
. Between 30% and 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory dictates that primary bone healing (direct Haversian remodeling without a cartilaginous intermediate or callus formation) requires absolute stability with an interfragmentary strain of less than 2%. Strain between 2% and 10% promotes secondary healing via endochondral ossification.

Question 14529

Topic: 1. General Principles & Basic Science

Which of the following human leukocyte antigen (HLA) serotypes is most strongly associated with an increased risk and aggressive clinical course of Rheumatoid Arthritis in Caucasian populations?

. HLA-B27
. HLA-DR4
. HLA-B8
. HLA-DQ2
. HLA-DR2

Correct Answer & Explanation

. HLA-DR4

Explanation

Rheumatoid arthritis is strongly associated with the HLA-DR4 and HLA-DR1 alleles. These alleles share a conserved amino acid sequence in the antigen-binding groove known as the 'shared epitope', which is linked to disease susceptibility and severity.

Question 14530

Topic: 1. General Principles & Basic Science

An orthopedic surgeon steps back from the operating table to reduce their radiation exposure during the use of a C-arm fluoroscope. If the surgeon increases their distance from the radiation source from 1 meter to 2 meters, to what fraction is their radiation exposure reduced compared to the 1-meter position?

. Reduced to 1/2 (50%)
. Reduced to 1/4 (25%)
. Reduced to 1/8 (12.5%)
. Reduced to 1/16 (6.25%)
. No significant reduction

Correct Answer & Explanation

. Reduced to 1/4 (25%)

Explanation

According to the inverse square law of radiation physics, the intensity of radiation exposure is inversely proportional to the square of the distance from the source. Doubling the distance (from 1m to 2m) reduces the radiation exposure to one-fourth (1 / 2^2), or 25% of the original dose.

Question 14531

Topic: Biomechanics & Biomaterials
In ultra-high molecular weight polyethylene (UHMWPE) components utilized in total joint arthroplasty, which of the following mechanical terms describes the progressive, time-dependent permanent deformation of the polymer under a constant compressive load?
. Fatigue failure
. Abrasive wear
. Creep
. Stress relaxation
. Yield deformation

Correct Answer & Explanation

. Creep

Explanation

Creep (often referred to as cold flow in polymers) is the time-dependent, permanent plastic deformation of a material subjected to a constant static load below its yield strength. In joint replacements, this can alter the congruency of the articulation over time without actual material loss (unlike wear).

Question 14532

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with progressive bowing of his lower extremities. Labs reveal normal serum calcium, low serum phosphate, and elevated alkaline phosphatase. Parathyroid hormone levels are normal. Genetic testing reveals a mutation in the PHEX gene. What is the primary mechanism responsible for his condition?

. Decreased renal production of 1,25-dihydroxyvitamin D
. Impaired mineralization of bone osteoid due to lack of calcium
. Excessive renal phosphate excretion due to elevated FGF23
. Defective osteoclast ruffled border formation
. Mutation in type I collagen

Correct Answer & Explanation

. Excessive renal phosphate excretion due to elevated FGF23

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX mutation, leading to elevated FGF23. FGF23 decreases renal phosphate reabsorption (causing phosphaturia) and downregulates 1-alpha-hydroxylase (decreasing the active form of Vitamin D).

Question 14533

Topic: Biology, Genetics & Bone Healing

An infant presents with multiple fractures, cranial nerve palsies, and hepatosplenomegaly. Radiographs show a generalized 'bone-within-bone' appearance and loss of medullary canals. The underlying pathogenesis is most likely due to a deficiency in which of the following?

. Cathepsin K
. Carbonic anhydrase II
. Fibroblast growth factor receptor 3
. Core binding factor alpha-1 (CBFA1)
. Type I collagen

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Autosomal recessive malignant osteopetrosis is commonly caused by a mutation in the TCIRG1 gene or carbonic anhydrase II, leading to failure of the osteoclast to acidify the Howship lacuna. This results in impaired bone resorption and dense but extremely brittle bones.

Question 14534

Topic: 1. General Principles & Basic Science

A 60-year-old woman undergoes total knee arthroplasty. During the procedure, chalky white deposits are noted in the menisci and articular cartilage. Synovial fluid analysis reveals weakly positively birefringent rhomboid-shaped crystals under polarized light. These crystals are composed of:

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Basic calcium phosphate
. Hydroxyapatite
. Cholesterol

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate

Explanation

The description of weakly positively birefringent rhomboid-shaped crystals is classic for pseudogout, which is caused by the deposition of calcium pyrophosphate dihydrate (CPPD) crystals. Monosodium urate crystals (gout) are needle-shaped and strongly negatively birefringent.

Question 14535

Topic: 1. General Principles & Basic Science
A 9-year-old boy with recurrent hemarthroses of the knee is diagnosed with Hemophilia B. Which of the following correctly describes the inheritance pattern and the specific coagulation factor deficiency?
. Autosomal recessive, Factor VIII
. X-linked recessive, Factor VIII
. Autosomal dominant, Factor IX
. X-linked recessive, Factor IX
. Autosomal recessive, von Willebrand factor

Correct Answer & Explanation

. X-linked recessive, Factor IX

Explanation

Hemophilia B (Christmas disease) is an X-linked recessive disorder caused by a deficiency in Factor IX. Hemophilia A is a deficiency in Factor VIII. Both primarily affect males due to X-linked inheritance.

Question 14536

Topic: Biology, Genetics & Bone Healing

A 68-year-old woman is prescribed teriparatide for severe osteoporosis. How does this medication primarily exert its effect on bone metabolism?

. Inhibiting the farnesyl pyrophosphate synthase pathway in osteoclasts
. Binding to RANKL and preventing its interaction with RANK
. Acting as a selective estrogen receptor modulator
. Stimulating osteoblast activity via intermittent parathyroid hormone receptor activation
. Inhibiting cathepsin K activity

Correct Answer & Explanation

. Stimulating osteoblast activity via intermittent parathyroid hormone receptor activation

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently (e.g., daily subcutaneous injection), it paradoxically stimulates osteoblast activity more than osteoclast activity, resulting in a net anabolic effect on bone.

Question 14537

Topic: Infection, Pharmacology & VTE

A 12-year-old boy from Connecticut presents with an acute, massive, painless effusion of his right knee. He denies trauma. He had a brief febrile illness with an erythematous rash a few months ago. Joint aspiration yields 40,000 WBCs/mcL (mostly neutrophils). What is the most appropriate initial diagnostic test?

. Gram stain and bacterial culture of synovial fluid
. Crystal analysis under polarized light
. Serum Lyme enzyme-linked immunosorbent assay (ELISA)
. Serum Western blot for Borrelia burgdorferi
. Polymerase chain reaction (PCR) of synovial fluid for Neisseria gonorrhoeae

Correct Answer & Explanation

. Serum Lyme enzyme-linked immunosorbent assay (ELISA)

Explanation

Lyme arthritis commonly presents as a monoarticular large joint effusion (classically the knee) with inflammatory fluid, often with minimal pain compared to septic arthritis. The standard two-tiered diagnostic approach begins with a screening serum ELISA. If positive or equivocal, it is followed by a confirmatory Western blot.

Question 14538

Topic: Biology, Genetics & Bone Healing

A patient presents with hypermobility of the shoulders, allowing them to touch in the midline anteriorly. Skull radiographs show delayed fontanelle closure and wormian bones. Which transcription factor is primarily mutated in this syndrome?

. SOX9
. RUNX2 (CBFA1)
. GLI3
. COMP
. FGFR3

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is an autosomal dominant condition characterized by hypoplastic or absent clavicles, delayed skull ossification, and dental abnormalities. It is caused by a mutation in RUNX2 (also known as CBFA1), a master transcription factor essential for osteoblast differentiation.

Question 14539

Topic: 1. General Principles & Basic Science
Intravenous tranexamic acid (TXA) is routinely used to reduce blood loss during total joint arthroplasty. What is the specific mechanism of action of TXA?
. It inhibits the conversion of prothrombin to thrombin
. It blocks the binding of fibrinogen to the glycoprotein IIb/IIIa receptor
. It is a synthetic analog of lysine that competitively inhibits the activation of plasminogen to plasmin
. It enhances the activity of antithrombin III
. It stimulates the release of von Willebrand factor from endothelial cells

Correct Answer & Explanation

. It is a synthetic analog of lysine that competitively inhibits the activation of plasminogen to plasmin

Explanation

Tranexamic acid is an antifibrinolytic agent. It works by reversibly binding to the lysine-binding sites on plasminogen, which competitively inhibits its activation into plasmin, thereby preventing the degradation of fibrin clots.

Question 14540

Topic: Biology, Genetics & Bone Healing

A patient with osteoporosis and severe renal impairment is started on denosumab instead of a bisphosphonate. Denosumab increases bone mineral density by directly targeting and binding to which of the following?

. Farnesyl pyrophosphate synthase
. Osteoprotegerin (OPG)
. RANK receptor on osteoclasts
. RANK ligand (RANKL)
. Cathepsin K

Correct Answer & Explanation

. RANK ligand (RANKL)

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By neutralizing RANKL, it prevents it from interacting with the RANK receptor on osteoclasts, thereby inhibiting osteoclast formation, function, and survival.

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