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1. General Principles & Basic Science MCQs

Practice Set 699 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 13961

Topic: Infection, Pharmacology & VTE

A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the specific mechanism of action of this medication?

. Direct thrombin inhibitor
. Vitamin K antagonist
. Direct Factor Xa inhibitor
. Low molecular weight heparin
. Antiplatelet agent via COX-1 inhibition

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban is an oral anticoagulant that works by directly inhibiting Factor Xa, interrupting both the intrinsic and extrinsic pathways of the blood coagulation cascade. It does not require routine coagulation monitoring.

Question 13962

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a destructive, lytic lesion in the distal femur extending to the subchondral bone. Biopsy confirms a Giant Cell Tumor of bone. If medical therapy is considered, what is the primary mechanism of action of the most commonly utilized pharmacological agent?

. Inhibition of vascular endothelial growth factor (VEGF)
. Direct apoptosis of multinucleated giant cells
. Inhibition of RANK ligand (RANKL)
. Modulation of estrogen receptors
. Cross-linking of DNA strands

Correct Answer & Explanation

. Inhibition of RANK ligand (RANKL)

Explanation

Denosumab is a monoclonal antibody frequently used in the treatment of Giant Cell Tumor of bone. It works by binding to and inhibiting RANKL, which prevents the maturation and activation of the osteoclast-like multinucleated giant cells.

Question 13963

Topic: Biology, Genetics & Bone Healing

A 70-year-old male complains of increasing hat size and dull, deep bone pain in his pelvis and thighs. Laboratory tests show normal serum calcium, normal serum phosphorus, and significantly elevated alkaline phosphatase. Radiographs of the skull show a characteristic "cotton wool" appearance. Which cell type is primarily responsible for the initial phase of this disease process?

. Osteoblast
. Osteoclast
. Osteocyte
. Chondrocyte
. Macrophage

Correct Answer & Explanation

. Osteoclast

Explanation

The patient's presentation and labs are diagnostic of Paget's disease of bone. The disease process is characterized by an initial phase of excessive osteoclastic bone resorption, followed by chaotic osteoblastic bone formation resulting in structurally weak woven bone.

Question 13964

Topic: Biology, Genetics & Bone Healing

During the remodeling phase of secondary fracture healing, woven bone is gradually replaced by highly organized lamellar bone. According to Wolff's Law, this physiological process is primarily driven and directed by which of the following mechanisms?

. Hormonal regulation via parathyroid hormone
. Systemic inflammatory cytokines (IL-1, IL-6)
. Mechanical stress and piezoelectric forces
. Angiogenesis factors like VEGF
. Transforming growth factor-beta (TGF-b) concentration gradient

Correct Answer & Explanation

. Mechanical stress and piezoelectric forces

Explanation

Wolff's law dictates that bone models and remodels in response to the mechanical stresses placed upon it. Mechanical loading generates piezoelectric forces that stimulate osteoclasts and osteoblasts to align trabeculae along lines of stress.

Question 13965

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage has the highest concentration of proteoglycans and the lowest concentration of water?

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

Correct Answer & Explanation

. Deep zone

Explanation

The deep zone of articular cartilage has the highest proteoglycan content and the lowest water content. This composition provides maximal resistance to compressive loads. The collagen fibers in this zone are oriented perpendicularly to the articular surface.

Question 13966

Topic: Infection, Pharmacology & VTE

In prosthetic joint infections, bacterial biofilms confer significant resistance to systemic antibiotics. Which phase of biofilm formation is characterized by the production of extracellular polymeric substance (EPS) and irreversible attachment?

. Planktonic phase
. Reversible attachment
. Maturation phase
. Dispersion phase
. Quorum sensing initiation

Correct Answer & Explanation

. Maturation phase

Explanation

Following initial reversible attachment, bacteria undergo irreversible attachment and begin the maturation phase, which is characterized by the robust production of the extracellular polymeric substance (EPS) matrix. This matrix shields the bacteria from host defenses and antimicrobials.

Question 13967

Topic: 1. General Principles & Basic Science

When inserting a cortical screw, which of the following structural modifications will result in the greatest increase in the screw's pullout strength?

. Increasing the inner (root) diameter
. Increasing the outer (thread) diameter
. Decreasing the thread pitch
. Increasing the length of the screw by 2 mm
. Changing from a stainless steel to a titanium screw

Correct Answer & Explanation

. Increasing the outer (thread) diameter

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter and the length of thread engagement, and inversely proportional to thread pitch. Increasing the outer diameter has the most profound and direct effect on increasing pullout strength.

Question 13968

Topic: 1. General Principles & Basic Science

Following a peripheral nerve transection, Wallerian degeneration occurs distal to the injury site. Which cell type is primarily responsible for clearing myelin debris during the initial stages of this process in the peripheral nervous system?

. Astrocytes
. Microglia
. Schwann cells
. Oligodendrocytes
. Neutrophils

Correct Answer & Explanation

. Schwann cells

Explanation

In the peripheral nervous system, Schwann cells (and later recruited macrophages) are the primary cells responsible for phagocytosing myelin debris, clearing the path for regenerating axons to grow distally.

Question 13969

Topic: Biology, Genetics & Bone Healing
During secondary fracture healing, the soft callus transitions to a hard callus. Which type of collagen is predominantly synthesized during the cartilaginous phase of soft callus formation?
. Type I
. Type II
. Type III
. Type IX
. Type X

Correct Answer & Explanation

. Type II

Explanation

During secondary (indirect) fracture healing, the soft callus primarily consists of cartilage, which is rich in Type II collagen produced by proliferating chondrocytes. As the cartilage becomes hypertrophic and calcifies, Type X collagen is produced, before finally being replaced by Type I collagen in the hard bony callus.

Question 13970

Topic: Infection, Pharmacology & VTE
A 68-year-old woman is scheduled for a total hip arthroplasty. She is currently taking rivaroxaban for non-valvular atrial fibrillation. What is the specific mechanism of action of this medication?
. Direct thrombin inhibitor
. Vitamin K epoxide reductase inhibitor
. Direct factor Xa inhibitor
. Anti-thrombin III activator
. Glycoprotein IIb/IIIa inhibitor

Correct Answer & Explanation

. Direct factor Xa inhibitor

Explanation

Rivaroxaban and apixaban are direct oral anticoagulants (DOACs) that specifically inhibit Factor Xa. Dabigatran is a direct thrombin inhibitor, while warfarin inhibits Vitamin K epoxide reductase.

Question 13971

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with bowed legs, a waddling gait, and prominent costochondral junctions. Laboratory results show low serum calcium, low serum phosphate, and elevated parathyroid hormone (PTH). What is the most likely primary diagnosis?

. Hypophosphatemic rickets
. Vitamin D-dependent rickets
. Nutritional rickets
. Renal osteodystrophy
. Osteogenesis imperfecta

Correct Answer & Explanation

. Nutritional rickets

Explanation

Nutritional rickets is caused by Vitamin D deficiency, leading to decreased intestinal calcium and phosphate absorption. The resulting hypocalcemia triggers secondary hyperparathyroidism (elevated PTH), which normalizes calcium slightly at the expense of severe urinary phosphate wasting, leading to the classic low Ca, low P, high PTH laboratory profile.

Question 13972

Topic: Physiology & Rehabilitation

Which of the following physiological or biochemical characteristics is true regarding Type I (slow-twitch) skeletal muscle fibers compared to Type II fibers?

. Higher glycogen content
. Lower mitochondrial density
. Rely primarily on anaerobic glycolysis
. Higher concentration of myoglobin
. Faster rate of fatigue

Correct Answer & Explanation

. Higher concentration of myoglobin

Explanation

Type I muscle fibers are 'slow oxidative' fibers designed for endurance. They are highly fatigue-resistant and rely on aerobic metabolism. Consequently, they possess a high density of mitochondria and a high concentration of myoglobin (giving them a red appearance) to facilitate oxygen transport.

Question 13973

Topic: 1. General Principles & Basic Science

A 9-year-old boy with Hemophilia A presents with recurrent hemarthroses of the right knee. Chronic hemophilic arthropathy causes joint destruction primarily through the direct toxic effects of which substance on articular cartilage?

. Hemosiderin
. Uric acid
. Calcium pyrophosphate
. Homogentisic acid
. Amyloid

Correct Answer & Explanation

. Hemosiderin

Explanation

In hemophilic arthropathy, recurrent intra-articular bleeding leads to synovial hypertrophy and massive deposition of iron in the form of hemosiderin. Hemosiderin is directly toxic to chondrocytes, triggering oxidative stress and inflammatory cascades (like IL-1 and TNF-alpha) that ultimately destroy the articular cartilage.

Question 13974

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is widely used in orthopedic surgery to augment spinal fusion masses. What is the primary biologic property of DBM that facilitates bone healing?

. Osteogenesis
. Osteoconduction
. Osteoinduction
. Angiogenesis
. Mechanical structural support

Correct Answer & Explanation

. Osteoinduction

Explanation

Demineralized bone matrix (DBM) is produced by acid extraction of allograft bone, removing the mineralized component but preserving collagen and growth factors, including bone morphogenetic proteins (BMPs). Its primary utility is osteoinduction—the ability to stimulate undifferentiated mesenchymal stem cells to differentiate into osteoblasts.

Question 13975

Topic: Biomechanics & Biomaterials

Which of the following biomechanical terms describes the time-dependent increase in strain of a material under a constant applied load?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent deformation (increase in strain) under a constant load. Stress relaxation is the time-dependent decrease in stress under a constant strain. Hysteresis refers to the energy lost (as heat) during the loading and unloading cycles of a viscoelastic material.

Question 13976

Topic: Biology, Genetics & Bone Healing

A 4-year-old child presents with gingival bleeding, petechiae, and metaphyseal radiolucent bands on radiographs. The underlying condition is caused by a deficiency that impairs which of the following steps in collagen synthesis?

. Cleavage of procollagen C- and N-terminals
. Glycosylation of hydroxylysine residues
. Hydroxylation of proline and lysine residues
. Formation of cross-links by lysyl oxidase
. Transcription of alpha-1 collagen genes

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

The patient has scurvy (Vitamin C deficiency). Vitamin C is a necessary cofactor for prolyl hydroxylase and lysyl hydroxylase, the enzymes responsible for the hydroxylation of proline and lysine residues in procollagen. Without this step, the collagen triple helix cannot form properly, leading to fragile connective tissue.

Question 13977

Topic: 1. General Principles & Basic Science
Which of the following laboratory values is a specific component of the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score?
. Serum calcium
. Serum albumin
. Serum sodium
. Serum potassium
. Platelet count

Correct Answer & Explanation

. Serum sodium

Explanation

The LRINEC score utilizes CRP, total WBC count, hemoglobin, serum sodium, serum creatinine, and serum glucose to stratify the risk of necrotizing fasciitis. A serum sodium level < 135 mmol/L yields 2 points in this scoring system. Albumin, calcium, potassium, and platelet counts are not part of the score.

Question 13978

Topic: 1. General Principles & Basic Science

In articular cartilage, which zone 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 cartilage zone
. Subchondral bone plate

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the largest diameter collagen fibrils oriented perpendicular to the articular surface. It has the highest concentration of proteoglycans and the lowest water content. The superficial zone has the highest water content and collagen parallel to the joint surface.

Question 13979

Topic: Biology, Genetics & Bone Healing

A 30-year-old female is diagnosed with an unresectable giant cell tumor of the sacrum. She is started on denosumab therapy. What is the mechanism of action of this medication?

. Monoclonal antibody against RANK
. Monoclonal antibody against RANKL
. Inhibitor of farnesyl pyrophosphate synthase
. Recombinant human parathyroid hormone
. Selective estrogen receptor modulator

Correct Answer & Explanation

. Monoclonal antibody against RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand), preventing it from interacting with the RANK receptor on osteoclasts and their precursors. This inhibits osteoclast formation, function, and survival, which is highly effective in treating Giant Cell Tumor of bone.

Question 13980

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with bone pain and increasing hat size. Radiographs show cortical thickening and coarse trabeculae in the skull and pelvis. Laboratory testing reveals elevated alkaline phosphatase with normal calcium and phosphorus. Mutations in which of the following genes are most strongly associated with this condition?

. COL1A1
. FGFR3
. SQSTM1
. PHEX
. RUNX2

Correct Answer & Explanation

. SQSTM1

Explanation

The patient's presentation is classic for Paget's disease of bone. Up to 40-50% of familial cases and 5-10% of sporadic cases are associated with mutations in the SQSTM1 gene, which encodes the p62 protein. This mutation leads to increased osteoclastogenesis and hyperactive osteoclasts. COL1A1 is associated with osteogenesis imperfecta; FGFR3 with achondroplasia; PHEX with X-linked hypophosphatemic rickets; and RUNX2 with cleidocranial dysplasia.

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