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1. General Principles & Basic Science MCQs

Practice Set 704 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 14061

Topic: Biology, Genetics & Bone Healing

A patient with metastatic breast cancer to the bone is treated with denosumab. Which of the following best describes the molecular target of this monoclonal antibody?

. Receptor activator of nuclear factor kappa-B (RANK)
. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Sclerostin

Correct Answer & Explanation

. Receptor activator of nuclear factor kappa-B ligand (RANKL)

Explanation

Denosumab is a monoclonal antibody that specifically binds to RANKL, preventing it from binding to its receptor (RANK) on osteoclast precursors. This halts osteoclast differentiation and drastically reduces tumor-associated bone resorption.

Question 14062

Topic: Surgical Anatomy & Approaches

A patient sustains a midshaft humerus fracture resulting in a radial nerve palsy. According to Seddon's classification, which type of injury is characterized by axonal disruption with an intact endoneurial tube?

. Neurapraxia
. Axonotmesis
. Neurotmesis
. Sunderland Grade I
. Sunderland Grade V

Correct Answer & Explanation

. Axonotmesis

Explanation

Axonotmesis involves the loss of axonal continuity and subsequent Wallerian degeneration, but the surrounding connective tissue framework (endoneurium) remains intact. This structure guides spontaneous, albeit slow, axonal regeneration.

Question 14063

Topic: Biology, Genetics & Bone Healing

Which specific cellular defect is most commonly responsible for the dense, brittle bones seen in malignant infantile osteopetrosis?

. Deficiency of Type I collagen production
. Overactivity of the Wnt signaling pathway
. Defect in the carbonic anhydrase II enzyme
. Mutation in the FGFR3 gene
. Lack of matrix metalloproteinases

Correct Answer & Explanation

. Defect in the carbonic anhydrase II enzyme

Explanation

Osteopetrosis is caused by defective osteoclast function, preventing normal bone resorption. A common cause is a mutation in the carbonic anhydrase II gene, which prevents osteoclasts from generating the acidic environment needed to dissolve bone mineral.

Question 14064

Topic: Biomechanics & Biomaterials

Which characteristic is essential for an antibiotic to be effective and safe when mixed into polymethylmethacrylate (PMMA) bone cement for a joint spacer?

. High thermal lability
. Bacteriostatic rather than bactericidal mechanism
. Low water solubility to prevent rapid elution
. Availability in a liquid formulation
. Broad-spectrum coverage with high thermal stability

Correct Answer & Explanation

. Broad-spectrum coverage with high thermal stability

Explanation

Antibiotics used in PMMA must have high thermal stability to withstand the highly exothermic polymerization reaction of the cement. They must also be available as a powder and be water-soluble to allow for proper elution into the joint space.

Question 14065

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with bowing of the legs, frontal bossing, and widening of the wrists. Laboratory results show low serum phosphorus, normal calcium, and elevated alkaline phosphatase. Which condition is most likely?

. Nutritional rickets
. Achondroplasia
. X-linked hypophosphatemic rickets
. Osteogenesis imperfecta
. Renal osteodystrophy

Correct Answer & Explanation

. X-linked hypophosphatemic rickets

Explanation

X-linked hypophosphatemic rickets (PHEX mutation) leads to renal phosphate wasting, resulting in low phosphorus and normal calcium levels. This contrasts with nutritional rickets, where serum calcium is typically low or low-normal.

Question 14066

Topic: Biology, Genetics & Bone Healing

Which type of bone healing is primarily achieved when using absolute stability techniques, such as a lag screw and neutralization plate, on a simple transverse fracture?

. Endochondral ossification
. Intramembranous ossification
. Primary (Haversian) bone healing
. Secondary bone healing with callus formation
. Fibrous nonunion healing

Correct Answer & Explanation

. Primary (Haversian) bone healing

Explanation

Absolute stability eliminates micro-motion at the fracture site, bypassing callus formation. It allows cutting cones of osteoclasts to cross the fracture line directly, followed immediately by osteoblasts laying down new lamellar bone.

Question 14067

Topic: 1. General Principles & Basic Science
Which of the following represents the primary collagen type and the major proteoglycan found in the tensile region of a healthy human tendon?
. Type I collagen and Aggrecan
. Type II collagen and Decorin
. Type I collagen and Decorin
. Type III collagen and Aggrecan
. Type II collagen and Biglycan

Correct Answer & Explanation

. Type I collagen and Decorin

Explanation

Healthy tendons are predominantly composed of Type I collagen, which provides high tensile strength. Decorin is the most abundant proteoglycan in tendons and plays a crucial role in regulating collagen fibrillogenesis and fibril size.

Question 14068

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Protein-2 (BMP-2) signals primarily through which intracellular pathway to stimulate osteoblastic differentiation?

. Wnt/beta-catenin pathway
. Smad 1/5/8 pathway
. MAPK/ERK pathway
. RANK/RANKL pathway
. JAK/STAT pathway

Correct Answer & Explanation

. Smad 1/5/8 pathway

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, which then phosphorylate downstream intracellular Smad proteins (Smad 1, 5, and 8). These proteins translocate to the nucleus to upregulate osteogenic genes like Runx2.

Question 14069

Topic: Biomechanics & Biomaterials

A viscoelastic material subjected to a constant deformation will demonstrate a gradual decrease in the stress required to maintain that deformation. This mechanical phenomenon is known as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in stress over time when a material is held at a constant strain or deformation. In contrast, creep is the progressive deformation over time under a constant load.

Question 14070

Topic: 1. General Principles & Basic Science

A 10-year-old child presents with recurrent fractures, severe anemia, and hepatosplenomegaly. Radiographs reveal generalized uniform osteosclerosis with a "bone-in-bone" appearance. A genetic mutation affecting which of the following mechanisms is most likely responsible?

. Defective collagen type I synthesis
. Impaired mineralization of osteoid
. Inability of osteoclasts to acidify the resorption pit
. Overactivity of fibroblast growth factor receptor 3 (FGFR3)
. Deficiency of tissue nonspecific alkaline phosphatase

Correct Answer & Explanation

. Inability of osteoclasts to acidify the resorption pit

Explanation

This presentation is typical of osteopetrosis, characterized by defective osteoclastic bone resorption. The most common defect is in carbonic anhydrase II or the proton pump, which prevents the acidification necessary for hydroxyapatite dissolution.

Question 14071

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) initiate the osteoinductive signaling cascade by binding to serine/threonine kinase receptors on the cell surface. Which of the following intracellular proteins acts as the primary downstream messenger to translocate into the nucleus and regulate gene expression?

. JAK-STAT
. Beta-catenin
. SMAD
. c-Fos
. NF-kappaB

Correct Answer & Explanation

. SMAD

Explanation

BMPs bind to cell surface receptors that phosphorylate intracellular SMAD proteins (typically SMAD 1, 5, and 8). These form a complex with SMAD 4, which translocates to the nucleus to initiate osteogenic gene transcription.

Question 14072

Topic: Biology, Genetics & Bone Healing

An asymptomatic 65-year-old man has an incidentally discovered elevated alkaline phosphatase. Pelvic radiographs show coarse trabecular markings and cortical thickening of the right ilium. A mutation in which of the following genes is most commonly associated with this condition?

. COL1A1
. SQSTM1
. FGFR3
. COMP
. CBFA1 (RUNX2)

Correct Answer & Explanation

. SQSTM1

Explanation

Paget's disease of bone is associated with mutations in the SQSTM1 (p62) gene in familial cases. This leads to increased osteoclast activity and disorganized bone remodeling.

Question 14073

Topic: Biomechanics & Biomaterials

Which of the following scenarios describes galvanic corrosion in orthopedic implants?

. Micro-motion between the screw head and the plate hole
. Release of metal ions due to a localized drop in pH from infection
. Electrochemical breakdown when two dissimilar metals are in contact within an electrolytic environment
. Fatigue failure of a stainless steel plate after repetitive cyclical loading
. Formation of a passivation layer on the surface of a titanium rod

Correct Answer & Explanation

. Electrochemical breakdown when two dissimilar metals are in contact within an electrolytic environment

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are placed in direct physical contact within a conductive fluid. The less noble metal undergoes accelerated corrosion acting as the anode.

Question 14074

Topic: Biology, Genetics & Bone Healing

A 70-year-old female with severe osteoporosis is started on denosumab therapy. Which of the following best describes the specific mechanism of action of this medication?

. Inhibits farnesyl pyrophosphate synthase, inducing osteoclast apoptosis
. Binds directly to hydroxyapatite and resists osteoclastic dissolution
. Monoclonal antibody that binds to RANKL, preventing osteoclast activation
. Recombinant parathyroid hormone analog that stimulates osteoblast activity
. Selective estrogen receptor modulator that decreases bone resorption

Correct Answer & Explanation

. Monoclonal antibody that binds to RANKL, preventing osteoclast activation

Explanation

Denosumab is a human monoclonal antibody that binds to RANK Ligand (RANKL), preventing it from interacting with the RANK receptor on osteoclasts. This effectively inhibits osteoclast formation, function, and survival.

Question 14075

Topic: 1. General Principles & Basic Science
During the reparative phase of tendon healing following acute rupture, fibroblasts rapidly proliferate and synthesize an initial extracellular matrix. Which type of collagen dominates this early provisional matrix before it is remodeled?
. Type I
. Type II
. Type III
. Type IV
. Type X

Correct Answer & Explanation

. Type III

Explanation

During the early proliferative phase of tendon healing, the initial scar tissue is predominantly composed of Type III collagen. During the subsequent remodeling phase, this is gradually replaced by the stronger, more aligned Type I collagen.

Question 14076

Topic: 1. General Principles & Basic Science
In the pathogenesis of osteoarthritis, which specific enzyme is primarily responsible for the irreversible cleavage and degradation of Type II collagen in the articular cartilage matrix?
. Matrix metalloproteinase-1 (MMP-1)
. Matrix metalloproteinase-3 (MMP-3)
. Matrix metalloproteinase-13 (MMP-13)
. Cathepsin K
. Aggrecanase (ADAMTS-4)

Correct Answer & Explanation

. Matrix metalloproteinase-13 (MMP-13)

Explanation

MMP-13 (collagenase-3) is the primary enzyme responsible for the degradation of Type II collagen in osteoarthritis. While ADAMTS enzymes degrade the proteoglycan aggrecan, MMP-13 directly targets the core collagen framework.

Question 14077

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is routinely used to reduce blood loss in orthopedic surgery. What is the precise molecular target of this medication?
. Inhibits cyclooxygenase-1 (COX-1)
. Competitively binds to the lysine receptor sites on plasminogen
. Directly inhibits Factor Xa
. Blocks the cross-linking of fibrin polymers by Factor XIII
. Antagonizes vitamin K-dependent clotting factors

Correct Answer & Explanation

. Competitively binds to the lysine receptor sites on plasminogen

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It works by competitively binding to the lysine-binding sites on plasminogen, preventing its conversion to plasmin and thereby inhibiting fibrinolysis.

Question 14078

Topic: Biology, Genetics & Bone Healing

A 5-year-old child presents with bowing of the lower extremities, a waddling gait, and radiographic evidence of widened growth plates. Laboratory results show low serum phosphorus, normal calcium, normal parathyroid hormone, and elevated alkaline phosphatase. Which condition is most likely?

. Nutritional rickets
. Hypophosphatasia
. X-linked hypophosphatemic rickets
. Renal osteodystrophy
. Osteogenesis imperfecta

Correct Answer & Explanation

. X-linked hypophosphatemic rickets

Explanation

X-linked hypophosphatemic rickets is characterized by renal phosphate wasting due to a mutation in the PHEX gene. This leads to normal calcium and PTH levels, but low phosphorus and characteristic rachitic bone changes.

Question 14079

Topic: Biology, Genetics & Bone Healing

A patient with a history of severe gastric bypass presents with fatigue, generalized bone pain, and proximal muscle weakness. Radiographs reveal bilateral pseudo-fractures (Looser zones) in the femoral neck. What is the underlying pathophysiology?

. Inadequate mineralization of newly formed osteoid
. Defective cross-linking of collagen fibers
. Uncoupled osteoclast resorption causing rapid bone loss
. Primary hypersecretion of parathyroid hormone
. Accumulation of unmineralized cartilage at the physis

Correct Answer & Explanation

. Inadequate mineralization of newly formed osteoid

Explanation

The patient has osteomalacia resulting from Vitamin D deficiency secondary to malabsorption. Osteomalacia is characterized by the accumulation of unmineralized osteoid, which appears radiographically as Looser zones.

Question 14080

Topic: Biology, Genetics & Bone Healing

During the process of secondary fracture healing, enchondral ossification relies on a cartilaginous callus intermediate. Which transcription factor is the master regulator responsible for driving mesenchymal cells to differentiate into chondrocytes?

. Runx2 (Cbfa1)
. Sox9
. Osterix
. HIF-1 alpha
. NFATc1

Correct Answer & Explanation

. Sox9

Explanation

Sox9 is the master transcription factor for chondrogenesis, directing mesenchymal stem cells to become chondrocytes. Runx2 and Osterix are the key regulators for osteoblast differentiation.

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