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1. General Principles & Basic Science MCQs

Practice Set 682 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 13621

Topic: Biology, Genetics & Bone Healing

A 4-year-old child presents with gingival bleeding, petechiae, and bone pain. Radiographs reveal generalized osteopenia and a dense zone of provisional calcification (white line of Frankel). The child is diagnosed with scurvy. The underlying pathophysiologic defect is a failure of:

. Mineralization of osteoid by osteoblasts
. Hydroxylation of proline and lysine residues
. Cleavage of procollagen to tropocollagen
. Cross-linking of tropocollagen molecules by lysyl oxidase
. Transcription of the COL1A1 gene

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

Scurvy is caused by Vitamin C (ascorbic acid) deficiency. Vitamin C is an essential cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. Failure to hydroxylate proline and lysine residues prevents the proper formation of the procollagen triple helix, resulting in defective Type I collagen.

Question 13622

Topic: 1. General Principles & Basic Science

In patients with X-linked hypophosphatemic rickets (XLH), a mutation in the PHEX gene leads to elevated levels of Fibroblast Growth Factor 23 (FGF23). What is the primary renal effect of elevated FGF23?

. Increases calcium reabsorption in the distal tubule
. Decreases 1-alpha-hydroxylase activity and downregulates sodium-phosphate cotransporters
. Increases parathyroid hormone (PTH) receptor sensitivity
. Decreases 24-hydroxylase activity
. Increases intestinal absorption of phosphate

Correct Answer & Explanation

. Decreases 1-alpha-hydroxylase activity and downregulates sodium-phosphate cotransporters

Explanation

FGF23 is a phosphatonin that acts on the kidney to induce phosphate wasting by downregulating sodium-phosphate cotransporters (NaPi-IIa and NaPi-IIc) in the proximal tubule. It also decreases the activity of 1-alpha-hydroxylase, thereby reducing the production of active 1,25-dihydroxyvitamin D. This leads to hypophosphatemia and rickets.

Question 13623

Topic: Biology, Genetics & Bone Healing

Denosumab is used in the treatment of osteoporosis and giant cell tumor of bone. Which of the following best describes its mechanism of action?

. It binds to the ruffled border of osteoclasts, disrupting the proton pump
. It competitively inhibits the binding of parathyroid hormone to its receptor
. It acts as a monoclonal antibody against RANKL, preventing RANK activation
. It stimulates the Wnt signaling pathway via sclerostin inhibition
. It incorporates into the bone matrix and induces osteoclast apoptosis upon ingestion

Correct Answer & Explanation

. It acts as a monoclonal antibody against RANKL, preventing RANK activation

Explanation

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

Question 13624

Topic: 1. General Principles & Basic Science

Following primary surgical repair of a lacerated flexor tendon in Zone II, the biomechanical strength of the repair undergoes predictable changes over time. At which time point post-repair is the tendon repair typically at its weakest?

. Immediately post-operation
. Days 1 to 3
. Days 5 to 10
. Days 14 to 21
. Days 28 to 35

Correct Answer & Explanation

. Days 5 to 10

Explanation

Tendon healing proceeds through inflammatory, proliferative, and remodeling phases. During the late inflammatory and early proliferative phase (typically days 5 to 10), collagen degradation outpaces collagen synthesis. Consequently, the holding power of the suture in the softened tendon ends decreases, making the repair weakest at this time.

Question 13625

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into distinct structural zones. Which of the following characteristics accurately describes the superficial (tangential) zone of articular cartilage?

. Highest concentration of proteoglycans and lowest water content
. Chondrocytes are arranged in vertical columns
. Collagen fibers are oriented perpendicular to the joint surface
. Highest water content and collagen fibers oriented parallel to the joint surface
. Separated from the deep zone by the tidemark

Correct Answer & Explanation

. Highest water content and collagen fibers oriented parallel to the joint surface

Explanation

The superficial (tangential) zone of articular cartilage comprises 10-20% of the cartilage thickness. It contains the highest water content, the lowest proteoglycan content, and densely packed collagen fibers that are oriented parallel to the joint surface. This zone is primarily responsible for resisting shear stresses. The tidemark separates the deep zone from the calcified cartilage zone.

Question 13626

Topic: 1. General Principles & Basic Science

A 65-year-old male undergoes arthrocentesis for an acutely swollen knee. Synovial fluid analysis reveals weakly positively birefringent rhomboid-shaped crystals. Which of the following conditions is most closely associated with these findings?

. Gout
. Calcium pyrophosphate deposition disease (Pseudogout)
. Septic arthritis
. Rheumatoid arthritis
. Hydroxyapatite arthropathy

Correct Answer & Explanation

. Calcium pyrophosphate deposition disease (Pseudogout)

Explanation

The finding of weakly positively birefringent rhomboid-shaped crystals under polarized light microscopy is diagnostic of Calcium Pyrophosphate Deposition (CPPD) disease, or pseudogout. Gout is characterized by needle-shaped, negatively birefringent monosodium urate crystals.

Question 13627

Topic: Biomechanics & Biomaterials

When a titanium alloy component and a 316L stainless steel component are placed in direct physical contact within the corrosive physiological environment of the human body, galvanic corrosion may occur. Which of the following statements is correct regarding this couple?

. Titanium becomes the anode and undergoes accelerated corrosion.
. Stainless steel becomes the anode and undergoes accelerated corrosion.
. Both metals corrode equally due to their identical galvanic potentials.
. Titanium acts as the cathode and undergoes crevice corrosion.
. Galvanic corrosion is impossible between these two metals in vivo.

Correct Answer & Explanation

. Stainless steel becomes the anode and undergoes accelerated corrosion.

Explanation

In a galvanic couple, the more noble metal acts as the cathode and the less noble metal acts as the anode. Titanium is more noble than 316L stainless steel. Therefore, when mixed, the stainless steel becomes the anode and will undergo accelerated galvanic corrosion, while the titanium component (cathode) is protected.

Question 13628

Topic: Biology, Genetics & Bone Healing

When a massive cortical bone allograft is utilized for reconstruction, it undergoes incorporation via a process called creeping substitution. Which of the following best describes the initial cellular event in the incorporation of a cortical graft?

. Appositional new bone formation directly on the graft surface by osteoblasts
. Rapid vascular ingrowth facilitated by existing allograft vessels
. Osteoclastic resorption leading the cutting cone
. Differentiation of allograft mesenchymal stem cells into osteocytes
. Immediate transformation into woven bone via endochondral ossification

Correct Answer & Explanation

. Osteoclastic resorption leading the cutting cone

Explanation

Cortical bone grafts incorporate via creeping substitution, which begins with osteoclastic resorption. Osteoclasts bore out 'cutting cones' into the Haversian systems of the necrotic graft bone. This is followed closely by osteoblasts laying down new bone. Conversely, cancellous bone grafts initially undergo appositional new bone formation on the trabecular surfaces before significant resorption occurs.

Question 13629

Topic: Biology, Genetics & Bone Healing

Osteopetrosis is a rare genetic disorder characterized by dense, brittle bones due to impaired osteoclast function. A common mutation responsible for the autosomal recessive infantile form affects the enzyme Carbonic Anhydrase II. What is the normal function of this enzyme in the osteoclast?

. It synthesizes Cathepsin K for matrix degradation
. It generates protons (H+) to acidify the clear zone at the ruffled border
. It acts as a receptor for RANKL on the osteoclast membrane
. It facilitates the apoptosis of osteoclasts to limit bone resorption
. It produces tartrate-resistant acid phosphatase (TRAP)

Correct Answer & Explanation

. It generates protons (H+) to acidify the clear zone at the ruffled border

Explanation

In the osteoclast, Carbonic Anhydrase II catalyzes the conversion of CO2 and H2O into carbonic acid, which dissociates into protons (H+) and bicarbonate. The protons are pumped across the ruffled border via vacuolar H+-ATPases to acidify the resorption pit (Howship's lacuna), which dissolves bone mineral. Deficient CA II prevents this acidification, leading to non-functional osteoclasts and osteopetrosis.

Question 13630

Topic: 1. General Principles & Basic Science

A new diagnostic physical examination test is developed to screen for anterior cruciate ligament (ACL) tears. A study determines that the test has a Sensitivity of 98% and a Specificity of 40%. Based on these properties, which of the following statements is most accurate?

. A positive test strongly confirms the presence of an ACL tear.
. A negative test is highly reliable for ruling out an ACL tear.
. The test has a high Positive Predictive Value in all populations.
. The test frequently produces false negatives.
. The test should only be used as a confirmatory test rather than a screening tool.

Correct Answer & Explanation

. A negative test is highly reliable for ruling out an ACL tear.

Explanation

A test with high sensitivity (98%) accurately identifies those with the disease. Therefore, if the test is negative, it is highly likely the patient does not have the disease (SnNout: highly Sensitive test, when Negative, rules OUT the disease). The low specificity means there will be many false positives; thus, a positive result does not reliably confirm the disease.

Question 13631

Topic: Biology, Genetics & Bone Healing

Bone Morphogenetic Proteins (BMPs) are members of the TGF-beta superfamily and are potently osteoinductive. Upon binding to their transmembrane cell-surface receptors, which intracellular signaling molecules are directly phosphorylated to translocate to the nucleus and initiate transcription of osteogenic genes?

. JAK and STAT
. Beta-catenin and TCF/LEF
. Smad 1, 5, and 8
. cAMP and PKA
. Ras and MAP kinase

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface. This binding phosphorylates intracellular receptor-regulated Smads (R-Smads), specifically Smad 1, 5, and 8. These phosphorylated R-Smads then form a complex with the common-partner Smad (Co-Smad 4) and translocate into the nucleus to regulate the transcription of target osteogenic genes.

Question 13632

Topic: 1. General Principles & Basic Science

Following a traumatic transection of a peripheral nerve, the distal nerve stump undergoes Wallerian degeneration. Which cell type is primarily responsible for the rapid initial clearance of myelin debris in the peripheral nervous system, facilitating subsequent axonal regeneration?

. Oligodendrocytes
. Astrocytes
. Microglia
. Schwann cells and macrophages
. Fibroblasts

Correct Answer & Explanation

. Schwann cells and macrophages

Explanation

In the peripheral nervous system, Wallerian degeneration involves the breakdown of the axon and myelin sheath distal to the injury. Schwann cells initially degrade their own myelin via autophagy and recruit hematogenous macrophages, which quickly phagocytose and clear the myelin debris. This efficient clearance creates a favorable environment for axonal regeneration, unlike in the CNS where myelin clearance by microglia is sluggish and inhibitory.

Question 13633

Topic: Biology, Genetics & Bone Healing

Fibrous dysplasia is a benign developmental anomaly of bone characterized by the replacement of normal cancellous bone with immature fibrous tissue and poorly formed woven bone ('Chinese character' trabeculae). The somatic mosaic mutation responsible for this condition occurs in the GNAS1 gene. What is the physiological consequence of this mutation?

. Inactivation of the Wnt/beta-catenin pathway
. Constitutive activation of the Gs-alpha protein, leading to increased intracellular cAMP
. Inhibition of the RANKL-OPG axis, preventing osteoclast formation
. Defect in the mineralization of newly formed osteoid
. Overproduction of basic Fibroblast Growth Factor (bFGF)

Correct Answer & Explanation

. Constitutive activation of the Gs-alpha protein, leading to increased intracellular cAMP

Explanation

Fibrous dysplasia and McCune-Albright syndrome are caused by an activating missense mutation in the GNAS1 gene. This gene encodes the alpha subunit of the stimulatory G protein (Gs). The mutation causes constitutive activation of adenylate cyclase, leading to inappropriately high intracellular levels of cyclic AMP (cAMP). This excessive cAMP signaling drives the abnormal proliferation and differentiation of skeletal progenitor cells.

Question 13634

Topic: 1. General Principles & Basic Science

In the context of fracture healing, Stephan Perren's 'strain theory' defines the mechanical environment required for different types of bone healing. According to this theory, mechanical strain is defined as:

. The axial force applied across the fracture gap
. The change in fracture gap length divided by the original gap length
. The total absolute displacement of the bone ends in millimeters
. The inherent modulus of elasticity of the fixation construct
. The micro-motion measured in Newtons per square meter

Correct Answer & Explanation

. The change in fracture gap length divided by the original gap length

Explanation

According to Perren's strain theory, 'strain' is defined as the relative deformation of the tissue in the fracture gap, mathematically expressed as the change in gap length divided by the original gap length (Delta L / L). Primary bone healing requires absolute stability (strain < 2%), allowing cutting cones to cross the fracture. Secondary bone healing (callus) occurs with relative stability (strain 2-10%). Granulation tissue can tolerate up to 100% strain.

Question 13635

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which of the following accurately describes the orientation and predominant type of collagen fibers in the superficial (tangential) zone?

. Type I collagen, oriented perpendicular to the joint surface
. Type I collagen, oriented parallel to the joint surface
. Type II collagen, oriented perpendicular to the joint surface
. Type II collagen, oriented parallel to the joint surface
. Type II collagen, randomly oriented

Correct Answer & Explanation

. Type I collagen, oriented parallel to the joint surface

Explanation

The superficial zone of articular cartilage is primarily composed of Type II collagen. These fibers are tightly packed and oriented parallel to the joint surface to maximally resist physiological shear forces.

Question 13636

Topic: Biology, Genetics & Bone Healing
During the process of secondary fracture healing, what is the primary collagen type synthesized by chondrocytes during the soft callus phase?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IX collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

During the soft callus phase of endochondral ossification, proliferating chondrocytes predominantly produce Type II collagen to form a cartilaginous template. As the matrix calcifies later, hypertrophic chondrocytes express Type X collagen before it is replaced by Type I collagen.

Question 13637

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage is characterized by the highest concentration of proteoglycans, lowest concentration of water, and collagen fibrils aligned perpendicular to the articular surface?

. Superficial zone
. Transitional (middle) zone
. Deep zone
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Deep zone

Explanation

The deep zone of articular cartilage provides the greatest resistance to compressive loads due to its high proteoglycan content and perpendicular collagen fibrils. Water content is highest in the superficial zone and lowest in the deep zone.

Question 13638

Topic: 1. General Principles & Basic Science

Following a Zone II flexor digitorum profundus (FDP) repair, a patient starts early active mobilization. At what postoperative time point is the repaired tendon characteristically at its weakest?

. 1-3 days
. 7-10 days
. 21-28 days
. 6 weeks
. 12 weeks

Correct Answer & Explanation

. 7-10 days

Explanation

Tendons undergo an inflammatory phase followed by a fibroblastic phase. Due to early collagen degradation occurring before sufficient new collagen is synthesized, the repaired flexor tendon is weakest between days 7 and 10.

Question 13639

Topic: Biology, Genetics & Bone Healing

A 45-year-old male undergoes open reduction and internal fixation of a transverse radial shaft fracture using a dynamic compression plate, achieving absolute stability. Which of the following best describes the primary mode of bone healing expected in this scenario?

. Endochondral ossification with callus formation
. Intramembranous ossification with primary bone healing
. Cartilage intermediate replacement
. Fibrous tissue calcification
. Secondary bone healing driven by micromotion

Correct Answer & Explanation

. Intramembranous ossification with primary bone healing

Explanation

Rigid internal fixation with absolute stability (e.g., dynamic compression plating) eliminates micromotion at the fracture site. This leads to primary bone healing via cutting cones and direct Haversian remodeling without the formation of an intermediate fracture callus.

Question 13640

Topic: 1. General Principles & Basic Science
A 55-year-old diabetic male presents with an erythematous, extremely painful lower leg. There is crepitus on palpation and dishwater-like fluid draining from a small blister. Which of the following laboratory findings is a key component of the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score used to evaluate this condition?
. Elevated serum calcium
. Decreased serum sodium
. Elevated serum albumin
. Decreased C-reactive protein
. Elevated serum potassium

Correct Answer & Explanation

. Decreased serum sodium

Explanation

The LRINEC score incorporates CRP, total white cell count, hemoglobin, serum sodium, serum creatinine, and blood glucose. Hyponatremia (decreased serum sodium < 135 mmol/L) is a critical marker indicating systemic toxicity and third-spacing in necrotizing fasciitis.

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