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1. General Principles & Basic Science MCQs

Practice Set 536 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 10701

Topic: Biology, Genetics & Bone Healing

A 32-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion extending into the subchondral bone of the distal femur. A biopsy confirms a giant cell tumor of bone. If medical therapy is indicated to shrink the tumor prior to intralesional curettage, which of the following mechanisms best describes the action of the most appropriate drug?

. Inhibition of the mTOR pathway
. Direct inhibition of osteoclast proton pumps
. Binding to the RANK ligand (RANKL) to prevent osteoclast activation
. Inhibition of vascular endothelial growth factor (VEGF)
. Competitive binding to estrogen receptors

Correct Answer & Explanation

. Binding to the RANK ligand (RANKL) to prevent osteoclast activation

Explanation

Denosumab is a monoclonal antibody used to treat giant cell tumors of bone by binding to RANKL, preventing the activation of RANK on osteoclasts and osteoclast-like giant cells. This halts bone resorption and allows the stroma to form woven bone, facilitating easier surgical curettage.

Question 10702

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) initiate osteoinductive signaling pathways. Upon BMP binding to its surface receptor, which intracellular signaling molecules are directly phosphorylated to translocate to the nucleus?

. Wnt/beta-catenin
. Smad 1, 5, and 8
. Receptor activator of NF-kB (RANK)
. Osteoprotegerin
. Mitogen-activated protein kinases (MAPK)

Correct Answer & Explanation

. Smad 1, 5, and 8

Explanation

BMPs bind to serine-threonine kinase receptors, which then phosphorylate receptor-regulated Smads (Smad 1, 5, and 8). These form a complex with co-Smad 4 and translocate to the nucleus to regulate target gene transcription for osteoblast differentiation.

Question 10703

Topic: Biology, Genetics & Bone Healing

Denosumab is increasingly used as a neoadjuvant treatment for large, marginally resectable Giant Cell Tumors (GCT) of bone. What is the specific mechanism of action of this medication?

. Inhibition of matrix metalloproteinases
. Direct induction of osteoblast apoptosis
. Monoclonal antibody binding to RANKL
. Inhibition of the Wnt/beta-catenin pathway
. Tyrosine kinase inhibition

Correct Answer & Explanation

. Monoclonal antibody binding to RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). This prevents RANKL from binding to RANK on osteoclasts and giant cells, halting osteoclast-mediated bone destruction.

Question 10704

Topic: 1. General Principles & Basic Science

Following a complete peripheral nerve transection (neurotmesis) and primary epineural repair, at what approximate rate does the regenerating axonal cone advance down the distal nerve sheath?

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

Correct Answer & Explanation

. 1.0 mm/day

Explanation

After Wallerian degeneration and a brief latent period, axonal regeneration proceeds at an average rate of approximately 1 mm/day (or 1 inch/month). This rate is highly dependent on patient age, nerve type, and the local injury environment.

Question 10705

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic properties. Which of the following terms describes the phenomenon where a tissue is held at a constant length over time, resulting in a gradual decrease in the force required to maintain that length?

. Creep
. Stress relaxation
. Hysteresis
. Strain hardening
. Isotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the stress (force) required to maintain a tissue at a constant strain (length) decreases over time. Creep, conversely, is the continued deformation of a tissue over time when subjected to a constant load.

Question 10706

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum strain tolerated by lamellar bone formation during secondary fracture healing?

. < 2%
. 2-10%
. 10-30%
. 30-100%
. > 100%

Correct Answer & Explanation

. < 2%

Explanation

Perren's strain theory dictates that specific tissues tolerate different maximum strains before rupturing and failing to bridge a fracture gap. Lamellar bone is highly rigid and tolerates <2% strain. Woven bone tolerates up to 10%, cartilage up to 30%, and granulation tissue can tolerate up to 100% strain.

Question 10707

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, highly cross-linked polyethylene (HXLPE) is used to decrease wear rates. Irradiation used to create these cross-links also generates free radicals. Which manufacturing process is primarily used to eliminate these free radicals and prevent in vivo oxidation?

. Gamma irradiation in air
. Ethylene oxide sterilization
. Melting or annealing the polyethylene
. Adding benzoyl peroxide
. Coating with hydroxyapatite

Correct Answer & Explanation

. Melting or annealing the polyethylene

Explanation

Irradiation generates free radicals that can lead to oxidation and subsequent degradation of the polyethylene over time. To prevent this, manufacturers either 'melt' the polyethylene (heating it above its melting point) or 'anneal' it (heating it below its melting point) to mobilize and extinguish residual free radicals. Vitamin E doping is a newer alternative method.

Question 10708

Topic: 1. General Principles & Basic Science

In normal articular cartilage, which zone contains the highest concentration of proteoglycans and chondrocytes arranged in vertical columns?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage contains the highest proteoglycan content, the lowest water content, and chondrocytes that are arranged in vertical columns (perpendicular to the joint surface). The superficial zone has the highest water content and collagen fibers oriented parallel to the surface.

Question 10709

Topic: 1. General Principles & Basic Science
The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score is used to distinguish necrotizing fasciitis from severe cellulitis or abscess. Which of the following laboratory values is a specific component of the LRINEC score?
. Serum Lactate
. Serum Creatinine
. Serum Potassium
. Platelet count
. Erythrocyte Sedimentation Rate (ESR)

Correct Answer & Explanation

. Serum Creatinine

Explanation

The LRINEC score utilizes six routine laboratory parameters: CRP, Total WBC count, Hemoglobin, Serum Sodium, Serum Creatinine, and Serum Glucose. Elevated serum creatinine (>1.6 mg/dL) awards points in this system. Lactate, potassium, platelets, and ESR are not components of the LRINEC score.

Question 10710

Topic: Biology, Genetics & Bone Healing

A 55-year-old woman with a history of gastric bypass surgery presents with bilateral groin pain. Radiographs reveal bilateral Looser zones in the femoral necks. Laboratory evaluation for her underlying metabolic bone disease will most likely show which of the following profiles?

. High calcium, low phosphorus, normal alkaline phosphatase
. Low calcium, low phosphorus, high alkaline phosphatase
. Normal calcium, normal phosphorus, high alkaline phosphatase
. Low calcium, high phosphorus, low alkaline phosphatase
. Normal calcium, normal phosphorus, normal alkaline phosphatase

Correct Answer & Explanation

. Low calcium, low phosphorus, high alkaline phosphatase

Explanation

The patient has osteomalacia secondary to vitamin D malabsorption post-gastric bypass (Looser zones/pseudofractures are pathognomonic). Malabsorption leads to low calcium, triggering secondary hyperparathyroidism. Elevated PTH increases renal phosphate excretion (lowering phosphorus) while attempting to normalize calcium. High alkaline phosphatase reflects increased osteoblast activity attempting to mineralize excess osteoid.

Question 10711

Topic: Biomechanics & Biomaterials

When a stainless steel screw is placed through a titanium alloy plate to stabilize a fracture, which mode of corrosion is most likely to occur at the interface due to the dissimilar metals being immersed in tissue fluid?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (like stainless steel and titanium) are in direct physical contact within an electrolytic medium (blood/tissue fluid). The less noble metal acts as an anode and undergoes accelerated corrosion, which can lead to implant failure or localized tissue toxicity.

Question 10712

Topic: 1. General Principles & Basic Science

During the incorporation of a massive structural cortical bone allograft, what is the primary mechanism of remodeling and its resulting effect on the graft's biomechanical strength over the first year?

. Osteoblastic formation precedes osteoclastic resorption, leading to a steady increase in structural strength.
. Osteoclastic resorption precedes osteoblastic formation, causing a transient but significant decrease in structural strength.
. Direct vascular ingrowth causes immediate ossification without an initial resorptive phase, maintaining strength.
. Chondroblastic proliferation occurs first, leading to endochondral ossification and increased flexibility.
. Fibrous encapsulation occurs without cellular penetration, leading to permanent biomechanical weakness.

Correct Answer & Explanation

. Osteoclastic resorption precedes osteoblastic formation, causing a transient but significant decrease in structural strength.

Explanation

Cortical bone allografts incorporate via creeping substitution, where osteoclastic resorption precedes osteoblastic bone formation. This initially leads to increased porosity and a transient but significant decrease in the mechanical strength of the graft (often resulting in stress fractures), before new bone is laid down.

Question 10713

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with deep bone pain, increasing hat size, and bowing of the tibiae. Laboratory evaluation shows a markedly elevated alkaline phosphatase with normal serum calcium and phosphorus. Which cellular defect drives the primary initial phase of this disease process?

. Defective mineralization of osteoid by osteoblasts due to vitamin D deficiency.
. Increased, disorganized osteoclast activity often linked to SQSTM1 mutations.
. Malignant proliferation of plasma cells stimulating osteoclast-activating factors.
. Overproduction of parathyroid hormone leading to cortical bone resorption.
. Deficient Type I collagen synthesis leading to brittle woven bone.

Correct Answer & Explanation

. Increased, disorganized osteoclast activity often linked to SQSTM1 mutations.

Explanation

The patient has Paget's disease of bone. The primary defect in Paget's disease is intense, localized, and disorganized osteoclastic bone resorption (the lytic phase), often associated with mutations in the SQSTM1 gene (encoding p62). This is followed by a compensatory but disorganized osteoblastic response (blastic/sclerotic phase).

Question 10714

Topic: 1. General Principles & Basic Science

According to Sunderland's classification of peripheral nerve injuries, a third-degree nerve injury represents disruption of which of the following microanatomical structures?

. Axon only, with intact endoneurium, perineurium, and epineurium
. Axon and myelin sheath, with intact endoneurium, perineurium, and epineurium
. Axon, myelin sheath, and endoneurium, with intact perineurium and epineurium
. Axon, myelin sheath, endoneurium, and perineurium, with intact epineurium
. Complete transection of all nerve components including the epineurium

Correct Answer & Explanation

. Axon, myelin sheath, endoneurium, and perineurium, with intact epineurium

Explanation

Sunderland classification: 1st degree = myelin damage (neurapraxia). 2nd degree = axon severed, endoneurium intact (axonotmesis). 3rd degree = axon and endoneurium severed, perineurium intact. 4th degree = axon, endoneurium, and perineurium severed, epineurium intact. 5th degree = complete transection (neurotmesis).

Question 10715

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a bone graft substitute in orthopedic surgery. Which of the following best describes its biological properties?

. Osteogenic and osteoinductive
. Osteoconductive and osteogenic
. Osteoinductive and osteoconductive
. Osteoconductive only
. Osteogenic only

Correct Answer & Explanation

. Osteoinductive and osteoconductive

Explanation

Demineralized bone matrix (DBM) contains bone morphogenetic proteins (BMPs) exposed during the demineralization process, providing osteoinductive properties. Its residual collagenous matrix acts as a scaffold, providing osteoconductive properties. Because it lacks live cells, it is not osteogenic.

Question 10716

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with progressive bowing of the lower extremities. Laboratory findings show normal serum calcium, markedly decreased serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. What is the most appropriate medical treatment?

. High-dose Vitamin D3 (Cholecalciferol)
. Oral calcium and Vitamin D supplementation
. Oral phosphate and calcitriol (1,25-dihydroxyvitamin D)
. Intravenous Bisphosphonates
. Subcutaneous Calcitonin

Correct Answer & Explanation

. Oral phosphate and calcitriol (1,25-dihydroxyvitamin D)

Explanation

The clinical and laboratory presentation is consistent with X-linked hypophosphatemic rickets (Vitamin D-resistant rickets). It is caused by a PHEX mutation leading to excess FGF23, which causes renal phosphate wasting. Standard treatment consists of oral phosphate supplementation and active vitamin D (calcitriol).

Question 10717

Topic: 1. General Principles & Basic Science

In normal adult articular cartilage, which zone contains the highest concentration of proteoglycans and is primarily responsible for resisting compressive forces?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. The tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage has the highest concentration of proteoglycans and the lowest water content. The collagen fibers are oriented perpendicularly to the articular surface, making this the primary zone responsible for resisting compressive loads.

Question 10718

Topic: Infection, Pharmacology & VTE

Staphylococcus epidermidis is a frequent cause of prosthetic joint infections. Which of the following molecules primarily mediates the accumulation phase and the structural integrity of its biofilm?

. Autolysin (AtlE)
. Polysaccharide intercellular adhesin (PIA)
. Fibronectin-binding protein
. Protein A
. Teichoic acid

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

Biofilm formation occurs in sequential stages. Initial attachment to a bare polymer is facilitated by surface proteins such as autolysin (AtlE). The subsequent accumulation phase and the three-dimensional structural integrity of the biofilm are mediated by polysaccharide intercellular adhesin (PIA), which is synthesized by the icaADBC operon.

Question 10719

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of bone healing, what is the maximum strain environment that allows for the formation of lamellar bone across a fracture gap?

. Less than 2%
. 2% to 10%
. 10% to 30%
. 30% to 50%
. Greater than 50%

Correct Answer & Explanation

. Less than 2%

Explanation

Perren's strain theory posits that specific tissues tolerate different amounts of mechanical strain before failure. Granulation tissue tolerates up to 100% strain, fibrous tissue and cartilage up to 10-20%, woven bone up to 10%, but lamellar bone can only form in a rigid, low-strain environment of less than 2%.

Question 10720

Topic: 1. General Principles & Basic Science
A new diagnostic test for a rare orthopedic condition has a sensitivity of 90% and a specificity of 90%. If the prevalence of the condition in the tested population is 1%, what is the approximate positive predictive value (PPV) of the test?
. 1%
. 8%
. 50%
. 81%
. 99%

Correct Answer & Explanation

. 8%

Explanation

Using a hypothetical population of 10,000: A 1% prevalence means 100 have the disease and 9,900 do not. Sensitivity of 90% yields 90 true positives. Specificity of 90% yields 8,910 true negatives and 990 false positives. PPV = True Positives / (True Positives + False Positives) = 90 / (90 + 990) = 90 / 1080 ≈ 8.3%. Therefore, despite high sensitivity and specificity, the PPV is low due to the low disease prevalence.

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