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1. General Principles & Basic Science MCQs

Practice Set 616 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 12301

Topic: Biomechanics & Biomaterials

A bioengineering researcher is studying the mechanical behavior of articular cartilage. She applies a constant compressive load to a cartilage sample over a sustained period of time and measures a progressive, continuous increase in tissue deformation. This viscoelastic phenomenon is best described as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the progressive deformation of a viscoelastic material over time when subjected to a constant load. In contrast, stress relaxation is the decrease in stress over time when the material is held at a constant deformation.

Question 12302

Topic: 1. General Principles & Basic Science

In articular cartilage, which structural boundary acts as an anchor for collagen fibrils, separating the deep zone of uncalcified cartilage from the calcified cartilage?

. Superficial tangential zone
. Middle (transitional) zone
. Tidemark
. Subchondral bone plate
. Lamina splendens

Correct Answer & Explanation

. Superficial tangential zone

Explanation

The tidemark is a distinct histologic boundary visible in adult articular cartilage that separates the uncalcified deep radial zone from the calcified cartilage zone. Collagen fibrils cross the tidemark to anchor into the calcified layer, securing the articular cartilage to the underlying bone.

Question 12303

Topic: Biology, Genetics & Bone Healing
Secondary bone healing relies on endochondral ossification to bridge a fracture gap with callus. During the transition from the soft callus stage to the hard callus stage, which major shift in collagen types takes place within the extracellular matrix?
. Type I collagen is replaced by Type II collagen
. Type II collagen is replaced by Type I collagen
. Type III collagen is replaced by Type IV collagen
. Type X collagen is replaced by Type II collagen
. Type I collagen is replaced by Type III collagen

Correct Answer & Explanation

. Type II collagen is replaced by Type I collagen

Explanation

In secondary bone healing, the soft callus primarily consists of fibrocartilage, which is rich in Type II collagen. As endochondral ossification progresses, this cartilage is calcified, resorbed, and replaced by woven bone (hard callus), which is composed predominantly of Type I collagen.

Question 12304

Topic: Biomechanics & Biomaterials

A surgeon considers using a combination of titanium and stainless steel implants in a single fracture construct. Which of the following principles best describes the primary risk of galvanic corrosion in this scenario?

. Titanium acts as the anode and undergoes accelerated corrosion
. Stainless steel acts as the cathode and is protected from corrosion
. Stainless steel acts as the anode and undergoes accelerated corrosion
. Titanium acts as the cathode and is aggressively corroded by the local cellular response
. Passivation layers on both metals prevent any measurable galvanic corrosion in vivo

Correct Answer & Explanation

. Titanium acts as the anode and undergoes accelerated corrosion

Explanation

In a galvanic cell formed by dissimilar metals, the less noble metal (stainless steel) acts as the anode and undergoes accelerated corrosion. The more noble metal (titanium) acts as the cathode and is protected. This can lead to rapid implant failure and local metallosis.

Question 12305

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is frequently used in orthopedic surgery to augment fracture healing and spinal fusion. The primary physiological mechanism by which DBM promotes bone formation is characterized by which of the following properties?

. Osteogenesis
. Osteoinduction
. Osteoconduction
. Angiogenesis
. Chondrogenesis

Correct Answer & Explanation

. Osteogenesis

Explanation

DBM is primarily osteoinductive. The manufacturing process of acid demineralization exposes bone morphogenetic proteins (BMPs) and other growth factors hidden within the bone matrix. These factors recruit host mesenchymal stem cells and induce them to differentiate into osteoblasts (osteoinduction). DBM is not osteogenic because it contains no viable cells.

Question 12306

Topic: 1. General Principles & Basic Science

Articular cartilage has a highly specialized, layered structural organization designed to withstand different types of mechanical stress. In which zone of the articular cartilage are the type II collagen fibers predominantly oriented perpendicular to the joint surface to best resist compressive loads?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. Subchondral bone plate

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

In the deep (radial) zone of articular cartilage, the type II collagen fibers are arranged perpendicularly to the joint surface. They anchor the cartilage to the underlying calcified zone and subchondral bone, providing maximum resistance to compressive forces. In contrast, fibers in the superficial zone are parallel to the joint surface to resist shear stress.

Question 12307

Topic: Infection, Pharmacology & VTE

A 2-year-old child presents to the emergency department with an acute limp and refusal to bear weight on the right leg. There is a low-grade fever and a recent history of an upper respiratory tract infection. Joint aspiration reveals purulent fluid. Gram stain is initially negative. Which of the following organisms is a fastidious Gram-negative coccobacillus that is a leading cause of osteoarticular infections in this specific age group?

. Staphylococcus aureus
. Streptococcus pneumoniae
. Kingella kingae
. Haemophilus influenzae type b
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Staphylococcus aureus

Explanation

Kingella kingae is a fastidious Gram-negative coccobacillus and a leading cause of septic arthritis and osteomyelitis in children aged 6 months to 4 years. It often follows an upper respiratory infection (stomatitis or pharyngitis). It is difficult to isolate on routine solid culture media; detection rates are significantly improved by inoculating joint fluid into blood culture vials or using PCR.

Question 12308

Topic: Biology, Genetics & Bone Healing

Which of the following intracellular signaling proteins is directly phosphorylated by the Type I bone morphogenetic protein (BMP) receptor following ligand binding?

. STAT3
. beta-catenin
. SMAD 1/5/8
. ERK 1/2
. NF-kappaB

Correct Answer & Explanation

. STAT3

Explanation

BMPs bind to serine/threonine kinase receptors, causing phosphorylation of SMAD 1, 5, and 8. These receptor-regulated SMADs then form a complex with SMAD 4 to translocate to the nucleus and regulate gene transcription.

Question 12309

Topic: Biology, Genetics & Bone Healing

A 28-year-old female presents with a destructive, lytic lesion in the distal femur. Biopsy confirms a Giant Cell Tumor of bone. She is prescribed denosumab prior to surgical intervention. What is the mechanism of action of this medication?

. Inhibits VEGF, preventing tumor angiogenesis
. Binds to RANKL, preventing activation of osteoclasts
. Directly induces apoptosis in neoplastic stromal cells
. Inhibits tyrosine kinase activity
. Binds to the RANK receptor on osteoblasts

Correct Answer & Explanation

. Inhibits VEGF, preventing tumor angiogenesis

Explanation

Denosumab is a monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on osteoclasts and their precursors. This halts osteoclastogenesis and bone resorption in Giant Cell Tumors.

Question 12310

Topic: 1. General Principles & Basic Science

In 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
. Tidemark

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The deep (radial) zone has the highest concentration of proteoglycans and the lowest water content. Its vertical collagen fibers and high proteoglycan content make it the primary zone responsible for resisting compressive loads.

Question 12311

Topic: Biology, Genetics & Bone Healing

Following a rigid open reduction and internal fixation of a transverse radius fracture using a compression plate, bone healing occurs primarily via which of the following mechanisms?

. Endochondral ossification
. Intramembranous ossification
. Primary bone healing via cutting cones
. Callus formation
. Chondrocyte hypertrophy and calcification

Correct Answer & Explanation

. Endochondral ossification

Explanation

Absolute stability achieved by rigid compression plating prevents interfragmentary motion, leading to primary (direct) bone healing. This occurs via Haversian remodeling where osteoclast "cutting cones" cross the fracture site.

Question 12312

Topic: Biology, Genetics & Bone Healing
A 4-year-old boy with Osteogenesis Imperfecta (OI) Type III is treated with intravenous pamidronate. What is the primary cellular mechanism of action of this medication in this patient population?
. Stimulates osteoblast proliferation and differentiation
. Inhibits osteoclast-mediated bone resorption
. Increases intestinal calcium absorption
. Enhances type I collagen cross-linking
. Promotes mineralization of uncalcified osteoid

Correct Answer & Explanation

. Inhibits osteoclast-mediated bone resorption

Explanation

Bisphosphonates, such as pamidronate, are structural analogs of pyrophosphate that bind to hydroxyapatite crystals in bone. They are ingested by osteoclasts and induce osteoclast apoptosis, thereby inhibiting osteoclast-mediated bone resorption. In OI, this increases bone mineral density and cortical thickness, reducing fracture frequency.

Question 12313

Topic: Infection, Pharmacology & VTE
According to the Kocher criteria, what is the probability of septic arthritis in a pediatric hip if a patient presents with a fever >38.5 C, non-weight-bearing status, ESR >40 mm/hr, and a serum WBC >12,000/mm3?
. <10%
. 30%
. 59%
. 93%
. 99%

Correct Answer & Explanation

. 99%

Explanation

The Kocher criteria use four independent predictors to differentiate septic arthritis from transient synovitis: fever > 38.5 C, non-weight-bearing, ESR > 40, and WBC > 12,000. The probability of septic arthritis is approximately 3% for 1 predictor, 40% for 2, 93% for 3, and 99% when all 4 predictors are present.

Question 12314

Topic: Surgical Anatomy & Approaches

A 5-year-old boy presents with an extension-type supracondylar humerus fracture. Radiographs show posterolateral displacement of the distal fragment. Based on this displacement pattern, which nerve is at the highest risk of injury?

. Anterior interosseous nerve (AIN)
. Radial nerve
. Ulnar nerve
. Musculocutaneous nerve
. Axillary nerve

Correct Answer & Explanation

. Anterior interosseous nerve (AIN)

Explanation

In extension-type supracondylar humerus fractures, the distal fragment dictates the direction of the proximal fragment. With posterolateral displacement of the distal fragment, the sharp proximal fragment displaces anteromedially. This places the structures in the anteromedial compartment—specifically the median nerve (AIN branch) and the brachial artery—at the greatest risk of injury. Posteromedial displacement endangers the radial nerve.

Question 12315

Topic: Infection, Pharmacology & VTE
A 4-year-old boy is brought to the ED with right hip pain. He is refusing to bear weight on the right leg. His temperature is 38.6°C (101.5°F). Labs reveal an ESR of 45 mm/hr and a serum WBC of 10,000 cells/mm³. According to the Kocher criteria, what is the probability that this child has septic arthritis of the hip?
. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 93%

Explanation

The Kocher criteria for differentiating septic arthritis from transient synovitis include: 1) Non-weight-bearing, 2) Temperature > 38.5°C, 3) ESR > 40 mm/hr, and 4) Serum WBC > 12,000 cells/mm³. This patient meets 3 criteria (NWB, Temp > 38.5, ESR > 40). According to Kocher's original study, the probability of septic arthritis is approximately 3% for 1 criterion, 40% for 2, 93% for 3, and 99% for 4 criteria.

Question 12316

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with right hip pain, fever (38.8 C), and inability to bear weight. His ESR is 55 mm/hr, CRP is 35 mg/L, and WBC count is 14,000/mm3. According to the Kocher criteria, what is the probability that this child has septic arthritis rather than transient synovitis?

. Less than 10%
. Approximately 40%
. Approximately 70%
. Greater than 90%
. 100% diagnostic certainty

Correct Answer & Explanation

. Less than 10%

Explanation

The patient meets all four Kocher criteria: non-weight bearing, temperature > 38.5 C, ESR > 40 mm/hr, and WBC > 12,000/mm3. The presence of four criteria yields a 93-99% predictive probability for septic arthritis.

Question 12317

Topic: Infection, Pharmacology & VTE

A 4-year-old boy presents with an acute onset of a right-sided limp. He has a temperature of 38.6 C (101.5 F), an ESR of 45 mm/hr, a WBC count of 13,000/mm3, and refuses to bear weight. According to the Kocher criteria, what is the approximate probability that this child has septic arthritis of the hip?

. 3%
. 40%
. 71%
. 93%
. 99%

Correct Answer & Explanation

. 3%

Explanation

The Kocher criteria for septic arthritis include non-weight-bearing, temperature > 38.5 C, ESR > 40 mm/hr, and WBC > 12,000/mm3. The presence of all four criteria indicates a 99% probability of septic arthritis.

Question 12318

Topic: Biology, Genetics & Bone Healing

A 2-year-old child presents with multiple fractures, blue sclerae, and dentinogenesis imperfecta. Genetic testing reveals a mutation in the COL1A1 gene. Which of the following is the primary mechanism of action of the most commonly prescribed medical therapy for this condition?

. Inhibition of osteoclast-mediated bone resorption
. Stimulation of osteoblast differentiation
. Supplementation of defective type 1 collagen
. Inhibition of matrix metalloproteinases
. Stimulation of calcium absorption in the gut

Correct Answer & Explanation

. Inhibition of osteoclast-mediated bone resorption

Explanation

Bisphosphonates are the medical treatment of choice for Osteogenesis Imperfecta. They work by inhibiting osteoclast-mediated bone resorption, which increases bone density and decreases fracture rates.

Question 12319

Topic: Biology, Genetics & Bone Healing

A 32-year-old female complains of knee pain. Radiographs demonstrate an eccentric, lytic, epiphyseal lesion in the proximal tibia extending to the subchondral bone without a sclerotic margin. Histology shows multinucleated giant cells in a stroma of mononuclear cells. Which of the following medical treatments can be used as an adjuvant to surgery or for unresectable disease?

. Imatinib
. Denosumab
. Doxorubicin
. Methotrexate
. Rituximab

Correct Answer & Explanation

. Imatinib

Explanation

The presentation is classic for a Giant Cell Tumor (GCT) of bone. Denosumab, a monoclonal antibody that acts as a RANKL inhibitor, is highly effective in treating GCT by preventing the RANKL-mediated maturation and activation of osteoclast-like giant cells, leading to tumor consolidation.

Question 12320

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with an expansile, eccentric lytic lesion in the proximal tibia extending to the subchondral bone. Biopsy confirms Giant Cell Tumor of Bone. She is started on denosumab. What is the primary mechanism of action of this drug?

. Inhibition of the RANK receptor on osteoclasts
. Binding directly to RANKL, preventing its interaction with RANK
. Inhibition of farnesyl pyrophosphate synthase
. Inhibition of vascular endothelial growth factor (VEGF)
. Direct induction of apoptosis in mononuclear stromal cells

Correct Answer & Explanation

. Inhibition of the RANK receptor on osteoclasts

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). By binding to RANKL, it prevents RANKL from binding to the RANK receptor on the surface of osteoclasts and their precursors, thereby inhibiting osteoclast formation, function, and survival. It does not bind to the RANK receptor itself. Bisphosphonates inhibit farnesyl pyrophosphate synthase.

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