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1. General Principles & Basic Science MCQs

Practice Set 669 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 13361

Topic: Biology, Genetics & Bone Healing

A diaphyseal fracture is treated with an unreamed, locked intramedullary nail, allowing micromotion at the fracture site. Which of the following best describes the predominant type of bone healing that will occur?

. Primary bone healing with cutting cones
. Intramembranous ossification only
. Endochondral ossification
. Creeping substitution
. Haversian remodeling

Correct Answer & Explanation

. Endochondral ossification

Explanation

Intramedullary nailing provides relative stability, allowing micromotion that promotes secondary (indirect) bone healing. This process involves callus formation and occurs primarily via endochondral ossification (where a cartilage intermediate is formed and then replaced by bone), supplemented by intramembranous ossification at the periphery.

Question 13362

Topic: Biomechanics & Biomaterials

Joint fluid aspiration from an acutely swollen knee reveals rhomboid-shaped crystals that exhibit weakly positive birefringence under polarized light microscopy. What is the biochemical composition of these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Basic calcium phosphate
. Hydroxyapatite
. Cholesterol

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate

Explanation

Calcium pyrophosphate dihydrate (CPPD) crystals, seen in pseudogout, are classically rhomboid-shaped and exhibit weakly positive birefringence. In contrast, monosodium urate crystals (gout) are needle-shaped and strongly negatively birefringent.

Question 13363

Topic: Biology, Genetics & Bone Healing

A 30-year-old woman presents with knee pain. Radiographs reveal an eccentric, purely lytic, expansile lesion in the epiphysis of the proximal tibia extending to the subchondral bone. Histology shows multinucleated giant cells in a stroma of mononuclear cells. Which of the following targeted therapies acts by inhibiting RANKL in the management of this tumor?

. Imatinib
. Denosumab
. Bisphosphonates
. Methotrexate
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

The clinical, radiographic, and histologic picture is classic for a Giant Cell Tumor (GCT) of bone. Denosumab is a monoclonal antibody that binds to RANKL, preventing the activation of the RANK receptor on osteoclast-like giant cells, thereby reducing osteolysis and shrinking the tumor.

Question 13364

Topic: Biology, Genetics & Bone Healing

Teriparatide is utilized in the treatment of severe osteoporosis. What is its exact mechanism of action?

. Inhibits osteoclast activity via binding to hydroxyapatite
. Binds to RANKL to prevent osteoclast differentiation
. Acts as a selective estrogen receptor modulator
. Recombinant PTH analogue that stimulates osteoblast activity when given intermittently
. Inhibits sclerostin to increase bone formation

Correct Answer & Explanation

. Recombinant PTH analogue that stimulates osteoblast activity when given intermittently

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. When administered intermittently (e.g., daily subcutaneous injection), it has a paradoxical anabolic effect on bone by stimulating osteoblast activity over osteoclast activity, thereby increasing overall bone formation.

Question 13365

Topic: 1. General Principles & Basic Science
Which type of collagen is the predominant structural component of the annulus fibrosus of the intervertebral disc?
. Type I
. Type II
. Type III
. Type IX
. Type X

Correct Answer & Explanation

. Type I

Explanation

The annulus fibrosus is primarily composed of Type I collagen, which helps resist tensile forces during bending and twisting motions. In contrast, the nucleus pulposus is rich in Type II collagen and proteoglycans (aggrecan) to resist compressive forces.

Question 13366

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is commonly used in total joint arthroplasty. However, cross-linking via irradiation introduces free radicals. Which of the following processes is primarily utilized to eliminate these free radicals during manufacturing?
. Gamma irradiation in air
. Ethylene oxide sterilization
. Melting or annealing
. Adding barium sulfate
. Coating with hydroxyapatite

Correct Answer & Explanation

. Melting or annealing

Explanation

Cross-linking of UHMWPE creates free radicals that can lead to long-term oxidative degradation. To prevent this, the material is treated by melting (heating above the melting point) or annealing (heating just below the melting point) to increase polymer chain mobility, allowing free radicals to recombine and be eliminated.

Question 13367

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage has the highest concentration of water, the lowest concentration of proteoglycans, and collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial zone

Explanation

The superficial zone possesses the highest water content (approx 80%) and the lowest proteoglycan content. Its collagen fibers align parallel to the joint surface to maximally resist shear forces.

Question 13368

Topic: Biology, Genetics & Bone Healing

A 6-year-old boy presents with multiple fractures and a history of recurrent infections. Radiographs reveal generalized osteosclerosis with a "bone-within-a-bone" appearance. A genetic defect in which of the following is most likely responsible for this condition?

. Type I collagen synthesis
. Fibroblast growth factor receptor 3
. Carbonic anhydrase II
. Cbfa1/Runx2 transcription factor
. Lysyl hydroxylase

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

This patient has osteopetrosis, characterized by a failure of osteoclast function. The most common defect is a mutation in carbonic anhydrase II, which prevents the acidification of the resorption pit needed to dissolve bone mineral.

Question 13369

Topic: 1. General Principles & Basic Science

During the incorporation of a massive cortical structural allograft, which cellular or vascular event strictly occurs first?

. Osteoconduction
. Osteoinduction
. Creeping substitution
. Osteoclastic resorption
. Vascular invasion

Correct Answer & Explanation

. Vascular invasion

Explanation

The incorporation of a cortical allograft begins with a localized inflammatory response, followed strictly by vascular invasion into the preexisting haversian canals. Osteoclastic resorption then creates space for new bone formation via creeping substitution.

Question 13370

Topic: Infection, Pharmacology & VTE
A patient is prescribed rivaroxaban for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the specific molecular mechanism of action of this medication?
. Inhibition of vitamin K epoxide reductase
. Direct inhibition of thrombin (Factor IIa)
. Direct inhibition of Factor Xa
. Activation of antithrombin III
. Irreversible inhibition of cyclooxygenase

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Rivaroxaban and apixaban are oral anticoagulants that work by directly inhibiting Factor Xa. This efficiently prevents the conversion of prothrombin to thrombin within the common pathway of the coagulation cascade.

Question 13371

Topic: Biomechanics & Biomaterials

According to the Blix length-tension curve for skeletal muscle biomechanics, maximal active tension is generated under which of the following conditions?

. When the muscle is fully contracted
. At the muscle's resting length
. When stretched 20% beyond its resting length
. When stretched 50% beyond its resting length
. When passive tension reaches its peak

Correct Answer & Explanation

. At the muscle's resting length

Explanation

The Blix curve demonstrates that maximum active tension in a muscle is generated at its resting length. At this exact length, there is optimal overlap and cross-bridge formation between actin and myosin filaments.

Question 13372

Topic: Biomechanics & Biomaterials

When a stainless steel screw is placed through a titanium plate in a fracture fixation construct, which specific type of corrosion is most likely to accelerate device failure?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within a conductive fluid environment, such as human blood or serum. The less noble metal (stainless steel) acts as an anode and corrodes rapidly.

Question 13373

Topic: 1. General Principles & Basic Science

Which of the following laboratory profiles is the hallmark of a patient presenting with primary hyperparathyroidism?

. Low serum calcium, high serum phosphate, elevated alkaline phosphatase
. High serum calcium, low serum phosphate, elevated alkaline phosphatase
. Normal serum calcium, normal serum phosphate, elevated alkaline phosphatase
. Low serum calcium, low serum phosphate, normal alkaline phosphatase
. High serum calcium, high serum phosphate, low alkaline phosphatase

Correct Answer & Explanation

. High serum calcium, low serum phosphate, elevated alkaline phosphatase

Explanation

Primary hyperparathyroidism induces increased bone resorption, leading to elevated serum calcium and alkaline phosphatase levels. Parathyroid hormone concurrently decreases renal tubular phosphate reabsorption, resulting in low serum phosphate.

Question 13374

Topic: Infection, Pharmacology & VTE

A 28-year-old patient with homozygous sickle cell disease presents with acute hematogenous osteomyelitis of the femur. While Staphylococcus aureus remains the most common overall organism, which of the following pathogens has a uniquely high incidence in this specific demographic?

. Pseudomonas aeruginosa
. Escherichia coli
. Salmonella species
. Kingella kingae
. Streptococcus pneumoniae

Correct Answer & Explanation

. Salmonella species

Explanation

Patients with sickle cell disease suffer from functional asplenia and bowel ischemia, creating a uniquely high susceptibility to Salmonella osteomyelitis. However, S. aureus remains the most common overall cause of bone infection in this population.

Question 13375

Topic: Physiology & Rehabilitation

Which of the following physiologic and morphologic characteristics best describes Type I skeletal muscle fibers?

. High glycogen content, anaerobic metabolism, fatigue rapidly
. High myoglobin content, aerobic metabolism, fatigue resistant
. Large fiber diameter, primarily utilized for explosive sprinting
. Low capillary density, rely on glycolytic enzymes
. Fast contraction speed, high anaerobic capacity

Correct Answer & Explanation

. High myoglobin content, aerobic metabolism, fatigue resistant

Explanation

Type I muscle fibers are "slow-twitch" fibers that rely heavily on aerobic metabolism. They possess high myoglobin content, high capillary density, and are highly fatigue-resistant, making them ideal for postural control and endurance.

Question 13376

Topic: 1. General Principles & Basic Science

In Sunderland's classification of peripheral nerve injuries, a second-degree injury corresponds directly to which of Seddon's classic categories?

. Neuropraxia
. Axonotmesis
. Neurotmesis
. Neuritis
. Wallerian degeneration

Correct Answer & Explanation

. Axonotmesis

Explanation

A Sunderland second-degree injury involves disruption of the axon but complete preservation of the surrounding endoneurium, perineurium, and epineurium. This perfectly corresponds to Seddon's definition of axonotmesis, allowing for predictable regeneration.

Question 13377

Topic: Biology, Genetics & Bone Healing

Which cytokine is universally considered the primary pathological mediator driving articular cartilage degradation in osteoarthritis?

. Interleukin-1 (IL-1)
. Interleukin-4 (IL-4)
. Interleukin-10 (IL-10)
. Transforming growth factor beta (TGF-b)
. Bone morphogenetic protein 2 (BMP-2)

Correct Answer & Explanation

. Interleukin-1 (IL-1)

Explanation

Interleukin-1 (IL-1) and Tumor Necrosis Factor-alpha (TNF-a) are the predominant pro-inflammatory cytokines driving articular cartilage destruction. They heavily stimulate the production of matrix metalloproteinases (MMPs) while actively inhibiting proteoglycan synthesis.

Question 13378

Topic: Biology, Genetics & Bone Healing

A severely malnourished patient presents with bleeding gums, petechiae, and severe joint pain. Radiographs show a Pelkan spur and a Wimberger ring sign. This condition is caused by a dietary deficiency that directly impairs which step of collagen synthesis?

. Cleavage of procollagen C- and N-terminals
. Hydroxylation of proline and lysine residues
. Glycosylation of hydroxylysine residues
. Formation of the triple helix
. Cross-linking of tropocollagen molecules by lysyl oxidase

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

Scurvy is caused by a severe Vitamin C deficiency. Vitamin C is a required cofactor for prolyl and lysyl hydroxylases, enzymes that perform the hydroxylation of proline and lysine residues necessary to stabilize the collagen triple helix.

Question 13379

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is widely and effectively used in orthopedic surgery to reduce perioperative blood loss. What is the precise molecular mechanism of action of TXA?

. Inhibits the conversion of fibrinogen to fibrin
. Competitively blocks the lysine-binding sites on plasminogen
. Stimulates the release of von Willebrand factor from endothelium
. Directly activates the extrinsic coagulation pathway
. Irreversibly inhibits cyclooxygenase-1 in platelets

Correct Answer & Explanation

. Competitively blocks the lysine-binding sites on plasminogen

Explanation

Tranexamic acid is a synthetic antifibrinolytic agent. It works by competitively inhibiting the activation of plasminogen to plasmin via binding to its lysine-binding sites, thereby preventing the enzymatic degradation of established fibrin clots.

Question 13380

Topic: 1. General Principles & Basic Science

Following a traumatic peripheral nerve transection, what is the earliest clinical time frame in which fibrillations and positive sharp waves can be reliably detected on electromyography (EMG)?

. 24 to 48 hours
. 1 to 2 weeks
. 3 to 4 weeks
. 6 to 8 weeks
. 12 to 16 weeks

Correct Answer & Explanation

. 3 to 4 weeks

Explanation

Fibrillations and positive sharp waves are electrophysiologic markers of active muscle denervation. Wallerian degeneration must occur before these signs manifest, taking roughly 3 to 4 weeks to reliably appear on a needle EMG.

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