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1. General Principles & Basic Science MCQs

Practice Set 619 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 12361

Topic: Infection, Pharmacology & VTE
A patient is prescribed Enoxaparin for deep vein thrombosis prophylaxis following a total hip arthroplasty. What is the primary mechanism of action of this pharmacological agent?
. Direct inhibition of thrombin (Factor IIa)
. Inhibition of Vitamin K epoxide reductase
. Potentiation of antithrombin III to preferentially inhibit Factor Xa
. Irreversible inhibition of platelet cyclooxygenase
. Direct inhibition of Factor Xa without binding antithrombin III

Correct Answer & Explanation

. Potentiation of antithrombin III to preferentially inhibit Factor Xa

Explanation

Enoxaparin is a Low Molecular Weight Heparin (LMWH). It exerts its anticoagulant effect by binding to antithrombin III, which then preferentially inactivates Factor Xa over Factor IIa (thrombin).

Question 12362

Topic: Physiology & Rehabilitation

During normal human ambulation, articular cartilage experiences varying loads and velocities. Which lubrication mechanism is most responsible for minimizing friction during high-load, high-velocity phases of the gait cycle?

. Boundary lubrication
. Weeping lubrication
. Elastohydrodynamic lubrication
. Boosted lubrication
. Solid-phase lubrication

Correct Answer & Explanation

. Elastohydrodynamic lubrication

Explanation

Elastohydrodynamic (fluid-film) lubrication dominates during high-velocity, dynamic motion, where fluid pressure deforms the cartilage surface to maintain a fluid gap. Boundary lubrication is key during low-velocity or stationary periods.

Question 12363

Topic: Surgical Anatomy & Approaches

A patient sustains a closed fracture of the humerus resulting in a radial nerve palsy. According to the Sunderland classification, a third-degree nerve injury is characterized by disruption of the axon and which of the following structures?

. Myelin sheath only
. Endoneurium only
. Endoneurium and perineurium
. Perineurium and epineurium
. Complete transection of the nerve

Correct Answer & Explanation

. Endoneurium only

Explanation

A Sunderland 3rd degree injury involves disruption of the axon and the endoneurium, but the perineurium and epineurium remain intact. Recovery is unpredictable and often requires surgical exploration if no clinical improvement is seen.

Question 12364

Topic: Biology, Genetics & Bone Healing

A 4-year-old child presents with frequent fractures, cranial nerve palsies, and diffuse osteosclerosis on radiographs. A defect in which of the following is the most likely underlying pathophysiological cause?

. Osteoblast alkaline phosphatase activity
. Osteoclast carbonic anhydrase II activity
. Chondrocyte proliferation in the resting zone
. Type I collagen cross-linking
. Fibroblast growth factor receptor 3 (FGFR3)

Correct Answer & Explanation

. Osteoclast carbonic anhydrase II activity

Explanation

The patient's presentation is classic for osteopetrosis (marble bone disease). The most common mutation impairs osteoclast function via carbonic anhydrase II deficiency, preventing proper bone resorption.

Question 12365

Topic: Biomechanics & Biomaterials

During intraoperative stretching of a contracted knee joint, the surgeon applies a constant deformation (length) to the collateral ligaments over a period of time. The surgeon notices that the force required to maintain this stretch gradually decreases. This biomechanical property is known as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the force (stress) required to maintain a tissue at a constant length decreases over time. Creep is the continuous deformation of a tissue under a constant load.

Question 12366

Topic: 1. General Principles & Basic Science

A massive cortical bone allograft is used for reconstruction after a distal femur tumor resection. The process by which this graft is slowly resorbed and replaced by host bone over years is best described by which of the following terms?

. Osteoinduction
. Osteoconduction
. Creeping substitution
. Neovascularization
. Contact healing

Correct Answer & Explanation

. Creeping substitution

Explanation

Cortical allografts heal via creeping substitution, a process where host osteoclasts slowly resorb the graft while osteoblasts lay down new viable bone. This process is often incomplete, leaving a chronic mixture of necrotic allograft and viable host bone.

Question 12367

Topic: Biology, Genetics & Bone Healing

Alendronate is prescribed for a 70-year-old female with a fragility fracture of the distal radius. What is the precise intracellular target of this medication within the osteoclast?

. Cathepsin K
. Farnesyl pyrophosphate synthase
. Carbonic anhydrase II
. RANK receptor
. Matrix metalloproteinase-9

Correct Answer & Explanation

. Farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates like alendronate inhibit farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents the prenylation of small GTPases, ultimately disrupting osteoclast ruffled border formation and promoting apoptosis.

Question 12368

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, what is the maximum strain tolerated by lamellar bone before it fails?

. 2%
. 10%
. 30%
. 50%
. 100%

Correct Answer & Explanation

. 2%

Explanation

Lamellar bone is highly rigid and can only tolerate up to 2% strain before fracturing. In contrast, granulation tissue can tolerate up to 100% strain, allowing it to bridge highly mobile fracture gaps during the early phases of secondary bone healing.

Question 12369

Topic: 1. General Principles & Basic Science
During the remodeling phase of ligament healing, the provisional extracellular matrix is gradually replaced to maximize tensile strength. Which collagen transition characterizes this final phase?
. Type I to Type II
. Type II to Type I
. Type III to Type I
. Type I to Type III
. Type III to Type II

Correct Answer & Explanation

. Type III to Type I

Explanation

In the early proliferative phase of ligament and tendon healing, fibroblasts primarily synthesize disorganized Type III collagen. During the prolonged remodeling phase, this is gradually replaced by stronger, longitudinally aligned Type I collagen.

Question 12370

Topic: Biology, Genetics & Bone Healing

A 4-year-old girl is evaluated for short stature and dense, brittle bones demonstrating an Erlenmeyer flask deformity on radiographs. Laboratory analysis reveals absent function of carbonic anhydrase II. Which cellular process is directly impaired in this condition?

. Osteoblast matrix synthesis
. Osteoclast generation of an acidic microenvironment
. Chondrocyte hypertrophy in the physis
. Macrophage phagocytosis of debris
. Fibroblast secretion of Type I collagen

Correct Answer & Explanation

. Osteoclast generation of an acidic microenvironment

Explanation

Carbonic anhydrase II is essential for generating protons (H+) that are pumped into the osteoclast's ruffled border. This creates the highly acidic environment required to dissolve bone mineral, and its deficiency leads to malignant infantile osteopetrosis.

Question 12371

Topic: 1. General Principles & Basic Science

When inserting a cortical bone screw, the pullout strength is directly proportional to which of the following variables?

. Core diameter
. Thread pitch
. Outer diameter
. Insertion torque
. Shaft length

Correct Answer & Explanation

. Outer diameter

Explanation

The pullout strength of a screw is directly proportional to its outer (thread) diameter, the length of thread engagement, and the shear strength of the bone. It is inversely proportional to the thread pitch (distance between threads).

Question 12372

Topic: 1. General Principles & Basic Science

Which zone of articular cartilage provides the greatest resistance to shear forces and contains collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

The superficial (tangential) zone of articular cartilage contains flattened chondrocytes and collagen fibrils oriented parallel to the joint surface. This highly organized, dense parallel structure provides the primary resistance to shear forces.

Question 12373

Topic: 1. General Principles & Basic Science

A patient with end-stage renal disease develops renal osteodystrophy. Which of the following best describes the classical pathophysiological sequence of secondary hyperparathyroidism in this setting?

. Increased phosphorus, decreased calcitriol, decreased calcium, increased PTH
. Decreased phosphorus, increased calcitriol, increased calcium, decreased PTH
. Increased phosphorus, increased calcitriol, increased calcium, increased PTH
. Decreased phosphorus, decreased calcitriol, decreased calcium, increased PTH
. Normal phosphorus, decreased calcitriol, normal calcium, increased PTH

Correct Answer & Explanation

. Increased phosphorus, decreased calcitriol, decreased calcium, increased PTH

Explanation

Chronic kidney disease leads to phosphate retention and impaired 1-alpha-hydroxylation of 25(OH)D to active calcitriol. The resulting hypocalcemia and hyperphosphatemia strongly stimulate the parathyroid glands to overproduce Parathyroid Hormone (PTH).

Question 12374

Topic: Infection, Pharmacology & VTE

In the pathogenesis of implant-associated osteomyelitis, Staphylococcus aureus establishes a dense biofilm. What is the primary constituent of the extracellular polymeric substance (EPS) that protects the bacteria from host immunity?

. Peptidoglycan
. Polysaccharide intercellular adhesin (PIA)
. Lipopolysaccharide (LPS)
. Fibronectin-binding protein
. Protein A

Correct Answer & Explanation

. Polysaccharide intercellular adhesin (PIA)

Explanation

The biofilm matrix in Staphylococcus aureus infections is primarily composed of Polysaccharide Intercellular Adhesin (PIA), also known as poly-N-acetylglucosamine (PNAG). This slime layer anchors the biofilm and shields bacteria from phagocytosis and systemic antibiotics.

Question 12375

Topic: Biology, Genetics & Bone Healing

Which of the following members of the Transforming Growth Factor-beta (TGF-b) superfamily is FDA approved for use in acute, open tibial shaft fractures treated with an intramedullary nail?

. BMP-2
. BMP-7
. TGF-b1
. FGF-2
. PDGF

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human Bone Morphogenetic Protein-2 (rhBMP-2) is FDA approved for acute, open tibial shaft fractures treated with an intramedullary nail. BMPs stimulate bone formation by promoting the differentiation of mesenchymal stem cells into osteoblasts via the Smad signaling pathway.

Question 12376

Topic: 1. General Principles & Basic Science

The blood supply to a healthy flexor tendon within the digital sheath is provided by both intrinsic and extrinsic sources. Where do the vincula brevia and longa, representing the extrinsic supply, enter the tendon?

. Dorsal (epitenon) surface
. Volar (synovial) surface
. Proximal musculotendinous junction
. Distal bony insertion
. Lateral borders

Correct Answer & Explanation

. Dorsal (epitenon) surface

Explanation

The vincular system provides the extrinsic blood supply to the flexor tendons within the digital sheath. These vessels enter the tendons exclusively on their dorsal surface to avoid compression against the pulleys during active digital flexion.

Question 12377

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) regulates serum calcium by exerting effects on bone. Intermittent, low-dose administration of synthetic PTH (e.g., Teriparatide) has what primary cellular effect?

. Direct stimulation of osteoclast resorption
. Increased osteoblast survival and bone formation
. Inhibition of RANKL expression
. Direct stimulation of intestinal calcium absorption
. Decreased renal reabsorption of calcium

Correct Answer & Explanation

. Increased osteoblast survival and bone formation

Explanation

While continuous high levels of PTH stimulate bone resorption via increased RANKL expression, intermittent low-dose PTH (Teriparatide) exerts a strong anabolic effect. It directly increases osteoblast proliferation and inhibits osteoblast apoptosis, leading to net bone formation.

Question 12378

Topic: Surgical Anatomy & Approaches

Following a closed humerus fracture, a patient exhibits a complete radial nerve palsy. Electromyography (EMG) performed at 4 weeks shows fibrillation potentials in the brachioradialis but no voluntary motor unit action potentials. This finding indicates:

. Neuropraxia with an intact axon
. Axonotmesis or neurotmesis with Wallerian degeneration
. Normal reinnervation already in progress
. Transient ischemic conduction block
. Central nervous system upper motor neuron pathology

Correct Answer & Explanation

. Axonotmesis or neurotmesis with Wallerian degeneration

Explanation

Fibrillation potentials on an EMG indicate denervated muscle fibers, confirming that axonal discontinuity (axonotmesis or neurotmesis) has occurred and Wallerian degeneration is present. Neuropraxia (a pure conduction block) would not demonstrate fibrillations because the axon itself remains intact.

Question 12379

Topic: Infection, Pharmacology & VTE
A patient is prescribed oral Rivaroxaban for deep vein thrombosis prophylaxis following a total knee arthroplasty. What is the specific mechanism of action of this medication?
. Direct thrombin (Factor IIa) inhibitor
. Direct Factor Xa inhibitor
. Vitamin K epoxide reductase antagonist
. Enhances antithrombin III activity
. Irreversible platelet cyclooxygenase inhibitor

Correct Answer & Explanation

. Direct Factor Xa inhibitor

Explanation

Rivaroxaban and Apixaban are highly selective, direct oral inhibitors of Factor Xa. By inhibiting Factor Xa, they halt the coagulation cascade at the crucial intersection of the intrinsic and extrinsic pathways, preventing the conversion of prothrombin to thrombin.

Question 12380

Topic: 1. General Principles & Basic Science

Tranexamic acid (TXA) is widely used to reduce surgical blood loss in orthopedics. How does TXA chemically exert its antifibrinolytic effect?

. Inhibiting thrombin generation directly
. Binding to plasminogen to prevent its conversion to plasmin
. Cross-linking fibrin polymers to stabilize the clot
. Stimulating platelet aggregation and degranulation
. Increasing von Willebrand factor release from the endothelium

Correct Answer & Explanation

. Binding to plasminogen to prevent its conversion to plasmin

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively binds to the lysine-binding sites on plasminogen, blocking its activation into the active enzyme plasmin, thereby strongly inhibiting the degradation of fibrin clots.

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