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1. General Principles & Basic Science MCQs

Practice Set 398 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 7941

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction during fracture healing. Following the binding of a BMP (such as BMP-2) to its cell-surface serine/threonine kinase receptor, which of the following intracellular signaling molecules is directly phosphorylated to translocate to the nucleus and regulate gene transcription?

. Beta-catenin
. STAT3
. Smad 1/5/8
. NF-kappaB
. JAK2

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs bind to serine/threonine kinase receptors on the cell surface, leading to the phosphorylation of receptor-regulated Smads (Smad 1, 5, and 8). These phosphorylated Smads form a complex with the common-partner Smad (Smad 4) and translocate to the nucleus to regulate target gene transcription, promoting osteoblast differentiation (e.g., upregulating Runx2). Beta-catenin is involved in the Wnt signaling pathway, while NF-kappaB is downstream of RANKL.

Question 7942

Topic: Biomechanics & Biomaterials

Cortical bone exhibits viscoelastic properties, meaning its biomechanical response is dependent on the rate of loading. When cortical bone is subjected to a rapid rate of loading (high strain rate) compared to a slow rate of loading, how do its mechanical properties change?

. It becomes less stiff and absorbs less energy before failure
. It becomes stiffer and absorbs more energy before failure
. It becomes more ductile with a significantly lower yield point
. Its ultimate tensile strength decreases
. Its modulus of elasticity remains unchanged while energy absorption decreases

Correct Answer & Explanation

. It becomes stiffer and absorbs more energy before failure

Explanation

Bone is a viscoelastic material, meaning its mechanical properties are strain-rate dependent. At higher strain rates (e.g., high-speed motor vehicle trauma), cortical bone becomes stiffer (exhibits an increased modulus of elasticity), sustains higher loads before failing (increased ultimate strength), and absorbs more energy before fracture compared to slower loading rates.

Question 7943

Topic: 1. General Principles & Basic Science

A basic science researcher is analyzing a full-thickness sample of human articular cartilage. Compared to the superficial tangential zone, the deep zone of normal articular cartilage is characterized by which of the following?

. Higher water content and collagen fibers oriented parallel to the joint surface
. Lower proteoglycan content and round chondrocytes
. Higher proteoglycan content and collagen fibers oriented perpendicular to the joint surface
. Highest concentration of collagen and flattened chondrocytes
. Lower compressive modulus and random collagen orientation

Correct Answer & Explanation

. Higher proteoglycan content and collagen fibers oriented perpendicular to the joint surface

Explanation

The deep zone (radial zone) of articular cartilage has the highest proteoglycan content, the lowest water content, and thick collagen fibers oriented perpendicular to the joint surface to resist high compressive forces. The superficial (tangential) zone has the highest water content, highest collagen content, flattened chondrocytes, and collagen fibers oriented parallel to the surface to resist shear forces.

Question 7944

Topic: Physiology & Rehabilitation

A 24-year-old female is undergoing physical therapy for patellofemoral pain syndrome. Her therapist prescribes a rehabilitation protocol utilizing both open and closed kinetic chain exercises. To minimize the patellofemoral joint reaction force (PFJRF) and resultant joint stress, in which ranges of motion are open and closed kinetic chain exercises respectively most safely performed?

. Open chain: 0 to 45 degrees of flexion; Closed chain: 0 to 45 degrees of flexion
. Open chain: 90 to 45 degrees of flexion; Closed chain: 0 to 45 degrees of flexion
. Open chain: 0 to 45 degrees of flexion; Closed chain: 90 to 45 degrees of flexion
. Open chain: 90 to 45 degrees of flexion; Closed chain: 90 to 45 degrees of flexion
. Open chain: 45 to 0 degrees of flexion; Closed chain: 45 to 0 degrees of flexion

Correct Answer & Explanation

. Open chain: 90 to 45 degrees of flexion; Closed chain: 0 to 45 degrees of flexion

Explanation

In open kinetic chain (OKC) exercises (e.g., seated leg extension), the PFJRF and stress are highest in early flexion (0-45 degrees) due to decreasing patellofemoral contact area and an increasing lever arm of the lower leg; therefore, OKC is safest performed in deeper flexion (90 to 45 degrees). Conversely, in closed kinetic chain (CKC) exercises (e.g., squats), the PFJRF and stress are highest in deep flexion due to the significantly increased quadriceps force required to resist the body weight lever arm; thus, CKC is safest in early flexion (0-45 degrees).

Question 7945

Topic: Biomechanics & Biomaterials

The addition of antibiotics to polymethylmethacrylate (PMMA) bone cement is routinely used for the treatment of periprosthetic joint infection. To optimize the elution profile and mechanical properties of an antibiotic-loaded PMMA spacer, which of the following principles must be adhered to?

. Antibiotics should be provided in liquid form to enhance homogenous distribution and rapid elution
. Increasing the porosity of the cement by adding more monomer will increase antibiotic elution and mechanical strength
. The chosen antibiotic must be thermally stable to withstand the exothermic polymerization reaction
. Total antibiotic dose should exceed 20% of the cement powder weight to ensure sustained long-term release above the MIC
. Adding antibiotics under a strict vacuum mixing environment maximizes elution rates compared to hand mixing

Correct Answer & Explanation

. The chosen antibiotic must be thermally stable to withstand the exothermic polymerization reaction

Explanation

PMMA polymerization is highly exothermic, reaching core temperatures that can easily degrade heat-sensitive medications. Therefore, antibiotics added to PMMA must be thermally stable (e.g., vancomycin, tobramycin, gentamicin). Liquid antibiotics severely degrade the mechanical properties of PMMA. Doses exceeding 10-15% significantly compromise the structural integrity of the cement. Furthermore, hand mixing (rather than vacuum mixing) is preferred for spacer creation because it increases porosity, which beneficially increases the surface area for antibiotic elution.

Question 7946

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with chronic kidney disease presents with secondary hyperparathyroidism. The persistently elevated levels of parathyroid hormone (PTH) have a profound effect on bone remodeling. Which of the following accurately describes the primary cellular mechanism by which PTH stimulates bone resorption?

. Direct binding of PTH to receptors on osteoclasts, leading to the release of cathepsin K
. Binding to receptors on osteoblasts, stimulating the expression of RANKL and decreasing the secretion of osteoprotegerin (OPG)
. Binding to receptors on osteocytes, inducing apoptosis and the subsequent recruitment of osteoclast precursors
. Direct stimulation of the renal hydroxylation of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D, which solely mediates osteoclast activation
. Inhibition of calcitonin secretion from the parafollicular C-cells of the thyroid, removing the inhibitory effect on osteoclasts

Correct Answer & Explanation

. Binding to receptors on osteoblasts, stimulating the expression of RANKL and decreasing the secretion of osteoprotegerin (OPG)

Explanation

Osteoclasts do not possess receptors for Parathyroid Hormone (PTH). Instead, PTH binds to specific receptors on osteoblasts, stimulating them to upregulate the expression of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL) and downregulate the secretion of Osteoprotegerin (OPG), a decoy receptor. The increased RANKL binds to RANK on osteoclast precursors, driving their differentiation and activation into mature, active bone-resorbing osteoclasts.

Question 7947

Topic: Biomechanics & Biomaterials

A 65-year-old male undergoes revision total hip arthroplasty due to an adverse local tissue reaction. Intraoperatively, significant black debris and tissue necrosis are noted localized strictly around the modular head-neck taper junction, while the articular bearing surfaces show minimal wear. What is the primary mechanism of corrosion initiating at this specific modular interface?

. Galvanic corrosion
. Mechanically assisted crevice corrosion (MACC)
. Pitting corrosion
. Intergranular corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Mechanically assisted crevice corrosion (MACC)

Explanation

Modular tapers in total joint arthroplasty are primarily susceptible to mechanically assisted crevice corrosion (MACC). This process is initiated by fretting (micromotion) which disrupts the protective passive titanium oxide layer. Once the oxide layer is breached, crevice corrosion ensues in the oxygen-depleted, acidic environment of the taper junction, leading to the release of metal ions and subsequent adverse local tissue reactions (ALTR).

Question 7948

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis sustains a distal radius fracture. She is started on daily subcutaneous teriparatide to improve bone mass and potentially assist with fracture healing. Through which primary cellular mechanism does intermittent administration of this medication promote an anabolic effect on bone?

. Inhibition of osteoclast ruffled border formation via disruption of the mevalonate pathway
. Stimulation of Wnt/beta-catenin signaling via downregulation of sclerostin in osteocytes
. Direct inhibition of RANKL secretion by osteoblasts
. Activation of the calcium-sensing receptor on parafollicular C-cells
. Increased expression of osteoprotegerin (OPG) from bone marrow macrophages

Correct Answer & Explanation

. Stimulation of Wnt/beta-catenin signaling via downregulation of sclerostin in osteocytes

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. While continuous PTH exposure is catabolic, intermittent PTH administration is highly anabolic. It exerts its anabolic effect by increasing osteoblast lifespan (preventing apoptosis), stimulating osteoblast differentiation, and activating the Wnt/beta-catenin signaling pathway. A key part of this mechanism is the downregulation of sclerostin (a Wnt inhibitor encoded by the SOST gene) expressed by osteocytes.

Question 7949

Topic: Physiology & Rehabilitation

A physical therapist designs a rehabilitation protocol for a patient recovering from a hamstring injury, emphasizing exercises that generate the absolute maximum muscle force to stimulate tendon remodeling. According to muscle physiology and the force-velocity relationship, which type of muscle contraction generates the highest maximal tension?

. Fast concentric contraction
. Slow concentric contraction
. Isometric contraction
. Slow eccentric contraction
. Fast eccentric contraction

Correct Answer & Explanation

. Fast eccentric contraction

Explanation

The force-velocity curve of muscle physiology demonstrates that eccentric contractions (lengthening under tension) generate significantly more force than isometric and concentric contractions. Within eccentric contractions, higher velocity (fast eccentric) yields higher tension/force up to a plateau, whereas in concentric contractions, slower velocity generates more force. Therefore, fast eccentric contractions are capable of producing the greatest absolute muscle force.

Question 7950

Topic: Surgical Anatomy & Approaches
A 28-year-old male sustains a midshaft humerus fracture resulting in an acute radial nerve palsy. At 4 weeks, EMG confirms denervation. During the ongoing process of Wallerian degeneration and subsequent peripheral nerve regeneration, which cell type undergoes dedifferentiation, forms the bands of Büngner, and upregulates the production of neurotrophic factors (e.g., NGF) to guide the regenerating axon?
. Fibroblasts
. Macrophages
. Schwann cells
. Astrocytes
. Perineurial cells

Correct Answer & Explanation

. Schwann cells

Explanation

Following a peripheral nerve injury, Schwann cells in the distal nerve stump undergo a massive phenotypic modulation. They dedifferentiate, assist in initial myelin clearance, proliferate, and align to form longitudinal conduits known as the bands of Büngner. Crucially, they upregulate the synthesis of neurotrophic factors (such as Nerve Growth Factor, NGF) and cell adhesion molecules that physically and chemically guide the regenerating axonal sprouts.

Question 7951

Topic: 1. General Principles & Basic Science
A 68-year-old female is scheduled for a bilateral total knee arthroplasty. To minimize perioperative blood loss, the surgeon administers intravenous tranexamic acid (TXA). What is the specific molecular mechanism of action of tranexamic acid in this setting?
. Irreversible inhibition of cyclooxygenase-1 (COX-1)
. Competitive inhibition of vitamin K epoxide reductase
. Direct inhibition of Factor Xa in the coagulation cascade
. Reversible blockade of lysine binding sites on plasminogen
. Activation of antithrombin III leading to thrombin neutralization

Correct Answer & Explanation

. Reversible blockade of lysine binding sites on plasminogen

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It acts as a powerful antifibrinolytic agent by reversibly binding to the lysine receptor sites on plasminogen. This competitive binding prevents plasminogen from adhering to fibrin. Consequently, it inhibits the activation of plasminogen to plasmin by tissue plasminogen activator (tPA), effectively stabilizing the fibrin clot and preventing premature fibrinolysis.

Question 7952

Topic: Biomechanics & Biomaterials

A researcher is performing biomechanical testing on a novel synthetic graft for anterior cruciate ligament (ACL) reconstruction. The graft is clamped in a testing machine, instantly elongated to a fixed length, and held constant over time. The researcher observes that the force required to maintain this exact length progressively decreases. Which viscoelastic property is being demonstrated?

. Creep
. Hysteresis
. Stress relaxation
. Isotropic elasticity
. Fatigue failure

Correct Answer & Explanation

. Stress relaxation

Explanation

Viscoelastic materials exhibit time-dependent mechanical behaviors. 'Stress relaxation' is defined as the steady decrease in stress (or force) over time when the material is deformed and held at a constant strain (or length). Conversely, 'creep' is the progressive deformation (increase in length/strain) over time when a material is subjected to a constant load (or force). 'Hysteresis' refers to the energy lost as heat during the loading and unloading cycle.

Question 7953

Topic: Biology, Genetics & Bone Healing

A 35-year-old female presents with a destructive, eccentric, lytic lesion in the distal femur extending to the subchondral bone. Biopsy confirms a Giant Cell Tumor of Bone (GCTB). Due to the size and joint proximity, neoadjuvant denosumab is prescribed. Denosumab exerts its therapeutic effect in this condition by targeting which molecule, and which cell population primarily expresses this target?

. Targets RANK; expressed by the reactive multinucleated giant cells
. Targets RANKL; expressed by the neoplastic mononuclear stromal cells
. Targets Osteoprotegerin (OPG); expressed by the neoplastic mononuclear stromal cells
. Targets RANKL; expressed by the reactive multinucleated giant cells
. Targets Macrophage Colony-Stimulating Factor (M-CSF); expressed by osteoblasts

Correct Answer & Explanation

. Targets RANKL; expressed by the neoplastic mononuclear stromal cells

Explanation

Denosumab is a fully human monoclonal antibody that binds to and inhibits Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). In Giant Cell Tumor of Bone (GCTB), the neoplastic cells are actually the spindle-shaped mononuclear stromal cells. These stromal cells pathologically overexpress RANKL, which aggressively recruits and stimulates the formation of the reactive, non-neoplastic multinucleated giant cells (osteoclasts) responsible for the massive bone destruction. Thus, Denosumab targets RANKL secreted by the neoplastic mononuclear stromal cells.

Question 7954

Topic: Biology, Genetics & Bone Healing

A 45-year-old man undergoes a posterolateral lumbar fusion using recombinant human bone morphogenetic protein-2 (rhBMP-2). Upon binding to its specific cell surface receptor, which of the following intracellular signaling molecules is directly phosphorylated to propagate the osteoinductive signal?

. JAK
. STAT
. SMAD
. Beta-catenin
. NF-kappaB

Correct Answer & Explanation

. SMAD

Explanation

Bone morphogenetic proteins (BMPs) are members of the TGF-beta superfamily. When a BMP binds to its specific heterodimeric serine/threonine kinase receptor, it causes the intracellular phosphorylation of receptor-regulated SMADs (typically SMAD 1, 5, and 8). These phosphorylated SMADs then form a complex with a Co-SMAD (SMAD 4) and translocate to the nucleus to regulate the transcription of osteogenic genes, such as Runx2. Beta-catenin is involved in the Wnt signaling pathway. The JAK/STAT pathway is typically utilized by cytokines, and NF-kappaB is central to the RANKL pathway in osteoclasts.

Question 7955

Topic: Biomechanics & Biomaterials

A 62-year-old woman presents with groin pain three years after a total hip arthroplasty using a cobalt-chromium modular head on a titanium alloy stem. Joint aspiration is negative for infection, but MRI demonstrates a solid periprosthetic pseudotumor. Revision surgery reveals black debris at the head-neck junction. Which of the following mechanisms is primarily responsible for the generation of this specific debris?

. Abrasive wear
. Adhesive wear
. Fretting corrosion
. Galvanic corrosion alone
. Third-body wear

Correct Answer & Explanation

. Fretting corrosion

Explanation

The scenario describes trunnionosis, which manifests as an adverse local tissue reaction (ALTR) or pseudotumor due to metal debris at the modular head-neck junction. This is primarily caused by mechanically assisted crevice corrosion (MACC), also known as fretting corrosion. Micro-motion at the junction mechanically disrupts the protective passive oxide layer on the metals (fretting), which exposes the underlying reactive metal to the physiologic fluid environment. This accelerates electrochemical dissolution (corrosion). While galvanic corrosion plays a role due to dissimilar metals, the primary driver at a modular THA junction is the mechanical disruption coupled with crevice corrosion.

Question 7956

Topic: Biomechanics & Biomaterials

A researcher is studying the biomechanical properties of human articular cartilage in an osteoarthritic knee model. During normal joint kinematics, which zone of articular cartilage is primarily responsible for resisting shear stresses, and what is the predominant orientation of its collagen fibers?

. Superficial zone; parallel to the articular surface
. Transitional zone; oblique to the articular surface
. Deep zone; perpendicular to the articular surface
. Calcified zone; random orientation
. Tidemark; parallel to the articular surface

Correct Answer & Explanation

. Superficial zone; parallel to the articular surface

Explanation

Articular cartilage is divided into distinct structural zones. The superficial (tangential) zone makes up the top 10-20% of articular cartilage and has a high concentration of water and collagen (predominantly Type II). The collagen fibers in this zone are densely packed and oriented strictly parallel to the articular surface. This orientation provides the highest tensile strength and is primarily responsible for resisting the severe shear stresses generated during joint motion. In contrast, the deep zone features collagen fibers oriented perpendicularly to resist compressive loads.

Question 7957

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is routinely utilized in major orthopedic procedures to reduce perioperative blood loss. Which of the following best describes its mechanism of action at the molecular level?
. Direct inhibition of Factor Xa
. Reversible, competitive antagonism of the lysine-binding sites on plasminogen
. Irreversible acetylation of cyclooxygenase-1
. Enhancement of antithrombin III activity
. Direct inhibition of thrombin (Factor IIa)

Correct Answer & Explanation

. Reversible, competitive antagonism of the lysine-binding sites on plasminogen

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It acts as a potent antifibrinolytic agent by reversibly and competitively binding to the lysine-binding sites on plasminogen molecules. This action prevents plasminogen from binding to the surface of fibrin, thereby inhibiting its subsequent activation into plasmin. Without active plasmin, the degradation (fibrinolysis) of formed blood clots is halted, preserving the integrity of the clot and reducing surgical bleeding.

Question 7958

Topic: Biology, Genetics & Bone Healing
A 28-year-old athlete undergoes an Achilles tendon repair. During the remodeling phase of tendon healing, the biomechanical strength of the tendon gradually increases. This process is primarily driven by the replacement of the initial scar tissue matrix with a more organized collagen structure. Which of the following best describes the predominant collagen transition during this phase?
. Type I collagen is replaced by Type II collagen
. Type I collagen is replaced by Type III collagen
. Type II collagen is replaced by Type X collagen
. Type III collagen is replaced by Type I collagen
. Type X collagen is replaced by Type I collagen

Correct Answer & Explanation

. Type III collagen is replaced by Type I collagen

Explanation

Tendon healing proceeds through three overlapping phases: inflammatory, proliferative (repair), and remodeling. During the early proliferative phase, fibroblasts primarily synthesize Type III collagen, which is disorganized, thinner, and mechanically weak. During the remodeling phase (which can last for months to years), this provisional Type III collagen matrix is gradually degraded and replaced by mature Type I collagen. The newly synthesized Type I collagen fibers orient longitudinally parallel to the axis of tension, which dramatically increases the tensile strength of the healed tendon.

Question 7959

Topic: Surgical Anatomy & Approaches
A 34-year-old man sustains a mid-shaft humerus fracture resulting in a radial nerve palsy. Electromyography (EMG) performed 3 weeks later shows fibrillation potentials in the brachioradialis. Which of the following processes predominantly characterizes the Wallerian degeneration occurring distal to the injury site?
. Proliferation of Schwann cells and upregulation of neurotrophic factors
. Immediate death of the anterior horn cell in the spinal cord
. Remyelination of the intact axon by oligodendrocytes
. Phagocytosis of the myelin sheath solely by circulating neutrophils
. Retrograde axonal transport of inflammatory cytokines leading to cortical reorganization

Correct Answer & Explanation

. Proliferation of Schwann cells and upregulation of neurotrophic factors

Explanation

Wallerian degeneration is the process of anterograde breakdown of the axon and myelin sheath distal to a nerve injury (axonotmesis or neurotmesis). Following the injury, local macrophages and Schwann cells phagocytose the axonal and myelin debris (neutrophils are not the primary phagocytes here). Critically, Schwann cells then proliferate within the remaining endoneurial tubes and upregulate neurotrophic factors (such as NGF and BDNF) and surface adhesion molecules. These cells align to form the Bands of Büngner, which provide a supportive microenvironment and physically guide the regenerating axonal sprouts from the proximal stump toward the target organ.

Question 7960

Topic: Biology, Genetics & Bone Healing

A 70-year-old woman with severe osteoporosis and a recent vertebral compression fracture is started on romosozumab therapy. What is the primary mechanism of action of this medication at the cellular and molecular level?

. Inhibition of farnesyl pyrophosphate synthase in osteoclasts
. Binding to RANKL to prevent osteoclast activation and survival
. Monoclonal antibody binding to sclerostin, thereby enhancing Wnt/beta-catenin signaling
. Recombinant PTH analog that intermittently stimulates osteoblast activity
. Selective estrogen receptor modulation to decrease bone resorption

Correct Answer & Explanation

. Monoclonal antibody binding to sclerostin, thereby enhancing Wnt/beta-catenin signaling

Explanation

Romosozumab is a monoclonal antibody that targets and binds to sclerostin, a glycoprotein secreted by osteocytes. Sclerostin normally acts as an endogenous inhibitor of the Wnt/beta-catenin signaling pathway, which is crucial for osteoblast differentiation and bone formation. By inhibiting sclerostin, romosozumab enhances Wnt signaling, resulting in a dual effect: markedly increasing bone formation and moderately decreasing bone resorption.

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