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1. General Principles & Basic Science MCQs

Practice Set 585 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 11681

Topic: 1. General Principles & Basic Science

Which of the following characteristics accurately describes the superficial (tangential) zone of articular cartilage compared to the deep zone?

. Highest proteoglycan content
. Lowest water content
. Collagen fibers oriented perpendicularly to the joint surface
. Highest concentration of chondrocytes
. Lowest tensile strength

Correct Answer & Explanation

. Lowest tensile strength

Explanation

The superficial zone of articular cartilage has the highest water content, the highest density of chondrocytes (which are flattened), and collagen fibers oriented parallel to the joint surface to resist shear forces. It has the lowest proteoglycan content. The deep zone has the highest proteoglycan content and collagen perpendicular to the joint surface.

Question 11682

Topic: Biomechanics & Biomaterials

In materials science, the area under the entire stress-strain curve up to the point of failure represents the material's:

. Stiffness
. Yield strength
. Toughness
. Ductility
. Ultimate tensile strength

Correct Answer & Explanation

. Toughness

Explanation

The area under the entire stress-strain curve represents toughness, which is the amount of energy a material can absorb before fracturing. Stiffness is represented by the slope of the elastic region (Young's modulus). Yield strength is the point where plastic deformation begins. Ductility is the amount of plastic deformation before failure.

Question 11683

Topic: Biomechanics & Biomaterials
High-dose gamma irradiation of ultra-high-molecular-weight polyethylene (UHMWPE) followed by remelting is primarily performed to improve which of the following properties?
. Fracture toughness
. Fatigue strength
. Wear resistance
. Oxidation resistance
. Yield strength

Correct Answer & Explanation

. Wear resistance

Explanation

Highly cross-linking UHMWPE significantly increases its wear resistance by forming covalent bonds between polymer chains. However, this process decreases mechanical properties such as fracture toughness, fatigue strength, and ultimate tensile strength. Remelting or annealing is done subsequently to eliminate free radicals and prevent oxidation, though remelting further reduces mechanical properties compared to annealing.

Question 11684

Topic: Biology, Genetics & Bone Healing

Which of the following cell types is the primary effector responsible for recognizing polyethylene wear debris and initiating the biological cascade that leads to periprosthetic osteolysis?

. Osteoblasts
. Osteoclasts
. Macrophages
. T-lymphocytes
. Polymorphonuclear leukocytes

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages phagocytose polyethylene particles (optimally sized between 0.1 and 10 micrometers) and release pro-inflammatory cytokines such as IL-1, IL-6, TNF-alpha, and PGE2. This stimulates osteoblasts to express RANKL, which subsequently activates osteoclasts, leading to bone resorption and periprosthetic osteolysis.

Question 11685

Topic: Biology, Genetics & Bone Healing

Denosumab is used in the treatment of osteoporosis and giant cell tumors of bone. It functions by mimicking the action of which naturally occurring molecule?

. RANK
. RANKL
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Sclerostin

Correct Answer & Explanation

. RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from binding to the RANK receptor on osteoclast precursors. This mechanism directly mimics the action of osteoprotegerin (OPG), a soluble decoy receptor produced by osteoblasts that competitively binds to RANKL to inhibit osteoclastogenesis.

Question 11686

Topic: 1. General Principles & Basic Science

Following a peripheral nerve transection and subsequent epineurial repair, at approximately what rate does axonal regeneration occur once the growth cone has crossed the repair site?

. 0.1 mm/day
. 1 mm/day
. 5 mm/day
. 10 mm/day
. 1 inch/day

Correct Answer & Explanation

. 1 mm/day

Explanation

After peripheral nerve injury and Wallerian degeneration, axonal regeneration occurs at a rate of approximately 1 mm per day (or about 1 inch per month) after an initial latent period. This rate is determined by the slow component of axonal transport.

Question 11687

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, primary (contact) bone healing without callus formation requires the interfragmentary strain to be kept below what percentage?

. 2%
. 5%
. 10%
. 15%
. 20%

Correct Answer & Explanation

. 5%

Explanation

Perren's strain theory dictates the type of tissue that can form in a fracture gap. Absolute stability with interfragmentary strain < 2% allows for primary bone healing (cutting cones) without visible callus. Strain between 2% and 10% promotes secondary bone healing via endochondral ossification (callus formation). Strain > 10% leads to nonunion (fibrous tissue).

Question 11688

Topic: Biomechanics & Biomaterials

A 45-year-old patient undergoes an Ilizarov frame application with gradual distraction for a tibial defect. Over several hours after tensioning the wires, the tension in the wires gradually decreases without any change in their length. This phenomenon is known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the stress (tension) in a material decreases over time when it is held at a constant strain (constant length). Creep is the progressive deformation (increase in strain) over time under a constant load (stress). Hysteresis represents energy lost during the loading and unloading cycles of a viscoelastic material.

Question 11689

Topic: Biology, Genetics & Bone Healing

Romosozumab is a bone-building medication that binds to and inhibits sclerostin. By inhibiting sclerostin, which intracellular signaling pathway is primarily disinhibited, leading to increased bone formation?

. Notch signaling pathway
. Hedgehog signaling pathway
. Wnt/Beta-catenin pathway
. Smad 1/5/8 pathway
. JAK/STAT pathway

Correct Answer & Explanation

. Wnt/Beta-catenin pathway

Explanation

Sclerostin, a glycoprotein secreted primarily by osteocytes, binds to LRP5/6 receptors on osteoblasts and inhibits the canonical Wnt/Beta-catenin signaling pathway. By inhibiting sclerostin with romosozumab, the Wnt pathway is activated, leading to the accumulation of Beta-catenin, which translocates to the nucleus to upregulate osteoblastic bone formation.

Question 11690

Topic: 1. General Principles & Basic Science

During the formation of a bacterial biofilm on an orthopedic implant, which phenomenon regulates the coordinated shift from the reversible attachment phase to irreversible adherence and extracellular polymeric substance (EPS) production based on bacterial density?

. Chemotaxis
. Quorum sensing
. Opsonization
. Phagocytosis evasion
. Galvanic corrosion

Correct Answer & Explanation

. Quorum sensing

Explanation

Quorum sensing is a cell-to-cell communication mechanism used by bacteria that allows them to coordinate gene expression based on local population density. Once a critical concentration of signaling molecules (autoinducers) is reached, genes responsible for biofilm formation (EPS matrix production) and virulence factors are upregulated, transitioning the bacteria from a planktonic state to a sessile, biofilm-protected state.

Question 11691

Topic: Physiology & Rehabilitation

A marathon runner predominantly relies on specific muscle fibers during a race. Which of the following characteristics best describes the primary muscle fiber type utilized during this endurance activity?

. Fast twitch, anaerobic, low myoglobin content
. Fast twitch, aerobic, high glycogen content
. Slow twitch, oxidative metabolism, high myoglobin content
. Slow twitch, glycolytic metabolism, fast fatigue rate
. Intermediate twitch, large fiber diameter, low capillary density

Correct Answer & Explanation

. Slow twitch, oxidative metabolism, high myoglobin content

Explanation

Endurance athletes like marathon runners rely heavily on Type I muscle fibers. These are slow-twitch fibers that utilize oxidative (aerobic) metabolism. They are rich in mitochondria, capillary density, and myoglobin, which gives them a red appearance and makes them highly resistant to fatigue.

Question 11692

Topic: 1. General Principles & Basic Science

When a stainless steel screw is used in conjunction with a titanium plate in an orthopedic construct, corrosion may occur due to the electrochemical potential difference between the two metals. In this scenario, what role does the stainless steel component typically play?

. It acts as the cathode and undergoes oxidation
. It acts as the anode and is protected from corrosion
. It acts as the anode and preferentially corrodes
. It acts as the cathode and preferentially corrodes
. It remains inert due to its high titanium content

Correct Answer & Explanation

. It acts as the anode and preferentially corrodes

Explanation

In a galvanic couple formed by mixed metals (e.g., stainless steel and titanium), the less noble (more reactive) metal becomes the anode and undergoes preferential corrosion (oxidation). Titanium is more noble (cathodic) compared to standard orthopedic stainless steel (anodic), which increases the risk of the stainless steel corroding when they are in direct contact in an electrolytic environment (like body fluid).

Question 11693

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) is commonly used to reduce perioperative blood loss in orthopedic surgery. Its primary mechanism of action involves:
. Inhibition of cyclooxygenase, preventing thromboxane A2 synthesis
. Direct inhibition of Factor Xa
. Binding to plasminogen, preventing its activation to plasmin
. Activation of antithrombin III
. Stimulation of von Willebrand factor release

Correct Answer & Explanation

. Binding to plasminogen, preventing its activation to plasmin

Explanation

Tranexamic acid is an antifibrinolytic agent. It functions as a synthetic analog of the amino acid lysine and reversibly binds to the lysine receptor sites on plasminogen. This competitive binding prevents plasminogen from being converted to the active enzyme plasmin, thereby preventing the degradation of fibrin clots (fibrinolysis).

Question 11694

Topic: Infection, Pharmacology & VTE

A patient is started on warfarin for DVT prophylaxis following total hip arthroplasty. Warfarin inhibits the vitamin K-dependent gamma-carboxylation of several coagulation factors. Which of the following factors has the shortest half-life and is affected first, potentially causing a transient prothrombotic state?

. Factor II (Prothrombin)
. Factor VII
. Factor IX
. Factor X
. Protein C

Correct Answer & Explanation

. Protein C

Explanation

Warfarin inhibits vitamin K epoxide reductase, affecting Factors II, VII, IX, X, and Proteins C and S. Protein C and Factor VII have the shortest half-lives. However, because Protein C is an endogenous anticoagulant, its rapid depletion prior to the depletion of the procoagulant factors (II, IX, X) can cause a transient hypercoagulable (prothrombotic) state, which is why bridging with heparin is historically used in high-risk patients.

Question 11695

Topic: 1. General Principles & Basic Science
Following a rupture of the medial collateral ligament (MCL), the healing process progresses through overlapping phases. During the remodeling phase, what is the primary change occurring at the cellular/extracellular matrix level?
. Infiltration of polymorphonuclear leukocytes
. Synthesis of an exuberant Type III collagen matrix
. Replacement of Type III collagen with Type I collagen
. Formation of a hematoma
. Angiogenesis and fibroblast migration

Correct Answer & Explanation

. Replacement of Type III collagen with Type I collagen

Explanation

Ligament healing occurs in three phases: inflammatory, proliferative, and remodeling. During the proliferative phase, fibroblasts synthesize predominantly Type III collagen, which forms disorganized scar tissue. During the remodeling phase (which can last months to years), this Type III collagen is gradually replaced by stronger, more organized Type I collagen, and the fibers align along the lines of mechanical stress.

Question 11696

Topic: Biology, Genetics & Bone Healing

A 60-year-old female presents with diffuse bone pain and proximal muscle weakness. Laboratory studies reveal a low serum calcium, low serum 25-hydroxyvitamin D, elevated parathyroid hormone (PTH), and elevated alkaline phosphatase. What is the most likely pathological finding on a bone biopsy?

. Thickened woven bone with a mosaic pattern of lamellar bone
. Increased osteoid seam width and unmineralized bone matrix
. Empty lacunae with necrotic marrow architecture
. Massive replacement of marrow by plasma cells
. Hypermineralized bone with defective osteoclasts

Correct Answer & Explanation

. Increased osteoid seam width and unmineralized bone matrix

Explanation

The patient's clinical and laboratory profile is diagnostic of osteomalacia caused by severe Vitamin D deficiency (low Ca, low Vit D, secondary hyperparathyroidism, and elevated ALP). Histologically, osteomalacia is characterized by a defect in bone mineralization, leading to an accumulation of unmineralized osteoid (increased osteoid seam width/thickness). A mosaic pattern is seen in Paget's disease. Empty lacunae indicate osteonecrosis. Defective osteoclasts are seen in osteopetrosis.

Question 11697

Topic: Biology, Genetics & Bone Healing

A surgeon decides to use a synthetic bone graft substitute to fill a void after curettage of a benign bone cyst.

Which of the following bone graft substitutes is characterized as being purely osteoconductive without any native osteoinductive or osteogenic properties?

. Demineralized bone matrix (DBM)
. Calcium phosphate
. Recombinant human bone morphogenetic protein-2 (rhBMP-2)
. Autologous iliac crest bone graft
. Bone marrow aspirate concentrate (BMAC)

Correct Answer & Explanation

. Calcium phosphate

Explanation

Calcium phosphate ceramics provide a three-dimensional scaffold for bone ingrowth (osteoconduction) but lack the cells (osteogenic) and native proteins (osteoinductive) necessary to stimulate de novo bone formation. Demineralized bone matrix (DBM) contains varying levels of inherent osteoinductive proteins depending on processing, while autologous bone graft provides osteoconductive, osteoinductive, and osteogenic properties.

Question 11698

Topic: Biomechanics & Biomaterials

During fracture fixation, a surgeon inadvertently uses a stainless steel screw to secure a titanium alloy plate. Several months later, rapid corrosion is noted at the screw-plate interface. Which of the following electrochemical phenomena best explains this specific type of corrosion?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic environment (such as physiologic tissue fluid or blood). An electrochemical cell is created, and the less noble metal acts as the anode, undergoing accelerated corrosion while protecting the more noble metal.

Question 11699

Topic: 1. General Principles & Basic Science

Articular cartilage relies on a precise architectural arrangement to distribute loads. Which zone of articular cartilage contains the highest concentration of proteoglycans and the lowest water content?

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

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone of articular cartilage has the lowest water content and the highest proteoglycan concentration. Chondrocytes in this zone are arranged in vertical columns parallel to collagen fibers, optimizing the tissue's resistance to compressive forces. Conversely, the superficial zone has the highest water content and lowest proteoglycan concentration.

Question 11700

Topic: Biomechanics & Biomaterials

During mechanical testing of a native human ligament, the initial non-linear portion of the stress-strain curve exhibits increasing stiffness with elongation. What structural event primarily dictates this initial 'toe region'?

. Microscopic failure of individual collagen fibers
. Plastic deformation of the extracellular matrix
. Irreversible sliding of proteoglycan molecules
. Uncrimping of the resting wavy collagen fibers
. Macroscopic yield of the entire ligament structure

Correct Answer & Explanation

. Uncrimping of the resting wavy collagen fibers

Explanation

The non-linear 'toe region' of the stress-strain curve for ligaments and tendons is caused by the uncrimping (straightening) of the naturally wavy collagen fibrils. As the fibers straighten, the structure becomes stiffer, transitioning into the linear elastic region where further deformation stretches the actual collagen molecules.

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