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1. General Principles & Basic Science MCQs

Practice Set 426 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 8501

Topic: Biomechanics & Biomaterials

A researcher is studying articular cartilage biomechanics. Which zone of articular cartilage possesses the highest concentration of water and has collagen fibers oriented parallel to the joint surface?

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

Correct Answer & Explanation

. Superficial zone (tangential)

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content (up to 80%), the lowest proteoglycan content, and features collagen fibers (primarily type II) arranged parallel to the articular surface. This specialized structure allows the cartilage to resist shear stresses associated with joint motion.

Question 8502

Topic: Biomechanics & Biomaterials

In comparing the mechanical properties of cortical bone to cancellous bone on a stress-strain curve, cortical bone demonstrates which of the following characteristics?

. Lower Young's modulus and lower yield point
. Higher Young's modulus and lower ultimate strain
. Lower Young's modulus and higher ultimate strain
. Higher Young's modulus and higher ultimate strain
. Equal Young's modulus and higher yield point

Correct Answer & Explanation

. Higher Young's modulus and lower ultimate strain

Explanation

Cortical bone is much stiffer than cancellous bone, meaning it has a steeper slope in the elastic region of the stress-strain curve, which translates to a higher Young's modulus. However, it is more brittle and fails at a lower percentage of deformation (lower ultimate strain, typically ~2%), whereas cancellous bone is highly porous and can undergo significant deformation before ultimate failure.

Question 8503

Topic: Biomechanics & Biomaterials

A 55-year-old man undergoes a revision total hip arthroplasty. The surgeon plans to use a titanium alloy (Ti-6Al-4V) femoral stem with a cobalt-chromium (CoCr) head. Which of the following is the primary mechanism that mitigates severe galvanic corrosion between these two dissimilar metals in vivo?

. Similar galvanic potentials of the two metals
. Spontaneous formation of a passivating oxide layer on the titanium surface
. Use of a polyethylene liner to electrically isolate the components
. Addition of molybdenum to the cobalt-chromium alloy
. High oxygen tension in the synovial fluid

Correct Answer & Explanation

. Spontaneous formation of a passivating oxide layer on the titanium surface

Explanation

When combining titanium and cobalt-chromium in vivo, galvanic corrosion is minimized primarily by the spontaneous formation of dense, passivating oxide layers on both metals (such as TiO2 for titanium). This passivating layer electrically isolates the bulk metal from the physiological fluid (electrolyte), drastically increasing the resistance and minimizing the corrosion current.

Question 8504

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) has been approved by the FDA as an alternative to autogenous bone graft for acute, open tibial shaft fractures treated with an intramedullary nail?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for acute, open tibial shaft fractures stabilized with an intramedullary nail, as well as for certain anterior lumbar interbody fusions. It induces bone formation via the SMAD signaling pathway. BMP-7 (OP-1) previously held a humanitarian device exemption for recalcitrant tibial nonunions but is not approved for acute open tibial fractures.

Question 8505

Topic: Surgical Anatomy & Approaches

A patient sustains a mid-shaft humerus fracture and presents with a dense radial nerve palsy. Electromyography (EMG) performed at 3 weeks shows fibrillation potentials and positive sharp waves in the brachioradialis. This finding is indicative of which of the following?

. Early reinnervation
. A neuropraxia injury
. Wallerian degeneration of the distal nerve segment
. Intact axons with a conduction block
. Successful collateral sprouting

Correct Answer & Explanation

. Wallerian degeneration of the distal nerve segment

Explanation

Fibrillation potentials and positive sharp waves on an EMG typically appear 2-3 weeks after a nerve injury and indicate denervation of the muscle fibers. This means the axon has been physically disrupted (as seen in axonotmesis or neurotmesis) and has undergone Wallerian degeneration distal to the site of injury. A neuropraxia (conduction block) leaves the axon intact and does not produce fibrillation potentials.

Question 8506

Topic: Physiology & Rehabilitation

During a marathon, an athlete primarily relies on slow-twitch (Type I) muscle fibers. Compared to fast-twitch (Type IIb) muscle fibers, Type I fibers are characterized by which of the following profiles?

. High glycogen content, low mitochondrial density, and rapid fatigue
. Low oxidative capacity, high glycolytic capacity, and low myoglobin content
. High mitochondrial density, high myoglobin content, and resistance to fatigue
. High myosin ATPase activity, low capillary density, and high anaerobic capacity
. Fast contraction speed, high oxidative capacity, and rapid fatigue

Correct Answer & Explanation

. High mitochondrial density, high myoglobin content, and resistance to fatigue

Explanation

Type I (slow-twitch) muscle fibers are specialized for endurance activities. They are characterized by a high density of mitochondria, high myoglobin content (giving them a characteristic red appearance), dense capillary networks, and high oxidative capacity, which makes them highly resistant to fatigue. Type IIb fibers are fast-twitch, have low myoglobin, rely heavily on anaerobic glycolysis, and fatigue rapidly.

Question 8507

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced volumetric wear rates compared to conventional UHMWPE. However, the process of cross-linking has a known adverse effect on which of the following mechanical properties?
. Ultimate tensile strength only
. Fatigue strength only
. Elastic modulus only
. Yield strength only
. Both ultimate tensile strength and fatigue strength

Correct Answer & Explanation

. Both ultimate tensile strength and fatigue strength

Explanation

Highly cross-linking polyethylene drastically reduces adhesive and abrasive wear. However, it decreases both its ultimate tensile strength and fatigue strength (resistance to crack propagation). To mitigate the reduction in fatigue strength, modern HXLPE is cross-linked with optimal radiation doses and often thermally treated (remelted or annealed) to eliminate free radicals.

Question 8508

Topic: Infection, Pharmacology & VTE

A 65-year-old woman presents with an acutely infected total knee arthroplasty. Cultures from the joint aspiration grow Methicillin-resistant Staphylococcus aureus (MRSA). Which of the following mechanisms is primarily responsible for this organism's methicillin resistance?

. Alteration of bacterial DNA gyrase
. Hyperproduction of beta-lactamase enzyme
. Modification of penicillin-binding protein via the mecA gene (PBP2a)
. Upregulation of transmembrane efflux pumps
. Ribosomal RNA methylation protecting the drug target

Correct Answer & Explanation

. Modification of penicillin-binding protein via the mecA gene (PBP2a)

Explanation

MRSA resistance to beta-lactam antibiotics is primarily mediated by the acquisition of the staphylococcal cassette chromosome mec (SCCmec) containing the mecA gene. This gene encodes for a novel penicillin-binding protein, PBP2a, which has a significantly lower binding affinity for beta-lactam antibiotics, allowing cell wall synthesis to continue even in the presence of these drugs.

Question 8509

Topic: Biomechanics & Biomaterials




When evaluating the mechanical properties of a metallic implant on a stress-strain curve, the point at which the material undergoes non-reversible deformation but continues to bear increasing loads before reaching its ultimate failure is best described as occurring within which of the following regions?

. Elastic region
. Plastic region
. Yield point
. Failure point
. Viscoelastic creep phase

Correct Answer & Explanation

. Plastic region

Explanation

The plastic region on a stress-strain curve represents the phase where the material undergoes irreversible (plastic) deformation but can still accept higher stress before reaching its ultimate tensile strength and eventually failing. The yield point is the specific transition locus between the elastic (reversible) and plastic deformation phases.

Question 8510

Topic: Biology, Genetics & Bone Healing

Sclerostin is a critical regulatory glycoprotein in bone metabolism and is therapeutically targeted by the monoclonal antibody romosozumab. What is the precise cellular mechanism of action by which sclerostin inhibition leads to an increase in bone mass?

. Binding to RANKL to prevent osteoclast activation
. Direct inhibition of the Wnt/beta-catenin signaling pathway in osteoblasts
. Activation of Wnt/beta-catenin signaling by preventing Sclerostin from binding to LRP5/6 receptors
. Direct stimulation of alkaline phosphatase production in the osteocytes
. Upregulation of osteoprotegerin (OPG) production

Correct Answer & Explanation

. Activation of Wnt/beta-catenin signaling by preventing Sclerostin from binding to LRP5/6 receptors

Explanation

Sclerostin (produced by osteocytes) normally inhibits the Wnt/beta-catenin pathway by binding to the LRP5/6 co-receptors on osteoblasts, leading to decreased bone formation. Inhibiting sclerostin prevents this binding, allowing Wnt signaling to proceed unhindered, which drastically increases osteoblast activity and bone formation.

Question 8511

Topic: Biology, Genetics & Bone Healing

Articular cartilage is a highly specialized connective tissue designed to withstand repetitive compressive forces. In the deep (basal) zone of articular cartilage, the arrangement of type II collagen fibers and the morphology of chondrocytes are best described by which of the following statements?

. Collagen fibers are parallel to the joint surface; chondrocytes are flattened.
. Collagen fibers are parallel to the joint surface; chondrocytes are spherical.
. Collagen fibers are perpendicular to the joint surface; chondrocytes are arranged in a columnar orientation.
. Collagen fibers are randomly oriented; chondrocytes are sparse and irregular.
. Collagen fibers are oblique to the joint surface; chondrocytes are hypertrophic.

Correct Answer & Explanation

. Collagen fibers are perpendicular to the joint surface; chondrocytes are arranged in a columnar orientation.

Explanation

In the deep (basal) zone of articular cartilage, collagen type II fibers are arranged perpendicular (vertical) to the joint surface to provide resistance to high compressive loads. The chondrocytes in this zone are typically spherical and arranged in columns parallel to these collagen fibers. The superficial zone, by contrast, contains flattened chondrocytes with fibers running parallel to the articular surface to resist shear forces.

Question 8512

Topic: Biology, Genetics & Bone Healing




During secondary fracture healing in a long bone treated with a cast, the progression from a soft cartilaginous callus to a hard bony callus occurs primarily via which of the following physiological processes?

. Intramembranous ossification
. Endochondral ossification
. Appositional bone growth
. Haversian remodeling
. Creeping substitution

Correct Answer & Explanation

. Endochondral ossification

Explanation

Secondary fracture healing occurs under conditions of relative stability (e.g., casting, intramedullary nailing) and involves callus formation. The critical transition from a soft (cartilage) callus to a hard (woven bone) callus takes place primarily through endochondral ossification. While intramembranous ossification (bone forming directly from mesenchymal cells without a cartilage model) can occur subperiosteally at the periphery of the fracture site, the central bridging of the gap relies on endochondral ossification.

Question 8513

Topic: Infection, Pharmacology & VTE
A 70-year-old patient is scheduled for a primary total hip arthroplasty and will be placed on oral Apixaban for deep vein thrombosis prophylaxis postoperatively. Which of the following best describes the specific pharmacological mechanism of action of this medication?
. Direct inhibition of Thrombin (Factor IIa)
. Direct inhibition of Factor Xa
. Irreversible inhibition of cyclooxygenase-1 (COX-1)
. Vitamin K epoxide reductase inhibition
. Activation of antithrombin III

Correct Answer & Explanation

. Direct inhibition of Factor Xa

Explanation

Apixaban and Rivaroxaban are direct, oral Factor Xa inhibitors. Dabigatran is a direct thrombin (Factor IIa) inhibitor. Warfarin acts by inhibiting Vitamin K epoxide reductase. Aspirin irreversibly inhibits COX-1. Low molecular weight heparins (like enoxaparin) work by binding to and activating antithrombin III, which subsequently inactivates Factor Xa and, to a lesser extent, Factor IIa.

Question 8514

Topic: Biology, Genetics & Bone Healing

A 28-year-old male sustains a closed tibia fracture and undergoes intramedullary nailing. He has delayed union and receives recombinant human bone morphogenetic protein-2 (rhBMP-2). BMPs stimulate bone formation primarily by acting through which of the following intracellular signaling pathways?

. Binding to intracellular steroid receptors to stimulate transcription
. Binding to serine/threonine kinase receptors and signaling via Smad proteins
. Activating tyrosine kinase receptors and the MAPK pathway
. Inhibiting osteoclastogenesis via the RANK/RANKL pathway
. Acting as a structural scaffold for osteoblast attachment

Correct Answer & Explanation

. Binding to serine/threonine kinase receptors and signaling via Smad proteins

Explanation

Bone morphogenetic proteins (BMPs) belong to the TGF-beta superfamily. They bind to cell-surface transmembrane serine/threonine kinase receptors. Upon binding, the receptor complex phosphorylates intracellular Smad proteins (Smad 1, 5, 8), which then complex with Smad 4, translocate to the nucleus, and regulate the transcription of target genes necessary for osteoblastic differentiation.

Question 8515

Topic: Biology, Genetics & Bone Healing

A 45-year-old woman presents with knee pain. Radiographs reveal an eccentric, lytic lesion in the distal femoral epiphysis extending to the articular surface. Biopsy demonstrates mononuclear cells intermixed with multinucleated giant cells. Which of the following best describes the molecular mechanism of the targeted medical therapy for this condition?

. Inhibition of tyrosine kinase signaling
. Monoclonal antibody binding to RANKL, preventing RANK activation
. Monoclonal antibody binding directly to RANK, blocking RANKL binding
. Bisphosphonate-mediated inhibition of farnesyl pyrophosphate synthase
. Inhibition of the hedgehog signaling pathway

Correct Answer & Explanation

. Monoclonal antibody binding to RANKL, preventing RANK activation

Explanation

The clinical presentation and histology describe a giant cell tumor (GCT) of bone. The neoplastic mononuclear cells in GCT express RANKL, which recruits and activates the reactive multinucleated osteoclast-like giant cells that cause bone resorption. Denosumab, a human monoclonal antibody, specifically targets and binds to RANKL, thereby preventing the activation of the RANK receptor on osteoclasts and osteoclast precursors. This leads to reduced bone resorption and tumor stabilization.

Question 8516

Topic: 1. General Principles & Basic Science

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

. Superficial (tangential) zone
. Transitional (middle) zone
. Deep (radial) zone
. Tidemark
. Calcified cartilage zone

Correct Answer & Explanation

. Superficial (tangential) zone

Explanation

Articular cartilage is divided into four main zones: superficial, middle (transitional), deep, and calcified. The superficial zone represents the top 10-20% of the articular cartilage. It contains the highest concentration of water, the highest density of collagen (oriented parallel to the joint surface to resist shear forces), and the lowest concentration of proteoglycans. The deep zone has the highest concentration of proteoglycans and the lowest water content, with collagen oriented perpendicularly.

Question 8517

Topic: Biology, Genetics & Bone Healing
Which of the following cellular components is essential for the sealing zone formation and subsequent osteoclast attachment to the bone matrix during bone resorption?
. Integrin alpha-v beta-3
. Cadherin-11
. Connexin 43
. CD44
. Fibronectin

Correct Answer & Explanation

. Integrin alpha-v beta-3

Explanation

Osteoclasts attach to the bone matrix to create an isolated extracellular microenvironment for resorption. This attachment is mediated primarily by integrin alpha-v beta-3 (αvβ3), which binds to bone matrix proteins containing an RGD (Arg-Gly-Asp) sequence, such as osteopontin and bone sialoprotein. This interaction forms the 'sealing zone' and leads to the polarization of the osteoclast and formation of the ruffled border.

Question 8518

Topic: 1. General Principles & Basic Science

During the repair of a peripheral nerve injury, wallerian degeneration must occur distal to the injury site before axonal regeneration can begin. Which of the following cells are primarily responsible for clearing myelin debris during the early phases of wallerian degeneration in the peripheral nervous system?

. Astrocytes
. Oligodendrocytes
. Schwann cells and macrophages
. Microglia
. Ependymal cells

Correct Answer & Explanation

. Schwann cells and macrophages

Explanation

In the peripheral nervous system (PNS), wallerian degeneration involves the breakdown of the axon and its myelin sheath distal to the site of injury. Schwann cells initially dedifferentiate and begin phagocytosing the myelin debris. Soon after, blood-borne macrophages are recruited to the site and take over the bulk of the phagocytosis, clearing the path for axonal regeneration. Astrocytes, oligodendrocytes, and microglia are cells of the central nervous system (CNS).

Question 8519

Topic: Biomechanics & Biomaterials
Which of the following factors has the greatest influence on increasing volumetric wear in ultra-high molecular weight polyethylene (UHMWPE) acetabular components in total hip arthroplasty?
. Increasing the thickness of the polyethylene liner
. Decreasing the femoral head-to-neck ratio
. Increasing the femoral head diameter
. Using highly cross-linked polyethylene
. Utilizing a ceramic-on-ceramic bearing surface

Correct Answer & Explanation

. Increasing the femoral head diameter

Explanation

Volumetric wear in conventional UHMWPE is directly proportional to the sliding distance, which increases with a larger femoral head diameter. While larger heads increase volumetric wear, linear wear may remain unchanged or slightly decrease. Utilizing highly cross-linked polyethylene significantly decreases wear rates.

Question 8520

Topic: Biology, Genetics & Bone Healing
During the process of secondary fracture healing, which type of collagen is predominantly synthesized first by chondrocytes during the soft callus phase?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Secondary fracture healing proceeds through hematoma, soft callus, hard callus, and remodeling phases. The soft callus is primarily cartilaginous and is rich in Type II collagen, which is produced by proliferating chondrocytes. Type X collagen appears later during chondrocyte hypertrophy, and Type I collagen replaces the cartilage matrix during the hard callus and remodeling phases.

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