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1. General Principles & Basic Science MCQs

Practice Set 556 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 11101

Topic: 1. General Principles & Basic Science

Which distinct mode of joint lubrication predominates in healthy diarthrodial articular cartilage under biomechanical conditions of extremely high physiological compressive loading but minimal or zero sliding velocity (for example, standing completely still)?

. Hydrodynamic lubrication
. Elastohydrodynamic lubrication
. Boundary lubrication
. Boosted lubrication
. Squeeze-film lubrication

Correct Answer & Explanation

. Hydrodynamic lubrication

Explanation

Squeeze-film lubrication occurs when joint surfaces approach each other under high compressive loads with little to no relative sliding motion (zero velocity). As the surfaces are driven together, the viscous synovial fluid between them cannot instantly escape and acts as a trapped cushion, supporting the load. Hydrodynamic and elastohydrodynamic lubrication require significant relative sliding velocity to generate a supportive fluid wedge. Boundary lubrication relies on molecules like lubricin directly coating the surfaces, preventing adhesion at low speeds or high loads.

Question 11102

Topic: Biomechanics & Biomaterials

Stress shielding around an orthopedic implant is directly related to the mismatch in Young's modulus of elasticity between the implant and the host bone. Which of the following materials has a Young's modulus most similar to that of human cortical bone (~15-20 GPa)?

. Trabecular metal (Tantalum)
. Polymethylmethacrylate (PMMA)
. Carbon fiber-reinforced polyetheretherketone (CFR-PEEK)
. Titanium alloy (Ti-6Al-4V)
. Cobalt-chromium alloy (Co-Cr-Mo)

Correct Answer & Explanation

. Trabecular metal (Tantalum)

Explanation

CFR-PEEK has a Young's modulus of approximately 18 GPa, which closely approximates that of human cortical bone (15-20 GPa). By comparison, Titanium alloy is ~110 GPa, Cobalt-chromium is ~220 GPa, PMMA is ~3 GPa, and Trabecular metal is ~3 GPa (mimicking cancellous bone).

Question 11103

Topic: 1. General Principles & Basic Science

A researcher is designing a randomized controlled trial to evaluate a new protocol for DVT prophylaxis. The study fails to find a statistically significant difference between the two groups, but a true difference actually exists in the population. To have minimized the risk of this specific type of error, which of the following parameters should have been optimized?

. Positive predictive value
. Alpha level
. Specificity
. Statistical power
. Confidence interval

Correct Answer & Explanation

. Positive predictive value

Explanation

The scenario describes a Type II error (false negative), where a study fails to detect a true difference that exists in the population. The probability of a Type II error is represented by beta. Statistical power is defined as 1 minus beta. Therefore, maximizing statistical power (typically achieved by adequately increasing the sample size) minimizes the risk of committing a Type II error.

Question 11104

Topic: 1. General Principles & Basic Science

Following a severe peripheral nerve crush injury (Sunderland second-degree/Seddon axonotmesis), Wallerian degeneration occurs distal to the injury site. Which cellular mechanism is primarily responsible for clearing myelin debris to create an environment conducive to axonal regeneration?

. Phagocytosis by astrocytes and microglia
. Phagocytosis by Schwann cells and recruited hematogenous macrophages
. Enzymatic degradation by matrix metalloproteinases from ependymal cells
. Apoptosis of oligodendrocytes
. Direct absorption into the endoneurial vasculature

Correct Answer & Explanation

. Phagocytosis by astrocytes and microglia

Explanation

In the peripheral nervous system, Wallerian degeneration involves the breakdown of the axon and myelin sheath distal to the injury. Schwann cells dedifferentiate, proliferate, and work synergistically with recruited hematogenous macrophages to phagocytose and clear myelin debris, which paves the way for axonal sprouts to regenerate.

Question 11105

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly utilized as a bone graft extender in spinal fusions and fracture nonunions. By definition, which of the following biological properties does DBM completely lack?

. Osteoconductivity
. Osteoinductivity
. Osteogenicity
. A structural collagen scaffold
. Transforming growth factor-beta (TGF-beta)

Correct Answer & Explanation

. Osteoconductivity

Explanation

DBM provides an osteoconductive scaffold (Type I collagen) and is osteoinductive due to the preservation of bone morphogenetic proteins (BMPs) and other growth factors trapped within the matrix. However, the acid extraction and sterilization processes destroy all viable cells, meaning DBM completely lacks osteogenicity (live, bone-forming cells).

Question 11106

Topic: Biology, Genetics & Bone Healing

Osteoclasts are multinucleated giant cells responsible for bone resorption. They create an acidic microenvironment at the ruffled border. A genetic deficiency in the enzyme carbonic anhydrase II impairs this process and directly leads to which of the following clinical conditions?

. Osteogenesis imperfecta
. Paget's disease of bone
. Osteopetrosis
. Hypophosphatemic rickets
. Fibrous dysplasia

Correct Answer & Explanation

. Osteogenesis imperfecta

Explanation

Carbonic anhydrase II catalyzes the hydration of carbon dioxide to form carbonic acid, which then dissociates into protons (H+) and bicarbonate. The protons are actively pumped via V-ATPases into the sealed resorption pit to dissolve hydroxyapatite. A deficiency in CA II leads to autosomal recessive osteopetrosis associated with renal tubular acidosis.

Question 11107

Topic: Biomechanics & Biomaterials
When preparing antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for the treatment of a chronic periprosthetic joint infection (e.g., formulating an articulating spacer), what is the primary consequence of using a 'high-dose' mixture (e.g., >10% antibiotic by weight) compared to standard prophylactic doses?
. Increased exothermic reaction temperature
. Decreased elution profile over time
. Accelerated polymerization time
. Decreased compressive and tensile strength
. Increased risk of immediate anaphylaxis

Correct Answer & Explanation

. Decreased compressive and tensile strength

Explanation

Adding 'high-dose' antibiotics (typically defined as >2g per 40g bag, and often >10% by weight for spacers) significantly compromises the mechanical properties of PMMA, specifically decreasing its compressive, tensile, and shear strengths. While acceptable for temporary spacers, this high ratio is contraindicated for the final fixation of permanent prosthetic components.

Question 11108

Topic: 1. General Principles & Basic Science

The compressive stiffness and osmotic swelling pressure of articular cartilage are primarily maintained by the interaction between interstitial water and which of the following highly negatively charged molecules?

. Type II collagen
. Hyaluronic acid
. Aggrecan
. Link protein
. Decorin

Correct Answer & Explanation

. Type II collagen

Explanation

Aggrecan is the most abundant large aggregating proteoglycan found in articular cartilage. Its glycosaminoglycan side chains (chondroitin sulfate and keratan sulfate) are highly negatively charged. This fixed negative charge density attracts cations (like Na+) and water via the Donnan osmotic effect, creating a swelling pressure that allows cartilage to withstand compressive loads.

Question 11109

Topic: 1. General Principles & Basic Science

Non-steroidal anti-inflammatory drugs (NSAIDs) are frequently withheld in the acute post-operative period following fracture fixation due to concerns regarding impaired bone healing. NSAIDs primarily inhibit fracture healing by directly suppressing which of the following processes?

. Primary (intramembranous) bone healing
. Endochondral ossification
. Osteoclast-mediated remodeling
. Angiogenesis via direct VEGF inhibition
. Initial fracture hematoma formation

Correct Answer & Explanation

. Primary (intramembranous) bone healing

Explanation

NSAIDs exert their effects by inhibiting cyclooxygenase (COX) enzymes. COX-2 activity, specifically the production of prostaglandin E2 (PGE2), is critical for mesenchymal stem cell differentiation into osteoblasts and for the progression of normal endochondral ossification. Inhibition of COX-2 delays the maturation of the cartilaginous fracture callus into woven bone.

Question 11110

Topic: Biomechanics & Biomaterials

Tendons and ligaments are viscoelastic structures. If a dynamic splint applies a constant load (force) to a contracted joint over an extended period of time, the soft tissues will gradually elongate. This specific biomechanical property is known as:

. Stress relaxation
. Hysteresis
. Creep
. Fatigue
. Plastic deformation

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is defined as the progressive, time-dependent deformation (elongation) of a viscoelastic tissue when subjected to a constant load or stress over time. Dynamic splinting relies on the principle of creep to safely lengthen contracted tissues. 'Stress relaxation', by contrast, is the gradual decrease in stress experienced by a tissue when it is held at a constant length.

Question 11111

Topic: 1. General Principles & Basic Science

According to the sliding filament theory of skeletal muscle contraction, the release of calcium ions from the sarcoplasmic reticulum initiates the contraction cycle. To which specific molecular structure does calcium bind to unblock the myosin-binding sites on the actin filament?

. Tropomyosin
. Troponin I
. Troponin T
. Troponin C
. Myosin light chain

Correct Answer & Explanation

. Tropomyosin

Explanation

Calcium released from the sarcoplasmic reticulum binds to Troponin C. This binding induces a conformational change in the troponin complex, causing the associated tropomyosin molecule to shift its position. This exposes the myosin-binding sites on the actin filament, allowing the myosin heads to attach and initiate the power stroke.

Question 11112

Topic: 1. General Principles & Basic Science
Tranexamic acid (TXA) has become a standard of care in major orthopedic surgeries to minimize blood loss. What is the specific molecular mechanism of action of this synthetic amino acid derivative?
. It acts as a direct thrombin inhibitor.
. It irreversibly inhibits cyclooxygenase-1 in platelets.
. It competitively inhibits the activation of plasminogen to plasmin.
. It enhances the cross-linking of fibrin via Factor XIIIa.
. It stimulates the rapid release of von Willebrand factor from endothelial cells.

Correct Answer & Explanation

. It competitively inhibits the activation of plasminogen to plasmin.

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It functions as an antifibrinolytic by competitively binding to the lysine-binding sites on plasminogen molecules. This action prevents the conversion of plasminogen to plasmin. Since plasmin is the primary enzyme responsible for fibrinolysis (breaking down clots), TXA stabilizes the fibrin clot matrix and significantly reduces surgical bleeding.

Question 11113

Topic: Biology, Genetics & Bone Healing

A 50-year-old male with a history of severe alcohol use disorder presents with easy bruising, perifollicular hemorrhages, and gingival bleeding. He is diagnosed with scurvy secondary to Vitamin C deficiency. Which specific step in collagen biosynthesis is directly impaired by this deficiency?

. Transcription of pro-alpha chain mRNA in the nucleus
. Translation of preprocollagen in the rough endoplasmic reticulum
. Hydroxylation of proline and lysine residues
. Cleavage of procollagen C- and N-terminal propeptides
. Covalent cross-linking of tropocollagen molecules by lysyl oxidase

Correct Answer & Explanation

. Transcription of pro-alpha chain mRNA in the nucleus

Explanation

Vitamin C (ascorbic acid) acts as an essential electron donor (reducing agent) for the enzymes prolyl hydroxylase and lysyl hydroxylase. These enzymes mediate the hydroxylation of specific proline and lysine residues on pro-alpha collagen chains in the rough endoplasmic reticulum. Without adequate hydroxylation, stable hydrogen bonds cannot form between the chains, leading to a defective, weak collagen triple helix and the classic clinical signs of scurvy.

Question 11114

Topic: Biomechanics & Biomaterials

Modular hip stems often employ a titanium alloy stem and a cobalt-chromium head. Which type of corrosion is most likely to occur at the modular head-neck taper junction strictly due to local oxygen depletion in a restricted fluid space?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Crevice corrosion occurs in narrow spaces like taper junctions where oxygen depletion leads to a localized acidic environment. While fretting corrosion also occurs here due to micromotion, oxygen depletion specifically defines crevice corrosion.

Question 11115

Topic: 1. General Principles & Basic Science

The pullout strength of a cortical screw is directly proportional to which of the following geometric parameters?

. Core diameter
. Thread pitch
. Outer diameter
. Insertion torque
. Head diameter

Correct Answer & Explanation

. Core diameter

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter and length of thread engagement, and inversely proportional to thread pitch. The core diameter determines the screw's bending and torsional strength, not its pullout strength.

Question 11116

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly utilized in orthopaedic applications to aid spinal fusion and fracture healing. Which of the following best describes its biologic properties?

. Osteoconductive only
. Osteoinductive only
. Osteoconductive and osteoinductive
. Osteogenic and osteoinductive
. Osteogenic, osteoinductive, and osteoconductive

Correct Answer & Explanation

. Osteoconductive only

Explanation

DBM provides a collagenous scaffold (osteoconductive) and contains bone morphogenetic proteins (BMPs) that stimulate bone formation (osteoinductive). It lacks viable cells, so it does not possess osteogenic properties.

Question 11117

Topic: 1. General Principles & Basic Science

Following a peripheral nerve transection, Wallerian degeneration occurs distal to the injury site. Which cell type is primarily responsible for clearing myelin debris during the initial phase of this process before macrophages arrive?

. Schwann cells
. Astrocytes
. Microglia
. Macrophages
. Fibroblasts

Correct Answer & Explanation

. Schwann cells

Explanation

In the peripheral nervous system, Schwann cells are the first to respond to injury by shedding their myelin and clearing debris via autophagy. They subsequently recruit circulating macrophages to take over the bulk of phagocytosis.

Question 11118

Topic: Biomechanics & Biomaterials
During tensile testing of a normal flexor tendon, the initial 'toe region' of the stress-strain curve is primarily due to which structural phenomenon?
. Plastic deformation of collagen fibers
. Uncrimping of type I collagen fibers
. Microfailure of type III collagen fibers
. Fluid exudation from the proteoglycan matrix
. Complete macroscopic failure of the tendon fascicles

Correct Answer & Explanation

. Uncrimping of type I collagen fibers

Explanation

The non-linear toe region of the ligament or tendon stress-strain curve represents the uncrimping (straightening) of the normally wavy collagen fibrils. Once the fibers are fully uncrimped, the tissue enters the linear elastic region.

Question 11119

Topic: Biology, Genetics & Bone Healing

Denosumab is increasingly utilized to treat osteoporosis and prevent skeletal-related events in metastatic bone disease. What is its exact mechanism of action at the cellular level?

. Inhibits farnesyl pyrophosphate synthase
. Binds to the Wnt signaling antagonist sclerostin
. Acts as an endogenous decoy receptor for RANKL
. Binds directly to RANKL preventing RANK receptor activation
. Stimulates osteoblast differentiation via BMP-2 upregulation

Correct Answer & Explanation

. Inhibits farnesyl pyrophosphate synthase

Explanation

Denosumab is a monoclonal antibody that binds directly to RANKL, preventing it from activating the RANK receptor on osteoclast precursors. Osteoprotegerin (OPG) is the endogenous decoy receptor, which Denosumab mimics therapeutically.

Question 11120

Topic: 1. General Principles & Basic Science

Boundary lubrication in articular cartilage is most critical under conditions of high loads and low velocities. Which molecule is primarily responsible for this specific lubrication mechanism at the articular surface?

. Aggrecan
. Type II collagen
. Lubricin (PRG4)
. Hyaluronic acid
. Chondroitin sulfate

Correct Answer & Explanation

. Aggrecan

Explanation

Lubricin (proteoglycan 4) is secreted by superficial zone chondrocytes and synoviocytes, providing boundary lubrication that reduces friction under high-load, low-velocity conditions. Fluid-film lubrication predominates during high-velocity motions.

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