Menu

1. General Principles & Basic Science MCQs

Practice Set 333 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 6641

Topic: 1. General Principles & Basic Science

Which of the following molecules is primarily responsible for boundary lubrication in articular joints?

. Hyaluronic acid
. Lubricin
. Type II collagen
. Aggrecan
. Fibronectin

Correct Answer & Explanation

. Hyaluronic acid

Explanation

Lubricin (PRG4) is a highly glycosylated protein secreted by superficial zone chondrocytes and synoviocytes. It provides boundary lubrication, significantly reducing friction at the articular cartilage surface.

Question 6642

Topic: Biology, Genetics & Bone Healing

The primary cellular defect in Paget disease of bone resides in the:

. Osteoblast
. Osteoclast
. Osteocyte
. Chondrocyte
. Macrophage

Correct Answer & Explanation

. Osteoblast

Explanation

Paget disease is primarily characterized by hyperactive, multinucleated osteoclasts that cause excessive and disorganized bone resorption. This is followed by a compensatory but structurally abnormal increase in osteoblastic bone formation.

Question 6643

Topic: Biomechanics & Biomaterials

Mixing stainless steel and titanium implants in a highly saline environment (e.g., the human body) increases the risk of which type of corrosion?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within a conductive fluid environment. This leads to accelerated corrosion of the less noble metal.

Question 6644

Topic: 1. General Principles & Basic Science

The earliest biochemical change observed in articular cartilage during the development of osteoarthritis is:

. Increased water content
. Decreased water content
. Increased proteoglycan concentration
. Increased type II collagen synthesis
. Decreased chondrocyte metabolism

Correct Answer & Explanation

. Increased water content

Explanation

The earliest biochemical change in osteoarthritic cartilage is an increase in water content. This occurs due to the breakdown of the superficial collagen network, allowing hydrophilic proteoglycans to swell excessively.

Question 6645

Topic: Biology, Genetics & Bone Healing

Nutritional rickets is characterized by an initial defect in which of the following processes?

. Osteoid synthesis
. Collagen cross-linking
. Mineralization of the physis and osteoid
. Osteoclast differentiation
. Intramembranous ossification

Correct Answer & Explanation

. Osteoid synthesis

Explanation

Rickets (and osteomalacia in adults) is typically caused by a deficiency in Vitamin D or calcium. This results in a failure to mineralize the osteoid matrix and, in growing children, the cartilaginous growth plate (physis).

Question 6646

Topic: 1. General Principles & Basic Science

Which of the following design modifications will most effectively increase the pullout strength of a bone screw?

. Decreasing the outer diameter
. Increasing the inner (root) diameter
. Decreasing the thread pitch
. Increasing the thread pitch
. Decreasing the length of engagement

Correct Answer & Explanation

. Decreasing the outer diameter

Explanation

Screw pullout strength is directly proportional to the outer diameter and the length of engagement, and inversely proportional to thread pitch. Therefore, decreasing the pitch (more threads per unit length) increases pullout strength.

Question 6647

Topic: Biology, Genetics & Bone Healing

A patient presents with generalized bone pain and proximal muscle weakness. Laboratory tests reveal low serum calcium, low phosphorus, elevated alkaline phosphatase, and elevated parathyroid hormone. What is the most likely diagnosis?

. Osteoporosis
. Primary hyperparathyroidism
. Paget disease
. Osteomalacia
. Osteopetrosis

Correct Answer & Explanation

. Osteoporosis

Explanation

These laboratory findings represent the classic profile of osteomalacia, often due to severe Vitamin D deficiency. It triggers secondary hyperparathyroidism, leading to low/normal calcium, low phosphorus, and elevated alkaline phosphatase.

Question 6648

Topic: 1. General Principles & Basic Science

Articular cartilage has a remarkably limited intrinsic capacity for healing following injury primarily because it:

. Has a highly vascularized subchondral bone layer
. Lacks a blood supply, lymphatics, and nerves
. Contains an overabundance of undifferentiated stem cells
. Has a highly cellular extracellular matrix
. Continuously remodels its type II collagen

Correct Answer & Explanation

. Has a highly vascularized subchondral bone layer

Explanation

Articular cartilage is unique in that it is avascular, aneural, and alymphatic. The lack of a local blood supply severely restricts its ability to mount a typical inflammatory response and recruit progenitor cells for repair.

Question 6649

Topic: Biology, Genetics & Bone Healing

Denosumab is an effective pharmacologic treatment for severe osteoporosis because it functions as a monoclonal antibody that directly targets and inhibits:

. RANK
. RANKL
. OPG
. Sclerostin
. Cathepsin K

Correct Answer & Explanation

. RANK

Explanation

Denosumab is a human monoclonal antibody that specifically binds to RANKL, preventing it from activating RANK on the surface of osteoclasts. This mechanism mimics the endogenous action of osteoprotegerin (OPG), robustly inhibiting bone resorption.

Question 6650

Topic: Biomechanics & Biomaterials

The total area under the load-deformation (or stress-strain) curve of a bone specimen up to the point of structural failure represents its:

. Stiffness
. Strength
. Energy absorbed to failure (Toughness)
. Ductility
. Elastic limit

Correct Answer & Explanation

. Stiffness

Explanation

The area under the entire load-deformation curve represents the material's toughness. It quantifies the total amount of energy the bone can absorb before fracturing.

Question 6651

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) regulates bone remodeling. Continuous administration of PTH leads to net bone resorption. Through which direct cellular mechanism does PTH stimulate osteoclastogenesis?

. Direct binding to PTH receptors on osteoclast precursors
. Inhibition of macrophage colony-stimulating factor (M-CSF)
. Stimulation of osteoblasts to secrete RANKL
. Direct inhibition of osteoprotegerin (OPG) secretion by osteocytes
. Activation of the Wnt/beta-catenin pathway

Correct Answer & Explanation

. Direct binding to PTH receptors on osteoclast precursors

Explanation

PTH binds to receptors on osteoblasts, stimulating them to express RANKL and M-CSF while inhibiting OPG. RANKL then binds to RANK on osteoclast precursors, promoting their differentiation and activation into mature osteoclasts. Osteoclasts themselves do not possess PTH receptors.

Question 6652

Topic: 1. General Principles & Basic Science

In adult articular cartilage, which zone is characterized by the highest concentration of water, the lowest concentration of proteoglycans, and 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 zone of articular cartilage contains the highest water content and lowest proteoglycan concentration. Its collagen fibers are densely packed and aligned parallel to the articular surface to resist shear forces.

Question 6653

Topic: Biomechanics & Biomaterials

When utilizing an intramedullary nail for fracture fixation, the torsional rigidity of a solid cylindrical nail is proportional to its radius raised to which power?

. Radius squared (r^2)
. Radius cubed (r^3)
. Radius to the fourth power (r^4)
. Radius to the fifth power (r^5)
. Radius to the sixth power (r^6)

Correct Answer & Explanation

. Radius squared (r^2)

Explanation

The torsional rigidity of a solid cylinder is proportional to its polar moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, even small increases in nail diameter significantly increase its resistance to torsional loads.

Question 6654

Topic: 1. General Principles & Basic Science

Which of the following represents the earliest biochemical and structural change observed in articular cartilage during the pathogenesis of osteoarthritis?

. Decreased water content
. Increased water content
. Increased proteoglycan concentration
. Decreased collagen synthesis
. Calcification of the superficial zone

Correct Answer & Explanation

. Decreased water content

Explanation

The earliest change in osteoarthritis is the damage and cleavage of the collagen network. This breakdown allows the hydrophilic proteoglycans to swell, resulting in a paradoxical increased water content before overall proteoglycan depletion occurs.

Question 6655

Topic: Biomechanics & Biomaterials

A surgeon considers using a 316L stainless steel screw to secure a titanium alloy plate. This practice is strongly contraindicated because mixing these distinct metals in an electrolytic biological fluid leads to which type of corrosion?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices are placed in contact within a conductive fluid (like physiological body fluids). The less noble metal acts as an anode and undergoes accelerated dissolution.

Question 6656

Topic: 1. General Principles & Basic Science

In the extracellular matrix of articular cartilage, aggrecan monomers assemble into massive proteoglycan aggregates by non-covalently binding to which of the following molecules?

. Type II collagen
. Chondroitin sulfate
. Hyaluronic acid
. Fibronectin
. Decorin

Correct Answer & Explanation

. Type II collagen

Explanation

Aggrecan monomers form large aggregates by binding non-covalently to a central backbone of hyaluronic acid. This critical interaction is highly stabilized by the presence of link proteins.

Question 6657

Topic: Biology, Genetics & Bone Healing

A patient with frequent fractures and a dense "rugger jersey" spine on radiographs is diagnosed with osteopetrosis. Genetic testing reveals a defect in carbonic anhydrase II. This primary defect impairs the function of which cell by what mechanism?

. Osteoblasts; failure to mineralize osteoid
. Osteoclasts; inability to acidify the clear zone/Howship's lacuna
. Osteocytes; defective mechanotransduction signaling
. Chondrocytes; failure of endochondral ossification
. Macrophages; excessive production of IL-1

Correct Answer & Explanation

. Osteoblasts; failure to mineralize osteoid

Explanation

Osteopetrosis is characterized by defective osteoclast-mediated bone resorption. Carbonic anhydrase II is required to generate the protons that osteoclasts secrete via vacuolar H+-ATPases to acidify the resorption pit (Howship's lacuna) and dissolve bone mineral.

Question 6658

Topic: Biomechanics & Biomaterials

A ligament that is subjected to a constant, sustained load over a prolonged period will progressively elongate. This specific viscoelastic behavior is defined as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the progressive deformation (elongation) of a viscoelastic material when subjected to a constant load over time. In contrast, stress relaxation refers to the decrease in stress over time when the material is held at a constant length.

Question 6659

Topic: 1. General Principles & Basic Science

During normal joint function under high-loading and high-velocity conditions, articular cartilage lubrication is primarily achieved by fluid being dragged into the joint space and deforming the cartilage surfaces. This mechanism is known as:

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

Correct Answer & Explanation

. Boundary lubrication

Explanation

Elastohydrodynamic lubrication is the dominant fluid-film mechanism under high loads in diarthrodial joints. The fluid pressure deforms the resilient articular cartilage, increasing the surface area and maintaining a thick layer of pressurized fluid between the opposing asperities.

Question 6660

Topic: Biology, Genetics & Bone Healing

A 65-year-old male presents with increasing hat size, bowing of tibiae, and hearing loss.

Laboratory values demonstrate normal calcium, normal phosphate, and markedly elevated alkaline phosphatase. Which of the following is the primary cellular abnormality in this disease?

. Defective mineralization of osteoid by osteoblasts
. Excessive bone resorption by large, multinucleated osteoclasts
. Overproduction of parathyroid hormone
. Inadequate production of 1,25-dihydroxyvitamin D
. Monoclonal proliferation of plasma cells

Correct Answer & Explanation

. Defective mineralization of osteoid by osteoblasts

Explanation

The clinical picture is classic for Paget's disease of bone. The primary pathologic event is excessive and haphazard bone resorption driven by hyperactive, highly multinucleated osteoclasts, which is followed by a disorganized osteoblastic response (woven bone).

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page