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1. General Principles & Basic Science MCQs

Practice Set 295 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 5881

Topic: Biomechanics & Biomaterials

Which of the following combinations of orthopedic metals is most likely to result in significant galvanic corrosion when placed in direct contact within the body?

. Titanium alloy and commercially pure titanium
. 316L stainless steel and cobalt-chromium alloy
. Cobalt-chromium alloy and titanium alloy
. 316L stainless steel and titanium alloy
. Tantalum and titanium alloy

Correct Answer & Explanation

. 316L stainless steel and titanium alloy

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact in an electrolytic environment. Mixing 316L stainless steel with titanium or cobalt-chromium leads to severe galvanic corrosion of the less noble metal (stainless steel).

Question 5882

Topic: 1. General Principles & Basic Science

Nonsteroidal anti-inflammatory drugs (NSAIDs) are thought to negatively impact early fracture healing primarily by inhibiting the synthesis of which of the following?

. Leukotrienes
. Prostaglandin E2 (PGE2)
. Transforming growth factor-beta (TGF-b)
. Bone morphogenetic protein-2 (BMP-2)
. Interleukin-1 (IL-1)

Correct Answer & Explanation

. Prostaglandin E2 (PGE2)

Explanation

NSAIDs inhibit cyclooxygenase (COX) enzymes, leading to decreased production of prostaglandins, particularly PGE2. PGE2 is essential for early fracture healing as it stimulates osteoblast and osteoclast activity as well as local angiogenesis.

Question 5883

Topic: Biology, Genetics & Bone Healing

Which of the following proteins, secreted primarily by osteocytes, acts as a negative regulator of bone formation by inhibiting the Wnt/beta-catenin signaling pathway?

. Sclerostin
. Osteocalcin
. Osteopontin
. RANKL
. Osteoprotegerin (OPG)

Correct Answer & Explanation

. Sclerostin

Explanation

Sclerostin is a glycoprotein secreted by osteocytes that binds to LRP5/6 receptors on osteoblasts, inhibiting the Wnt signaling pathway. This results in decreased osteoblast differentiation and bone formation.

Question 5884

Topic: 1. General Principles & Basic Science

When transitioning from a two-legged stance to a single-leg stance, the resultant force across the weight-bearing hip joint typically increases to approximately what multiple of body weight?

. 1 times body weight
. 1.5 times body weight
. 2.5 to 3 times body weight
. 5 to 6 times body weight
. 8 to 10 times body weight

Correct Answer & Explanation

. 2.5 to 3 times body weight

Explanation

In a single-leg stance, the abductor muscles must forcefully contract to balance the body weight acting on the longer lever arm of the pelvis. This muscle force adds to the body weight vector, resulting in a joint reaction force of approximately 2.5 to 3 times body weight.

Question 5885

Topic: 1. General Principles & Basic Science

What is the primary cause of the severe cardiac toxicity associated with an accidental intravascular injection of bupivacaine during a regional block?

. Rapid activation of voltage-gated calcium channels
. Blockade of cardiac fast voltage-gated sodium channels during systole
. Irreversible binding to beta-1 adrenergic receptors
. Massive histamine release from mast cells
. Direct central respiratory depression leading to hypoxia

Correct Answer & Explanation

. Blockade of cardiac fast voltage-gated sodium channels during systole

Explanation

Bupivacaine binds strongly to fast voltage-gated sodium channels in the myocardium and dissociates very slowly. This leads to a cumulative blockade during successive cardiac cycles, which can cause refractory arrhythmias and cardiovascular collapse.

Question 5886

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit stress relaxation, which is a viscoelastic property defined as:

. Increasing deformation over time under a constant load
. Decreasing stress over time under a constant deformation
. Energy lost as heat during a loading and unloading cycle
. Increased stiffness when loaded at higher strain rates
. Permanent deformation remaining after load removal

Correct Answer & Explanation

. Decreasing stress over time under a constant deformation

Explanation

Stress relaxation is the decrease in stress (internal force) required to maintain a tissue at a constant strain (length) over time. In contrast, creep is the increasing deformation (lengthening) over time under a constant load.

Question 5887

Topic: Biology, Genetics & Bone Healing

A mutation in the gene encoding Carbonic Anhydrase II leads to an autosomal recessive form of osteopetrosis. Which of the following best describes the fundamental cellular defect resulting from this mutation?

. Decreased bone resorption due to defective acidification at the ruffled border
. Decreased osteoclast differentiation due to absent RANKL expression
. Increased bone mass due to excessive osteoprotegerin secretion
. Failure of osteoblast-osteoclast coupling via EphrinB2 signaling
. Defective collagen cross-linking within the osteoid matrix

Correct Answer & Explanation

. Decreased bone resorption due to defective acidification at the ruffled border

Explanation

Carbonic anhydrase II generates protons that are pumped by vacuolar H+-ATPase into the resorption pit (Howship's lacuna). A defect prevents matrix acidification, which is essential for the dissolution of hydroxyapatite by osteoclasts.

Question 5888

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, bending stiffness of a solid circular implant is proportional to the area moment of inertia. If the radius of a solid intramedullary rod is doubled, the bending stiffness increases by a factor of:

. 2
. 4
. 8
. 16
. 64

Correct Answer & Explanation

. 16

Explanation

The area moment of inertia for a solid cylinder is proportional to the radius to the fourth power (r^4). Therefore, doubling the radius (2^4) increases the bending stiffness 16-fold.

Question 5889

Topic: Biology, Genetics & Bone Healing

Sclerostin, a glycoprotein produced primarily by osteocytes, is a critical regulator of bone formation and the target of the monoclonal antibody romosozumab. What is its mechanism of action?

. Binds to RANKL to prevent osteoclastogenesis
. Inhibits the Wnt/beta-catenin pathway by binding to LRP5/6 receptors
. Stimulates Runx2 expression in mesenchymal stem cells
. Cleaves type I collagen in the extracellular matrix
. Acts as a decoy receptor for bone morphogenetic proteins

Correct Answer & Explanation

. Inhibits the Wnt/beta-catenin pathway by binding to LRP5/6 receptors

Explanation

Sclerostin inhibits osteoblastogenesis and bone formation by antagonizing the Wnt signaling pathway. It specifically binds to the LRP5/6 co-receptors, preventing Wnt ligand binding and subsequent beta-catenin accumulation.

Question 5890

Topic: Biomechanics & Biomaterials
To improve the wear characteristics of ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty, it undergoes highly cross-linking via irradiation followed by remelting. What is the primary biomechanical tradeoff of the remelting process?
. Increases free radical concentration leading to in vivo oxidation
. Increases yield strength and fatigue resistance
. Decreases crystallinity and reduces yield strength/fatigue resistance
. Increases the rate of in vivo oxidation compared to annealing
. Promotes adhesive wear over abrasive wear

Correct Answer & Explanation

. Decreases crystallinity and reduces yield strength/fatigue resistance

Explanation

Remelting UHMWPE (heating above its melting point) effectively eliminates residual free radicals, significantly reducing long-term oxidation risk. However, it decreases the polymer's crystallinity, which subsequently lowers its yield strength and fatigue resistance.

Question 5891

Topic: 1. General Principles & Basic Science

Articular cartilage is divided into specific structural zones. Which of the following best characterizes the superficial (tangential) zone of articular cartilage?

. Lowest water content, perpendicular collagen fibers
. Highest water content, parallel collagen fibers to the joint surface
. Highest proteoglycan content, random collagen orientation
. Lowest cell density, highest Type X collagen content
. Highest compressive modulus, primarily resisting axial loads

Correct Answer & Explanation

. Highest water content, parallel collagen fibers to the joint surface

Explanation

The superficial zone has the highest water content, lowest proteoglycan content, and highly organized collagen fibers aligned parallel to the articular surface. It is specialized to resist shear forces.

Question 5892

Topic: 1. General Principles & Basic Science

During skeletal muscle excitation-contraction coupling, the release of intracellular calcium initiates the cross-bridge cycle. To which specific protein does calcium bind to facilitate this process?

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

Correct Answer & Explanation

. Troponin C

Explanation

Calcium binds to Troponin C, causing a conformational change that moves tropomyosin away from the myosin-binding sites on the actin filament. Troponin I inhibits actin-myosin interaction, and Troponin T binds the troponin complex to tropomyosin.

Question 5893

Topic: Biology, Genetics & Bone Healing
X-linked hypophosphatemic rickets (XLH) is the most common heritable form of rickets. What is the underlying pathophysiology of this condition?
. Defective 1-alpha-hydroxylase activity in the kidney
. Mutation in COL1A1 leading to defective collagen synthesis
. Mutation in the PHEX gene resulting in elevated FGF-23
. Deficiency of tissue-nonspecific alkaline phosphatase (TNSALP)
. Overproduction of parathyroid hormone due to a chief cell adenoma

Correct Answer & Explanation

. Mutation in the PHEX gene resulting in elevated FGF-23

Explanation

XLH is caused by a PHEX gene mutation, leading to unchecked levels of FGF-23. High FGF-23 causes renal phosphate wasting and downregulates 1-alpha-hydroxylase, leading to low 1,25-dihydroxyvitamin D.

Question 5894

Topic: Biomechanics & Biomaterials

A surgeon plans to revise a fractured femoral plate but decides to mix a titanium locking plate with stainless steel screws. What is the primary concern regarding galvanic corrosion in this construct?

. Titanium undergoes rapid anodic dissolution
. Stainless steel acts as the anode and preferentially corrodes
. Both metals corrode equally due to fretting wear
. Titanium acts as the anode and preferentially corrodes
. A passive oxide layer completely prevents galvanic corrosion in both

Correct Answer & Explanation

. Stainless steel acts as the anode and preferentially corrodes

Explanation

In a galvanic cell with dissimilar metals, the less noble metal acts as the anode and undergoes corrosion. Titanium is highly noble and acts as the cathode, causing the less noble stainless steel (anode) to preferentially corrode.

Question 5895

Topic: Biology, Genetics & Bone Healing

Scurvy results from a severe deficiency of Vitamin C, leading to impaired wound healing, weakened capillary walls, and fragile bones. What is the specific biochemical role of Vitamin C in collagen synthesis?

. Cleavage of procollagen to tropocollagen in the extracellular space
. Cofactor for the hydroxylation of proline and lysine residues
. Formation of the triple helix structure in the rough endoplasmic reticulum
. Cofactor for lysyl oxidase to create stable cross-links
. Glycosylation of hydroxylysine residues in the Golgi apparatus

Correct Answer & Explanation

. Cofactor for the hydroxylation of proline and lysine residues

Explanation

Vitamin C is a required cofactor for prolyl hydroxylase and lysyl hydroxylase. These enzymes hydroxylate proline and lysine residues, a step crucial for the formation of stable collagen triple helices.

Question 5896

Topic: 1. General Principles & Basic Science

The pullout strength of an orthopedic cortical screw is directly proportional to several design factors. Which of the following screw parameters most significantly increases its pullout strength?

. Inner (root) diameter
. Outer (major) diameter
. Thread pitch squared
. Screw core area
. Insertion torque

Correct Answer & Explanation

. Outer (major) diameter

Explanation

Screw pullout strength is primarily determined by the volume of bone caught between the threads, which is mathematically proportional to the outer (major) diameter, thread engagement length, and shear strength of the bone.

Question 5897

Topic: Biomechanics & Biomaterials

Viscoelastic materials, such as ligaments and articular cartilage, exhibit time-dependent mechanical properties. Which of the following correctly describes 'stress relaxation'?

. Progressive deformation of a material under a constant load over time
. A decrease in stress within a material maintained at a constant deformation over time
. Energy lost as heat during a single loading-unloading cycle
. A strain-rate-dependent increase in stiffness during rapid loading
. Permanent structural damage after exceeding the material's yield point

Correct Answer & Explanation

. A decrease in stress within a material maintained at a constant deformation over time

Explanation

Stress relaxation refers to the decrease in applied stress required to maintain a given, constant strain (deformation) over time. Creep, in contrast, is the progressive deformation under a constant load.

Question 5898

Topic: 1. General Principles & Basic Science

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to delay fracture healing in animal models. What is the primary molecular mechanism by which selective COX-2 inhibitors impair bone repair?

. Inhibition of COX-1 preventing initial fracture hematoma formation
. Decreased synthesis of Prostaglandin E2 (PGE2), impairing endochondral ossification
. Direct toxic effects on osteoclasts preventing callus remodeling
. Upregulation of osteoprotegerin leading to premature union
. Inhibition of BMP-2 synthesis by mesenchymal stem cells

Correct Answer & Explanation

. Decreased synthesis of Prostaglandin E2 (PGE2), impairing endochondral ossification

Explanation

COX-2 mediates the synthesis of prostaglandins, specifically PGE2, which are essential for both intramembranous and endochondral ossification during the early stages of fracture healing.

Question 5899

Topic: 1. General Principles & Basic Science

Aggrecan is the most abundant proteoglycan in articular cartilage and is essential for its compressive properties. Which of the following best describes the molecular assembly of aggrecan in the extracellular matrix?

. It binds directly to Type II collagen via decorin bridges
. It contains predominantly dermatan sulfate and heparan sulfate chains
. It binds to a central hyaluronic acid backbone via a link protein
. It is synthesized primarily by synoviocytes and diffuses into the matrix
. It provides primarily tensile strength to withstand shear forces

Correct Answer & Explanation

. It binds to a central hyaluronic acid backbone via a link protein

Explanation

Aggrecan monomers consist of a core protein with chondroitin sulfate and keratan sulfate side chains. Dozens of these monomers bind non-covalently to a single hyaluronic acid chain, stabilized by a link protein, creating large aggregates that draw in water to resist compression.

Question 5900

Topic: Biology, Genetics & Bone Healing

The insertion of a tendon or ligament into bone, known as a direct enthesis, gradually transitions to dissipate mechanical stress. What is the correct sequential histological arrangement of the four zones from tendon to bone?

. Tendon, uncalcified fibrocartilage, calcified fibrocartilage, bone
. Tendon, loose areolar tissue, woven bone, lamellar bone
. Tendon, hyaline cartilage, calcified cartilage, woven bone
. Tendon, calcified fibrocartilage, uncalcified fibrocartilage, bone
. Tendon, Sharpey's fibers, hyaline cartilage, bone

Correct Answer & Explanation

. Tendon, uncalcified fibrocartilage, calcified fibrocartilage, bone

Explanation

A direct (fibrocartilaginous) enthesis consists of four distinct continuous zones: tendon (or ligament), uncalcified fibrocartilage, calcified fibrocartilage (separated by the tidemark), and bone.

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