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1. General Principles & Basic Science MCQs

Practice Set 360 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 7181

Topic: Biomechanics & Biomaterials

Highly cross-linked polyethylene used in total joint arthroplasty aims to reduce wear but is associated with which of the following trade-offs?

. Increased oxidative degradation if not remelted or annealed
. Increased adhesive wear
. Decreased modulus of elasticity
. Increased fatigue strength
. Decreased risk of impingement

Correct Answer & Explanation

. Increased oxidative degradation if not remelted or annealed

Explanation

Cross-linking polyethylene with gamma irradiation generates free radicals that can cause oxidative degradation over time. Thermal treatments like remelting or annealing are required to quench these free radicals, though remelting can reduce fatigue strength.

Question 7182

Topic: Biology, Genetics & Bone Healing

During the repair phase of secondary fracture healing, the soft callus is gradually replaced by hard callus primarily through which of the following processes?

. Intramembranous ossification
. Endochondral ossification
. Osteoclastic cutting cones
. Apoptosis of osteoblasts
. Wnt/beta-catenin inhibition

Correct Answer & Explanation

. Intramembranous ossification

Explanation

In secondary fracture healing, the initial cartilaginous soft callus undergoes endochondral ossification. Chondrocytes hypertrophy, the matrix is calcified, and it is subsequently replaced by woven bone to form the hard callus.

Question 7183

Topic: Biology, Genetics & Bone Healing

Sclerostin, a glycoprotein produced by osteocytes, regulates bone mass by inhibiting which of the following pathways?

. RANK/RANKL pathway
. Wnt/beta-catenin pathway
. TGF-beta signaling
. BMP/Smad pathway
. Notch signaling

Correct Answer & Explanation

. RANK/RANKL pathway

Explanation

Sclerostin inhibits the Wnt/beta-catenin pathway by binding to LRP5/6 receptors on osteoblasts, thereby decreasing osteoblast differentiation and bone formation. Romosozumab is a monoclonal antibody that targets sclerostin to treat osteoporosis.

Question 7184

Topic: Biomechanics & Biomaterials

Galvanic corrosion is most likely to occur in orthopedic implants under which of the following conditions?

. Use of a titanium alloy plate with titanium alloy screws
. Use of a stainless steel plate with titanium alloy screws
. Cyclic loading of a pure titanium implant
. Implantation of an ultra-high molecular weight polyethylene component
. Use of a cobalt-chromium femoral head with a highly cross-linked polyethylene liner

Correct Answer & Explanation

. Use of a titanium alloy plate with titanium alloy screws

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as stainless steel and titanium) are in contact within a conductive fluid. This creates an electrochemical gradient leading to the corrosion of the less noble metal.

Question 7185

Topic: 1. General Principles & Basic Science

The pullout strength of a cortical bone screw is most significantly increased by increasing which of the following parameters?

. Inner (root) diameter
. Screw length
. Outer (thread) diameter
. Thread pitch
. Screw head diameter

Correct Answer & Explanation

. Inner (root) diameter

Explanation

Pullout strength is directly proportional to the outer (thread) diameter, the length of thread engagement in the bone, and the shear strength of the bone. Increasing the outer diameter has the greatest mathematical impact on maximizing pullout strength.

Question 7186

Topic: 1. General Principles & Basic Science

Which of the following molecules is primarily responsible for boundary lubrication at the articular cartilage surface during high-load, low-velocity conditions?

. Hyaluronic acid
. Aggrecan
. Lubricin
. Type II collagen
. Chondroitin sulfate

Correct Answer & Explanation

. Hyaluronic acid

Explanation

Lubricin (PRG4) is a glycoprotein synthesized by superficial zone chondrocytes and synovial fibroblasts. It binds to the articular surface to provide boundary lubrication, drastically reducing friction under high-load and low-velocity conditions.

Question 7187

Topic: 1. General Principles & Basic Science

Which phase of tendon healing is characterized by the highest synthesis of disorganized Type III collagen?

. Inflammatory phase
. Proliferative (fibroblastic) phase
. Remodeling (maturation) phase
. Consolidation phase
. Ossification phase

Correct Answer & Explanation

. Inflammatory phase

Explanation

During the proliferative phase (days 3 to 6 weeks), fibroblasts migrate into the wound and synthesize a disorganized matrix primarily composed of Type III collagen. This is later replaced by stronger, organized Type I collagen during the remodeling phase.

Question 7188

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials has a modulus of elasticity most similar to that of human cortical bone?

. Cobalt-chromium alloy
. 316L Stainless steel
. Titanium alloy (Ti-6Al-4V)
. Tantalum
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Cobalt-chromium alloy

Explanation

Titanium alloys have a modulus of elasticity (approx. 100-110 GPa) that is much closer to cortical bone (approx. 15-20 GPa) than stainless steel (approx. 200 GPa) or cobalt-chromium (approx. 240 GPa). This closer match helps minimize stress shielding.

Question 7189

Topic: Biology, Genetics & Bone Healing

According to Wolff's Law, bone undergoes remodeling in response to mechanical stress. Which cellular mechanism directly senses fluid shear stress within the bone matrix?

. Osteoblast differentiation
. Osteoclast resorption
. Osteocyte mechanotransduction
. Chondrocyte hypertrophy
. Macrophage activation

Correct Answer & Explanation

. Osteoblast differentiation

Explanation

Osteocytes are the primary mechanosensory cells in bone. Fluid flow through the lacunocanalicular network resulting from mechanical loading creates shear stress, which is sensed by osteocyte dendritic processes to regulate bone remodeling.

Question 7190

Topic: 1. General Principles & Basic Science

In the normal human brachial plexus, the posterior cord is formed by the union of which of the following structures?

. Anterior divisions of the upper and middle trunks
. Anterior division of the lower trunk
. Posterior divisions of the upper, middle, and lower trunks
. C5 and C6 nerve roots
. C8 and T1 nerve roots

Correct Answer & Explanation

. Anterior divisions of the upper and middle trunks

Explanation

The posterior cord of the brachial plexus is formed by the convergence of the posterior divisions of all three trunks (upper, middle, and lower). It receives contributions from nerve roots C5 through T1.

Question 7191

Topic: Biology, Genetics & Bone Healing

The normal human intervertebral disc exhibits distinct collagen distributions to resist different biomechanical loads. What is the predominant collagen type found in the nucleus pulposus?

. Type I collagen
. Type II collagen
. Type III collagen
. Type IX collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

The nucleus pulposus is rich in proteoglycans and Type II collagen, which gives it a gel-like consistency to resist compressive forces. In contrast, the annulus fibrosus is composed primarily of Type I collagen to resist tensile and torsional forces.

Question 7192

Topic: Biology, Genetics & Bone Healing

A novel osteoporosis medication targets sclerostin. What is the primary mechanism by which this medication increases bone mass?

. Stimulation of the Wnt/beta-catenin signaling pathway
. Inhibition of RANKL binding to RANK
. Direct activation of osteoclast apoptosis
. Stimulation of PTH receptors on osteoblasts
. Inhibition of cathepsin K activity

Correct Answer & Explanation

. Stimulation of the Wnt/beta-catenin signaling pathway

Explanation

Sclerostin is produced by osteocytes and inhibits the Wnt/beta-catenin pathway, which normally stimulates osteoblastogenesis. Monoclonal antibodies against sclerostin block this inhibition, thereby directly increasing bone formation.

Question 7193

Topic: 1. General Principles & Basic Science

Which of the following best describes the structural composition and biomechanical role of the superficial zone of normal articular cartilage?

. Highest concentration of proteoglycans with collagen fibers oriented perpendicularly
. Lowest concentration of water with collagen fibers oriented obliquely
. Contains the tidemark with the highest concentration of type X collagen
. Highest concentration of water with collagen fibers oriented parallel to the surface
. Highest concentration of chondrocytes arranged in vertical columns

Correct Answer & Explanation

. Highest concentration of proteoglycans with collagen fibers oriented perpendicularly

Explanation

The superficial zone of articular cartilage contains the highest water content and lowest proteoglycan content. Its collagen fibers are oriented parallel to the joint surface to effectively resist applied shear forces.

Question 7194

Topic: Biomechanics & Biomaterials

During the surgical correction of a relapsed clubfoot, a surgeon applies a sequential series of corrective casts. The gradual stretching of the contracted soft tissues over time under a constant applied load is an example of which viscoelastic property?

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a viscoelastic material over time when it is subjected to a constant load. Stress relaxation is the decrease in stress over time when the material is held at a constant strain.

Question 7195

Topic: Biology, Genetics & Bone Healing

Rigid internal fixation of a transverse diaphyseal radius fracture with absolute stability and no fracture gap promotes bone healing primarily through which of the following cellular processes?

. Intramembranous ossification from the periosteum
. Direct osteonal remodeling via cutting cones
. Endochondral ossification
. Formation of a soft cartilaginous callus
. Chondrocyte hypertrophy and apoptosis

Correct Answer & Explanation

. Intramembranous ossification from the periosteum

Explanation

Rigid internal fixation with absolute stability results in primary bone healing. This occurs via direct osteonal remodeling, where cutting cones cross the fracture site without an intermediate cartilaginous stage or macroscopic callus.

Question 7196

Topic: Biology, Genetics & Bone Healing

Which of the following enzymes is primarily responsible for the degradation of the organic bone matrix within the Howship lacuna during osteoclastic bone resorption?

. Matrix metalloproteinase-9
. Cathepsin K
. Carbonic anhydrase II
. Tartrate-resistant acid phosphatase
. Alkaline phosphatase

Correct Answer & Explanation

. Matrix metalloproteinase-9

Explanation

Osteoclasts dissolve inorganic minerals using hydrogen ions and degrade the organic matrix (primarily Type I collagen) through the secretion of Cathepsin K. Carbonic anhydrase II is essential for generating the protons used to dissolve the mineral phase.

Question 7197

Topic: Biomechanics & Biomaterials

In the stress-strain curve of a cortical bone specimen under tension, which of the following mechanical properties is determined by the total area under the curve up to the point of failure?

. Elasticity
. Yield strength
. Ultimate strength
. Toughness
. Ductility

Correct Answer & Explanation

. Elasticity

Explanation

Toughness is the ability of a material to absorb energy and deform before fracturing, represented by the total area under the stress-strain curve. Ductility refers only to the amount of plastic deformation before failure.

Question 7198

Topic: Surgical Anatomy & Approaches

During a posterior approach to the humerus, the radial nerve is identified as it travels through the spiral groove. Which of the following vascular structures travels directly with the radial nerve in this location?

. Posterior circumflex humeral artery
. Profunda brachii artery
. Brachial artery
. Superior ulnar collateral artery
. Anterior circumflex humeral artery

Correct Answer & Explanation

. Posterior circumflex humeral artery

Explanation

The radial nerve runs intimately with the profunda brachii artery (deep brachial artery) in the spiral groove on the posterior aspect of the humerus. The posterior circumflex humeral artery travels with the axillary nerve in the quadrangular space.

Question 7199

Topic: Biology, Genetics & Bone Healing

Sclerostin plays a critical role in the regulation of bone mass by osteocytes. What is the primary mechanism by which sclerostin exerts its inhibitory effect on bone formation?

. Binding to RANKL to prevent osteoclast activation
. Inhibiting Cathepsin K secretion
. Binding to LRP5/6 to antagonize Wnt signaling
. Activating the BMP signaling pathway
. Downregulating osteoprotegerin (OPG) expression

Correct Answer & Explanation

. Binding to RANKL to prevent osteoclast activation

Explanation

Sclerostin, secreted by osteocytes, inhibits osteoblastic bone formation by competitively binding to LRP5/6 receptors. This action antagonizes the canonical Wnt/beta-catenin signaling pathway.

Question 7200

Topic: 1. General Principles & Basic Science

Which of the following alterations to a cortical bone screw design will most significantly increase its pullout strength?

. Decreasing the major (outer) diameter
. Increasing the major (outer) diameter
. Increasing the minor (inner) diameter
. Increasing the thread pitch
. Cannulating the screw

Correct Answer & Explanation

. Decreasing the major (outer) diameter

Explanation

Screw pullout strength is directly proportional to the major (outer) diameter and length of thread engagement. Increasing the major diameter provides the greatest increase in holding power.

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