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1. General Principles & Basic Science MCQs

Practice Set 357 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 7121

Topic: 1. General Principles & Basic Science

Which of the following modifications to a cortical bone screw will yield the greatest increase in its pullout strength?

. Decreasing the root diameter
. Increasing the outer diameter
. Increasing the thread pitch
. Decreasing the length of engagement
. Changing from a solid to a cannulated core

Correct Answer & Explanation

. Decreasing the root diameter

Explanation

Pullout strength is most significantly influenced by the outer diameter of the screw. It is directly proportional to outer diameter, length of engagement, and shear strength of the bone, and inversely proportional to thread pitch.

Question 7122

Topic: Biomechanics & Biomaterials

During the application of a dynamic splint to address a knee flexion contracture, a constant force is applied over time, leading to a gradual increase in tissue elongation. This biomechanical phenomenon is known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the viscoelastic property where a material undergoes progressive deformation under a constant load over time. Stress relaxation occurs when a constant deformation is applied, leading to a gradual decrease in stress.

Question 7123

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman is prescribed alendronate for osteoporosis. Which of the following describes the primary mechanism of action of this medication at the cellular level?

. Binding directly to the RANK receptor to prevent activation
. Inhibiting the enzyme farnesyl pyrophosphate synthase
. Stimulating osteoblast differentiation via Wnt signaling
. Blocking the action of cathepsin K
. Reducing the secretion of osteoprotegerin (OPG)

Correct Answer & Explanation

. Binding directly to the RANK receptor to prevent activation

Explanation

Nitrogen-containing bisphosphonates like alendronate inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This disrupts GTPase protein prenylation, leading to osteoclast apoptosis and loss of ruffled border function.

Question 7124

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain tolerated by the tissue required for primary bone healing to occur?

. <2%
. 2-10%
. 10-30%
. 30-50%
. >100%

Correct Answer & Explanation

. <2%

Explanation

Primary bone healing (direct Haversian remodeling) occurs only under conditions of absolute stability when interfragmentary strain is less than 2%. Strains between 2% and 10% promote secondary bone healing with callus formation.

Question 7125

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, utilizing highly cross-linked polyethylene (HXLPE) instead of conventional ultra-high molecular weight polyethylene (UHMWPE) alters the material properties. Which of the following best describes the biomechanical tradeoff of highly cross-linking the polyethylene?

. Decreased adhesive wear but increased abrasive wear
. Increased wear resistance but decreased fatigue strength
. Increased ductility but decreased yield strength
. Decreased oxidation potential but increased third-body wear
. Increased elastic modulus but decreased tensile strength

Correct Answer & Explanation

. Decreased adhesive wear but increased abrasive wear

Explanation

High cross-linking of polyethylene significantly improves wear resistance, reducing adhesive and abrasive wear. However, this process alters the mechanical properties by decreasing the material's fatigue strength, ductility, and fracture toughness.

Question 7126

Topic: 1. General Principles & Basic Science

A patient with secondary hyperparathyroidism secondary to chronic kidney disease will typically demonstrate which of the following serum laboratory profiles?

. Elevated calcium and elevated phosphate
. Elevated calcium and decreased phosphate
. Decreased calcium and elevated phosphate
. Decreased calcium and decreased phosphate
. Normal calcium and markedly elevated alkaline phosphatase only

Correct Answer & Explanation

. Elevated calcium and elevated phosphate

Explanation

In chronic kidney disease, impaired phosphate excretion and decreased 1-alpha-hydroxylase activity lead to hyperphosphatemia and hypocalcemia. This chronic hypocalcemia directly stimulates the parathyroid glands, resulting in secondary hyperparathyroidism.

Question 7127

Topic: Biomechanics & Biomaterials

When a stainless steel screw is used to secure a titanium plate to bone, the resulting electrochemical potential difference causes localized degradation. Which of the following types of corrosion does this represent?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting 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. The less noble metal acts as the anode and corrodes faster, while the more noble metal acts as the cathode.

Question 7128

Topic: Biology, Genetics & Bone Healing

Which of the following factors is directly secreted by osteocytes to inhibit osteoblast-mediated bone formation in response to mechanical unloading?

. Osteocalcin
. Sclerostin
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Bone morphogenetic protein-2 (BMP-2)

Correct Answer & Explanation

. Osteocalcin

Explanation

Sclerostin is a glycoprotein secreted primarily by osteocytes, especially in states of mechanical unloading. It acts by binding to LRP5/6 receptors on osteoblasts, thereby inhibiting the Wnt/beta-catenin signaling pathway and decreasing bone formation.

Question 7129

Topic: Biomechanics & Biomaterials



In the stress-strain curve of cortical bone, the point at which the material ceases to deform elastically and begins to undergo permanent deformation is defined as the:

. Ultimate tensile strength
. Yield point
. Failure point
. Elastic modulus
. Toughness limit

Correct Answer & Explanation

. Ultimate tensile strength

Explanation

The yield point on a stress-strain curve marks the transition from elastic (reversible) deformation to plastic (irreversible) deformation. Beyond this point, the material will not return to its original shape when the applied load is removed.

Question 7130

Topic: 1. General Principles & Basic Science

Cortical bone exhibits different mechanical properties depending upon the direction of the applied load. It is strongest in compression along its longitudinal axis and weakest in shear. This property is termed:

. Viscoelasticity
. Anisotropy
. Isotropy
. Hysteresis
. Ductility

Correct Answer & Explanation

. Viscoelasticity

Explanation

Anisotropy is the material property where mechanical behavior depends on the direction of the applied load. Due to the longitudinal orientation of osteons, cortical bone resists compressive forces parallel to its axis better than transverse forces.

Question 7131

Topic: Biology, Genetics & Bone Healing

A 72-year-old female with severe osteoporosis is treated with denosumab. This biologic agent mimics the action of which naturally occurring endogenous molecule?

. RANK ligand
. Interleukin-1
. Osteoprotegerin (OPG)
. Calcitonin
. Parathyroid hormone

Correct Answer & Explanation

. RANK ligand

Explanation

Denosumab is a monoclonal antibody that specifically targets and binds to RANKL, preventing it from activating the RANK receptor on osteoclasts. This mimics the biological action of osteoprotegerin (OPG), an endogenous decoy receptor that also binds RANKL to inhibit bone resorption.

Question 7132

Topic: 1. General Principles & Basic Science

Increasing the inner (core) diameter of a cortical bone screw, while maintaining the same outer diameter and thread pitch, will have which of the following biomechanical effects?

. Increased pullout strength and increased bending strength
. Decreased pullout strength and increased bending strength
. Increased pullout strength and decreased bending strength
. Decreased pullout strength and decreased bending strength
. No change in pullout strength and increased bending strength

Correct Answer & Explanation

. Increased pullout strength and increased bending strength

Explanation

Decreasing thread depth by increasing the core diameter reduces the volume of bone engaged, lowering pullout strength. However, the core diameter dictates the area moment of inertia, meaning a thicker core significantly increases bending strength.

Question 7133

Topic: Biomechanics & Biomaterials

What mechanical property of a material is defined by the slope of the linear portion of its stress-strain curve?

. Toughness
. Ductility
. Yield strength
. Modulus of elasticity
. Ultimate tensile strength

Correct Answer & Explanation

. Toughness

Explanation

The modulus of elasticity (Young's modulus) is the measure of a material's stiffness, represented by the slope of the linear (elastic) portion of the stress-strain curve. Toughness is represented by the total area under the entire stress-strain curve.

Question 7134

Topic: Surgical Anatomy & Approaches

During an anterior (Smith-Petersen) approach to the hip, the internervous plane between the sartorius and tensor fasciae latae is utilized. Which of the following nerves is at greatest risk of iatrogenic injury during the superficial dissection?

. Femoral nerve
. Superior gluteal nerve
. Lateral femoral cutaneous nerve
. Obturator nerve
. Sciatic nerve

Correct Answer & Explanation

. Femoral nerve

Explanation

The lateral femoral cutaneous nerve crosses the sartorius approximately 2 cm distal to the anterior superior iliac spine (ASIS). It is highly susceptible to traction or transection injury during the superficial dissection of the anterior approach to the hip.

Question 7135

Topic: 1. General Principles & Basic Science

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

. Inner (root) diameter of the screw
. Outer (thread) diameter of the screw
. Length of the screw head
. Pitch of the screw threads
. Core radius squared

Correct Answer & Explanation

. Inner (root) diameter of the screw

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter, the length of thread engagement, and the shear strength of the surrounding bone. It is inversely proportional to the thread pitch.

Question 7136

Topic: Biology, Genetics & Bone Healing

Which of the following represents the correct sequence of events during the incorporation of a structural cortical bone allograft?

. Osteoconduction followed by osteoinduction
. Osteoclastic resorption followed by osteoblastic formation
. Immediate revascularization followed by callus formation
. Direct intramembranous ossification without resorption
. Chondrogenesis followed by endochondral ossification

Correct Answer & Explanation

. Osteoconduction followed by osteoinduction

Explanation

Cortical allograft incorporation occurs via a process known as creeping substitution. This process begins with osteoclastic resorption of the graft material, followed subsequently by osteoblastic bone formation.

Question 7137

Topic: Surgical Anatomy & Approaches

In a posterior approach to the humerus, the radial nerve is identified crossing the posterior humerus. At what average distance proximal to the olecranon fossa does the radial nerve cross the posterior aspect of the humerus?

. 5 cm
. 10 cm
. 15 cm
. 20 cm
. 25 cm

Correct Answer & Explanation

. 5 cm

Explanation

The radial nerve crosses the posterior humerus in the spiral groove approximately 14 to 15 cm proximal to the radiocapitellar joint (or olecranon fossa) and roughly 20 cm distal to the acromion.

Question 7138

Topic: Biology, Genetics & Bone Healing

Which intracellular signaling pathway is directly activated by the binding of Bone Morphogenetic Proteins (BMPs) to their cell surface receptors during osteoinduction?

. Wnt/beta-catenin
. JAK/STAT
. Smad 1/5/8
. MAP kinase
. RANK/RANKL

Correct Answer & Explanation

. Wnt/beta-catenin

Explanation

BMPs bind to serine/threonine kinase receptors, leading to the phosphorylation and activation of Smad 1, 5, and 8. These activated Smads form a complex with Smad 4, which translocates to the nucleus to regulate the transcription of osteogenic genes.

Question 7139

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what type of tissue is expected to form in a fracture gap when the interfragmentary strain is between 2% and 10%?

. Lamellar bone
. Woven bone
. Fibrocartilage
. Granulation tissue
. Hyaline cartilage

Correct Answer & Explanation

. Lamellar bone

Explanation

Perren's strain theory dictates that tissue tolerance limits healing. Fibrocartilage can tolerate strains up to 10-15%, making it the predominant tissue in a 2-10% strain environment. Primary bone healing requires less than 2% strain.

Question 7140

Topic: Biomechanics & Biomaterials

A surgeon considers using a stainless steel screw through a titanium plate. What biomechanical principle strongly discourages this specific practice?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Stress shielding
. Notch sensitivity

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within a conductive fluid medium, such as body fluids. The less noble metal (in this case, stainless steel) acts as an anode and undergoes accelerated corrosion.

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