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Biomechanics & Biomaterials MCQs

Practice Set 76 of 88

This practice set contains high-yield board review questions covering key concepts in Biomechanics & Biomaterials. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 1501

Topic: Biomechanics & Biomaterials

A surgeon decides to use a titanium plate with stainless steel screws to fix a femur fracture. Which type of corrosion is most likely to occur at the interface between these two different metals?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in contact within a conductive fluid (like body tissue), causing the less noble metal to act as an anode and corrode. To prevent this, implants made of different metals are generally not mixed.

Question 1502

Topic: Biomechanics & Biomaterials

A surgeon uses a stainless steel screw to secure a titanium plate during an internal fixation procedure. Which type of corrosion is most likely to occur at the interface of these two different metals?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within an electrolytic environment, such as body fluids. The less noble metal undergoes accelerated corrosion due to electron transfer.

Question 1503

Topic: Biomechanics & Biomaterials

In orthopedic implant constructs, which form of corrosion is characterized by a localized, accelerated breakdown of the passivation layer in restricted spaces, such as between a screw head and a plate hole?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Crevice corrosion occurs in shielded areas where oxygen depletion prevents the reformation of the protective oxide layer. This is frequently seen at the interface between screw heads and plate holes.

Question 1504

Topic: Biomechanics & Biomaterials

Mixing stainless steel and titanium implants within the same surgical site increases the risk of galvanic corrosion. Which of the following factors is the primary driving force for this specific type of corrosion?

. Differences in the elastic modulus between the two metals
. Friction at the metal-to-metal interface
. Differences in the electrochemical potential of the metals
. Release of reactive oxygen species from local macrophages
. Fatigue failure of the passivation layer on the implants

Correct Answer & Explanation

. Differences in the electrochemical potential of the metals

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are connected in a conductive fluid (body fluids). The metal with the lower electrochemical potential acts as an anode and undergoes accelerated corrosion.

Question 1505

Topic: Biomechanics & Biomaterials

What specific element is added to 316L stainless steel orthopedic implants to increase resistance to pitting corrosion and crevice corrosion in the chloride-rich environment of the human body?

. Carbon
. Molybdenum
. Nickel
. Chromium
. Vanadium

Correct Answer & Explanation

. Molybdenum

Explanation

Molybdenum (usually 2-3%) is added to 316L stainless steel specifically to enhance resistance to pitting and crevice corrosion. Chromium is added to provide a passivating surface oxide layer. Nickel is used to stabilize the austenitic crystal structure at room temperature.

Question 1506

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials has a Young's modulus most closely matching that of cortical bone?

. Titanium alloy (Ti-6Al-4V)
. Cobalt-chromium alloy
. 316L Stainless steel
. Polyetheretherketone (PEEK)
. Alumina ceramic

Correct Answer & Explanation

. Polyetheretherketone (PEEK)

Explanation

Cortical bone has a Young's modulus of approximately 15-20 GPa. Polyetheretherketone (PEEK) has a modulus of around 3-4 GPa, and carbon-fiber-reinforced PEEK can be tailored to ~18 GPa, making it nearly isoelastic with cortical bone. This minimizes stress shielding compared to Titanium (~110 GPa), Stainless steel (~200 GPa), and CoCr (~240 GPa).

Question 1507

Topic: Biomechanics & Biomaterials

A 45-year-old patient undergoes open reduction and internal fixation of a distal radius fracture using a titanium plate and stainless steel screws. Which of the following forms of corrosion is most likely to occur at the implant interface?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within a conductive fluid (such as serum or interstitial fluid), creating an electrochemical cell. This leads to the accelerated corrosion of the less noble metal (in this case, stainless steel). Mixing metals like titanium and stainless steel should generally be avoided in orthopedics to prevent this phenomenon.

Question 1508

Topic: Biomechanics & Biomaterials
In modern total hip arthroplasty, highly cross-linked polyethylene (HXLPE) is routinely utilized. Increasing the radiation dose during the manufacturing of the polyethylene achieves which of the following biomechanical tradeoffs?
. Increases wear resistance but decreases fatigue strength
. Increases both wear resistance and fatigue strength
. Decreases wear resistance but increases fracture toughness
. Increases wear resistance but increases ultimate tensile strength
. Decreases oxidation resistance and increases fatigue strength

Correct Answer & Explanation

. Increases wear resistance but decreases fatigue strength

Explanation

Irradiating ultra-high molecular weight polyethylene (UHMWPE) creates free radicals that recombine to form cross-links between polymer chains. This drastically increases wear resistance (reducing osteolysis) but simultaneously decreases mechanical properties such as fatigue strength, ultimate tensile strength, and fracture toughness.

Question 1509

Topic: Biomechanics & Biomaterials

During the clinical examination of a knee ligament, a constant force is applied, and the ligament is observed to slowly elongate over time. Which viscoelastic property does this describe?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation (elongation) of a viscoelastic material when subjected to a constant load (force) over time. Stress relaxation is the decrease in stress (force) over time when a material is held at a constant length (strain). Hysteresis is the energy lost as heat during the loading and unloading cycle.

Question 1510

Topic: Biomechanics & Biomaterials

A surgeon decides to use a stainless steel screw to secure a titanium plate during open reduction and internal fixation of a femur fracture. The patient subsequently develops a localized reaction. Which of the following types of corrosion is most likely occurring at the implant interface?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are in physical contact within a conductive fluid medium (such as body fluids). This creates an electrochemical cell, leading to the accelerated corrosion of the less noble metal.

Question 1511

Topic: Biomechanics & Biomaterials

In orthopedic implant constructs, combining a stainless steel plate with titanium screws is generally discouraged primarily due to the increased risk of which of the following processes?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices (electropotentials) are in direct physical contact within an electrolytic medium (such as bodily fluids). The less noble metal (stainless steel) acts as an anode and corrodes at an accelerated rate, while the more noble metal (titanium) acts as a cathode.

Question 1512

Topic: Biomechanics & Biomaterials

When evaluating the mechanical properties of orthopedic implant materials, the stiffness of a material is represented on the stress-strain curve. Which of the following best defines the Young's modulus of a material?

. The area under the entire stress-strain curve
. The slope of the curve in the elastic region
. The point at which the material undergoes permanent deformation
. The maximum stress a material can withstand before failure
. The area under the curve in the plastic region

Correct Answer & Explanation

. The slope of the curve in the elastic region

Explanation

Young's modulus (modulus of elasticity) is determined by the slope of the stress-strain curve in the linear, elastic region. It represents the inherent stiffness of the material, with a steeper slope indicating a stiffer material.

Question 1513

Topic: Biomechanics & Biomaterials

An orthopedic surgeon plans to use a stainless steel screw to secure a titanium plate during fracture fixation. This combination of different metals in an electrolytic environment places the construct at highest risk for which type of corrosion?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

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

Question 1514

Topic: Biomechanics & Biomaterials

A surgeon plans to use a stainless steel plate with titanium screws for a fracture fixation. Which of the following best describes the primary risk associated with mixing these two metals in vivo?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution like body fluid, creating an electrochemical gradient. The less noble metal acts as an anode and undergoes accelerated corrosion.

Question 1515

Topic: Biomechanics & Biomaterials

When two dissimilar metals, such as a titanium plate and stainless steel screws, are placed in contact within the body's electrolyte-rich environment, which type of corrosion is most likely to occur?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are in direct contact within an electrolyte solution, leading to an electrochemical gradient and material breakdown.

Question 1516

Topic: Biomechanics & Biomaterials

Stress shielding around an orthopedic implant occurs because the metallic implant is significantly stiffer than the surrounding bone. Among the following orthopedic biomaterials, which has a modulus of elasticity closest to that of human cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Alumina
. Zirconia

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a modulus of elasticity of approximately 110 GPa, which is lower than stainless steel (~200 GPa) and cobalt-chromium (~240 GPa), making it the closest metal to human cortical bone (~15-20 GPa).

Question 1517

Topic: Biomechanics & Biomaterials

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

. Cyclic loading of a single metal implant
. Fretting between the screw head and the plate
. Contact between two dissimilar metals in an electrolytic environment
. Lack of oxygen at the interface of the implant and bone
. Excessive release of metal ions due to high wear rates

Correct Answer & Explanation

. Contact between two dissimilar metals in an electrolytic environment

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are in electrical contact within an electrolytic medium (like body fluids). This leads to an electrochemical potential difference, causing the less noble metal to corrode.

Question 1518

Topic: Biomechanics & Biomaterials

Joint fluid aspiration from an acutely swollen knee reveals rhomboid-shaped crystals that exhibit weakly positive birefringence under polarized light microscopy. What is the biochemical composition of these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Basic calcium phosphate
. Hydroxyapatite
. Cholesterol

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate

Explanation

Calcium pyrophosphate dihydrate (CPPD) crystals, seen in pseudogout, are classically rhomboid-shaped and exhibit weakly positive birefringence. In contrast, monosodium urate crystals (gout) are needle-shaped and strongly negatively birefringent.

Question 1519

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is commonly used in total joint arthroplasty. However, cross-linking via irradiation introduces free radicals. Which of the following processes is primarily utilized to eliminate these free radicals during manufacturing?
. Gamma irradiation in air
. Ethylene oxide sterilization
. Melting or annealing
. Adding barium sulfate
. Coating with hydroxyapatite

Correct Answer & Explanation

. Melting or annealing

Explanation

Cross-linking of UHMWPE creates free radicals that can lead to long-term oxidative degradation. To prevent this, the material is treated by melting (heating above the melting point) or annealing (heating just below the melting point) to increase polymer chain mobility, allowing free radicals to recombine and be eliminated.

Question 1520

Topic: Biomechanics & Biomaterials

According to the Blix length-tension curve for skeletal muscle biomechanics, maximal active tension is generated under which of the following conditions?

. When the muscle is fully contracted
. At the muscle's resting length
. When stretched 20% beyond its resting length
. When stretched 50% beyond its resting length
. When passive tension reaches its peak

Correct Answer & Explanation

. At the muscle's resting length

Explanation

The Blix curve demonstrates that maximum active tension in a muscle is generated at its resting length. At this exact length, there is optimal overlap and cross-bridge formation between actin and myosin filaments.

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