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Biomechanics & Biomaterials MCQs

Practice Set 66 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 1301

Topic: Biomechanics & Biomaterials

Modular junctions in total joint arthroplasty, such as the head-neck taper interface in a total hip replacement, are most primarily susceptible to which type of corrosion?

. Galvanic corrosion
. Intergranular corrosion
. Fretting corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs at loaded contact areas subjected to microscopic relative motion, such as a modular head-neck taper. This micromotion continually disrupts the protective passivation layer, accelerating local corrosion.

Question 1302

Topic: Biomechanics & Biomaterials

When mixing antibiotic powder into polymethylmethacrylate (PMMA) bone cement, which of the following characteristics is absolute necessary for the antibiotic to maintain clinical efficacy?

. Heat lability
. Bacteriostatic mechanism of action
. Liquid formulation compatibility
. Thermal stability
. High molecular weight

Correct Answer & Explanation

. Thermal stability

Explanation

The polymerization of PMMA is a highly exothermic chemical reaction. Antibiotics incorporated into the cement (such as vancomycin or tobramycin) must possess thermal stability to survive the high curing temperatures without degrading.

Question 1303

Topic: Biomechanics & Biomaterials

When evaluating the mechanical properties of a novel orthopedic implant alloy, a load-deformation curve is generated. What biomechanical property is represented by the total area under the stress-strain curve up to the point of failure?

. Elasticity
. Yield strength
. Toughness
. Brittleness
. Young's modulus

Correct Answer & Explanation

. Elasticity

Explanation

Toughness is defined as the total amount of energy a material can absorb before it fractures, which corresponds to the entire area under the stress-strain curve. Young's modulus is the slope of the elastic region, measuring stiffness. Yield strength is the point where plastic (irreversible) deformation begins.

Question 1304

Topic: Biomechanics & Biomaterials

When a constant sustained load is applied to an anterior cruciate ligament allograft over a prolonged period, the ligament slowly elongates over time without any increase in the applied force. Which of the following viscoelastic properties does this describe?

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

Correct Answer & Explanation

. Hysteresis

Explanation

Creep is defined as the progressive deformation (elongation) of a viscoelastic material when subjected to a constant load over time. Stress relaxation, conversely, is the decrease in stress (force) within a material over time when it is held at a constant length or strain.

Question 1305

Topic: Biomechanics & Biomaterials

A surgeon uses a stainless steel screw to secure a titanium plate during the open reduction and internal fixation of a distal radius fracture. 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
. Intergranular corrosion

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices are placed in electrical contact within a conductive fluid. The less noble metal (anode) undergoes accelerated corrosion. Stainless steel and titanium should generally not be mixed to prevent this electrochemical process.

Question 1306

Topic: Biomechanics & Biomaterials

A surgeon plans to use a stainless steel screw through a titanium locking plate to treat a periarticular fracture. What specific biomechanical or biomaterial phenomenon is most likely to occur at the screw-plate interface?

. Fretting corrosion
. Galvanic corrosion with titanium acting as the anode
. Galvanic corrosion with stainless steel acting as the anode
. Crevice corrosion due to low oxygen tension
. Stress shielding of the underlying bone

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic environment. Stainless steel is less noble (more anodic) than titanium, causing the stainless steel to corrode while the titanium is protected.

Question 1307

Topic: Biomechanics & Biomaterials

During a biomechanical study, a human Achilles tendon is subjected to tensile testing at varying strain rates. According to the viscoelastic properties of ligaments and tendons, what is the expected result when the tendon is loaded at a very high strain rate compared to a low strain rate?

. Decreased stiffness and decreased ultimate failure load
. Increased stiffness and increased ultimate failure load
. Increased deformation before failure
. A prolonged toe region on the stress-strain curve
. Decreased Young's modulus

Correct Answer & Explanation

. Decreased stiffness and decreased ultimate failure load

Explanation

Ligaments and tendons exhibit viscoelasticity, meaning their biomechanical behavior is strain-rate dependent. At high strain rates, they become stiffer and can withstand a higher ultimate failure load before rupturing.

Question 1308

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is frequently utilized to improve longevity. What is the primary biomechanical tradeoff of increasing the radiation dose to increase cross-linking in UHMWPE?
. Increased volumetric wear
. Decreased oxidation resistance
. Decreased yield strength and fatigue crack propagation resistance
. Increased adhesive wear
. Decreased elastic modulus

Correct Answer & Explanation

. Decreased yield strength and fatigue crack propagation resistance

Explanation

Highly cross-linked polyethylene significantly reduces volumetric and adhesive wear in joint arthroplasty. However, the cross-linking process decreases the material's ductility, fracture toughness, and resistance to fatigue crack propagation.

Question 1309

Topic: Biomechanics & Biomaterials

A surgeon plans to use a stainless steel screw through a titanium plate. What is the primary mechanism of implant failure associated with mixing these two metals?

. Crevice corrosion
. Galvanic corrosion
. Fretting corrosion
. Fatigue failure
. Abrasive wear

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution like body fluid. This leads to the transfer of electrons and accelerated corrosion of the less noble metal, which is why mixing titanium and stainless steel is generally avoided.

Question 1310

Topic: Biomechanics & Biomaterials

During material testing of a new orthopedic alloy, the specimen is loaded in tension. The point on the stress-strain curve where the material transitions from elastic to plastic deformation is known as the:

. Ultimate tensile strength
. Failure point
. Yield point
. Young's modulus
. Proportional limit

Correct Answer & Explanation

. Ultimate tensile strength

Explanation

The yield point marks the transition between elastic (reversible) and plastic (irreversible) deformation on a stress-strain curve. Loading beyond this point results in permanent deformation of the implant.

Question 1311

Topic: Biomechanics & Biomaterials
Aseptic loosening is a leading cause for late revision in total hip arthroplasty. The osteolytic cascade is primarily initiated by the macrophage phagocytosis of which specific type of wear particle?
. Titanium alloy
. Cobalt-chromium
. Ceramic
. Polymethylmethacrylate (PMMA)
. Ultra-high-molecular-weight polyethylene (UHMWPE)

Correct Answer & Explanation

. Ultra-high-molecular-weight polyethylene (UHMWPE)

Explanation

Macrophage phagocytosis of ultra-high-molecular-weight polyethylene (UHMWPE) wear particles in the 0.1 to 1.0 micrometer range triggers the release of pro-inflammatory cytokines like IL-1 and TNF-alpha. This inflammatory cascade directly leads to osteoclast activation and periprosthetic osteolysis.

Question 1312

Topic: Biomechanics & Biomaterials

A revision total hip arthroplasty is performed for a failed implant. Intraoperatively, significant black debris and tissue necrosis are noted around the modular head-neck junction. Which of the following types of corrosion is most likely responsible for this phenomenon at a modular junction of dissimilar metals?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in electrical contact within an electrolytic solution (like body fluids). The less noble metal undergoes accelerated anodic dissolution, leading to implant degradation and adverse local tissue reactions.

Question 1313

Topic: Biomechanics & Biomaterials

A synthetic polymer is being evaluated for use as an intervertebral disc replacement. When a constant sustained load is applied to the material over a prolonged period, it continues to deform progressively over time. What biomechanical property does this behavior describe?

. Stress relaxation
. Creep
. Fatigue
. Hysteresis
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is a viscoelastic property where a material undergoes time-dependent progressive deformation under a constant load. In contrast, stress relaxation is the decrease in stress over time when a material is held at a constant strain.

Question 1314

Topic: Biomechanics & Biomaterials
The introduction of highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) in total hip arthroplasty has significantly reduced volumetric wear rates. This improvement in wear resistance is typically achieved at the expense of decreasing which of the following mechanical properties?
. Fracture toughness
. Hardness
. Wettability
. Creep resistance
. Compressive modulus

Correct Answer & Explanation

. Fracture toughness

Explanation

While high-dose irradiation and cross-linking of UHMWPE significantly improve wear resistance, these processes alter the polymer chain structure. This results in a reduction of mechanical properties such as fracture toughness, ductility, and fatigue crack propagation resistance.

Question 1315

Topic: Biomechanics & Biomaterials

Titanium alloys (e.g., Ti-6Al-4V) are frequently used in orthopedic implants due to their excellent biocompatibility and fatigue strength. Which of the following characteristics best explains the superior in vivo corrosion resistance of titanium compared to stainless steel?

. Formation of a stable passive oxide layer
. High carbon content
. Presence of molybdenum
. Increased nickel concentration
. Lower modulus of elasticity

Correct Answer & Explanation

. Formation of a stable passive oxide layer

Explanation

Titanium alloys exhibit excellent corrosion resistance due to the spontaneous formation of a highly stable, self-healing passive titanium dioxide (TiO2) layer on the implant surface when exposed to oxygen in body fluids.

Question 1316

Topic: Biomechanics & Biomaterials

A 25-year-old structural engineer asks about the biomechanical properties of a new titanium alloy compared to stainless steel for a fracture plate. When evaluating the stress-strain curve of the material, which of the following best represents the total energy absorbed by the material before structural failure?

. Young's modulus
. Yield strength
. Ultimate tensile strength
. Toughness
. Resilience

Correct Answer & Explanation

. Young's modulus

Explanation

Toughness is defined as the total amount of energy a material can absorb before it fails, represented by the total area under the stress-strain curve up to the point of failure. Resilience is the energy absorbed up to the yield point (elastic deformation). Young's modulus is the slope of the elastic region, indicating stiffness.

Question 1317

Topic: Biomechanics & Biomaterials

A 65-year-old male undergoes revision total hip arthroplasty for a painful, sterile joint effusion 7 years after the index procedure with a modular titanium-alloy stem and a cobalt-chromium head. Intraoperatively, significant black debris is noted precisely at the head-neck junction. Which mechanism is primarily responsible for the generation of this debris?

. Abrasive wear
. Adhesive wear
. Fretting and crevice corrosion
. Galvanic corrosion alone
. Third-body wear

Correct Answer & Explanation

. Abrasive wear

Explanation

Mechanically assisted crevice corrosion (MACC), or trunnionosis, occurs at modular junctions (like the head-neck taper). It is driven by the combination of micromotion (fretting), which breaks the passivation layer, and a confined fluid environment (crevice corrosion) leading to acidic degradation of the metal.

Question 1318

Topic: Biomechanics & Biomaterials

An orthopedic surgeon is selecting an intramedullary nail for an unstable femur fracture. The surgeon considers a solid titanium nail versus a hollow titanium nail of the exact same outer diameter. The solid nail has a higher bending stiffness. According to the principles of biomechanics, the bending stiffness of a solid cylindrical implant is proportional to its radius raised to what power?

. Radius squared (r^2)
. Radius cubed (r^3)
. Radius to the fourth power (r^4)
. Radius to the fifth power (r^5)
. Square root of the radius (r^0.5)

Correct Answer & Explanation

. Radius squared (r^2)

Explanation

Bending stiffness is determined by the material's modulus of elasticity and its cross-sectional area moment of inertia. For a solid cylinder, the area moment of inertia is proportional to the radius to the fourth power (r^4). Therefore, small increases in radius profoundly increase bending stiffness.

Question 1319

Topic: Biomechanics & Biomaterials
To improve the wear resistance of ultra-high molecular weight polyethylene (UHMWPE) utilized in total joint arthroplasty, the material is subjected to irradiation to induce cross-linking. Which of the following is the primary purpose of subsequent remelting or the addition of Vitamin E during manufacturing?
. Increase the yield strength of the polymer
. Eliminate free radicals to prevent oxidative degradation
. Improve the hydrophilicity for better boundary lubrication
. Decrease the elastic modulus to match cortical bone
. Enhance the osteoinductivity of the eventual wear debris

Correct Answer & Explanation

. Eliminate free radicals to prevent oxidative degradation

Explanation

Irradiation of UHMWPE creates cross-links that vastly improve wear resistance, but it also generates free radicals. If left untreated, these free radicals react with oxygen in vivo, leading to oxidative degradation and embrittlement. Remelting or adding antioxidants like Vitamin E quenches these free radicals.

Question 1320

Topic: Biomechanics & Biomaterials

A basic science researcher is studying the biomechanical properties of the anterior cruciate ligament (ACL). A constant length of deformation (strain) is abruptly applied to the ligament in a testing machine, and the load (stress) required to maintain this specific length is observed to decrease exponentially over time. Which viscoelastic property is being demonstrated?

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

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is a classic viscoelastic property defined as the decrease in internal stress (or load) over time when a material is held at a constant strain (length). Creep, conversely, is an increase in strain (deformation) over time when the material is subjected to a constant load.

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