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Biomechanics & Biomaterials MCQs

Practice Set 85 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 1681

Topic: Biomechanics & Biomaterials
Which of the following manufacturing processes most effectively reduces adhesive and abrasive wear in ultra-high-molecular-weight polyethylene (UHMWPE) for total hip arthroplasty?
. Sterilization in air
. Gamma irradiation followed by melting
. Ethylene oxide sterilization
. Decreasing the cross-linking density
. Adding barium sulfate

Correct Answer & Explanation

. Gamma irradiation followed by melting

Explanation

Highly cross-linked polyethylene is created using gamma or electron beam irradiation to create free radicals that form cross-links. Subsequent melting or annealing quenches these free radicals, preventing long-term oxidative degradation.

Question 1682

Topic: Biomechanics & Biomaterials
To decrease volumetric wear in ultra-high molecular weight polyethylene (UHMWPE) acetabular liners, cross-linking is performed via irradiation. What is the primary mechanical trade-off of utilizing highly cross-linked polyethylene compared to conventional UHMWPE?
. Increased yield strength
. Decreased fatigue and fracture resistance
. Increased oxidation potential if melted post-irradiation
. Increased elastic modulus
. Decreased oxidative stability if remelted

Correct Answer & Explanation

. Decreased fatigue and fracture resistance

Explanation

Highly cross-linking UHMWPE significantly improves its wear resistance by reducing the generation of submicron wear particles. However, the process fundamentally alters the polymer chain network, which compromises its bulk mechanical properties, most notably decreasing its fatigue strength, fracture resistance, and ultimate tensile strength.

Question 1683

Topic: Biomechanics & Biomaterials

When a viscoelastic material like a tendon is subjected to a constant deformation (strain) over time, the force required to maintain that deformation gradually decreases. What is this biomechanical phenomenon called?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation occurs when a viscoelastic material is held at a constant length, leading to a gradual decrease in the internal stress (force) over time. Creep, conversely, is the continuous deformation of a material under a constant load.

Question 1684

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopedic implants occurs when dissimilar metals are placed in contact within a conductive fluid environment. Which combination of metals is generally considered the most susceptible to this type of severe corrosion?

. Titanium and titanium alloy
. Stainless steel and cobalt-chromium
. Cobalt-chromium and cobalt-chromium alloy
. Titanium and porous tantalum
. Zirconium and titanium

Correct Answer & Explanation

. Stainless steel and cobalt-chromium

Explanation

Galvanic corrosion is driven by the difference in electropotential between two dissimilar metals in an electrolyte solution. Mixing stainless steel with cobalt-chromium creates a high potential difference and a significant risk for clinically relevant galvanic corrosion.

Question 1685

Topic: Biomechanics & Biomaterials

Bone behaves as a viscoelastic material. Because of this property, how does an intact long bone respond to a rapidly applied, high-strain-rate load compared to a slowly applied load?

. It becomes more elastic and absorbs less energy
. It becomes stiffer and can absorb more energy before failure
. Its ultimate tensile strength decreases significantly
. It demonstrates increased creep properties
. Its modulus of elasticity completely degrades

Correct Answer & Explanation

. It becomes stiffer and can absorb more energy before failure

Explanation

Due to the viscoelastic nature of bone, it exhibits strain-rate dependency. At higher rates of loading, bone becomes significantly stiffer and stronger, allowing it to absorb more energy before fracturing compared to lower loading rates.

Question 1686

Topic: Biomechanics & Biomaterials

When evaluating the viscoelastic properties of ligaments and tendons, which of the following best describes the biomechanical phenomenon of 'creep'?

. Constant deformation of a material under a varying cyclical load
. Progressive and increasing deformation of a material over time under a constant load
. A steady decrease in internal stress over time while maintained at a constant deformation
. Complete and immediate recovery of the original length after load removal
. Increased material stiffness associated with a rapid loading rate

Correct Answer & Explanation

. Progressive and increasing deformation of a material over time under a constant load

Explanation

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

Question 1687

Topic: Biomechanics & Biomaterials

Titanium alloys are frequently selected for orthopedic implants due to their biocompatibility. Compared to stainless steel alloys, titanium is characterized by which of the following mechanical properties?

. Higher modulus of elasticity
. Higher ultimate tensile strength
. Lower modulus of elasticity
. Increased susceptibility to galvanic corrosion
. Greater resistance to fatigue failure from fretting

Correct Answer & Explanation

. Lower modulus of elasticity

Explanation

Titanium alloys possess a significantly lower modulus of elasticity than stainless steel or cobalt-chrome, making them biomechanically closer to the modulus of cortical bone. This property reduces stress shielding but renders the implant more flexible.

Question 1688

Topic: Biomechanics & Biomaterials

In the context of internal fixation biomechanics, maximizing the radius of a solid intramedullary nail will increase its torsional rigidity by a factor proportional to the radius raised to what power?

. First power
. Second power
. Third power
. Fourth power
. Fifth power

Correct Answer & Explanation

. Fourth power

Explanation

The torsional rigidity of a solid cylindrical implant is determined by its polar moment of inertia, which is proportional to the radius raised to the fourth power (r^4). Therefore, even a small increase in the nail diameter dramatically enhances its resistance to torsional deformation.

Question 1689

Topic: Biomechanics & Biomaterials

During hardware removal, a surgeon notes significant degradation around a stainless steel screw that was inadvertently placed through a titanium plate. This accelerated localized degradation is primarily an example of which type of corrosion?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in direct electrical contact within an electrolytic physiological fluid. The metal with the lower electrochemical potential (more anodic) corrodes at an accelerated rate, while the more cathodic metal is protected.

Question 1690

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is frequently utilized for the fixation of total joint arthroplasty components. Which of the following statements is true regarding its fundamental biomechanical properties and clinical function?

. It acts as a true adhesive, bonding chemically directly to the surrounding bone
. It possesses its highest strength in tension and its lowest strength in compression
. It functions purely as a mechanical grout to evenly distribute compressive loads
. It undergoes significant volumetric expansion during the exothermic polymerization phase
. It promotes direct cellular osseointegration over its long-term lifespan

Correct Answer & Explanation

. It functions purely as a mechanical grout to evenly distribute compressive loads

Explanation

PMMA bone cement does not possess true adhesive properties; rather, it acts as a mechanical grout that creates an interlocking fit with the cancellous bone to transfer and distribute compressive loads. It is mechanically strongest in compression and highly vulnerable to failure under tension and shear forces.

Question 1691

Topic: Biomechanics & Biomaterials

A surgeon places a titanium screw through a stainless steel plate. What type of corrosion is most likely to occur at the interface of these two metals?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Uniform corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in a conductive fluid, creating an electrochemical gradient. The less noble metal acts as an anode and selectively corrodes.

Question 1692

Topic: Biomechanics & Biomaterials

When combining different orthopedic implants, galvanic corrosion can occur due to differences in electrochemical potential. Which combination of metals is most likely to result in significant galvanic corrosion if placed in direct physical contact?

. Titanium and Cobalt-Chrome
. Stainless Steel and Titanium
. Cobalt-Chrome and Cobalt-Chrome
. Titanium and Titanium
. Stainless Steel and Cobalt-Chrome

Correct Answer & Explanation

. Stainless Steel and Titanium

Explanation

Stainless steel and titanium have significantly different electrochemical potentials, making them highly susceptible to galvanic corrosion when in contact. Titanium and cobalt-chrome have closer potentials and are generally safe to mix in modular implants.

Question 1693

Topic: Biomechanics & Biomaterials

On a load-deformation curve for bone, the point at which the material transitions from elastic to plastic deformation is known as what?

. Ultimate failure point
. Yield point
. Proportional limit
. Toe region
. Fatigue limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the transition from elastic (reversible) to plastic (irreversible) deformation. Loading past this point causes permanent structural change before ultimate failure occurs.

Question 1694

Topic: Biomechanics & Biomaterials

A surgeon plans to revise a failed nonunion utilizing a stainless steel plate and titanium screws. Which of the following forms of corrosion is most likely to occur due to mixing these metals?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Pitting corrosion
. Fatigue corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic environment, like body fluid. The less noble metal acts as an anode and corrodes faster, which is why mixing stainless steel and titanium is generally contraindicated.

Question 1695

Topic: Biomechanics & Biomaterials
Increasing the radiation cross-linking of ultra-high molecular weight polyethylene (UHMWPE) used in total joint arthroplasty has which of the following biomechanical effects?
. Increases fatigue resistance
. Increases ductility
. Decreases wear resistance
. Decreases fracture toughness
. Increases ultimate tensile strength

Correct Answer & Explanation

. Decreases fracture toughness

Explanation

Highly cross-linked polyethylene significantly decreases volumetric wear but at the cost of decreasing fracture toughness, ductility, and fatigue resistance. This makes it more susceptible to rim fractures under certain loading conditions.

Question 1696

Topic: Biomechanics & Biomaterials

When comparing titanium alloy (Ti-6Al-4V) to stainless steel (316L) for orthopedic implants, which biomechanical property of titanium provides a more favorable stress transfer to surrounding bone?

. Higher ultimate tensile strength
. Lower modulus of elasticity
. Higher yield strength
. Greater ductility
. Increased galvanic corrosion

Correct Answer & Explanation

. Lower modulus of elasticity

Explanation

Titanium alloy has a significantly lower modulus of elasticity compared to stainless steel, making it much closer to the modulus of cortical bone. This reduces stress shielding and promotes better load sharing with the surrounding bone.

Question 1697

Topic: Biomechanics & Biomaterials

A surgeon incorrectly uses a stainless steel screw to secure a titanium alloy plate during fracture fixation. Which type of corrosion is most likely to occur at the screw-plate interface?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are placed in direct contact within an electrolytic medium like bodily fluids. The less noble metal acts as an anode and undergoes accelerated corrosion.

Question 1698

Topic: Biomechanics & Biomaterials

A 45-year-old male undergoes open reduction and internal fixation for a femur fracture. The surgeon inadvertently uses a stainless steel screw with a titanium plate. Which of the following best describes the resulting electrochemical process that leads to early implant failure?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are in physical contact within an electrolytic medium (such as body fluid). This creates an electrochemical cell, leading to the accelerated corrosion of the less noble metal (stainless steel in this case). Fretting corrosion is mechanically induced by micromotion, while crevice corrosion happens in restricted spaces with oxygen depletion.

Question 1699

Topic: Biomechanics & Biomaterials

When a sustained, constant load is applied to a viscoelastic structure such as a ligament over a period of time, the tissue will continue to slowly elongate. This biomechanical phenomenon is known as:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent, progressive deformation (elongation) of a viscoelastic material when it is subjected to a constant, continuous load. Stress relaxation is the inverse phenomenon: the decrease in internal stress over time when a material is held at a constant length. Hysteresis represents the energy lost (dissipated as heat) between the loading and unloading curves.

Question 1700

Topic: Biomechanics & Biomaterials

When analyzing the mechanical behavior of ligaments, the phenomenon where the tension within a ligament gradually decreases while it is held at a constant length is known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the stress (tension) within a material decreases over time when it is held at a constant strain (length). Conversely, creep refers to continuous deformation over time under a constant load.

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