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Biomechanics & Biomaterials MCQs

Practice Set 31 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 601

Topic: Biomechanics & Biomaterials

According to the principles of external fixation biomechanics, which of the following modifications will most significantly increase the bending stiffness of a half-pin?

. Increasing the core diameter of the pin
. Decreasing the distance from the bone to the external bar
. Increasing the total number of pins
. Placing pins in multiple different planes
. Changing the pin material from titanium to stainless steel

Correct Answer & Explanation

. Increasing the core diameter of the pin

Explanation

While bringing the bar closer to the bone increases construct stiffness, increasing the core diameter of the pin has the most profound effect on the individual pin's bending stiffness, as it is proportional to the radius to the fourth power (r^4).

Question 602

Topic: Biomechanics & Biomaterials

On a load-deformation or stress-strain curve for a structural material, what biomechanical property is represented by the slope of the linear portion?

. Toughness
. Yield strength
. Ultimate tensile strength
. Stiffness (Young's modulus)
. Ductility

Correct Answer & Explanation

. Toughness

Explanation

Young's modulus (or modulus of elasticity) is the slope of the linear, elastic portion of the stress-strain curve. It represents the intrinsic stiffness of the material being tested.

Question 603

Topic: Biomechanics & Biomaterials

The time-dependent increase in strain of articular cartilage when subjected to a constant, prolonged compressive load is termed:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is defined as the progressive time-dependent deformation (increase in strain) of a viscoelastic material under a constant load. In contrast, stress relaxation is the decrease in stress over time when held at a constant strain.

Question 604

Topic: Biomechanics & Biomaterials

Which of the following combinations of orthopedic implants is most likely to result in significant galvanic corrosion if placed in direct physical contact in vivo?

. Titanium alloy and Commercially pure titanium
. Cobalt-chromium and Cobalt-chromium
. Titanium alloy and Stainless steel
. Stainless steel and Stainless steel
. Titanium alloy and Tantalum

Correct Answer & Explanation

. Titanium alloy and Commercially pure titanium

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are in direct contact within an electrolytic environment. The combination of titanium and stainless steel is highly prone to severe galvanic corrosion and must be avoided.

Question 605

Topic: Biomechanics & Biomaterials

On a stress-strain curve of a normal human tendon, what does the initial non-linear "toe region" represent?

. Yielding of collagen fibers
. Uncrimping of collagen fibers
. Microscopic failure of fascicles
. Macroscopic failure of the tendon
. Plastic deformation

Correct Answer & Explanation

. Yielding of collagen fibers

Explanation

The initial toe region occurs at low strains and represents the straightening or "uncrimping" of the naturally wavy collagen fibers in the resting tendon. Beyond this region, the curve becomes linear as the fibers themselves begin to stretch.

Question 606

Topic: Biomechanics & Biomaterials

The primary inorganic mineral constituent that provides mature human bone with its compressive strength is:

. Calcium carbonate
. Hydroxyapatite
. Calcium pyrophosphate
. Calcium oxalate
. Brushite

Correct Answer & Explanation

. Calcium carbonate

Explanation

The mineral phase of bone is primarily composed of carbonated, calcium-deficient hydroxyapatite. This inorganic crystalline matrix is embedded within the collagen network and provides bone with its high compressive strength.

Question 607

Topic: Biomechanics & Biomaterials

During biomechanical testing of a new orthopedic implant material, a load is applied and the material undergoes deformation. The slope of the linear portion of the resulting stress-strain curve represents which of the following mechanical properties?

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

Correct Answer & Explanation

. Yield strength

Explanation

The modulus of elasticity (Young's modulus) is defined by the slope of the linear (elastic) portion of the stress-strain curve. It is a measure of the material's stiffness.

Question 608

Topic: Biomechanics & Biomaterials
Polymer materials used in orthopedics, such as ultra-high-molecular-weight polyethylene (UHMWPE), exhibit viscoelastic properties. The phenomenon where a material continues to slowly deform over time while subjected to a constant load is known as:
. Creep
. Stress relaxation
. Fatigue failure
. Hysteresis
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is a viscoelastic property defined as progressive, time-dependent deformation under a constant load or stress.

Question 609

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) was introduced to improve the longevity of total hip replacements. Which of the following describes the mechanical tradeoff associated with heavily cross-linking UHMWPE?
. Increased wear resistance and decreased fatigue strength
. Increased wear resistance and increased fatigue strength
. Decreased wear resistance and increased fatigue strength
. Decreased wear resistance and decreased fatigue strength
. Increased oxidative stability with no change in fatigue strength

Correct Answer & Explanation

. Increased wear resistance and decreased fatigue strength

Explanation

Cross-linking UHMWPE significantly improves its wear resistance but at the cost of decreasing its mechanical properties, including fatigue strength, ductility, and fracture toughness.

Question 610

Topic: Biomechanics & Biomaterials

In materials science, 'toughness' is a critical property for fracture fixation hardware. Toughness is best defined mechanically as:

. The maximum stress a material can withstand before failure
. The material's resistance to surface indentation
. The total energy absorbed by a material before failure
. The point on the stress-strain curve where plastic deformation begins
. The amount of stress required to propagate a pre-existing crack

Correct Answer & Explanation

. The maximum stress a material can withstand before failure

Explanation

Toughness is the capacity of a material to absorb energy and deform plastically before fracturing. It is represented by the total area under the stress-strain curve.

Question 611

Topic: Biomechanics & Biomaterials

Orthopedic implants are manufactured from various biomaterials. Which of the following metallic alloys has a modulus of elasticity closest to that of human cortical bone, thereby theoretically reducing stress shielding?

. 316L Stainless steel
. Cobalt-chromium-molybdenum
. Titanium-6Aluminum-4Vanadium
. Commercially pure tantalum
. Alumina

Correct Answer & Explanation

. 316L Stainless steel

Explanation

Titanium alloys have a modulus of elasticity (approx. 110 GPa) that is lower than that of cobalt-chromium or stainless steel, making it closer to cortical bone (approx. 15-20 GPa) and reducing stress shielding.

Question 612

Topic: Biomechanics & Biomaterials

A ligament subjected to a constant, sustained load elongates progressively over time. This viscoelastic property is best described as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue
. Strain rate dependency

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the progressive deformation (elongation) of a viscoelastic material when subjected to a constant load over time. Stress relaxation, conversely, occurs when a material is held at a constant length and the internal force decreases.

Question 613

Topic: Biomechanics & Biomaterials

On a stress-strain curve for an orthopedic biomaterial, the area under the curve strictly within the elastic region represents the material's:

. Toughness
. Yield strength
. Ultimate tensile strength
. Resilience
. Ductility

Correct Answer & Explanation

. Toughness

Explanation

The area under the stress-strain curve in the elastic region represents resilience, defined as the energy a material can absorb and release without undergoing permanent deformation. Toughness, by contrast, is the total area under the entire curve until failure.

Question 614

Topic: Biomechanics & Biomaterials

An orthopedic implant undergoes cyclical loading well below its ultimate yield strength but eventually fails. On an S-N (Stress-Number of cycles) curve, what does the endurance limit represent?

. The maximum stress an implant can withstand for a single loading cycle
. The point at which macroscopic plastic deformation begins
. The stress level below which the material will theoretically never fail regardless of the number of cycles
. The total number of cycles to failure at the ultimate tensile stress
. The yield strength of a viscoelastic material at a constant strain rate

Correct Answer & Explanation

. The maximum stress an implant can withstand for a single loading cycle

Explanation

The endurance limit (or fatigue limit) is the specific stress threshold on an S-N curve below which a material can endure an infinite number of loading cycles without fatigue failure. Not all materials, such as aluminum, exhibit a true endurance limit.

Question 615

Topic: Biomechanics & Biomaterials

In comparing orthopedic implant materials, which of the following accurately describes the relationship between the Young's modulus of elasticity of titanium, stainless steel, and cortical bone?

. Stainless steel > Titanium > Cortical bone
. Titanium > Stainless steel > Cortical bone
. Cortical bone > Titanium > Stainless steel
. Stainless steel > Cortical bone > Titanium
. Titanium > Cortical bone > Stainless steel

Correct Answer & Explanation

. Stainless steel > Titanium > Cortical bone

Explanation

Stainless steel has a higher modulus of elasticity (~200 GPa) than titanium alloys (~100 GPa). Both are significantly stiffer than cortical bone (~15-20 GPa), which can lead to stress shielding.

Question 616

Topic: Biomechanics & Biomaterials

Cortical bone exhibits viscoelastic properties, meaning its biomechanical behavior depends on the rate of loading. Which of the following best describes the response of cortical bone to high-rate loading compared to low-rate loading?

. Decreased stiffness and decreased ultimate strength
. Increased stiffness and increased ultimate strength
. Unchanged stiffness with increased ductility
. Decreased modulus of elasticity with increased brittleness
. Increased plasticity before failure

Correct Answer & Explanation

. Decreased stiffness and decreased ultimate strength

Explanation

As a viscoelastic material, cortical bone becomes stiffer and can withstand higher loads before failing when it is loaded at higher strain rates. This increases both its modulus and ultimate strength.

Question 617

Topic: Biomechanics & Biomaterials

A surgeon considers using a titanium locking plate with stainless steel screws for fracture fixation. Why is this combination traditionally contraindicated in orthopedic surgery?

. It prevents adequate osseointegration of the plate
. It increases the risk of galvanic corrosion due to differences in electropotential
. It causes severe stress shielding due to mismatched Young's moduli
. It leads to immediate brittle failure of the screws
. It significantly alters the magnetic resonance imaging artifact

Correct Answer & Explanation

. It prevents adequate osseointegration of the plate

Explanation

Mixing dissimilar metals with different electropotentials in a conductive fluid environment (like the human body) creates a battery effect. This can lead to accelerated galvanic corrosion of the less noble metal.

Question 618

Topic: Biomechanics & Biomaterials

A patient presents with a pseudotumor around a modular total hip arthroplasty secondary to adverse local tissue reaction. The primary mechanism generating metal ions at the modular head-neck taper interface is:

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion is mechanically assisted crevice corrosion caused by micromotion at the interface of two contacting surfaces. This micromotion continually disrupts the protective passive oxide layer on modular tapers.

Question 619

Topic: Biomechanics & Biomaterials

A clubfoot is treated with serial Ponseti casting. The gradual stretching and elongation of the tightened medial ligaments and tendons under a constant applied load over time demonstrates which viscoelastic property?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the progressive deformation of a viscoelastic material over time when subjected to a constant force. Stress relaxation, by contrast, is a decrease in internal stress over time when held at a constant deformation.

Question 620

Topic: Biomechanics & Biomaterials

Which of the following material properties represents the total energy absorbed by a material before it fails, corresponding to the total area under the stress-strain curve?

. Toughness
. Stiffness
. Ductility
. Fatigue limit
. Viscoelasticity

Correct Answer & Explanation

. Toughness

Explanation

Toughness is the energy absorbed by a material prior to failure, represented by the total area under the stress-strain curve. Stiffness refers to the elastic region's slope (Young's modulus), while ductility is the amount of plastic deformation before failure.

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