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Biomechanics & Biomaterials MCQs

Practice Set 40 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 781

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 782

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 783

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 784

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 785

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 786

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.

Question 787

Topic: Biomechanics & Biomaterials

Ligaments exhibit viscoelastic properties, meaning their mechanical behavior is highly dependent on the rate of loading. How does a ligament respond to a rapid, high-velocity load compared to a slow load?

. It becomes less stiff and fails at a lower load
. It becomes stiffer and absorbs more energy before failure
. Its modulus of elasticity decreases significantly
. It elongates further before reaching the yield point
. It demonstrates increased stress relaxation

Correct Answer & Explanation

. It becomes less stiff and fails at a lower load

Explanation

Viscoelastic materials like ligaments and bone become stiffer (increased modulus of elasticity) and can absorb more energy before failure when subjected to high loading rates compared to slow loading rates.

Question 788

Topic: Biomechanics & Biomaterials

In the stress-strain curve of a given orthopaedic material, what does the area under the curve in the elastic region represent?

. Toughness
. Resilience
. Yield strength
. Ultimate tensile strength
. Plastic deformation

Correct Answer & Explanation

. Toughness

Explanation

The area under the stress-strain curve in the elastic region represents the resilience of the material. The total area under the entire curve (elastic and plastic regions combined) represents the material's toughness.

Question 789

Topic: Biomechanics & Biomaterials

When increasing the outer diameter of a solid intramedullary nail by a factor of 2, the torsional rigidity increases by a factor of:

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 2

Explanation

For a solid cylinder, torsional rigidity is proportional to the polar moment of inertia, which scales with the radius to the fourth power (r^4). Therefore, doubling the diameter increases the torsional rigidity by a factor of 16.

Question 790

Topic: Biomechanics & Biomaterials

A viscoelastic material subjected to a constant load demonstrates a progressive increase in deformation over time. This phenomenon is known as:

. Hysteresis
. Fatigue
. Creep
. Stress relaxation
. Anisotropy

Correct Answer & Explanation

. Hysteresis

Explanation

Creep is the time-dependent increase in deformation (strain) under a constant load (stress). In contrast, stress relaxation is the decrease in stress over time under a constant state of deformation.

Question 791

Topic: Biomechanics & Biomaterials

Which of the following combinations of orthopaedic implant materials is most likely to result in severe galvanic corrosion when placed in direct contact in vivo?

. Titanium and Titanium alloy
. Stainless steel and Cobalt-chrome
. Titanium alloy and Cobalt-chrome
. 316L Stainless steel and Titanium
. Ceramic and Titanium

Correct Answer & Explanation

. Titanium and Titanium alloy

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact in an electrolytic environment. The combination of stainless steel and titanium creates a significant difference in electrochemical potential, leading to severe galvanic corrosion of the less noble metal (stainless steel).

Question 792

Topic: Biomechanics & Biomaterials

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

. Core diameter
. Inner diameter
. Outer thread diameter
. Pitch
. Thread depth

Correct Answer & Explanation

. Core diameter

Explanation

The pullout strength of a screw is directly proportional to the outer (major) diameter of the thread, the length of thread engagement, and the shear strength of the bone. The core (inner) diameter determines the screw's tensile strength and resistance to fatigue failure.

Question 793

Topic: Biomechanics & Biomaterials

Cortical bone exhibits different mechanical properties depending on the direction of the applied load. This material property is defined as:

. Viscoelasticity
. Anisotropy
. Isotropic behavior
. Creep
. Hysteresis

Correct Answer & Explanation

. Viscoelasticity

Explanation

Anisotropy refers to a material exhibiting varying mechanical properties when loaded in different directions. Cortical bone is highly anisotropic, being strongest when resisting longitudinal compression and weakest under transverse tension.

Question 794

Topic: Biomechanics & Biomaterials

In total joint arthroplasty, cross-linking of ultra-high-molecular-weight polyethylene (UHMWPE) alters its mechanical properties by:

. Decreasing wear rate and increasing fatigue strength
. Decreasing wear rate and decreasing toughness
. Increasing wear rate and increasing ductility
. Increasing both wear rate and toughness
. Eliminating the potential for oxidation completely

Correct Answer & Explanation

. Decreasing wear rate and increasing fatigue strength

Explanation

Highly cross-linked UHMWPE demonstrates a significantly decreased wear rate, which effectively reduces particle-induced osteolysis. However, the cross-linking process negatively alters mechanical properties, leading to decreased toughness, reduced fatigue strength, and lower ductility.

Question 795

Topic: Biomechanics & Biomaterials

A patient undergoes internal fixation with a titanium alloy plate. Compared to stainless steel, titanium alloy exhibits which of the following mechanical properties?

. Higher modulus of elasticity and decreased fatigue strength
. Higher modulus of elasticity and increased fatigue strength
. Lower modulus of elasticity and decreased biocompatibility
. Lower modulus of elasticity and decreased stress shielding
. Lower modulus of elasticity and increased stress shielding

Correct Answer & Explanation

. Higher modulus of elasticity and decreased fatigue strength

Explanation

Titanium alloy has a lower modulus of elasticity compared to stainless steel, bringing it closer to that of cortical bone. This leads to less stress shielding of the underlying bone, preserving bone density.

Question 796

Topic: Biomechanics & Biomaterials

When a constant load is applied to a viscoelastic material such as a ligament over a prolonged period, the material will undergo a time-dependent increase in length. This phenomenon is known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

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

Question 797

Topic: Biomechanics & Biomaterials

A surgeon uses a stainless steel screw to secure a titanium plate during fracture fixation. The construct is at high risk for which of the following complications?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are placed in contact within a conductive fluid environment like the human body. The less noble metal acts as an anode and undergoes accelerated corrosion.

Question 798

Topic: Biomechanics & Biomaterials

Which of the following biomechanical principles is the primary advantage of utilizing a locked plating construct over a conventional compression plate in osteoporotic bone?

. Increased frictional force between the plate and bone
. Dependence on the pullout strength of individual screws
. Functioning as a fixed-angle construct that resists toggling
. Dynamic compression of the fracture gap
. Lower modulus of elasticity of the entire construct

Correct Answer & Explanation

. Increased frictional force between the plate and bone

Explanation

Locked plating constructs function as single-beam, fixed-angle devices where the screw heads thread directly into the plate. This resists toggling and secondary loss of reduction, making them mechanically superior in osteoporotic bone where friction-based conventional plates often fail.

Question 799

Topic: Biomechanics & Biomaterials

Which of the following best describes the phenomenon of 'creep' in the viscoelastic behavior of ligaments?

. A decrease in stress over time under a constant strain
. An increase in strain over time under a constant stress
. The failure of a material after repeated cyclic loading
. The loss of energy during a loading and unloading cycle
. The increase in stiffness with an increased rate of loading

Correct Answer & Explanation

. A decrease in stress over time under a constant strain

Explanation

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

Question 800

Topic: Biomechanics & Biomaterials

Highly cross-linked polyethylene used in total joint arthroplasty aims to reduce wear but is associated with which of the following trade-offs?

. Increased oxidative degradation if not remelted or annealed
. Increased adhesive wear
. Decreased modulus of elasticity
. Increased fatigue strength
. Decreased risk of impingement

Correct Answer & Explanation

. Increased oxidative degradation if not remelted or annealed

Explanation

Cross-linking polyethylene with gamma irradiation generates free radicals that can cause oxidative degradation over time. Thermal treatments like remelting or annealing are required to quench these free radicals, though remelting can reduce fatigue strength.

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