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Biomechanics & Biomaterials MCQs

Practice Set 27 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 521

Topic: Biomechanics & Biomaterials

Which of the following combinations of orthopedic metals is most likely to result in significant galvanic corrosion when placed in direct contact within the body?

. Titanium alloy and commercially pure titanium
. 316L stainless steel and cobalt-chromium alloy
. Cobalt-chromium alloy and titanium alloy
. 316L stainless steel and titanium alloy
. Tantalum and titanium alloy

Correct Answer & Explanation

. 316L stainless steel and titanium alloy

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact in an electrolytic environment. Mixing 316L stainless steel with titanium or cobalt-chromium leads to severe galvanic corrosion of the less noble metal (stainless steel).

Question 522

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit stress relaxation, which is a viscoelastic property defined as:

. Increasing deformation over time under a constant load
. Decreasing stress over time under a constant deformation
. Energy lost as heat during a loading and unloading cycle
. Increased stiffness when loaded at higher strain rates
. Permanent deformation remaining after load removal

Correct Answer & Explanation

. Decreasing stress over time under a constant deformation

Explanation

Stress relaxation is the decrease in stress (internal force) required to maintain a tissue at a constant strain (length) over time. In contrast, creep is the increasing deformation (lengthening) over time under a constant load.

Question 523

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, bending stiffness of a solid circular implant is proportional to the area moment of inertia. If the radius of a solid intramedullary rod is doubled, the bending stiffness increases by a factor of:

. 2
. 4
. 8
. 16
. 64

Correct Answer & Explanation

. 16

Explanation

The area moment of inertia for a solid cylinder is proportional to the radius to the fourth power (r^4). Therefore, doubling the radius (2^4) increases the bending stiffness 16-fold.

Question 524

Topic: Biomechanics & Biomaterials
To improve the wear characteristics of ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty, it undergoes highly cross-linking via irradiation followed by remelting. What is the primary biomechanical tradeoff of the remelting process?
. Increases free radical concentration leading to in vivo oxidation
. Increases yield strength and fatigue resistance
. Decreases crystallinity and reduces yield strength/fatigue resistance
. Increases the rate of in vivo oxidation compared to annealing
. Promotes adhesive wear over abrasive wear

Correct Answer & Explanation

. Decreases crystallinity and reduces yield strength/fatigue resistance

Explanation

Remelting UHMWPE (heating above its melting point) effectively eliminates residual free radicals, significantly reducing long-term oxidation risk. However, it decreases the polymer's crystallinity, which subsequently lowers its yield strength and fatigue resistance.

Question 525

Topic: Biomechanics & Biomaterials

A surgeon plans to revise a fractured femoral plate but decides to mix a titanium locking plate with stainless steel screws. What is the primary concern regarding galvanic corrosion in this construct?

. Titanium undergoes rapid anodic dissolution
. Stainless steel acts as the anode and preferentially corrodes
. Both metals corrode equally due to fretting wear
. Titanium acts as the anode and preferentially corrodes
. A passive oxide layer completely prevents galvanic corrosion in both

Correct Answer & Explanation

. Stainless steel acts as the anode and preferentially corrodes

Explanation

In a galvanic cell with dissimilar metals, the less noble metal acts as the anode and undergoes corrosion. Titanium is highly noble and acts as the cathode, causing the less noble stainless steel (anode) to preferentially corrode.

Question 526

Topic: Biomechanics & Biomaterials

Viscoelastic materials, such as ligaments and articular cartilage, exhibit time-dependent mechanical properties. Which of the following correctly describes 'stress relaxation'?

. Progressive deformation of a material under a constant load over time
. A decrease in stress within a material maintained at a constant deformation over time
. Energy lost as heat during a single loading-unloading cycle
. A strain-rate-dependent increase in stiffness during rapid loading
. Permanent structural damage after exceeding the material's yield point

Correct Answer & Explanation

. A decrease in stress within a material maintained at a constant deformation over time

Explanation

Stress relaxation refers to the decrease in applied stress required to maintain a given, constant strain (deformation) over time. Creep, in contrast, is the progressive deformation under a constant load.

Question 527

Topic: Biomechanics & Biomaterials

The phenomenon where an orthopaedic biomaterial subjected to a constant load exhibits a progressive increase in strain over time is known as:

. Stress relaxation
. Creep
. Fatigue
. Hysteresis
. Toughness

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent deformation of a viscoelastic material under a constant load. Stress relaxation, conversely, is the decrease in stress over time under a constant strain.

Question 528

Topic: Biomechanics & Biomaterials

Which of the following factors is the primary driving force for galvanic corrosion when two dissimilar metals are implanted in the body?

. Difference in yield strength
. Difference in electrochemical potential
. Difference in Young's modulus
. Difference in surface roughness
. Difference in thermal expansion coefficients

Correct Answer & Explanation

. Difference in electrochemical potential

Explanation

Galvanic corrosion occurs when two metals with different electrochemical potentials are placed in contact within a conductive fluid. The less noble metal acts as an anode and corrodes.

Question 529

Topic: Biomechanics & Biomaterials

On a stress-strain curve representing an orthopaedic biomaterial, the area under the elastic region is defined as:

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

Correct Answer & Explanation

. Resilience

Explanation

Resilience is the capacity of a material to absorb energy in the elastic range, represented by the area under the elastic portion of the stress-strain curve. Toughness is the total area under the entire curve.

Question 530

Topic: Biomechanics & Biomaterials

Which of the following best describes the phenomenon of "creep" in viscoelastic orthopaedic materials?

. Increasing deformation under a constant load over time
. Decreasing stress under a constant deformation over time
. Energy loss during a loading and unloading cycle
. Microfracture accumulation under cyclic submaximal loading
. Immediate plastic deformation past the yield point

Correct Answer & Explanation

. Increasing deformation under a constant load over time

Explanation

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

Question 531

Topic: Biomechanics & Biomaterials
Gamma irradiation of ultra-high molecular weight polyethylene (UHMWPE) in an inert environment (e.g., argon or vacuum) followed by remelting is primarily performed to achieve which of the following?
. Increase the crystalline content of the polyethylene
. Eliminate free radicals and reduce oxidative degradation
. Increase the elastic modulus of the bearing surface
. Decrease the cross-linking density
. Enhance water absorption for better lubrication

Correct Answer & Explanation

. Eliminate free radicals and reduce oxidative degradation

Explanation

Gamma irradiation facilitates cross-linking to improve wear resistance but also creates free radicals that can lead to oxidative degradation. Remelting the polyethylene eliminates these free radicals, stabilizing the material against oxidation at the cost of slight decreases in mechanical strength.

Question 532

Topic: Biomechanics & Biomaterials

Which of the following orthopaedic biomaterials has a Young's modulus of elasticity most closely matching that of human cortical bone?

. Alumina ceramic
. Cobalt-chromium alloy
. Stainless steel
. Titanium alloy
. Ultra-high molecular weight polyethylene

Correct Answer & Explanation

. Titanium alloy

Explanation

Human cortical bone has a Young's modulus of approximately 15-20 GPa. Titanium alloys (~110 GPa) are closer to cortical bone than stainless steel (~200 GPa) or cobalt-chromium alloys (~220 GPa), resulting in less stress shielding.

Question 533

Topic: Biomechanics & Biomaterials

Figure 1 displays a stress-strain curve for a typical metallic orthopaedic implant.

The exact point on the curve where the material transitions from completely recoverable elastic deformation to non-recoverable plastic deformation is defined as the:

. Ultimate tensile strength
. Failure point
. Yield point
. Modulus of elasticity
. Endurance limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point characterizes the transition from elastic to plastic behavior on a stress-strain curve. Loading the material beyond this specific point results in permanent (plastic) deformation.

Question 534

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopaedic implants occurs under which of the following conditions?

. Repeated cyclic loading of a single metal component causing micro-cracks
. Mechanical wear between a metal head and a polyethylene liner
. Contact between two dissimilar metals in an electrolytic fluid environment
. Depletion of oxygen in a localized crevice such as a screw hole
. Release of metallic ions due to third-body abrasive wear

Correct Answer & Explanation

. Contact between two dissimilar metals in an electrolytic fluid environment

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are in direct physical contact within a conductive fluid environment (e.g., body fluids). The less noble metal acts as an anode and undergoes accelerated corrosion.

Question 535

Topic: Biomechanics & Biomaterials

In the context of tendon biomechanics, which of the following best describes the phenomenon of stress relaxation?

. Deformation of a material over time under a constant load
. Decrease in stress over time when a material is held at a constant length or deformation
. Energy lost as heat during a loading and unloading cycle
. Increase in stiffness with faster rates of loading
. Microscopic failure of collagen fibers prior to macroscopic failure

Correct Answer & Explanation

. Decrease in stress over time when a material is held at a constant length or deformation

Explanation

Stress relaxation is a viscoelastic property where the stress in a material decreases over time when it is held at a constant deformation. In contrast, creep is the continued deformation over time under a constant load.

Question 536

Topic: Biomechanics & Biomaterials

A surgeon considers using a titanium screw to secure a stainless steel plate. Which of the following best describes the primary biomechanical and biologic concern regarding this construct?

. Decreased construct stiffness
. Galvanic corrosion
. Crevice corrosion
. Fretting corrosion
. Increased osteolysis from titanium debris

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Mixing different metals, such as stainless steel and titanium, in an aqueous environment like the human body sets up an electrochemical cell. This leads to galvanic corrosion, where the less noble metal undergoes accelerated corrosion.

Question 537

Topic: Biomechanics & Biomaterials

The torsional strength of a solid intramedullary nail is proportional to its radius raised to which power?

. 1
. 2
. 3
. 4
. 5

Correct Answer & Explanation

. 5

Explanation

The polar moment of inertia for a solid cylinder, which determines torsional stiffness and strength, is proportional to the radius to the fourth power (r^4). Therefore, small increases in nail diameter exponentially increase its torsional strength.

Question 538

Topic: Biomechanics & Biomaterials

Which of the following orthopedic materials has a Young's modulus (modulus of elasticity) that most closely matches that of cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Alumina ceramic
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a Young's modulus much closer to that of cortical bone compared to stiffer materials like stainless steel and cobalt-chromium. This closer modulus match helps reduce stress shielding around implants.

Question 539

Topic: Biomechanics & Biomaterials

Galvanic corrosion is most likely to occur in an orthopaedic implant under which of the following conditions?

. Using a titanium screw in a stainless steel plate
. Using a cobalt-chrome femoral head on a cobalt-chrome stem
. Using a stainless steel screw in a stainless steel plate
. Scratching the passivation layer of an isolated titanium implant
. Cyclic loading of a polyethylene liner

Correct Answer & Explanation

. Using a titanium screw in a stainless steel plate

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in electrical contact within a conductive fluid medium, such as body fluid. The less noble metal serves as the anode and undergoes accelerated corrosion.

Question 540

Topic: Biomechanics & Biomaterials

Stress shielding around a femoral stem is most strongly influenced by which of the following material properties of the implant?

. Yield strength
. Ultimate tensile strength
. Modulus of elasticity
. Fatigue limit
. Ductility

Correct Answer & Explanation

. Modulus of elasticity

Explanation

Modulus of elasticity relates to a material's stiffness. Implants with a high modulus of elasticity bear most of the load when placed in bone, causing stress shielding and subsequent resorption of the unloaded surrounding bone.

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