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Biomechanics & Biomaterials MCQs

Practice Set 51 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 1001

Topic: Biomechanics & Biomaterials

A surgeon applies a constant, continuous distraction force to a contracted joint capsule using a hinged external fixator. Over several days, the capsule gradually elongates without any increase in the applied force. What is the biomechanical term for this viscoelastic phenomenon?

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

Correct Answer & Explanation

. Creep

Explanation

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

Question 1002

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) is widely used for implant fixation in joint arthroplasty. Which of the following statements accurately describes its biomechanical properties?

. It acts as a biological adhesive that covalently bonds to bone.
. It possesses its highest mechanical strength in tension.
. It relies on mechanical interlock and is strongest in compression.
. Increasing its porosity improves its fatigue life.
. Its polymerization process is highly endothermic.

Correct Answer & Explanation

. It relies on mechanical interlock and is strongest in compression.

Explanation

PMMA is a brittle grout, not a true adhesive; it provides fixation through micromodular mechanical interlock with cancellous bone. It is significantly stronger in compression than in tension or shear, and its setting reaction is highly exothermic.

Question 1003

Topic: Biomechanics & Biomaterials

A trauma surgeon uses a stainless steel dynamic compression plate but places titanium alloy screws for fixation of a diaphyseal femur fracture due to lack of inventory. 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 dissimilar metals (e.g., stainless steel and titanium) are placed in direct physical contact within a conductive electrolytic medium, such as human body fluid. This leads to accelerated corrosion of the less noble metal.

Question 1004

Topic: Biomechanics & Biomaterials

When a constant tensile force is applied to a ligament over a prolonged period, the ligament gradually continues to elongate. Which biomechanical term best describes this time-dependent property?

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

Correct Answer & Explanation

. Creep

Explanation

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

Question 1005

Topic: Biomechanics & Biomaterials
Which of the following sterilization methods for ultra-high-molecular-weight polyethylene (UHMWPE) acetabular liners is most strongly associated with increased free radical formation and subsequent in vivo oxidative degradation?
. Ethylene oxide gas
. Gamma irradiation in air
. Hydrogen peroxide gas plasma
. Gamma irradiation in a vacuum
. Autoclaving

Correct Answer & Explanation

. Gamma irradiation in air

Explanation

Gamma irradiation of UHMWPE in an oxygen-rich environment (air) generates free radicals that react with oxygen. This leads to chain scission, oxidative degradation, and ultimately increases the risk of catastrophic wear and delamination.

Question 1006

Topic: Biomechanics & Biomaterials
What is the primary mechanical disadvantage of increasing the radiation dose to produce highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty?
. Increased adhesive wear rate
. Decreased fracture toughness and fatigue strength
. Increased susceptibility to oxidative degradation
. Decreased elastic modulus leading to stress shielding
. Increased rate of osteolysis

Correct Answer & Explanation

. Decreased fracture toughness and fatigue strength

Explanation

Increasing the radiation dose to cross-link UHMWPE significantly reduces wear, but it concomitantly decreases its mechanical properties, including fracture toughness, fatigue strength, and ultimate tensile strength. Post-irradiation melting is used to eliminate free radicals and reduce oxidative degradation.

Question 1007

Topic: Biomechanics & Biomaterials

A patient undergoes revision total hip arthroplasty for unexplained pain and a pseudo-tumor associated with a modular neck prosthesis. Black particulate debris is noted at the head-neck junction. What type of corrosion primarily initiates this specific failure cascade?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs at modular interfaces (like the trunnion-head junction) due to micromotion under cyclical loading. This mechanical disruption destroys the passivating oxide layer, leading to mechanically assisted crevice corrosion (trunnionosis).

Question 1008

Topic: Biomechanics & Biomaterials

A researcher is evaluating the mechanical properties of a newly developed orthopaedic alloy. On the generated stress-strain curve, the point at which the material ceases to deform elastically and begins to deform permanently is known as the:

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

Correct Answer & Explanation

. Proportional limit (Yield point)

Explanation

The yield point, or proportional limit, represents the transition from elastic (reversible) deformation to plastic (permanent) deformation on a stress-strain curve. The modulus of elasticity represents the slope of the elastic region.

Question 1009

Topic: Biomechanics & Biomaterials

Which of the following best describes the viscoelastic property of "creep" in orthopedic tissues?

. Progressive deformation over time under a constant load
. Decreasing stress over time under a constant deformation
. Increased stiffness with higher rates of loading
. Energy lost during a loading and unloading cycle
. Failure of a material after repeated cyclic loading

Correct Answer & Explanation

. Progressive deformation over time under a constant load

Explanation

Creep is the gradual, time-dependent deformation of a viscoelastic material when subjected to a constant load. In contrast, stress relaxation is the decrease in stress over time when held at a constant deformation.

Question 1010

Topic: Biomechanics & Biomaterials

Titanium alloy (Ti-6Al-4V) is frequently used in orthopedic implants due to its biocompatibility. Compared to cobalt-chromium alloys, titanium alloy exhibits which of the following mechanical properties?

. Higher modulus of elasticity
. Higher density
. Lower notch sensitivity
. Lower modulus of elasticity
. Greater galvanic potential

Correct Answer & Explanation

. Lower modulus of elasticity

Explanation

Titanium alloys have a lower modulus of elasticity than cobalt-chromium alloys or stainless steel, making them closer to the elasticity of cortical bone. This helps reduce stress shielding around implants.

Question 1011

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is commonly used in total joint arthroplasty. Which of the following occurs during the polymerization process of PMMA?

. Endothermic reaction resulting in localized cooling
. Release of nitrogen gas to create porosity
. Exothermic reaction that can cause thermal necrosis
. Expansion of the cement volume upon curing
. Cross-linking initiated by exposure to ultraviolet light

Correct Answer & Explanation

. Exothermic reaction that can cause thermal necrosis

Explanation

The polymerization of PMMA is a highly exothermic reaction. Temperatures can exceed 80-100°C, which poses a risk of thermal necrosis to the surrounding bone.

Question 1012

Topic: Biomechanics & Biomaterials
A patient presents with acute knee swelling. Aspiration yields cloudy synovial fluid with a white blood cell count of 65,000 cells/mm³, predominantly polymorphonuclear leukocytes. Polarized light microscopy shows negatively birefringent, needle-shaped crystals. What is the composition of these crystals?
. Calcium pyrophosphate dihydrate
. Monosodium urate
. Basic calcium phosphate
. Cholesterol
. Hydroxyapatite

Correct Answer & Explanation

. Monosodium urate

Explanation

The clinical picture and fluid analysis are diagnostic of acute gout. Monosodium urate crystals are classically needle-shaped and exhibit strong negative birefringence under polarized light.

Question 1013

Topic: Biomechanics & Biomaterials

When comparing the mechanical properties of orthopedic implant materials, which of the following correctly orders the Young's modulus of elasticity from highest (stiffest) to lowest (most flexible)?

. Cortical bone, Titanium, Cobalt-Chrome
. Cobalt-Chrome, Titanium, Cortical bone
. Titanium, Cobalt-Chrome, Cortical bone
. Cobalt-Chrome, Cortical bone, Titanium
. Titanium, Cortical bone, Cobalt-Chrome

Correct Answer & Explanation

. Cobalt-Chrome, Titanium, Cortical bone

Explanation

Cobalt-chrome is the stiffest (highest modulus), followed by stainless steel (not listed), then titanium alloys. Cortical bone has a much lower modulus of elasticity than these metals, which can lead to stress shielding.

Question 1014

Topic: Biomechanics & Biomaterials

Placing a stainless steel screw through a titanium plate in an orthopaedic construct can lead to accelerated degradation of the less noble metal. This phenomenon is known as:

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within an electrolytic environment, such as bodily fluids. The less noble metal acts as an anode and undergoes accelerated oxidation compared to a monometallic construct.

Question 1015

Topic: Biomechanics & Biomaterials

A viscoelastic material, such as a tendon or ligament, is subjected to a constant, prolonged load. Over time, the material continues to deform despite the load remaining unchanged. This biomechanical property is known as:

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

Correct Answer & Explanation

. Creep

Explanation

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

Question 1016

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, which of the following terms best describes the time-dependent increase in strain of a viscoelastic material under a constant applied stress?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the continuous deformation (strain) of a material over time when subjected to a constant load (stress). Stress relaxation is the decrease in stress over time under a constant strain.

Question 1017

Topic: Biomechanics & Biomaterials

Which of the following implant combinations poses the highest risk for galvanic corrosion in orthopedic surgery?

. A titanium alloy screw used with a titanium alloy plate
. A stainless steel screw used with a titanium alloy plate
. A cobalt-chromium head on a titanium stem
. A ceramic head on a cobalt-chromium stem
. A PMMA mantle surrounding a cobalt-chromium stem

Correct Answer & Explanation

. A stainless steel screw used with a titanium alloy plate

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in direct contact within an electrolytic environment, such as bodily fluids. Combining stainless steel and titanium implants creates a strong galvanic cell that accelerates corrosion.

Question 1018

Topic: Biomechanics & Biomaterials
To decrease the rate of adhesive and abrasive wear in total joint arthroplasty, ultra-high-molecular-weight polyethylene (UHMWPE) can be highly cross-linked via irradiation. Which of the following processes is required to eliminate the resulting free radicals and prevent subsequent oxidative degradation?
. Gamma irradiation in air
. Ethylene oxide sterilization
. Remelting or annealing
. Cold working
. Addition of barium sulfate

Correct Answer & Explanation

. Remelting or annealing

Explanation

Irradiating polyethylene creates cross-links but also generates free radicals that can lead to oxidation and structural degradation over time. Thermal processing, either by remelting or annealing, extinguishes these free radicals and improves long-term oxidation resistance.

Question 1019

Topic: Biomechanics & Biomaterials
In the manufacturing of ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty, the addition of Vitamin E (alpha-tocopherol) primarily serves to:
. Increase the degree of polymer cross-linking
. Scavenge free radicals to prevent oxidative degradation
. Enhance the elastic modulus of the bearing surface
. Decrease the melting temperature of the polymer
. Promote osteointegration at the bone-implant interface

Correct Answer & Explanation

. Scavenge free radicals to prevent oxidative degradation

Explanation

Vitamin E is blended into highly cross-linked UHMWPE to act as a potent antioxidant. It actively scavenges residual free radicals produced during gamma irradiation, thereby preventing long-term oxidative degradation without the mechanical compromises of post-irradiation melting.

Question 1020

Topic: Biomechanics & Biomaterials

According to fundamental biomechanical principles, if the diameter of a solid titanium intramedullary nail is doubled, its overall torsional rigidity will theoretically increase by a factor of:

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 16

Explanation

The torsional rigidity of a solid cylindrical implant is directly proportional to its polar moment of inertia. Because the polar moment of inertia scales with the radius to the fourth power (r^4), doubling the diameter increases the rigidity by a factor of 16.

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