Menu

Biomechanics & Biomaterials MCQs

Practice Set 57 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 1121

Topic: Biomechanics & Biomaterials

During revision hip arthroplasty, a surgeon considers placing a stainless steel cable around a titanium femoral stem. What is the primary concern regarding mixed-metal combinations in this orthopaedic setting?

. Titanium will act as the anode, rapidly corroding the stem
. Galvanic corrosion will occur, with stainless steel acting as the anode and dissolving
. Crevice corrosion will exclusively occur due to poor local oxygen tension
. The combination promotes an accelerated type IV hypersensitivity reaction to titanium
. The modulus of elasticity mismatch will cause immediate stem fracture

Correct Answer & Explanation

. Galvanic corrosion will occur, with stainless steel acting as the anode and dissolving

Explanation

Mixing dissimilar metals in an electrolytic environment (the human body) causes galvanic corrosion. The less noble metal (stainless steel) becomes the anode and undergoes accelerated dissolution, while titanium acts as the cathode.

Question 1122

Topic: Biomechanics & Biomaterials

A 75-year-old man undergoes a cemented hemiarthroplasty for a displaced femoral neck fracture. During cement pressurization and stem insertion, his blood pressure acutely drops, and his oxygen saturation falls to 82%. Which of the following is the primary pathophysiological mechanism responsible for this acute intraoperative event?

. Anaphylactic reaction to the polymethylmethacrylate (PMMA) monomer
. Thermal necrosis of the endosteal blood vessels causing vasospasm
. Embolization of fat and marrow contents into the pulmonary circulation
. Acute systemic toxicity from the release of unreacted barium sulfate
. Rapid systemic absorption of the liquid monomer causing profound bradycardia

Correct Answer & Explanation

. Embolization of fat and marrow contents into the pulmonary circulation

Explanation

Bone cement implantation syndrome is primarily caused by the embolization of fat, marrow, and air into the pulmonary circulation during cement pressurization. While monomer toxicity was historically suspected, transesophageal echocardiography has repeatedly demonstrated massive embolic showers during stem insertion.

Question 1123

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic properties. Which of the following terms describes the phenomenon where a tissue is held at a constant length over time, resulting in a gradual decrease in the force required to maintain that length?

. Creep
. Stress relaxation
. Hysteresis
. Strain hardening
. Isotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the stress (force) required to maintain a tissue at a constant strain (length) decreases over time. Creep, conversely, is the continued deformation of a tissue over time when subjected to a constant load.

Question 1124

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, highly cross-linked polyethylene (HXLPE) is used to decrease wear rates. Irradiation used to create these cross-links also generates free radicals. Which manufacturing process is primarily used to eliminate these free radicals and prevent in vivo oxidation?

. Gamma irradiation in air
. Ethylene oxide sterilization
. Melting or annealing the polyethylene
. Adding benzoyl peroxide
. Coating with hydroxyapatite

Correct Answer & Explanation

. Melting or annealing the polyethylene

Explanation

Irradiation generates free radicals that can lead to oxidation and subsequent degradation of the polyethylene over time. To prevent this, manufacturers either 'melt' the polyethylene (heating it above its melting point) or 'anneal' it (heating it below its melting point) to mobilize and extinguish residual free radicals. Vitamin E doping is a newer alternative method.

Question 1125

Topic: Biomechanics & Biomaterials

When a stainless steel screw is placed through a titanium alloy plate to stabilize a fracture, which mode of corrosion is most likely to occur at the interface due to the dissimilar metals being immersed in tissue fluid?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (like stainless steel and titanium) are in direct physical contact within an electrolytic medium (blood/tissue fluid). The less noble metal acts as an anode and undergoes accelerated corrosion, which can lead to implant failure or localized tissue toxicity.

Question 1126

Topic: Biomechanics & Biomaterials

In total joint arthroplasty, the phenomenon where microscopic asperities on the surface of an implant cold-weld together and are subsequently torn away during continuous motion is classified as which type of wear?

. Abrasive wear
. Adhesive wear
. Third-body wear
. Corrosive wear
. Fretting wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear occurs when two smooth surfaces articulate and localized microscopic welding occurs at asperities due to high contact stresses. As motion continues, these micro-welds fracture, tearing material from the softer articulating surface (often the polyethylene).

Question 1127

Topic: Biomechanics & Biomaterials

A 45-year-old male undergoes tendon lengthening. Which viscoelastic property describes the continuous increase in length of the tendon over time under a constant load?

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

Correct Answer & Explanation

. Creep

Explanation

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

Question 1128

Topic: Biomechanics & Biomaterials

A hamstring graft used for anterior cruciate ligament reconstruction is subjected to a constant physiological load over time, resulting in a gradual, time-dependent increase in deformation. Which of the following viscoelastic properties does this describe?

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

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 a decrease in internal stress over time when the material is held at a constant deformation.

Question 1129

Topic: Biomechanics & Biomaterials

During fracture fixation, a surgeon considers combining stainless steel screws with a titanium plate. Why is this combination strictly avoided in orthopedic surgery?

. Increased risk of severe stress shielding
. Susceptibility to aggressive galvanic corrosion
. Significant mismatch in ultimate tensile strength
. Induction of severe local hypersensitivity reactions
. Inability to achieve primary cortical bone healing

Correct Answer & Explanation

. Susceptibility to aggressive galvanic corrosion

Explanation

Mixing dissimilar metals, such as stainless steel and titanium, creates an electrochemical potential difference when exposed to the electrolytic environment of human bodily fluids. This predictable reaction leads to galvanic corrosion, accelerated implant failure, and local tissue toxicity.

Question 1130

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, which of the following modifications to ultra-high molecular weight polyethylene (UHMWPE) most effectively increases its resistance to adhesive and abrasive wear?
. Sterilization in an oxygen-rich environment
. Increasing the crystalline lamellar thickness
. Highly cross-linking the polyethylene via irradiation
. Addition of barium sulfate
. Gamma irradiation at extremely low doses

Correct Answer & Explanation

. Highly cross-linking the polyethylene via irradiation

Explanation

Highly cross-linked polyethylene (HXLPE) is created by exposing UHMWPE to ionizing radiation, which creates free radicals that recombine to form strong cross-links. This significantly increases wear resistance and reduces particulate debris, though it necessitates subsequent thermal treatment to extinguish residual free radicals.

Question 1131

Topic: Biomechanics & Biomaterials

Which of the following metal combinations represents the highest risk for galvanic corrosion when used together in an orthopaedic implant construct?

. Cobalt-chromium and Titanium
. Stainless steel and Titanium
. Cobalt-chromium and Tantalum
. Titanium and Tantalum
. Cobalt-chromium and Zirconium

Correct Answer & Explanation

. Stainless steel and Titanium

Explanation

Mixing stainless steel with either titanium or cobalt-chromium alloys is contraindicated due to a high risk of galvanic corrosion. Because stainless steel is significantly less noble (more anodic) than titanium, the stainless steel component will undergo rapid and severe corrosion when coupled with titanium in the body's electrolytic environment. Titanium and cobalt-chromium are more compatible with each other due to similar nobility profiles, though mixing them is still generally minimized.

Question 1132

Topic: Biomechanics & Biomaterials

In the biomechanical evaluation of viscoelastic materials such as ligaments and tendons, which of the following best defines the phenomenon of 'creep'?

. Decreasing peak force over time under a constant deformation
. Increasing deformation over time under a constant load
. Energy lost as heat during a loading and unloading cycle
. Rate-dependent increase in stiffness during rapid loading
. Microfailure of collagen fibers prior to macroscopic failure

Correct Answer & Explanation

. Increasing deformation over time under a constant load

Explanation

Creep is the progressive deformation of a viscoelastic material over time when it is subjected to a constant load. Stress relaxation (Option A) is the gradual decrease in stress over time when the material is held at a constant deformation. Hysteresis (Option C) is the energy lost during the loading and unloading cycle.

Question 1133

Topic: Biomechanics & Biomaterials

When dissimilar metals are used in adjacent orthopaedic implants (e.g., placing a stainless steel screw through a titanium plate), galvanic corrosion may occur. Which of the following accurately describes the primary electrochemical process governing this phenomenon?

. The more noble metal acts as the anode and preferentially corrodes.
. The less noble metal acts as the anode and preferentially corrodes.
. The more noble metal acts as the cathode and preferentially corrodes.
. The less noble metal acts as the cathode and preferentially corrodes.
. Corrosion occurs symmetrically in both metals due to equal electron sharing.

Correct Answer & Explanation

. The less noble metal acts as the anode and preferentially corrodes.

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution (like body fluid). The less noble (more reactive) metal acts as the anode and undergoes oxidation (corrosion), while the more noble metal acts as the cathode and is protected. For example, stainless steel is less noble than titanium and will preferentially corrode if the two are coupled.

Question 1134

Topic: Biomechanics & Biomaterials

A patient with a previously retained stainless steel plate for a distal femur fracture undergoes a total hip arthroplasty. The surgeon uses a titanium alloy stem that extends distally and makes physical contact with the proximal edge of the stainless steel plate. Over several years, accelerated localized corrosion occurs at the contact site. This scenario is a classic example of which type of corrosion?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (e.g., stainless steel and titanium alloys) are placed in physical contact within an electrolyte solution (conductive body fluid). This creates an electrochemical cell, resulting in accelerated dissolution (corrosion) of the less noble metal. Fretting corrosion is mechanically driven by micromotion. Crevice corrosion occurs in shielded areas with oxygen depletion.

Question 1135

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit distinct viscoelastic properties. Which of the following biomechanical terms best describes the phenomenon where a tissue subjected to a constant, sustained load demonstrates progressive deformation over time?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a viscoelastic material when it is placed under a constant load over time. Conversely, stress relaxation refers to the decrease in stress over time when the material is held at a constant length.

Question 1136

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, highly cross-linked polyethylene (HXLPE) is widely used. Which of the following material property changes occurs as a direct result of the irradiation process used to increase cross-linking?

. Increased ultimate tensile strength
. Decreased fatigue resistance
. Increased oxidation resistance without melting
. Decreased wear debris particle size
. Increased modulus of elasticity

Correct Answer & Explanation

. Decreased fatigue resistance

Explanation

High-dose irradiation increases cross-linking and dramatically reduces volumetric wear in polyethylene. However, it concomitantly decreases mechanical properties, specifically reducing fatigue resistance and ultimate tensile strength.

Question 1137

Topic: Biomechanics & Biomaterials

Which type of corrosion is most likely to occur at the modular head-neck taper junction of a total hip arthroplasty implant?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs at the contact site between two materials under cyclical load, such as the taper junction of a modular hip implant. Micromotion disrupts the protective oxide layer, accelerating the localized corrosion process.

Question 1138

Topic: Biomechanics & Biomaterials

Which of the following terms describes the property of a viscoelastic material where the stress required to maintain a constant tissue deformation decreases over time?

. Creep
. Stress relaxation
. Hysteresis
. Fatigue
. Young's modulus

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the phenomenon where less force (stress) is required over time to maintain a constant deformation (strain) in a viscoelastic material. Creep, conversely, is progressive deformation under a constant applied load.

Question 1139

Topic: Biomechanics & Biomaterials
The introduction of highly cross-linked polyethylene (HXLPE) has significantly reduced wear rates in total hip arthroplasty. Which step in the manufacturing process of HXLPE is specifically designed to eliminate free radicals and prevent subsequent oxidative degradation?
. Gamma irradiation in a vacuum
. Ethylene oxide sterilization
. Melting or annealing
. Doping with barium sulfate
. Cold forging

Correct Answer & Explanation

. Melting or annealing

Explanation

Highly cross-linked polyethylene is produced by exposing UHMWPE to gamma or electron beam irradiation, which creates cross-links, drastically improving wear resistance. However, this process also creates free radicals, which can react with oxygen over time (oxidation), leading to embrittlement. To eliminate these free radicals, the material is either melted (heated above its melting point) or annealed (heated just below its melting point). Alternatively, an antioxidant like Vitamin E can be blended into the polyethylene.

Question 1140

Topic: Biomechanics & Biomaterials

To mitigate the risk of oxidative degradation while preserving fatigue strength in highly cross-linked polyethylene used in THA, which of the following manufacturing treatments is most modernly utilized?

. Gamma irradiation in an oxygen-rich environment
. Post-irradiation remelting above 135 degrees Celsius
. Post-irradiation annealing below the melting point
. Blending or infusing the polyethylene with alpha-tocopherol (Vitamin E)
. Sterilization via gas plasma prior to cross-linking

Correct Answer & Explanation

. Blending or infusing the polyethylene with alpha-tocopherol (Vitamin E)

Explanation

Cross-linking polyethylene improves wear resistance but generates free radicals that can cause oxidative degradation and embrittlement. Historically, remelting was used to eliminate free radicals, but this reduces fatigue strength. Modern techniques blend or infuse the polyethylene with Vitamin E (alpha-tocopherol), a natural antioxidant, which scavenges free radicals without the need for remelting, thereby maintaining fatigue strength.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page