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Biomechanics & Biomaterials MCQs

Practice Set 67 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 1321

Topic: Biomechanics & Biomaterials

A 60-year-old male presents with an acute, severely painful, and swollen knee without antecedent trauma. Aspiration yields cloudy synovial fluid with 25,000 WBCs/mcL. Under compensated polarized light microscopy, weakly positively birefringent rhomboid-shaped crystals are visualized. What is the chemical composition of these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Calcium hydroxyapatite
. Cholesterol
. Basic calcium phosphate

Correct Answer & Explanation

. Monosodium urate

Explanation

The diagnosis is pseudogout, which is caused by the deposition of calcium pyrophosphate dihydrate (CPPD) crystals in the joint. They appear rhomboid-shaped and demonstrate weak positive birefringence under polarized light. Monosodium urate crystals (gout) are needle-shaped and strongly negatively birefringent.

Question 1322

Topic: Biomechanics & Biomaterials

Placing a stainless steel screw through a titanium plate in a fracture fixation construct increases the risk of which type of implant corrosion?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals, such as stainless steel and titanium, are placed in electrical contact within a conductive fluid (such as physiologic body fluid). The less noble metal undergoes accelerated corrosion. It is generally advised not to mix these metals in internal fixation constructs to prevent hardware failure and local tissue reactions.

Question 1323

Topic: Biomechanics & Biomaterials

When a constant tensile load is applied to a ligament over time, the ligament will gradually elongate. This time-dependent mechanical property is known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Viscoelastic materials exhibit time-dependent mechanical properties. Creep is defined as the progressive deformation (elongation) of a material over time when subjected to a constant load (stress). Stress relaxation, another viscoelastic property, refers to the decrease in stress over time when a material is held at a constant strain. Ligaments and tendons exhibit both of these properties.

Question 1324

Topic: Biomechanics & Biomaterials

A basic science researcher is evaluating the viscoelastic properties of a human anterior cruciate ligament. When the ligament is subjected to a constant physiological load over time, it continues to deform slowly. Which of the following terms best describes this phenomenon?

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Isotropy

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 occurs when a material experiences a decrease in stress under a constant deformation.

Question 1325

Topic: Biomechanics & Biomaterials
To reduce wear rates in total joint arthroplasty, highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is often utilized. Which of the following is the most significant disadvantage of highly cross-linked UHMWPE compared to conventional UHMWPE?
. Increased oxidative degradation over time
. Decreased ultimate tensile strength and fatigue resistance
. Increased adhesive wear
. Higher rate of volumetric wear
. Increased risk of galvanic corrosion

Correct Answer & Explanation

. Decreased ultimate tensile strength and fatigue resistance

Explanation

While highly cross-linked UHMWPE significantly reduces volumetric wear, the cross-linking process decreases its mechanical properties, such as ultimate tensile strength, fatigue resistance, and fracture toughness. To mitigate oxidation, it is often remelted, annealed, or doped with Vitamin E.

Question 1326

Topic: Biomechanics & Biomaterials

A surgeon revises a fractured stainless steel plate by placing a new titanium screw into one of the remaining empty holes of the stainless steel plate. Over time, significant corrosion occurs at the screw-plate interface. This is an example of which type of corrosion?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., titanium and stainless steel) are in contact within a conductive fluid (body fluid), leading to an electrochemical gradient. The less noble metal undergoes accelerated corrosion.

Question 1327

Topic: Biomechanics & Biomaterials

A modular total hip arthroplasty prosthesis develops corrosion at the trunnion-head interface. The repetitive micromotion between the two mechanically loaded parts disrupts the protective oxide layer, leading to corrosion. Which term best describes this phenomenon?

. Galvanic corrosion
. Pitting corrosion
. Fretting corrosion
. Crevice corrosion
. Fatigue corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion occurs at the contact areas between materials under load subject to minute relative motion (micromotion). This mechanical wear continually removes the passivation (oxide) layer, exposing underlying metal to electrochemical corrosion.

Question 1328

Topic: Biomechanics & Biomaterials

A surgeon decides to use a stainless steel screw to secure a titanium alloy plate for a complex femoral shaft fracture. Two years later, the implant fails and the screw is found to be heavily degraded. Which specific type of corrosion is most likely responsible for this failure?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in electrical contact within a conductive fluid (like the human body). This creates an electrochemical cell, causing the less noble metal (stainless steel) to corrode at an accelerated rate.

Question 1329

Topic: Biomechanics & Biomaterials

A patient undergoes an ACL reconstruction with a hamstring autograft. The graft is pre-tensioned on a board before implantation. Over a period of 20 minutes under a constant load, the graft demonstrates a gradual increase in length. This biomechanical phenomenon is best described as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is a property of viscoelastic materials characterized by continuous, progressive deformation occurring under a constant applied load over time. Stress relaxation, conversely, is a decrease in stress over time when the material is held at a constant deformation.

Question 1330

Topic: Biomechanics & Biomaterials

What enzyme is primarily responsible for generating the acidic environment necessary for osteoclastic bone resorption at the ruffled border?

. Alkaline phosphatase
. Carbonic anhydrase II
. Cathepsin K
. Tartrate-resistant acid phosphatase
. Matrix metalloproteinase

Correct Answer & Explanation

. Alkaline phosphatase

Explanation

Carbonic anhydrase II catalyzes the formation of carbonic acid, which dissociates into hydrogen ions. These ions are pumped across the ruffled border via H+-ATPase to lower the pH and dissolve hydroxyapatite.

Question 1331

Topic: Biomechanics & Biomaterials
To improve the wear resistance of ultra-high molecular weight polyethylene (UHMWPE) in total joint arthroplasty, highly cross-linked polyethylene is often used. Which of the following is a known trade-off of the cross-linking process?
. Increased oxidative degradation
. Decreased fatigue strength and fracture toughness
. Decreased melting temperature
. Increased abrasive wear
. Increased osteolysis potential

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

While cross-linking UHMWPE significantly improves its wear resistance, it simultaneously decreases its mechanical properties, such as fatigue strength and fracture toughness. Remelting is often used post-irradiation to reduce free radicals and prevent oxidative degradation.

Question 1332

Topic: Biomechanics & Biomaterials

Which of the following combinations of orthopedic implant metals has the highest risk of galvanic corrosion when placed in direct contact within the body?

. Titanium alloy and pure titanium
. Cobalt-chrome and titanium alloy
. Stainless steel and pure titanium
. Stainless steel and cobalt-chrome
. Tantalum and titanium

Correct Answer & Explanation

. Titanium alloy and pure titanium

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic environment. Stainless steel and titanium have a large difference in their electrochemical potentials, resulting in a high risk of severe galvanic corrosion.

Question 1333

Topic: Biomechanics & Biomaterials

When evaluating the material properties of a new orthopedic implant, the provided load-deformation data is converted to a stress-strain curve.

The slope of the linear portion of this curve is a measure of the material's:

. Toughness
. Yield strength
. Ultimate tensile strength
. Stiffness (Modulus of Elasticity)
. Ductility

Correct Answer & Explanation

. Toughness

Explanation

The slope of the linear (elastic) portion of the stress-strain curve represents the Modulus of Elasticity (Young's modulus), which is a measure of the material's stiffness. Toughness is the total area under the curve. Ductility is the amount of plastic deformation a material can undergo before failure.

Question 1334

Topic: Biomechanics & Biomaterials

A 65-year-old patient undergoes revision of a total hip arthroplasty due to local tissue reaction. The retrieved implant demonstrates significant surface degradation at the modular head-neck junction.

Which of the following corrosion mechanisms is primarily driven by micro-motion between two closely apposed metal surfaces disrupting the protective oxide layer?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion occurs when small-amplitude, oscillatory motion (micro-motion) between two loaded surfaces mechanically disrupts the protective oxide (passivation) layer, leading to accelerated chemical degradation. It is a classic failure mode for modular junctions, such as head-neck tapers in total hip arthroplasty.

Question 1335

Topic: Biomechanics & Biomaterials

A surgeon places a self-retaining retractor to spread the soft tissues during an exposure. Initially, a high force is required to hold the tissues apart, but over time, the force required to maintain the retractor at that exact same width decreases. This phenomenon is a biomechanical property of viscoelastic materials known as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Isotropy

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is the property of a viscoelastic material where the internal stress (force) decreases over time when the material is held at a constant strain (constant deformation). Creep, conversely, is the continuous deformation (increasing strain) of a material over time when subjected to a constant load (constant stress).

Question 1336

Topic: Biomechanics & Biomaterials

The torsional rigidity of a long bone or an intramedullary nail is heavily dependent on its cross-sectional geometry. For a hollow cylinder, the polar moment of inertia is proportional to which of the following geometric parameters?

. The difference between the outer radius squared and inner radius squared
. The outer radius cubed
. The difference between the outer radius cubed and inner radius cubed
. The difference between the outer radius to the fourth power and inner radius to the fourth power
. The square root of the outer radius

Correct Answer & Explanation

. The difference between the outer radius squared and inner radius squared

Explanation

The polar moment of inertia (J) dictates a structure's resistance to torsional deformation. For a hollow cylinder (such as the diaphysis of a long bone or a cannulated nail), J is proportional to the difference between the outer radius to the fourth power and the inner radius to the fourth power (r_outer^4 - r_inner^4). Therefore, even a small increase in the outer diameter exponentially increases torsional strength.

Question 1337

Topic: Biomechanics & Biomaterials



Polymethylmethacrylate (PMMA) bone cement is routinely used for implant fixation. Adding an antibiotic powder or a radiopacifier (such as barium sulfate) to the PMMA prior to mixing has what primary biomechanical effect on the cured cement mantle?

. Increases the ultimate compressive strength
. Decreases the ultimate tensile strength and fatigue life
. Increases the fatigue life under tensile load
. Decreases the modulus of elasticity making it highly ductile
. Has no significant effect on the mechanical properties if added at less than 10% by weight

Correct Answer & Explanation

. Increases the ultimate compressive strength

Explanation

PMMA is a viscoelastic material that is strong in compression but relatively weak in tension and shear. The addition of powders, antibiotics, or radiopacifiers (like barium sulfate or zirconium dioxide) introduces impurities and microscopic stress risers into the cement mantle. This reliably decreases its ultimate tensile strength and reduces its fatigue life.

Question 1338

Topic: Biomechanics & Biomaterials

Which combination of orthopedic metals has the highest risk of significant galvanic corrosion when placed in direct contact in a conductive physiologic environment?

. Titanium alloy (Ti-6Al-4V) and Cobalt-Chrome
. Stainless Steel 316L and Titanium alloy (Ti-6Al-4V)
. Cobalt-Chrome and Tantalum
. Titanium alloy (Ti-6Al-4V) and Tantalum
. Zirconium and Cobalt-Chrome

Correct Answer & Explanation

. Titanium alloy (Ti-6Al-4V) and Cobalt-Chrome

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct electrical contact within an electrolyte solution (such as body fluid). The severity of corrosion is dictated by the difference in their resting potentials on the galvanic series. Stainless steel and titanium alloys have a significant difference in their electrochemical potentials, leading to a high risk of galvanic corrosion of the less noble metal (stainless steel). Cobalt-chrome and titanium are close enough on the galvanic series that they are routinely mixed (e.g., a cobalt-chrome femoral head on a titanium stem) with negligible clinical galvanic corrosion.

Question 1339

Topic: Biomechanics & Biomaterials

A viscoelastic orthopedic implant material is subjected to a constant load over a prolonged period, resulting in a progressive increase in strain (deformation). What is this biomechanical phenomenon termed?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is defined as the progressive deformation (increasing strain) of a viscoelastic material when subjected to a constant load (stress) over time. In contrast, stress relaxation occurs when a material is held at a constant strain, and the stress within the material decreases over time. Hysteresis represents the energy lost (usually as heat) during the loading and unloading cycles of a viscoelastic material.

Question 1340

Topic: Biomechanics & Biomaterials

The in vivo elution of locally delivered antibiotics from polymethylmethacrylate (PMMA) bone cement is best characterized by which of the following release profiles?

. Zero-order kinetics (constant release rate over time)
. Biphasic, with an initial burst release followed by a prolonged low-level release
. Exponential continuous increase peaking at 6 weeks
. Delayed release beginning 14 days post-implantation
. Strictly dependent on the host's renal clearance rates

Correct Answer & Explanation

. Zero-order kinetics (constant release rate over time)

Explanation

Antibiotic elution from PMMA is famously biphasic. There is a high initial 'burst' release of antibiotic from the surface of the cement within the first 24 to 72 hours, producing high local concentrations. This is followed by a prolonged, exponentially decreasing, low-level release that can persist for weeks to months, often dropping below the minimum inhibitory concentration (MIC).

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