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Biomechanics & Biomaterials MCQs

Practice Set 33 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 641

Topic: Biomechanics & Biomaterials

A surgeon decides to use a stainless steel screw to secure a titanium plate during fracture fixation. Which of the following modes of corrosion is most likely to occur at the interface of these two metals?

. 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 anodic indices are placed in contact within an electrolytic solution like bodily fluids. This causes an electrochemical reaction that accelerates the corrosion of the less noble metal.

Question 642

Topic: Biomechanics & Biomaterials

When a compressive load is applied to cortical bone at a very high strain rate compared to a low strain rate, how do the mechanical properties of the bone change?

. It becomes less stiff and fails at a lower load
. It becomes more stiff and absorbs more energy before failure
. The stiffness remains unchanged, but it fails at a lower load
. It undergoes significantly more plastic deformation before failure
. It exhibits purely elastic behavior independent of the strain rate

Correct Answer & Explanation

. It becomes less stiff and fails at a lower load

Explanation

Bone is a viscoelastic material, meaning its mechanical behavior depends on the rate of loading. At higher strain rates, bone becomes stiffer, requires a higher load to fail, and absorbs more energy prior to fracture.

Question 643

Topic: Biomechanics & Biomaterials

Cortical bone exhibits viscoelastic properties. As the strain rate increases, such as during a high-energy traumatic impact, how does the mechanical behavior of the bone change?

. It becomes stiffer and stronger
. It becomes less stiff and weaker
. It becomes more ductile and weaker
. It becomes stiffer but fails at a lower load
. Its Young's modulus remains completely unchanged

Correct Answer & Explanation

. It becomes stiffer and stronger

Explanation

Cortical bone is viscoelastic, meaning its mechanical properties are strain-rate dependent. At higher strain rates, cortical bone becomes both stiffer (higher modulus) and stronger (can absorb more energy before failure).

Question 644

Topic: Biomechanics & Biomaterials

On a stress-strain curve for a structural orthopaedic implant material, what does the total area under the curve (up to the point of structural failure) represent?

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

Correct Answer & Explanation

. Ultimate tensile strength

Explanation

The area under the entire stress-strain curve represents the material's toughness, which is the total amount of energy absorbed before structural failure. Young's modulus is represented by the slope of the linear elastic region.

Question 645

Topic: Biomechanics & Biomaterials

A surgeon is mixing antibiotic-loaded PMMA bone cement for a spacer in the treatment of a prosthetic joint infection. To maximize the local elution of the antibiotic, which technique should be employed?

. Vacuum mixing to eliminate porosity
. Using a low liquid-to-powder ratio
. Hand mixing to deliberately increase porosity
. Adding a radiopacifier at 50 percent total volume
. Centrifuging the monomer before mixing

Correct Answer & Explanation

. Vacuum mixing to eliminate porosity

Explanation

Antibiotic elution from PMMA cement is highly dependent on surface area and porosity. Hand mixing (as opposed to vacuum mixing) increases the porosity of the cement mantle, thereby maximizing the elution profile of the incorporated antibiotics.

Question 646

Topic: Biomechanics & Biomaterials

Stress shielding around a femoral stem can lead to proximal bone resorption. Which of the following orthopaedic biomaterials possesses a Young's modulus closest to that of human cortical bone, thereby minimizing stress shielding?

. Stainless steel (316L)
. Cobalt-chromium alloy
. Titanium alloy (Ti-6Al-4V)
. Polymethylmethacrylate (PMMA)
. Alumina ceramic

Correct Answer & Explanation

. Stainless steel (316L)

Explanation

Human cortical bone has a Young's modulus of approximately 15-20 GPa. Titanium alloy (approx. 110 GPa) is the metallic biomaterial with a modulus closest to bone, significantly lower than stainless steel (200 GPa) and Co-Cr (220 GPa).

Question 647

Topic: Biomechanics & Biomaterials

A viscoelastic material subjected to a constant applied load over a prolonged period of time will exhibit progressive, time-dependent deformation. This specific biomechanical phenomenon is known as:

. Stress relaxation
. Fatigue failure
. Hysteresis
. Creep
. Yielding

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is defined as the progressive, time-dependent deformation of a viscoelastic material under a constant load, such as the gradual deformation of a polyethylene liner. Stress relaxation, in contrast, is a decrease in stress over time under a constant strain.

Question 648

Topic: Biomechanics & Biomaterials

Which of the following common orthopedic implant materials has the highest modulus of elasticity (stiffness)?

. Cortical bone
. Titanium alloy (Ti-6Al-4V)
. Stainless steel (316L)
. Cobalt-chromium alloy
. Cancellous bone

Correct Answer & Explanation

. Cortical bone

Explanation

Cobalt-chromium alloy has the highest modulus of elasticity at approximately 220-240 GPa, making it the stiffest among the choices. In comparison, stainless steel is roughly 200 GPa, titanium alloy is about 110 GPa, and human cortical bone is approximately 15-20 GPa.

Question 649

Topic: Biomechanics & Biomaterials

A surgeon utilizing the Ponseti method for clubfoot casting applies a constant stretching force to the soft tissues. Over time, the Achilles tendon gradually elongates without any increase in the applied force. Which viscoelastic property does this describe?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the progressive deformation or elongation of a viscoelastic material when it is subjected to a constant load over time. Conversely, stress relaxation refers to the decrease in stress required to maintain a constant deformation.

Question 650

Topic: Biomechanics & Biomaterials
The historical sterilization of ultra-high-molecular-weight polyethylene (UHMWPE) components using gamma irradiation in the presence of oxygen is associated with which of the following adverse effects?
. Increased cross-linking and improved wear resistance
. Chain scission and oxidation leading to accelerated wear
. Complete elimination of free radicals
. Enhancement of the material's modulus of elasticity
. Decreased risk of third-body wear

Correct Answer & Explanation

. Chain scission and oxidation leading to accelerated wear

Explanation

Gamma irradiation of UHMWPE in an oxygen-rich environment creates free radicals that react with oxygen, causing oxidation and chain scission. This degrades the material's mechanical properties and significantly increases the rate of abrasive and adhesive wear.

Question 651

Topic: Biomechanics & Biomaterials

A surgeon encounters a nonunion of a femur fracture previously stabilized with a stainless steel plate. The surgeon plans to augment the construct but only has titanium screws available. Using titanium screws through a stainless steel plate is contraindicated primarily due to the risk of:

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with differing electrochemical potentials are in direct contact within an electrolytic environment, such as bodily fluids. The less noble metal acts as an anode and undergoes accelerated corrosion, compromising implant integrity.

Question 652

Topic: Biomechanics & Biomaterials

During the cementation and pressurization phase of a cemented hemiarthroplasty for a femoral neck fracture, the patient's blood pressure drops acutely to 70/40 mmHg, accompanied by severe hypoxia. What is the primary pathophysiologic mechanism of this event?

. Anaphylactic reaction to polymethylmethacrylate (PMMA)
. Acute hypovolemic shock secondary to unrecognized intraoperative bleeding
. Embolization of marrow contents and fat during cement pressurization
. Toxic systemic reaction to unpolymerized liquid monomer
. Myocardial infarction triggered by surgical stress

Correct Answer & Explanation

. Anaphylactic reaction to polymethylmethacrylate (PMMA)

Explanation

Bone cement implantation syndrome (BCIS) presents with hypoxia, hypotension, and arrhythmias during cementation. It is primarily caused by the embolization of marrow, fat, and air into the pulmonary venous circulation during medullary pressurization.

Question 653

Topic: Biomechanics & Biomaterials

During the insertion of cemented hemiarthroplasty for a femoral neck fracture, the patient's blood pressure drops acutely and oxygen saturation falls. Bone cement implantation syndrome (BCIS) is suspected. The primary hemodynamic derangement in severe BCIS is characterized by:

. Left ventricular failure secondary to severe systemic hypertension
. Right ventricular failure and acute pulmonary hypertension
. Acute hypovolemic shock from vasodilation
. Anaphylactic shock mediated by IgE
. Pulmonary venous hypertension

Correct Answer & Explanation

. Left ventricular failure secondary to severe systemic hypertension

Explanation

BCIS is triggered by the embolization of marrow fat and debris during cement pressurization, leading to acute pulmonary hypertension, hypoxia, right ventricular strain, and subsequent right heart failure with hypotension.

Question 654

Topic: Biomechanics & Biomaterials

A 68-year-old man undergoes a cemented unipolar hemiarthroplasty for a displaced femoral neck fracture. During cement pressurization and stem insertion, the patient experiences sudden profound hypotension and hypoxia. What is the primary pathophysiologic mechanism of this complication?

. Fat and marrow embolization to the pulmonary vasculature
. Anaphylactic reaction to polymethylmethacrylate (PMMA)
. Acute myocardial infarction secondary to hypovolemia
. Thermal necrosis of the femoral canal leading to bleeding
. Vagal reflex from endosteal stretch

Correct Answer & Explanation

. Fat and marrow embolization to the pulmonary vasculature

Explanation

Bone cement implantation syndrome (BCIS) is primarily caused by the embolization of fat, marrow, and air into the pulmonary circulation during cement pressurization. It presents with hypoxia, hypotension, and potentially cardiac arrest.

Question 655

Topic: Biomechanics & Biomaterials

An 81-year-old woman with a displaced femoral neck fracture is undergoing a cemented bipolar hemiarthroplasty. During the pressurization of the cement and insertion of the femoral stem, she experiences sudden hypoxia, hypotension, and right heart failure. What is the primary pathophysiologic mechanism of this complication?

. Anaphylactic reaction to polymethylmethacrylate
. Embolization of marrow fat and surgical debris
. Exothermic thermal necrosis of the endosteum
. Vagal reflex from femoral canal distension
. Hemorrhagic shock from unnoticed vessel injury

Correct Answer & Explanation

. Anaphylactic reaction to polymethylmethacrylate

Explanation

Bone cement implantation syndrome (BCIS) is characterized by hypoxia and hypotension during cementation. It is primarily caused by the embolization of marrow fat, air, and bone debris into the pulmonary circulation due to high intramedullary pressures during cement pressurization and stem insertion.

Question 656

Topic: Biomechanics & Biomaterials

Current evidence suggests that in elderly patients undergoing hemiarthroplasty for a displaced femoral neck fracture, the use of a cemented femoral stem compared to an uncemented stem is associated with which of the following?

. Higher rate of intraoperative mortality
. Higher rate of long-term implant loosening
. Lower incidence of postoperative periprosthetic fractures
. Increased incidence of deep vein thrombosis
. Shorter operative time and less blood loss

Correct Answer & Explanation

. Higher rate of intraoperative mortality

Explanation

Cemented stems in elderly hemiarthroplasty patients have a significantly lower risk of postoperative periprosthetic fractures compared to uncemented stems. While there is a risk of bone cement implantation syndrome, overall survival rates remain comparable.

Question 657

Topic: Biomechanics & Biomaterials

Highly cross-linked polyethylene is now commonly used in THA. The primary negative biomechanical effect of increasing the cross-linking radiation dose in polyethylene is:

. Increased volumetric wear
. Decreased oxidation resistance
. Decreased fatigue and fracture resistance
. Increased coefficient of friction
. Increased risk of squeaking

Correct Answer & Explanation

. Increased volumetric wear

Explanation

While high levels of cross-linking significantly decrease the volumetric wear rate of polyethylene, they also diminish its ultimate tensile strength, fatigue strength, and fracture toughness.

Question 658

Topic: Biomechanics & Biomaterials

A 65-year-old patient undergoes an isolated tibial shaft fracture fixation. A stainless steel plate is accidentally secured with titanium screws. This construct is at high risk for which of the following types of corrosion?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within a conductive fluid environment (like body fluid). The difference in their electrochemical potentials drives an accelerated corrosion of the less noble metal.

Question 659

Topic: Biomechanics & Biomaterials

An anterior cruciate ligament (ACL) graft undergoes gradual, progressive elongation over time when subjected to a constant physiological load. This viscoelastic phenomenon is best described as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

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

Question 660

Topic: Biomechanics & Biomaterials

Of the following orthopedic implant materials, which has a modulus of elasticity that is closest to that of human cortical bone, thereby potentially reducing stress shielding?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Ultra-high-molecular-weight polyethylene (UHMWPE)
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Stainless steel

Explanation

Cortical bone has an elastic modulus of approximately 15-20 GPa. Titanium alloys (approx. 110 GPa) are significantly closer to cortical bone than stainless steel (200 GPa) or cobalt-chromium (240 GPa), minimizing stress shielding.

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