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Biomechanics & Biomaterials MCQs

Practice Set 86 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 1701

Topic: Biomechanics & Biomaterials

A 65-year-old patient receives a cemented total hip arthroplasty. By what primary mechanism does polymethylmethacrylate (PMMA) secure the femoral component to the surrounding bone?

. Covalent chemical bonding
. Osteoconductive integration
. Mechanical interlock
. Piezoelectric stimulation
. Galvanic adhesion

Correct Answer & Explanation

. Mechanical interlock

Explanation

PMMA bone cement acts as a grout rather than a chemical adhesive. It achieves fixation primarily through mechanical interlock by firmly interdigitating with the interstices of the prepared cancellous bone.

Question 1702

Topic: Biomechanics & Biomaterials

Among commonly used metallic orthopedic implants, which material possesses a modulus of elasticity most closely resembling that of human cortical bone?

. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Tantalum
. Nitinol

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloys have a modulus of elasticity (approximately 110 GPa) that is significantly closer to that of cortical bone (15-20 GPa) than stainless steel (approx. 200 GPa) or cobalt-chromium (approx. 220 GPa). This helps to minimize the negative biomechanical effects of stress shielding.

Question 1703

Topic: Biomechanics & Biomaterials

A bone-patellar tendon-bone graft is tensioned and fixed during an anterior cruciate ligament reconstruction. Over the next 10 minutes, the surgeon notes that the tension in the graft steadily decreases despite the length remaining perfectly constant. Which of the following viscoelastic properties does this describe?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in stress (or tension) over time when a viscoelastic material is held at a constant strain (length). Creep, by contrast, is the increase in strain (length) over time when held at a constant stress (load).

Question 1704

Topic: Biomechanics & Biomaterials
A surgeon is selecting an intramedullary nail for a tibial shaft fracture and wishes to minimize stress shielding of the diaphyseal bone. Which of the following orthopedic implant materials has a modulus of elasticity that most closely approximates that of cortical bone?
. Stainless steel
. Cobalt-chromium alloy
. Titanium alloy
. Polymethylmethacrylate (PMMA)
. Ultra-high-molecular-weight polyethylene (UHMWPE)

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a modulus of elasticity closer to that of cortical bone compared to stiffer metals like stainless steel or cobalt-chromium. This lower stiffness reduces stress shielding and promotes better load sharing with the healing host bone.

Question 1705

Topic: Biomechanics & Biomaterials

An anterior cruciate ligament (ACL) graft subjected to a constant physiological load over a prolonged period demonstrates a gradual and progressive increase in length. Which biomechanical property of viscoelastic materials does this describe?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation (lengthening) of a viscoelastic material when subjected to a constant load over time. Conversely, stress relaxation is the decrease in stress (force) over time when a material is held at a constant length.

Question 1706

Topic: Biomechanics & Biomaterials
The stability of fracture fixation relies heavily on screw biomechanics. The pullout strength of a cortical screw is directly proportional to all of the following parameters EXCEPT:
. Outer (major) diameter of the thread
. Thread pitch (threads per inch)
. Length of screw engagement in the bone
. Core (minor) diameter of the screw
. Shear strength of the host bone

Correct Answer & Explanation

. Core (minor) diameter of the screw

Explanation

Pullout strength is directly proportional to the outer diameter, thread pitch, length of engagement, and host bone shear strength. Increasing the core diameter (while maintaining a constant outer diameter) decreases thread depth, which actually decreases pullout strength while increasing the screw's tensile and bending strength.

Question 1707

Topic: Biomechanics & Biomaterials
To optimize the wear characteristics of ultra-high molecular weight polyethylene (UHMWPE) used in total joint arthroplasty, cross-linking is highly dependent on the sterilization process. Which of the following sterilization methods is associated with the lowest long-term wear rates and minimal oxidative degradation?
. Gamma irradiation in air
. Gamma irradiation in an inert gas (argon) followed by remelting
. Ethylene oxide gas sterilization
. Standard steam autoclaving
. Hydrogen peroxide gas plasma

Correct Answer & Explanation

. Gamma irradiation in an inert gas (argon) followed by remelting

Explanation

Gamma irradiation of UHMWPE in an inert environment creates cross-linking, which improves wear resistance. Subsequent remelting extinguishes free radicals, preventing late oxidative degradation and structural failure.

Question 1708

Topic: Biomechanics & Biomaterials

When evaluating the biomechanical properties of a native ligament undergoing tensile loading, what physiological change correlates with the 'toe region' of the stress-strain curve?

. Microscopic failure of collagen cross-links
. Macroscopic structural failure
. Uncrimping of the resting collagen fibers
. Progressive creep under constant load
. Stress relaxation over time

Correct Answer & Explanation

. Uncrimping of the resting collagen fibers

Explanation

The toe region of a ligament's stress-strain curve represents initial elongation under low load. This corresponds physically to the straightening or 'uncrimping' of the naturally crimped collagen fibers.

Question 1709

Topic: Biomechanics & Biomaterials

When applying continuous traction to a deformed viscoelastic structure (such as a clubfoot casting or ligament stretching), the material slowly elongates over time under a constant load. This biomechanical property is known as:

. Stress relaxation
. Hysteresis
. Creep
. Fatigue failure
. Plastic deformation

Correct Answer & Explanation

. Creep

Explanation

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

Question 1710

Topic: Biomechanics & Biomaterials

Mixing titanium and stainless steel in surgical implants can lead to galvanic corrosion. Which of the following factors primarily determines the severity of corrosion between these two metals in vivo?

. The electropotential difference (anodic index) between the two metals
. The similarity in their elastic moduli
. The presence of a passivation layer on stainless steel only
. The relative thickness of the titanium oxide layer
. The use of a cobalt-chromium alloy as an intermediary

Correct Answer & Explanation

. The electropotential difference (anodic index) between the two metals

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolyte solution like body fluid. The severity is driven by the electropotential difference between the metals.

Question 1711

Topic: Biomechanics & Biomaterials

When comparing various orthopedic implant materials, which of the following possesses a modulus of elasticity that most closely approximates that of human cortical bone, thereby reducing stress shielding?

. Stainless steel
. Titanium alloy
. Cobalt-chromium alloy
. Alumina ceramic
. Zirconia ceramic

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a lower modulus of elasticity (closer to cortical bone) compared to stainless steel or cobalt-chromium. This similarity helps reduce stress shielding and subsequent bone resorption.

Question 1712

Topic: Biomechanics & Biomaterials
To decrease wear in ultra-high-molecular-weight polyethylene (UHMWPE) components for total joint arthroplasty, highly cross-linked polyethylene is frequently used. What is the primary mechanical disadvantage of increasing the degree of cross-linking?
. Increased oxidative degradation
. Decreased fatigue and fracture resistance
. Increased adhesive wear
. Decreased melting point
. Increased volumetric wear

Correct Answer & Explanation

. Decreased fatigue and fracture resistance

Explanation

Highly cross-linked polyethylene significantly reduces adhesive and abrasive wear. However, the cross-linking process alters the polymer chain mobility, which decreases the material's fatigue resistance and makes it more susceptible to fracture.

Question 1713

Topic: Biomechanics & Biomaterials

In orthopedic hardware selection, mixing certain metals can lead to destructive galvanic corrosion. Which of the following implant combinations in direct physical contact poses the highest risk for severe galvanic corrosion?

. Titanium alloy and Commercially pure titanium
. Cobalt-Chrome and Titanium
. Stainless Steel and Cobalt-Chrome
. Stainless Steel and Titanium
. Cobalt-Chrome and Zirconium

Correct Answer & Explanation

. Stainless Steel and Titanium

Explanation

Mixing stainless steel and titanium implants creates a strong galvanic couple due to their significant differences in electrochemical potential. The titanium acts as a large cathode, leading to rapid, destructive anodic dissolution of the stainless steel.

Question 1714

Topic: Biomechanics & Biomaterials
Cross-linking of ultra-high molecular weight polyethylene (UHMWPE) in total hip arthroplasty affects its mechanical properties. Highly cross-linking UHMWPE primarily results in which of the following biomechanical changes?
. Increased wear resistance and decreased fatigue strength
. Increased wear resistance and increased fatigue strength
. Decreased wear resistance and decreased yield strength
. Increased elongation to failure
. Decreased oxidation potential without the need for additives

Correct Answer & Explanation

. Increased wear resistance and decreased fatigue strength

Explanation

Highly cross-linked polyethylene significantly improves wear resistance, which reduces osteolysis. However, this comes at the cost of reduced mechanical properties, specifically decreased fatigue strength and ductility.

Question 1715

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, the use of highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) has significantly reduced volumetric wear. However, the cross-linking and subsequent melting processes negatively affect which of the following mechanical properties?
. Oxidation resistance
. Elastic modulus
. Ultimate tensile strength and fatigue resistance
. Creep resistance
. Biocompatibility

Correct Answer & Explanation

. Ultimate tensile strength and fatigue resistance

Explanation

Highly cross-linked polyethylene significantly decreases adhesive and abrasive wear. However, the radiation and subsequent thermal treatment (remelting or annealing) to eliminate free radicals lead to a reduction in ultimate tensile strength, fatigue resistance, and fracture toughness, which can increase the risk of mechanical failure (e.g., rim fracture).

Question 1716

Topic: Biomechanics & Biomaterials

A ligament is stretched to a constant specific length. Over time, the amount of force required to maintain this length progressively decreases. This biomechanical phenomenon is known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the stress (force) decreases over time when a material is held at a constant strain (length). Creep is the opposite: an increase in strain (deformation) over time when subjected to a constant stress (load).

Question 1717

Topic: Biomechanics & Biomaterials

Titanium alloys (e.g., Ti-6Al-4V) are frequently used in orthopedic implants. Compared to 316L stainless steel, titanium alloy possesses which of the following mechanical advantages that reduces stress shielding in bone?

. A lower modulus of elasticity
. A higher ultimate tensile strength
. A greater risk of galvanic corrosion
. Increased ductility allowing intraoperative contouring
. Higher density and weight

Correct Answer & Explanation

. A lower modulus of elasticity

Explanation

Titanium alloys have a modulus of elasticity (stiffness) closer to that of cortical bone compared to stainless steel or cobalt-chromium alloys. This decreased stiffness allows for more physiological load sharing with the host bone, thereby reducing the phenomenon of stress shielding (which leads to osteopenia around the implant).

Question 1718

Topic: Biomechanics & Biomaterials

A surgeon revises a failed total hip arthroplasty where a cobalt-chrome femoral head was placed on a titanium alloy stem. Intraoperatively, black debris and significant tissue staining are observed near the modular junction, without signs of infection. Which of the following best describes the primary mechanism of this specific implant degradation?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., cobalt-chrome and titanium) are in electrical contact within an electrolytic environment (body fluid). The less noble metal undergoes accelerated corrosion. While fretting (micromotion) may also contribute, the interaction of dissimilar metals classically defines galvanic corrosion.

Question 1719

Topic: Biomechanics & Biomaterials
In ultra-high molecular weight polyethylene (UHMWPE) components utilized in total joint arthroplasty, which of the following mechanical terms describes the progressive, time-dependent permanent deformation of the polymer under a constant compressive load?
. Fatigue failure
. Abrasive wear
. Creep
. Stress relaxation
. Yield deformation

Correct Answer & Explanation

. Creep

Explanation

Creep (often referred to as cold flow in polymers) is the time-dependent, permanent plastic deformation of a material subjected to a constant static load below its yield strength. In joint replacements, this can alter the congruency of the articulation over time without actual material loss (unlike wear).

Question 1720

Topic: Biomechanics & Biomaterials

In orthopedic implant design, selecting materials with an appropriate modulus of elasticity is critical to minimize stress shielding. Which of the following implant materials has a modulus of elasticity closest to that of human cortical bone?

. Cobalt-chromium alloy
. Titanium alloy
. Stainless steel (316L)
. Polymethylmethacrylate (PMMA)
. Zirconium

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a lower modulus of elasticity (closer to that of cortical bone) compared to stainless steel or cobalt-chromium. This relatively lower stiffness allows for more load sharing with the host bone, thereby minimizing stress shielding and secondary osteopenia.

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