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Biomechanics & Biomaterials MCQs

Practice Set 68 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 1341

Topic: Biomechanics & Biomaterials

A loose fragment of polymethylmethacrylate (PMMA) cement becomes interposed between the femoral head and the polyethylene liner in a total hip arthroplasty, resulting in gouging and accelerated destruction of the liner. This is a classic example of which mode of wear?

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

Correct Answer & Explanation

. Adhesive wear

Explanation

Third-body wear occurs when hard, unattached particles (such as PMMA cement debris, bone fragments, or loose metallic beads) become trapped between two articulating bearing surfaces. The trapped particles gouge and scratch the softer surface (like polyethylene), significantly accelerating wear. Adhesive wear involves microscopic bonding and tearing between the two primary surfaces, while abrasive wear is scratching caused by one primary surface being rougher and harder than the other.

Question 1342

Topic: Biomechanics & Biomaterials

Which of the following clinical scenarios poses the highest theoretical risk for galvanic corrosion in orthopedic implants?

. Implanting a stainless steel screw through a titanium plate
. Using a highly cross-linked polyethylene liner with a cobalt-chrome head
. Fretting of a titanium screw in a titanium locking plate
. Implanting an alumina ceramic head on a titanium trunnion
. Utilizing two stainless steel components of the exact same alloy

Correct Answer & Explanation

. Implanting a stainless steel screw through a titanium plate

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within an electrolytic fluid medium. Mixing stainless steel and titanium implants generates an electrochemical potential difference, leading to accelerated corrosion of the less noble metal.

Question 1343

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic behavior. The biomechanical phenomenon where tissue deformation steadily increases over time while subjected to a constant, continuous load is defined as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the time-dependent continuous deformation of a viscoelastic material under a constant load. Conversely, stress relaxation is the decrease in required stress over time to maintain a constant deformation.

Question 1344

Topic: Biomechanics & Biomaterials

To minimize stress shielding around a diaphysis, an orthopedic implant should have a modulus of elasticity closely matching that of cortical bone. Among standard solid metals, which of the following is closest?

. Cobalt-chromium alloy
. Stainless steel
. Titanium alloy
. Zirconium oxide (Ceramic)
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Cobalt-chromium alloy

Explanation

Titanium alloy has a modulus of elasticity around 110 GPa, which is roughly half that of CoCr (210 GPa) or stainless steel (190 GPa). Although still stiffer than cortical bone (15-20 GPa), titanium is the closest among standard solid metallic structural implants, reducing stress shielding.

Question 1345

Topic: Biomechanics & Biomaterials

When combining a titanium alloy (Ti-6Al-4V) femoral stem with a cobalt-chromium (CoCr) modular head in total hip arthroplasty, the construct is at risk for which specific type of corrosion at the trunnion?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (like Ti alloy and CoCr) are in contact in an electrolytic solution (body fluid), leading to the preferential corrosion of the less noble metal. Fretting corrosion can also occur concurrently due to micromotion.

Question 1346

Topic: Biomechanics & Biomaterials

A viscoelastic material is subjected to a constant load over a prolonged period. The observation that the material continues to deform progressively over time under this constant load is defined as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue
. Strain rate dependency

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the progressive deformation of a viscoelastic material when subjected to a constant load. Stress relaxation is the decrease in internal stress over time when the material is held at a constant deformation.

Question 1347

Topic: Biomechanics & Biomaterials

Titanium alloy (Ti-6Al-4V) is frequently used in orthopedic implants due to its excellent biocompatibility. Compared to 316L stainless steel, titanium alloy is characterized by:

. Higher modulus of elasticity
. Lower modulus of elasticity
. Greater resistance to abrasive wear
. Higher density
. Greater ductility

Correct Answer & Explanation

. Higher modulus of elasticity

Explanation

Titanium alloys have a lower modulus of elasticity (closer to that of cortical bone) compared to stainless steel and cobalt-chromium alloys, reducing stress shielding. However, titanium is highly notch-sensitive and has poor resistance to abrasive wear.

Question 1348

Topic: Biomechanics & Biomaterials

The myotendinous junction is the most common site of strain injuries in skeletal muscle. Structurally, the cell membrane of the muscle fiber at this junction is highly folded. What is the primary biomechanical advantage of this folding?

. Decreases the modulus of elasticity
. Increases the surface area to reduce applied shear stress
. Facilitates calcium ion transfer during contraction
. Provides a reservoir for satellite cells
. Converts tensile stress into compressive stress

Correct Answer & Explanation

. Decreases the modulus of elasticity

Explanation

The extensive folding of the sarcolemma at the myotendinous junction significantly increases the surface area over which force is transmitted. This effectively decreases the shear stress acting on the interface, reducing the risk of failure.

Question 1349

Topic: Biomechanics & Biomaterials
In the manufacturing of ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty, the polymer is exposed to gamma irradiation followed by a melting or annealing process. What is the primary purpose of this post-irradiation thermal treatment?
. To increase the ultimate tensile strength
. To eliminate free radicals and prevent oxidation
. To decrease the degree of cross-linking
. To lower the modulus of elasticity
. To sterilize the final packaged component

Correct Answer & Explanation

. To eliminate free radicals and prevent oxidation

Explanation

Gamma irradiation induces cross-linking, which dramatically improves wear resistance but also generates free radicals. Post-irradiation thermal treatment (melting or annealing) is performed to quench these free radicals, thereby preventing long-term in vivo oxidation and degradation.

Question 1350

Topic: Biomechanics & Biomaterials

A ligament stretched to a constant length over time will exhibit a gradual decrease in the force required to maintain that specific length. This viscoelastic property is known as:

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

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is a viscoelastic property where the stress (force) within a material decreases over time when it is held at a constant strain (length). Creep, in contrast, is continued deformation under a constant load.

Question 1351

Topic: Biomechanics & Biomaterials

Compared to stainless steel and cobalt-chromium alloys, titanium alloy (Ti-6Al-4V) used in orthopedic implants is characterized by:

. A higher modulus of elasticity
. Greater notch sensitivity
. Better resistance to abrasive wear
. Increased risk of galvanic corrosion when used alone
. A higher density

Correct Answer & Explanation

. A higher modulus of elasticity

Explanation

Titanium alloy is highly notch sensitive, meaning surface scratches can significantly reduce its fatigue strength. However, it has a lower modulus of elasticity (closer to bone) than stainless steel or cobalt-chromium, reducing stress shielding.

Question 1352

Topic: Biomechanics & Biomaterials

Mixing a stainless steel screw with a titanium plate in an orthopedic construct is generally avoided due to the increased risk of which specific type of corrosion?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within an electrolytic solution (e.g., body fluids). This drives an electrochemical reaction that accelerates metal breakdown.

Question 1353

Topic: Biomechanics & Biomaterials

A surgeon removes a modular total hip arthroplasty and notices black debris and pitting at the head-neck taper junction. Which type of corrosion is most likely responsible for this finding?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion occurs due to micromotion between two closely fitted surfaces (such as the modular head-neck taper in a total hip arthroplasty), leading to the mechanical disruption of the passive oxide layer and subsequent chemical attack. This is heavily implicated in mechanically assisted crevice corrosion, commonly referred to as trunnionosis.

Question 1354

Topic: Biomechanics & Biomaterials
The process of highly cross-linking ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty achieves which of the following mechanical trade-offs?
. Increases wear resistance but decreases fatigue strength
. Increases wear resistance and increases fracture toughness
. Decreases wear resistance but increases ductility
. Decreases wear resistance and increases ultimate tensile strength
. Increases oxidation resistance without altering mechanical strength

Correct Answer & Explanation

. Increases wear resistance but decreases fatigue strength

Explanation

Highly cross-linking UHMWPE (usually via irradiation) significantly increases its resistance to adhesive and abrasive wear. However, this process alters the polymer chains such that it decreases several bulk mechanical properties, including fatigue strength, ultimate tensile strength, ductility, and fracture toughness, making the material more brittle.

Question 1355

Topic: Biomechanics & Biomaterials

Which element is added to 316L stainless steel orthopedic implants to specifically reduce its susceptibility to pitting corrosion and crevice corrosion?

. Carbon
. Chromium
. Nickel
. Molybdenum
. Titanium

Correct Answer & Explanation

. Carbon

Explanation

The 'L' in 316L stainless steel stands for low carbon, preventing intergranular corrosion. Chromium provides the passivation (oxide) layer. Nickel stabilizes the austenitic crystal structure. Molybdenum (2-3%) is added specifically to significantly improve resistance to pitting and crevice corrosion in chloride-rich environments like the human body.

Question 1356

Topic: Biomechanics & Biomaterials

During tensile testing of a normal anterior cruciate ligament, a stress-strain curve is generated. The initial non-linear 'toe region' of the curve represents which of the following microstructural events?

. Yielding of collagen intermolecular cross-links
. Plastic deformation of the ligament substance
. Uncrimping of the resting Type I collagen fibrils
. Failure of intrafibrillar hydrogen bonds
. Macroscopic tearing of individual collagen bundles

Correct Answer & Explanation

. Yielding of collagen intermolecular cross-links

Explanation

Ligaments and tendons possess a crimped (wavy) collagen structure at rest. When tensile force is first applied, the 'toe region' of the stress-strain curve reflects the uncrimping of these Type I collagen fibrils. Once uncrimped, the curve enters the linear (elastic) region.

Question 1357

Topic: Biomechanics & Biomaterials

A surgeon incorrectly utilizes a 316L stainless steel plate with titanium alloy screws for internal fixation of a femur fracture. Which specific type of corrosion is most likely to be accelerated at the interface between these two distinct implant materials?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in physical contact within an electrolytic medium (like body fluid). The less noble metal acts as an anode and corrodes at an accelerated rate, while the more noble metal acts as a cathode.

Question 1358

Topic: Biomechanics & Biomaterials

Titanium alloys demonstrate excellent biocompatibility and high resistance to physiological corrosion. This characteristic is primarily dependent upon which of the following surface phenomena?

. High carbon content preventing sub-surface oxidation
. Spontaneous formation of a highly stable passivation layer of titanium dioxide
. Addition of nickel to stabilize the austenitic crystalline phase
. Complete absence of grain boundaries within the alpha-beta lattice
. Inherent antimicrobial properties of the titanium metal ions

Correct Answer & Explanation

. High carbon content preventing sub-surface oxidation

Explanation

Titanium and its alloys spontaneously form a thin, tenacious, and self-healing oxide layer (primarily TiO2) immediately upon exposure to oxygen or bodily fluids. This passivation layer protects the underlying bulk metal from chemical attack and provides excellent corrosion resistance and biocompatibility.

Question 1359

Topic: Biomechanics & Biomaterials

Stress shielding around a rigid intramedullary or joint replacement implant is directly related to the mismatch in stiffness between the implant material and the host bone. Which of the following orthopedic solid metal implant materials has the lowest modulus of elasticity (Young's modulus), making it biomechanically closest to cortical bone?

. Cobalt-chromium-molybdenum alloy
. 316L Stainless steel
. Titanium-6Aluminum-4Vanadium alloy
. Alumina ceramic
. Tantalum solid alloy

Correct Answer & Explanation

. Cobalt-chromium-molybdenum alloy

Explanation

Cortical bone has a Young's modulus of approximately 15-20 GPa. Among the standard structural metals, Titanium alloy (Ti-6Al-4V) has a modulus of roughly 110 GPa, which is the lowest and closest to bone. Stainless steel is ~200 GPa, and Cobalt-chromium alloys are the stiffest at ~210-240 GPa. (Trabecular/porous metals are lower, but solid Ti-alloy is the correct choice among structural solids).

Question 1360

Topic: Biomechanics & Biomaterials

A revision total hip arthroplasty is performed for a fractured modular femoral stem. Black debris is noted at the morse taper junction between the head and the neck. The primary mechanism of failure at this junction is best described as:

. Galvanic corrosion
. Mechanically assisted crevice corrosion (MACC)
. Pitting corrosion
. Intergranular corrosion
. Abrasive wear

Correct Answer & Explanation

. Galvanic corrosion

Explanation

The failure at the modular morse taper junction in THA is primarily driven by Mechanically Assisted Crevice Corrosion (MACC), also known as fretting corrosion. Micromotion disrupts the protective titanium oxide passivation layer, allowing crevice corrosion to accelerate in the localized low-oxygen, high-chloride environment.

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