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Biomechanics & Biomaterials MCQs

Practice Set 70 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 1381

Topic: Biomechanics & Biomaterials
Highly cross-linked polyethylene (HXLPE) was developed to reduce wear rates in total hip arthroplasty. Which of the following represents the primary mechanism by which cross-linking reduces wear compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE)?
. Elimination of free radicals through remelting or annealing.
. Formation of intermolecular covalent bonds that prevent polymer chain alignment, fibril formation, and subsequent pull-out.
. Decreased overall crystallinity of the polymer matrix.
. Increased oxidative degradation resistance at the bearing surface.
. Conversion of the amorphous region to a strictly crystalline region.

Correct Answer & Explanation

. Formation of intermolecular covalent bonds that prevent polymer chain alignment, fibril formation, and subsequent pull-out.

Explanation

Highly cross-linked polyethylene (HXLPE) undergoes irradiation to break polymer chains, which then recombine to form strong intermolecular covalent bonds (cross-links). This prevents the linear polymer chains from aligning in the direction of motion, completely disrupting the process of fibril formation and subsequent adhesive wear (chain pull-out). While remelting and annealing eliminate free radicals to prevent oxidation, the cross-linking itself is what primarily reduces the mechanical wear.

Question 1382

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopedic implants is most likely to occur when which of the following conditions is met?

. Two identical metals are subjected to repeated cyclic loading
. A stainless steel plate is used with a titanium screw in a fluid medium
. A titanium implant is placed in a highly oxygenated environment
. Polyethylene debris accumulates around a cobalt-chrome femoral head
. Ceramic implants undergo micro-fractures under compression

Correct Answer & Explanation

. Two identical metals are subjected to repeated cyclic loading

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as stainless steel and titanium) are in physical contact within an electrolytic solution (like bodily fluids). The difference in their electrochemical potentials drives an electron transfer, causing the more anodic metal to corrode.

Question 1383

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, which of the following wear mechanisms is primarily responsible for the generation of submicron polyethylene particles that lead to macrophage-mediated osteolysis?
. Adhesive wear
. Abrasive wear
. Fatigue wear
. Third-body wear
. Fretting wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear is the primary mechanism generating submicron ultra-high-molecular-weight polyethylene (UHMWPE) wear debris in total joint arthroplasty, which initiates the macrophage-mediated osteolytic cascade.

Question 1384

Topic: Biomechanics & Biomaterials

A total hip arthroplasty with a cobalt-chromium (CoCr) femoral head and a titanium alloy stem is revised for aseptic loosening. Black debris is noted at the modular head-neck junction. Which type of corrosion initiates the mechanically assisted crevice corrosion (MACC) at this modular interface?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion initiates mechanically assisted crevice corrosion (MACC) at the modular head-neck junction (trunnionosis) of a THA. Fretting (micromotion) continuously breaks the protective oxide passivation layer, allowing subsequent crevice and galvanic corrosion to proceed.

Question 1385

Topic: Biomechanics & Biomaterials

A 65-year-old man undergoes revision total hip arthroplasty where a cobalt-chromium femoral head is placed onto a titanium alloy femoral stem. Which of the following types of corrosion is most likely to occur at the head-neck junction?

. Pitting corrosion
. Crevice corrosion
. Galvanic corrosion
. Fretting corrosion
. Uniform corrosion

Correct Answer & Explanation

. Pitting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as cobalt-chromium and titanium alloy) are placed in physical contact within an electrolytic solution like body fluid. The less noble metal undergoes accelerated corrosion. Fretting corrosion can also occur at modular junctions due to micromotion, but the presence of dissimilar metals specifically defines galvanic corrosion.

Question 1386

Topic: Biomechanics & Biomaterials

Articular cartilage exhibits highly predictable viscoelastic properties. When a constant compressive load is applied to cartilage, it deforms rapidly at first, followed by a slow, progressive increase in deformation until an equilibrium is reached. This time-dependent biomechanical phenomenon is known as:

. Stress relaxation
. Creep
. Hysteresis
. Anisotropy
. Boundary lubrication

Correct Answer & Explanation

. Stress relaxation

Explanation

'Creep' is defined as the progressive deformation of a viscoelastic material under a constant load over time. In articular cartilage, this is primarily due to the exudation of interstitial fluid from the extracellular matrix. 'Stress relaxation', by contrast, is the decrease in stress over time when a material is held at a constant strain (constant deformation).

Question 1387

Topic: Biomechanics & Biomaterials

Which type of corrosion occurs in modular junctions of orthopedic implants, such as the head-neck taper of a total hip arthroplasty, primarily due to micromotion that mechanically disrupts the protective passive oxide layer?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion occurs at contact sites between materials under load subject to minute relative motion (micromotion). This micromotion constantly disrupts the protective passive oxide film on the metal surface, exposing the underlying metal and leading to accelerated localized corrosion. This is the primary mechanism of trunnionosis in the modular head-neck taper of a THA.

Question 1388

Topic: Biomechanics & Biomaterials

During a cemented total knee arthroplasty, the surgeon mixes polymethylmethacrylate (PMMA) bone cement. What is the primary role of barium sulfate in the PMMA powder mixture?

. Initiator of the polymerization reaction
. Accelerator of the curing process
. Radiopacifier
. Stabilizer to prevent premature polymerization
. Cross-linking agent to increase tensile strength

Correct Answer & Explanation

. Initiator of the polymerization reaction

Explanation

Barium sulfate (or zirconium dioxide) is added to the PMMA powder specifically to act as a radiopacifier, allowing the cement mantle to be visualized on postoperative radiographs. Benzoyl peroxide is the initiator, N,N-dimethyl-p-toluidine is the accelerator, and hydroquinone is the stabilizer.

Question 1389

Topic: Biomechanics & Biomaterials

During revision of a modular metal-on-polyethylene total hip arthroplasty, the surgeon observes significant black corrosive debris and tissue staining localized specifically at the modular head-neck taper junction. Which type of corrosion is primarily responsible for this localized wear mechanism?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

The localized wear and corrosion at the modular head-neck taper junction is classically referred to as trunnionosis. This is primarily caused by mechanically assisted crevice corrosion, commonly termed fretting corrosion. Micro-motion at the interface (fretting) repeatedly disrupts the passive oxide layer of the metal, accelerating corrosive degradation in the fluid-filled crevice.

Question 1390

Topic: Biomechanics & Biomaterials

A surgeon uses a titanium alloy screw to secure a stainless steel plate in a fracture fixation. Over time, the implant site demonstrates significant corrosion and osteolysis. What specific type of corrosion is occurring due to the use of these two different metals?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic fluid environment (like human serum). The less noble metal becomes the anode and undergoes accelerated corrosion.

Question 1391

Topic: Biomechanics & Biomaterials

In the context of biomechanics of ligaments and tendons, which of the following terms describes the gradual increase in deformation of a viscoelastic material over time when subjected to a constant, sustained load?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep refers to the progressive deformation of a viscoelastic material when subjected to a constant load over time. This concept is utilized clinically in serial casting and traction. Stress relaxation, conversely, is the decrease in stress over time when the material is held at a constant length.

Question 1392

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is widely used in total hip arthroplasty. While cross-linking significantly reduces adhesive and abrasive wear, it has which of the following detrimental effects on the mechanical properties of the polyethylene?
. Decreased oxidation resistance
. Increased elastic modulus
. Decreased fatigue strength
. Increased ultimate tensile strength
. Decreased melting temperature

Correct Answer & Explanation

. Decreased fatigue strength

Explanation

Increasing the cross-linking of UHMWPE significantly improves its wear resistance but at the cost of decreasing its mechanical properties, including fatigue strength, yield strength, and ultimate tensile strength. To mitigate oxidation, free radicals generated during cross-linking are eliminated through processes like remelting or annealing, or by adding antioxidants like Vitamin E.

Question 1393

Topic: Biomechanics & Biomaterials

When comparing titanium alloy (Ti-6Al-4V) to 316L stainless steel for orthopedic implants, which of the following is a characteristic biomechanical property of titanium?

. Higher modulus of elasticity
. Lower notch sensitivity
. Greater biocompatibility due to a passivating oxide layer
. Increased susceptibility to galvanic corrosion when used alone
. Higher density

Correct Answer & Explanation

. Higher modulus of elasticity

Explanation

Titanium alloy has a highly stable passivating titanium dioxide layer, conferring excellent biocompatibility and corrosion resistance. It has a lower modulus of elasticity (closer to bone) and higher notch sensitivity compared to stainless steel.

Question 1394

Topic: Biomechanics & Biomaterials

A patient undergoes anterior cruciate ligament (ACL) reconstruction with a soft tissue allograft. Tension is applied to the graft prior to fixation. Over time, the tension required to maintain the graft at a constant length decreases. This viscoelastic property is known as:

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

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is the decrease in stress (tension) over time when a viscoelastic material is held at a constant length. Creep is the increase in deformation (length) over time under a constant load.

Question 1395

Topic: Biomechanics & Biomaterials

A surgeon plans to perform a revision open reduction and internal fixation utilizing both stainless steel plates and titanium screws. This combination is generally avoided due to the risk of which type of corrosion?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within a conductive electrolyte solution (such as body fluid). The less noble metal (anode) undergoes accelerated corrosion.

Question 1396

Topic: Biomechanics & Biomaterials

Following a primary repair of a lacerated flexor digitorum profundus (FDP) and superficialis (FDS) in Zone II of the index finger, a patient begins a controlled mobilization protocol. Which of the following biomechanical principles best supports early active motion protocols compared to prolonged immobilization?

. Early active motion decreases tendon excursion thereby minimizing rupture
. Early active motion increases peritendinous adhesion formation
. Early active motion stimulates intrinsic tendon healing and increases tensile strength
. Prolonged immobilization leads to stronger core suture biomechanics
. Immobilization increases the gliding coefficient of the tendon

Correct Answer & Explanation

. Early active motion decreases tendon excursion thereby minimizing rupture

Explanation

Early motion (whether active or passive) applies controlled mechanical stress to the repaired tendon, which stimulates intrinsic healing (via tenocyte proliferation and parallel collagen orientation). This process reduces restrictive peritendinous adhesions and ultimately increases the ultimate tensile strength of the repair compared to static immobilization.

Question 1397

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked polyethylene significantly improves implant longevity primarily by reducing which specific type of wear?
. Adhesive wear
. Abrasive wear
. Third-body wear
. Fatigue wear
. Corrosive wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Highly cross-linked polyethylene primarily decreases adhesive wear, which is the main mechanism of volumetric wear in standard ultra-high-molecular-weight polyethylene (UHMWPE) bearings. The cross-linking process restricts polymer chain mobility. Note that while wear resistance increases, fatigue strength may decrease slightly.

Question 1398

Topic: Biomechanics & Biomaterials

During revision of a failed internal fixation, a surgeon contemplates using titanium screws in conjunction with a stainless steel plate. Which of the following biomaterial principles makes this combination potentially problematic?

. Titanium is significantly stiffer than stainless steel
. Galvanic corrosion may occur due to differing anodic indices
. Crevice corrosion is prevented by combining dissimilar metals
. Stainless steel induces rapid osteolysis when contacting titanium
. Titanium prevents the formation of a passivation layer on stainless steel

Correct Answer & Explanation

. Titanium is significantly stiffer than stainless steel

Explanation

Mixing dissimilar metals, such as stainless steel and titanium, in an electrolytic environment (like the human body) can lead to galvanic corrosion. The less noble metal acts as an anode and corrodes at an accelerated rate.

Question 1399

Topic: Biomechanics & Biomaterials

During a fracture fixation procedure, a surgeon places a 316L stainless steel screw through a titanium alloy plate. This mixed-metal construct risks galvanic corrosion. Which of the following accurately describes the resulting electrochemical process?

. Titanium acts as the anode and corrodes rapidly.
. Stainless steel acts as the anode and undergoes accelerated corrosion.
. Both metals corrode equally due to identical galvanic potentials.
. Titanium acts as the cathode and undergoes accelerated corrosion.
. Stainless steel acts as the cathode and is protected by the sacrificial titanium.

Correct Answer & Explanation

. Titanium acts as the anode and corrodes rapidly.

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution (body fluid). The less noble metal acts as the anode and undergoes accelerated corrosion by giving up electrons, while the more noble metal acts as the cathode. Stainless steel is less noble than titanium, so the stainless steel screw acts as the anode and corrodes.

Question 1400

Topic: Biomechanics & Biomaterials

Which specific type of corrosion is most likely to occur when a 316L stainless steel screw is placed through a titanium alloy plate in an orthopaedic internal fixation construct?

. 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 (such as stainless steel and titanium) are placed in direct electrical contact within an electrolytic environment (such as bodily fluids), causing the less noble metal to corrode.

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