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Biomechanics & Biomaterials MCQs

Practice Set 15 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 281

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is commonly used to reduce wear. Which of the following mechanical properties is significantly decreased as a direct result of the irradiation used to create highly cross-linked polyethylene?
. Abrasive wear resistance
. Oxidation resistance
. Fatigue strength
. Elastic modulus
. Hardness

Correct Answer & Explanation

. Fatigue strength

Explanation

Irradiation is used to cross-link UHMWPE chains, which significantly improves its adhesive and abrasive wear resistance. However, cross-linking decreases certain mechanical properties, particularly fatigue strength, yield strength, ultimate tensile strength, and ductility. To prevent oxidation from free radicals generated during irradiation, the material is typically remelted, annealed, or blended with an antioxidant like vitamin E.

Question 282

Topic: Biomechanics & Biomaterials

In the context of modularity in total hip arthroplasty (THA), which of the following is the primary mechanism of failure associated with trunnionosis at the head-neck junction?

. Galvanic corrosion due to dissimilar metals in a static environment
. Mechanically assisted crevice corrosion and fretting
. Pitting corrosion from high chloride physiological fluids
. Intergranular corrosion at grain boundaries
. Stress corrosion cracking from cyclic loading only

Correct Answer & Explanation

. Mechanically assisted crevice corrosion and fretting

Explanation

Trunnionosis refers to wear and corrosion at the modular head-neck junction of a THA. The primary mechanism is mechanically assisted crevice corrosion (MACC), which involves a combination of fretting (micromotion between the surfaces) that disrupts the passive oxide layer, and crevice corrosion (a localized drop in pH and oxygen depletion in the crevice) once the bulk material is exposed. While galvanic corrosion can contribute when mixed metals are used (e.g., CoCr head on Ti stem), fretting and MACC are the predominant driving factors.

Question 283

Topic: Biomechanics & Biomaterials

Galvanic corrosion between orthopedic implants occurs when two dissimilar metals are in contact within an electrolytic environment. Which of the following combinations of metals is most likely to result in significant galvanic corrosion in vivo and is generally contraindicated?

. Titanium and Titanium alloy
. Stainless steel and Cobalt-Chromium
. Stainless steel and Titanium
. Cobalt-Chromium and Titanium
. Zirconium and Titanium

Correct Answer & Explanation

. Stainless steel and Cobalt-Chromium

Explanation

Stainless steel and titanium have a large electrochemical potential difference. When placed in contact (e.g., a stainless steel plate with a titanium screw), the stainless steel acts as the anode and corrodes rapidly. Cobalt-chromium and titanium are routinely used together (e.g., THA stems and heads) with an acceptable passivation layer preventing severe corrosion.

Question 284

Topic: Biomechanics & Biomaterials

Articular cartilage exhibits complex viscoelastic properties under loading. When a constant deformation (strain) is rapidly applied and maintained on articular cartilage, the internal peak stress gradually decreases over time until it reaches an equilibrium. Which of the following terms best describes this specific biomechanical phenomenon?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a hallmark of viscoelastic materials, defined as the decrease in internal stress over time when subjected to a constant strain (deformation). Creep, conversely, is the progressive increase in strain (deformation) over time when subjected to a constant stress (load). Hysteresis refers to the energy lost (usually as heat) during the loading and unloading cycle of a viscoelastic material.

Question 285

Topic: Biomechanics & Biomaterials

In total hip arthroplasty (THA), the adoption of highly cross-linked polyethylene (HXLPE) has significantly reduced wear rates compared to conventional polyethylene. However, the high-dose irradiation process alters the mechanical properties of the material. Which mechanical property is most significantly decreased as a direct result of irradiation for cross-linking?

. Modulus of elasticity
. Wear resistance
. Fatigue crack propagation resistance
. Coefficient of friction
. Oxidation resistance prior to remelting

Correct Answer & Explanation

. Fatigue crack propagation resistance

Explanation

While high-dose irradiation creates cross-links that greatly improve wear resistance, it also makes the polyethylene more brittle. This results in a decrease in ductility, ultimate tensile strength, and most notably, fatigue crack propagation resistance (fracture toughness). This is why highly cross-linked polyethylene is generally avoided in unicompartmental knees or very thin tibial inserts where high stress concentrations might lead to component fracture.

Question 286

Topic: Biomechanics & Biomaterials

Titanium alloy (Ti-6Al-4V) is frequently utilized in orthopedic implants, including fracture plates and intramedullary nails. Compared to stainless steel (316L) and cobalt-chrome (Co-Cr) alloys, which of the following is a primary biomechanical advantage of titanium?

. Higher modulus of elasticity leading to better load sharing
. Lower modulus of elasticity resulting in decreased stress shielding
. Superior resistance to galvanic corrosion when mixed with other metals
. Higher density providing increased implant weight and stability
. Greater resistance to wear and scratching in articulating surfaces

Correct Answer & Explanation

. Lower modulus of elasticity resulting in decreased stress shielding

Explanation

Titanium has a significantly lower modulus of elasticity (closer to that of cortical bone) compared to stainless steel and cobalt-chrome. This allows for more load sharing with the host bone, thereby decreasing the phenomenon of stress shielding (which can lead to bone resorption around the implant). Titanium is famously poor for wear resistance on articulating surfaces.

Question 287

Topic: Biomechanics & Biomaterials

When a constant magnitude of load is applied to a viscoelastic material over a prolonged period, the material undergoes increasing progressive deformation. This biomechanical property is known as:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive, time-dependent deformation of a viscoelastic material under a constant load. Stress relaxation is the decrease in stress (force) over time when the material is held at a constant deformation. Hysteresis is the energy lost (usually as heat) during the loading and unloading cycle.

Question 288

Topic: Biomechanics & Biomaterials

A revision total hip arthroplasty is performed for a fractured modular neck. Examination of the taper junction reveals black debris and pitting. What is the primary initiating mechanism of corrosion at the modular taper junction of a titanium stem and cobalt-chrome head?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion (mechanically assisted crevice corrosion) is the primary initiating mode of failure at modular junctions in total joint arthroplasty. Micro-motion mechanically disrupts the protective passivation (oxide) layer, which then allows crevice and galvanic corrosion to occur.

Question 289

Topic: Biomechanics & Biomaterials

Following a traumatic laceration and subsequent zone II flexor tendon repair in the index finger, preservation or reconstruction of the pulley system is mandatory for optimal biomechanics. Which of the following sets of annular pulleys are considered the most mechanically critical to prevent bowstringing and flexion contractures?

. A1 and A3
. A2 and A4
. A3 and A5
. A1, A3, and A5
. C1, C2, and C3

Correct Answer & Explanation

. A2 and A4

Explanation

The A2 and A4 pulleys are the most mechanically critical annular pulleys in the flexor tendon sheath. They arise directly from the periosteum of the proximal and middle phalanges, respectively. Loss of these two pulleys leads to significant bowstringing of the flexor tendons, decreased excursion efficiency, reduced grip strength, and progressive flexion contractures.

Question 290

Topic: Biomechanics & Biomaterials



In the manufacturing of modern orthopedic implants, titanium alloys are frequently utilized due to their excellent biocompatibility and mechanical profile. Which of the following best explains the primary mechanism underlying titanium's exceptional corrosion resistance in vivo?

. Galvanic coupling with surrounding soft tissues and bone
. Spontaneous formation of a passive, inert titanium dioxide (TiO2) layer on its surface
. Its extremely high modulus of elasticity closely matching cortical bone
. Constant release of osteoinductive titanium ions inhibiting macrophage activation
. A low coefficient of friction when articulating against ultra-high-molecular-weight polyethylene

Correct Answer & Explanation

. Spontaneous formation of a passive, inert titanium dioxide (TiO2) layer on its surface

Explanation

Titanium and its alloys owe their high biocompatibility and excellent corrosion resistance to the spontaneous formation of a thin, passive, adherent oxide layer (primarily titanium dioxide, TiO2) on their surface when exposed to air or bodily fluids. This inert layer prevents further oxidation and interaction with the surrounding biological environment.

Question 291

Topic: Biomechanics & Biomaterials

Trunnionosis in total hip arthroplasty is a phenomenon of mechanically assisted crevice corrosion. It is historically most strongly associated with which of the following combinations of head and stem materials?

. Cobalt-chrome head on titanium stem
. Ceramic head on titanium stem
. Ceramic head on cobalt-chrome stem
. Oxidized zirconium head on titanium stem
. Cobalt-chrome head on cobalt-chrome stem

Correct Answer & Explanation

. Cobalt-chrome head on titanium stem

Explanation

Trunnionosis, or mechanically assisted crevice corrosion at the modular head-neck junction, has been most commonly observed in combinations utilizing a large cobalt-chrome (CoCr) femoral head on a titanium alloy stem due to galvanic and fretting corrosion mechanics.

Question 292

Topic: Biomechanics & Biomaterials

During an anterior cruciate ligament (ACL) reconstruction, improper tunnel placement can lead to graft failure or loss of motion. If the femoral tunnel is placed too far anteriorly (shallow) in the intercondylar notch, which of the following graft tension patterns will result?

. Tight in extension and tight in flexion
. Tight in flexion and lax in extension
. Lax in flexion and tight in extension
. Lax in both extension and flexion
. Isotropic tension throughout the entire range of motion

Correct Answer & Explanation

. Tight in flexion and lax in extension

Explanation

Proper femoral tunnel placement is critical for ACL graft isometry. If the femoral tunnel is placed too far anteriorly (shallow, moving away from the anatomic footprint towards the anterior cortex), the distance between the femoral and tibial attachments increases as the knee flexes. This results in the graft being overly tight in flexion (often restricting flexion or leading to graft stretch/failure) and lax in extension. Conversely, placement too far posteriorly leads to a graft that is tight in extension and lax in flexion.

Question 293

Topic: Biomechanics & Biomaterials

Articular cartilage is a highly specialized connective tissue. The primary structural proteoglycan of articular cartilage is aggrecan. Which of the following is the most abundant glycosaminoglycan (GAG) attached to the aggrecan core protein?

. Type I collagen
. Chondroitin sulfate
. Fibronectin
. Elastin
. Hydroxyapatite

Correct Answer & Explanation

. Chondroitin sulfate

Explanation

Aggrecan is the major proteoglycan in articular cartilage and provides the osmotic properties necessary to resist compressive loads. It consists of a core protein with numerous covalently attached glycosaminoglycan (GAG) side chains. The two primary GAGs on aggrecan are chondroitin sulfate and keratan sulfate, with chondroitin sulfate being the most abundant. Type I collagen is primarily found in bone and tendon; articular cartilage is predominantly Type II collagen.

Question 294

Topic: Biomechanics & Biomaterials
To reduce wear rates in total hip arthroplasty, highly cross-linked polyethylene (HXLPE) was developed. However, the process of irradiation creates free radicals that can lead to long-term oxidation and material degradation. Which of the following manufacturing processes is specifically utilized to neutralize or eliminate these free radicals without requiring post-irradiation thermal treatment (melting or annealing)?
. Gamma irradiation in an inert argon environment
. Ethylene oxide gas sterilization
. Blending or diffusing with Vitamin E (alpha-tocopherol)
. Cold drawing of the ultra-high molecular weight polyethylene
. Addition of barium sulfate to the polymer matrix

Correct Answer & Explanation

. Blending or diffusing with Vitamin E (alpha-tocopherol)

Explanation

Irradiation of UHMWPE creates cross-links that improve wear resistance but also generates free radicals that predispose the material to oxidation. Historically, thermal treatments like remelting or annealing were used to quench these free radicals, but remelting reduces mechanical strength. The addition of Vitamin E (alpha-tocopherol) acts as an antioxidant, quenching free radicals without the need for thermal treatment, thereby preserving the material's mechanical properties while preventing oxidative degradation.

Question 295

Topic: Biomechanics & Biomaterials
When evaluating the biomaterials used in total hip arthroplasty, the sterilization process of ultra-high molecular weight polyethylene (UHMWPE) profoundly affects its long-term wear characteristics. Which of the following sterilization environments for UHMWPE is most strongly associated with free radical formation leading to oxidative chain scission, structural degradation, and accelerated clinical wear?
. Gamma irradiation in an inert gas (Argon)
. Gamma irradiation in air
. Ethylene oxide gas
. Hydrogen peroxide gas plasma
. Gamma irradiation in a vacuum

Correct Answer & Explanation

. Gamma irradiation in air

Explanation

Gamma irradiation of UHMWPE in air (oxygen-containing environment) leads to the formation of free radicals that react with oxygen to form hydroperoxides. Over time, this oxidation leads to chain scission, decreased molecular weight, embrittlement, and catastrophic delamination and wear of the polyethylene bearing surface. Modern sterilization techniques use inert gases (like argon), vacuum packaging, or non-irradiation methods (like ethylene oxide) followed by highly cross-linking and annealing or remelting to eliminate free radicals.

Question 296

Topic: Biomechanics & Biomaterials

A 65-year-old male undergoes a primary total hip arthroplasty using a titanium alloy (Ti-6Al-4V) femoral stem and a cobalt-chromium (CoCr) alloy femoral head. Five years later, he presents with progressive groin pain and a large cystic mass on MRI, without evidence of infection. Revision surgery reveals black debris and damage at the head-neck taper junction. What is the primary pathophysiologic mechanism of this wear pattern?

. Galvanic corrosion exclusively
. Mechanically assisted crevice corrosion
. Intergranular corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Mechanically assisted crevice corrosion

Explanation

The scenario describes trunnionosis, which is primarily caused by mechanically assisted crevice corrosion (MACC), also known as fretting and crevice corrosion. Micro-motion at the modular junction (fretting) disrupts the protective passivating oxide layer of the metals. Because this occurs in a restricted space (crevice), local fluid chemistry changes (decreased pH, decreased oxygen), which accelerates the corrosion process. While galvanic corrosion can play a minor role when dissimilar metals are used, MACC is the dominant mechanism for taper failure in modern THA.

Question 297

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, ultra-high-molecular-weight polyethylene (UHMWPE) is subjected to gamma irradiation to induce extensive cross-linking. While this process significantly improves wear resistance, what is the primary mechanical disadvantage introduced by highly cross-linking the polyethylene?
. Increased susceptibility to oxidative degradation in vivo
. Decreased fatigue strength and fracture toughness
. Accelerated rate of volumetric wear compared to conventional polyethylene
. Increased generation of smaller, highly biologically active wear debris particles
. A drastic increase in the modulus of elasticity leading to stress shielding

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

Highly cross-linking UHMWPE dramatically improves its resistance to adhesive and abrasive wear. However, the process of cross-linking alters the polymer's internal structure, resulting in decreased mechanical properties, specifically diminished fatigue strength, yield strength, and fracture toughness. This makes the material more susceptible to catastrophic failure, such as rim fracture in thin acetabular liners.

Question 298

Topic: Biomechanics & Biomaterials
What primary manufacturing process decreases the wear rate of highly cross-linked polyethylene (HXLPE) compared to conventional polyethylene in total hip arthroplasty?
. Addition of Vitamin E as an antioxidant only
. Irradiation followed by remelting or annealing
. Ethylene oxide gas sterilization
. Forging and hot isostatic pressing
. Cold working and subsequent rapid cooling

Correct Answer & Explanation

. Irradiation followed by remelting or annealing

Explanation

Highly cross-linked polyethylene (HXLPE) is created by subjecting the ultra-high-molecular-weight polyethylene (UHMWPE) to gamma or electron beam irradiation, which creates cross-links between the polymer chains, significantly increasing wear resistance. This process also generates free radicals that can cause oxidative degradation over time. To eliminate these free radicals, the material is subsequently heated through either remelting (above the melting point) or annealing (below the melting point).

Question 299

Topic: Biomechanics & Biomaterials

To avoid galvanic corrosion in orthopedic implants, dissimilar metals should generally not be in physical contact. However, combining a cobalt-chromium femoral head with a titanium alloy femoral stem is clinically common and highly successful. What is the primary electrochemical reason this specific modular combination is acceptable?

. Titanium acts as a sacrificial anode, corroding preferentially to protect the cobalt-chromium.
. Both metals spontaneously form stable passivating oxide layers that drastically limit electron transfer.
. Cobalt-chromium is highly electronegative, chemically repelling ionic degradation.
. The taper junction becomes quickly biologically sealed by an ingrowth of a fibrous tissue capsule.
. Galvanic currents are naturally neutralized by the buffering capacity of the body's physiological saline environment.

Correct Answer & Explanation

. Both metals spontaneously form stable passivating oxide layers that drastically limit electron transfer.

Explanation

Both titanium alloys and cobalt-chromium alloys naturally form dense, highly stable, protective oxide layers (TiO2 and Cr2O3, respectively) on their surfaces through a process called passivation. These oxide layers are excellent insulators and substantially prevent the transfer of electrons between the dissimilar metals, virtually eliminating clinically significant galvanic corrosion as long as the passivating layers remain intact.

Question 300

Topic: Biomechanics & Biomaterials

A 45-year-old female presents with sudden onset medial knee pain while squatting. MRI shows a medial meniscus posterior root tear. Biomechanically, what is the consequence of this specific injury on the knee joint?

. Increased contact area in the medial compartment
. Decreased peak contact pressure during weight-bearing
. Kinematics equivalent to a total medial meniscectomy
. Increased anterior tibial translation during the Lachman test
. Decreased varus laxity in full extension

Correct Answer & Explanation

. Kinematics equivalent to a total medial meniscectomy

Explanation

A complete posterior root tear of the medial meniscus leads to a complete loss of hoop stresses, resulting in radial extrusion of the meniscus during axial loading. Biomechanically, this is equivalent to a total medial meniscectomy, significantly decreasing the contact area and markedly increasing peak contact pressures, leading to accelerated osteoarthritis.

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