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Biomechanics & Biomaterials MCQs

Practice Set 19 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 361

Topic: Biomechanics & Biomaterials

Trunnionosis, observed at the head-neck modular junction in total hip arthroplasty, is predominantly initiated by which of the following mechanisms?

. Galvanic corrosion
. Fretting corrosion
. Pitting corrosion
. Intergranular corrosion
. Uniform corrosion

Correct Answer & Explanation

. Fretting corrosion

Explanation

Trunnionosis is primarily an example of mechanically assisted crevice corrosion, initiated by fretting corrosion. Micromotion at the modular head-neck taper (fretting) mechanically breaks down the protective passive oxide layer of the metal, exposing raw metal to the body fluids and leading to accelerated localized crevice corrosion.

Question 362

Topic: Biomechanics & Biomaterials

The scapholunate interosseous ligament is the primary stabilizer of the scapholunate articulation. Which anatomical subregion of this ligament possesses the greatest tensile strength and is biomechanically the most important to repair?

. Volar portion
. Dorsal portion
. Proximal (membranous) portion
. Central portion
. Distal portion

Correct Answer & Explanation

. Dorsal portion

Explanation

The scapholunate interosseous ligament has three distinct regions: dorsal, proximal (membranous), and volar. The dorsal portion is the thickest and biomechanically the strongest, being the most critical region to repair to restore normal kinematics. Conversely, the volar portion is the strongest for the lunotriquetral ligament.

Question 363

Topic: Biomechanics & Biomaterials

A patient undergoes revision of a total hip arthroplasty composed of a titanium alloy stem and a modular cobalt-chromium femoral head. The revision is performed for an adverse local tissue reaction (ALTR) secondary to metallosis. The primary mechanism of metal degradation at the modular head-neck junction in this scenario is classified as:

. Galvanic corrosion
. Mechanically assisted crevice corrosion (fretting corrosion)
. Pitting corrosion
. Intergranular corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Mechanically assisted crevice corrosion (fretting corrosion)

Explanation

Corrosion at the modular head-neck taper junction (trunnionosis) is primarily caused by mechanically assisted crevice corrosion, commonly referred to as fretting corrosion. Micromotion between the head and the neck disrupts the protective passivation layer of the metals, exposing raw metal to the body fluid environment (crevice corrosion), which accelerates the release of metal ions and debris, leading to ALTR.

Question 364

Topic: Biomechanics & Biomaterials

A surgeon revises a failed hip arthroplasty and notices significant corrosion at the modular head-neck junction. The femoral stem is titanium alloy and the femoral head is cobalt-chromium. Which of the following best describes the primary mechanism of galvanic corrosion in this setting?

. Fretting motion disrupting the passivation layer, exposing different metals to an electrolyte.
. Micro-organism induced acidic environment dissolving the titanium alloy.
. Excessive compressive loads causing plastic deformation of the cobalt-chromium head.
. Release of free radicals from the polyethylene liner interacting with the metal junction.
. High levels of systemic chromium leading to a hypersensitivity reaction at the junction.

Correct Answer & Explanation

. Fretting motion disrupting the passivation layer, exposing different metals to an electrolyte.

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., Titanium and Cobalt-Chromium) are in contact within an electrolyte solution (body fluid). Fretting (micro-motion) disrupts the protective oxide (passivation) layer, accelerating the electrochemical dissolution of the less noble metal.

Question 365

Topic: Biomechanics & Biomaterials
Which of the following modifications to ultra-high molecular weight polyethylene (UHMWPE) most effectively increases its wear resistance in total hip arthroplasty?
. Decreasing overall crystallinity
. Gamma irradiation in air
. Electron beam or gamma irradiation followed by remelting
. Adding barium sulfate for radiopacity
. Sterilization with ethylene oxide gas

Correct Answer & Explanation

. Electron beam or gamma irradiation followed by remelting

Explanation

Highly cross-linked polyethylene is produced by exposing UHMWPE to irradiation (gamma or electron beam), which creates free radicals that form cross-links. This significantly improves wear resistance. Subsequent remelting or annealing eliminates residual free radicals to prevent long-term in vivo oxidation.

Question 366

Topic: Biomechanics & Biomaterials

In the context of preparing polymethylmethacrylate (PMMA) bone cement, which of the following modifications significantly decreases the mechanical strength and fatigue life of the cement mantle?

. Adding antibiotics in powder form rather than liquid form
. Vacuum mixing the cement
. Centrifuging the cement prior to application
. Adding liquid antibiotics or excessive fluid
. Pre-chilling the monomer

Correct Answer & Explanation

. Adding liquid antibiotics or excessive fluid

Explanation

Adding aqueous/liquid substances (like liquid antibiotics) or excessive fluid significantly increases porosity and radically decreases the ultimate mechanical strength and fatigue life of PMMA bone cement. Antibiotics should only be added in fine powder form. Vacuum mixing and centrifugation both decrease porosity and thereby increase fatigue life. Pre-chilling the monomer prolongs the working time but does not weaken the cement.

Question 367

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) compared to conventional ultra-high molecular weight polyethylene (UHMWPE) results in which of the following material property changes?
. Increased ultimate tensile strength
. Increased resistance to abrasive wear
. Increased fatigue crack propagation resistance
. Increased oxidation resistance post-gamma irradiation in air
. Increased risk of osteolysis at 10 years

Correct Answer & Explanation

. Increased fatigue crack propagation resistance

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured to significantly increase resistance to adhesive and abrasive wear, thereby reducing wear debris and subsequent osteolysis. However, the cross-linking process and subsequent thermal treatments decrease mechanical properties such as ultimate tensile strength, yield strength, and fatigue crack propagation resistance.

Question 368

Topic: Biomechanics & Biomaterials

During biomechanical testing of a tendon graft, the graft is rapidly stretched to a specific length and held at that constant length. Over time, the force required to maintain that length progressively decreases. This viscoelastic property is termed:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Isotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in stress (force) over time when a viscoelastic material is held at a constant strain (length). Creep is the progressive increase in strain (length) over time when the material is held at a constant stress (load).

Question 369

Topic: Biomechanics & Biomaterials

In the metallurgical design of titanium alloys for orthopaedic implants (such as Ti-6Al-4V), specific elements are added to stabilize different phases of the metal at room temperature. What is the primary role of vanadium in this alloy?

. It stabilizes the alpha-phase, increasing tensile strength.
. It stabilizes the beta-phase, lowering the modulus of elasticity.
. It promotes passivation by forming a dense oxide layer.
. It acts as an interstitial strengthener to prevent galvanic corrosion.
. It limits stress shielding by increasing the metal's density.

Correct Answer & Explanation

. It stabilizes the beta-phase, lowering the modulus of elasticity.

Explanation

In the Ti-6Al-4V alloy, titanium undergoes an allotropic phase transformation. Aluminum is added to stabilize the alpha-phase (hexagonal close-packed structure), which provides strength. Vanadium is a beta-phase (body-centered cubic) stabilizer. Retaining the beta-phase at room temperature lowers the overall modulus of elasticity of the implant, bringing it closer to that of cortical bone and thereby reducing stress shielding.

Question 370

Topic: Biomechanics & Biomaterials

A 45-year-old patient undergoes revision osteosynthesis of a nonunion using a titanium locking plate and stainless steel screws. Which of the following best describes the likely electrochemical outcome at the implant interface?

. The titanium plate undergoes rapid galvanic corrosion
. The stainless steel screws undergo rapid galvanic corrosion
. Fretting corrosion is completely eliminated
. Crevice corrosion occurs preferentially at the diaphyseal bone
. Both metals are passivated equally due to the formation of a titanium dioxide layer

Correct Answer & Explanation

. The stainless steel screws undergo rapid galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution (e.g., bodily fluids). Stainless steel is anodic (less noble) relative to titanium. Therefore, when they are in direct contact, the stainless steel acts as the anode and preferentially corrodes, releasing ions, while the titanium acts as the cathode and remains protected.

Question 371

Topic: Biomechanics & Biomaterials
What is the primary mechanism by which highly cross-linked polyethylene (HXLPE) achieves significantly reduced wear rates compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE) in total hip arthroplasty?
. Addition of vitamin E to increase surface hardness
. Reduction of free radicals through remelting or annealing
. Creation of transverse covalent bonds between polymer chains via gamma or electron beam irradiation
. Increasing the crystalline structure density through cold forging
. Sterilization in an oxygen-rich environment

Correct Answer & Explanation

. Creation of transverse covalent bonds between polymer chains via gamma or electron beam irradiation

Explanation

Highly cross-linked polyethylene is manufactured by exposing UHMWPE to high doses of gamma or electron beam irradiation. This radiation breaks carbon-hydrogen bonds, allowing free radicals to combine and form strong transverse covalent bonds (cross-links) between adjacent polymer chains. This highly interlinked network vastly improves resistance to adhesive and abrasive wear. Post-irradiation melting or annealing is then done to eliminate residual free radicals and prevent long-term oxidation.

Question 372

Topic: Biomechanics & Biomaterials

A researcher is testing the viscoelastic properties of the anterior cruciate ligament in a laboratory setting. When a constant tensile force is applied to the ligament over an extended period, the ligament is observed to gradually elongate. Which biomechanical term best describes this phenomenon?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent deformation (elongation) of a viscoelastic material when subjected to a constant load over time. In contrast, stress relaxation is the time-dependent decrease in internal stress when the tissue is held at a constant deformation/strain. Hysteresis is the energy lost (as heat) during the loading and unloading cycle.

Question 373

Topic: Biomechanics & Biomaterials

In orthopedic implant metallurgy, what specific type of corrosion occurs in restricted spaces, such as under the head of a bone screw, where the oxygen concentration becomes locally depleted compared to the surrounding fluid environment?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Crevice corrosion occurs in shielded areas, such as the interface between a screw head and a plate. In these crevices, oxygen is quickly depleted, preventing the reformation of the protective passive oxide layer (passivation). The resulting oxygen concentration gradient between the crevice and the surrounding fluid causes the crevice to become anodic, leading to localized metal dissolution.

Question 374

Topic: Biomechanics & Biomaterials

Which of the following biomechanical terms best describes the phenomenon where a constant force applied to a viscoelastic material over a prolonged period results in increasing deformation?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a material under a constant load over time. Stress relaxation is the decrease in stress over time when the material is held at a constant strain (constant deformation). Hysteresis relates to the loss of energy (usually as heat) during the loading and unloading cycles of a viscoelastic material. Orthopedic tissues like ligaments and cartilage exhibit both creep and stress relaxation.

Question 375

Topic: Biomechanics & Biomaterials

In orthopaedic biomechanics, which of the following terms describes the time-dependent increase in strain (deformation) of a viscoelastic material when subjected to a constant stress (load)?

. Stress relaxation
. Creep
. Hysteresis
. Fatigue failure
. Young's modulus

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation (strain) of a viscoelastic material over time when it is subjected to a constant force (stress). This is a foundational concept in the serial casting of deformities (e.g., clubfoot). Stress relaxation, conversely, is the decrease in stress over time when a material is held at a constant strain.

Question 376

Topic: Biomechanics & Biomaterials

A 22-year-old collegiate baseball pitcher presents with profound shoulder pain during the 'late cocking' phase of throwing. MRI arthrogram demonstrates a Type II SLAP (Superior Labrum Anterior to Posterior) lesion. After 6 months of targeted physical therapy, he remains unable to throw. What is the primary surgical recommendation?

. Open biceps tenodesis
. Arthroscopic biceps tenotomy
. Arthroscopic debridement of the superior labrum
. Arthroscopic repair of the superior labrum and biceps anchor
. Open capsular shift

Correct Answer & Explanation

. Arthroscopic repair of the superior labrum and biceps anchor

Explanation

A Type II SLAP lesion involves detachment of the superior labrum and the origin of the long head of the biceps tendon from the glenoid. In a young, high-demand, overhead throwing athlete, the standard of care after failed conservative management is arthroscopic repair of the labrum back to the glenoid footprint. Biceps tenodesis or tenotomy is generally reserved for older patients, non-throwers, or salvage after failed repairs, as it alters the normal throwing kinematics.

Question 377

Topic: Biomechanics & Biomaterials

An orthopedic surgeon is preparing antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for a spacer during the first stage of a two-stage exchange arthroplasty for a periprosthetic joint infection. To ensure the antibiotic remains biologically active and does not compromise the curing process, the chosen antibiotic MUST possess which of the following properties?

. High molecular weight to delay elution
. Thermostability
. A purely bacteriostatic mechanism of action
. High lipophilicity
. Susceptibility to rapid hydrolysis

Correct Answer & Explanation

. Thermostability

Explanation

The polymerization of PMMA bone cement is an exothermic reaction that can reach temperatures exceeding 80°C (176°F) in vivo. Therefore, any antibiotic incorporated into the cement must be highly thermostable to survive the curing process without degrading. Common thermostable antibiotics used include Vancomycin, Tobramycin, and Gentamicin.

Question 378

Topic: Biomechanics & Biomaterials

During a biomechanical testing session on human tendons, a researcher applies a constant load to a tendon specimen over an extended period. Over time, the tendon demonstrates a progressive increase in length (deformation). What viscoelastic property does this describe?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the viscoelastic property where a tissue undergoes progressive deformation (lengthening) under a constant load over time. Stress relaxation, conversely, is the decrease in load/stress over time when a tissue is held at a constant length (deformation). Hysteresis refers to the energy lost as heat during the loading and unloading cycle.

Question 379

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic behavior. Which of the following statements best defines the mechanical concept of "stress relaxation" in an orthopedic biologic tissue?

. Increasing deformation over time when subjected to a constant load
. Decreasing internal stress over time when held at a constant deformation
. Energy loss that occurs during a complete loading and unloading cycle
. Increased stiffness demonstrated when the tissue is loaded at higher strain rates
. The microfailure of collagen fibrils immediately preceding macroscopic failure

Correct Answer & Explanation

. Decreasing internal stress over time when held at a constant deformation

Explanation

Stress relaxation is a classic viscoelastic property where the stress (internal force) within a material decreases over time when it is stretched and held at a constant length (constant deformation/strain). Creep (Option A) is the gradual increase in length (deformation) when a constant load/stress is applied. Hysteresis (Option C) refers to the energy dissipated (usually as heat) during the loading and unloading cycle. Strain-rate dependency (Option D) explains why tissues become stiffer when loaded rapidly.

Question 380

Topic: Biomechanics & Biomaterials

In the field of orthopedic biomaterials, implant failure can occasionally be traced to corrosion. Galvanic corrosion is most accurately described by which of the following scenarios?

. Mechanical friction wearing away the passivation layer on a single titanium screw
. Corrosion occurring in a localized area of low oxygen tension beneath a screw head
. Electrochemical degradation occurring when two dissimilar metals are in direct contact within an electrolytic environment
. Cyclic loading causing microscopic cracking and subsequent fluid ingress
. Oxidation of a polyethylene liner after prolonged shelf storage

Correct Answer & Explanation

. Electrochemical degradation occurring when two dissimilar metals are in direct contact within an electrolytic environment

Explanation

Galvanic corrosion occurs when two different metals with differing anodic indices (e.g., stainless steel and titanium) are placed in direct electrical contact within a conductive fluid (such as serum or interstitial fluid), creating an electrochemical cell where the less noble metal corrodes rapidly. Option B describes crevice corrosion (low oxygen tension). Option A describes fretting corrosion.

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