Menu

Biomechanics & Biomaterials MCQs

Practice Set 60 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 1181

Topic: Biomechanics & Biomaterials
To reduce volumetric wear and subsequent osteolysis in total joint arthroplasty, manufacturers often utilize highly cross-linked ultra-high molecular weight polyethylene (UHMWPE). What is the primary mechanical trade-off resulting from the irradiation and cross-linking of UHMWPE?
. Decreased resistance to adhesive wear
. Decreased resistance to abrasive wear
. Decreased fatigue crack propagation resistance (decreased toughness)
. Increased oxidation potential in vivo
. Decreased modulus of elasticity

Correct Answer & Explanation

. Decreased fatigue crack propagation resistance (decreased toughness)

Explanation

Cross-linking UHMWPE (usually via gamma or electron beam irradiation) significantly increases its resistance to adhesive and abrasive wear. However, this process alters the polymer's mechanical properties, leading to decreased ductility, decreased ultimate tensile strength, and reduced fatigue crack propagation resistance (toughness). Remelting post-irradiation decreases oxidation potential.

Question 1182

Topic: Biomechanics & Biomaterials

Minimizing the mismatch in the modulus of elasticity between an orthopaedic implant and the host bone is critical to reduce stress shielding and subsequent bone resorption. Which of the following implant materials has a Young's modulus most closely approximating that of human cortical bone?

. 316L Stainless Steel
. Cobalt-Chromium-Molybdenum alloy
. Titanium alloy (Ti-6Al-4V)
. Polymethylmethacrylate (PMMA)
. Alumina ceramic

Correct Answer & Explanation

. 316L Stainless Steel

Explanation

Human cortical bone has a Young's modulus of approximately 15-20 GPa. Titanium alloys (Ti-6Al-4V) have a modulus of roughly 110 GPa, which is significantly lower and closer to bone than Stainless Steel (~200 GPa) or Cobalt-Chromium alloys (~220-240 GPa). This lower modulus makes titanium more flexible, reducing stress shielding.

Question 1183

Topic: Biomechanics & Biomaterials

A patient presents with pain and a sterile effusion 4 years after a metal-on-polyethylene total hip arthroplasty utilizing a modular titanium neck and cobalt-chromium head.

Retrieval analysis of the head-neck taper junction would most likely reveal which primary mechanism of failure?

. Galvanic corrosion alone
. Fretting corrosion
. Abrasive wear
. Adhesive wear
. Third-body wear

Correct Answer & Explanation

. Galvanic corrosion alone

Explanation

Mechanically assisted crevice corrosion (MACC), often initiated by fretting corrosion, is the primary mode of failure at modular junctions in total hip arthroplasty. Micromotion at the taper junction disrupts the passivating oxide layer (fretting), exposing reactive metal to fluid, which then undergoes crevice and galvanic corrosion.

Question 1184

Topic: Biomechanics & Biomaterials

A freshly harvested tendon is subjected to biomechanical testing. The tendon is stretched to a specific length, and that length is maintained constant over time. The gradual decrease in the measured force required to maintain this constant length is best defined as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

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

Question 1185

Topic: Biomechanics & Biomaterials

Titanium alloy (Ti-6Al-4V) is widely used in orthopedic implants due to its excellent biocompatibility and a modulus of elasticity closer to bone than cobalt-chromium. However, its primary biomechanical disadvantage, which limits its use in certain articulating applications, is:

. High galvanic corrosion potential
. Poor notch sensitivity and wear resistance
. Low fatigue strength
. High density
. Excessive stiffness

Correct Answer & Explanation

. High galvanic corrosion potential

Explanation

Titanium alloys have poor wear characteristics and are highly notch sensitive, meaning surface scratches significantly reduce their fatigue life. Consequently, they are rarely used for articulating surfaces (e.g., femoral heads) and are typically reserved for stems, cups, and fracture fixation where wear is less of an issue.

Question 1186

Topic: Biomechanics & Biomaterials

Among the following synthetic bone graft substitutes, which has the slowest in vivo resorption rate, providing the longest-lasting structural scaffold?

. Calcium sulfate
. Tricalcium phosphate
. Coralline hydroxyapatite
. Demineralized bone matrix
. Cancellous allograft

Correct Answer & Explanation

. Calcium sulfate

Explanation

Hydroxyapatite (HA) has the slowest resorption rate among synthetic calcium-based bone graft substitutes and can remain in the body for years. Calcium sulfate resorbs very rapidly (weeks), and tricalcium phosphate resorbs at an intermediate rate (months).

Question 1187

Topic: Biomechanics & Biomaterials



A resident applies a Ponseti cast to an infant with idiopathic clubfoot. Initially, there is significant resistance from the tight Achilles tendon and posteromedial structures. Over the next several minutes, while the resident holds the foot in the corrected position, the resident notes that less force is required to maintain the exact same degree of dorsiflexion and abduction. Which biomechanical property of viscoelastic materials does this clinical scenario represent?

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

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is a fundamental viscoelastic property characterized by a progressive decrease in internal stress (the force required by the resident) over time when the material (ligament/tendon) is held at a constant strain (deformation or position). Creep, conversely, is the continued deformation of a material over time when subjected to a constant load (stress). Hysteresis is the loss of energy (usually as heat) during a loading and unloading cycle.

Question 1188

Topic: Biomechanics & Biomaterials



A patient undergoes revision open reduction and internal fixation of a femoral nonunion. Due to a shortage of hardware sets, a stainless steel screw is inadvertently placed into a titanium plate. Which of the following modes of corrosion is most likely to be significantly accelerated at the screw-plate interface?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in direct physical contact within an electrolytic conductive fluid medium (such as body interstitial fluid). The difference in electrochemical potential between the two metals causes the less noble metal (the anode, typically stainless steel when mixed with titanium) to undergo accelerated oxidation and dissolve, while the more noble metal (cathode, titanium) is protected.

Question 1189

Topic: Biomechanics & Biomaterials
In modern total hip arthroplasty, the high cross-linking of ultra-high molecular weight polyethylene (UHMWPE) through gamma or electron beam irradiation is routinely performed. What is the primary clinical tribological benefit and the most significant structural trade-off of utilizing highly cross-linked polyethylene compared to conventional non-cross-linked polyethylene?
. Decreased abrasive wear; increased ultimate tensile strength
. Decreased adhesive wear; decreased fatigue resistance and fracture toughness
. Increased adhesive wear; significantly increased fracture toughness
. Decreased oxidative degradation; decreased modulus of elasticity
. Increased fatigue resistance; dramatically decreased abrasive wear

Correct Answer & Explanation

. Decreased adhesive wear; decreased fatigue resistance and fracture toughness

Explanation

Highly cross-linking UHMWPE restricts the mobility of the polymer chains, significantly reducing adhesive wear and lowering the total volumetric wear rate, which critically decreases the risk of macrophage-mediated osteolysis. However, the cross-linking process, and the subsequent necessary thermal treatments (re-melting or annealing to eliminate free radicals), reduce key mechanical properties, including fatigue resistance, fracture toughness, and ultimate tensile and yield strengths.

Question 1190

Topic: Biomechanics & Biomaterials

Stress shielding around an orthopedic implant is directly related to the mismatch in Young's modulus of elasticity between the implant and the host bone. Which of the following materials has a Young's modulus most similar to that of human cortical bone (~15-20 GPa)?

. Trabecular metal (Tantalum)
. Polymethylmethacrylate (PMMA)
. Carbon fiber-reinforced polyetheretherketone (CFR-PEEK)
. Titanium alloy (Ti-6Al-4V)
. Cobalt-chromium alloy (Co-Cr-Mo)

Correct Answer & Explanation

. Trabecular metal (Tantalum)

Explanation

CFR-PEEK has a Young's modulus of approximately 18 GPa, which closely approximates that of human cortical bone (15-20 GPa). By comparison, Titanium alloy is ~110 GPa, Cobalt-chromium is ~220 GPa, PMMA is ~3 GPa, and Trabecular metal is ~3 GPa (mimicking cancellous bone).

Question 1191

Topic: Biomechanics & Biomaterials
When preparing antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for the treatment of a chronic periprosthetic joint infection (e.g., formulating an articulating spacer), what is the primary consequence of using a 'high-dose' mixture (e.g., >10% antibiotic by weight) compared to standard prophylactic doses?
. Increased exothermic reaction temperature
. Decreased elution profile over time
. Accelerated polymerization time
. Decreased compressive and tensile strength
. Increased risk of immediate anaphylaxis

Correct Answer & Explanation

. Decreased compressive and tensile strength

Explanation

Adding 'high-dose' antibiotics (typically defined as >2g per 40g bag, and often >10% by weight for spacers) significantly compromises the mechanical properties of PMMA, specifically decreasing its compressive, tensile, and shear strengths. While acceptable for temporary spacers, this high ratio is contraindicated for the final fixation of permanent prosthetic components.

Question 1192

Topic: Biomechanics & Biomaterials

Tendons and ligaments are viscoelastic structures. If a dynamic splint applies a constant load (force) to a contracted joint over an extended period of time, the soft tissues will gradually elongate. This specific biomechanical property is known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is defined as the progressive, time-dependent deformation (elongation) of a viscoelastic tissue when subjected to a constant load or stress over time. Dynamic splinting relies on the principle of creep to safely lengthen contracted tissues. 'Stress relaxation', by contrast, is the gradual decrease in stress experienced by a tissue when it is held at a constant length.

Question 1193

Topic: Biomechanics & Biomaterials

Modular hip stems often employ a titanium alloy stem and a cobalt-chromium head. Which type of corrosion is most likely to occur at the modular head-neck taper junction strictly due to local oxygen depletion in a restricted fluid space?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Crevice corrosion occurs in narrow spaces like taper junctions where oxygen depletion leads to a localized acidic environment. While fretting corrosion also occurs here due to micromotion, oxygen depletion specifically defines crevice corrosion.

Question 1194

Topic: Biomechanics & Biomaterials
During tensile testing of a normal flexor tendon, the initial 'toe region' of the stress-strain curve is primarily due to which structural phenomenon?
. Plastic deformation of collagen fibers
. Uncrimping of type I collagen fibers
. Microfailure of type III collagen fibers
. Fluid exudation from the proteoglycan matrix
. Complete macroscopic failure of the tendon fascicles

Correct Answer & Explanation

. Uncrimping of type I collagen fibers

Explanation

The non-linear toe region of the ligament or tendon stress-strain curve represents the uncrimping (straightening) of the normally wavy collagen fibrils. Once the fibers are fully uncrimped, the tissue enters the linear elastic region.

Question 1195

Topic: Biomechanics & Biomaterials
The introduction of highly cross-linked polyethylene (HXLPE) has significantly reduced wear rates and osteolysis in THA. However, the cross-linking process alters the mechanical properties of the material. Which of the following properties is primarily DECREASED by the irradiation process?
. Ultimate tensile strength
. Wear resistance
. Hardness
. Oxidation potential
. Elastic modulus

Correct Answer & Explanation

. Ultimate tensile strength

Explanation

While the irradiation process used to create highly cross-linked polyethylene significantly improves its adhesive and abrasive wear resistance, it comes at a cost to its mechanical properties. Irradiation decreases ultimate tensile strength, yield strength, ductility, and fracture toughness, making the material more susceptible to fatigue fracture or rim failure.

Question 1196

Topic: Biomechanics & Biomaterials

In the manufacturing of highly cross-linked polyethylene (XLPE) for THA, irradiation is used to create cross-links that improve wear resistance. What is the primary biomechanical tradeoff of using a 'remelting' process compared to an 'annealing' process to eliminate free radicals?

. Remelting severely decreases oxidation resistance over time.
. Remelting increases the risk of early severe volumetric wear.
. Remelting causes a significant decrease in fatigue and yield strength.
. Remelting leads to an increased risk of third-body wear generation.
. Remelting fails to eliminate the majority of free radicals.

Correct Answer & Explanation

. Remelting severely decreases oxidation resistance over time.

Explanation

Irradiation creates free radicals that can cause oxidation. Heating the polyethylene eliminates these free radicals. Remelting (heating above the melting point) completely extinguishes free radicals but decreases the material's mechanical properties (fatigue and yield strength). Annealing (heating below the melting point) maintains mechanical strength but leaves residual free radicals, which require adding antioxidants like Vitamin E to prevent oxidation.

Question 1197

Topic: Biomechanics & Biomaterials

A 45-year-old active male with a ceramic-on-ceramic (CoC) THA reports a loud squeaking noise with walking that is socially embarrassing. Which factor is most strongly associated with the etiology of this phenomenon?

. Loss of fluid-film lubrication secondary to edge loading
. Type IV delayed hypersensitivity to ceramic particulates
. Mechanically assisted crevice corrosion at the trunnion
. Third-body wear from retained bone cement
. Galvanic corrosion between the ceramic head and titanium stem

Correct Answer & Explanation

. Loss of fluid-film lubrication secondary to edge loading

Explanation

Squeaking in Ceramic-on-Ceramic (CoC) bearings is heavily associated with edge loading (often due to component malposition, such as excessive cup anteversion or inclination, or micro-separation during swing phase). Edge loading disrupts the normal fluid-film lubrication, leading to stripe wear and high-frequency vibrations (squeaking).

Question 1198

Topic: Biomechanics & Biomaterials
Highly cross-linked polyethylene (HXLPE) is standardly used in total hip arthroplasty to minimize particulate wear debris. While high-dose gamma irradiation followed by remelting decreases wear rates, it results in a clinically relevant decrease in which of the following mechanical properties compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE)?
. Fatigue crack propagation resistance and ultimate tensile strength
. Resistance to in vivo oxidation
. Elastic modulus
. Surface hardness
. Yield strength under direct axial load

Correct Answer & Explanation

. Fatigue crack propagation resistance and ultimate tensile strength

Explanation

Increasing the radiation dose to highly cross-linked polyethylene reduces abrasive wear, which significantly lowers osteolysis rates. However, the process of cross-linking and subsequent thermal treatment (remelting to eliminate free radicals) adversely affects the bulk mechanical properties. Specifically, it significantly decreases ultimate tensile strength, yield strength, and fatigue crack propagation resistance, making the liner theoretically more susceptible to fracture, especially in thinner liners.

Question 1199

Topic: Biomechanics & Biomaterials

During the biomechanical evaluation of a ligament's viscoelastic properties, researchers observe that when the ligament is subjected to a constant, sustained mechanical load over a period of time, it experiences a gradual, continuous increase in length. This specific phenomenon is defined as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

'Creep' is a fundamental viscoelastic property of biological tissues like ligaments and tendons. It is defined as the progressive deformation (elongation) of a material over time when it is subjected to a constant load or stress. 'Stress relaxation' is the gradual decrease in stress when a material is held at a constant length. 'Hysteresis' is the loss of energy (as heat) between the loading and unloading curves.

Question 1200

Topic: Biomechanics & Biomaterials

In the context of galvanic corrosion in orthopedic implants, which of the following combinations of metals has the highest risk of severe galvanic corrosion when in direct contact in a saline environment?

. Titanium and Tantalum
. Cobalt-Chromium and Titanium
. Stainless Steel 316L and Titanium
. Cobalt-Chromium and Zirconium
. Titanium and Niobium

Correct Answer & Explanation

. Titanium and Tantalum

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct electrical contact within an electrolytic solution (like body fluids). Stainless steel is more anodic (less noble) compared to Titanium, which is highly cathodic (noble). When mixed, the stainless steel acts as the anode and corrodes rapidly. Mixing Stainless Steel 316L and Titanium is a classic contraindication in orthopedics.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page