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Biomechanics & Biomaterials MCQs

Practice Set 78 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 1541

Topic: Biomechanics & Biomaterials

A viscoelastic material subjected to a constant load will continuously deform over time. This specific biomechanical phenomenon is known as which of the following?

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

Correct Answer & Explanation

. Creep

Explanation

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

Question 1542

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is used primarily to reduce volumetric wear. Which of the following mechanical properties is typically decreased as a result of the cross-linking process?
. Yield strength
. Fatigue crack propagation resistance
. Elastic modulus
. Hardness
. Melting point

Correct Answer & Explanation

. Fatigue crack propagation resistance

Explanation

Highly cross-linking UHMWPE significantly reduces abrasive and adhesive wear but reduces its fatigue resistance and ductility. This makes the material more susceptible to fatigue crack propagation and fracture.

Question 1543

Topic: Biomechanics & Biomaterials

A 60-year-old male presents with acute knee pain and effusion. Joint aspiration yields synovial fluid with 45,000 WBCs/mcL. Polarized light microscopy reveals weakly positively birefringent rhomboid-shaped crystals. What is the most likely composition of these crystals?

. Monosodium urate
. Calcium pyrophosphate dihydrate
. Calcium hydroxyapatite
. Cholesterol
. Basic calcium phosphate

Correct Answer & Explanation

. Calcium pyrophosphate dihydrate

Explanation

Weakly positively birefringent, rhomboid-shaped crystals are diagnostic of calcium pyrophosphate dihydrate (CPPD) deposition disease (pseudogout). Monosodium urate crystals are needle-shaped and strongly negatively birefringent.

Question 1544

Topic: Biomechanics & Biomaterials

The slope of the linear elastic region of a material's stress-strain curve represents which of the following biomechanical properties?

. Toughness
. Yield point
. Young's modulus
. Ultimate tensile strength
. Ductility

Correct Answer & Explanation

. Young's modulus

Explanation

Young's modulus (modulus of elasticity) is defined as the slope of the stress-strain curve in the linear elastic region, representing the stiffness of the material. Toughness is the area under the entire stress-strain curve.

Question 1545

Topic: Biomechanics & Biomaterials

A modular total hip arthroplasty fails due to micro-motion at the head-neck taper junction, leading to wear debris and local tissue reaction. Which type of corrosion primarily occurs as a result of this mechanical disruption of the passivation layer?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs at the contact areas between materials under load, such as taper junctions. Micro-motion repeatedly strips the protective oxide passivation layer, accelerating oxidative wear.

Question 1546

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, what term describes the phenomenon where a viscoelastic material (like a ligament) demonstrates a continuous increase in strain over time when subjected to a constant load?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation (increasing strain) of a viscoelastic material under a constant load. Stress relaxation, conversely, is the decrease in stress over time when the material is held at a constant strain.

Question 1547

Topic: Biomechanics & Biomaterials
Historically, catastrophic early failure and severe oxidative wear in ultra-high-molecular-weight polyethylene (UHMWPE) components for total knee arthroplasty were traced back to which specific manufacturing and sterilization process?
. Gamma irradiation in an inert argon environment
. Highly cross-linking combined with remelting
. Ethylene oxide gas sterilization
. Gamma irradiation in ambient air
. Infusion of Vitamin E (alpha-tocopherol)

Correct Answer & Explanation

. Gamma irradiation in ambient air

Explanation

Gamma irradiation in air generates free radicals that react with ambient oxygen over time, leading to severe oxidative degradation. This process caused catastrophic subsurface delamination and accelerated wear in early generation UHMWPE.

Question 1548

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is widely utilized in cemented total joint arthroplasty. By what primary mechanism does PMMA secure the metallic prosthesis to the host bone?

. Direct chemical bonding to hydroxyapatite
. Osteoinduction leading to biologic osseointegration
. Covalent bonding to type I collagen fibrils
. Micro-interlocking as a mechanical grout
. Piezoelectric stimulation of local osteoblasts

Correct Answer & Explanation

. Micro-interlocking as a mechanical grout

Explanation

PMMA bone cement acts strictly as a mechanical grout, not an adhesive. It achieves fixation by physically micro-interlocking with the porous spaces of cancellous bone and the roughened surface of the metallic implant, without any true chemical or biological bonding.

Question 1549

Topic: Biomechanics & Biomaterials

A patient undergoes revision open reduction and internal fixation of a nonunion. The surgeon places a stainless steel screw through a titanium plate. Which of the following best describes the predominant type of corrosion that is most likely to occur at the screw-plate interface?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are placed in direct physical contact within an electrolytic environment (human body fluids). The metal with the lower anodic index (less noble, typically stainless steel in this pairing) undergoes accelerated corrosion.

Question 1550

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, the wear of ultra-high molecular weight polyethylene (UHMWPE) can lead to osteolysis. Which process during the manufacturing of UHMWPE is primarily used to increase its wear resistance?
. Ethylene oxide sterilization
. Gamma irradiation in oxygen
. Highly cross-linking the polymer chains via irradiation and subsequent thermal treatment
. Addition of polymethylmethacrylate (PMMA)
. Cold working the polyethylene prior to machining

Correct Answer & Explanation

. Highly cross-linking the polymer chains via irradiation and subsequent thermal treatment

Explanation

Highly cross-linking UHMWPE significantly increases its wear resistance. This is achieved by irradiating the material to create free radicals that bond to form cross-links. Subsequent thermal treatment (melting or annealing) is necessary to extinguish residual free radicals and prevent long-term oxidative degradation.

Question 1551

Topic: Biomechanics & Biomaterials

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic environment. Which of the following combinations of orthopedic implants is most likely to undergo severe galvanic corrosion and is strictly contraindicated?

. Cobalt-chromium alloy and Titanium alloy
. Titanium alloy and Tantalum
. Zirconium and Titanium alloy
. 316L Stainless steel and Titanium alloy
. Cobalt-chromium alloy and Tantalum

Correct Answer & Explanation

. 316L Stainless steel and Titanium alloy

Explanation

Mixing 316L stainless steel and titanium alloy creates a strong galvanic cell due to their disparate positions on the anodic/cathodic index. Titanium is highly noble (cathodic) and stainless steel is relatively anodic, leading to rapid, severe corrosion of the stainless steel.

Question 1552

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is commonly used in total joint arthroplasty. The addition of barium sulfate to PMMA serves what specific purpose?

. Increases compressive strength
. Increases porosity for bone ingrowth
. Acts as a radiopacifier
. Delays the setting time
. Acts as an antibiotic eluter

Correct Answer & Explanation

. Acts as a radiopacifier

Explanation

Barium sulfate (or zirconium dioxide) is added to PMMA to act as a radiopacifier, allowing the cement mantle to be visualized on postoperative radiographs. Its addition actually slightly decreases the mechanical strength of the cement.

Question 1553

Topic: Biomechanics & Biomaterials

A major advantage of using titanium alloy (Ti-6Al-4V) over cobalt-chromium (Co-Cr) for the femoral stem in cementless total hip arthroplasty is related to its mechanical properties. Which of the following best describes this advantage?

. Higher modulus of elasticity reducing stress shielding
. Lower modulus of elasticity reducing stress shielding
. Greater wear resistance at the bearing surface
. Higher yield strength preventing stem fracture
. Increased resistance to galvanic corrosion

Correct Answer & Explanation

. Lower modulus of elasticity reducing stress shielding

Explanation

Titanium alloy has a lower modulus of elasticity (closer to that of cortical bone) compared to cobalt-chromium. This decreases the stiffness mismatch between the implant and bone, significantly minimizing stress shielding.

Question 1554

Topic: Biomechanics & Biomaterials

Orthopedic materials such as ligaments and tendons exhibit viscoelastic properties. If a tendon is subjected to a constant, sustained elongation (constant strain), the force required to maintain that elongation decreases over time. What is the biomechanical term for this phenomenon?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a primary viscoelastic property defined as the decrease in stress (internal force) over time when a material is held at a constant strain (constant length). Conversely, creep is defined as the progressive deformation (increase in strain) over time when a material is subjected to a constant force (constant stress).

Question 1555

Topic: Biomechanics & Biomaterials
What is the primary advantage of highly cross-linking ultra-high molecular weight polyethylene (UHMWPE) via gamma irradiation, followed by remelting, in total joint arthroplasty?
. Increases ultimate tensile strength of the polyethylene
. Significantly reduces adhesive and abrasive wear
. Eliminates the risk of rim cracking in the liner
. Increases fatigue strength and resistance to fracture
. Reduces the melting temperature to improve molding

Correct Answer & Explanation

. Significantly reduces adhesive and abrasive wear

Explanation

Cross-linking UHMWPE significantly reduces abrasive and adhesive wear, which is the primary driver of macrophage-induced osteolysis. However, the process of cross-linking and subsequent remelting (done to eliminate free radicals and prevent oxidation) actually decreases the mechanical properties of the polyethylene, such as fatigue strength, yield strength, and ultimate tensile strength.

Question 1556

Topic: Biomechanics & Biomaterials
Two solid titanium rods, Rod A and Rod B, have the exact same length, but Rod B has twice the radius of Rod A. By what factor is the torsional stiffness of Rod B greater than that of Rod A?
. 2 times
. 4 times
. 8 times
. 16 times
. 32 times

Correct Answer & Explanation

. 16 times

Explanation

The torsional stiffness of a solid cylinder is directly proportional to its polar moment of inertia (J = πr⁴ / 2). Because the radius is raised to the fourth power, doubling the radius increases the torsional stiffness by a factor of 2⁴, which equals 16.

Question 1557

Topic: Biomechanics & Biomaterials

In the biomechanical assessment of viscoelastic materials such as ligaments and tendons, what is the term for the time-dependent decrease in applied stress when the tissue is held at a constant strain (deformation)?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a hallmark of viscoelasticity defined as the decrease in stress over time when a material is subjected to a constant strain (held at a constant length). Creep is the opposite counterpart: a time-dependent increase in strain (deformation) when the material is subjected to a constant load (stress).

Question 1558

Topic: Biomechanics & Biomaterials

A surgeon implants a 316L stainless steel screw to temporarily secure a titanium alloy plate. This combination creates a risk of galvanic corrosion. In this scenario, which component acts as the anode, and what is the consequence?

. Titanium plate acts as the anode, leading to dissolution of the plate
. Titanium plate acts as the anode, leading to passivation of the metal
. Stainless steel screw acts as the anode, leading to accelerated corrosion of the screw
. Stainless steel screw acts as the anode, leading to deposition of titanium on the screw
. Both metals corrode equally due to identical electronegativity

Correct Answer & Explanation

. Stainless steel screw acts as the anode, leading to accelerated corrosion of the screw

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic solution (like bodily fluids). The less noble (more reactive) metal, which is stainless steel in this pairing, becomes the anode and undergoes accelerated dissolution/corrosion. The more noble metal (titanium) acts as the cathode and is protected.

Question 1559

Topic: Biomechanics & Biomaterials
Which of the following modifications is utilized in the manufacturing of highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) to reduce the concentration of free radicals and improve oxidation resistance, albeit at the expense of mechanical properties such as fatigue strength?
. Ethylene oxide gas sterilization
. Remelting above the melting temperature (approx. 150°C)
. Annealing below the melting temperature (approx. 110°C)
. Gamma irradiation in an oxygen-rich environment
. Addition of polymethylmethacrylate (PMMA) during polymerization

Correct Answer & Explanation

. Remelting above the melting temperature (approx. 150°C)

Explanation

Remelting highly cross-linked UHMWPE above its melting temperature eliminates residual free radicals created during the gamma irradiation cross-linking process. This significantly improves oxidation resistance but reduces the polymer's crystallinity and, consequently, its mechanical and fatigue strength. Annealing reduces but does not completely eliminate free radicals. Ethylene oxide does not create free radicals but does not cross-link the material.

Question 1560

Topic: Biomechanics & Biomaterials

When a titanium alloy component and a 316L stainless steel component are placed in direct physical contact within the corrosive physiological environment of the human body, galvanic corrosion may occur. Which of the following statements is correct regarding this couple?

. Titanium becomes the anode and undergoes accelerated corrosion.
. Stainless steel becomes the anode and undergoes accelerated corrosion.
. Both metals corrode equally due to their identical galvanic potentials.
. Titanium acts as the cathode and undergoes crevice corrosion.
. Galvanic corrosion is impossible between these two metals in vivo.

Correct Answer & Explanation

. Stainless steel becomes the anode and undergoes accelerated corrosion.

Explanation

In a galvanic couple, the more noble metal acts as the cathode and the less noble metal acts as the anode. Titanium is more noble than 316L stainless steel. Therefore, when mixed, the stainless steel becomes the anode and will undergo accelerated galvanic corrosion, while the titanium component (cathode) is protected.

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