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Biomechanics & Biomaterials MCQs

Practice Set 62 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 1221

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for an orthopedic biomaterial, what does the area under the curve in the elastic region represent?

. Toughness
. Modulus of elasticity
. Yield strength
. Modulus of resilience
. Ultimate tensile strength

Correct Answer & Explanation

. Toughness

Explanation

The area under the stress-strain curve in the elastic region represents the modulus of resilience, which is the amount of energy a material can absorb without undergoing permanent, plastic deformation. The total area under the entire curve (elastic + plastic regions) represents toughness (the energy absorbed before complete failure). The slope of the elastic region is the modulus of elasticity.

Question 1222

Topic: Biomechanics & Biomaterials
A viscoelastic orthopedic implant is subjected to a constant physiological load over a prolonged period. Over time, the material undergoes increasing progressive deformation despite the applied stress remaining unchanged. Which of the following best describes this biomechanical property?
. Stress relaxation
. Fatigue failure
. Creep
. Hysteresis
. Toughness

Correct Answer & Explanation

. Creep

Explanation

Creep is a viscoelastic property characterized by progressive deformation of a material under a constant load over time. This is clinically relevant in ultra-high-molecular-weight polyethylene (UHMWPE) components. Stress relaxation, in contrast, refers to a decrease in internal stress over time when the material is held at a constant deformation.

Question 1223

Topic: Biomechanics & Biomaterials

During a total hip arthroplasty, the surgeon opts for a highly cross-linked polyethylene liner instead of conventional polyethylene. Which of the following best describes the primary advantage of highly cross-linked polyethylene?

. Increased resistance to catastrophic fatigue failure
. Decreased volumetric wear
. Improved resistance to oxidative degradation without further processing
. Enhanced fracture toughness
. Lower elastic modulus

Correct Answer & Explanation

. Increased resistance to catastrophic fatigue failure

Explanation

High cross-linking of polyethylene significantly reduces volumetric wear, leading to a lower incidence of particle-induced osteolysis. However, the cross-linking process can decrease the material's mechanical properties, such as fracture toughness.

Question 1224

Topic: Biomechanics & Biomaterials

During total hip arthroplasty, what characteristic of irradiated (10 Mrad) and subsequently melted highly

cross-linked polyethylene should provide a more wear-resistant construct than traditional gamma- irradiated (2.5-4 Mrad)-in-air polyethylene mated with the same head?

. Resistance to adhesive wear
. Resistance to abrasive wear
. Resistance to fatigue wear
. Resistance to creep

Correct Answer & Explanation

. Resistance to adhesive wear

Explanation

Highly cross-linked polyethylene makes material resistant to adhesive wear. Abrasive wear from third bodies does not decrease wear. The fatigue strength of such material is inferior to that of traditional polyethylene, and its resistance to creep is the same, if not lower, than that of traditional polyethylene.

Question 1225

Topic: Biomechanics & Biomaterials
In modern total hip arthroplasty, the advent of highly cross-linked polyethylene (HXLPE) has dramatically reduced wear rates and associated osteolysis. Which of the following best describes the mechanical trade-off resulting from the high-dose irradiation and subsequent thermal treatment (remelting or annealing) process used to create HXLPE?
. Increased wear resistance coupled with decreased oxidative stability
. Increased wear resistance coupled with decreased fatigue crack propagation resistance
. Decreased wear resistance coupled with increased ultimate tensile strength
. Increased oxidative stability coupled with increased fatigue strength
. Increased wear resistance coupled with increased elongation to failure

Correct Answer & Explanation

. Increased wear resistance coupled with decreased fatigue crack propagation resistance

Explanation

Highly cross-linked polyethylene (HXLPE) is created by exposing standard UHMWPE to high doses of gamma or electron-beam radiation, creating free radicals that bond to form cross-links. This massively increases the wear resistance of the material. To eliminate residual free radicals and prevent long-term oxidation, the material is then heated (either below the melting point [annealing] or above [remelting]). The major trade-off of this high cross-linking process is a reduction in mechanical properties, specifically decreased yield strength, ultimate tensile strength, elongation to failure, and fatigue crack propagation resistance. This makes the polyethylene more susceptible to catastrophic fracture under high focal stresses, requiring adequate minimum thickness and careful component design.

Question 1226

Topic: Biomechanics & Biomaterials
Which sterilization method of Ultra-High Molecular Weight Polyethylene (UHMWPE) components in total joint arthroplasty results in the highest risk of oxidation, decreased fatigue strength, and severe delamination wear if the component is implanted without subsequent protective processing?
. Gamma irradiation in air
. Ethylene oxide gas
. Gas plasma sterilization
. Gamma irradiation in a vacuum followed by remelting
. Electron beam irradiation in an inert gas environment

Correct Answer & Explanation

. Gamma irradiation in air

Explanation

Gamma irradiation in air generates free radicals within the UHMWPE. If exposed to oxygen (during shelf storage or in vivo), these free radicals react to form oxidized chains, leading to chain scission. This increases the density and brittleness of the polyethylene, severely decreasing its fatigue strength and leading to subsurface delamination wear. Modern processing avoids this by using inert environments and post-irradiation thermal treatments (annealing or remelting).

Question 1227

Topic: Biomechanics & Biomaterials

When evaluating the mechanical properties of an orthopedic biomaterial via a stress-strain curve, the area under the entire curve up to the point of material failure represents which of the following mechanical properties?

. Yield strength
. Ultimate tensile strength
. Toughness
. Resilience
. Young's modulus

Correct Answer & Explanation

. Yield strength

Explanation

Toughness is defined as the total amount of energy a material can absorb before it fractures or fails. It is graphically represented by the total area under the stress-strain curve. In contrast, 'resilience' is the area under the elastic portion of the curve only, representing energy absorbed without permanent deformation.

Question 1228

Topic: Biomechanics & Biomaterials

In orthopedic biomaterials, combining a titanium femoral stem with a stainless steel cerclage wire increases the risk of which specific type of corrosion?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within a conductive fluid environment. The more anodic metal in the galvanic series (stainless steel) will preferentially corrode.

Question 1229

Topic: Biomechanics & Biomaterials

A surgeon decides to use a titanium locking plate with stainless steel cortical screws to treat a femoral shaft fracture. Which type of material degradation is most likely to occur at the screw-plate interface?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electronegativities are placed in contact within an electrolytic solution (like bodily fluids). This sets up a battery effect where the less noble metal corrodes. Mixing titanium and stainless steel implants greatly increases this risk.

Question 1230

Topic: Biomechanics & Biomaterials

A surgeon plans to use a stainless steel screw with a titanium plate. What is the primary reason this combination of metals should be avoided in orthopedic implants?

. Galvanic corrosion with titanium acting as the anode
. Galvanic corrosion with stainless steel acting as the anode
. Fretting corrosion secondary to modulus mismatch
. Crevice corrosion due to poor oxygen tension at the interface
. Pitting corrosion from chloride ion accumulation

Correct Answer & Explanation

. Galvanic corrosion with titanium acting as the anode

Explanation

Mixing different metals can lead to galvanic corrosion. In the case of stainless steel and titanium, stainless steel is less noble (more anodic) than titanium. Therefore, the stainless steel will act as the anode and undergo accelerated corrosion, while the titanium acts as the cathode.

Question 1231

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked polyethylene has significantly reduced wear rates. However, increasing the radiation dose to achieve higher cross-linking primarily compromises which of the following material properties?
. Elastic modulus
. Ultimate tensile strength
. Fatigue crack propagation resistance
. Wettability
. Melting point

Correct Answer & Explanation

. Fatigue crack propagation resistance

Explanation

While high-dose gamma irradiation improves the wear resistance of ultra-high molecular weight polyethylene (UHMWPE) by increasing cross-linking, it simultaneously decreases its ductility and fatigue crack propagation resistance, making the material more brittle and susceptible to fracture under cyclical loading.

Question 1232

Topic: Biomechanics & Biomaterials

Normal synovial fluid exhibits non-Newtonian flow characteristics. Which of the following properties describes the ability of synovial fluid to decrease in viscosity under high shear rates, thereby facilitating joint lubrication during rapid movement?

. Thixotropy
. Elasticity
. Galvanism
. Creep
. Hysteresis

Correct Answer & Explanation

. Thixotropy

Explanation

Thixotropy is the property of certain non-Newtonian fluids to show a time-dependent change in viscosity; specifically, they become less viscous (thinner) when subjected to shear stress. Synovial fluid is thixotropic due to hyaluronic acid, allowing it to act as a viscous shock absorber at rest and a highly fluid lubricant during rapid joint motion.

Question 1233

Topic: Biomechanics & Biomaterials

During revision of a total hip arthroplasty, examination of the explanted femoral head reveals multiple deep scratches. Histology of the surrounding tissue shows acrylic bone cement particles embedded within the articular surface of the polyethylene liner. This phenomenon represents which specific wear mechanism?

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

Correct Answer & Explanation

. Adhesive wear

Explanation

Third-body wear occurs when hard particles (such as bone cement, metal debris, or bone fragments) become trapped between two articulating surfaces. They embed into the softer surface (polyethylene) and act like sandpaper, scratching the harder surface (metal or ceramic head) and severely accelerating wear rates.

Question 1234

Topic: Biomechanics & Biomaterials

In articular cartilage biomechanics, boundary lubrication is essential for reducing friction under high-load, low-speed conditions. Which molecule is primarily responsible for boundary lubrication at the articular surface?

. Hyaluronic acid
. Lubricin (PRG4)
. Aggrecan
. Type II collagen
. Chondroitin sulfate

Correct Answer & Explanation

. Hyaluronic acid

Explanation

Boundary lubrication prevents wear in the articular cartilage under high-load, low-speed conditions. It is mediated by lubricin (proteoglycan 4 or PRG4), a glycoprotein secreted by superficial zone chondrocytes and synovial fibroblasts. Elastohydrodynamic lubrication is more relevant at higher speeds.

Question 1235

Topic: Biomechanics & Biomaterials

Analysis of a synovial fluid aspirate from an acutely swollen, painful knee reveals rhomboid-shaped crystals that exhibit weak positive birefringence under polarized light microscopy. What is the chemical composition of these crystals?

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

Correct Answer & Explanation

. Monosodium urate

Explanation

Calcium pyrophosphate dihydrate (CPPD) crystals are the hallmark of pseudogout. They appear rhomboid-shaped and exhibit weak positive birefringence. Monosodium urate crystals, seen in gout, are needle-shaped and show strong negative birefringence.

Question 1236

Topic: Biomechanics & Biomaterials

When analyzing the biomechanical properties of a tendon or ligament on a standard stress-strain curve, the initial nonlinear phase known as the "toe region" represents which physiological phenomenon?

. Microscopic failure of individual collagen fibers
. Macroscopic failure of the ligament structure
. Uncrimping of the resting wavy collagen fibers
. Elastic deformation of the bone-ligament interface
. The yield point transitioning to plastic deformation

Correct Answer & Explanation

. Microscopic failure of individual collagen fibers

Explanation

The initial 'toe region' of the stress-strain curve for ligaments and tendons is characterized by a low amount of stress resulting in a relatively large amount of strain. This corresponds structurally to the un-crimping, or straightening, of the naturally wavy collagen fibers.

Question 1237

Topic: Biomechanics & Biomaterials
During total joint arthroplasty, ultra-high molecular weight polyethylene (UHMWPE) is used. Over time, constant load leads to progressive, permanent deformation of the polyethylene without fracture. What is this biomechanical property called?
. Fatigue failure
. Creep
. Stress shielding
. Hysteresis
. Galvanic corrosion

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive, time-dependent permanent deformation of a material under a constant load below its yield strength. It is a classic characteristic of viscoelastic materials like UHMWPE used in arthroplasty.

Question 1238

Topic: Biomechanics & Biomaterials
When selecting an intramedullary nail for a tibial shaft fracture, a surgeon considers the material's modulus of elasticity. Which of the following lists materials in order of DECREASING modulus of elasticity (from stiffest to most flexible)?
. Cortical bone, Titanium, Stainless Steel, Cobalt-Chromium
. Cobalt-Chromium, Stainless Steel, Titanium, Cortical bone
. Stainless Steel, Cobalt-Chromium, Titanium, Cortical bone
. Titanium, Stainless Steel, Cobalt-Chromium, Cortical bone
. Cortical bone, Cobalt-Chromium, Stainless Steel, Titanium

Correct Answer & Explanation

. Cobalt-Chromium, Stainless Steel, Titanium, Cortical bone

Explanation

Cobalt-Chromium is the stiffest (approx 220 GPa), followed by Stainless Steel (approx 200 GPa), Titanium (approx 100 GPa), and Cortical bone (approx 15-20 GPa). Matching the modulus closer to bone reduces stress shielding.

Question 1239

Topic: Biomechanics & Biomaterials

According to the principles of plate biomechanics, how does the bending stiffness of a plate change if its thickness is doubled?

. It increases by a factor of 2
. It increases by a factor of 4
. It increases by a factor of 8
. It increases by a factor of 16
. It decreases by half

Correct Answer & Explanation

. It increases by a factor of 2

Explanation

The bending stiffness (area moment of inertia) of a rectangular plate is proportional to the base times the height cubed (bh^3 / 12). Therefore, doubling the thickness (height) increases stiffness by a factor of 2^3, or 8.

Question 1240

Topic: Biomechanics & Biomaterials

Which of the following best describes the phenomenon of 'stress relaxation' in orthopedic viscoelastic materials such as tendons and ligaments?

. Increased deformation over time under a constant load
. Decreased stress over time under a constant deformation
. Energy lost as heat during cyclic loading and unloading
. Increased stiffness when subjected to a rapid loading rate
. Brittle failure following repetitive cyclical stress

Correct Answer & Explanation

. Increased deformation over time under a constant load

Explanation

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

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