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Biomechanics & Biomaterials MCQs

Practice Set 22 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 421

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is widely used in total joint arthroplasty to reduce wear rates. However, the process of extensive cross-linking significantly decreases which of the following mechanical properties?
. Wear resistance
. Oxidative stability
. Modulus of elasticity
. Fracture toughness
. Surface hardness

Correct Answer & Explanation

. Fracture toughness

Explanation

While high cross-linking of UHMWPE significantly improves wear resistance, it inversely reduces fatigue crack propagation resistance, yield strength, and fracture toughness. This increases the risk of component fracture under high stress.

Question 422

Topic: Biomechanics & Biomaterials

When analyzing the stress-strain curve of an orthopedic biomaterial, the total area under the curve prior to the point of material failure represents which biomechanical property?

. Toughness
. Stiffness
. Ductility
. Yield strength
. Elastic limit

Correct Answer & Explanation

. Toughness

Explanation

Toughness is defined as the total amount of energy a material can absorb before catastrophic failure, represented by the entire area under the stress-strain curve. Resilience is the energy absorbed only up to the elastic limit.

Question 423

Topic: Biomechanics & Biomaterials

In an experiment, a cadaveric anterior cruciate ligament is rapidly stretched to a constant, fixed length. Over the next several minutes, the force required to maintain this specific length gradually decreases. This viscoelastic phenomenon is known as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Strain hardening

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation occurs when a viscoelastic material is held at a constant strain (length), and the stress (internal force) decreases over time. Creep, conversely, is the gradual increase in strain when held at a constant stress.

Question 424

Topic: Biomechanics & Biomaterials

Titanium alloy (Ti-6Al-4V) is frequently chosen over Cobalt-Chromium for the manufacturing of diaphyseal-engaging femoral stems in uncemented total hip arthroplasty. What is the primary biomechanical advantage of Titanium in this application?

. Higher modulus of elasticity, increasing stability
. Lower modulus of elasticity, reducing stress shielding
. Higher resistance to abrasive wear
. Less susceptibility to notch sensitivity
. Increased radiopacity for postoperative imaging

Correct Answer & Explanation

. Lower modulus of elasticity, reducing stress shielding

Explanation

Titanium alloy has a modulus of elasticity approximately half that of Cobalt-Chromium, making it significantly closer to the modulus of cortical bone. This increased flexibility reduces stress shielding and subsequent proximal femoral osteolysis.

Question 425

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is supplied as a powder and a liquid monomer. What is the specific function of Barium sulfate or Zirconium dioxide, which are added to the powder component?

. Accelerate the polymerization reaction
. Serve as a free radical scavenger
. Increase the maximum exothermic temperature
. Act as a radiopacifier
. Improve the ultimate tensile strength

Correct Answer & Explanation

. Act as a radiopacifier

Explanation

Barium sulfate and Zirconium dioxide are added to PMMA purely as radiopacifiers to allow visualization of the cement mantle on postoperative radiographs. They do not strengthen the cement and can actually act as stress risers.

Question 426

Topic: Biomechanics & Biomaterials
In orthopedic biomechanics, materials are often compared by their stiffness. Which of the following sequences correctly ranks the materials in order of decreasing modulus of elasticity (stiffest to most flexible)?
. Cobalt-Chromium, Titanium, Cortical Bone, PMMA
. Titanium, Cobalt-Chromium, Cortical Bone, PMMA
. Cobalt-Chromium, Cortical Bone, Titanium, PMMA
. Cortical Bone, Cobalt-Chromium, Titanium, PMMA
. PMMA, Cortical Bone, Titanium, Cobalt-Chromium

Correct Answer & Explanation

. Cobalt-Chromium, Titanium, Cortical Bone, PMMA

Explanation

Cobalt-Chromium is the stiffest (approx. 200 GPa), followed by Titanium alloy (approx. 100 GPa). Cortical bone is much less stiff (15-20 GPa), and PMMA bone cement is highly flexible (2-3 GPa).

Question 427

Topic: Biomechanics & Biomaterials

When two dissimilar metals are placed in physical contact within the electrolytic environment of the human body, galvanic corrosion may occur. Which of the following implant combinations represents the greatest risk for severe galvanic corrosion?

. Titanium and Tantalum
. Cobalt-Chromium and Titanium
. Stainless Steel and Titanium
. Cobalt-Chromium and Alumina
. Titanium and Trabecular Metal

Correct Answer & Explanation

. Stainless Steel and Titanium

Explanation

Stainless steel and titanium are far apart on the anodic index. Mixing them (e.g., a stainless steel screw in a titanium plate) creates a strong electrochemical cell, leading to accelerated pitting and corrosion of the less noble stainless steel.

Question 428

Topic: Biomechanics & Biomaterials

A ligament subjected to a constant, prolonged tensile load demonstrates a gradual increase in length over time. Which of the following terms best describes this biomechanical property?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation of a viscoelastic material over time under a constant load. Stress relaxation, conversely, is the decrease in stress over time when the material is held at a constant length.

Question 429

Topic: Biomechanics & Biomaterials

A 45-year-old patient receives a cementless total hip arthroplasty. To minimize stress shielding of the proximal femur, the femoral stem should be manufactured from a material with a modulus of elasticity closest to that of cortical bone. Which of the following materials has the lowest modulus of elasticity?

. Cobalt-chromium alloy
. Stainless steel
. Titanium alloy
. Alumina ceramic
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a lower modulus of elasticity (approx 110 GPa) compared to stainless steel (approx 200 GPa) and cobalt-chromium (approx 210 GPa). This makes it biomechanically closer to cortical bone (approx 15-20 GPa), effectively reducing proximal femoral stress shielding.

Question 430

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is commonly used. What is the primary intended effect of increasing the cross-linking of UHMWPE, and what is a known negative biomechanical consequence?
. Decreased wear rate; decreased fracture toughness
. Decreased wear rate; increased oxidation potential
. Increased fatigue strength; decreased wear rate
. Increased elastic modulus; increased fracture toughness
. Decreased oxidation potential; decreased yield strength

Correct Answer & Explanation

. Decreased wear rate; decreased fracture toughness

Explanation

Highly cross-linked polyethylene significantly reduces adhesive and abrasive wear rates in joint replacements. However, this cross-linking process reduces the material's fracture toughness and ductility, making it more susceptible to fatigue crack propagation.

Question 431

Topic: Biomechanics & Biomaterials

On a stress-strain curve representing a typical human tendon, a non-linear "toe region" is observed at very low strains. This specific region primarily represents which of the following microscopic events?

. Failure of cross-links between collagen fibrils
. Microscopic tearing of individual collagen fibers
. Plastic deformation of the collagen matrix
. Uncrimping of the resting wavy collagen fibers
. Water exudation from the proteoglycan matrix

Correct Answer & Explanation

. Uncrimping of the resting wavy collagen fibers

Explanation

The "toe region" of the tendon stress-strain curve represents the initial straightening out, or "uncrimping," of the wavy collagen fibers as tension is applied. Once the fibers are fully straightened, the curve enters the steeper, linear elastic region.

Question 432

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is widely used in arthroplasty for implant fixation. The primary mechanism by which PMMA provides stability to the implant is best described as:

. Chemical covalent bonding to the titanium oxide layer
. Osteointegration into the micro-porous cement surface
. Mechanical interlock with the interstices of cancellous bone
. Cross-linking with host bone collagen fibers
. Adhesive chemical bonding to bone hydroxyapatite

Correct Answer & Explanation

. Mechanical interlock with the interstices of cancellous bone

Explanation

PMMA bone cement does not possess adhesive properties nor does it chemically bond to host bone or metal implants. It functions essentially as a grout, providing rigid fixation via an intricate mechanical interlock by penetrating the trabecular interstices of cancellous bone.

Question 433

Topic: Biomechanics & Biomaterials

During a complex revision trauma surgery, a surgeon considers using a stainless steel screw to secure a cobalt-chromium plate. This practice is contraindicated due to the risk of accelerated degradation of the less noble metal when bathed in host body fluids. This phenomenon is termed:

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct physical contact within an electrolytic environment, such as human tissue fluid. The less noble metal acts as an anode and undergoes accelerated oxidative degradation.

Question 434

Topic: Biomechanics & Biomaterials

Cortical bone exhibits distinct mechanical properties depending on the direction of the applied load. For instance, it is significantly stronger in longitudinal compression than in transverse tension. This structural biomechanical property is known as:

. Viscoelasticity
. Isotropy
. Anisotropy
. Creep
. Biphasic behavior

Correct Answer & Explanation

. Anisotropy

Explanation

Anisotropy describes a material that exhibits different mechanical properties depending on the direction of the applied load. Cortical bone is highly anisotropic because its osteonal structure aligns to optimally resist physiological longitudinal compressive loads.

Question 435

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is frequently used in total joint arthroplasty to reduce wear debris. What mechanical property is most significantly decreased as a direct result of increasing the cross-linking in UHMWPE?
. Young's modulus
. Yield strength
. Fatigue crack propagation resistance
. Surface hardness
. Compressive strength

Correct Answer & Explanation

. Fatigue crack propagation resistance

Explanation

While highly cross-linking UHMWPE significantly reduces adhesive and abrasive wear, it simultaneously decreases its ductility, toughness, and resistance to fatigue crack propagation. This makes it more susceptible to fracture in high-stress applications or thin liners.

Question 436

Topic: Biomechanics & Biomaterials

Stress shielding in cementless femoral stems leads to proximal bone loss. Which of the following implant materials has a Young's modulus closest to that of cortical bone, thereby theoretically minimizing stress shielding?

. Cobalt-Chromium alloy
. Stainless steel (316L)
. Titanium alloy (Ti-6Al-4V)
. Alumina ceramic
. Zirconia ceramic

Correct Answer & Explanation

. Titanium alloy (Ti-6Al-4V)

Explanation

Titanium alloy has a Young's modulus (approx. 110 GPa) that is lower than Cobalt-Chromium (approx. 210 GPa) and Stainless Steel (approx. 200 GPa), making it closer to that of cortical bone (approx. 15-20 GPa). This reduced stiffness mismatch helps decrease stress shielding.

Question 437

Topic: Biomechanics & Biomaterials

Which of the following forms of corrosion is most likely to occur at the modular junction between a titanium femoral stem and a cobalt-chromium femoral head due to variations in local oxygen tension?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Crevice corrosion occurs in restricted spaces (like modular tapers) where oxygen depletion prevents the reformation of the protective oxide layer. While galvanic corrosion can also occur with dissimilar metals, taper corrosion is primarily a mechanically assisted crevice corrosion (fretting-crevice mechanism).

Question 438

Topic: Biomechanics & Biomaterials

When testing the viscoelastic properties of cortical bone, how does an increased rate of loading (strain rate) affect the biomechanical behavior of the bone?

. Decreases stiffness and decreases ultimate strength
. Decreases stiffness and increases ultimate strength
. Increases stiffness and increases energy absorption to failure
. Increases stiffness but decreases energy absorption to failure
. No change in stiffness but decreases ultimate strength

Correct Answer & Explanation

. Increases stiffness and increases energy absorption to failure

Explanation

Because bone is a viscoelastic material, its mechanical properties change with the rate of loading. At higher strain rates (e.g., trauma), bone becomes both stiffer and stronger, absorbing more energy before failure.

Question 439

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) bone cement is primarily utilized in arthroplasty for implant fixation. Which of the following best describes its mechanical characteristics?

. It acts as a true adhesive bonding to bone and metal
. It is stronger in tension than in compression
. It undergoes an endothermic reaction during polymerization
. It is strongest in compression and weak in tension and shear
. It expands significantly during the curing phase

Correct Answer & Explanation

. It is strongest in compression and weak in tension and shear

Explanation

PMMA does not act as an adhesive; it provides fixation via mechanical interlock. It is highly resistant to compressive forces but is notably weak in tension and shear, and it undergoes an exothermic reaction, shrinking slightly during polymerization.

Question 440

Topic: Biomechanics & Biomaterials

In the stress-strain curve of a normal human ligament, the initial 'toe region' is characterized by low stiffness. What microscopic structural change corresponds to this region?

. Microfailure of collagen bundles
. Straightening out of the natural crimp of collagen fibers
. Plastic deformation of elastin fibers
. Slippage of proteoglycan molecules
. Macroscopic complete failure of the ligament

Correct Answer & Explanation

. Straightening out of the natural crimp of collagen fibers

Explanation

The non-linear 'toe region' of a ligament or tendon stress-strain curve occurs at low strains. It represents the straightening (uncrimping) of the resting, wavy collagen fibers before they begin to stretch elastically.

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