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Biomechanics & Biomaterials MCQs

Practice Set 82 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 1621

Topic: Biomechanics & Biomaterials

Which of the following terms best describes the viscoelastic property where a biological material continues to slowly deform over time when subjected to a constant, sustained load?

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

Correct Answer & Explanation

. Creep

Explanation

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

Question 1622

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, highly cross-linking ultra-high-molecular-weight polyethylene (UHMWPE) is performed primarily to alter its material properties. How does this manufacturing process alter the polyethylene compared to conventional UHMWPE?
. Increases wear resistance but decreases fatigue strength
. Decreases wear resistance but increases fatigue strength
. Increases both wear resistance and fracture toughness
. Decreases both wear resistance and fracture toughness
. Increases wear resistance but increases susceptibility to oxidation

Correct Answer & Explanation

. Increases wear resistance but decreases fatigue strength

Explanation

Highly cross-linked polyethylene significantly improves wear resistance, thereby reducing osteolysis in total joint arthroplasty. However, the cross-linking and subsequent thermal treatments reduce mechanical properties such as fatigue strength and fracture toughness.

Question 1623

Topic: Biomechanics & Biomaterials

When combining orthopedic implant components made of different metals, galvanic corrosion may occur. Which of the following combinations of metals carries the highest risk of clinically significant galvanic corrosion when placed in direct contact in vivo?

. Titanium and Titanium alloy
. Cobalt-Chrome and Cobalt-Chrome
. Stainless Steel and Titanium
. Ceramic and Titanium
. Highly cross-linked polyethylene and Cobalt-Chrome

Correct Answer & Explanation

. Stainless Steel and Titanium

Explanation

Galvanic corrosion occurs when two dissimilar metals with significantly different anodic indices are placed in contact in an electrolyte fluid. The coupling of stainless steel and titanium creates a strong galvanic cell, leading to rapid corrosion, and should be avoided in orthopedic constructs.

Question 1624

Topic: Biomechanics & Biomaterials

Which of the following biomechanical terms describes the time-dependent increase in strain of a material under a constant applied load?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent deformation (increase in strain) under a constant load. Stress relaxation is the time-dependent decrease in stress under a constant strain. Hysteresis refers to the energy lost (as heat) during the loading and unloading cycles of a viscoelastic material.

Question 1625

Topic: Biomechanics & Biomaterials

When a stainless steel screw is placed through a titanium plate in an orthopedic construct, the resulting corrosion at the interface is best described as:

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials (e.g., stainless steel and titanium) are placed in contact within a conductive medium (such as body fluids). The less noble metal undergoes accelerated corrosion while the more noble metal is protected.

Question 1626

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit distinct viscoelastic properties. When a constant length (deformation) is maintained on a ligament over a period of time, the load or force required to maintain that specific deformation progressively decreases. This biomechanical phenomenon is termed:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation occurs when a viscoelastic material is held at a constant strain (deformation), and the stress (load) required to maintain that strain decreases over time. Creep is the continuous increase in deformation (strain) over time when a constant load (stress) is applied. Hysteresis represents the energy lost as heat during the loading and unloading cycle.

Question 1627

Topic: Biomechanics & Biomaterials

An orthopedic surgeon utilizes a stainless steel screw through a titanium alloy fracture plate. Postoperatively, there is an increased risk of accelerated implant degradation due to the transfer of electrons between the two dissimilar metals in the presence of the body's saline environment. This specific type of corrosion 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 with different anodic indices are placed in contact within an electrolytic solution (like body fluids). The less noble metal acts as an anode and corrodes faster, while the more noble metal acts as a cathode.

Question 1628

Topic: Biomechanics & Biomaterials

During an ACL reconstruction, a hamstring autograft is tensioned to a constant length before fixation. Over the next several minutes, the tension registered within the graft gradually decreases. This time-dependent biomechanical property is termed:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation occurs when a viscoelastic material is held at a constant length or strain, leading to a gradual decrease in applied force or stress over time. Conversely, creep is defined as progressive deformation over time under a constant load.

Question 1629

Topic: Biomechanics & Biomaterials

A surgeon retrieves a failed modular total hip arthroplasty implant and notes severe degradation at the head-neck taper junction. Which of the following mechanisms best describes the galvanic corrosion contributing to this failure?

. Micromotion between two components of the identical metal alloy
. Breakdown of the passivation layer in an oxygen-depleted crevice
. Electrochemical destruction due to contact between two dissimilar metals in a conductive fluid
. Accelerated wear caused by third-body particulate debris
. Cyclic loading leading to propagation of microscopic cracks

Correct Answer & Explanation

. Electrochemical destruction due to contact between two dissimilar metals in a conductive fluid

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic potentials are in direct physical contact within an electrolytic solution, such as body fluid. The less noble metal becomes the anode and undergoes accelerated electrochemical corrosion.

Question 1630

Topic: Biomechanics & Biomaterials

During biomechanical tensile testing of a normal human flexor tendon, the initial "toe region" of the load-elongation curve represents functional physiological stretching. This specific phase is structurally due to which of the following?

. Microscopic failure of collagen cross-links
. Plastic deformation of collagen fibrils
. Uncrimping of the relaxed collagen fibers
. Sliding of collagen fibrils past one another
. Rupture of individual tendon fascicles

Correct Answer & Explanation

. Uncrimping of the relaxed collagen fibers

Explanation

The initial non-linear "toe region" of a ligament or tendon stress-strain curve occurs under low loads. It represents the natural, wavy, crimped collagen fibers straightening out and aligning parallel to the direction of the applied tensile load.

Question 1631

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant materials has a modulus of elasticity (Young's modulus) that most closely resembles that of cortical bone?

. Cobalt-chromium alloy
. Stainless steel
. Titanium alloy
. Tantalum
. Ultra-high-molecular-weight polyethylene

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a modulus of elasticity closer to cortical bone compared to stainless steel or cobalt-chromium. This similarity helps reduce stress shielding and subsequent osteopenia around the implant.

Question 1632

Topic: Biomechanics & Biomaterials
To reduce the incidence of wear debris and subsequent aseptic loosening in total joint arthroplasty, ultra-high-molecular-weight polyethylene (UHMWPE) is often highly cross-linked. What is a known mechanical trade-off of highly cross-linking UHMWPE?
. Increased fatigue strength
. Decreased ultimate tensile strength and ductility
. Increased oxidation susceptibility if not remelted
. Decreased elastic modulus
. Increased surface roughness

Correct Answer & Explanation

. Decreased ultimate tensile strength and ductility

Explanation

While highly cross-linking UHMWPE significantly improves wear resistance, it concurrently decreases its ultimate tensile strength, ductility, and fracture toughness. Therefore, highly cross-linked polyethylene is more susceptible to catastrophic mechanical failure if used in very thin liners.

Question 1633

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for a ductile orthopedic material like stainless steel, which of the following points marks the transition from elastic to plastic deformation?

. Proportional limit
. Ultimate tensile strength
. Yield point
. Failure point
. Toughness threshold

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the transition from elastic (reversible) to plastic (irreversible) deformation on a stress-strain curve. Prior to this point, the material will return to its original shape if the load is removed.

Question 1634

Topic: Biomechanics & Biomaterials

A surgeon inadvertently uses a titanium screw to secure a stainless steel plate during fracture fixation. Months later, the implant site becomes painful, and revision surgery reveals localized tissue reaction with dark metallic debris. What is the primary mechanism of implant degradation in this scenario?

. Fretting corrosion
. Galvanic corrosion
. Crevice corrosion
. Pitting corrosion
. Fatigue failure

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (like titanium and stainless steel) are in physical contact within an electrolytic solution (body fluid). An electrochemical cell is created, leading to accelerated corrosion of the less noble metal (anodic dissolution).

Question 1635

Topic: Biomechanics & Biomaterials
In modern total joint arthroplasty, highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is extensively used to decrease adhesive and abrasive wear. Which of the following mechanical properties is most significantly reduced as a direct consequence of the cross-linking process?
. Ultimate tensile strength
. Hardness
. Fatigue resistance (Toughness)
. Elastic modulus
. Yield strength

Correct Answer & Explanation

. Fatigue resistance (Toughness)

Explanation

While high-dose irradiation cross-linking dramatically decreases the wear rate of UHMWPE, it significantly decreases its mechanical toughness, fatigue resistance, and ductility, making it more vulnerable to fracture or failure under high-stress conditions.

Question 1636

Topic: Biomechanics & Biomaterials

When optimizing the biomechanics of a cortical bone screw, which of the following design modifications will most effectively increase its pullout strength?

. Decreasing the outer diameter
. Increasing the inner (root) diameter
. Decreasing the thread pitch
. Increasing the screw length beyond the far cortex by 10mm
. Decreasing the working length

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Pullout strength is directly proportional to the outer diameter and the total surface area of thread engagement. Decreasing the thread pitch increases the number of threads per unit length, thereby increasing the amount of bone engaged and maximizing pullout strength.

Question 1637

Topic: Biomechanics & Biomaterials

Among common metallic orthopedic implants, which has a modulus of elasticity that most closely approximates that of cortical bone?

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

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a modulus of elasticity (approx. 110 GPa) that is closer to cortical bone (15-20 GPa) compared to stainless steel (200 GPa) and cobalt-chromium (220 GPa). This closer biomechanical match helps minimize stress shielding.

Question 1638

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, which of the following wear mechanisms is fundamentally responsible for the generation of ultra-high-molecular-weight polyethylene (UHMWPE) wear debris at the articulating interface?
. Adhesive wear
. Abrasive wear
. Corrosive wear
. Galvanic wear
. Third-body wear

Correct Answer & Explanation

. Adhesive wear

Explanation

Adhesive wear is the primary continuous wear mechanism for UHMWPE. It occurs when microscopic asperities on the hard metal surface temporarily bond with the softer polyethylene, tearing off submicron particles during motion.

Question 1639

Topic: Biomechanics & Biomaterials

Which of the following best defines the biomechanical phenomenon of 'creep' in orthopedic biomaterials?

. Progressive deformation of a material under a constant load over time
. Decrease in stress over time when a material is held at a constant strain
. Microstructural failure due to cyclic loading below the yield strength
. Loss of mechanical strength due to environmental corrosion
. Energy lost as heat during the loading and unloading cycle

Correct Answer & Explanation

. Progressive deformation of a material under a constant load over time

Explanation

Creep is defined as the progressive, time-dependent plastic deformation of a material subjected to a constant stress (load). Conversely, stress relaxation refers to the decrease in stress over time under a constant strain.

Question 1640

Topic: Biomechanics & Biomaterials

When a stainless steel screw is placed through a titanium plate, galvanic corrosion may occur. Which of the following factors primarily determines the rate of this electrochemical degradation?

. The modulus of elasticity of the metals
. The difference in the anodic index between the two metals
. The thickness of the passivation layer on the stainless steel
. The ultimate tensile strength of the titanium
. The degree of cyclic loading applied to the construct

Correct Answer & Explanation

. The difference in the anodic index between the two metals

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic environment. The rate and severity of corrosion are driven by the difference in their electrochemical potentials, known as the anodic index.

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