Menu

Biomechanics & Biomaterials MCQs

Practice Set 73 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 1441

Topic: Biomechanics & Biomaterials
To reduce wear rates in total joint arthroplasty, ultra-high molecular weight polyethylene (UHMWPE) undergoes highly cross-linking. To prevent in vivo oxidation and premature degradation, the cross-linked UHMWPE must be subjected to which of the following processes?
. Gamma irradiation in ambient air
. Ethylene oxide sterilization
. Remelting or annealing to eliminate free radicals
. Addition of polymethylmethacrylate (PMMA)
. Cold drawing of the polymer chains

Correct Answer & Explanation

. Remelting or annealing to eliminate free radicals

Explanation

Gamma irradiation creates cross-links but also leaves behind free radicals. Remelting or annealing the polyethylene after irradiation eliminates these free radicals, preventing subsequent oxidation and degradation.

Question 1442

Topic: Biomechanics & Biomaterials

A surgeon applies a stainless steel plate to a femur fracture and secures it using titanium alloy screws. This mixing of dissimilar metals primarily increases the risk of which type of corrosion?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Mixing dissimilar metals in an electrolytic environment (like the human body) creates an electrochemical cell, leading to galvanic corrosion. The less noble metal becomes the anode and corrodes faster.

Question 1443

Topic: Biomechanics & Biomaterials

A surgeon is revising a nonunion and plans to use a combination of implants. To minimize the risk of clinically significant galvanic corrosion, which of the following combinations of metals should be strictly avoided in direct contact?

. Cobalt-chromium and Titanium
. Stainless steel and Titanium
. Titanium and Tantalum
. Cobalt-chromium and Zirconium
. Commercially pure Titanium and Titanium alloy (Ti-6Al-4V)

Correct Answer & Explanation

. Stainless steel and Titanium

Explanation

Mixing stainless steel and titanium implants can lead to severe galvanic corrosion of the less noble metal (stainless steel), causing implant failure and adverse local tissue reactions.

Question 1444

Topic: Biomechanics & Biomaterials

When applying a bridging plate to a highly comminuted diaphyseal fracture, how does decreasing the working length of the plate (placing the innermost screws closer to the fracture site) alter the biomechanics of the construct?

. It significantly increases the axial stiffness of the construct
. It decreases the torsional stiffness of the construct
. It increases the overall flexibility of the fixation
. It decreases the stress concentration at the innermost screw holes
. It promotes greater micromotion to stimulate secondary healing

Correct Answer & Explanation

. It significantly increases the axial stiffness of the construct

Explanation

Decreasing the working length of a plate concentrates stress over a shorter segment of the implant, substantially increasing the overall stiffness of the construct and reducing interfragmentary motion.

Question 1445

Topic: Biomechanics & Biomaterials

Stress shielding around a stiff orthopedic implant can lead to localized osteopenia. Which of the following solid metallic implant materials possesses an elastic modulus most closely approximating that of human cortical bone?

. Cobalt-chromium alloy
. Stainless steel (316L)
. Titanium alloy (Ti-6Al-4V)
. Solid tantalum
. Zirconium alloy

Correct Answer & Explanation

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

Explanation

Titanium alloy has an elastic modulus (approx. 110 GPa) closer to cortical bone (15-20 GPa) than stainless steel (200 GPa) or cobalt-chromium (240 GPa), thereby reducing stress shielding.

Question 1446

Topic: Biomechanics & Biomaterials
What is the primary mechanical trade-off associated with the use of highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) compared to conventional UHMWPE in total hip arthroplasty?
. Decreased wear resistance with increased fracture toughness
. Increased wear resistance with decreased fracture toughness
. Increased oxidative degradation with decreased elasticity
. Decreased oxidative degradation with increased fatigue crack propagation
. Improved elasticity with decreased ultimate tensile strength

Correct Answer & Explanation

. Increased wear resistance with decreased fracture toughness

Explanation

Highly cross-linked UHMWPE provides excellent wear resistance, significantly reducing particulate debris and subsequent osteolysis. However, the radiation and thermal processes used to cross-link the material decrease its mechanical properties, particularly fracture toughness and resistance to fatigue crack propagation.

Question 1447

Topic: Biomechanics & Biomaterials

During an anterior cruciate ligament (ACL) reconstruction, the surgeon pre-tensions the soft-tissue graft by securing it on a board and holding it at a constant length for 10 minutes. The surgeon notes that the tension required to maintain this specific length gradually decreases over time. This biomechanical phenomenon is known as:

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Strain rate dependency

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the stress (internal tension) within a material gradually decreases when it is held at a constant strain (length). In contrast, creep is the gradual increase in length (strain) when a material is subjected to a constant load (stress).

Question 1448

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic properties. When a tendon is subjected to a constant, sustained strain over time, the measurable stress within the tendon decreases. What is this biomechanical phenomenon called?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in applied stress over time when a viscoelastic material is held at a constant length (strain). Creep, in contrast, is the gradual increase in length (strain) when a constant load (stress) is applied.

Question 1449

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is often sterilized with gamma irradiation, which generates free radicals. To eliminate these free radicals and prevent long-term in vivo oxidation, the material is frequently remelted. What is the primary mechanical trade-off associated with remelting UHMWPE?
. Decreased fatigue strength
. Increased oxidation risk
. Decreased wear resistance
. Increased elastic modulus
. Decreased cross-linking density

Correct Answer & Explanation

. Decreased fatigue strength

Explanation

Remelting UHMWPE above its melting point eliminates free radicals and prevents oxidation but alters its crystalline structure. This thermal treatment reduces mechanical properties, specifically leading to decreased fatigue strength and yield strength.

Question 1450

Topic: Biomechanics & Biomaterials

Trunnionosis, or mechanically assisted crevice corrosion at the head-neck junction, has emerged as a significant complication in modern total hip arthroplasty (THA). Which of the following implant combinations represents the highest risk factor for this phenomenon?

. Large-diameter cobalt-chrome head on a titanium alloy stem
. Ceramic head on a titanium alloy stem
. Small-diameter titanium head on a cobalt-chrome stem
. Highly cross-linked polyethylene liner with a ceramic head
. Use of a cemented, highly polished cobalt-chrome femoral stem

Correct Answer & Explanation

. Large-diameter cobalt-chrome head on a titanium alloy stem

Explanation

Trunnionosis is most strongly associated with the use of large-diameter cobalt-chrome heads on titanium alloy stems. The mismatch in metals promotes galvanic corrosion, while the larger head size and increased offset exert greater torque at the head-neck junction, exacerbating fretting wear.

Question 1451

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, the use of large-diameter femoral heads with modular titanium necks has been associated with early failure. What is the primary mechanism of wear leading to adverse local tissue reactions at the head-neck junction?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion (mechanochemical wear) occurs at the modular taper junctions, such as the trunnion. Micro-motion disrupts the passive oxide layer, leading to localized corrosion and the release of metal ions.

Question 1452

Topic: Biomechanics & Biomaterials

To minimize the risk of galvanic corrosion, which combination of orthopedic implant metals should strictly be avoided in a single construct?

. Cobalt-chrome and Titanium
. Stainless steel and Titanium
. Tantalum and Titanium
. Stainless steel and Cobalt-chrome
. Titanium and Titanium alloy

Correct Answer & Explanation

. Cobalt-chrome and Titanium

Explanation

Combining stainless steel and titanium in the same implant construct creates a high risk for galvanic corrosion due to their significant differences in electrochemical potential. If mixed metals are necessary, cobalt-chrome and titanium are generally safe to combine.

Question 1453

Topic: Biomechanics & Biomaterials

In comparing orthopedic implant materials, which of the following alloys has a Young's modulus of elasticity most similar to that of human cortical bone?

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

Correct Answer & Explanation

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

Explanation

Young's modulus is a measure of a material's stiffness. Cortical bone has a modulus of approximately 15-20 GPa. Among metallic implants, Titanium alloy (approx. 110 GPa) is closer to cortical bone than Stainless Steel (~200 GPa) or Cobalt-Chromium (~210-240 GPa), resulting in less stress shielding compared to stiffer metals.

Question 1454

Topic: Biomechanics & Biomaterials

When evaluating the biomechanics of cortical bone screws, which of the following alterations to the screw design would most significantly increase its pullout strength?

. Decreasing the outer (major) diameter
. Increasing the inner (core/minor) diameter
. Decreasing the thread pitch
. Decreasing the length of thread engagement
. Using a self-tapping tip instead of a standard tip

Correct Answer & Explanation

. Decreasing the outer (major) diameter

Explanation

Screw pullout strength is primarily determined by the volume of bone caught between the threads. It is directly proportional to the major (outer) diameter, the length of thread engagement, and inversely proportional to the thread pitch (finer pitch = more threads engaged, hence decreasing pitch increases pullout strength).

Question 1455

Topic: Biomechanics & Biomaterials

An orthopedic surgeon considers using a titanium alloy screw to secure a stainless steel plate in a fracture construct. What is the primary biological or mechanical reason this mixed-metal combination is generally avoided?

. Excessive stress shielding
. Increased risk of third-body wear
. Risk of galvanic corrosion
. Inability to achieve a rigid construct
. Differences in the coefficient of thermal expansion

Correct Answer & Explanation

. Risk of galvanic corrosion

Explanation

Mixing dissimilar metals, such as stainless steel and titanium, within a conductive medium (body fluid) creates an electrochemical cell, leading to galvanic corrosion. The more anodic metal will corrode at an accelerated rate, potentially leading to implant failure or adverse local tissue reactions.

Question 1456

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, the pullout strength of a cortical screw is directly proportional to which of the following geometric factors?

. Inner root diameter
. Thread pitch
. Outer thread diameter
. Screw head diameter
. Insertion torque

Correct Answer & Explanation

. Outer thread diameter

Explanation

Screw pullout strength represents the force required to pull the screw axially out of the bone. It is directly proportional to the outer (major) diameter of the thread, the length of thread engagement in the bone, and the shear strength of the bone material. It is inversely proportional to the thread pitch (distance between threads).

Question 1457

Topic: Biomechanics & Biomaterials

A surgeon is revising a failed internal fixation of a femur. The original construct consisted of a stainless steel plate with several titanium screws used as replacements during a previous reoperation. Severe localized corrosion is noted at the plate-screw interfaces. Which of the following best describes the electrochemical phenomenon occurring in this mixed-metal construct?

. Crevice corrosion due to oxygen depletion
. Fretting corrosion from micromotion
. Galvanic corrosion with titanium acting as the anode
. Galvanic corrosion with stainless steel acting as the anode
. Pitting corrosion due to chloride ion attack

Correct Answer & Explanation

. Galvanic corrosion with stainless steel acting as the anode

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic solution (body fluid). Titanium is more noble (more cathodic) in the body environment due to its highly stable oxide layer, forcing the stainless steel to act as the anode and undergo accelerated corrosion.

Question 1458

Topic: Biomechanics & Biomaterials

A patient undergoes revision surgery for a failed dynamic compression plate. Intraoperatively, black debris is noted at the plate-screw interface with no evidence of infection. Both the plate and screws are made of titanium. What is the most likely mechanism of this wear?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs due to micromotion at the interface between two highly loaded components, such as a screw head and a plate hole, even if they are made of the same metal. Galvanic corrosion requires dissimilar metals.

Question 1459

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for an orthopedic metal implant, the exact point at which the material ceases to exhibit elastic behavior and begins to permanently deform is known as the:

. Ultimate tensile strength
. Proportional limit
. Yield point
. Failure point
. Elastic modulus

Correct Answer & Explanation

. Yield point

Explanation

The yield point represents the transition from elastic deformation (where the material returns to its original shape) to plastic deformation (where permanent structural changes occur). The slope of the elastic region is the Young's elastic modulus.

Question 1460

Topic: Biomechanics & Biomaterials
Increasing the radiation dose during the cross-linking process of ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty has which of the following biomechanical effects?
. Increases both wear resistance and fatigue strength
. Increases wear resistance but decreases fatigue strength
. Decreases wear resistance and decreases fatigue strength
. Decreases wear resistance but increases fatigue strength
. Increases wear resistance without affecting fatigue strength

Correct Answer & Explanation

. Increases wear resistance but decreases fatigue strength

Explanation

Highly cross-linked polyethylene significantly improves adhesive and abrasive wear resistance, reducing osteolysis. However, the cross-linking process reduces the material's mechanical properties, including fatigue strength and fracture toughness.

Test Yourself

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

On this Page