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Biomechanics & Biomaterials MCQs

Practice Set 71 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 1401

Topic: Biomechanics & Biomaterials

A bioengineering researcher is studying the mechanical behavior of articular cartilage. She applies a constant compressive load to a cartilage sample over a sustained period of time and measures a progressive, continuous increase in tissue deformation. This viscoelastic phenomenon is best described as:

. Stress relaxation
. Creep
. Hysteresis
. Fatigue
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is the progressive deformation of a viscoelastic material over time when subjected to a constant load. In contrast, stress relaxation is the decrease in stress over time when the material is held at a constant deformation.

Question 1402

Topic: Biomechanics & Biomaterials

A surgeon considers using a combination of titanium and stainless steel implants in a single fracture construct. Which of the following principles best describes the primary risk of galvanic corrosion in this scenario?

. Titanium acts as the anode and undergoes accelerated corrosion
. Stainless steel acts as the cathode and is protected from corrosion
. Stainless steel acts as the anode and undergoes accelerated corrosion
. Titanium acts as the cathode and is aggressively corroded by the local cellular response
. Passivation layers on both metals prevent any measurable galvanic corrosion in vivo

Correct Answer & Explanation

. Titanium acts as the anode and undergoes accelerated corrosion

Explanation

In a galvanic cell formed by dissimilar metals, the less noble metal (stainless steel) acts as the anode and undergoes accelerated corrosion. The more noble metal (titanium) acts as the cathode and is protected. This can lead to rapid implant failure and local metallosis.

Question 1403

Topic: Biomechanics & Biomaterials

During material testing of an orthopedic implant, a stress-strain curve is generated. The total area under the stress-strain curve up to the point of material failure represents which of the following biomechanical properties?

. Yield strength
. Ultimate tensile strength
. Toughness
. Ductility
. Stiffness

Correct Answer & Explanation

. Toughness

Explanation

Toughness is defined as the amount of energy a material can absorb before it fractures or fails. It is graphically represented by the entire area under the stress-strain curve. Yield strength is the stress at which a material begins to plastically deform, and stiffness is represented by the slope of the elastic portion of the curve (Young's modulus).

Question 1404

Topic: Biomechanics & Biomaterials
In orthopedic implant surgery, mixing different metals can lead to galvanic corrosion due to differences in electrochemical potential. Which of the following combinations of implant materials poses the highest risk of clinically significant galvanic corrosion when placed in direct contact in vivo?
. Titanium alloy and Commercially pure titanium
. 316L Stainless Steel and Cobalt-Chromium alloy
. Cobalt-Chromium alloy and Titanium alloy
. Tantalum (trabecular metal) and Titanium alloy
. UHMWPE and Cobalt-Chromium alloy

Correct Answer & Explanation

. 316L Stainless Steel and Cobalt-Chromium alloy

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are in contact within an electrolyte solution (like body fluid). 316L stainless steel has a significantly different anodic index compared to cobalt-chromium or titanium. Mixing stainless steel with cobalt-chromium leads to rapid galvanic corrosion of the less noble metal (the stainless steel). Titanium and cobalt-chromium can often be used together with minimal risk (e.g., modular total hips).

Question 1405

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic properties. When a constant static load is continuously applied to a ligament over an extended period, the ligament will gradually elongate over time. This specific biomechanical phenomenon is known as:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the property of a viscoelastic material to progressively deform (elongate) when subjected to a constant load (stress) over time. In contrast, stress relaxation is the phenomenon where the stress within a material decreases over time when it is held at a constant length (strain).

Question 1406

Topic: Biomechanics & Biomaterials
In the manufacturing of joint arthroplasty components, Ultra-High Molecular Weight Polyethylene (UHMWPE) undergoes gamma irradiation to increase cross-linking and decrease wear. However, if this irradiation is performed in an environment containing oxygen, which deleterious effect is most likely to occur over time?
. Increased formation of favorable cross-links
. Oxidation resulting in chain scission and embrittlement
. Increased percentage of crystalline domains leading to higher toughness
. Melting of the amorphous phase resulting in implant deformation
. Conversion of the material to a thermoset plastic

Correct Answer & Explanation

. Oxidation resulting in chain scission and embrittlement

Explanation

Gamma irradiation generates free radicals within the UHMWPE. If oxygen is present during irradiation or storage (shelf aging), these free radicals combine with oxygen to cause oxidation and chain scission (breaking of polymer chains). This severely decreases the mechanical properties (embrittlement) and increases wear debris in vivo. Modern highly cross-linked polyethylene is irradiated in an inert gas or vacuum and subsequently melted or annealed to extinguish residual free radicals.

Question 1407

Topic: Biomechanics & Biomaterials

When a constant continuous load is applied to a viscoelastic material such as a ligament or tendon, the material will undergo continued deformation over time. This biomechanical phenomenon is known as:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation of a material over time when subjected to a constant load or stress. Stress relaxation is the decrease in stress over time when a material is held at a constant strain/deformation. Hysteresis represents the energy lost during a loading and unloading cycle.

Question 1408

Topic: Biomechanics & Biomaterials

A surgeon revises a hip arthroplasty, placing a cobalt-chromium femoral head onto a titanium alloy femoral stem. Which type of corrosion is most likely to occur at the modular head-neck junction due to the mixing of these dissimilar metals?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within a conductive fluid (like body fluid). The less noble metal undergoes accelerated corrosion. Fretting corrosion is also possible due to micromotion, but the specific electrochemical mechanism driven by dissimilar metals is galvanic corrosion.

Question 1409

Topic: Biomechanics & Biomaterials

On a load-deformation curve for a metallic orthopedic implant, the point at which the material ceases to deform elastically and begins to deform plastically is known as the:

. Ultimate tensile strength
. Proportional limit
. Yield point
. Failure point
. Modulus of elasticity

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the transition from elastic (reversible) to plastic (irreversible) deformation on a load-deformation or stress-strain curve. The ultimate tensile strength is the maximum stress the material can withstand before necking and failure.

Question 1410

Topic: Biomechanics & Biomaterials
To reduce the wear rate of ultra-high-molecular-weight polyethylene (UHMWPE) components in total joint arthroplasty, manufacturers use high-dose gamma irradiation. What is the primary structural effect of this process on the polyethylene?
. Decreases crystallinity
. Induces highly cross-linked molecular bonds
. Increases the molecular weight by chain elongation
. Removes free radicals through oxidation
. Increases the elastic modulus to match cortical bone

Correct Answer & Explanation

. Induces highly cross-linked molecular bonds

Explanation

High-dose gamma irradiation of UHMWPE breaks the carbon-hydrogen bonds, forming free radicals that recombine to form cross-links between the polymer chains. This highly cross-linked structure significantly reduces adhesive and abrasive wear.

Question 1411

Topic: Biomechanics & Biomaterials

When comparing orthopedic implant materials, Titanium alloy (Ti-6Al-4V) is often preferred for diaphyseal stems due to its specific biomechanical properties. Which of the following best describes its advantage over Cobalt-Chromium (CoCr)?

. Higher modulus of elasticity leading to increased stress shielding
. Lower modulus of elasticity closer to that of cortical bone
. Higher rate of galvanic corrosion when combined with other metals
. Increased stiffness resulting in lower fatigue strength
. Greater ferromagnetism allowing for better MRI imaging

Correct Answer & Explanation

. Lower modulus of elasticity closer to that of cortical bone

Explanation

Titanium alloy has a modulus of elasticity closer to that of cortical bone compared to CoCr or stainless steel. This relative flexibility helps reduce stress shielding around the implant.

Question 1412

Topic: Biomechanics & Biomaterials

During intraoperative stretching of a contracted knee joint, the surgeon applies a constant deformation (length) to the collateral ligaments over a period of time. The surgeon notices that the force required to maintain this stretch gradually decreases. This biomechanical property is known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the force (stress) required to maintain a tissue at a constant length decreases over time. Creep is the continuous deformation of a tissue under a constant load.

Question 1413

Topic: Biomechanics & Biomaterials

A surgeon uses a stainless steel screw to secure a titanium plate during an open reduction and internal fixation. Which of the following describes the most likely mechanism of failure if corrosion occurs?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in direct electrical contact within a conductive body fluid environment. The less noble metal undergoes accelerated anodic dissolution, compromising the implant construct.

Question 1414

Topic: Biomechanics & Biomaterials

Which of the following non-collagenous proteins is primarily responsible for initiating the mineralization process within the bone matrix by binding calcium and hydroxyapatite?

. Osteonectin
. Osteopontin
. Osteocalcin
. Bone sialoprotein
. Decorin

Correct Answer & Explanation

. Osteocalcin

Explanation

Osteocalcin, the most abundant non-collagenous bone protein, contains vitamin K-dependent gamma-carboxyglutamic acid residues that tightly bind calcium. It plays a critical role in regulating bone mineralization and maturation.

Question 1415

Topic: Biomechanics & Biomaterials

During an ACL reconstruction, a hamstring autograft is subjected to a constant tension load on a preparation board. Over the next 15 minutes, the graft gradually elongates. Which viscoelastic property does this phenomenon represent?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the viscoelastic property where a tissue undergoes progressive deformation (elongation) over time when subjected to a constant load. In contrast, stress relaxation refers to the decrease in tension over time when the tissue is held at a constant length.

Question 1416

Topic: Biomechanics & Biomaterials

Which of the following thermal processing methods for highly cross-linked polyethylene (HXLPE) is associated with the lowest level of measurable free radicals, but also results in a reduction of the material's yield and fatigue strength?

. Annealing below the melting point
. Remelting above the melting point
. Vitamin E (alpha-tocopherol) infusion
. Ethylene oxide sterilization
. Gamma irradiation in an inert gas environment

Correct Answer & Explanation

. Remelting above the melting point

Explanation

Remelting HXLPE (heating above its melting point, typically >135ยฐC) eliminates nearly all free radicals, providing excellent oxidative resistance. However, it alters the crystalline structure, which decreases mechanical properties such as yield strength, ultimate tensile strength, and fatigue strength. Annealing (heating below the melting point) preserves mechanical strength but leaves residual free radicals, increasing the risk of in vivo oxidation over time.

Question 1417

Topic: Biomechanics & Biomaterials

During a primary THA, the surgeon chooses a 36-mm femoral head over a 28-mm femoral head to improve hip stability. Assuming the same head-neck ratio, what is the primary biomechanical advantage that decreases the risk of dislocation with the larger femoral head?

. It increases the combined anteversion of the hip
. It decreases the volumetric wear of the polyethylene
. It increases the jump distance required for the head to dislocate
. It creates a more medialized center of rotation
. It directly increases the tension in the abductor musculature

Correct Answer & Explanation

. It increases the jump distance required for the head to dislocate

Explanation

Larger femoral heads provide greater stability primarily by increasing the 'jump distance'โ€”the distance the femoral head must translate laterally before it completely escapes the acetabular rim. A larger head also increases the head-neck ratio (assuming the neck diameter remains constant), which improves the impingement-free range of motion. However, the direct mechanical barrier to dislocation once subluxation begins is the increased jump distance. Note that larger heads increase (not decrease) volumetric wear, though modern highly cross-linked polyethylene handles this well.

Question 1418

Topic: Biomechanics & Biomaterials

Kinematic studies of the normal human knee demonstrate specific coupled motions during deep flexion. Which of the following best describes the normal kinematic movement of the femoral condyles on the tibia from 0 to 120 degrees of flexion?

. Symmetrical posterior rollback of both the medial and lateral femoral condyles
. Anterior translation of the lateral femoral condyle with a fixed medial condyle
. A medial pivot pattern with significant posterior translation (rollback) of the lateral femoral condyle
. A lateral pivot pattern with significant posterior translation (rollback) of the medial femoral condyle
. Pure rotation around a fixed transverse axis with no anteroposterior translation

Correct Answer & Explanation

. A medial pivot pattern with significant posterior translation (rollback) of the lateral femoral condyle

Explanation

Normal knee kinematics follow a 'medial pivot' pattern. The medial femoral condyle acts as a ball-and-socket joint with minimal anteroposterior translation, while the lateral femoral condyle undergoes significant posterior translation (rollback) as the knee flexes. This coupled internal rotation of the tibia (or external rotation of the femur) aids in maximizing deep flexion.

Question 1419

Topic: Biomechanics & Biomaterials

Antibiotic-loaded acrylic bone cement (ALABC) is commonly used for prophylaxis and treatment of periprosthetic joint infection. Which of the following antibiotics is NOT appropriate for incorporation into PMMA bone cement due to its severe heat lability?

. Tobramycin
. Vancomycin
. Gentamicin
. Erythromycin
. Penicillin G

Correct Answer & Explanation

. Penicillin G

Explanation

The polymerization of polymethyl methacrylate (PMMA) bone cement is a highly exothermic reaction that can reach temperatures over 80-100 degrees Celsius in vivo. Antibiotics mixed into PMMA must be heat-stable, water-soluble, and available in powder form. Penicillins and most cephalosporins are heat-labile and degrade during polymerization, whereas aminoglycosides (tobramycin, gentamicin) and vancomycin are heat-stable.

Question 1420

Topic: Biomechanics & Biomaterials

During a revision trauma surgery, a surgeon contemplates using a titanium alloy plate in direct contact with stainless steel screws. This combination of dissimilar metals within the body's electrolyte-rich fluid environment initiates a process known as galvanic corrosion. Which of the following describes the most likely electrochemical outcome of this pairing?

. Both metals will corrode at an equally accelerated rate
. The titanium will act as the cathode and undergo rapid corrosion
. The stainless steel will act as the anode and undergo accelerated corrosion
. The titanium will act as the anode and undergo accelerated corrosion
. The stainless steel will act as the cathode and remain completely protected

Correct Answer & Explanation

. The stainless steel will act as the anode and undergo accelerated corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within a conductive solution (like body fluid). The metal with the lower corrosion potential (the less noble metal) becomes the anode and corrodes, while the metal with the higher potential (more noble) becomes the cathode and is protected. Stainless steel is less noble than titanium; therefore, the stainless steel acts as the anode and undergoes accelerated corrosion.

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