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Biomechanics & Biomaterials MCQs

Practice Set 72 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 1421

Topic: Biomechanics & Biomaterials

During the intraoperative tensioning phase of an anterior cruciate ligament (ACL) reconstruction, the soft-tissue graft is pulled to a specific, constant length and secured. The surgeon notes that over several minutes, the tension dynamically measured within the graft progressively decreases. This specific viscoelastic behavior is termed:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Viscoelastic materials (such as ligaments and tendons) exhibit time-dependent mechanical properties. 'Stress relaxation' is the phenomenon where the internal stress (tension) of a material decreases over time when it is held at a constant strain (constant length). Conversely, 'creep' refers to the progressive increase in strain (elongation) over time when the material is subjected to a constant applied stress (constant load).

Question 1422

Topic: Biomechanics & Biomaterials

In orthopedic biomaterials, the Young's modulus (modulus of elasticity) of an implant is a crucial factor in load sharing with host bone. Titanium alloy (Ti-6Al-4V) is frequently chosen for femoral stems over Cobalt-Chromium (Co-Cr) alloys primarily to reduce 'stress shielding'. Which of the following accurately compares their Young's moduli relative to cortical bone?

. Titanium has a higher modulus than Co-Cr, closer to cortical bone
. Titanium has a lower modulus than Co-Cr, closer to cortical bone
. Cortical bone has a higher modulus than both Titanium and Co-Cr
. Titanium and Co-Cr have identical moduli, but Titanium is less toxic
. Co-Cr has a lower modulus than Titanium, matching cancellous bone

Correct Answer & Explanation

. Titanium has a lower modulus than Co-Cr, closer to cortical bone

Explanation

Young's modulus represents the stiffness of a material. Cortical bone has a modulus of approx. 15-20 GPa. Titanium alloy has a modulus of approx. 110 GPa, while Cobalt-Chromium has a modulus of approx. 210-240 GPa. Because Titanium's modulus is lower than Co-Cr (making it more flexible and closer to the modulus of cortical bone), it transfers more mechanical stress to the adjacent bone, thereby reducing bone resorption due to stress shielding.

Question 1423

Topic: Biomechanics & Biomaterials

In orthopedic biomaterials, galvanic corrosion can lead to significant implant failure or adverse local tissue reactions. Which of the following exact conditions is required for galvanic corrosion to occur?

. Cyclic mechanical loading of a single uniform metal type
. Fretting wear between a polyethylene liner and a metal cup
. Contact between two dissimilar metals in the presence of an electrolytic fluid
. Exposure of titanium to highly oxygenated arterial blood
. Sterilization of stainless steel hardware with gamma irradiation

Correct Answer & Explanation

. Contact between two dissimilar metals in the presence of an electrolytic fluid

Explanation

Galvanic corrosion is an electrochemical process that is driven by differences in the electrical potential of distinct materials. It occurs strictly when two dissimilar metals (e.g., stainless steel and titanium) are placed in direct physical contact with one another while simultaneously immersed in a conductive electrolytic solution (such as human extracellular fluid or blood). The metal with the lower electrical potential acts as an anode and undergoes accelerated corrosion.

Question 1424

Topic: Biomechanics & Biomaterials

In the biomechanical evaluation of tendons and ligaments, the phenomenon where a tissue subjected to a constant load deforms continuously over time is best described by which of the following terms?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent continuous deformation of a viscoelastic material under a constant load. Stress relaxation refers to the decrease in stress over time when the material is held at a constant length.

Question 1425

Topic: Biomechanics & Biomaterials

A researcher is studying articular cartilage biomechanics. Which zone of articular cartilage is characterized by the highest concentration of proteoglycans and collagen fibers oriented perpendicular to the joint surface?

. Superficial (tangential) zone
. Middle (transitional) zone
. Deep (radial) zone
. Calcified cartilage zone
. Tidemark

Correct Answer & Explanation

. Deep (radial) zone

Explanation

The deep (radial) zone contains the highest concentration of proteoglycans and features collagen fibers aligned vertically to resist compressive loads. The superficial zone has horizontal fibers to resist shear stress.

Question 1426

Topic: Biomechanics & Biomaterials

A surgeon revises a failed internal fixation of a femur fracture where a stainless steel plate was used with titanium screws. Extensive black debris and localized osteolysis are noted. What specific type of corrosion is primarily responsible for this failure?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (e.g., stainless steel and titanium) are in contact within an electrolytic fluid medium like blood. This electrochemical process accelerates the corrosion of the less noble metal.

Question 1427

Topic: Biomechanics & Biomaterials

In the context of limb salvage surgery for osteosarcoma, what is the main purpose of cement augmentation or polymethylmethacrylate (PMMA) during prosthetic fixation?

. To provide an osteoinductive surface for bone ingrowth.
. To act as a heat sink, preventing thermal injury to surrounding tissues.
. To provide immediate rigid fixation and potentially local chemotherapy delivery.
. To reduce the risk of infection by releasing antibiotics.
. To stimulate bone remodeling and healing around the implant.

Correct Answer & Explanation

. To provide immediate rigid fixation and potentially local chemotherapy delivery.

Explanation

PMMA (bone cement) is primarily used in prosthetic reconstruction to provide immediate, rigid fixation of the implant to the bone. Its rapid polymerization and mechanical interlock create a strong interface. Additionally, antibiotics (e.g., gentamicin, vancomycin) can be mixed into the cement, providing local antibiotic delivery and reducing the risk of infection, which is a major concern in these complex surgeries. It does not provide osteoinduction, act as a heat sink (it produces heat during polymerization), or primarily stimulate bone remodeling.

Question 1428

Topic: Biomechanics & Biomaterials

Which of the following contributes most significantly to the viscoelastic properties of the meniscus?

. Predominant type II collagen content.
. High concentration of elastin fibers.
. Interaction between water and proteoglycans within the extracellular matrix.
. The specific orientation of radial collagen fibers.
. Dense innervation by Pacinian corpuscles.

Correct Answer & Explanation

. Interaction between water and proteoglycans within the extracellular matrix.

Explanation

The viscoelastic properties of the meniscus, which allow it to absorb energy and deform under load while slowly recovering, are largely attributed to the interaction between its high water content (70-80%) and the negatively charged proteoglycan aggregates (primarily aggrecan). These proteoglycans attract and retain water, creating a fluid-filled matrix that resists compression and dissipates energy.

Question 1429

Topic: Biomechanics & Biomaterials

During a complex flexor tendon reconstruction in Zone II, the surgeon must prioritize preserving or reconstructing specific pulleys to prevent bowstringing and maintain digital kinematics. Which two pulleys are the most critical biomechanically?

. A1 and A3
. A2 and A4
. A3 and A5
. A1 and A5
. C1 and C2

Correct Answer & Explanation

. A2 and A4

Explanation

The A2 and A4 pulleys are the most crucial annular pulleys for preventing bowstringing and maintaining the functional excursion of the flexor tendons. They have broad osseous insertions onto the proximal and middle phalanges, respectively.

Question 1430

Topic: Biomechanics & Biomaterials

Regarding polymethylmethacrylate (PMMA) bone cement, which of the following statements is FALSE?

. It functions as a mechanical interlock rather than an adhesive bond.
. It undergoes an exothermic reaction during polymerization.
. Antibiotics can be safely mixed into the cement for local delivery.
. Its strength significantly increases with the addition of barium sulfate.
. The monomer is a known allergen and tissue irritant.

Correct Answer & Explanation

. The monomer is a known allergen and tissue irritant.

Explanation

The addition of barium sulfate (or zirconium dioxide) to PMMA bone cement is for radiopacity, allowing the cement to be visible on X-ray. It does not significantly increase thestrengthof the cement; in fact, it can slightly decrease mechanical properties. PMMA functions via mechanical interlock (macro- and micro-interlock) with trabecular bone. Its polymerization is an exothermic reaction. Antibiotics are commonly mixed in for prophylaxis or treatment of infection. The monomer (methyl methacrylate) is a known irritant and allergen.

Question 1431

Topic: Biomechanics & Biomaterials

The 'creep' phenomenon in viscoelastic materials like articular cartilage refers to:

. The rapid deformation under immediate load.
. The time-dependent increase in deformation under a constant load.
. The ability to recover original shape after load removal.
. The constant deformation regardless of applied load.
. The decrease in stress over time under constant deformation.

Correct Answer & Explanation

. The time-dependent increase in deformation under a constant load.

Explanation

Creep is the time-dependent increase in deformation (strain) of a material under a constant applied load (stress). In articular cartilage, this is due to the slow exudation of fluid from the matrix under sustained compression. Viscoelastic materials also exhibit stress relaxation (decrease in stress under constant strain) and hysteresis. The rapid deformation is instantaneous elastic response, recovery is elasticity/viscoelasticity, and constant deformation regardless of load is incorrect. Decrease in stress over time under constant deformation is stress relaxation.

Question 1432

Topic: Biomechanics & Biomaterials
Which type of collagen is the most abundant in mature, healthy bone and provides its primary tensile strength?
. Type I
. Type II
. Type III
. Type IX
. Type X

Correct Answer & Explanation

. Type I

Explanation

Type I collagen is the most abundant protein in the human body and constitutes approximately 90% of the organic matrix of bone. Its fibrous structure provides the bone's primary tensile strength and flexibility, complementing the compressive strength provided by the mineralized hydroxyapatite crystals. Type II collagen is found predominantly in cartilage, Type III in highly extensible tissues like skin and blood vessels (and early wound healing), and Types IX and X are associated with cartilage and the growth plate, respectively.

Question 1433

Topic: Biomechanics & Biomaterials

The mechanical behavior of articular cartilage is highly dependent on the interactions between collagen, proteoglycans, and water. What is the primary role of water in enabling cartilage's load-bearing function?

. Provides direct tensile strength.
. Acts as a lubricating agent only.
. Creates an osmotic pressure that resists compression.
. Initiates collagen synthesis.
. Maintains chondrocyte viability through oxygen transport.

Correct Answer & Explanation

. Creates an osmotic pressure that resists compression.

Explanation

Water, held within the aggrecan-hyaluronic acid complexes, creates a significant osmotic (swelling) pressure within the cartilage matrix. When compressive loads are applied, water is exuded, but the trapped proteoglycans resist this outflow, creating a fluid-pressurization effect that supports the load. This fluid-solid interaction is fundamental to cartilage's ability to resist compression and allows for its viscoelastic properties. While water aids lubrication and nutrient transport, its primary load-bearing role is via osmotic pressure.

Question 1434

Topic: Biomechanics & Biomaterials

Regarding implant materials, what is the primary advantage of titanium alloys (e.g., Ti-6Al-4V) over stainless steel (e.g., 316L) for orthopedic implants?

. Higher modulus of elasticity, reducing stress shielding.
. Superior corrosion resistance and biocompatibility.
. Greater ultimate tensile strength.
. Lower manufacturing cost.
. Significantly higher wear resistance.

Correct Answer & Explanation

. Superior corrosion resistance and biocompatibility.

Explanation

Titanium alloys are generally preferred for long-term orthopedic implants due to their superior corrosion resistance and excellent biocompatibility compared to stainless steel. They form a stable, passive oxide layer (TiO2) that prevents ion release. Titanium also has a lower modulus of elasticity than stainless steel (closer to bone), which can reduce stress shielding, making 'A' a plausible distractor but 'B' is a more encompassing primary advantage. Stainless steel often has higher ultimate tensile strength but is less bioinert. Titanium wear resistance is not universally superior; for example, ceramic is superior.

Question 1435

Topic: Biomechanics & Biomaterials

Which of the following statements about the mechanical properties of cancellous (trabecular) bone is MOST accurate?

. It is anisotropic, with strength varying significantly with load direction.
. It is typically stronger in tension than in compression.
. Its mechanical properties are largely independent of bone density.
. It has a lower modulus of elasticity and is more ductile than cortical bone.
. It is primarily designed to resist high torsional forces.

Correct Answer & Explanation

. It is anisotropic, with strength varying significantly with load direction.

Explanation

Cancellous bone, like cortical bone, is anisotropic. Its strength and stiffness vary significantly depending on the direction of loading, due to the orientation of its trabecular network along lines of stress. It is stronger in compression than tension. Its mechanical properties are highly dependent on bone density (volume fraction) and architecture. It is more compliant (lower modulus) and ductile than cortical bone, but this option isn't themostaccurate overall descriptor of its specific mechanical nature regarding anisotropy and density dependence. It is not primarily designed to resist high torsional forces, which are better handled by cortical bone.

Question 1436

Topic: Biomechanics & Biomaterials

The 'fatigue life' of an orthopedic implant refers to its ability to:

. Resist corrosion over its expected lifespan.
. Undergo plastic deformation without fracture.
. Withstand repeated cycles of loading without catastrophic failure.
. Maintain its mechanical properties at elevated temperatures.
. Undergo substantial elastic deformation before permanent change.

Correct Answer & Explanation

. Withstand repeated cycles of loading without catastrophic failure.

Explanation

Fatigue life is a critical material property for orthopedic implants. It refers to the number of stress cycles an implant can withstand before fracturing. Implants in the body are subjected to millions of loading cycles (e.g., walking, running) at stresses below their ultimate tensile strength. Fatigue failure is a common mode of implant failure, making high fatigue life a crucial design consideration. Plastic deformation without fracture is ductility; elastic deformation is elasticity.

Question 1437

Topic: Biomechanics & Biomaterials

The 'creep' phenomenon in a cancellous bone graft, if significant, could lead to:

. Accelerated revascularization of the graft.
. Increased mechanical stability of the construct.
. Loss of initial reduction and graft collapse.
. Enhanced osteoinduction within the graft.
. Reduced risk of infection due to improved perfusion.

Correct Answer & Explanation

. Loss of initial reduction and graft collapse.

Explanation

Creep in a bone graft refers to its time-dependent deformation under sustained load. If a cancellous bone graft, which has viscoelastic properties, is subjected to significant sustained compressive forces, it can slowly deform and collapse over time. This 'creep' can lead to a loss of initial reduction, settling of the construct, and potential instability, especially in reconstructive surgery where structural integrity is paramount. It does not directly affect revascularization, stability, osteoinduction, or infection risk in this manner.

Question 1438

Topic: Biomechanics & Biomaterials

The 'creep' property of a material refers to its time-dependent deformation under constant stress. In the context of orthopedic implants, a material with high creep resistance is generally preferred for components subjected to:

. Acute, high-impact loads.
. Cyclic, low-magnitude loads.
. Sustained, constant loads.
. Rapid, dynamic torsional loads.
. Loads primarily in shear.

Correct Answer & Explanation

. Sustained, constant loads.

Explanation

High creep resistance is desirable for implants subjected to sustained, constant loads, such as the acetabular component of a total hip arthroplasty, where the body weight can exert a continuous load. Creep deformation over time under these constant loads can lead to dimensional changes, implant loosening, or failure. Fatigue resistance is more relevant for cyclic loads, and yield strength/ultimate tensile strength for acute high-impact loads.

Question 1439

Topic: Biomechanics & Biomaterials

Which pre-viva preparation method is most effective for improving your ability to answer 'why' questions (e.g., 'Why do we use this implant?')?

. Memorizing only the steps of the implant insertion.
. Focusing on the biomechanical principles, material science, and clinical outcomes associated with different implants and techniques.
. Reading only the marketing brochures for various implants.
. Asking senior residents for their personal preferences.
. Reviewing the history of implant development.

Correct Answer & Explanation

. Focusing on the biomechanical principles, material science, and clinical outcomes associated with different implants and techniques.

Explanation

Answering 'why' questions requires understanding the underlying principles. For implants, this includes biomechanics, material properties, and evidence-based outcomes, which justify their selection and use in specific clinical scenarios.

Question 1440

Topic: Biomechanics & Biomaterials

During a revision open reduction and internal fixation of a nonunion, a surgeon considers supplementing an existing titanium alloy (Ti-6Al-4V) intramedullary nail with stainless steel (316L) cerclage wires. If these two different metals are placed in direct physical contact within the corrosive physiological environment of the human body, which of the following is the most likely biomechanical or biochemical consequence?

. Fretting corrosion of the titanium implant
. Galvanic corrosion of the titanium implant
. Galvanic corrosion of the stainless steel implant
. Crevice corrosion of the titanium implant
. Passivation of both implants preventing any further corrosion

Correct Answer & Explanation

. Galvanic corrosion of the stainless steel implant

Explanation

Mixing dissimilar metals in a conductive fluid environment (like the human body) leads to galvanic corrosion. The metal that is less noble (more anodic) will undergo accelerated corrosion. In the orthopaedic hierarchy of metals, titanium is more noble (cathodic) than 316L stainless steel. Therefore, the stainless steel implants will undergo accelerated galvanic corrosion when in direct contact with a titanium implant.

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