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Biomechanics & Biomaterials MCQs

Practice Set 45 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 881

Topic: Biomechanics & Biomaterials

A stress-strain curve representing a typical metallic orthopedic implant under tension is analyzed.

Which of the following accurately describes the 'yield point' on this curve?

. The point at which the material undergoes complete structural failure
. The transition point from reversible elastic deformation to irreversible plastic deformation
. The total area under the elastic portion of the curve
. The maximum stress the material can withstand before necking occurs
. The linear slope of the initial portion of the curve

Correct Answer & Explanation

. The transition point from reversible elastic deformation to irreversible plastic deformation

Explanation

The yield point marks the transition from elastic deformation (where the material returns to its original shape when unloaded) to plastic deformation (where irreversible deformation occurs). The total area under the elastic curve is resilience. The maximum stress is the ultimate tensile strength. The linear slope represents Young's modulus of elasticity.

Question 882

Topic: Biomechanics & Biomaterials

Orthopedic stainless steel implants (e.g., 316L) are composed primarily of iron, chromium, and nickel. What is the primary functional reason for adding molybdenum to this alloy?

. To increase the modulus of elasticity to match cortical bone
. To improve fatigue strength and limit brittle failure
. To enhance resistance to pitting and crevice corrosion in chloride-rich environments
. To minimize the host foreign-body giant cell reaction
. To stabilize the alpha phase of the internal crystalline structure

Correct Answer & Explanation

. To enhance resistance to pitting and crevice corrosion in chloride-rich environments

Explanation

The 'L' in 316L stainless steel stands for low carbon, which prevents intergranular corrosion. The addition of molybdenum (usually 2-3%) specifically improves the alloy's resistance to pitting and crevice corrosion, which is critical in the chloride-rich physiological environment of the human body. Chromium provides a passivating oxide layer, and nickel stabilizes the austenitic face-centered cubic crystal structure.

Question 883

Topic: Biomechanics & Biomaterials
Highly cross-linked polyethylene (HXLPE) is widely used in total hip arthroplasty due to its superior wear characteristics. However, the process of cross-linking and subsequent remelting/annealing directly diminishes which of the following mechanical properties?
. Abrasive wear resistance
. Adhesive wear resistance
. Resistance to oxidative degradation
. Galvanic corrosion resistance
. Fatigue strength and fracture toughness

Correct Answer & Explanation

. Fatigue strength and fracture toughness

Explanation

While high-dose irradiation cross-linking of ultra-high-molecular-weight polyethylene (UHMWPE) dramatically reduces adhesive and abrasive wear, the cross-linking process and subsequent thermal treatments (remelting) significantly decrease mechanical properties such as fatigue strength, fracture toughness, and ultimate tensile strength. This makes HXLPE more vulnerable to rim cracking or failure under high-stress conditions or thin components.

Question 884

Topic: Biomechanics & Biomaterials

A load-deformation curve of a bone specimen is shown in Figure 1.

Which of the following parameters represents the material's toughness?

. The slope of the linear elastic region
. The peak load achieved before failure
. The area under the entire stress-strain curve
. The point at which the curve transitions from linear to non-linear
. The maximum deformation before yield

Correct Answer & Explanation

. The area under the entire stress-strain curve

Explanation

Toughness is defined as the amount of energy a material can absorb before it fractures, represented by the total area under the stress-strain curve. The slope of the linear elastic region represents the elastic modulus (stiffness). The peak load is the ultimate strength. The transition point from linear to non-linear is the yield point, marking the end of elastic deformation and the beginning of plastic deformation.

Question 885

Topic: Biomechanics & Biomaterials
Cross-linking of ultra-high-molecular-weight polyethylene (UHMWPE) components in total joint arthroplasty is primarily performed to improve which of the following properties?
. Tensile strength
. Fatigue resistance
. Abrasive wear resistance
. Fracture toughness
. Yield strength

Correct Answer & Explanation

. Abrasive wear resistance

Explanation

Highly cross-linked polyethylene (HXLPE) is irradiated to create free radicals that form cross-links, which significantly increases the material's abrasive wear resistance. However, this cross-linking process inherently decreases other mechanical properties, including tensile strength, fracture toughness, and fatigue resistance. Post-irradiation melting or annealing is done to extinguish remaining free radicals and prevent oxidation.

Question 886

Topic: Biomechanics & Biomaterials

During the biomechanical testing of a native human tendon, the initial portion of the stress-strain curve exhibits a non-linear, concave upward slope prior to entering the linear elastic region. This specific portion of the curve, known as the 'toe region,' is primarily due to:

. Microfailure of individual collagen fibrils
. Macroscopic tearing of the tendon substance
. The un-crimping of naturally wavy collagen fibers
. The transition from elastic to plastic deformation
. Expulsion of water from the proteoglycan matrix

Correct Answer & Explanation

. The un-crimping of naturally wavy collagen fibers

Explanation

The 'toe region' is the initial, non-linear segment of the stress-strain curve for ligaments and tendons where relatively little stress causes significant initial strain. Biologically, this corresponds to the 'un-crimping' or straightening of the naturally crimped (wavy) type I collagen fibers. Once the fibers are completely straight, the curve enters the linear elastic region. Microfailure occurs later, past the yield point in the plastic region.

Question 887

Topic: Biomechanics & Biomaterials

A patient presents with a painful, swollen thigh 5 years after an open reduction and internal fixation of a femur fracture. Radiographs show localized radiolucency around a stainless steel screw that was inadvertently placed through a titanium alloy plate. What is the primary mechanism of implant failure in this scenario?

. Crevice corrosion
. Galvanic corrosion
. Fretting 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 placed in direct physical contact within a conductive electrolytic fluid (such as body fluids). This creates an electrochemical potential difference, leading to an exchange of electrons and accelerated corrosion of the less noble metal (anode). This is why mixing dissimilar metals in a single construct is generally contraindicated.

Question 888

Topic: Biomechanics & Biomaterials

During tensile mechanical testing of a normal, healthy ligament, a characteristic stress-strain curve is generated. What structural phenomenon is responsible for the initial 'toe region' of this curve?

. Microscopic tearing of individual collagen fibers
. Macroscopic failure of the tendon mid-substance
. Uncrimping of the naturally wavy collagen fibrils
. Plastic deformation of the extracellular matrix
. Elastic stretching of the completely straightened collagen fibers

Correct Answer & Explanation

. Uncrimping of the naturally wavy collagen fibrils

Explanation

The 'toe region' is the initial non-linear portion of the stress-strain curve for ligaments and tendons. It represents the elongation of the tissue with very little applied stress. This occurs due to the 'uncrimping' or straightening of the relaxed, naturally wavy collagen fibrils. Once the fibers are straight, the tissue enters the linear elastic region where stiffness increases.

Question 889

Topic: Biomechanics & Biomaterials
Which of the following modifications to ultra-high molecular weight polyethylene (UHMWPE) used in total joint arthroplasty most effectively reduces adhesive and abrasive wear while preserving oxidation resistance?
. Gamma irradiation in the presence of an oxygen-rich environment
. Decreasing the overall degree of crystallinity of the polymer
. Highly cross-linking the polymer chains followed by remelting
. Increasing the free radical concentration within the polymer matrix
. Utilizing a non-cross-linked, non-irradiated pristine resin

Correct Answer & Explanation

. Highly cross-linking the polymer chains followed by remelting

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured using gamma or electron beam irradiation, which breaks polymer chains and facilitates cross-linking. This significantly improves wear resistance, reducing adhesive and abrasive wear. However, irradiation creates free radicals that can react with oxygen over time, leading to oxidative degradation and embrittlement. To combat this, the polyethylene is often remelted (heated above its melting point) to extinguish these free radicals, thereby preserving oxidation resistance, although remelting can cause a slight decrease in fatigue strength compared to annealing (heating below the melting point).

Question 890

Topic: Biomechanics & Biomaterials

A surgeon is revising a nonunion of a femoral shaft fracture initially treated with a stainless steel dynamic compression plate. The surgeon plans to retain a broken stainless steel screw embedded in the far cortex but will place a new titanium intramedullary nail. What specific mode of corrosion is at greatest risk of occurring if these two distinct metals are in direct contact within the biologic environment?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in direct physical contact within a conductive fluid medium (e.g., serum or body fluids). An electrochemical potential difference is established, which drives the accelerated corrosion of the less noble metal (anodic dissolution). For this reason, combining stainless steel and titanium implants in direct contact is generally contraindicated.

Question 891

Topic: Biomechanics & Biomaterials



A load-deformation (stress-strain) curve for a standard orthopedic structural construct is evaluated. The specific point on the curve where the construct permanently transitions from elastic deformation to plastic deformation is known as the:

. Yield point
. Ultimate failure point
. Proportional limit
. Point of catastrophic failure
. Endurance limit

Correct Answer & Explanation

. Yield point

Explanation

The yield point marks the precise transition between the elastic region (where removal of the load results in full recovery of the material's original shape) and the plastic region (where microscopic structural changes occur, and permanent deformation remains after load removal). The proportional limit is slightly earlier on the curve, representing the true end of the linear elastic relationship (Hooke's Law), though the two points are typically located very close together.

Question 892

Topic: Biomechanics & Biomaterials

Tendons and ligaments exhibit distinct viscoelastic properties, meaning their biomechanical response depends heavily on the rate and duration of loading. Which of the following best describes the phenomenon of 'creep' in an orthopaedic viscoelastic tissue?

. Progressive and increasing deformation over time under a constant load
. Progressive decrease in load over time required to maintain a constant deformation
. Energy loss during a cyclical loading and unloading cycle
. The failure of a material after repeated loading below its ultimate tensile strength
. The nonlinear initial portion of a load-deformation curve where collagen fibers un-crimp

Correct Answer & Explanation

. Progressive and increasing deformation over time under a constant load

Explanation

Creep is a fundamental viscoelastic property defined as the progressive deformation of a material over time when subjected to a constant load. Option B describes stress relaxation. Option C describes hysteresis. Option D describes fatigue failure. Option E describes the 'toe region' of the load-deformation curve.

Question 893

Topic: Biomechanics & Biomaterials

A 45-year-old patient requires a revision of a previously placed plate and screw construct for a nonunion. Intraoperatively, black metallosis debris is noted specifically at the screw-plate interface.

Assuming both the plate and the screws are composed of the exact same 316L stainless steel alloy, which of the following represents the primary mechanism for this localized corrosion?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Fretting corrosion occurs when there is micromotion between two closely apposed surfaces of the same material, such as the interface between a screw head and a plate hole. This mechanical micromotion repeatedly destroys the self-passivating oxide layer, leading to localized corrosion and black debris. Galvanic corrosion requires dissimilar metals. Crevice corrosion occurs in oxygen-depleted zones but is not primarily driven by the mechanical micromotion described.

Question 894

Topic: Biomechanics & Biomaterials
A patient undergoes a total hip arthroplasty using a highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) liner. Evaluation of the liner mechanics in a laboratory model shows dimensional changes over time when subjected to a constant physiological load, without the generation of particulate debris. Which of the following biomechanical phenomena best describes this finding?
. Abrasive wear
. Creep
. Adhesive wear
. Fatigue failure
. Galvanic corrosion

Correct Answer & Explanation

. Creep

Explanation

Creep, or cold flow, is the progressive deformation of a viscoelastic material under a constant load over time. In UHMWPE components, this dimensional change occurs without the generation of wear debris. This is distinct from abrasive or adhesive wear, which involve the physical removal of material and generation of particulate debris that can lead to osteolysis.

Question 895

Topic: Biomechanics & Biomaterials

When comparing a solid titanium alloy (Ti-6Al-4V) intramedullary nail to a solid stainless steel (316L) intramedullary nail of the identical diameter and cross-sectional design, which of the following biomechanical statements is most accurate?

. The titanium nail has a higher modulus of elasticity.
. The titanium nail has a lower modulus of elasticity.
. The stainless steel nail provides superior biocompatibility and osteointegration.
. The stainless steel nail is more susceptible to galvanic corrosion when used in isolation.
. The titanium nail exhibits higher yield strength but lower ultimate tensile strength.

Correct Answer & Explanation

. The titanium nail has a lower modulus of elasticity.

Explanation

Titanium alloys have a lower modulus of elasticity (closer to that of cortical bone) compared to stainless steel. This property makes titanium more flexible and reduces stress shielding at the fracture site. Stainless steel has a much higher modulus of elasticity, making it significantly stiffer. Both materials are highly biocompatible, though titanium generally exhibits superior osteointegration.

Question 896

Topic: Biomechanics & Biomaterials

A surgeon is revising a failed subtrochanteric femur fracture fixation. The original construct consisted of a titanium intramedullary nail and a stainless steel cerclage wire. Upon removal, significant dark tissue staining and localized metal degradation are noted precisely at the contact point between the wire and the nail. Which of the following principles best explains this phenomenon?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (e.g., titanium and stainless steel) are in direct physical contact within an electrolytic medium (such as human body fluids). This creates a galvanic cell, leading to accelerated corrosion of the less noble (more anodic) metal. Fretting corrosion is a mechanically induced process caused by micromotion, while crevice corrosion occurs in oxygen-depleted micro-environments like the interface between a screw head and a plate of the same material.

Question 897

Topic: Biomechanics & Biomaterials

Stress-shielding around a rigid femoral stem is a well-known cause of aseptic loosening and proximal femoral bone resorption. To minimize stress shielding based on material properties, an implant should theoretically possess a modulus of elasticity that closely mimics that of cortical bone. Which of the following structural implant biomaterials has a modulus of elasticity closest to that of human cortical bone?

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

Correct Answer & Explanation

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

Explanation

Cortical bone has a modulus of elasticity of roughly 15-20 GPa. Titanium alloys (e.g., Ti-6Al-4V) have a modulus of elasticity of approximately 110 GPa. While still stiffer than bone, titanium is much closer to cortical bone's modulus than other structural metals such as 316L stainless steel (~200 GPa) or cobalt-chromium alloys (~220 GPa). Ceramics like alumina have even higher stiffness (~380-400 GPa). Thus, titanium alloy is widely used for cementless femoral stems to help decrease stress shielding.

Question 898

Topic: Biomechanics & Biomaterials

An orthopedic resident proposes using a titanium alloy plate fixed with 316L stainless steel screws for a complex forearm fracture. The attending surgeon correctly rejects this plan due to the risk of accelerated degradation. The primary reason for avoiding this mixture of metals in vivo is:

. Titanium causes rapid osteolysis when placed adjacent to stainless steel.
. The significant difference in their modulus of elasticity causes extreme stress shielding.
. Mixing these dissimilar metals creates a galvanic cell, leading to accelerated corrosion of the stainless steel.
. The titanium plate will undergo rapid fretting corrosion due to its lower hardness.
. Stainless steel screws cannot achieve adequate torque in titanium plate holes.

Correct Answer & Explanation

. Mixing these dissimilar metals creates a galvanic cell, leading to accelerated corrosion of the stainless steel.

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic solution, such as bodily fluids. The metals have different resting electrochemical potentials, establishing a galvanic cell. The metal that is more anodic (less noble)โ€”in this case, stainless steel compared to titaniumโ€”will act as the anode and undergo accelerated corrosion. This can lead to implant failure, loosening, and adverse local tissue reactions to the metallic ions released.

Question 899

Topic: Biomechanics & Biomaterials

During the clinical management of a severe clubfoot, a pediatric orthopedist applies a serial corrective cast. The constant, fixed deformation (stretch) applied to the medial soft tissues and Achilles tendon over several days results in a gradual decrease in the internal load (tension) required to maintain that specific stretch. Which viscoelastic property does this describe?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the viscoelastic phenomenon where a material experiences a decrease in stress (internal load or tension) over time when subjected to a constant strain (a fixed deformation or length, as in a cast). Creep, conversely, is the progressive increase in strain (deformation) over time under a constant stress (load, such as constant traction). Hysteresis refers to the energy lost as heat during a loading and unloading cycle. Anisotropy refers to mechanical properties varying depending on the direction of loading.

Question 900

Topic: Biomechanics & Biomaterials

A surgeon performs an open reduction and internal fixation of a distal femur fracture. Due to a shortage of matching inventory, a stainless steel plate is secured using titanium alloy screws. Six months later, the patient experiences pain, and radiographs reveal localized osteolysis and loosening around the screws. What type of biomaterial corrosion is most likely responsible for this failure?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as stainless steel and titanium) are placed in direct physical contact within a conducting fluid medium (e.g., serum or extracellular fluid). This creates an electrochemical cell where the less noble metal acts as an anode and corrodes rapidly. To prevent this, orthopedic implants of different metallurgical compositions should generally not be mixed in a single construct.

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