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Biomechanics & Biomaterials MCQs

Practice Set 47 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 921

Topic: Biomechanics & Biomaterials

In the design and selection of femoral stems for total hip arthroplasty, varying metal alloys are utilized based on their distinct mechanical properties. Compared to Cobalt-Chromium (CoCr) alloys, Titanium (Ti-6Al-4V) alloys exhibit which of the following characteristics?

. Higher modulus of elasticity
. Lower notch sensitivity
. Greater ultimate tensile strength
. Lower modulus of elasticity
. Increased resistance to abrasive wear

Correct Answer & Explanation

. Lower modulus of elasticity

Explanation

Titanium alloys (e.g., Ti-6Al-4V) have a lower modulus of elasticity compared to Cobalt-Chromium (CoCr) and stainless steel alloys. This lower modulus closer approximates the stiffness of cortical bone, which is highly beneficial for reducing stress shielding around femoral implants. However, titanium is highly notch sensitive (scratches act as significant stress risers) and has poor resistance to abrasive wear, making it inappropriate for use as a bearing surface (e.g., femoral heads).

Question 922

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) is the standard bearing surface in modern total hip arthroplasty due to its superior wear characteristics. Which of the following mechanical properties is significantly decreased as a direct consequence of increasing the cross-linking of UHMWPE?
. Fatigue crack propagation resistance
. Oxidation resistance
. Modulus of elasticity
. Melting temperature
. Adhesive wear resistance

Correct Answer & Explanation

. Fatigue crack propagation resistance

Explanation

While highly cross-linking UHMWPE dramatically improves its resistance to adhesive and abrasive wear (thereby reducing osteolysis), it negatively impacts several bulk mechanical properties. The most significant decreases are seen in ductility, ultimate tensile strength, fracture toughness, and fatigue crack propagation resistance. This reduction in fatigue strength makes highly cross-linked polyethylene more susceptible to mechanical failure, such as rim fracture in thin acetabular liners or post breakage in posterior-stabilized knee designs.

Question 923

Topic: Biomechanics & Biomaterials

A 65-year-old man undergoes total hip arthroplasty using a highly cross-linked polyethylene (HXLPE) liner. Which of the following manufacturing processes is primarily responsible for reducing the wear rate of HXLPE compared to conventional polyethylene, while simultaneously decreasing its fatigue strength?

. Addition of vitamin E prior to consolidation
. Electron beam or gamma irradiation
. Ethylene oxide gas sterilization
. Remelting below the melting temperature (annealing)
. Cold forging of the polymer resin

Correct Answer & Explanation

. Electron beam or gamma irradiation

Explanation

Highly cross-linked polyethylene (HXLPE) is created by exposing conventional polyethylene to high doses of gamma or electron beam irradiation. This process cleaves carbon-hydrogen bonds, creating free radicals that combine to form cross-links between polymer chains. This drastically improves adhesive and abrasive wear resistance but concurrently reduces mechanical properties such as fatigue strength, ultimate tensile strength, and ductility. Remelting or adding Vitamin E is done to eliminate or neutralize residual free radicals to prevent long-term oxidation, rather than to create the cross-links.

Question 924

Topic: Biomechanics & Biomaterials

An orthopedic surgeon applies a dynamic splint to correct a knee flexion contracture in a 12-year-old child. The splint is designed to hold the knee at a constant, fixed amount of extension. Over a 30-minute period, the patient notes that the splint feels less tight, and the surgeon measures a decrease in the force required to maintain this exact degree of extension. Which viscoelastic property of ligaments best explains this phenomenon?

. Creep
. Stress relaxation
. Hysteresis
. Strain-rate dependency
. Anisotropy

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a hallmark viscoelastic property defined as the decrease in stress (force) over time when a material is held at a constant strain (deformation or length). Because the dynamic splint holds the knee at a constant degree of extension (constant strain), the decline in the resisting force over time is due to stress relaxation. Creep, by contrast, is the progressive deformation (increase in length) over time when a material is subjected to a constant stress (force). Hysteresis refers to the energy lost as heat during a full cycle of loading and unloading.

Question 925

Topic: Biomechanics & Biomaterials

During the application of a cast to correct a clubfoot deformity using the Ponseti method, the orthopedist applies a constant corrective stretch to the ligaments over time. The observed gradual decrease in the force required to hold the foot in the corrected position is an example of which of the following viscoelastic properties?

. Creep
. Hysteresis
. Stress relaxation
. Anisotropy
. Isotropic behavior

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property defined as the progressive decrease in stress (or internal force) over time when a material is held at a constant strain (or deformation). In serial casting, holding the foot in a fixed, deformed position allows the soft tissues to undergo stress relaxation. In contrast, creep is the progressive deformation of a material over time under a constant load. Hysteresis refers to the energy lost (usually as heat) during the cyclic loading and unloading of a viscoelastic material.

Question 926

Topic: Biomechanics & Biomaterials

A 65-year-old man undergoes revision of a total hip arthroplasty. The surgeon utilizes a titanium alloy femoral stem and a cobalt-chromium femoral head. What type of corrosion is specifically driven by the electrochemical potential difference between these two dissimilar metals?

. 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 contact within an electrolytic solution (such as body fluid). The less noble metal acts as an anode and corrodes, while the more noble metal acts as a cathode. While fretting and crevice corrosion also occur at modular junctions, galvanic corrosion is the specific term for corrosion driven by the coupling of mixed metals.

Question 927

Topic: Biomechanics & Biomaterials

In the stress-strain curve of a healthy human ligament, the initial non-linear 'toe region' represents which of the following microscopic physiological events?

. Breaking of cross-links between collagen fibrils
. Plastic deformation of the extracellular matrix
. Uncrimping of the relaxed collagen fibers
. Microfailure of individual collagen bundles
. Complete macroscopic failure of the ligament

Correct Answer & Explanation

. Uncrimping of the relaxed collagen fibers

Explanation

The stress-strain curve for ligaments and tendons begins with a non-linear 'toe region.' This phase represents the physiological uncrimping or straightening of the wavy collagen fibers as tension is initially applied. After uncrimping, the curve enters the linear (elastic) region where the fibers themselves are stretched. Microfailure begins later at the yield point, entering the plastic region.

Question 928

Topic: Biomechanics & Biomaterials



A researcher is studying the failure mechanisms of orthopedic implants in an animal model. A stainless steel screw is deliberately used to secure a titanium alloy plate. What is the most likely mode of corrosion to occur at the interface of these two implants in vivo?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals are placed in direct contact within an electrolytic medium, such as bodily fluids. The less noble metal becomes the anode and undergoes accelerated corrosion, while the more noble metal becomes the cathode. To prevent this, mixing dissimilar metals like stainless steel and titanium in a single construct is generally avoided.

Question 929

Topic: Biomechanics & Biomaterials

During the static stretching phase of a physical therapy protocol for Achilles tendinopathy, a therapist notes that when the tendon is stretched to a specific length and held constant, the internal force required to maintain that length gradually decreases over time. This specific biomechanical property is termed:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a hallmark viscoelastic property characterized by a decrease in stress (force) over time when a material is held at a constant strain (length or deformation). Creep, conversely, is the progressive increase in strain (deformation) over time when a constant stress (load) is applied. Hysteresis refers to the energy lost as heat during the loading and unloading cycles of a viscoelastic material.

Question 930

Topic: Biomechanics & Biomaterials

Which of the following statements best describes the biomechanical property of an implant that determines its rigidity and is represented by the slope of the linear portion of the stress-strain curve?

. Toughness
. Fatigue limit
. Yield strength
. Modulus of elasticity
. Ultimate tensile strength

Correct Answer & Explanation

. Modulus of elasticity

Explanation

Modulus of elasticity (Young's modulus) is the measure of a material's intrinsic stiffness. It is calculated as the slope of the linear (elastic) portion of the stress-strain curve. A higher modulus indicates a stiffer material. Toughness is the energy absorbed up to the point of failure (area under the entire curve). Yield strength is the stress at which plastic deformation begins. Ultimate tensile strength is the maximum stress the material can withstand.

Question 931

Topic: Biomechanics & Biomaterials



Mixed-metal constructs, such as using a stainless steel screw with a titanium plate, are generally avoided in orthopedic surgery. Which specific type of corrosion is most likely to occur in this scenario?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two electrochemically dissimilar metals (e.g., stainless steel and titanium) are placed in physical contact within a conductive electrolyte medium, such as human bodily fluid. The less noble metal becomes the anode and undergoes accelerated corrosion, while the more noble metal acts as the cathode. Fretting corrosion, by contrast, is caused by micromotion between two surfaces.

Question 932

Topic: Biomechanics & Biomaterials

During an anterior cruciate ligament (ACL) reconstruction, a surgeon tensions the tendon graft to a specific length and fixes it. Over the next several minutes, the tension (force) required by the fixation device to maintain that exact length slowly decreases. Which of the following viscoelastic properties best describes this phenomenon?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Tendons and ligaments are viscoelastic materials, meaning their mechanical response depends on the rate and duration of loading. Stress relaxation is defined as the decrease in stress (or force) over time when the material is held at a constant strain (constant length). Conversely, creep is the progressive deformation (increase in length) over time when a material is subjected to a constant load (constant stress). Hysteresis refers to the energy lost (usually as heat) during a loading and unloading cycle.

Question 933

Topic: Biomechanics & Biomaterials

A surgeon performs an open reduction and internal fixation of a diaphyseal fracture using a titanium alloy (Ti-6Al-4V) plate and secures it with 316L stainless steel screws. The physiologic environment surrounding this mixed-metal construct will most likely predispose it to which of the following phenomena?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Intergranular corrosion
. Passivation

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different electrochemical potentials are placed in contact within a conductive electrolytic solution (like bodily fluids). The less noble metal (anode) will corrode more rapidly, while the more noble metal (cathode) remains protected. In a titanium-stainless steel construct, stainless steel acts as the anode and corrodes, while titanium acts as the cathode. Thus, mixing these specific metals is generally avoided in orthopedic surgery.

Question 934

Topic: Biomechanics & Biomaterials

Biomechanical compatibility between orthopedic implants and native bone is essential to prevent stress shielding. Which of the following lists correctly orders orthopedic materials from the lowest modulus of elasticity (most flexible) to the highest modulus of elasticity (stiffest)?

. Cortical bone, Titanium alloy, Stainless steel, Cobalt-chromium alloy
. Titanium alloy, Cortical bone, Stainless steel, Cobalt-chromium alloy
. Cortical bone, Stainless steel, Titanium alloy, Cobalt-chromium alloy
. Cancellous bone, Cobalt-chromium alloy, Titanium alloy, Cortical bone
. Titanium alloy, Cortical bone, Cobalt-chromium alloy, Stainless steel

Correct Answer & Explanation

. Cortical bone, Stainless steel, Titanium alloy, Cobalt-chromium alloy

Explanation

The modulus of elasticity (Young's modulus) represents the stiffness of a material. To minimize stress shielding, implant materials ideally should have a modulus closer to that of bone. Cortical bone has a modulus of approximately 15-20 GPa. Titanium alloy (Ti-6Al-4V) is approximately 110 GPa. Stainless steel (316L) is approximately 200 GPa. Cobalt-chromium alloys are the stiffest, with a modulus around 220-240 GPa. Thus, the correct order from lowest to highest stiffness is Cortical bone < Titanium alloy < Stainless steel < Cobalt-chromium alloy.

Question 935

Topic: Biomechanics & Biomaterials

When evaluating the mechanical properties of an orthopedic implant, the stress-strain curve provides essential data.

Which of the following points on the curve represents the maximum stress a material can withstand before it begins to neck and ultimately fail?

. Yield point
. Proportional limit
. Ultimate tensile strength
. Failure point
. Endurance limit

Correct Answer & Explanation

. Ultimate tensile strength

Explanation

The Ultimate Tensile Strength (UTS) is the peak point on the stress-strain curve and represents the maximum stress a material can withstand before failure. After this point, the material begins to 'neck' (in ductile materials) and stress decreases until the failure point is reached. The yield point is the point at which elastic deformation transitions to plastic (irreversible) deformation.

Question 936

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, the wear properties of ultra-high-molecular-weight polyethylene (UHMWPE) are critical to long-term implant survival. Which of the following processing techniques optimizes wear resistance while minimizing the risk of oxidative degradation?
. Gamma irradiation in an oxygen-rich environment
. Ethylene oxide sterilization followed by natural aging
. Gamma irradiation in an inert gas environment followed by remelting
. Non-irradiated UHMWPE sterilized with hydrogen peroxide plasma
. Autoclave sterilization at 120°C

Correct Answer & Explanation

. Gamma irradiation in an inert gas environment followed by remelting

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured by subjecting UHMWPE to gamma or electron beam irradiation, which creates free radicals that form cross-links between polymer chains. This significantly improves wear resistance. However, residual free radicals can react with oxygen over time, leading to oxidative degradation and embrittlement. To prevent this, the irradiated polyethylene undergoes a thermal treatment—either remelting (heating above the melting point) or annealing (heating just below the melting point)—often in an inert gas environment or vacuum, to quench the residual free radicals.

Question 937

Topic: Biomechanics & Biomaterials

During the clinical examination of a patient with a chronic knee flexion contracture, dynamic splinting is applied to provide a constant, low-load stretch to the posterior soft tissues. Over time, the contracted ligaments and capsule gradually elongate. Which of the following viscoelastic properties does this process demonstrate?

. Stress relaxation
. Creep
. Hysteresis
. Isotropic deformation
. Anisotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation (elongation) of a viscoelastic material when subjected to a constant, sustained load over time. This principle is applied clinically in dynamic splinting and serial casting. In contrast, stress relaxation refers to the decrease in stress (force) within a material over time when it is held at a constant deformation (length). Hysteresis is the energy lost as heat during the loading and unloading cycle of a viscoelastic material.

Question 938

Topic: Biomechanics & Biomaterials

A 45-year-old man undergoes revision internal fixation of a femoral nonunion. The surgeon plans to use a titanium alloy plate for stabilization. Which of the following screw materials, if used in combination with this titanium plate, would be most likely to result in significant galvanic corrosion, and which material would preferentially undergo corrosive degradation?

. Stainless steel screws; the stainless steel will preferentially corrode.
. Stainless steel screws; the titanium will preferentially corrode.
. Cobalt-chromium screws; the cobalt-chromium will preferentially corrode.
. Cobalt-chromium screws; the titanium will preferentially corrode.
. Titanium alloy screws; the titanium will preferentially corrode.

Correct Answer & Explanation

. Stainless steel screws; the stainless steel will preferentially corrode.

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in an electrolytic solution (like bodily fluids), causing the less noble (more anodic) metal to corrode. In the galvanic series, titanium and cobalt-chromium are more noble (cathodic) compared to 316L stainless steel (anodic). If stainless steel screws are used with a titanium plate, the stainless steel acts as the anode and will preferentially corrode. Mixing stainless steel with titanium or cobalt-chromium implants is generally contraindicated in orthopedics for this reason.

Question 939

Topic: Biomechanics & Biomaterials
In the manufacturing of ultra-high-molecular-weight polyethylene (UHMWPE) for total joint arthroplasty, highly cross-linking the polyethylene via gamma irradiation provides which of the following combinations of material property changes when compared to conventional UHMWPE?
. Increased wear resistance, increased ultimate tensile strength, and decreased oxidative stability.
. Increased wear resistance, decreased fatigue strength, and decreased yield strength.
. Decreased wear resistance, increased fatigue strength, and increased toughness.
. Increased wear resistance, increased fatigue strength, and increased toughness.
. Decreased wear resistance, decreased fatigue strength, and increased oxidative stability.

Correct Answer & Explanation

. Increased wear resistance, decreased fatigue strength, and decreased yield strength.

Explanation

Highly cross-linked polyethylene (HXLPE) is created by exposing UHMWPE to gamma or electron beam irradiation, which forms covalent bonds between adjacent polymer chains. This cross-linking significantly improves the adhesive and abrasive wear resistance of the material, substantially reducing osteolysis rates. However, this process alters the crystalline structure, resulting in a degradation of mechanical properties, including decreased ductility, decreased fracture toughness, decreased fatigue strength, and decreased yield/ultimate tensile strength.

Question 940

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced the rate of wear. What is the primary trade-off or disadvantage associated with increasing the cross-linking dose in ultra-high-molecular-weight polyethylene (UHMWPE)?
. Increased adhesive wear
. Decreased ultimate tensile strength and fatigue resistance
. Decreased oxidative stability
. Increased third-body wear
. Increased generation of submicron particles per volume of wear

Correct Answer & Explanation

. Decreased ultimate tensile strength and fatigue resistance

Explanation

Increasing the radiation dose to cross-link UHMWPE decreases its ultimate tensile strength, yield strength, and fatigue resistance (fracture toughness). To mitigate oxidative degradation, it is often remelted or annealed, or doped with Vitamin E. However, the primary mechanical trade-off of high cross-linking is reduced fatigue strength, making it more susceptible to fracture under high-stress conditions or when used in thin liners.

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