Menu

Biomechanics & Biomaterials MCQs

Practice Set 46 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 901

Topic: Biomechanics & Biomaterials
To reduce wear and improve longevity in total joint arthroplasty, ultra-high molecular weight polyethylene (UHMWPE) is subjected to irradiation to induce cross-linking. In newer generations of highly cross-linked polyethylene, Vitamin E (alpha-tocopherol) is often blended into the polymer. The primary function of Vitamin E in this context is to:
. Increase the degree of cross-linking
. Increase the crystallinity of the polymer
. Reduce the elastic modulus of the bearing surface
. Quench free radicals and prevent oxidation
. Promote osteoblast adhesion to the liner

Correct Answer & Explanation

. Quench free radicals and prevent oxidation

Explanation

Gamma irradiation of UHMWPE creates cross-links that improve wear resistance, but it also generates free radicals that can react with oxygen over time, leading to oxidative degradation and embrittlement. Historically, post-irradiation melting was used to eliminate free radicals, but this reduced crystallinity and mechanical strength. Vitamin E is a biologic antioxidant that is added to quench these free radicals, preventing oxidation without the need for melting, thereby preserving the mechanical properties of the highly cross-linked polyethylene.

Question 902

Topic: Biomechanics & Biomaterials

During an anterior cruciate ligament (ACL) reconstruction, a surgeon pre-tensions a quadrupled hamstring graft on a back table. The graft is held at a constant stretched length for 10 minutes. The surgical assistant notes that the force required to hold the graft at this length gradually decreases over time. This viscoelastic property is best termed:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a fundamental viscoelastic property of ligaments and tendons where the stress (force) within the material decreases over time when it is held at a constant strain (deformation or length). In contrast, creep is the progressive increase in deformation (strain) over time when a constant load (stress) is applied. Hysteresis refers to the energy lost as heat during the loading and unloading cycle of a viscoelastic material.

Question 903

Topic: Biomechanics & Biomaterials

A 65-year-old man undergoes revision total hip arthroplasty for a painful, failing implant. Intraoperatively, black debris and significant tissue necrosis are noted around the modular head-neck junction of the femoral component, which consists of a cobalt-chromium head on a titanium alloy stem. What is the primary mechanism of this localized corrosion?

. Galvanic corrosion
. Mechanically assisted crevice corrosion
. Pitting corrosion
. Stress corrosion cracking
. Uniform attack corrosion

Correct Answer & Explanation

. Mechanically assisted crevice corrosion

Explanation

Trunnionosis at the modular head-neck junction of a total hip arthroplasty is primarily due to mechanically assisted crevice corrosion (MACC). Fretting (micro-motion) between the two metal surfaces disrupts the protective passive titanium dioxide oxide layer, allowing crevice corrosion to rapidly occur in the localized, confined space of the taper where oxygen depletion changes the local chemical environment.

Question 904

Topic: Biomechanics & Biomaterials

A surgeon performs an open reduction and internal fixation of a comminuted femur fracture using a 316L stainless steel plate and titanium alloy screws due to a shortage of matching stainless steel screws. Two years later, the patient presents with thigh pain and radiographic evidence of hardware failure and localized osteolysis.

What specific type of biomaterial degradation is predominantly driven by the electrochemical potential difference between these two intimately mixed metals in a physiological fluid medium?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct electrical contact within a conductive fluid medium (such as human serum or interstitial fluid). The metal with the lower electrochemical potential (less noble) acts as an anode and preferentially corrodes, while the more noble metal acts as the cathode. Mixing stainless steel (less noble) with titanium (more noble) can lead to accelerated galvanic corrosion of the stainless steel. Crevice corrosion occurs in restricted spaces (like under a screw head) due to oxygen depletion. Fretting corrosion is mechanically driven by micromotion disrupting the passivation layer. Pitting is localized corrosion forming small holes, and intergranular corrosion occurs at grain boundaries, often related to manufacturing impurities.

Question 905

Topic: Biomechanics & Biomaterials
To improve the wear characteristics of total hip arthroplasty bearing surfaces, ultra-high-molecular-weight polyethylene (UHMWPE) is often subjected to gamma irradiation to induce cross-linking. While highly cross-linked polyethylene (HXLPE) demonstrates significantly reduced adhesive and abrasive wear, which of the following is an expected mechanical trade-off when compared to conventional UHMWPE?
. Increased ultimate tensile strength
. Decreased fatigue strength and fracture toughness
. Increased adhesive wear volume
. Decreased resistance to oxidative degradation prior to thermal stabilization
. Elimination of all free radicals without the need for thermal treatment

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured by exposing UHMWPE to gamma or electron beam irradiation, which breaks carbon-hydrogen bonds and allows adjacent polymer chains to cross-link. This dramatically reduces adhesive and abrasive wear. However, the cross-linking process decreases the polymer's ductility, yield strength, ultimate tensile strength, fatigue strength, and fracture toughness. Additionally, irradiation creates free radicals that can lead to oxidative degradation over time; thus, thermal treatments (melting or annealing) or the addition of antioxidants (like Vitamin E) are required to quench these free radicals. Melting further reduces the mechanical properties.

Question 906

Topic: Biomechanics & Biomaterials
A 65-year-old active male undergoes a total hip arthroplasty using a highly cross-linked polyethylene (HXLPE) liner. While cross-linking polyethylene significantly improves its wear characteristics, the process of irradiation and subsequent thermal treatment alters other mechanical properties. Compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE), which of the following is an expected biomechanical trade-off of using HXLPE?
. Decreased resistance to adhesive wear
. Increased yield strength
. Decreased ultimate tensile strength
. Increased oxidation potential
. Increased fatigue crack propagation resistance

Correct Answer & Explanation

. Decreased ultimate tensile strength

Explanation

Highly cross-linked polyethylene is manufactured by exposing UHMWPE to gamma or electron beam irradiation, creating free radicals that bond to form cross-links. While this significantly decreases adhesive and abrasive wear, it negatively impacts other mechanical properties. The necessary thermal treatments (melting or annealing) used to extinguish residual free radicals decrease the material's crystallinity. This results in decreased ultimate tensile strength, yield strength, and fracture toughness (fatigue crack propagation resistance).

Question 907

Topic: Biomechanics & Biomaterials

Stress shielding and subsequent bone resorption around a femoral stem are related to the difference in the modulus of elasticity between the metallic implant and the host bone. Cortical bone has a modulus of elasticity of approximately 15-20 GPa. Which of the following standard orthopedic implant materials has a modulus of elasticity that most closely approximates that of native cortical bone?

. Alumina ceramic
. Cobalt-chromium alloy
. Stainless steel
. Titanium alloy
. Zirconia ceramic

Correct Answer & Explanation

. Titanium alloy

Explanation

The modulus of elasticity (Young's modulus) represents a material's stiffness. Cortical bone has a modulus of roughly 15-20 GPa. Titanium alloy is roughly 100-110 GPa, which is the closest of the commonly used bulk structural metals. Stainless steel has a modulus of roughly 200 GPa, and Cobalt-chromium alloy is approximately 220-240 GPa. Ceramics like alumina and zirconia are much stiffer (>300 GPa). Because titanium is closest to cortical bone, it typically generates less stress shielding than stainless steel or cobalt-chromium.

Question 908

Topic: Biomechanics & Biomaterials

A neonate with a clubfoot deformity undergoes weekly manipulations and applications of a Ponseti cast. The cast holds the foot in a constantly deformed, corrected position. Over the course of the week, the tension felt within the contracted medial soft tissues gradually decreases without any further manipulation. Which biomechanical property of viscoelastic materials does this clinical phenomenon best represent?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a classic viscoelastic property defined as a decrease in stress (tension or internal force) over time when a material is held under a constant deformation (constant strain). This is exactly what happens when a cast is applied holding a joint in a static position. Creep, in contrast, is the progressive deformation of a material over time when subjected to a constant load (stress). Hysteresis is the loss of energy (usually as heat) between the loading and unloading cycles.

Question 909

Topic: Biomechanics & Biomaterials

A patient who previously underwent total hip arthroplasty with a cobalt-chromium femoral head impacted onto a titanium alloy stem presents with groin pain and an expanding pseudotumor. Retrieval analysis of the explanted components demonstrates significant material degradation, pitting, and black debris exclusively at the modular head-neck taper junction. Which of the following is the primary initiating mode of corrosion responsible for this phenomenon?

. Galvanic corrosion
. Uniform attack corrosion
. Fretting corrosion
. Pitting corrosion
. Intergranular corrosion

Correct Answer & Explanation

. Fretting corrosion

Explanation

The failure at the modular head-neck taper in total hip arthroplasty (often termed trunnionosis) is primarily initiated by fretting corrosion. Micro-motion at the taper junction physically disrupts the protective passivation (oxide) layer on the metal surfaces (fretting). Once this layer is breached, local changes in the micro-environment (depletion of oxygen, drop in pH) lead to mechanically assisted crevice corrosion (MACC). While galvanic potential exists between differing metals, fretting is recognized as the necessary inciting mechanical event.

Question 910

Topic: Biomechanics & Biomaterials

Cortical bone exhibits viscoelastic properties, meaning its biomechanical response is dependent on the rate of loading. When cortical bone is subjected to a rapid rate of loading (high strain rate) compared to a slow rate of loading, how do its mechanical properties change?

. It becomes less stiff and absorbs less energy before failure
. It becomes stiffer and absorbs more energy before failure
. It becomes more ductile with a significantly lower yield point
. Its ultimate tensile strength decreases
. Its modulus of elasticity remains unchanged while energy absorption decreases

Correct Answer & Explanation

. It becomes stiffer and absorbs more energy before failure

Explanation

Bone is a viscoelastic material, meaning its mechanical properties are strain-rate dependent. At higher strain rates (e.g., high-speed motor vehicle trauma), cortical bone becomes stiffer (exhibits an increased modulus of elasticity), sustains higher loads before failing (increased ultimate strength), and absorbs more energy before fracture compared to slower loading rates.

Question 911

Topic: Biomechanics & Biomaterials

The addition of antibiotics to polymethylmethacrylate (PMMA) bone cement is routinely used for the treatment of periprosthetic joint infection. To optimize the elution profile and mechanical properties of an antibiotic-loaded PMMA spacer, which of the following principles must be adhered to?

. Antibiotics should be provided in liquid form to enhance homogenous distribution and rapid elution
. Increasing the porosity of the cement by adding more monomer will increase antibiotic elution and mechanical strength
. The chosen antibiotic must be thermally stable to withstand the exothermic polymerization reaction
. Total antibiotic dose should exceed 20% of the cement powder weight to ensure sustained long-term release above the MIC
. Adding antibiotics under a strict vacuum mixing environment maximizes elution rates compared to hand mixing

Correct Answer & Explanation

. The chosen antibiotic must be thermally stable to withstand the exothermic polymerization reaction

Explanation

PMMA polymerization is highly exothermic, reaching core temperatures that can easily degrade heat-sensitive medications. Therefore, antibiotics added to PMMA must be thermally stable (e.g., vancomycin, tobramycin, gentamicin). Liquid antibiotics severely degrade the mechanical properties of PMMA. Doses exceeding 10-15% significantly compromise the structural integrity of the cement. Furthermore, hand mixing (rather than vacuum mixing) is preferred for spacer creation because it increases porosity, which beneficially increases the surface area for antibiotic elution.

Question 912

Topic: Biomechanics & Biomaterials

A 65-year-old male undergoes revision total hip arthroplasty due to an adverse local tissue reaction. Intraoperatively, significant black debris and tissue necrosis are noted localized strictly around the modular head-neck taper junction, while the articular bearing surfaces show minimal wear. What is the primary mechanism of corrosion initiating at this specific modular interface?

. Galvanic corrosion
. Mechanically assisted crevice corrosion (MACC)
. Pitting corrosion
. Intergranular corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Mechanically assisted crevice corrosion (MACC)

Explanation

Modular tapers in total joint arthroplasty are primarily susceptible to mechanically assisted crevice corrosion (MACC). This process is initiated by fretting (micromotion) which disrupts the protective passive titanium oxide layer. Once the oxide layer is breached, crevice corrosion ensues in the oxygen-depleted, acidic environment of the taper junction, leading to the release of metal ions and subsequent adverse local tissue reactions (ALTR).

Question 913

Topic: Biomechanics & Biomaterials

A researcher is performing biomechanical testing on a novel synthetic graft for anterior cruciate ligament (ACL) reconstruction. The graft is clamped in a testing machine, instantly elongated to a fixed length, and held constant over time. The researcher observes that the force required to maintain this exact length progressively decreases. Which viscoelastic property is being demonstrated?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Viscoelastic materials exhibit time-dependent mechanical behaviors. 'Stress relaxation' is defined as the steady decrease in stress (or force) over time when the material is deformed and held at a constant strain (or length). Conversely, 'creep' is the progressive deformation (increase in length/strain) over time when a material is subjected to a constant load (or force). 'Hysteresis' refers to the energy lost as heat during the loading and unloading cycle.

Question 914

Topic: Biomechanics & Biomaterials

A 62-year-old woman presents with groin pain three years after a total hip arthroplasty using a cobalt-chromium modular head on a titanium alloy stem. Joint aspiration is negative for infection, but MRI demonstrates a solid periprosthetic pseudotumor. Revision surgery reveals black debris at the head-neck junction. Which of the following mechanisms is primarily responsible for the generation of this specific debris?

. Abrasive wear
. Adhesive wear
. Fretting corrosion
. Galvanic corrosion alone
. Third-body wear

Correct Answer & Explanation

. Fretting corrosion

Explanation

The scenario describes trunnionosis, which manifests as an adverse local tissue reaction (ALTR) or pseudotumor due to metal debris at the modular head-neck junction. This is primarily caused by mechanically assisted crevice corrosion (MACC), also known as fretting corrosion. Micro-motion at the junction mechanically disrupts the protective passive oxide layer on the metals (fretting), which exposes the underlying reactive metal to the physiologic fluid environment. This accelerates electrochemical dissolution (corrosion). While galvanic corrosion plays a role due to dissimilar metals, the primary driver at a modular THA junction is the mechanical disruption coupled with crevice corrosion.

Question 915

Topic: Biomechanics & Biomaterials

A researcher is studying the biomechanical properties of human articular cartilage in an osteoarthritic knee model. During normal joint kinematics, which zone of articular cartilage is primarily responsible for resisting shear stresses, and what is the predominant orientation of its collagen fibers?

. Superficial zone; parallel to the articular surface
. Transitional zone; oblique to the articular surface
. Deep zone; perpendicular to the articular surface
. Calcified zone; random orientation
. Tidemark; parallel to the articular surface

Correct Answer & Explanation

. Superficial zone; parallel to the articular surface

Explanation

Articular cartilage is divided into distinct structural zones. The superficial (tangential) zone makes up the top 10-20% of articular cartilage and has a high concentration of water and collagen (predominantly Type II). The collagen fibers in this zone are densely packed and oriented strictly parallel to the articular surface. This orientation provides the highest tensile strength and is primarily responsible for resisting the severe shear stresses generated during joint motion. In contrast, the deep zone features collagen fibers oriented perpendicularly to resist compressive loads.

Question 916

Topic: Biomechanics & Biomaterials

During an anterior cruciate ligament reconstruction, the surgeon tensions the soft tissue graft and secures it at a constant length for several minutes before final fixation. The surgeon notices that the force required to hold the graft at this specific length gradually decreases over time. Which biomechanical property does this phenomenon represent?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the viscoelastic property defined as a time-dependent decrease in stress (or force) when a material is held at a constant strain (or length). Creep, conversely, is the gradual increase in strain (deformation) when a material is held under a constant stress (load). Hysteresis refers to the energy lost as heat during a loading and unloading cycle.

Question 917

Topic: Biomechanics & Biomaterials

A 55-year-old male undergoes a total hip arthroplasty using highly cross-linked polyethylene (HXLPE). During manufacturing, the polyethylene is subjected to gamma irradiation followed by a remelting process. What is the primary purpose of the remelting step?

. To increase the ultimate tensile strength of the polyethylene
. To extinguish free radicals and reduce long-term oxidation
. To increase the crystalline content to improve elasticity
. To promote chain scission to allow smoother articulation
. To decrease the overall density of the polyethylene bearing

Correct Answer & Explanation

. To extinguish free radicals and reduce long-term oxidation

Explanation

Irradiation is used to create highly cross-linked polyethylene to significantly improve wear resistance. However, irradiation cleaves polymer chains, generating free radicals. If left untreated, these free radicals react with oxygen in vivo, leading to oxidation, embrittlement, and catastrophic failure. Remelting the plastic above its melting temperature extinguishes these free radicals, preventing oxidation, though it slightly decreases the ultimate yield and fatigue strength.

Question 918

Topic: Biomechanics & Biomaterials

A surgeon secures a titanium alloy plate with a stainless steel screw to stabilize a complex periarticular fracture. Over the next year, the patient develops localized pain and swelling. Radiographs show lucency around the screw without signs of infection. Which of the following electrochemical processes is most likely responsible for this complication?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as titanium and stainless steel) are placed in direct physical contact within an electrolytic environment (like body fluids). The metal with the lower electrochemical potential (anodic metal) undergoes accelerated corrosion to protect the more noble (cathodic) metal. Mixing implant metals should generally be avoided to prevent this complication.

Question 919

Topic: Biomechanics & Biomaterials

According to the Blix length-tension curve for skeletal muscle biomechanics, maximum active isometric tension is generated at an optimal sarcomere resting length. This peak in force production is directly attributed to which of the following?

. Actin filaments completely overlapping and colliding in the center of the sarcomere
. Maximal overlap between actin filaments and myosin cross-bridges
. The muscle being stretched to the point of zero overlap between actin and myosin
. Complete relaxation of the series elastic components within the tendon
. Maximum plastic deformation of the titin filaments

Correct Answer & Explanation

. Maximal overlap between actin filaments and myosin cross-bridges

Explanation

The length-tension relationship dictates that maximum active tension in a muscle fiber is produced at the resting length where there is optimal spatial overlap between the actin and myosin filaments. This allows for the maximum number of cross-bridge formations. If the sarcomere is overly shortened, actin filaments overlap and interfere with each other; if excessively stretched, overlap decreases, reducing cross-bridge potential.

Question 920

Topic: Biomechanics & Biomaterials

A 25-year-old athlete undergoes an anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone autograft. During graft preparation, the surgeon applies a constant load of 20 Newtons to the graft for 10 minutes on the back table, observing that the graft slowly elongates over time before its length stabilizes. Which of the following viscoelastic properties does this phenomenon describe?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is a classic viscoelastic property defined as the time-dependent increase in strain (deformation) of a material when subjected to a constant stress (load). In ligament reconstruction, pre-tensioning the graft relies on the principle of creep to reduce post-implantation elongation. Stress relaxation, conversely, is the time-dependent decrease in stress under a constant strain. Hysteresis refers to the energy lost (usually as heat) during the loading and unloading cycle of a viscoelastic material.

Test Yourself

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

On this Page