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Biomechanics & Biomaterials MCQs

Practice Set 16 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 301

Topic: Biomechanics & Biomaterials

Which of the following best defines 'stress relaxation' in the context of orthopedic biomechanics and viscoelastic materials?

. Increasing deformation over time under a constant load
. Decreasing force over time under a constant deformation
. Energy lost as heat during a loading-unloading cycle
. Increased stiffness with an increased rate of loading
. The point at which a material transitions from elastic to plastic deformation

Correct Answer & Explanation

. Decreasing force over time under a constant deformation

Explanation

Viscoelastic materials exhibit time-dependent properties. 'Stress relaxation' is the decrease in stress (force) over time when the material is held at a constant strain (deformation). 'Creep' is the progressive deformation (strain) over time under a constant load (stress).

Question 302

Topic: Biomechanics & Biomaterials
Which of the following sterilization methods for ultra-high molecular weight polyethylene (UHMWPE) components in total joint arthroplasty promotes cross-linking but also generates free radicals that can lead to oxidation and degradation if not properly treated?
. Ethylene oxide gas
. Gamma irradiation in air
. Autoclaving
. Gas plasma
. Dry heat

Correct Answer & Explanation

. Gamma irradiation in air

Explanation

Gamma irradiation induces cross-linking, which improves wear resistance. However, if performed in air, it generates free radicals that react with oxygen, leading to oxidation, chain scission, and subsequent degradation of the polyethylene. Modern techniques involve irradiation in an inert environment (e.g., argon or vacuum) and subsequent melting or annealing to quench free radicals.

Question 303

Topic: Biomechanics & Biomaterials

When analyzing the biomechanical properties of a viscoelastic orthopedic implant, the device is subjected to a constant applied load over a prolonged period. The material demonstrates a progressive, time-dependent increase in deformation. What is the correct biomechanical term for this phenomenon?

. Stress relaxation
. Hysteresis
. Fatigue
. Creep

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive deformation of a viscoelastic material under a constant load over time. In contrast, stress relaxation is the time-dependent decrease in internal stress under a constant state of deformation. Hysteresis is the energy lost (usually as heat) during a loading-unloading cycle.

Question 304

Topic: Biomechanics & Biomaterials

In orthopedic implant manufacturing, the mechanical properties of an alloy dictate its behavior within the host bone. Which of the following standard solid metallic biomaterials exhibits the lowest modulus of elasticity, thereby minimizing stress shielding when utilized as a diaphyseal stem?

. Cobalt-Chromium-Molybdenum (CoCrMo) alloy
. 316L Stainless Steel
. Titanium alloy (Ti-6Al-4V)
. Zirconia toughened Alumina (ZTA)
. Commercially pure Iron

Correct Answer & Explanation

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

Explanation

The modulus of elasticity (Young's modulus) is a measure of material stiffness. Cortical bone has a modulus of roughly 15-20 GPa. Titanium alloys (like Ti-6Al-4V) have a modulus of about 110 GPa, which is much closer to bone than 316L Stainless Steel (~200 GPa) or CoCrMo alloys (~210-240 GPa). The closer the implant's modulus is to cortical bone, the less load it shields from the bone, thereby reducing periprosthetic bone resorption (stress shielding).

Question 305

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is subjected to irradiation to improve wear resistance. However, irradiation creates free radicals that can cause oxidative degradation. Which post-irradiation thermal treatment completely eliminates free radicals but significantly reduces the mechanical properties (e.g., yield strength) of the polyethylene?
. Annealing
. Remelting
. Vitamin E blending
. Cold drawing
. Ethylene oxide sterilization

Correct Answer & Explanation

. Remelting

Explanation

Remelting (heating above the melting point of ~135 degrees C) completely extinguishes residual free radicals, enhancing oxidation resistance, but it decreases crystallinity, thereby reducing yield strength and fatigue resistance. Annealing heats below the melting point, preserving mechanical properties but leaving some free radicals.

Question 306

Topic: Biomechanics & Biomaterials
In the manufacturing of ultra-high molecular weight polyethylene (UHMWPE) for total joint arthroplasty, highly cross-linked polyethylene is utilized to reduce volumetric wear. However, the cross-linking process introduces free radicals. Which secondary process is most commonly used to extinguish these free radicals and prevent long-term oxidative degradation?
. Cold irradiation
. Ethylene oxide sterilization
. Remelting or annealing
. Calcium hydroxyapatite coating
. Addition of barium sulfate

Correct Answer & Explanation

. Remelting or annealing

Explanation

Gamma irradiation is used to cross-link UHMWPE to reduce wear, but it inherently creates free radicals that cause long-term oxidative degradation. Thermal treatments, such as remelting or annealing, are utilized to extinguish these free radicals and stabilize the polyethylene.

Question 307

Topic: Biomechanics & Biomaterials

A 21-year-old collegiate baseball pitcher undergoes ulnar collateral ligament (UCL) reconstruction via the docking technique after failing nonoperative management for a full-thickness anterior bundle tear. What is the most critical anatomical consideration when creating the ulnar tunnel to ensure proper biomechanics?

. Recreating the isometric footprint on the anteroinferior medial epicondyle
. Positioning the tunnel at the level of the radial head articulation
. Recreating the eccentric attachment on the sublimis tubercle
. Ensuring the tunnel penetrates the intra-articular capsular reflection
. Placing the graft deep to the flexor pronator mass for dynamic compression

Correct Answer & Explanation

. Recreating the isometric footprint on the anteroinferior medial epicondyle

Explanation

The anterior bundle of the UCL is the primary restraint to valgus stress at the elbow. Recreating its nearly isometric origin on the anteroinferior surface of the medial epicondyle is the most critical technical step to restore stable, physiologic elbow kinematics throughout the arc of motion.

Question 308

Topic: Biomechanics & Biomaterials

When designing a hip prosthesis, the material used for the femoral stem must withstand millions of cyclic loads. Which material property is most critical to prevent fatigue failure under these conditions?

. Yield strength
. Ultimate tensile strength
. Elastic modulus
. Endurance limit
. Hardness

Correct Answer & Explanation

. Endurance limit

Explanation

Fatigue failure is a common mode of failure for orthopedic implants due to the repetitive nature of physiological loading. The endurance limit (also known as the fatigue limit) is the maximum stress level below which a material can theoretically withstand an infinite number of loading cycles without failure. For materials like titanium alloys and cobalt-chrome alloys used in femoral stems, which are subjected to millions of cycles of stress during a patient's lifetime, ensuring the operating stresses remain below the endurance limit is paramount to prevent long-term fatigue failure. While yield strength and ultimate tensile strength are important for initial structural integrity, they do not directly predict performance under cyclic loading. Elastic modulus relates to stiffness, and hardness relates to resistance to indentation and wear, not directly fatigue.

Question 309

Topic: Biomechanics & Biomaterials

Synovial fluid provides lubrication and nutrient supply to articular cartilage. Which component of synovial fluid is primarily responsible for its non-Newtonian, viscoelastic properties, and boundary lubrication?

. Hyaluronic acid
. Lubricin
. Albumin
. IgG
. Fibrinogen

Correct Answer & Explanation

. Hyaluronic acid

Explanation

Hyaluronic acid (HA), a very large, unsulfated glycosaminoglycan, is the key component responsible for the unique rheological properties of synovial fluid, including its non-Newtonian viscosity and viscoelasticity. Its long, entangled molecular chains create a viscous solution that acts as a lubricant and shock absorber, particularly important for boundary lubrication where surfaces are in direct contact under high load. Lubricin (proteoglycan 4) is also critical for boundary lubrication, but HA is primarily responsible for the bulk fluid's viscoelasticity. Albumin, IgG, and Fibrinogen are plasma proteins that contribute to osmotic pressure but not the primary viscoelastic properties.

Question 310

Topic: Biomechanics & Biomaterials

Hydroxyapatite is the primary mineral component of bone, providing its hardness and rigidity. What is the approximate percentage by weight that hydroxyapatite constitutes in mature cortical bone?

. 10-20%
. 30-40%
. 60-70%
. 80-90%
. >95%

Correct Answer & Explanation

. 60-70%

Explanation

Mature cortical bone is composed of both organic and inorganic components. The inorganic component, primarily hydroxyapatite crystals (calcium phosphate), accounts for approximately 60-70% of the dry weight of bone, providing its compressive strength and rigidity. The organic matrix, predominantly Type I collagen, constitutes about 20-30% and provides tensile strength and flexibility. The remaining percentage is water and other non-collagenous proteins.

Question 311

Topic: Biomechanics & Biomaterials

A bone specimen is subjected to increasing tensile load. It deforms elastically until it reaches its yield point, after which it deforms plastically. What happens to the specimen if the load is removed before the yield point is reached?

. It fractures immediately
. It retains its deformed shape permanently
. It returns to its original length
. It undergoes work hardening
. It experiences creep

Correct Answer & Explanation

. It returns to its original length

Explanation

The stress-strain curve of a material illustrates its mechanical properties under load. The elastic region is the initial phase where stress is proportional to strain (Hooke's Law). In this region, deformation is entirely reversible; if the load is removed, the material returns to its original dimensions. The yield point marks the transition from elastic to plastic deformation. Beyond the yield point, permanent deformation occurs, meaning the material will not fully recover its original shape even after the load is removed. Fracture occurs at the ultimate tensile strength or fracture point, which is typically well beyond the yield point.

Question 312

Topic: Biomechanics & Biomaterials
Ultra-high molecular weight polyethylene (UHMWPE) is widely used in total joint arthroplasty as the bearing surface. What is the primary long-term failure mechanism associated with conventional UHMWPE?
. Creep deformation
. Stress shielding
. Osteolysis due to wear particles
. Bulk fracture
. Corrosion

Correct Answer & Explanation

. Osteolysis due to wear particles

Explanation

While UHMWPE is an excellent bearing material, the primary long-term failure mechanism of conventional UHMWPE in total joint arthroplasty is aseptic loosening, which is largely driven by osteolysis induced by wear particles. Over time, microscopic UHMWPE particles are generated from the bearing surface due to friction and abrasion. These particles are phagocytosed by macrophages and other immune cells, triggering a chronic inflammatory response that leads to local bone resorption (osteolysis) around the implant, ultimately causing the implant to loosen. Cross-linking UHMWPE is a strategy to reduce wear particle generation. Creep can occur but is less of a primary failure mechanism than osteolysis. Stress shielding relates to bone adaptation to implant stiffness. Bulk fracture and corrosion are typically associated with metallic components, though fatigue fracture of UHMWPE can occur.

Question 313

Topic: Biomechanics & Biomaterials

Ligaments exhibit viscoelastic properties, meaning their mechanical response depends on the rate of loading. Which of the following phenomena is a direct manifestation of viscoelasticity in a ligament when subjected to a constant load over time?

. Increased stiffness
. Creep
. Hysteresis
. Fatigue
. Ultimate tensile strength

Correct Answer & Explanation

. Creep

Explanation

Viscoelastic materials, such as ligaments and tendons, exhibit both viscous and elastic characteristics. Creep is a key manifestation of viscoelasticity, referring to the tendency of a material to deform (e.g., elongate) permanently under the influence of persistent mechanical stress (constant load) over time. This is distinct from elastic deformation, which is instantaneous and reversible. Other viscoelastic phenomena include stress relaxation (decrease in stress over time under constant strain) and hysteresis (energy loss during loading-unloading cycles). Stiffness, fatigue, and ultimate tensile strength are general mechanical properties, not exclusively tied to creep.

Question 314

Topic: Biomechanics & Biomaterials

Cortical bone is anisotropic, meaning its mechanical properties vary with the direction of applied load. Under which loading condition is cortical bone strongest?

. Torsion
. Transverse tension
. Transverse compression
. Longitudinal tension
. Longitudinal compression

Correct Answer & Explanation

. Transverse compression

Explanation

Cortical bone is a complex composite material with anisotropic properties, meaning its strength and stiffness vary depending on the direction of the applied force. It is strongest when subjected to compressive loads along its longitudinal axis, followed by tensile loads along the longitudinal axis. It is significantly weaker in shear, torsion, and transverse loading (tension or compression). This reflects the architectural arrangement of osteons and collagen fibers, which are primarily oriented along the long axis of the bone, providing maximal resistance to axial compression and tension.

Question 315

Topic: Biomechanics & Biomaterials

When analyzing a stress-strain curve for a material, the slope of the elastic region represents which mechanical property?

. Yield strength
. Ultimate tensile strength
. Elastic modulus (Young's modulus)
. Ductility
. Toughness

Correct Answer & Explanation

. Elastic modulus (Young's modulus)

Explanation

The stress-strain curve illustrates a material's mechanical behavior under load. In the elastic region, stress is directly proportional to strain (Hooke's Law). The slope of this linear portion of the curve is defined as the Elastic Modulus, or Young's Modulus. This value represents the material's stiffness or resistance to elastic deformation. A steeper slope indicates a stiffer material. Yield strength is the stress at which plastic deformation begins. Ultimate tensile strength is the maximum stress the material can withstand. Ductility is the ability to deform plastically without fracture. Toughness is the energy absorbed before fracture.

Question 316

Topic: Biomechanics & Biomaterials

The main advantage of using titanium alloys over stainless steel for orthopedic implants is their superior:

. Hardness and wear resistance
. Corrosion resistance and biocompatibility
. Elastic modulus (stiffness)
. Cost-effectiveness
. Radiopacity

Correct Answer & Explanation

. Corrosion resistance and biocompatibility

Explanation

Titanium alloys (e.g., Ti-6Al-4V) are widely used in orthopedic implants due to several advantages over stainless steel. Theirsuperior corrosion resistancein the biological environment means they are less likely to release ions and elicit adverse tissue reactions, thus improving theirbiocompatibility. Titanium also has a lower elastic modulus (closer to bone) compared to stainless steel and cobalt-chrome, which can reduce stress shielding. While titanium is strong, cobalt-chrome alloys generally offer better hardness and wear resistance, particularly in bearing applications. Titanium is more expensive and less radiopaque than stainless steel.

Question 317

Topic: Biomechanics & Biomaterials

A surgeon revises a failed hip arthroplasty and plans to use a titanium stem with a cobalt-chrome head. What type of corrosion is most likely to occur at the modular head-neck junction due to the presence of two dissimilar metals in an electrolytic environment?

. 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 in contact within a conductive fluid (body fluid), leading to the anodic metal corroding. Fretting corrosion involves micro-motion, while crevice corrosion occurs in shielded areas with oxygen depletion.

Question 318

Topic: Biomechanics & Biomaterials

During a Ponseti casting treatment for clubfoot, the foot is held in a corrected position. Over time, the force required to maintain this specific degree of deformity correction decreases. This viscoelastic property is best described as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the decrease in stress (force) over time when a material is held at a constant strain (deformation). Creep is continued deformation over time under a constant load.

Question 319

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) significantly reduces volumetric wear. What is the primary disadvantage associated with the cross-linking and subsequent thermal melting process?
. Decreased yield strength
. Decreased fatigue resistance and fracture toughness
. Increased osteolysis potential per particle
. Increased risk of galvanic corrosion
. Decreased oxidative stability

Correct Answer & Explanation

. Decreased fatigue resistance and fracture toughness

Explanation

While highly cross-linked polyethylene significantly improves adhesive and abrasive wear resistance, the cross-linking and thermal treatment process (remelting to eliminate free radicals) reduces its mechanical properties, notably fatigue resistance, ductility, and fracture toughness.

Question 320

Topic: Biomechanics & Biomaterials
A surgeon is selecting an intramedullary nail for a tibial shaft fracture. Which of the following materials possesses a Young's elastic modulus closest to that of cortical bone, thereby minimizing stress shielding?
. Cobalt-chromium alloy
. 316L Stainless steel
. Titanium alloy (Ti-6Al-4V)
. Tantalum
. Ultra-high-molecular-weight polyethylene (UHMWPE)

Correct Answer & Explanation

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

Explanation

Cortical bone has a Young's modulus of roughly 15-20 GPa. Titanium alloy (approx. 110 GPa) is closer in stiffness to cortical bone than stainless steel (approx. 200 GPa) or cobalt-chrome (approx. 240 GPa), leading to less stress shielding.

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