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Biomechanics & Biomaterials MCQs

Practice Set 18 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 341

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, the phenomenon where a hard third body (such as a bone fragment or bone cement) becomes embedded in the polyethylene liner and subsequently scratches the femoral head is best described as what type of wear?

. Adhesive wear
. Abrasive wear
. Fatigue wear
. Corrosive wear
. Fretting wear

Correct Answer & Explanation

. Abrasive wear

Explanation

Abrasive wear occurs when a harder surface or particle plows into a softer surface. Third-body wear, where particles like bone or cement become embedded in the polyethylene and scratch the metal head, is a classic example of abrasive wear. Adhesive wear involves micro-welding between surfaces. Fatigue wear is due to cyclical loading causing subsurface cracking.

Question 342

Topic: Biomechanics & Biomaterials

Which of the following combinations of orthopedic implant materials is most likely to result in significant galvanic corrosion when placed in direct contact within the human body?

. Titanium alloy and cobalt-chromium alloy
. Stainless steel and titanium alloy
. Cobalt-chromium alloy and ultra-high-molecular-weight polyethylene
. Commercially pure titanium and titanium alloy
. Tantalum and titanium alloy

Correct Answer & Explanation

. Stainless steel and titanium alloy

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct contact within an electrolytic environment. Stainless steel and titanium have significantly different galvanic potentials, making this combination highly susceptible to severe galvanic corrosion and clinical failure, thus it should be strictly avoided.

Question 343

Topic: Biomechanics & Biomaterials

A resident is utilizing a ring external fixator for limb lengthening. Over the course of several days of continuous fixed distraction, the measurable force required by the tissue to maintain that specific distraction distance progressively decreases. Which viscoelastic property does this phenomenon represent?

. Creep
. Stress relaxation
. Hysteresis
. Fatigue failure
. Viscoplasticity

Correct Answer & Explanation

. Stress relaxation

Explanation

This scenario describes stress relaxation, a fundamental viscoelastic property of biological tissues. Stress relaxation occurs when a tissue is held at a constant length or strain, and the internal force or stress within the tissue gradually decreases over time. In contrast, creep is the progressive deformation or lengthening of a tissue when subjected to a constant load or stress over time. Hysteresis represents the energy lost (usually as heat) during the loading and unloading cycles of a viscoelastic material.

Question 344

Topic: Biomechanics & Biomaterials

During the non-operative management of a clubfoot using the Ponseti method, serial casting gradually stretches the contracted medial ligaments. The viscoelastic property allowing the ligament to progressively elongate under a constant, prolonged load over time is termed:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation (elongation) of a viscoelastic material when subjected to a constant load over time. In contrast, stress relaxation refers to the decrease in stress (force) within a material when it is held at a constant length/deformation. Serial casting utilizes both principles, but progressive elongation under constant tension is creep.

Question 345

Topic: Biomechanics & Biomaterials
Highly cross-linked polyethylene (HXLPE) was introduced in total hip arthroplasty to reduce wear and subsequent osteolysis. Which of the following mechanical properties is significantly reduced as a direct consequence of increasing the radiation dose used to cross-link the polyethylene?
. Wear resistance
. Fracture toughness
. Oxidation resistance
. Creep resistance
. Young's modulus

Correct Answer & Explanation

. Fracture toughness

Explanation

Increasing the radiation dose to cross-link polyethylene improves its wear resistance significantly but at the cost of reducing its mechanical properties, particularly fracture toughness, fatigue strength, and ultimate tensile strength. To mitigate oxidation, HXLPE must be remelted or annealed, or doped with an antioxidant like Vitamin E. Creep resistance is actually slightly improved or unchanged by cross-linking.

Question 346

Topic: Biomechanics & Biomaterials
To significantly decrease the wear rate of ultra-high-molecular-weight polyethylene (UHMWPE) in total joint arthroplasty, it is subjected to high-dose irradiation. However, this process requires a secondary step to prevent long-term failure. What is the primary purpose of this secondary step (e.g., melting or annealing)?
. To restore the tensile strength to pre-irradiation levels
. To eliminate residual free radicals and improve oxidative stability
. To increase the crystallinity of the polyethylene
. To cross-link the amorphous regions of the polymer
. To sterilize the component before packaging

Correct Answer & Explanation

. To eliminate residual free radicals and improve oxidative stability

Explanation

Highly cross-linking UHMWPE via gamma irradiation significantly improves wear resistance but generates free radicals. If left untreated, these free radicals react with oxygen in vivo, leading to oxidation, delamination, and embrittlement. A secondary thermal treatment (melting or annealing) or doping with Vitamin E is necessary to quench these free radicals and ensure oxidative stability.

Question 347

Topic: Biomechanics & Biomaterials
Cross-linking of ultra-high molecular weight polyethylene (UHMWPE) is heavily utilized in total hip arthroplasty to reduce wear. However, increasing the radiation dose to achieve higher cross-linking has which of the following detrimental effects on the mechanical properties of the polyethylene liner?
. Decreased fatigue strength and fracture toughness
. Increased oxidation potential over time
. Decreased elastic modulus leading to increased creep
. Increased adhesive wear against cobalt-chromium
. Increased melting temperature

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

Highly cross-linked polyethylene drastically reduces volumetric wear. However, the radiation process used to induce cross-linking significantly decreases mechanical properties, most notably fatigue strength, ultimate tensile strength, and fracture toughness, which can increase the risk of rim fracture or structural failure in certain applications.

Question 348

Topic: Biomechanics & Biomaterials

During an Anterior Cruciate Ligament (ACL) reconstruction, the surgeon tensions the quadrupled hamstring graft to a specific length and secures it. Over the next several minutes, the tension (force) required by the fixation device to maintain that exact length decreases. This physical phenomenon is characteristic of viscoelastic materials and is known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the property of a viscoelastic material whereby the stress (internal force/tension) decreases over time when the material is held at a constant strain (length). Conversely, 'creep' is the increase in strain (deformation/length) over time when the material is subjected to a constant stress (load).

Question 349

Topic: Biomechanics & Biomaterials

Biomechanical testing of a human anterior cruciate ligament graft is performed. When a constant load (stress) is applied to the ligament over an extended period, the ligament undergoes a gradual increase in length (strain). This viscoelastic property is best defined as:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the viscoelastic property where a tissue undergoes continuous, time-dependent deformation (elongation or strain) under a constant applied load (stress). In contrast, stress relaxation is the decrease in stress over time when the tissue is held at a constant length (strain).

Question 350

Topic: Biomechanics & Biomaterials

A trauma surgeon is selecting an intramedullary nail for a tibial fracture. Comparing titanium alloy (Ti-6Al-4V) to 316L stainless steel, titanium alloy exhibits:

. A higher modulus of elasticity, resulting in less stress shielding
. A lower modulus of elasticity, resulting in less stress shielding
. A higher modulus of elasticity, resulting in greater stress shielding
. A lower modulus of elasticity, resulting in greater stress shielding
. An identical modulus of elasticity but superior fatigue resistance

Correct Answer & Explanation

. A lower modulus of elasticity, resulting in less stress shielding

Explanation

Titanium alloy (Ti-6Al-4V) has a lower modulus of elasticity (closer to that of cortical bone) compared to stainless steel or cobalt-chrome alloys. Because it is less stiff, it shares load better with the surrounding bone, thereby reducing stress shielding and theoretically promoting better fracture healing and minimizing bone resorption compared to the stiffer stainless steel implants.

Question 351

Topic: Biomechanics & Biomaterials

The torsional rigidity of a solid cylindrical intramedullary nail is mathematically governed by its polar moment of inertia. Based on this formula, the torsional rigidity is proportional to which of the following regarding the radius of the nail?

. Radius
. Radius squared
. Radius to the third power
. Radius to the fourth power
. Inversely proportional to the radius

Correct Answer & Explanation

. Radius to the fourth power

Explanation

The torsional rigidity of a solid cylinder is proportional to its polar moment of inertia (J), which is calculated as J = (pi * r^4) / 2. Therefore, the torsional rigidity is directly proportional to the radius to the fourth power (r^4).

Question 352

Topic: Biomechanics & Biomaterials

During the repair of a Zone II flexor tendon injury in the hand, preservation or reconstruction of which of the following annular pulleys is most critical to prevent bowstringing and maintain proper finger biomechanics?

. A1 and A3 pulleys
. A2 and A4 pulleys
. A3 and A5 pulleys
. A1 and A5 pulleys
. A2 and A3 pulleys

Correct Answer & Explanation

. A2 and A4 pulleys

Explanation

The flexor tendon sheath contains five annular (A1-A5) and three cruciform (C1-C3) pulleys. The A2 and A4 pulleys are the most mechanically critical. They originate directly from the periosteum of the proximal and middle phalanges, respectively. Loss of the A2 or A4 pulleys leads to clinically significant bowstringing of the flexor tendons, resulting in a loss of active flexion at the IP joints and an overall decrease in the work capacity of the finger.

Question 353

Topic: Biomechanics & Biomaterials

'Trunnionosis' in modern total hip arthroplasty primarily occurs at the modular head-neck taper junction. This phenomenon, which can lead to adverse local tissue reactions (ALTR) even with metal-on-polyethylene bearings, is mechanically initiated by micro-motion at the taper interface. This micro-motion primarily leads to which of the following modes of implant degradation?

. Pitting corrosion
. Galvanic corrosion
. Fretting corrosion
. Intergranular corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Fretting corrosion

Explanation

Trunnionosis refers to the wear and corrosion at the modular head-neck taper junction in a total hip arthroplasty. It is initiated by micro-motion under load, which constantly disrupts the protective passive oxide layer on the metal surface. This specific process of mechanically assisted crevice corrosion initiated by oscillatory micro-motion is termed 'fretting corrosion'. While galvanic corrosion plays a secondary role once the passivating layer is breached (especially with mixed metals like CoCr on Ti), the mechanical initiator is fretting.

Question 354

Topic: Biomechanics & Biomaterials

In orthopedic biomechanics, what term describes the progressive deformation of a viscoelastic material over time when it is subjected to a constant load?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the property of a viscoelastic material wherein it undergoes progressive, time-dependent deformation when subjected to a constant force or stress. Conversely, stress relaxation refers to the decrease in stress over time when a material is held at a constant strain.

Question 355

Topic: Biomechanics & Biomaterials

Which of the following orthopedic implant combinations is most likely to result in clinically significant galvanic corrosion if placed in direct physical contact within the human body?

. Cobalt-Chromium (Co-Cr) alloy and ultra-high-molecular-weight polyethylene
. Stainless steel (316L) and Titanium alloy (Ti-6Al-4V)
. Commercially pure Titanium and Titanium alloy (Ti-6Al-4V)
. Cobalt-Chromium (Co-Cr) alloy and Titanium alloy (Ti-6Al-4V)
. Stainless steel (316L) and Tantalum

Correct Answer & Explanation

. Stainless steel (316L) and Titanium alloy (Ti-6Al-4V)

Explanation

Galvanic corrosion occurs when two dissimilar metals with significantly different electrochemical potentials (anodic index) are placed in direct physical contact within an electrolytic solution like body fluids. Stainless steel and titanium have a large difference in their electrochemical potentials, making them highly susceptible to severe galvanic corrosion when mixed. Titanium and Co-Cr have closer potentials and are routinely mixed safely in modular arthroplasty components.

Question 356

Topic: Biomechanics & Biomaterials

Normal articular cartilage is divided into distinct structural zones. Which of the following best describes the histologic and biochemical characteristics of the superficial (tangential) zone?

. Highest proteoglycan content and vertically aligned collagen fibers
. Highest water content and collagen fibers aligned parallel to the joint surface
. Lowest water content and randomly oriented collagen fibers
. Highest cell density and purely Type I collagen
. Lowest cell density and highest concentration of hydroxyapatite crystals

Correct Answer & Explanation

. Highest water content and collagen fibers aligned parallel to the joint surface

Explanation

The superficial (tangential) zone of articular cartilage represents 10-20% of the thickness. It has the highest water content (up to 80%), lowest proteoglycan content, and features densely packed collagen fibers aligned parallel to the joint surface to resist shear forces. The deep zone features vertically aligned collagen fibers, lowest water content, and highest proteoglycan content to resist compressive loads.

Question 357

Topic: Biomechanics & Biomaterials

Galvanic corrosion is most likely to occur in orthopedic surgery when which of the following combinations of metals are in direct physical contact within a conductive body fluid environment?

. Titanium alloy and commercially pure titanium
. Stainless steel and cobalt-chromium alloy
. Titanium alloy and cobalt-chromium alloy
. Stainless steel and titanium alloy
. Oxidized zirconium and cross-linked polyethylene

Correct Answer & Explanation

. Stainless steel and titanium alloy

Explanation

Galvanic corrosion occurs when two dissimilar metals with significantly different anodic indices are placed in contact within an electrolytic solution. The combination of stainless steel and titanium alloy leads to rapid galvanic corrosion of the stainless steel and should be avoided. Cobalt-chromium and titanium are closer on the galvanic series and are frequently used together safely.

Question 358

Topic: Biomechanics & Biomaterials

Galvanic corrosion can occur in orthopaedic implants when two dissimilar metals are in contact within the body's electrolytic environment. If a stainless steel screw is used in a titanium alloy plate, which of the following accurately describes the electrochemical process that occurs?

. The titanium plate acts as the anode and undergoes accelerated corrosion.
. The stainless steel screw acts as the anode and undergoes accelerated corrosion.
. The titanium plate acts as the cathode and undergoes accelerated corrosion.
. The stainless steel screw acts as the cathode and is protected from corrosion.
. Both metals act as anodes and undergo equal rates of galvanic corrosion.

Correct Answer & Explanation

. The stainless steel screw acts as the anode and undergoes accelerated corrosion.

Explanation

In a galvanic couple, the less noble metal acts as the anode and corrodes, while the more noble metal acts as the cathode and is protected. Titanium is more noble (more cathodic) than stainless steel. Therefore, when they are mixed, the stainless steel screw acts as the anode and undergoes accelerated galvanic corrosion.

Question 359

Topic: Biomechanics & Biomaterials

In total hip arthroplasty (THA), the adoption of highly cross-linked polyethylene (HXLPE) has significantly reduced volumetric wear. What is the primary mechanical trade-off associated with increasing the radiation dose to maximize cross-linking during manufacturing?

. Increased oxidative degradation over time
. Decreased fatigue strength and fracture toughness
. Increased elastic modulus leading to stress shielding
. Decreased biocompatibility of the generated wear debris
. Increased risk of galvanic corrosion at the trunnion

Correct Answer & Explanation

. Decreased fatigue strength and fracture toughness

Explanation

Increasing the radiation dose during the manufacturing of HXLPE enhances cross-linking, which dramatically improves wear resistance. However, the primary mechanical consequence of this process is a notable decrease in the material's fatigue strength, tensile strength, and fracture toughness. This makes the polyethylene liner more susceptible to fracture, particularly if thin liners are used or if the component is malpositioned.

Question 360

Topic: Biomechanics & Biomaterials
The introduction of highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) has significantly reduced volumetric wear rates in total hip arthroplasty. However, the radiation cross-linking process introduces a clinically relevant trade-off by reducing which of the following material properties?
. Oxidation resistance
. Surface wettability
. Elastic modulus
. Yield strength and fatigue resistance
. Thermal conductivity

Correct Answer & Explanation

. Yield strength and fatigue resistance

Explanation

Irradiation of UHMWPE creates free radicals that form cross-links, heavily increasing the material's resistance to adhesive and abrasive wear. However, this process alters the crystalline structure and polymer chain mobility, which results in a reduction of mechanical properties, specifically yield strength, ultimate tensile strength, and fatigue resistance. This makes it more susceptible to fracture, particularly in thin liners or high-stress applications.

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