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Biomechanics & Biomaterials MCQs

Practice Set 49 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 961

Topic: Biomechanics & Biomaterials

Articular cartilage has a complex hierarchical structure that allows it to withstand compressive and shear forces. In the superficial zone of articular cartilage, what is the primary orientation of type II collagen fibers and what is its biomechanical function?

. Perpendicular to the joint surface to resist compressive loads
. Parallel to the joint surface to resist shear forces
. Randomly oriented to provide isotropic strength
. Oblique to the joint surface to transmit loads to subchondral bone
. Circumferential around chondrocytes to protect against osmotic swelling

Correct Answer & Explanation

. Parallel to the joint surface to resist shear forces

Explanation

In the superficial zone (lamina splendens) of articular cartilage, collagen fibers (primarily type II) are densely packed and oriented parallel to the joint surface. This structural arrangement allows the cartilage to resist the significant shear, tensile, and frictional forces generated during joint motion. In the deep zone, collagen fibers are oriented perpendicular to the joint surface, anchoring into the calcified cartilage to resist compressive loads.

Question 962

Topic: Biomechanics & Biomaterials

During tensile testing of a human anterior cruciate ligament (ACL) graft, a load-elongation (stress-strain) curve is plotted. What does the non-linear 'toe region' of this curve represent physiologically?

. Plastic deformation of the collagen fibers
. Microfailure of the weakest ligament fibrils
. Straightening (uncrimping) of the naturally corrugated collagen fibers
. Complete macroscopic rupture of the ligament
. The region where the modulus of elasticity decreases dramatically

Correct Answer & Explanation

. Straightening (uncrimping) of the naturally corrugated collagen fibers

Explanation

The stress-strain curve of tendons and ligaments begins with a non-linear 'toe region.' In the resting state, collagen fibers exhibit a wavy or crimped microscopic pattern. As initial tension is applied, these fibers straighten (uncrimp), resulting in tissue elongation with relatively low applied load. Once uncrimped, the curve enters the linear (elastic) region, where actual stretching of the collagen molecular backbone requires significantly greater force.

Question 963

Topic: Biomechanics & Biomaterials

A 65-year-old woman presents with groin pain 5 years after a total hip arthroplasty utilizing a cobalt-chromium modular head on a titanium alloy stem. Aspiration yields fluid with elevated cobalt levels but no bacterial growth. What is the predominant mechanism of corrosion at the modular head-neck junction?

. Mechanically assisted crevice corrosion
. Pure galvanic corrosion
. Pitting corrosion
. Intergranular corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Mechanically assisted crevice corrosion

Explanation

Trunnionosis at the modular head-neck junction is primarily driven by mechanically assisted crevice corrosion (MACC), also known as fretting corrosion. Micro-motion at the interface disrupts the passive oxide layer (fretting), and the confined space of the modular junction leads to oxygen depletion and a drop in pH (crevice corrosion), accelerating material loss. While mixing dissimilar metals theoretically risks pure galvanic corrosion, the mechanical disruption of the passivation layer in a confined crevice is the primary driver in modern modular orthopedic implants.

Question 964

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic properties. During a continuous traction experiment on a cadaveric ACL, a constant load is applied over a prolonged period. The observation that the ligament continues to slowly elongate over time under this steady load is termed:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation (elongation) of a viscoelastic material when subjected to a constant load over time. Stress relaxation, conversely, is the decrease in internal stress over time when a material is held at a constant strain (constant length). Hysteresis represents the energy lost (as heat) during the loading and unloading cycles of a viscoelastic material.

Question 965

Topic: Biomechanics & Biomaterials

Orthopedic biomechanics heavily relies on understanding material properties. When evaluating a new titanium alloy for femoral stems, researchers plot a standardized stress-strain curve under tensile loading. Which of the following material properties is derived by calculating the slope of the linear (elastic) portion of this curve?

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

Correct Answer & Explanation

. Modulus of elasticity

Explanation

The slope of the linear, elastic portion of the stress-strain curve represents the Modulus of Elasticity (Young's modulus), which defines the material's stiffness. Toughness is represented by the total area under the entire stress-strain curve. Yield strength is the stress level at which the material ceases to behave entirely elastically and begins plastic (permanent) deformation. Ultimate tensile strength is the maximum stress the material can withstand before failure.

Question 966

Topic: Biomechanics & Biomaterials

Normal adult articular cartilage exhibits an anisotropic and depth-dependent structural organization essential for its biomechanical function. Compared to the deep zone, the superficial (tangential) zone of articular cartilage is uniquely characterized by which of the following structural properties?

. Lower water content and vertically oriented collagen fibers
. Higher water content, highest collagen concentration, and collagen fibers parallel to the joint surface
. Highest proteoglycan concentration and randomly oriented collagen fibers
. Lower collagen content and collagen fibers perpendicular to the joint surface
. Highest chondrocyte density arranged in distinct vertical columns

Correct Answer & Explanation

. Higher water content, highest collagen concentration, and collagen fibers parallel to the joint surface

Explanation

The superficial zone of articular cartilage has the highest water content (approx. 80%), the highest concentration of collagen, and the lowest concentration of proteoglycans. The collagen fibers (mostly Type II) are oriented parallel to the joint surface to resist sheer stress. In contrast, the deep zone has the lowest water content (approx. 65%), the highest proteoglycan content, and collagen fibers oriented perpendicular to the joint surface to resist compressive loads.

Question 967

Topic: Biomechanics & Biomaterials

When testing the viscoelastic properties of an anterior cruciate ligament graft, the structural testing apparatus holds the graft at a constant deformation (strain) and measures the load over time. Which of the following viscoelastic phenomena is best described by the observed decrease in peak load over time?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the hallmark viscoelastic property where the stress (or load) decreases over time when the material is held at a constant deformation (strain). Creep, conversely, is the progressive deformation (strain) over time when a material is subjected to a constant load. Hysteresis represents the energy lost (usually as heat) during the loading and unloading cycle of a viscoelastic material.

Question 968

Topic: Biomechanics & Biomaterials

A biomechanics researcher is testing the viscoelastic properties of a human Achilles tendon. When a constant tensile load is applied to the tendon over an extended period, the tendon continues to deform slowly over time. This viscoelastic phenomenon is best described as:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive, time-dependent deformation of a viscoelastic material when it is subjected to a constant load (or stress). Stress relaxation, by contrast, is the decrease in internal stress over time when a material is held at a constant deformation (or strain). Hysteresis represents the energy lost (usually dissipated as heat) during the loading and unloading cycle of a viscoelastic material.

Question 969

Topic: Biomechanics & Biomaterials

Which of the following alterations in screw design or insertion technique would most significantly increase the pullout strength of a cortical screw in diaphyseal bone?

. Decreasing the outer (thread) diameter of the screw
. Increasing the inner (root) diameter of the screw
. Decreasing the thread pitch
. Inserting the screw at a 45-degree angle to the long axis of the bone
. Using a cannulated screw instead of a solid screw

Correct Answer & Explanation

. Decreasing the thread pitch

Explanation

Screw pullout strength is directly proportional to the outer (thread) diameter, the length of thread engagement, and the shear strength of the bone, and inversely proportional to the thread pitch. Decreasing the thread pitch (meaning more threads per unit length) increases the volume of bone caught between the threads, thereby increasing the pullout strength. Increasing the inner (root) diameter increases the screw's resistance to bending and fatigue failure but does not increase pullout strength.

Question 970

Topic: Biomechanics & Biomaterials

Which of the following terms best describes a material's property to exhibit a time-dependent increase in strain when subjected to a constant applied stress?

. Creep
. Stress relaxation
. Viscoelasticity
. Fatigue
. Hysteresis

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the progressive, time-dependent deformation (increase in strain) of a material under a constant stress or load. Stress relaxation is the time-dependent decrease in stress under a constant strain. Hysteresis refers to the energy lost (as heat) during cyclic loading and unloading. Viscoelasticity is the overarching term for materials exhibiting both viscous and elastic characteristics.

Question 971

Topic: Biomechanics & Biomaterials

A researcher is studying articular cartilage biomechanics. Which zone of articular cartilage possesses the highest concentration of water and has collagen fibers oriented parallel to the joint surface?

. Superficial zone (tangential)
. Middle zone (transitional)
. Deep zone (radial)
. Calcified zone
. Tidemark

Correct Answer & Explanation

. Superficial zone (tangential)

Explanation

The superficial (tangential) zone of articular cartilage has the highest water content (up to 80%), the lowest proteoglycan content, and features collagen fibers (primarily type II) arranged parallel to the articular surface. This specialized structure allows the cartilage to resist shear stresses associated with joint motion.

Question 972

Topic: Biomechanics & Biomaterials

In comparing the mechanical properties of cortical bone to cancellous bone on a stress-strain curve, cortical bone demonstrates which of the following characteristics?

. Lower Young's modulus and lower yield point
. Higher Young's modulus and lower ultimate strain
. Lower Young's modulus and higher ultimate strain
. Higher Young's modulus and higher ultimate strain
. Equal Young's modulus and higher yield point

Correct Answer & Explanation

. Higher Young's modulus and lower ultimate strain

Explanation

Cortical bone is much stiffer than cancellous bone, meaning it has a steeper slope in the elastic region of the stress-strain curve, which translates to a higher Young's modulus. However, it is more brittle and fails at a lower percentage of deformation (lower ultimate strain, typically ~2%), whereas cancellous bone is highly porous and can undergo significant deformation before ultimate failure.

Question 973

Topic: Biomechanics & Biomaterials

A 55-year-old man undergoes a revision total hip arthroplasty. The surgeon plans to use a titanium alloy (Ti-6Al-4V) femoral stem with a cobalt-chromium (CoCr) head. Which of the following is the primary mechanism that mitigates severe galvanic corrosion between these two dissimilar metals in vivo?

. Similar galvanic potentials of the two metals
. Spontaneous formation of a passivating oxide layer on the titanium surface
. Use of a polyethylene liner to electrically isolate the components
. Addition of molybdenum to the cobalt-chromium alloy
. High oxygen tension in the synovial fluid

Correct Answer & Explanation

. Spontaneous formation of a passivating oxide layer on the titanium surface

Explanation

When combining titanium and cobalt-chromium in vivo, galvanic corrosion is minimized primarily by the spontaneous formation of dense, passivating oxide layers on both metals (such as TiO2 for titanium). This passivating layer electrically isolates the bulk metal from the physiological fluid (electrolyte), drastically increasing the resistance and minimizing the corrosion current.

Question 974

Topic: Biomechanics & Biomaterials
In total joint arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced volumetric wear rates compared to conventional UHMWPE. However, the process of cross-linking has a known adverse effect on which of the following mechanical properties?
. Ultimate tensile strength only
. Fatigue strength only
. Elastic modulus only
. Yield strength only
. Both ultimate tensile strength and fatigue strength

Correct Answer & Explanation

. Both ultimate tensile strength and fatigue strength

Explanation

Highly cross-linking polyethylene drastically reduces adhesive and abrasive wear. However, it decreases both its ultimate tensile strength and fatigue strength (resistance to crack propagation). To mitigate the reduction in fatigue strength, modern HXLPE is cross-linked with optimal radiation doses and often thermally treated (remelted or annealed) to eliminate free radicals.

Question 975

Topic: Biomechanics & Biomaterials




When evaluating the mechanical properties of a metallic implant on a stress-strain curve, the point at which the material undergoes non-reversible deformation but continues to bear increasing loads before reaching its ultimate failure is best described as occurring within which of the following regions?

. Elastic region
. Plastic region
. Yield point
. Failure point
. Viscoelastic creep phase

Correct Answer & Explanation

. Plastic region

Explanation

The plastic region on a stress-strain curve represents the phase where the material undergoes irreversible (plastic) deformation but can still accept higher stress before reaching its ultimate tensile strength and eventually failing. The yield point is the specific transition locus between the elastic (reversible) and plastic deformation phases.

Question 976

Topic: Biomechanics & Biomaterials
Which of the following factors has the greatest influence on increasing volumetric wear in ultra-high molecular weight polyethylene (UHMWPE) acetabular components in total hip arthroplasty?
. Increasing the thickness of the polyethylene liner
. Decreasing the femoral head-to-neck ratio
. Increasing the femoral head diameter
. Using highly cross-linked polyethylene
. Utilizing a ceramic-on-ceramic bearing surface

Correct Answer & Explanation

. Increasing the femoral head diameter

Explanation

Volumetric wear in conventional UHMWPE is directly proportional to the sliding distance, which increases with a larger femoral head diameter. While larger heads increase volumetric wear, linear wear may remain unchanged or slightly decrease. Utilizing highly cross-linked polyethylene significantly decreases wear rates.

Question 977

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopaedic implants occurs when dissimilar metals are in physical contact within a conductive physiological fluid. Which of the following combinations of implant materials is most strongly contraindicated due to the high risk of severe galvanic corrosion?

. Commercially pure titanium and titanium alloy (Ti-6Al-4V)
. Cobalt-chromium-molybdenum alloy and titanium alloy
. 316L stainless steel and titanium alloy
. Cobalt-chromium-molybdenum alloy and oxidized zirconium
. Tantalum and commercially pure titanium

Correct Answer & Explanation

. 316L stainless steel and titanium alloy

Explanation

Mixing 316L stainless steel and titanium alloy in direct contact is contraindicated due to a significant difference in their electrochemical potentials on the anodic index. This leads to severe galvanic corrosion of the less noble metal (stainless steel). Conversely, cobalt-chromium and titanium alloys are closer in the galvanic series and are frequently combined safely, such as in modular total hip arthroplasty.

Question 978

Topic: Biomechanics & Biomaterials



If a stainless steel screw is placed through a titanium alloy plate in a saline physiological environment, galvanic corrosion may occur. Which of the following best describes the resulting electrochemical process?

. Titanium acts as the anode and corrodes
. Titanium acts as the cathode and corrodes
. Stainless steel acts as the anode and corrodes
. Stainless steel acts as the cathode and corrodes
. Both metals act as anodes and corrode equally

Correct Answer & Explanation

. Stainless steel acts as the anode and corrodes

Explanation

In a mixed-metal galvanic couple between stainless steel and titanium, the less noble stainless steel acts as the anode and undergoes accelerated corrosion. Titanium is more noble and acts as the cathode.

Question 979

Topic: Biomechanics & Biomaterials

During the toe region of a tendon's stress-strain curve, which of the following events is primarily occurring?

. Microscopic failure of collagen fibers
. Uncrimping of collagen fibers
. Macroscopic failure of the tendon
. Plastic deformation of the tendon
. Elastic deformation of isolated collagen fibrils

Correct Answer & Explanation

. Uncrimping of collagen fibers

Explanation

The 'toe region' of the stress-strain curve corresponds to the uncrimping of collagen fibers. As the tendon is stretched further, it enters the linear elastic region where actual fiber stretching occurs.

Question 980

Topic: Biomechanics & Biomaterials

Titanium alloy (Ti-6Al-4V) is frequently used in orthopedic implants due to its biocompatibility. Compared to cobalt-chromium alloys, titanium has which of the following biomechanical properties?

. Higher modulus of elasticity and lower fatigue strength
. Lower modulus of elasticity and greater notch sensitivity
. Higher ultimate tensile strength and lower ductility
. Increased galvanic corrosion when coupled with stainless steel
. Superior wear characteristics in articulation with polyethylene

Correct Answer & Explanation

. Lower modulus of elasticity and greater notch sensitivity

Explanation

Titanium has a lower modulus of elasticity (closer to bone) compared to cobalt-chrome, which reduces stress shielding. However, it is highly notch-sensitive and has poor wear characteristics when articulating with polyethylene.

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