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Biomechanics & Biomaterials MCQs

Practice Set 59 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 1161

Topic: Biomechanics & Biomaterials
The process of highly cross-linking ultra-high-molecular-weight polyethylene (UHMWPE) using gamma or electron beam irradiation significantly alters its material properties. Which of the following best describes the effect of increasing the cross-linking in UHMWPE?
. Increased wear resistance and increased ductility
. Increased wear resistance and decreased fatigue crack propagation resistance
. Decreased wear resistance and increased yield strength
. Decreased wear resistance and decreased ultimate tensile strength
. Increased oxidation resistance and increased ductility

Correct Answer & Explanation

. Increased wear resistance and decreased fatigue crack propagation resistance

Explanation

Highly cross-linking UHMWPE significantly improves its abrasive wear resistance. However, this comes at the cost of diminished mechanical properties, including decreased ductility, fracture toughness, and resistance to fatigue crack propagation.

Question 1162

Topic: Biomechanics & Biomaterials

Galvanic corrosion can occur when two dissimilar metals are placed in physical contact within the electrolytic environment of the human body. If a 316L stainless steel screw is placed into a Ti-6Al-4V titanium plate, which of the following reactions is most likely to occur?

. The stainless steel becomes the anode and undergoes accelerated corrosion
. The titanium becomes the anode and undergoes accelerated corrosion
. The stainless steel becomes the cathode and undergoes accelerated corrosion
. The titanium becomes the cathode and is protected from corrosion
. Both metals corrode equally due to uniform electron transfer

Correct Answer & Explanation

. The stainless steel becomes the anode and undergoes accelerated corrosion

Explanation

Titanium is more noble (cathodic) than stainless steel in the galvanic series. Therefore, the less noble stainless steel acts as the anode, releasing electrons and undergoing accelerated galvanic corrosion when coupled with titanium.

Question 1163

Topic: Biomechanics & Biomaterials

A surgeon plans to use a titanium locking plate with 316L stainless steel screws to fix a complex periarticular fracture. This combination is generally avoided due to the risk of galvanic corrosion. In this mixed-metal construct, which of the following accurately describes the electrochemical reaction?

. Titanium acts as the anode and corrodes
. Stainless steel acts as the cathode and corrodes
. Stainless steel acts as the anode and corrodes
. Both metals corrode equally due to identical electronegativities
. Titanium undergoes passivation, preventing any corrosion in the construct

Correct Answer & Explanation

. Titanium acts as the anode and corrodes

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within an electrolytic environment (like body fluid). Titanium is more noble (cathodic), so the less noble stainless steel acts as the anode and undergoes accelerated corrosion.

Question 1164

Topic: Biomechanics & Biomaterials

A surgeon reams the femoral medullary canal to insert a larger diameter solid intramedullary nail. If the radius of the selected solid titanium nail is increased by a factor of 2, the theoretical torsional rigidity (polar moment of inertia) of the nail increases by a factor of:

. 2
. 4
. 8
. 16
. 32

Correct Answer & Explanation

. 2

Explanation

The torsional rigidity of a solid cylinder is proportional to its polar moment of inertia (J), which is defined mathematically as proportional to the radius to the fourth power (r^4). Therefore, doubling the radius increases the torsional rigidity by 2^4, which equals 16.

Question 1165

Topic: Biomechanics & Biomaterials

When preparing antibiotic-loaded polymethylmethacrylate (PMMA) bone cement for an articulating spacer in a two-stage revision for periprosthetic joint infection, which of the following antibiotic properties is most critical for ensuring its effective local elution?

. High molecular weight
. High lipid solubility
. High thermal stability
. Bacteriostatic action
. High protein binding

Correct Answer & Explanation

. High molecular weight

Explanation

The polymerization of PMMA is a highly exothermic reaction that can reach temperatures exceeding 100 degrees Celsius. Therefore, antibiotics mixed into the cement (such as vancomycin or tobramycin) must possess high thermal stability to remain chemically active.

Question 1166

Topic: Biomechanics & Biomaterials

During in vitro tensile testing of an intact anterior cruciate ligament (ACL), the initial portion of the stress-strain curve is non-linear and exhibits high compliance, a region known as the "toe region". This biomechanical behavior is primarily due to which of the following microstructural phenomena?

. Microfailure of individual collagen fibrils
. Viscoelastic stress relaxation
. Uncrimping of type I collagen fibers
. Expulsion of water from the proteoglycan matrix
. Plastic deformation of elastin fibers

Correct Answer & Explanation

. Microfailure of individual collagen fibrils

Explanation

The "toe region" of a ligament or tendon stress-strain curve represents the initial low-stiffness elongation. Histologically, this correlates to the straightening or "uncrimping" of the natural wavy pattern of the Type I collagen fibers before they take on significant tensile loads.

Question 1167

Topic: Biomechanics & Biomaterials

According to the principles of orthopedic screw biomechanics, which of the following variables has the most significant mathematical influence on the pull-out strength of a cortical screw?

. Inner (root) diameter
. Outer (major) diameter
. Screw pitch
. Thread depth
. Core size

Correct Answer & Explanation

. Inner (root) diameter

Explanation

The pull-out strength of a screw is most significantly determined by its outer (major) diameter. The formula for pull-out strength incorporates the outer diameter, thread length engaged in bone, and the shear strength of the bone material.

Question 1168

Topic: Biomechanics & Biomaterials

A surgeon plans to use a 316L stainless steel plate for a femur fracture but only has titanium screws available. Which type of corrosion is most likely to occur at the screw-plate interface?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices are placed in electrical contact within an electrolytic solution (like body fluid). The less noble metal undergoes accelerated corrosion.

Question 1169

Topic: Biomechanics & Biomaterials

A skeletal traction pin is placed in the proximal tibia, and a constant 15-pound weight is applied over several days. The progressive, time-dependent increase in deformation of the bone and soft tissues under this constant load is defined as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is a viscoelastic property where a material continues to deform over time when subjected to a constant load. In contrast, stress relaxation is the decrease in stress over time when a material is held at a constant deformation.

Question 1170

Topic: Biomechanics & Biomaterials

Titanium alloys (e.g., Ti-6Al-4V) are frequently used in orthopedics due to their excellent biocompatibility and favorable modulus of elasticity. Which of the following is a primary mechanical disadvantage of titanium alloys compared to stainless steel or cobalt-chromium?

. High modulus of elasticity
. Poor corrosion resistance
. High notch sensitivity
. High galvanic potential
. Low biocompatibility

Correct Answer & Explanation

. High modulus of elasticity

Explanation

Titanium alloys are highly notch-sensitive, meaning that scratches or surface defects significantly decrease their fatigue life and make them prone to failure. They otherwise possess excellent biocompatibility and a modulus closer to bone than stainless steel or Co-Cr.

Question 1171

Topic: Biomechanics & Biomaterials

A researcher is evaluating the mechanical properties of a newly designed intramedullary nail.

Which parameter on the stress-strain curve represents the material's stiffness (Young's modulus)?

. The area under the entire stress-strain curve
. The highest peak of the stress-strain curve
. The slope of the linear elastic region
. The point of permanent deformation
. The area under the plastic region

Correct Answer & Explanation

. The area under the entire stress-strain curve

Explanation

Young's modulus, or stiffness, is determined by the slope of the elastic (linear) portion of the stress-strain curve. The area under the curve represents toughness, while the peak represents ultimate tensile strength.

Question 1172

Topic: Biomechanics & Biomaterials

An orthopedic resident applies a dynamic flexion splint to a patient with knee stiffness. Over time, the force required to maintain the knee at a constant angle of deformation gradually decreases. This viscoelastic phenomenon is known as:

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

Correct Answer & Explanation

. Creep

Explanation

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

Question 1173

Topic: Biomechanics & Biomaterials

A surgeon uses a 316L stainless steel screw to secure a Ti-6Al-4V titanium alloy plate. Several months later, rapid localized corrosion is noted at the screw-plate interface. Which type of corrosion is most directly caused by using these two dissimilar metals?

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

Correct Answer & Explanation

. Fretting corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic/cathodic potentials are placed in electrical contact within an electrolytic solution (like body fluid). The less noble metal undergoes accelerated corrosion.

Question 1174

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is routinely used in total hip arthroplasty. Compared to conventional UHMWPE, the highly cross-linked variant provides which of the following biomechanical trade-offs?
. Increased wear resistance but decreased fatigue strength and toughness
. Increased wear resistance and increased fracture toughness
. Decreased wear resistance but increased fatigue strength
. Increased elastic modulus and decreased yield strength
. Decreased elastic modulus and increased ultimate tensile strength

Correct Answer & Explanation

. Increased wear resistance but decreased fatigue strength and toughness

Explanation

Radiation cross-linking of UHMWPE significantly improves its wear resistance, which is ideal for total hip arthroplasty. However, this process reduces its mechanical properties, including fatigue strength, ductility, and fracture toughness.

Question 1175

Topic: Biomechanics & Biomaterials

A patient presents with a painful total hip arthroplasty 5 years post-operation. Aspiration yields sterile, thick, metal-stained fluid. The biological process occurring at the modular head-neck taper (trunnionosis) is primarily driven by a combination of which two forms of corrosion?

. Galvanic and pitting corrosion
. Fretting and crevice corrosion
. Intergranular and uniform corrosion
. Stress corrosion cracking and fatigue failure
. Biological degradation and abrasive wear

Correct Answer & Explanation

. Galvanic and pitting corrosion

Explanation

Trunnionosis at the modular head-neck junction is mechanically driven by micromotion (fretting corrosion), which damages the passivating oxide layer. This is exacerbated by the restricted fluid environment in the junction (crevice corrosion).

Question 1176

Topic: Biomechanics & Biomaterials

A 45-year-old active male undergoes a total hip arthroplasty with a ceramic-on-ceramic bearing surface. Two years later, he complains of a new, audible sound coming from his hip during ambulation. What is the most likely specific cause of this phenomenon?

. Galvanic corrosion at the head-neck junction
. Aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL)
. Creep of the bearing material
. Edge loading and micro-separation leading to stripe wear
. Third-body wear from residual PMMA bone cement

Correct Answer & Explanation

. Galvanic corrosion at the head-neck junction

Explanation

Squeaking is a well-documented complication specific to ceramic-on-ceramic (CoC) bearings. It is strongly associated with component malpositioning (particularly excessive cup anteversion or inclination), which leads to edge loading. Edge loading results in stripe wear on the ceramic head and micro-separation during the swing phase of gait, producing the audible squeak.

Question 1177

Topic: Biomechanics & Biomaterials

Corrosion at modular junctions in total joint arthroplasty can lead to early implant failure. Which type of corrosion is defined as the mechanical destruction of the passivating oxide layer on the metal surface due to micromotion, followed by rapid electrochemical dissolution of the underlying exposed metal?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion occurs at the contact sites of two materials under load subjected to minute relative motion (micromotion), such as a modular head-neck junction. This micromotion mechanically strips the protective passive oxide film from the metal surface, exposing the highly reactive bare metal to the corrosive fluid environment, leading to accelerated wear and metal ion release. Galvanic corrosion, in contrast, requires two dissimilar metals electrically coupled in an electrolyte.

Question 1178

Topic: Biomechanics & Biomaterials

Viscoelasticity is a fundamental biomechanical property of biologic tissues such as ligaments and tendons. When these tissues are subjected to a high strain rate (rapid loading) compared to a low strain rate, how do their mechanical properties change?

. Increased stiffness and higher energy absorption before failure
. Decreased stiffness and lower energy absorption before failure
. Increased stiffness and lower energy absorption before failure
. Decreased stiffness and higher energy absorption before failure
. Modulus of elasticity decreases while ultimate tensile strength remains unchanged

Correct Answer & Explanation

. Increased stiffness and higher energy absorption before failure

Explanation

Viscoelastic materials demonstrate rate-dependent mechanical properties. At higher rates of strain, biologic tissues such as ligaments and tendons become stiffer (higher modulus) and absorb more energy before failing. This is protective during sudden, rapid loading events.

Question 1179

Topic: Biomechanics & Biomaterials

Mixing orthopaedic implant components made of 316L stainless steel and Ti-6Al-4V (titanium alloy) within the same fracture construct can precipitate galvanic corrosion. In this scenario, which metal serves as the anode and undergoes accelerated corrosion?

. Titanium alloy
. Cobalt-chromium-molybdenum alloy
. Stainless steel
. Tantalum
. Nitinol

Correct Answer & Explanation

. Titanium alloy

Explanation

When two dissimilar metals are in contact within an electrolytic environment (such as body fluid), the less noble metal acts as the anode and corrodes, while the more noble metal acts as the cathode. Stainless steel is less noble than titanium and therefore functions as the anode, undergoing galvanic corrosion.

Question 1180

Topic: Biomechanics & Biomaterials

Review the biomechanical concept illustrated by standard load-deformation curves.

On a stress-strain curve for a ductile material like stainless steel, the specific point beyond which the material will no longer return to its original shape and undergoes permanent, non-reversible plastic deformation is defined as the:

. Ultimate tensile strength
. Proportional limit
. Yield point
. Failure point
. Modulus of elasticity

Correct Answer & Explanation

. Ultimate tensile strength

Explanation

The yield point marks the transition from the elastic region to the plastic region on a stress-strain curve. Loading a material beyond its yield point results in permanent (plastic) deformation. The proportional limit is slightly before the yield point where the stress-strain relationship ceases to be perfectly linear, but for practical orthopaedic biomechanics, the yield point defines the start of plastic deformation.

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