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Biomechanics & Biomaterials MCQs

Practice Set 21 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 401

Topic: Biomechanics & Biomaterials

Fatigue failure of an orthopaedic implant is most likely to occur under which of the following conditions?

. A single applied stress that exceeds the ultimate tensile strength
. A single applied stress that exceeds the yield point but is below the ultimate tensile strength
. Cyclic loading at stress levels below the yield point
. Rapid application of an extremely high strain rate load
. Exposure to high temperatures during autoclave sterilization

Correct Answer & Explanation

. Cyclic loading at stress levels below the yield point

Explanation

Fatigue failure occurs when an implant is subjected to repetitive (cyclic) loading at stress levels well below its yield strength. In the presence of a nonunion, the implant absorbs continuous cyclic loads, eventually leading to hardware fracture.

Question 402

Topic: Biomechanics & Biomaterials

A surgeon secures a cerclage wire around a femoral shaft. Over several months, the wire remains intact but becomes loose due to continuous deformation of the bone under constant strain. What viscoelastic property is this?

. Hysteresis
. Creep
. Stress relaxation
. Anisotropy
. Isotropic degradation

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the internal stress within a material decreases over time when it is held at a constant strain or deformation. Creep is the opposite, characterized by increasing deformation under a constant load.

Question 403

Topic: Biomechanics & Biomaterials

Articular cartilage exhibits rate-dependent stiffness, acting much stiffer under rapid impact loading than under slow loading. This biomechanical property is primarily due to:

. The immediate synthesis of type II collagen
. Frictional drag of interstitial fluid flowing through the porous solid matrix
. Rapid crystallization of hydroxyapatite within the superficial zone
. Depolymerization of aggrecan molecules
. The purely elastic behavior of chondrocytes

Correct Answer & Explanation

. Frictional drag of interstitial fluid flowing through the porous solid matrix

Explanation

Articular cartilage is a biphasic material. Under rapid loading, the interstitial fluid cannot quickly escape the porous extracellular matrix, resulting in high internal pressure and increased stiffness due to fluid frictional drag.

Question 404

Topic: Biomechanics & Biomaterials

A 45-year-old male undergoes a revision total hip arthroplasty with a fully porous-coated diaphyseal fitting stem. Postoperatively, he experiences severe thigh pain attributed to stress shielding. Which of the following material properties of the stem is most responsible for this phenomenon?

. High ductility
. High modulus of elasticity
. Low yield strength
. High ultimate tensile strength
. Low fatigue limit

Correct Answer & Explanation

. High modulus of elasticity

Explanation

Stress shielding occurs when a rigid implant unloads the surrounding bone, leading to osteopenia. Materials with a high modulus of elasticity, such as cobalt-chromium, take on more physiologic loads and cause greater proximal bone resorption.

Question 405

Topic: Biomechanics & Biomaterials

A surgeon incorrectly mixes a stainless steel screw with a titanium plate during internal fixation of a femur fracture. Which type of corrosion is most likely to occur, and which metal will degrade?

. Crevice corrosion; titanium degrades
. Galvanic corrosion; titanium degrades
. Galvanic corrosion; stainless steel degrades
. Fretting corrosion; stainless steel degrades
. Pitting corrosion; titanium degrades

Correct Answer & Explanation

. Galvanic corrosion; stainless steel degrades

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in a conductive fluid like body tissue. The less noble metal, which is stainless steel in this scenario, acts as the anode and will undergo accelerated degradation.

Question 406

Topic: Biomechanics & Biomaterials

During a biomechanical study of the ACL, a constant tensile load is applied to the ligament over an extended period. The investigator notes that the ligament continues to slowly elongate despite the load remaining unchanged. What biomechanical property does this represent?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is defined as the time-dependent deformation of a viscoelastic material under a constant load. Stress relaxation, in contrast, is the decrease in internal stress over time when the material is held at a constant deformation.

Question 407

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for a ductile biomaterial like stainless steel, what does the total area under the curve up to the point of failure represent?

. Elasticity
. Yield strength
. Ultimate tensile strength
. Toughness
. Brittleness

Correct Answer & Explanation

. Toughness

Explanation

The total area under the stress-strain curve up to the exact point of fracture represents the material's toughness, which is the total energy it can absorb before failing. The area under just the linear elastic portion represents the resilience.

Question 408

Topic: Biomechanics & Biomaterials

An orthopaedic implant manufacturer is designing a new cementless hip stem. They wish to use a metal with the lowest modulus of elasticity that still provides adequate fatigue strength to minimize stress shielding. Which of the following metals should they select?

. Stainless Steel 316L
. Cobalt-Chromium-Molybdenum
. Titanium-6Aluminum-4Vanadium
. Tantalum
. Pure Zirconium

Correct Answer & Explanation

. Titanium-6Aluminum-4Vanadium

Explanation

Titanium alloys have a modulus of elasticity roughly half that of stainless steel and one-third that of cobalt-chromium. This lower stiffness more closely mimics cortical bone, reducing stress shielding while maintaining excellent fatigue strength.

Question 409

Topic: Biomechanics & Biomaterials

In total joint arthroplasty, stress shielding of the proximal femur is primarily determined by the mismatch in which of the following material properties between the metallic implant and the host bone?

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

Correct Answer & Explanation

. Modulus of elasticity

Explanation

Stress shielding occurs due to a mismatch in the modulus of elasticity (Young's modulus) between the stiffer metallic implant and the less stiff surrounding bone. This lack of physiologic loading leads to adaptive bone resorption according to Wolff's Law.

Question 410

Topic: Biomechanics & Biomaterials
An ultra-high-molecular-weight polyethylene (UHMWPE) acetabular liner undergoes progressive, time-dependent deformation under the constant compressive load of a patient's body weight. This specific biomechanical phenomenon is known as:
. Fatigue failure
. Stress relaxation
. Creep
. Galvanic corrosion
. Strain hardening

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive, time-dependent plastic deformation of a viscoelastic material when subjected to a constant load or stress over time. In contrast, stress relaxation is the decrease in stress over time when a material is held at a constant strain.

Question 411

Topic: Biomechanics & Biomaterials

An orthopaedic surgeon revises a nonunion of a femur fracture by placing a titanium locking plate adjacent to a previously retained stainless steel intramedullary nail. Which of the following modes of implant failure is most likely accelerated by this specific combination of metals?

. Fretting corrosion
. Crevice corrosion
. Galvanic corrosion
. Fatigue failure
. Stress shielding

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals (such as titanium and stainless steel) are placed in electrical contact within an electrolytic environment like body fluids. This electrochemical process leads to accelerated corrosion of the less noble metal (stainless steel).

Question 412

Topic: Biomechanics & Biomaterials

When evaluating the biomechanical properties of an intramedullary nail, its torsional rigidity is proportional to the radius to what power?

. Radius to the first power
. Radius squared (r^2)
. Radius cubed (r^3)
. Radius to the fourth power (r^4)
. Inversely proportional to the radius

Correct Answer & Explanation

. Radius to the fourth power (r^4)

Explanation

The torsional rigidity of a solid cylinder is governed by its polar moment of inertia, which is proportional to the radius to the fourth power (r^4). Therefore, small increases in nail diameter exponentially increase its resistance to torsional deformation.

Question 413

Topic: Biomechanics & Biomaterials

On a standard stress-strain curve for an orthopaedic implant material, the slope of the linear (elastic) portion represents which of the following biomechanical properties?

. Yield strength
. Toughness
. Modulus of elasticity
. Ultimate tensile strength
. Ductility

Correct Answer & Explanation

. Modulus of elasticity

Explanation

The slope of the linear portion of a stress-strain curve defines the Modulus of Elasticity (Young's modulus), which indicates a material's stiffness. Toughness is the total area under the curve, and yield strength is the point at which plastic deformation begins.

Question 414

Topic: Biomechanics & Biomaterials

According to the principles of screw biomechanics, which of the following geometric modifications most significantly increases the pullout strength of a cortical bone screw?

. Increasing the outer diameter of the screw
. Increasing the inner (core) diameter of the screw
. Increasing the thread pitch
. Decreasing the length of engagement
. Decreasing the thread depth

Correct Answer & Explanation

. Increasing the outer diameter of the screw

Explanation

Screw pullout strength is primarily determined by the outer diameter, thread length of engagement, and bone shear strength. Increasing the outer diameter directly and linearly increases the volume of bone captured between threads, maximizing pullout strength.

Question 415

Topic: Biomechanics & Biomaterials

During biomechanical testing of a viscoelastic tissue like articular cartilage, a constant load is applied, resulting in an immediate deformation that slowly continues to increase over time. This phenomenon is termed:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a viscoelastic material over time under a constant applied load. Stress relaxation, conversely, is the decrease in stress over time when the material is held at a constant strain (deformation).

Question 416

Topic: Biomechanics & Biomaterials

Polymethylmethacrylate (PMMA) acts as a grout rather than an adhesive in total joint arthroplasty. Biomechanically, PMMA exhibits its greatest structural strength against which type of applied load?

. Tension
. Compression
. Shear
. Torsion
. Bending

Correct Answer & Explanation

. Compression

Explanation

PMMA is highly resistant to compressive forces, making it an excellent grout for transferring physiological loads from an implant to the bone bed. It is notably weak under tensile and shear forces, which can lead to cement mantle failure.

Question 417

Topic: Biomechanics & Biomaterials

When examining the stress-strain curve of a healthy human ligament, the initial non-linear 'toe region' is anatomically explained by which of the following?

. Micro-failure of individual collagen fibrils
. Plastic deformation of the extracellular matrix
. Uncrimping of the resting collagen fibers
. Water exudation from the proteoglycan matrix
. Maximum cross-linking of elastin molecules

Correct Answer & Explanation

. Uncrimping of the resting collagen fibers

Explanation

The toe region reflects the stretching out, or 'uncrimping,' of the naturally wavy collagen fibers with initial load application. Once straightened, the ligament enters the linear elastic phase where the collagen backbone resists further strain.

Question 418

Topic: Biomechanics & Biomaterials

Trunnionosis, or failure at the modular head-neck taper junction of a total hip arthroplasty, is best described as mechanically assisted:

. Galvanic corrosion
. Crevice corrosion
. Pitting corrosion
. Intergranular corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Crevice corrosion

Explanation

Trunnionosis is primarily a form of mechanically assisted crevice corrosion. Micromotion (fretting) at the taper junction damages the protective oxide layer, accelerating local crevice corrosion in the fluid-filled, low-oxygen environment.

Question 419

Topic: Biomechanics & Biomaterials

The mechanical behavior of cortical bone varies depending on whether a load is applied longitudinally, transversely, or in shear. This characteristic is defined as:

. Viscoelasticity
. Anisotropy
. Isotropy
. Ductility
. Hysteresis

Correct Answer & Explanation

. Anisotropy

Explanation

Anisotropy refers to a material having different mechanical properties depending on the direction of the applied load. Cortical bone is highly anisotropic, being much stronger in longitudinal compression than in transverse tension or shear.

Question 420

Topic: Biomechanics & Biomaterials

A surgeon inadvertently utilizes a stainless steel plate with a titanium screw. The direct contact between these dissimilar metals in an electrolytic physiological fluid primarily predisposes the construct to:

. Stress shielding
. Third-body wear
. Galvanic corrosion
. Abrasive wear
. Fretting corrosion

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two metals with differing electrochemical potentials are in direct contact within an electrolytic medium (like blood or tissue fluid). The less noble metal becomes the anode and preferentially corrodes.

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