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Biomechanics & Biomaterials MCQs

Practice Set 17 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 321

Topic: Biomechanics & Biomaterials
A new highly cross-linked ultra-high molecular weight polyethylene (UHMWPE) acetabular liner is being evaluated for total hip arthroplasty. To reduce the risk of oxidative degradation while maintaining wear resistance, which of the following processes is most commonly utilized during manufacturing?
. Gamma irradiation in air
. Addition of vitamin C
. Doping with Vitamin E (alpha-tocopherol)
. Increasing the molecular weight above 10 million g/mol
. Cold drawing of the polymer

Correct Answer & Explanation

. Doping with Vitamin E (alpha-tocopherol)

Explanation

Vitamin E (alpha-tocopherol) acts as a free radical scavenger in highly cross-linked UHMWPE. This prevents oxidative degradation without the need for melting, which can otherwise decrease the mechanical strength of the polymer.

Question 322

Topic: Biomechanics & Biomaterials

To minimize stress shielding following total hip arthroplasty, a femoral stem material with a Young's modulus closest to that of cortical bone is theoretically ideal. Which of the following orthopedic materials has a Young's modulus most similar to cortical bone?

. Cobalt-chromium alloy
. Alumina ceramic
. Titanium alloy
. Stainless steel (316L)
. Polymethylmethacrylate (PMMA)

Correct Answer & Explanation

. Titanium alloy

Explanation

Titanium alloy has a Young's modulus (approximately 110 GPa) much closer to cortical bone (15-20 GPa) compared to Cobalt-chromium (approx 210 GPa) or Stainless steel (approx 200 GPa). This closer match helps reduce the degree of stress shielding.

Question 323

Topic: Biomechanics & Biomaterials

In orthopedic biomaterials, the addition of molybdenum to 316L stainless steel primarily serves to:

. Increase the ultimate tensile strength
. Improve the fatigue life of the implant
. Reduce the modulus of elasticity
. Make the alloy MRI compatible
. Enhance resistance to pitting corrosion

Correct Answer & Explanation

. Enhance resistance to pitting corrosion

Explanation

The addition of 2-3% molybdenum to 316L stainless steel helps create a stable, protective passive oxide layer. This significantly enhances the metal's resistance to localized pitting and crevice corrosion in the chloride-rich physiological environment.

Question 324

Topic: Biomechanics & Biomaterials
A 65-year-old female with a conventional ultra-high-molecular-weight polyethylene (UHMWPE) total hip arthroplasty placed 15 years ago presents with massive asymmetric head penetration on radiographs and severe osteolysis. The polyethylene was sterilized via gamma irradiation in air. What is the primary mechanism of this catastrophic failure?
. Adhesive wear
. Abrasive wear
. Oxidative degradation
. Third-body wear
. Galvanic corrosion

Correct Answer & Explanation

. Oxidative degradation

Explanation

Historically, gamma irradiation of UHMWPE in air led to free radical formation. Over time, these free radicals reacted with oxygen, causing oxidative degradation, chain scission, embrittlement, and subsequent catastrophic wear.

Question 325

Topic: Biomechanics & Biomaterials

When discussing the biomechanics of bone, an examiner asks about the unique property that allows bone to withstand repetitive loading without immediate failure, within physiological limits. What is this property primarily attributed to?

. Its purely elastic behavior, allowing full recovery from deformation.
. Its isotropic nature, with uniform properties in all directions.
. Its ability to undergo continuous remodeling in response to stress.
. Its high tensile strength, comparable to steel.
. Its composition solely of inorganic hydroxyapatite crystals.

Correct Answer & Explanation

. Its ability to undergo continuous remodeling in response to stress.

Explanation

Bone's ability to withstand repetitive loading and adapt to mechanical demands is primarily due to its continuous remodeling process (Wolff's Law), where old bone is resorbed and new bone is formed in response to stress. Bone is viscoelastic, meaning it exhibits both elastic and viscous properties, and its recovery is not purely elastic. Bone is anisotropic, meaning its properties vary with direction. While bone has good tensile strength, it's not comparable to steel, and its strength comes from a composite structure of both inorganic hydroxyapatite and organic collagen, not solely hydroxyapatite.

Question 326

Topic: Biomechanics & Biomaterials

A candidate is asked about the biomechanics of flexor tendon repairs in the hand. Which of the following modifications most significantly increases the tensile strength of a primary Zone 2 flexor tendon repair?

. Using a 2-strand core suture instead of a 4-strand
. Increasing the number of core suture strands crossing the repair site
. Omission of an epitendinous suture
. Using an absorbable monofilament suture
. Locking only the epitendinous suture rather than the core suture

Correct Answer & Explanation

. Increasing the number of core suture strands crossing the repair site

Explanation

The ultimate tensile strength of a tendon repair is directly proportional to the number of core suture strands crossing the repair site. Adding an epitendinous suture also increases strength and smooths the repair, reducing gliding resistance.

Question 327

Topic: Biomechanics & Biomaterials

An examiner questions you on screw biomechanics. You are asked how to maximize the pull-out strength of a cortical screw in osteoporotic bone. Which of the following design alterations most significantly increases pull-out strength?

. Decreasing the pitch of the screw threads
. Increasing the core diameter of the screw
. Decreasing the outer thread diameter
. Increasing the outer thread diameter while maintaining the core diameter
. Using a partially threaded rather than a fully threaded screw

Correct Answer & Explanation

. Increasing the outer thread diameter while maintaining the core diameter

Explanation

Pull-out strength is directly proportional to the volume of bone caught between threads. It is maximized by increasing the outer diameter of the threads, decreasing the core diameter, and decreasing the pitch (more threads per unit length).

Question 328

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) reduces wear primarily by altering its material properties. Which of the following best describes the trade-off of increasing cross-linking in UHMWPE?
. Decreased wear resistance, increased fracture toughness
. Increased wear resistance, decreased fatigue strength and toughness
. Decreased adhesive wear, increased elastic modulus
. Increased abrasive wear, decreased yield strength
. Increased osteolysis, increased tensile strength

Correct Answer & Explanation

. Increased wear resistance, decreased fatigue strength and toughness

Explanation

Highly cross-linked polyethylene significantly improves wear resistance but compromises mechanical properties such as fatigue strength, ductility, and fracture toughness. This trade-off must be considered, especially when using thin liners in younger, more active patients.

Question 329

Topic: Biomechanics & Biomaterials

In a viva on orthopedic biomaterials, an examiner asks about the consequences of combining different metals in an implant construct. If a 316L stainless steel screw is placed through a titanium alloy plate in a physiologic environment, what is the most likely outcome based on the galvanic series?

. The titanium plate undergoes accelerated galvanic corrosion.
. The stainless steel screw undergoes accelerated galvanic corrosion.
. Both metals undergo equal rates of crevice corrosion.
. Galvanic corrosion is completely prevented by the passivation layers of both metals.
. Fretting corrosion occurs, but galvanic corrosion is impossible in vivo.

Correct Answer & Explanation

. The stainless steel screw undergoes accelerated galvanic corrosion.

Explanation

In a galvanic couple, the less noble (more anodic) metal undergoes accelerated corrosion. Stainless steel is more anodic than titanium alloy, making the stainless steel screw susceptible to accelerated galvanic corrosion in the physiologic electrolyte environment.

Question 330

Topic: Biomechanics & Biomaterials

In evaluating the biochemical changes in articular cartilage, how does early osteoarthritis (OA) uniquely differ from the changes seen in normal aging?

. Early OA exhibits increased water content, whereas aging exhibits decreased water content
. Early OA exhibits increased chondroitin sulfate, whereas aging exhibits increased water content
. Early OA exhibits decreased collagen synthesis, whereas aging exhibits increased collagen synthesis
. Early OA exhibits an increase in total proteoglycan content, whereas aging exhibits a decrease
. Early OA exhibits decreased keratin sulfate, whereas aging exhibits increased water content

Correct Answer & Explanation

. Early OA exhibits increased water content, whereas aging exhibits decreased water content

Explanation

A hallmark of early osteoarthritis (OA) is the disruption of the collagen meshwork, leading to increased permeability and swelling of the cartilage matrix, thereby increasing the water content. Conversely, normal aging of cartilage is characterized by a decrease in water content due to changes in proteoglycan size and aggregation. In both aging and OA, the total proteoglycan content generally decreases and the modulus of elasticity changes, but the divergent direction of water content change is a classic differentiating factor.

Question 331

Topic: Biomechanics & Biomaterials

Articular cartilage exhibits viscoelastic properties during mechanical loading. Which of the following statements best defines the biomechanical phenomenon of 'stress relaxation'?

. A constant load is applied, leading to a slow, progressive increase in deformation over time.
. A constant deformation is applied, leading to a slow, progressive decrease in the internal stress over time.
. The energy lost as heat during a single continuous loading and unloading cycle.
. The point at which a material transitions from elastic to plastic deformation.
. The application of cyclic loading causing failure at a stress lower than the ultimate tensile strength.

Correct Answer & Explanation

. A constant deformation is applied, leading to a slow, progressive decrease in the internal stress over time.

Explanation

Stress relaxation occurs when a viscoelastic material is subjected to a constant deformation (strain), resulting in a gradual decrease in internal stress over time as the fluid within the matrix redistributes. Creep, by contrast, is the gradual increase in deformation when a constant load (stress) is applied.

Question 332

Topic: Biomechanics & Biomaterials

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic environment, such as the human body. Which of the following combinations of orthopedic implants poses the highest risk for significant galvanic corrosion and is thus generally contraindicated?

. Titanium alloy and commercially pure Titanium
. Cobalt-chromium alloy and Titanium alloy
. Cobalt-chromium alloy and oxidized Zirconium
. Stainless steel and Titanium alloy
. Tantalum and Titanium alloy

Correct Answer & Explanation

. Cobalt-chromium alloy and Titanium alloy

Explanation

Stainless steel and Titanium (or Cobalt-chromium) have vastly different electrochemical potentials (anodic indices). Mixing stainless steel with Titanium or CoCr in the same construct leads to severe galvanic corrosion, preferentially degrading the more anodic metal (stainless steel). Titanium and Cobalt-chromium are frequently used together (e.g., modular THA) because their electrochemical potentials are similar, making the risk of clinical galvanic corrosion minimal.

Question 333

Topic: Biomechanics & Biomaterials

During a biomechanical testing study of human ligaments, a graft is rapidly stretched to a specific, constant length. Over an extended period of observation, the testing machine records that the amount of force required to maintain that specific length gradually decreases. This viscoelastic material property is formally known as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is the property of a viscoelastic material whereby less force (stress) is required over time to maintain a constant deformation (length). 'Creep', conversely, is the progressive increase in deformation (length) over time when a constant force (load) is applied. Hysteresis is energy loss during a loading-unloading cycle.

Question 334

Topic: Biomechanics & Biomaterials

Which biomechanical property of tendons and ligaments is characterized by a decrease in stress over time when the tissue is held at a constant length?

. Creep
. Stress relaxation
. Hysteresis
. Anisotropy
. Fatigue

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the stress (force) within a material decreases over time when it is held at a constant strain (length). Creep is the increasing deformation (strain) over time under a constant load (stress). Hysteresis is the energy lost during a loading-unloading cycle.

Question 335

Topic: Biomechanics & Biomaterials

A surgeon incorrectly utilizes a stainless steel plate and secures it with titanium screws for a femur fracture. The patient subsequently develops implant failure and localized reaction due to corrosion. What specific type of corrosion has predominantly occurred?

. Crevice corrosion
. Fretting corrosion
. Galvanic corrosion
. Pitting corrosion
. Stress corrosion cracking

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic solution (like human body fluid). An electrochemical cell is created; the less noble metal (stainless steel) acts as the anode and corrodes, while the more noble metal (titanium) acts as the cathode.

Question 336

Topic: Biomechanics & Biomaterials

A structural orthopedic implant is subjected to a constant load below its yield strength over a prolonged period. Over time, the material exhibits a gradual and continuous increase in deformation. This specific viscoelastic property is best described as:

. Stress relaxation
. Hysteresis
. Creep
. Fatigue
. Isotropy

Correct Answer & Explanation

. Creep

Explanation

Creep is a viscoelastic property defined as the progressive deformation of a material over time when subjected to a constant load or stress. Stress relaxation is the decrease in stress over time when a material is held at a constant strain (deformation). Hysteresis refers to energy lost as heat during the loading and unloading cycles of a viscoelastic material.

Question 337

Topic: Biomechanics & Biomaterials

Which of the following viscoelastic principles describes the phenomenon where articular cartilage experiences a progressive decrease in internal stress over time when subjected to a constant, maintained displacement?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation occurs when a viscoelastic material is subjected to a constant deformation (strain or displacement), resulting in a gradual decrease in internal stress over time. Conversely, 'creep' refers to the progressive deformation (strain) of a material over time when subjected to a constant load (stress). Hysteresis represents energy lost as heat during the loading and unloading cycles. Articular cartilage exhibits both creep and stress relaxation due to fluid exudation and macromolecular rearrangement.

Question 338

Topic: Biomechanics & Biomaterials

Which of the following combinations of annular pulleys is absolutely essential to preserve or reconstruct during flexor tendon repair to prevent bowstringing and ensure nearly normal finger kinematics?

. A1 and A3
. A2 and A4
. A1, A3, and A5
. A2 and A5
. A3 and A4

Correct Answer & Explanation

. A2 and A4

Explanation

The A2 and A4 pulleys are the major biomechanical components of the flexor tendon sheath. They arise directly from the periosteum of the proximal and middle phalanges, respectively. Their preservation or reconstruction is critical to prevent tendon bowstringing and preserve mechanical advantage.

Question 339

Topic: Biomechanics & Biomaterials

In orthopedic biomaterials, galvanic corrosion occurs when two electrochemically dissimilar metals are placed in physical contact within a conductive fluid environment (e.g., serum). Which of the following combinations of metals carries the highest risk of severe galvanic corrosion and is therefore contraindicated?

. Titanium alloy and commercially pure titanium
. Cobalt-Chromium and Titanium alloy
. Stainless steel 316L and Titanium alloy
. Zirconium and oxidized Zirconium
. Cobalt-Chromium and oxidized Zirconium

Correct Answer & Explanation

. Stainless steel 316L and Titanium alloy

Explanation

Stainless steel 316L and Titanium have widely separated anodic potentials in the galvanic series. When coupled in vivo, the less noble metal (stainless steel) undergoes rapid, severe galvanic corrosion. Mixing these two metals in a single construct (e.g., steel screw in a titanium plate) is contraindicated. CoCr and Ti are closer in potential and are routinely mixed (e.g., CoCr head on Ti stem) with minimal clinical issue.

Question 340

Topic: Biomechanics & Biomaterials
During fracture fixation, achieving adequate screw purchase is paramount. Which of the following structural parameters has the greatest mathematical influence on the direct pull-out strength of a cortical bone screw?
. Outer (major) diameter of the screw threads
. Inner (core) diameter of the screw
. Pitch of the screw threads
. Length of the screw head
. Thread profile angle

Correct Answer & Explanation

. Outer (major) diameter of the screw threads

Explanation

The pull-out strength of a screw is mathematically defined as: F = S × L × π × D, where S is the shear strength of the bone, L is the length of thread engagement, and D is the outer (major) diameter of the screw. Therefore, increasing the outer major diameter directly and significantly increases pull-out strength. The inner (core) diameter dictates the screw's torsional strength and resistance to fatigue failure, not pull-out strength.

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