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Biomechanics & Biomaterials MCQs

Practice Set 20 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 381

Topic: Biomechanics & Biomaterials

In the context of orthopedic biomaterials, galvanic corrosion is most likely to occur under which of the following specific conditions?

. Fretting wear occurring between two identical metals at a modular junction
. Exposure of a single metallic implant to highly acidic synovial fluid
. Physical contact between two dissimilar metals in an electrolytic solution
. Fatigue failure of a highly polished ceramic articulating surface
. Polyethylene wear debris activating a local macrophage response

Correct Answer & Explanation

. Physical contact between two dissimilar metals in an electrolytic solution

Explanation

Galvanic corrosion is an electrochemical process that occurs when two dissimilar metals (having different anodic indices/electrochemical potentials) are placed in direct physical contact within a conductive electrolyte solution (such as human body fluid). The less noble metal acts as an anode and corrodes, while the more noble metal acts as a cathode.

Question 382

Topic: Biomechanics & Biomaterials

In the study of orthopaedic biomechanics, viscoelastic materials such as ligaments and tendons display time-dependent behaviors. When a ligament is subjected to a constant, sustained load over a period of time, it will undergo progressive elongation. This phenomenon is known as:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the time-dependent progressive deformation (elongation) of a viscoelastic material under a constant applied load. Stress relaxation is the decrease in stress over time when the material is held at a constant length/strain. Hysteresis is the energy lost (as heat) during the loading and unloading cycle.

Question 383

Topic: Biomechanics & Biomaterials
Highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) was developed to improve the longevity of total hip arthroplasty implants. While increasing the radiation dose during manufacturing increases cross-linking and dramatically reduces volumetric wear, it also has a detrimental effect on which of the following material properties?
. Oxidation resistance
. Melting temperature
. Ultimate tensile strength and fatigue resistance
. Biocompatibility of the wear debris
. Coefficient of friction

Correct Answer & Explanation

. Ultimate tensile strength and fatigue resistance

Explanation

Increasing the cross-linking of UHMWPE (via gamma or electron beam irradiation) significantly decreases its volumetric wear rate. However, high levels of cross-linking alter the polymer chain mobility, which leads to a decrease in mechanical properties, specifically ultimate tensile strength, fatigue resistance, and fracture toughness.

Question 384

Topic: Biomechanics & Biomaterials

Galvanic corrosion in orthopedic implants is most likely to occur when which of the following combinations of metals are placed in direct physical contact within the body?

. Titanium alloy and pure Titanium
. Cobalt-Chromium and Cobalt-Chromium
. Stainless steel 316L and Titanium alloy
. Trabecular metal and Tantalum
. Zirconium and Oxidized Zirconium

Correct Answer & Explanation

. Stainless steel 316L and Titanium alloy

Explanation

Galvanic corrosion occurs when two dissimilar metals with different anodic indices are in electrical contact within an electrolytic environment (like body fluid). Stainless steel and titanium are significantly dissimilar, leading to a galvanic couple where the less noble metal (stainless steel) undergoes accelerated corrosion.

Question 385

Topic: Biomechanics & Biomaterials

When evaluating the viscoelastic properties of tendons and ligaments, which of the following statements best defines the biomechanical phenomenon of 'stress relaxation'?

. Increasing deformation under a constant load over time
. Decreasing peak load (stress) required to maintain a constant tissue length (strain) over time
. Energy lost as heat during the loading and unloading cycle
. The dependence of the stress-strain curve on the rate of loading
. The sequential microfailure of collagen fibers just before macroscopic rupture

Correct Answer & Explanation

. Decreasing peak load (stress) required to maintain a constant tissue length (strain) over time

Explanation

Viscoelastic materials exhibit time-dependent behavior. 'Stress relaxation' is the decrease in stress (load) observed over time when a tissue is held at a constant strain (length). In contrast, 'creep' is the increase in strain (deformation) over time under a constant load. Energy lost as heat is 'hysteresis'.

Question 386

Topic: Biomechanics & Biomaterials
In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced volumetric wear rates compared to conventional ultra-high molecular weight polyethylene (UHMWPE). However, the cross-linking and subsequent thermal processing alter the mechanical properties of the material. What is the primary mechanical disadvantage of highly cross-linked polyethylene?
. Increased volumetric wear in large diameter femoral heads
. Decreased ultimate tensile strength and fatigue crack propagation resistance
. Increased susceptibility to in vivo oxidation and delamination
. Decreased biocompatibility of the generated wear debris
. Increased generation of biologically active metal ions

Correct Answer & Explanation

. Decreased ultimate tensile strength and fatigue crack propagation resistance

Explanation

Irradiation of polyethylene creates cross-links that dramatically reduce wear. However, the cross-linking process decreases ultimate tensile strength, yield strength, ductility, and fracture toughness (fatigue crack propagation resistance). Thermal treatment (remelting) is used to eliminate free radicals to prevent oxidation, but it further decreases mechanical strength. Therefore, HXLPE is more brittle than conventional PE.

Question 387

Topic: Biomechanics & Biomaterials

When evaluating the biomechanical properties of a tendon under tensile testing, the total area under the stress-strain curve represents which of the following material properties?

. Elastic modulus (stiffness)
. Ultimate tensile strength
. Yield point
. Toughness (energy absorbed before failure)
. Creep limit

Correct Answer & Explanation

. Toughness (energy absorbed before failure)

Explanation

The area under the stress-strain curve represents the toughness of a material, which is the total amount of strain energy absorbed by the material prior to failure. The elastic modulus is the slope of the linear elastic region, and the ultimate tensile strength is the peak stress achieved.

Question 388

Topic: Biomechanics & Biomaterials

Titanium alloy (Ti-6Al-4V) is frequently used in orthopedic implants. Compared to cobalt-chromium (CoCr) alloys, titanium alloy exhibits which of the following biomechanical characteristics?

. Higher modulus of elasticity
. Lower fatigue strength
. Lower modulus of elasticity
. Greater resistance to galvanic corrosion when mixed with stainless steel
. Higher density

Correct Answer & Explanation

. Lower modulus of elasticity

Explanation

Titanium alloys have a lower modulus of elasticity compared to Cobalt-Chromium or Stainless Steel, making them closer to the stiffness of cortical bone. This helps decrease stress shielding around the implant. Ti also has excellent biocompatibility but poor wear resistance.

Question 389

Topic: Biomechanics & Biomaterials
During a total hip arthroplasty, the surgeon elects to use a highly cross-linked polyethylene (HXLPE) liner. Compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE), the primary trade-off of the highly cross-linked polyethylene manufacturing process is a decrease in which of the following mechanical properties?
. Oxidation resistance
. Ultimate tensile and fatigue strength
. Resistance to abrasive wear
. Hardness
. Elastic modulus

Correct Answer & Explanation

. Ultimate tensile and fatigue strength

Explanation

Highly cross-linked polyethylene is manufactured by exposing conventional UHMWPE to radiation, which creates cross-links that dramatically improve resistance to adhesive and abrasive wear. However, this process alters the polymer structure, leading to a reduction in certain mechanical properties, most notably ultimate tensile strength, yield strength, and fatigue strength. To improve oxidation resistance, the material often undergoes thermal treatment (remelting or annealing), which can further reduce its mechanical strength.

Question 390

Topic: Biomechanics & Biomaterials
A 55-year-old man undergoes total hip arthroplasty using a highly cross-linked polyethylene (HXLPE) liner and a cobalt-chromium femoral head. Ten years later, he is asymptomatic, and radiographs show no evidence of osteolysis. Compared to conventional ultra-high molecular weight polyethylene (UHMWPE), what is the primary mechanism by which HXLPE reduces the incidence of osteolysis?
. Decreased generation of biologically active wear debris particles
. Elimination of impingement between the femoral neck and acetabular rim
. Increased material strength preventing liner fracture
. Release of anti-inflammatory mediators from the polymer matrix
. Enhanced osteoblast migration along the implant interface

Correct Answer & Explanation

. Decreased generation of biologically active wear debris particles

Explanation

Highly cross-linked polyethylene (HXLPE) undergoes irradiation to create cross-links between polymer chains, significantly increasing its resistance to adhesive and abrasive wear compared to conventional UHMWPE. This results in the generation of fewer wear debris particles, which are the primary drivers of macrophage-mediated osteolysis. Although HXLPE may produce smaller, more biologically active particles per unit volume, the total volume of particles is so drastically reduced that the overall biological response (osteolysis) is minimized. HXLPE actually has slightly decreased mechanical strength (fatigue and tensile strength) compared to conventional UHMWPE due to the irradiation and subsequent thermal treatment.

Question 391

Topic: Biomechanics & Biomaterials

Following a rigid instrumented lumbar fusion, symptomatic adjacent segment disease most frequently develops at which location relative to the fusion construct?

. One level caudal to the fusion
. One level rostral (cephalad) to the fusion
. Two levels rostral to the fusion
. The sacroiliac joints
. The exact middle segment of the fusion

Correct Answer & Explanation

. One level rostral (cephalad) to the fusion

Explanation

Adjacent segment disease most commonly occurs at the motion segment immediately rostral (cephalad) to a spinal fusion. This is attributed to altered biomechanics, increased lever arm, and concentrated stress at that un-fused level.

Question 392

Topic: Biomechanics & Biomaterials

Following a rigid lumbar fusion, adjacent segment degeneration (ASD) most commonly occurs at which specific anatomic level?

. Immediately cranial to the fusion construct
. Immediately caudal to the fusion construct
. Two levels above the fusion construct
. At the level of the fusion mass
. Two levels below the fusion construct

Correct Answer & Explanation

. Immediately cranial to the fusion construct

Explanation

Adjacent segment degeneration most commonly occurs at the level immediately cranial to the fused spinal segment. This is driven by increased biomechanical stress and altered kinematics at the unfused junction.

Question 393

Topic: Biomechanics & Biomaterials

When comparing the biomechanical properties of cortical bone to cancellous bone on a stress-strain curve, which of the following statements is true?

. Cortical bone fails at a higher strain than cancellous bone.
. Cortical bone is more porous and therefore less stiff than cancellous bone.
. Cancellous bone absorbs more energy before failure and fails at a higher strain.
. Cancellous bone exhibits a steeper slope in the elastic region of the curve.
. Cortical bone demonstrates greater viscoelastic creep under physiological loads.

Correct Answer & Explanation

. Cancellous bone absorbs more energy before failure and fails at a higher strain.

Explanation

Cortical bone is stiffer and fails at lower strain levels (around 2%), while cancellous bone is less stiff but can undergo significantly more strain (up to 50%) before failure. Therefore, cancellous bone absorbs more energy and fails at a higher strain.

Question 394

Topic: Biomechanics & Biomaterials

A surgeon removes a stainless steel plate that was previously placed adjacent to a titanium intramedullary nail. Significant corrosion is noted where the two metals were in contact. Which of the following principles best explains this phenomenon?

. Fretting corrosion from cyclic micromotion between identical metals
. Crevice corrosion due to an oxygen depletion gradient
. Galvanic corrosion where the less noble stainless steel acts as the anode
. Galvanic corrosion where the more noble titanium acts as the anode
. Pitting corrosion isolated to the titanium implant

Correct Answer & Explanation

. Galvanic corrosion where the less noble stainless steel acts as the anode

Explanation

Galvanic corrosion occurs when two dissimilar metals are in contact within a conductive fluid environment. The less noble metal (stainless steel) acts as the anode and preferentially corrodes, while the more noble metal (titanium) acts as the cathode.

Question 395

Topic: Biomechanics & Biomaterials

A new orthopedic implant is designed to minimize stress shielding in the adjacent host bone. To achieve this, the biomaterial should possess which of the following mechanical properties compared to traditional cobalt-chromium alloys?

. A higher ultimate tensile strength
. A higher modulus of elasticity
. A lower modulus of elasticity
. A decreased fatigue limit
. An increased yield point

Correct Answer & Explanation

. A lower modulus of elasticity

Explanation

Stress shielding occurs when a highly rigid implant unloads the adjacent bone, leading to osteopenia. Using a material with a lower modulus of elasticity (closer to that of cortical bone, like titanium rather than cobalt-chromium) allows more physiological load to be transferred to the bone.

Question 396

Topic: Biomechanics & Biomaterials

On a load-deformation curve for a native human ligament, the initial "toe region" is characterized by low stiffness and high deformation with minimal applied force. This region corresponds physiologically to:

. Microfailure of individual collagen fibrils
. Plastic deformation of the extracellular matrix
. Uncrimping of the naturally wavy collagen fibers
. Viscoelastic stress relaxation
. Macroscopic tissue failure

Correct Answer & Explanation

. Uncrimping of the naturally wavy collagen fibers

Explanation

The toe region of a ligament's load-deformation curve represents the physiological uncrimping or straightening of the relaxed, wavy collagen fibers. Once these fibers are straightened, the tissue enters the linear elastic region where its stiffness significantly increases.

Question 397

Topic: Biomechanics & Biomaterials

A pediatric patient treated with a dynamic orthosis experiences a progressive change in the shape of their limb over several weeks under a constant applied load. This biomechanical phenomenon is best described as:

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

Correct Answer & Explanation

. Creep

Explanation

Creep is a viscoelastic property where a biological material undergoes progressive, time-dependent deformation when subjected to a constant load. Stress relaxation, conversely, is the gradual decrease in stress over time when a material is held at a constant deformation.

Question 398

Topic: Biomechanics & Biomaterials

Cortical bone exhibits different mechanical properties depending on the direction of the applied load. For example, it is significantly stronger in longitudinal compression than in transverse tension. This fundamental material property is termed:

. Isotropy
. Anisotropy
. Viscoelasticity
. Plasticity
. Ductility

Correct Answer & Explanation

. Anisotropy

Explanation

Anisotropy refers to the characteristic of a material having highly variable mechanical properties when loaded in different directions. Bone is strongly anisotropic, being much more robust when loaded parallel to the longitudinal axis of its osteons.

Question 399

Topic: Biomechanics & Biomaterials

A patient develops a painful mass over a plated clavicle fracture 2 years post-operatively. Surgery reveals black debris where a stainless steel screw was placed through a titanium plate. Which electrochemical process is primarily responsible?

. 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 in contact within an electrolytic medium like body fluid. The less noble metal (stainless steel) acts as the anode and corrodes, while the more noble titanium acts as the cathode.

Question 400

Topic: Biomechanics & Biomaterials

On a stress-strain curve, the total area under the curve before the point of material failure represents which mechanical property?

. Elastic modulus
. Yield strength
. Ultimate tensile strength
. Toughness
. Brittleness

Correct Answer & Explanation

. Toughness

Explanation

Toughness is defined as the amount of energy a material can absorb before catastrophic failure, represented by the total area under the stress-strain curve. The slope of the linear elastic region represents stiffness or Young's modulus.

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