Menu

Biomechanics & Biomaterials MCQs

Practice Set 43 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 841

Topic: Biomechanics & Biomaterials

In the manufacturing of orthopedic implants, Titanium alloy (Ti-6Al-4V) is frequently chosen over 316L Stainless Steel for specific applications, such as the femoral stems of total hip arthroplasties. Which of the following best describes an inherent mechanical or biological advantage of Titanium alloy compared to Stainless Steel?

. Higher modulus of elasticity
. Lower notch sensitivity
. Superior biocompatibility and osteointegration
. Increased ductility
. Resistance to galvanic corrosion when coupled directly with stainless steel

Correct Answer & Explanation

. Higher modulus of elasticity

Explanation

Titanium alloys exhibit superior biocompatibility and excellent osteointegration characteristics compared to stainless steel, making them ideal for cementless implant fixation. They possess a lower modulus of elasticity (closer to that of human cortical bone), which helps reduce stress shielding. However, titanium is highly notch-sensitive and less ductile than stainless steel. Mixing titanium and stainless steel implants in the same construct is generally avoided due to the theoretical risk of galvanic corrosion.

Question 842

Topic: Biomechanics & Biomaterials

An orthopedic biomechanical study evaluates a novel titanium alloy for use in fracture fixation. A sample of the material is placed in a mechanical testing machine and loaded to failure to generate a stress-strain curve. The researchers calculate the total area beneath the entire stress-strain curve from the origin up to the point of complete fracture. This calculated value represents which of the following mechanical properties?

. Stiffness
. Yield strength
. Ductility
. Resilience
. Toughness

Correct Answer & Explanation

. Stiffness

Explanation

The total area under the entire stress-strain curve represents the material's 'toughness', which is the total amount of energy a material can absorb before undergoing catastrophic failure. 'Resilience' is the area strictly under the elastic portion of the curve, representing energy absorbed without permanent deformation. 'Stiffness' is the slope of the elastic region (Young's modulus). 'Yield strength' is the specific stress level at which plastic deformation begins. 'Ductility' relates to the amount of plastic strain a material can sustain before failure.

Question 843

Topic: Biomechanics & Biomaterials

Ligaments and tendons are viscoelastic structures, meaning their mechanical behavior is dependent on the rate of loading and the time over which the load is applied. When an orthopedic surgeon tensions an ACL graft during reconstruction, the graft is pulled to a specific, constant length and held there. Over the course of several minutes, the tension (force) required to maintain that specific length gradually decreases. Which of the following biomechanical terms best describes this specific phenomenon?

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

Correct Answer & Explanation

. Creep

Explanation

Viscoelastic materials exhibit characteristic time-dependent properties. 'Stress relaxation' is defined as the steady decrease in stress (force) over time when a material is held at a constant strain (constant length). This is clinically relevant during ligament reconstruction or serial casting. 'Creep', conversely, is the gradual increase in strain (deformation or lengthening) over time when a material is subjected to a constant applied stress (constant load). 'Hysteresis' refers to the energy lost (usually as heat) during a loading and unloading cycle, represented by the area between the loading and unloading curves on a stress-strain graph. 'Isotropy' refers to materials that have the same mechanical properties in all directions, whereas ligaments are anisotropic.

Question 844

Topic: Biomechanics & Biomaterials

The sterilization and processing methods of ultra-high-molecular-weight polyethylene (UHMWPE) heavily influence its long-term wear properties in total joint arthroplasty. Historically, UHMWPE components were sterilized using gamma irradiation in the presence of air. This practice was largely abandoned because it reliably led to which of the following detrimental outcomes?

. Insufficient initial sterilization against spore-forming bacteria
. Immediate catastrophic decrease in ultimate tensile strength
. Oxidative degradation leading to embrittlement and subsurface delamination
. Excessive cross-linking resulting in extreme stiffness
. Thermal melting and loss of component modularity

Correct Answer & Explanation

. Insufficient initial sterilization against spore-forming bacteria

Explanation

Historically, gamma irradiation in air (oxygen) was the standard sterilization method for UHMWPE. The high-energy gamma rays break polymer chains and generate free radicals. While this causes some beneficial cross-linking, the free radicals react rapidly with oxygen to form hydroperoxides and ketones, a process called oxidative degradation. This oxidation continues progressively over time, even while the implant sits on the shelf, leading to a profound decrease in molecular weight, severe embrittlement, and ultimately disastrous subsurface delamination and rapid wear in vivo. Modern polyethylene is irradiated in inert environments (vacuum or argon) and often thermally treated (remelted or annealed) or infused with Vitamin E to extinguish free radicals and prevent this oxidative degradation.

Question 845

Topic: Biomechanics & Biomaterials

A 32-year-old man sustained a femur fracture treated with a stainless steel plate and screws 2 years ago. He presents with a nonunion and broken hardware. During revision surgery, the surgeon considers using titanium screws through the retained intact stainless steel plate. Which of the following is the most likely consequence of mixing these two metals?

. Fretting corrosion leading to failure of the titanium screws
. Galvanic corrosion causing accelerated degradation of the stainless steel plate
. Galvanic corrosion causing accelerated degradation of the titanium screws
. Crevice corrosion isolated to the screw holes
. No significant corrosion due to the formation of a stable passivation layer on both metals

Correct Answer & Explanation

. Fretting corrosion leading to failure of the titanium screws

Explanation

Mixing dissimilar metals in a conductive environment (body fluid) leads to galvanic corrosion. The less noble (more anodic) metal undergoes accelerated corrosion, while the more noble (cathodic) metal is protected. Titanium is more noble than stainless steel. Therefore, if titanium screws are used with a stainless steel plate, the stainless steel plate will act as the anode and undergo accelerated galvanic corrosion.

Question 846

Topic: Biomechanics & Biomaterials

During a mechanical test of a human anterior cruciate ligament (ACL) graft, a constant tensile load is applied and maintained over an extended period. It is observed that the graft gradually elongates over time under this constant load. Which viscoelastic property is being demonstrated?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Creep is a fundamental viscoelastic property characterized by the progressive deformation (elongation) of a material when subjected to a constant load (stress) over a prolonged period. In contrast, stress relaxation occurs when a material is held at a constant length (strain), resulting in a gradual decrease in stress. Hysteresis is the energy lost (usually as heat) between the loading and unloading phases of a cycle.

Question 847

Topic: Biomechanics & Biomaterials

A researcher is evaluating different calcium phosphate bone void fillers for use in metaphyseal defects. Which of the following formulations is characterized by being formed via an exothermic reaction, possesses the highest compressive strength, and undergoes the slowest rate of in vivo resorption?

. Calcium sulfate
. Tricalcium phosphate
. Calcium phosphate cement (hydroxyapatite)
. Demineralized bone matrix
. Cancellous allograft chips

Correct Answer & Explanation

. Calcium sulfate

Explanation

Calcium phosphate cements harden in an exothermic reaction to form a poorly crystalline hydroxyapatite. They provide high compressive strength (similar to cancellous bone) but possess very low tensile strength. Due to their dense, crystalline structure and lack of macroporosity, they resorb very slowly in vivo, often remaining visible on radiographs for years. In contrast, calcium sulfate and tricalcium phosphate resorb much more rapidly.

Question 848

Topic: Biomechanics & Biomaterials

A 60-year-old active female is scheduled for a total hip arthroplasty. To minimize the risk of future particle-induced osteolysis, the surgeon selects a highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) liner. Which of the following is the most notable mechanical trade-off associated with the increased cross-linking of UHMWPE?

. Increased volumetric wear rate
. Increased susceptibility to oxidation in vivo
. Decreased elastic modulus
. Increased generation of submicron wear particles
. Decreased fatigue strength and fracture toughness

Correct Answer & Explanation

. Increased volumetric wear rate

Explanation

Highly cross-linked UHMWPE is manufactured by exposing the polymer to gamma or electron beam irradiation, creating chemical bonds (cross-links) between adjacent polymer chains. This markedly reduces adhesive and abrasive wear. However, the cross-linking process decreases the polymer's bulk mechanical properties, most notably reducing its fatigue strength, fracture toughness, and ultimate tensile strength, potentially making thin components more susceptible to rim failure or fracture.

Question 849

Topic: Biomechanics & Biomaterials

During a lecture on joint biomechanics, an attending asks a resident to describe the mechanism that protects the articular cartilage of the knee from wear when a patient stands up from a chair (a condition of high load and low relative motion). Which of the following forms of joint lubrication is primarily responsible for preventing cartilage-to-cartilage contact in this specific scenario?

. Hydrodynamic lubrication
. Boundary lubrication
. Elastohydrodynamic lubrication
. Weeping lubrication
. Squeeze-film lubrication

Correct Answer & Explanation

. Hydrodynamic lubrication

Explanation

Boundary lubrication is the primary protective mechanism under conditions of high compressive load and low relative sliding speeds (such as standing from a seated position). It relies on a monolayer of molecules, principally lubricin (PRG4) and hyaluronic acid, that adhere to the articular surfaces to reduce friction and prevent direct solid-to-solid contact. Hydrodynamic and elastohydrodynamic lubrication mechanisms are fluid-film based and require relative motion (speed) to drag fluid into the gap between surfaces.

Question 850

Topic: Biomechanics & Biomaterials

In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced the incidence of osteolysis compared to conventional ultra-high molecular weight polyethylene (UHMWPE). Which of the following manufacturing steps is primarily responsible for reducing the oxidative degradation of HXLPE?

. Gamma irradiation in a vacuum
. Electron beam irradiation at room temperature
. Remelting or annealing after irradiation
. Ethylene oxide sterilization
. Addition of barium sulfate

Correct Answer & Explanation

. Gamma irradiation in a vacuum

Explanation

The cross-linking process (via gamma or electron beam irradiation) breaks carbon-hydrogen bonds, creating free radicals. These free radicals can react with oxygen, leading to oxidative degradation and premature wear in vivo. To eliminate or reduce these free radicals, the polyethylene is thermally treated through either remelting (heating above the melting point) or annealing (heating below the melting point) after irradiation.

Question 851

Topic: Biomechanics & Biomaterials

A patient who underwent a revision total hip arthroplasty with a mixed-metal system (e.g., cobalt-chromium head on a titanium stem) is at risk for galvanic corrosion. Which of the following describes the primary mechanism of this process?

. Mechanical wear leading to particulate debris and third-body wear
. Release of free radicals from ultra-high-molecular-weight polyethylene
. Electrochemical potential difference between two dissimilar metals in an electrolytic solution
. Fatigue failure of the titanium stem due to mismatch in elastic modulus
. Biological reaction to metallic ions leading to aggressive local osteolysis

Correct Answer & Explanation

. Mechanical wear leading to particulate debris and third-body wear

Explanation

Galvanic corrosion occurs when two dissimilar metals are in direct physical contact within an electrolytic solution (such as body fluids). The metal with the lower electrochemical potential acts as the anode and corrodes, releasing ions, while the more noble metal acts as the cathode. This can lead to mechanically assisted crevice corrosion and adverse local tissue reactions.

Question 852

Topic: Biomechanics & Biomaterials

Ligaments and tendons exhibit viscoelastic properties, meaning their mechanical behavior is highly dependent on the rate of loading. Which of the following correctly describes the viscoelastic phenomenon of 'creep'?

. Progressive decrease in stress when the tissue is held at a constant length
. Progressive increase in length when the tissue is subjected to a constant force
. Higher tissue stiffness and ultimate load with faster rates of loading
. Energy lost as heat during a single loading and unloading cycle
. Ultimate failure of the tissue after repeated cyclical sub-maximal loading

Correct Answer & Explanation

. Progressive decrease in stress when the tissue is held at a constant length

Explanation

Creep is defined as the progressive deformation (increase in length or strain) of a viscoelastic material when it is subjected to a constant load (force or stress) over time. Stress relaxation is the progressive decrease in stress when held at a constant length. Hysteresis represents the energy lost during a loading-unloading cycle.

Question 853

Topic: Biomechanics & Biomaterials

In modern total hip arthroplasty, highly cross-linked ultra-high-molecular-weight polyethylene (UHMWPE) is frequently utilized. The process of cross-linking is performed primarily to achieve which of the following mechanical outcomes?

. Increase oxidative resistance over time
. Increase the yield strength and fracture toughness
. Decrease adhesive and abrasive wear rates
. Decrease the elastic modulus to match cortical bone
. Enhance osteointegration and biological fixation

Correct Answer & Explanation

. Increase oxidative resistance over time

Explanation

Highly cross-linked polyethylene (HXLPE) is manufactured via gamma or electron beam irradiation to create cross-links between polymer chains. This significantly decreases adhesive and abrasive wear rates, thus reducing the risk of osteolysis. However, cross-linking generates free radicals, which can lead to oxidation if not mitigated (via remelting or adding antioxidants like Vitamin E). Cross-linking also slightly reduces yield strength and fatigue resistance.

Question 854

Topic: Biomechanics & Biomaterials

When coupling a titanium alloy femoral stem with a cobalt-chromium modular head in a total hip arthroplasty, which of the following best describes the predominant type of corrosion that occurs at the head-neck trunnion?

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

Correct Answer & Explanation

. Crevice corrosion

Explanation

The predominant form of corrosion at the modular head-neck junction (trunnion) of a total hip arthroplasty is mechanically assisted crevice corrosion, commonly referred to as fretting corrosion. Although galvanic corrosion is theoretically possible due to the mixed-metal couple (titanium and cobalt-chromium), the stable passivating oxide layers on both metals largely prevent it. Micro-motion at the interface leads to mechanical disruption of this protective oxide layer (fretting), exposing the underlying metal to the fluid environment and initiating the localized corrosive process.

Question 855

Topic: Biomechanics & Biomaterials

An orthopedic surgeon is selecting an intramedullary nail for a highly comminuted tibial shaft fracture. When reviewing the mechanical properties of the available titanium and stainless steel implants, which of the following material properties most closely defines the stiffness of the implant, represented by the slope of the elastic region on a stress-strain curve?

. Yield point
. Ultimate tensile strength
. Young's modulus
. Fatigue limit
. Toughness

Correct Answer & Explanation

. Yield point

Explanation

Young's modulus (modulus of elasticity) represents the intrinsic stiffness of a material. On a stress-strain curve, it is defined as the slope of the linear, elastic portion of the curve. The yield point is the point at which plastic (irreversible) deformation begins. Ultimate tensile strength is the maximum stress a material can withstand, and toughness is defined by the total area under the stress-strain curve, representing the energy absorbed before failure.

Question 856

Topic: Biomechanics & Biomaterials

A 45-year-old man undergoes a revision of a total hip arthroplasty due to an adverse local tissue reaction (ALTR). Intraoperative evaluation of the retrieved modular femoral head-neck taper junction reveals significant material degradation. This degradation is attributed to an electrochemical process exacerbated by repetitive mechanical micromotion. Which of the following best describes this phenomenon?

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

Correct Answer & Explanation

. Galvanic corrosion

Explanation

Fretting corrosion (also known as mechanically assisted crevice corrosion) occurs at the contact interface of two modular components (such as a femoral head-neck taper) subjected to load. Repetitive micromotion mechanically disrupts the protective oxide (passivation) layer of the metal, allowing an accelerated electrochemical corrosion process to occur. Galvanic corrosion occurs when two dissimilar metals are placed in physical contact within an electrolytic solution, but the primary driver of taper failure in modern modular hips is fretting corrosion.

Question 857

Topic: Biomechanics & Biomaterials

A study evaluates the mechanical properties of the anterior cruciate ligament (ACL) under cyclic loading. The investigators observe that when the ACL is subjected to a constant displacement (strain), the corresponding holding force required to maintain that displacement progressively decreases over time. This viscoelastic phenomenon is best described as:

. Creep
. Load to failure
. Stress relaxation
. Hysteresis
. Fatigue failure

Correct Answer & Explanation

. Creep

Explanation

Stress relaxation is a viscoelastic property defined as the decrease in applied stress (or force) over time when a material is held at a constant strain (or displacement). Creep, another viscoelastic property, is the progressive deformation (strain) of a material over time when it is subjected to a constant load (stress). Hysteresis is the energy lost (usually as heat) during the loading and unloading cycle of a viscoelastic material.

Question 858

Topic: Biomechanics & Biomaterials

A 35-year-old competitive weightlifter presents to the emergency department with acute severe pain, swelling, and ecchymosis over the right anterior axilla and medial arm. He reports feeling a sudden 'tearing' sensation at the bottom phase of a maximal bench press. Physical examination demonstrates a notable loss of the anterior axillary contour. Based on the biomechanics of this injury pattern, which portion of the pectoralis major muscle is placed under the greatest tension during this movement and most commonly ruptures first?

. The clavicular head near its sternal origin
. The sternal head at the musculotendinous junction
. The sternal head at its humeral insertion
. The clavicular head at its humeral insertion
. The abdominal head near its rectus sheath fascial origin

Correct Answer & Explanation

. The sternal head at its humeral insertion

Explanation

Pectoralis major tendon ruptures classically occur in weightlifters performing the bench press, and the most common location of failure is at the humeral insertion (tendon avulsion). The pectoralis major tendon undergoes a complex 180-degree twist before inserting on the humerus, such that the inferior (sternocostal/sternal) fibers insert most superiorly and proximally. When the arm is in maximum extension, abduction, and external rotation (the lowest point of the bench press), these inferior sternal fibers are stretched maximally. Thus, the sternal head at its humeral insertion undergoes the highest disproportionate tension and is consistently the first portion to fail.

Question 859

Topic: Biomechanics & Biomaterials

During the arthroscopic repair of a Type II Superior Labrum Anterior to Posterior (SLAP) tear in a 21-year-old collegiate baseball pitcher, anchors are placed to secure the labrum. To avoid altering the complex biomechanics of the superior labrum and to minimize postoperative stiffness, anchor placement should strictly avoid which of the following areas?

. Posterior to the biceps root
. Anterior to the biceps root
. Directly through the biceps anchor
. At the 10 o'clock position of the glenoid
. At the 11 o'clock position of the glenoid

Correct Answer & Explanation

. Posterior to the biceps root

Explanation

In repairing a Type II SLAP lesion, anchors should be placed posterior to the biceps anchor (and sometimes anteriorly if the tear extends into that region) but NEVER directly through or securing the biceps tendon root itself. Tying down the biceps anchor directly restricts its normal physiologic rolling and excursion during overhead motions, which consistently leads to severe postoperative stiffness, particularly in overhead throwing athletes.

Question 860

Topic: Biomechanics & Biomaterials

A 23-year-old elite collegiate baseball pitcher is undergoing ulnar collateral ligament (UCL) reconstruction using a palmaris longus autograft. To accurately reproduce the kinematics of the native UCL and restore valgus stability, the surgeon must precisely locate the anatomic footprints. Which of the following accurately describes the anatomic insertion of the anterior bundle of the UCL on the ulna?

. It inserts as a distinct focal point exclusively on the tip of the sublime tubercle, 2 mm distal to the joint line
. It inserts broadly along the medial olecranon, 5 mm distal to the joint line
. It inserts on the sublime tubercle and extends distally along the ulnar ridge an average of 18 mm
. It inserts 2 mm proximal to the joint line on the coronoid process
. It inserts deep to the flexor carpi ulnaris, tapering towards the supinator crest

Correct Answer & Explanation

. It inserts on the sublime tubercle and extends distally along the ulnar ridge an average of 18 mm

Explanation

The anterior bundle of the UCL is the primary restraint to valgus stress at the elbow. Anatomic studies (such as those by Dugas et al.) have demonstrated that the ulnar footprint of the anterior bundle is not merely a single point at the sublime tubercle but rather a broad insertion that begins near the sublime tubercle and tapers distally along the ulnar ridge for an average length of approximately 18 mm. Recognizing this broad, tapering footprint is critical for proper tunnel placement and graft tensioning during reconstruction.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page