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Biomechanics & Biomaterials MCQs

Practice Set 88 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 1741

Topic: Biomechanics & Biomaterials

A stress-strain curve for a typical orthopaedic metallic implant is shown.

What does the area under the curve within the elastic region represent?

. Modulus of resilience
. Toughness
. Ultimate tensile strength
. Fatigue limit
. Plasticity

Correct Answer & Explanation

. Modulus of resilience

Explanation

The area under the stress-strain curve in the elastic region represents the modulus of resilience, which is the energy absorbed by a material before yielding. The total area under the entire curve (elastic and plastic regions) represents the material's toughness.

Question 1742

Topic: Biomechanics & Biomaterials

An orthopaedic surgeon uses a Taylor Spatial Frame (TSF)

to correct a complex multidirectional lower limb deformity. The software program requires the surgeon to define a 'reference fragment'. The mathematical algorithm utilized by the TSF to calculate strut adjustments is based on which of the following kinematic principles?

. Eulerian rigid body dynamics
. Stewart-Gough platform kinematics
. The Ilizarov principle of distraction histiogenesis
. Navier-Stokes equations
. Paley's Multiplier theorem

Correct Answer & Explanation

. Stewart-Gough platform kinematics

Explanation

The Taylor Spatial Frame is a hexapod external fixator based on the Stewart-Gough platform. It provides 6 degrees of freedom, allowing simultaneous correction of angulation, translation, rotation, and length via a web-based software algorithm.

Question 1743

Topic: Biomechanics & Biomaterials

When analyzing gait kinematics, what is the normal relationship between walking speed, cadence, and step length in a healthy adult?

. As walking speed increases, cadence decreases and step length increases.
. As walking speed increases, both cadence and step length increase.
. Cadence remains constant regardless of walking speed.
. Step length remains constant while cadence increases proportionally with speed.
. As walking speed increases, cadence increases and step length decreases.

Correct Answer & Explanation

. As walking speed increases, both cadence and step length increase.

Explanation

Walking speed is the product of cadence (steps per minute) and step length. In a healthy adult, increasing walking speed is accomplished by increasing both the cadence and the step length simultaneously.

Question 1744

Topic: Biomechanics & Biomaterials

A specialized orthopedic ligament graft is subjected to a constant, continuous displacement over time during biomechanical testing. The force required to maintain this constant displacement progressively decreases. This viscoelastic property is best defined as:

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation is a viscoelastic property where the internal stress (force) of a tissue decreases over time when it is held at a constant strain (displacement). Creep, conversely, is increasing deformation under a constant load.

Question 1745

Topic: Biomechanics & Biomaterials
When evaluating bearing surfaces for a total hip arthroplasty (THA), which of the following accurately describes the primary tribological advantage of highly cross-linked polyethylene compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE)?
. Increased yield strength
. Decreased adhesive and abrasive wear
. Increased fracture toughness
. Decreased oxidative degradation without vitamin E
. Increased fatigue strength

Correct Answer & Explanation

. Decreased adhesive and abrasive wear

Explanation

Highly cross-linked polyethylene significantly reduces both adhesive and abrasive wear compared to conventional UHMWPE. However, the radiation cross-linking process inherently decreases the material's fatigue strength, yield strength, and fracture toughness.

Question 1746

Topic: Biomechanics & Biomaterials

During biomechanical testing, a ligament is rapidly stretched to a specific, constant length and held rigidly in place. Over a period of minutes, the tensile force required to maintain this exact length is observed to gradually decrease. What specific viscoelastic property does this phenomenon represent?

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

Correct Answer & Explanation

. Stress relaxation

Explanation

Stress relaxation occurs when a viscoelastic material is held at a constant deformation/strain, and the internal stress (force) required to maintain that state decreases over time. Creep, inversely, is the progressive deformation of a material over time under a constant applied load.

Question 1747

Topic: Biomechanics & Biomaterials

In an orthopedic biomechanics laboratory, a viscoelastic tendon graft is subjected to a constant, sustained tensile load over a prolonged period. It is observed that the material continues to deform slowly over time despite the load remaining unchanged. Which biomechanical property does this phenomenon represent?

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

Correct Answer & Explanation

. Creep

Explanation

Creep is the progressive deformation of a viscoelastic material when it is subjected to a constant load over time. Stress relaxation, conversely, is the decrease in internal stress over time when a material is held at a constant strain or length.

Question 1748

Topic: Biomechanics & Biomaterials

The Taylor Spatial Frame (TSF) utilizes Stewart-Gough platform biomechanics. How many independent parameters (degrees of freedom) must be established to fully define the spatial deformity of the moving fragment relative to the reference fragment?

. Four
. Five
. Six
. Eight
. Nine

Correct Answer & Explanation

. Six

Explanation

The Taylor Spatial Frame corrects deformities in all six degrees of freedom: anterior-posterior translation, lateral-medial translation, axial translation (length), anterior-posterior angulation (procurvatum/recurvatum), lateral-medial angulation (varus/valgus), and axial rotation.

Question 1749

Topic: Biomechanics & Biomaterials

In biomechanical planning for fracture fixation, a surgeon contemplates replacing a stainless steel compression plate with a titanium plate of identical geometric dimensions. How will the bending stiffness of the construct change, and which material property is responsible?

. Stiffness will increase due to titanium's higher yield strength.
. Stiffness will decrease due to titanium's lower elastic (Young's) modulus.
. Stiffness will remain unchanged because the area moment of inertia is identical.
. Stiffness will increase due to titanium's higher area moment of inertia.
. Stiffness will decrease due to titanium's lower ultimate tensile strength.

Correct Answer & Explanation

. Stiffness will decrease due to titanium's lower elastic (Young's) modulus.

Explanation

Bending stiffness depends on both geometry (area moment of inertia) and the material's elastic modulus (Young's modulus). Titanium has a lower elastic modulus than stainless steel, making a plate of identical dimensions less stiff.

Question 1750

Topic: Biomechanics & Biomaterials

A 25-year-old female presents with groin pain. Radiographs reveal a lateral center-edge angle of Wiberg of 12 degrees. How does this structural abnormality alter hip biomechanics compared to a normal hip?

. Increases the contact area, reducing peak cartilage stress
. Shifts peak contact stress to the anterolateral acetabular rim
. Shifts peak contact stress to the medial acetabular wall
. Increases the abductor moment arm
. Reduces the joint reaction force during single-leg stance

Correct Answer & Explanation

. Shifts peak contact stress to the anterolateral acetabular rim

Explanation

A center-edge angle of less than 20 degrees indicates acetabular dysplasia. The shallow, uncovered roof significantly decreases the articular contact area, abnormally shifting peak stresses to the anterolateral acetabular rim.

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