4.7 of 72 Ratings
A 60-year-old patient presents to clinic complaining of left hip squeaking and stiffness following a ceramic-on-ceramic total hip replacement five years earlier. Initially, he was extremely pleased with the operation, but these symptoms of squeaking and stiffness have developed fairly abruptly over the past 6 months. On physical exam, he has a well-healed incision, a 1 centimeter leg length discrepancy (left shorter than right), decreased hip flexion, and decreased internal rotation. A radiograph is shown in Figure A. C-reactive protein is 0.2 mg/dL (nl <0.9 mg/dL) and erythrocyte sedimentation rate is 5 mm/hr (nl 0-15 mm/hr). What would you recommend for this patient?
Observation and physical therapy
Left hip corticosteroid injection
Left hip aspiration
Thorough debridement and two-stage revision
Thorough debridement and one-stage head and liner revision
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Which of the following statements is true regarding polymethylmethacrylate (PMMA)?
Barium sulfate initiates the polymerization of monomethacrylate
It is a ductile material
The Young's modulus is between cortical and cancellous bone
It resists shear better than compressive forces
The polymerization of PMMA is endothermic
Which of the following is a potential cause of fretting corrosion?
The micromotion at the femoral head-neck junction in a modular total hip replacement
A stainless-steel cerclage wire is in contact with a titanium-alloy femoral stem
Friction between polyethylene liner and femoral head leading to osteolysis
The formation of pits within a stainless-steel plate and the subsequent release of metal ions
The formation of an adherent oxide coating on titanium implants
Which of the following lists these materials in order of increasing modulus of elasticity?:
Cortical bone; Titanium; Cobalt-chrome; Stainless steel; Ceramic
Titanium; Cortical bone; Ceramic; Cobalt-chrome; Stainless steel
Cortical bone; Titanium; Stainless steel; Cobalt-chrome; Ceramic
Stainless steel; Titanium; Cortical bone; Ceramic; Cobalt Chrome
Cortical bone; Stainless steel; Titanium; Cobalt-chrome; Ceramic
Compared to cold-forged cobalt chrome, titanium alloys have which property?
Increased fatigue strength
Increased yield strength
Increased endurance limit
Decreased tensile strength
Which of the following statements defines creep, as it relates to material properties?
Progressive deformation response to constant force over an extended period of time
A solid material's ability to deform under tensile stress
The ability of a material's mechanical properties to vary according to the direction of load
The rupture of a material under repeated cyclic stresses, at a point below the normal static breaking strength
The ability of a material to absorb energy and plastically deform without fracturing
Which of the following definitions best describes the phenomenon of load relaxation?
Constant loading causing material to continue to deform over time
Stress at failure (the ultimate stress) divided by the strain at failure (the ultimate strain)
Decreased peak loads over time with the same amount of elongation
Stress is proportional to strain up to a limit
Strain divided by the time that the load is applied
Which of the following best describes plastic deformation?
Change in length of a material under loading that returns to its original length once the load is removed
Progressive deformation of a material in response to a constant force over an extended period
The ability of a material to resist deformation
Change in length of a material under loading that does not return to the original length once the load is removed
The relative measure of the deformation of an object due to a load
When discussing metal implants and devices, which of the following best describes fatigue?
Load at which a material fractures
Progressive deformation due to a constant force over an extended period
Change in the stress-strain relationship dependent on the rate of loading
Failure at a submaximal tensile strength level after numerous loading cycles
Change in mechanical properties as a result of the direction of a load
The elements chromium, molybdenum, and cobalt are basic components of which of the following implant materials?
What description below best describes galvanic corrosion?
Corrosion resulting from an electrochemical potential created between two metals in conductive medium
Corrosion resulting from contact sites between materials under load
Corrosion resulting from oxygen tension differences
Corrosion from localized pits on metal surfaces
Corrosion from allergic reaction
Which of the following defines the stress at which a material begins to undergo plastic deformation?
Which of the following most accurately describes stainless steel?
Composed of iron-carbon alloy, modulus of elasticity less stiff than bone
Composed of cobalt-chrome-molybdenum alloy, modulus of elasticity more stiff than bone
Composed of iron-carbon alloy, modulus of elasticity more stiff than titanium
Composed of cobalt-chrome-molybedenum alloy, modulus of elasticity less stiff than titanium
Composed of iron-carbon alloy, modulus of elasticity is more stiff than bone, cobalt-chrome, and aluminum-oxide (ceramic)
A typical load-elongation curve of a ligament is shown in Figure A. What region of the curve represents elastic deformation occurring after the crimped ligament fibrils have been straightened?
Which of the following best describes the process of galvanic corrosion?
Degradation from exposure to a harsh environment
Differences in oxygen tension within and outside of a crevice
Micromotion between material when under a load
Free radical oxidation
Electrochemical potential created between two metals in physical contact when immersed in a conductive medium
Bone is biomechanically weakest to resistance of which of the following forces?
What property of titanium alloys accounts for their high corrosion resistance in vivo?
Modulus of elasticity
Low toughness is a disadvantage of which of the following bearing surfaces used in total hip arthroplasty?
Ligaments are viscoelastic, meaning that their tensile strength is affected by:
Torsion and tension only
Orientation of applied strain
Rate of applied load
Which of the following materials has a Young's modulus of elasticity that is most similar to cortical bone
An 18-year-old female soccer player sustains a non-contact deceleration injury while making a sharp pivot to strike the ball. She hears a loud pop in her knee, is unable to bear weight initially following the injury, and develops an immediate knee effusion. The structure most likely injured in this athlete exhibits all of the following biomechanical properties EXCEPT:
The bending rigidity of the implant shown in Figure A is proportional to what power of the measured radius of the implant?
Which of the following materials is most susceptible to galvanic corrosion?