Definitions Biomaterials encompasses all synthetic and natural materials used during orthopaedic procedures Basic definitions load a force that acts on a body stress definition intensity of an internal force calculation force / area units Pascal's (Pa) or N/m2 strain definition relative measure of the deformation of an object calculation change in length / original length units none Mechanical property definitions elastic deformation reversible changes in shape to a material due to a load material returns to original shape when load is removed plastic deformation irreversible changes in shape to a material due to a load material DOES NOT return to original shape when load is removed toughness definition amount of energy per volume a material can absorb before failure (fracture) calculation area under the stress/strain curve units joules per meter cubed, J/m3 creep increased load deformation with time under constant load load relaxation decrease in applied stress under conditions of constant strain hysteresis (energy dissipation) characteristic of viseoelastic materials where the loading curve does not follow the unloading curve the difference between the two curves is the energy that is dissipated finite element analysis breaking up a complex shape into triangular or quadrilateral forms and balancing the forces and moments of each form to match it with its neighbor Material Strength: Stress vs Strain Curve Derived from axially loading an object and plotting the stress verses strain curve Elastic zone the zone where a material will return to its original shape for a given amount of stress "toe region" applies to a ligaments stress/strain curve represents straightening of the crimped ligament fibrils Yield point the transition point between elastic and plastic deformation Yield strength the amount of stress necessary to produce a specific amount of permanent deformation Plastic zone the zone where a material will not return to its orginal shape for a given amount of stress Breaking point the object fails and breaks Ultimate (Tensile) strength defined as the load to failure Hooke's law when a material is loaded in the elastic zone, the stress is proportional to the strain Young's modulus of elasticity measure of the stiffness (ability to resist deformation) of a material in the elastic zone calculated by measuring the slope of the stress/strain curve in the elastic zone a higher modulus of elasticity indicates a stiffer material Young's Modulus of Metals and Biologics Relative values of Young's modulus of elasticity 1. Ceramic (Al2O3) 2. Alloy (Co-Cr-Mo) 3. Stainless steel 4. Titanium 5. Cortical bone 6. Matrix polymers 7. PMMA 8. Polyethylene 9. Cancellous bone 10. Tendon / ligament 11. Cartilage Material Descriptions Brittle material a material that exhibits linear stress stain relationship up until the point of failure undergoes elastic deformation only, and little to no plastic deformation examples PMMA ceramics Ductile Material undergoes large amount of plastic deformation before failure example metal Viscoelastic material a material that exhibits a stress-strain relationship that is dependent on duration of applied load and the rate by which the load is applied (strain rate) a function of the internal friction of a material examples ligaments bone Isotropic materials possess the same mechanical properties in all directions example golf ball Anisotropic materials possess different mechanical properties depending on the direction of the applied load examples ligaments bone Metal Characteristics Fatigue failure failure at a point below the ultimate tensile strength secondary to repetitive loading depends on magnitude of stress and number of cycles Endurance limit defined as the maximal stress under which an object is immune to fatigue failure regardless of the number of cycles Creep phenomenon of progressive deformation of metal in response to a constant force over an extended period of time Corrosion refers to the chemical dissolving of metal. Types include galvanic corrosion dissimilar metals leads to electrochemical destruction mixing metals 316L stainless steel and cobalt chromium (Co-Cr) has highest risk of galvanic corrosion can be reduced by using similar metal crevice corrosion occurs in fatigue cracks due to differences in oxygen tension 316L stainless steel most prone to crevice corrosion titanium least prone to crevice corrosion fretting corrosion description a mode of destruction at the contact site from the relative micromotion of two materials or two components clinical significance common at the head-neck junction in hip arthroplasty most common cause of mid-stem failure in modular revision type stems arthroplasty involving modular implants are at risk for fretting corrosion and failure between the components of the final implant increased risk with the increased number of interfaces between the various components Specific Metals Titanium uses fracture plates screws intramedullary nails some femoral stems advantages very biocompatable forms adherent oxide coating through self passivation corrosion resistant low modulus of elasticity makes it more similar to biologic materials as cortical bone disadvantages poor resistance to wear (notch sensitivity) (do not use as a femoral head prosthesis) generates more metal debris than cobalt chrome Stainless Steel (316L) components primarily iron-carbon alloy with lesser elements of chromium molybdenum manganese nickel advantages very stiff fracture resistant disadvantages susceptible to corrosion stress shielding of bone due to superior stiffness Cobalt alloy components cobalt chromium molybdenum advantages very strong better resistance to corrosion than stainless steel Specific Non-Metals Ultra-high-molecular-weight polyethylene advantages tough ductile resilient resistant to wear disadvantages susceptible to abrasion wear usually caused by third body inclusions thermoplastic (may be altered by extreme temperatures) weaker than bone in tension other gamma irradiation increases polymer chain cross-linking which improves wear characteristics decreases fatigue and fracture resistance Polymethylmethacrylate (PMMA, bone cement) functions used for fixation and load distribution in conjunction with orthopaedic implants functions by interlocking with bone may be used to fill tumor defects and minimize local recurrence properties 2 component material powder polymer benzoyl peroxide (initiator) barium sulfate (radio-opacifier) coloring agent (green chlorophyll or blue cobalt) liquid monomer DMPT (N,N-Dimethyl para-toluidine, accelerator) hydroquinone (stabilizer) advantages reaches ultimate strength at 24 hours strongest in compression Young's modulus between cortical and cancellous bone disadvantages poor tensile and shear strength insertion can lead to dangerous drop in blood pressure failure often caused by microfracture and fragmentation Silicones polymers that are often used for replacement in non-weight bearing joints disadvantages poor strength and wear capability responsible for frequent synovitis Ceramics advantages best wear characteristics with PE high compressive strength disadvantages typically brittle, low fracture toughness high Young's modulus low tensile strength poor crack resistance characteristics Bone Bone composition composed of collagen and hydroxyapatite collagen low Young's modulus good tensile strength poor compressive strength hydroxyapatite stiff and brittle good compressive strength Mechanical properties advantages strongest in compression a dynamic structure remodels geometry to increase inner and outer cortex to alter the moment of inertia and minimize bending stresses disadvantages weakest in shear Failure (fracture) tension usually leads to transverse fracture secondary to muscle pull compression due to axial loading leading to a crush type fracture bone is strongest in resisting compression bending leads to butterfly fragment torsion leads to spiral fracture the longer the bone the greater the stresses on the outer cortex under torsion Ligaments & Tendons Characteristics viscoelastic with nonlinear elasticity displays hysteresis (see definition above) Advantages strong in tension (can withstand 5-10% as opposed to 1-4% in bone) Disadvantages demonstrate creep and stress relaxation
QUESTIONS 1 of 45 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 Previous Next (OBQ20.123) Figures A and B demonstrate two different fracture patterns. What is the percent change in strain at fracture site Y relative to fracture site X when the fractures are unloaded? QID: 215534 FIGURES: A B Type & Select Correct Answer 1 50% increase 8% (75/904) 2 80% decrease 47% (423/904) 3 100% increase 9% (82/904) 4 20% decrease 20% (179/904) 5 No change 15% (134/904) L 4 Question Complexity E Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (SBQ18BS.11) Which of the following types of corrosion is defined by the formation of pits, grooves, and oxide debris due to the relative micromotion between two affixed materials placed under a load? QID: 211222 Type & Select Correct Answer 1 Crevice 10% (182/1852) 2 Fretting 61% (1138/1852) 3 Galvanic 7% (136/1852) 4 Pitting 17% (321/1852) 5 Stress 3% (57/1852) L 3 Question Complexity A Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic (OBQ18.152) Based on the stress-strain curve in Figure A, which of the following materials has the highest modulus of elasticity? QID: 213048 FIGURES: A Type & Select Correct Answer 1 Ceramic 67% (1197/1799) 2 PMMA 2% (42/1799) 3 Titanium 3% (59/1799) 4 Cancellous bone 1% (14/1799) 5 Cartilage 26% (467/1799) N/A Question Complexity A Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 1 Review Tested Concept Review Full Topic (OBQ17.156) 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? QID: 210243 FIGURES: A Type & Select Correct Answer 1 Observation and physical therapy 7% (148/2136) 2 Left hip corticosteroid injection 0% (9/2136) 3 Left hip aspiration 7% (160/2136) 4 Thorough debridement and two-stage revision 2% (34/2136) 5 Thorough debridement and one-stage head and liner revision 83% (1767/2136) N/A Question Complexity A Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 5 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (OBQ13.189) Which of the following statements is true regarding polymethylmethacrylate (PMMA)? QID: 4824 Type & Select Correct Answer 1 Barium sulfate initiates the polymerization of monomethacrylate 11% (449/4140) 2 It is a ductile material 6% (243/4140) 3 The Young's modulus is between cortical and cancellous bone 76% (3167/4140) 4 It resists shear better than compressive forces 3% (128/4140) 5 The polymerization of PMMA is endothermic 3% (121/4140) L 2 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ13.134) Which of the following is a potential cause of fretting corrosion? QID: 4769 Type & Select Correct Answer 1 The micromotion at the femoral head-neck junction in a modular total hip replacement 74% (3269/4411) 2 A stainless-steel cerclage wire is in contact with a titanium-alloy femoral stem 11% (475/4411) 3 Friction between polyethylene liner and femoral head leading to osteolysis 3% (143/4411) 4 The formation of pits within a stainless-steel plate and the subsequent release of metal ions 10% (420/4411) 5 The formation of an adherent oxide coating on titanium implants 2% (72/4411) L 3 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 1 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (SBQ12SP.45) Which of the following lists these materials in order of increasing modulus of elasticity?: QID: 3743 Type & Select Correct Answer 1 Cortical bone; Titanium; Cobalt-chrome; Stainless steel; Ceramic 16% (722/4640) 2 Titanium; Cortical bone; Ceramic; Cobalt-chrome; Stainless steel 5% (233/4640) 3 Cortical bone; Titanium; Stainless steel; Cobalt-chrome; Ceramic 70% (3226/4640) 4 Stainless steel; Titanium; Cortical bone; Ceramic; Cobalt Chrome 4% (195/4640) 5 Cortical bone; Stainless steel; Titanium; Cobalt-chrome; Ceramic 5% (244/4640) L 3 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ12.76) Compared to cold-forged cobalt chrome, titanium alloys have which property? QID: 4436 Type & Select Correct Answer 1 Increased fatigue strength 15% (679/4554) 2 Increased yield strength 11% (521/4554) 3 Increased endurance limit 8% (382/4554) 4 Decreased ductility 8% (343/4554) 5 Decreased tensile strength 57% (2602/4554) L 3 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 5 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (OBQ11.121) Which of the following statements defines creep, as it relates to material properties? QID: 3544 Type & Select Correct Answer 1 Progressive deformation response to constant force over an extended period of time 87% (3021/3460) 2 A solid material's ability to deform under tensile stress 3% (88/3460) 3 The ability of a material's mechanical properties to vary according to the direction of load 2% (62/3460) 4 The rupture of a material under repeated cyclic stresses, at a point below the normal static breaking strength 2% (86/3460) 5 The ability of a material to absorb energy and plastically deform without fracturing 5% (177/3460) L 1 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 1 Review Tested Concept Review Full Topic (OBQ11.86) Which of the following definitions best describes the phenomenon of load relaxation? QID: 3509 Type & Select Correct Answer 1 Constant loading causing material to continue to deform over time 21% (408/1909) 2 Stress at failure (the ultimate stress) divided by the strain at failure (the ultimate strain) 2% (34/1909) 3 Decreased peak loads over time with the same amount of elongation 69% (1309/1909) 4 Stress is proportional to strain up to a limit 3% (60/1909) 5 Strain divided by the time that the load is applied 5% (88/1909) L 3 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ11.104) Which of the following best describes plastic deformation? QID: 3527 Type & Select Correct Answer 1 Change in length of a material under loading that returns to its original length once the load is removed 10% (283/2761) 2 Progressive deformation of a material in response to a constant force over an extended period 6% (166/2761) 3 The ability of a material to resist deformation 0% (11/2761) 4 Change in length of a material under loading that does not return to the original length once the load is removed 82% (2260/2761) 5 The relative measure of the deformation of an object due to a load 1% (28/2761) L 1 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 4 Review Tested Concept Review Full Topic (OBQ11.111) When discussing metal implants and devices, which of the following best describes fatigue? QID: 3534 Type & Select Correct Answer 1 Load at which a material fractures 5% (125/2592) 2 Progressive deformation due to a constant force over an extended period 10% (264/2592) 3 Change in the stress-strain relationship dependent on the rate of loading 4% (108/2592) 4 Failure at a submaximal tensile strength level after numerous loading cycles 78% (2029/2592) 5 Change in mechanical properties as a result of the direction of a load 2% (54/2592) L 1 Question Complexity B Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 4 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (OBQ10.58) The elements chromium, molybdenum, and cobalt are basic components of which of the following implant materials? QID: 3146 Type & Select Correct Answer 1 Aluminum oxide 0% (12/2502) 2 Cobalt alloy 85% (2118/2502) 3 Stainless steel 13% (320/2502) 4 PMMA 1% (17/2502) 5 Tantalum 1% (32/2502) L 2 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (OBQ09.47) What description below best describes galvanic corrosion? QID: 2860 Type & Select Correct Answer 1 Corrosion resulting from an electrochemical potential created between two metals in conductive medium 94% (1915/2043) 2 Corrosion resulting from contact sites between materials under load 2% (50/2043) 3 Corrosion resulting from oxygen tension differences 2% (41/2043) 4 Corrosion from localized pits on metal surfaces 1% (28/2043) 5 Corrosion from allergic reaction 0% (4/2043) L 1 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 1 Review Tested Concept Review Full Topic (OBQ09.115) Which of the following defines the stress at which a material begins to undergo plastic deformation? QID: 2928 Type & Select Correct Answer 1 Toughness 2% (27/1460) 2 Ultimate strength 2% (24/1460) 3 Yield strength 85% (1235/1460) 4 Fatigue strength 11% (154/1460) 5 Endurance limit 1% (13/1460) L 2 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic Sorry, this question is for PEAK Premium Subscribers only Upgrade to PEAK (OBQ08.191) Which of the following most accurately describes stainless steel? QID: 577 Type & Select Correct Answer 1 Composed of iron-carbon alloy, modulus of elasticity less stiff than bone 4% (33/937) 2 Composed of cobalt-chrome-molybdenum alloy, modulus of elasticity more stiff than bone 15% (145/937) 3 Composed of iron-carbon alloy, modulus of elasticity more stiff than titanium 66% (617/937) 4 Composed of cobalt-chrome-molybedenum alloy, modulus of elasticity less stiff than titanium 5% (47/937) 5 Composed of iron-carbon alloy, modulus of elasticity is more stiff than bone, cobalt-chrome, and aluminum-oxide (ceramic) 9% (85/937) L 2 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ08.259) 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? QID: 645 FIGURES: A Type & Select Correct Answer 1 A 9% (202/2203) 2 B 75% (1653/2203) 3 C 6% (134/2203) 4 D 4% (98/2203) 5 E 5% (107/2203) L 1 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 2 Review Tested Concept Review Full Topic (OBQ08.243) Which of the following best describes the process of galvanic corrosion? QID: 629 Type & Select Correct Answer 1 Degradation from exposure to a harsh environment 2% (18/1022) 2 Differences in oxygen tension within and outside of a crevice 2% (19/1022) 3 Micromotion between material when under a load 4% (45/1022) 4 Free radical oxidation 4% (40/1022) 5 Electrochemical potential created between two metals in physical contact when immersed in a conductive medium 88% (895/1022) L 1 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 5 Review Tested Concept Review Full Topic (OBQ08.155) Bone is biomechanically weakest to resistance of which of the following forces? QID: 541 Type & Select Correct Answer 1 Tension 29% (346/1187) 2 Compression 2% (20/1187) 3 Inertia 1% (13/1187) 4 Centripetal 6% (67/1187) 5 Shear 62% (736/1187) L 3 Question Complexity D Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 5 Review Tested Concept Review Full Topic This is an AAOS Self Assessment Exam (SAE) question. Orthobullets was not involved in the editorial process and does not have the ability to alter the question. If you prefer to hide SAE questions, simply turn them off in your Learning Goals. (SAE07HK.42) What property of titanium alloys accounts for their high corrosion resistance in vivo? QID: 6002 Type & Select Correct Answer 1 Self-passivation 57% (225/392) 2 Ductility 8% (33/392) 3 Hardness 10% (40/392) 4 Modulus of elasticity 9% (36/392) 5 Conductivity 15% (58/392) N/A Question Complexity E Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 1 Review Tested Concept Review Full Topic (OBQ06.211) Low toughness is a disadvantage of which of the following bearing surfaces used in total hip arthroplasty? QID: 222 Type & Select Correct Answer 1 Cobalt chromium 1% (45/3464) 2 Titanium 23% (803/3464) 3 Ceramic 48% (1680/3464) 4 Polyethylene 24% (844/3464) 5 Stainless steel 2% (80/3464) L 4 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ05.59) Ligaments are viscoelastic, meaning that their tensile strength is affected by: QID: 945 Type & Select Correct Answer 1 Torsion and tension only 5% (49/977) 2 Orientation of applied strain 18% (179/977) 3 Rate of applied load 73% (714/977) 4 Compression only 0% (4/977) 5 Tension only 3% (26/977) L 1 Question Complexity D Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ05.183) Which of the following materials has a Young's modulus of elasticity that is most similar to cortical bone QID: 1069 Type & Select Correct Answer 1 Titanium 88% (1297/1471) 2 Zirconia 1% (9/1471) 3 Stainless steel 4% (55/1471) 4 Ceramic (Al2O3) 4% (57/1471) 5 Alloy (Co-Cr-Mo) 3% (51/1471) L 1 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 1 Review Tested Concept Review Full Topic (OBQ04.202) 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: QID: 1307 Type & Select Correct Answer 1 Viscoelasticity 9% (88/969) 2 Creep 23% (226/969) 3 Isotropism 50% (482/969) 4 Stress relaxation 8% (79/969) 5 Nonlinear elasticity 9% (87/969) L 1 Question Complexity C Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ04.63) The bending rigidity of the implant shown in Figure A is proportional to what power of the measured radius of the implant? QID: 1168 FIGURES: A Type & Select Correct Answer 1 2 9% (153/1710) 2 3 20% (339/1710) 3 4 70% (1190/1710) 4 5 1% (14/1710) 5 6 1% (10/1710) L 2 Question Complexity D Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 3 Review Tested Concept Review Full Topic (OBQ04.181) Which of the following materials is most susceptible to galvanic corrosion? QID: 1286 Type & Select Correct Answer 1 Titanium 18% (153/858) 2 Zirconia 4% (34/858) 3 Polyethylene 3% (25/858) 4 Cobalt-chromium 58% (499/858) 5 Alumina 16% (141/858) L 3 Question Complexity D Question Importance Select Answer to see Preferred Response SUBMIT RESPONSE 4 Review Tested Concept Review Full Topic
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