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14 Cards in this Set
- Front
- Back
Osteopenia has what effect on the strength of the bone-cement interface in comparison to normal bone? 1-no effect; 2-improved mechanical integrity (higher fracture resistance); 3-diminished mechanical integrity (low fracture resistance); 4-reduced depth of cement penetration into bone
5-less affected by cement pressurization |
The increased porosity seen in osteopenia and osteoporosis actually helps create a stronger bone-cement interface. Graham et al studied the effects of bone porosity, trabecular orientation, cement pressure, and cement penetration depth on fracture toughness at the bone-cement interface in bovine femora. They found that improved mechanical integrity (higher fracture resistance) is correlated with increased bone porosity (worsening osteopenia) and maximum cement penetration depth. The authors also found that with increased cement pressurization, the cement penetration depth was increased and the fracture resistance was also increased.Ans2
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All of the following are independent risk factors for dislocation after total hip arthroplasty EXCEPT? 1-Female gender; 2-Osteonecrosis; 3-Inflammatory arthritis; 4-Post traumatic OA; 5-Age >70
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pts at > risk are female pts (relative risk 2.1), those with a dx of osteonecrosis of the femoral head (relative risk 1.9), an acute fx or nonunion proximal fem treated with THA (relative risk 1.8), hx of inflammatory arthritis (relative risk 1.5), and age > 70 (relative risk 1.3). The relative risk of dislocation for pts w/ posttraumatic arthritis of the hip was not significantly different from that for patients with osteoarthritis (relative risk, 1.3; 95% confidence interval, 0.6 to 2.8) (p = 0.59). Purely post traumatic arthritis should not have an increased risk of dislocation. However, if the post traumatic arthritis occurred after acetabular fixation or proximal femur fractures(mal unions/non unions), then the risk of dislocation is higher than primary OA.Ans4
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Hx: 70yo M underwent THA 4 months ago and has experienced 3 dislocations. xrays reveal no failure of the hardware and an acetabular component that has an abduction angle of 40 degrees and a version of 10 degrees retroverted. What is the most appropriate tx for the recurrent dislocations? 1-hip abduction brace; 2-revision of the acetabular liner to a constrained type; 3-revision of the entire acetabular component; 4-revision of the femoral head to a larger size; 5-revision to an extended offset prosthesis
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post-op hip instability can be caused by several factors: soft tissue imbalance, component malposition, or position. Component malposition, as in this case, should be treated with revision of the offending component. In this case the acetabulum was placed in retroversion when it should have been 15-20 degrees anteverted. None of the other options addresses the cause of the instability. According to Morrey, the most signficant risk factors to instability are prior hip surgery, trochanteric nonunion, and posterior surgical approach. He wrote that the most reliable way to correct instability is to reorient a retroverted acetabular cup.ans3
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Hx:68yo F 2 wks s/p L THA experiences a painful clunk getting out of bed in the morning, unable to bear any weight on the L leg. xray fig A. Following CR under sedation, the hip continues to dislocate with flexion up to 90 degrees. Each of the following operative interventions will increase the stability of the hip EXCEPT: 1-Revising the acetabular component to a more medialized position; 2- Advancing the trochanter distal on the femur
3-Converting to a femoral component w/extended offset; 4-Replacing the acetabular polyethylene w/ a constrained liner; 5-Replacing the fem head w/ a larger size |
Medializing the acetabulum < the lever arm of the abductors resulting in reduced soft tissue tensioning, greater laxity, and thus < stability, Conversely, stability >following ways: Revising to an extended offset femoral component and advancing the trochanter > the lever arm of the abd>soft tissue tension. Increasing the head to neck ratio (choice 5) > the ROM to impingement. Constrained liners > the functional depth of the cup. This increases> to excursion at the cost of greater contact stresses at the acetabular bone, cup, and liner interfaces.Ans1
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What is the MC complication p/ revision of THA polyethylene liner in a pt with well-fixed femoral and acetabular shell components? 1-dislocation
2-failure of the femoral component; 3-extensive osteolysis; 4-failure of the fixation between the liner and the acetabular shell; 5-fx of the polyethylene |
Multiple studies have shown the most common complication of revision surgery with polyethylene exchange is dislocation. In a study by Lachiewicz et al 35 hips with 1st generation components (Harris-Galante porous HGP I and II acetabular components) underwent polyethylene exchange without cement. There were no instances of loosening but 7 hips dislocated. Another study by Boucher et al assessed 24 hips which underwent polyethylene liner exchange and found 25% dislocated at least once.Ans1
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Hx:62yo F presents for her 1-yr f/u p/ a revision R THA. She has no c/o pain and has returned to all her ADL. An AP Fig A. The black arrow in the xray indicates she is at > risk for which of the following? 1-Aseptic loosening; 2-Aseptic lymphocytic vasculitis-associated lesions (ALVAL); 3-Dislocation
4-3rd body wear; 5-Catastrophic ceramic bearing failure |
radiographs reveal a constrained system by the metal ring of the constrained liner, and subsequent broken ring representing a dissociation of the liner. Ring failure is associated with increased risk of hip dislocation. The incidence of dislocation ranges from 0.5% to 10% after primary and up to 28% after revision THA.Ans3
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In order to determine the boundaries of the posterior-superior safe zone for acetabular screw placement during THA, a line is initially drawn through which of the following two anatomic landmarks, represented by dots on the illustration? 1-A and C; 2-B and C; 3-D and C; 4-C and E; 5-A and E
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Acetabular quadrants are formed from a line extending from the ASIS (Marker A) through the center of the acetabulum (Marker C) to the posterior fovea, forming acetabular halves. The second line is drawn perpendicular to the first at the center of acetabulum, forming four quadrants (Illustration A).Ans1
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Hx:64yo M undergoes acetabular revision of his failed THA using a large uncemented component. Post-op he is noted to have a foot drop & radicular pain in the operative extremity. A CT of the hip is obtained and reveals screw penetration into the sciatic notch. Where was this screw most likely inserted in the acetabulum? 1-Anterior superior quadrant; 2-Through the medial wall; 3-Anterior inferior quadrant; 4-Posterior superior quadrant
5-Through the femoral nerve |
Long screws placed into the posterior superior or posterior inferior quadrant may pass into sciatic notch and endanger the sciatic nerve and superior gluteal vessels. This is particularly a risk in revision surgery when the acetabular component may be placed in a high hip center position, as the sciatic nerve is at increased risk when placing transacetabular screws posteriorly, Of all the acetabular revision scenarios tested, the high hip center showed increase risk of neurovascular injury in the center and anterior portions of the posterior superior quadrant. Ans 4
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Hx:67yo F underwent a THA 6 months ago and has had recurrent prosthetic dislocations. Fig A is a drawing of the mechanism of her dislocation. During the time of surgery what is the most likely factor leading to the bone-on-bone impingement? 1-Lateralizing the acetabular cup; 2-Decreased femoral offset; 3-Increased femoral offset; 4-Increased acetabular inclination (>55 degrees)
5-Small head-neck ratio (<2) |
decreased hip offset places the hip at risk for the femoral bone impinging against the pelvis at the extremes of motion.
There are several ways the femoral offset can be decreased leading to bone-bone impingment. One such way is medializing and raising the center of rotation, which is often done to prevent metal neck-on-cup impingement , Methods to correct a decreased offset includes a higher osseous femoral neck cut, a longer modular head, a high-offset stem, or a combination of these, 4.9% total hip dislocation rate and emphasized the importance of maintaining the effective femoral neck length to increase prosthesis stability. Ans2 |
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Which of the following templates, will increase the offset while keeping the leg lengths the same? 1: acetebulum COR is superior & medial to femoral COR; 2: acetebulum COR is= & superior to femoral COR; 3: acetebulum COR is medial & medial to femoral COR; 4: acetebulum COR is inferior & lateral to femoral COR; 5: acetebulum COR is laterial & inferior to femoral COR
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If the COR of the prosthetic head lies lateral to that of the cup on templating, THEN the reconstruction will produce decreased offset, IF the femoral center of rotation on templating is inferior to that of the acetabular component, the limb will be shortened. Answer 1: Figure A will decrease leg length and decrease offset.
Answer 2: Figure B will maintain offset but decrease leg length. Answer 3: Figure C will decrease offset and maintain leg lengths. Answer 4: Figure D will increase leg length and increase offset.Ans5 |
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In total hip arthroplasty, which of the following techniques will lead to improved stability by increasing the abductor tension? 1-Use of a high offset femoral component; 2-Decreasing neck length; 3-Use of a low offset femoral component; 4. Increasing the head size; 5-Medializing the acetabular component
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high offset stems are a tool to assist in increasing tension and improving stability in the appropriate patient. A disadvantage of higher offset stems may be lateral prominence and trochanteric bursitis in thin patients, potential benefits of a high offset stem included improved joint stability and avoidance of leg lengthening. Stability is improved by increasing soft tissue tension through restoring the abductor moment arm laterally in high offset stems.Ans1
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Which of the following factors is most likely to increase the risk of hip dislocation after a total hip arthroplasty (THA)? 1-Large head-to-neck ratio; 2-Use of a skirted femoral head; 3-Femoral component in 15 deg of anteversion; 4-acetabular cup in 15 deg of anteversion; 5-Acetabular cup in 50 degrees of abduction
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The use of a skirted femoral head actually decreases the head to neck ratio as seen in illustration A, and leads to increased risk of hip impingement and dislocation after THAs. Illustration B shows an example of a smaller head-to-neck ratio causing decreased hip arc of motion before impingement occurs,Ways to minimize the risk of impingement and dislocation included avoiding the use of skirted heads, maximing head-to-neck ratio, and using chamfered acetabular liners whenever possible. With the use of computer modeling studies, he found that optimal femoral component anterversion is 10-20 degrees, while optimal acetabular component positioning is 10-20 degrees of anterversion and 45-55 degrees of abduction.Ans2
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All of the following are risk factors for developing a sciatic nerve palsy following total hip arthroplasty EXCEPT: Topic Review Topic
QID: 771 1. Female gender 2. Developmental dysplasia of the hip 3. Revision surgery 4. Rheumatoid arthritis 5. Lengthening of the extremity |
Female gender, DDH, Revision surgery, and extremity lengthening are all risk factor for the development of a post-operative sciatic nerve palsy following total hip arthroplasty. Rheumatoid arthritis is not a risk factor.
Nerve palsy is an uncommon but devastating injury following total hip arthroplasty. Common causes include compression from hematoma or tight dressings, direct injury, and excess heat from polymethylmethacralate polymerization. Initial management in the post-operative period is to place the hip in extension and the knee in flexion to take tension off the sciatic nerve. If a hematoma is thought to be the cause, excavation in the operating room is the preferred treatment.Ans4 |
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Which of the following has been shown to increase the rate of failure of cemented femoral components in total hip arthroplasty? 1-Stems that are precoated with polymethylmethacrylate
2-Calcar contact of the collar; 3-Smoother implant corners; 4-Cement mantle of 2 millimeters 5-Stem material with a Young's modulus higher than 115 GPa |
Precoating a stem with PMMA adds an additional inferface at risk of failure.
Stiffer stem materials (higher Young's modulus) improve performance. Titanium has a Young's modulus of 115 GPa with alloy and stainless steel having a higher Young's modulus than titanium. Calcar collar contact adds minimal strength to the construct, but does not lead to premature failure. Smoother corners decrease the rate of failure since they decrease stress risers. The ideal cement mantle is ~2mm. Obtaining less than this would decrease the strength of the construct.Ans1 |
