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8 Cards in this Set
- Front
- Back
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Acetabular screw fixation
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Using mechanical failure of fixation as the end point, Udomkiat and associates demonstrated a 12-year survivorship of 99.1% for titanium press-fit acetabular components without supplementary screw fixation. This study suggests that it is unlikely that the use of supplementary screws would lead to improved results. In addition, polyethylene wear debris tends to migrate through screw holes and along the course of screws. Screw holes also decrease the available surface for bone ingrowth. Screws that back up may be a source of backside polyethylene wear. This suggests that screw holes and the use of screws should be avoided when they are unnecessary for cup fixation.
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Cartilage structure
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Hyaluronate is a naturally occurring compound that is the backbone of the central core of the proteoglycan aggregate. Cartilage is made of two principal tissue structures. The connective tissue component includes collagen, which forms the framework for structural strength and elasticity. The proteoglycan aggregate provides a unique property of water incorporation and friction reduction capabilities. Hyaluronate forms the base or central core of the aggregate on which a link protein binds a protein core. Chondroitin sulfate and keratin sulfate are then bound to this protein core, forming the terminal extension of the aggregate.
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Embolic events
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Embolization of fat and bone marrow elements during total hip arthroplasty has been studied intraoperatively using transesophageal echocardiography. These studies showed the occurrence of a large number of embolic events during the insertion of a cemented femoral stem.
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Joint line
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Raising or lowering the joint line beyond an established threshold can cause limited range of motion, poor patellar function, and possible instability. It has been determined that a threshold of approximately 8 mm provides consistently good results after knee arthroplasty.
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Oblique rectus snip
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Has no effect on either range of motion or extensor lag compared to medial parapatellar arthrotomy.
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Patellar Resection
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studies have shown that over-resection of the patella to less than 12 to 15 mm increases anterior patellar surface strains to a point where the risk of fracture is increased
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PMMA
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PMMA has no adhesive properties and can be more accurately described as grout than glue. It does not chemically bond to bone or implants; however, mechanical bonding is accomplished with porous or coated components and with cancellous bone. PMMA is approximately three times stronger in compression than in tension. Peak blood levels of monomer are usually seen approximately 3 minutes after the cement is placed. The monomer is cleared by the lungs. Associated hypotension is more closely related to diminished blood volume than to circulating monomer levels. High porosity decreases the tensile and fatigue properties of cement. Manually mixed cement may have porosity as high as 27%. Porosity may be reduced to less than 1% through vacuum mixing or centrifugation of the cement. When adding antibiotics to cement, the compressive and tensile forces are not appreciably decreased, but the overall fatigue strength may be reduced.
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THA for acetabular fx
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Patients who undergo THA after acetabular fx have more intraop blood loss than typical THA. Those acetabular fx than undergo ORIF have less need for bonegrafting than those treated without ORIF.
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