Thursday, December 30, 2010

Additional questions for an orthopedic surgeon

1.  Is metal wear induced by debris from the implant the only cause of Osteolysis (loss or dissolution of bone around the implant) that results in loosening of the implant?

2.  Is it correct to state that pseudotumors will keep reemerging until all metal is removed from the body which entails revision surgery to a non metal replacement?

3. Why are metal toxicity tests indicated for patients experiencing pain with a metal implant if there are limitations to the measurements since they only measure free circulating ions in the blood rather than total levels? 

4.  How can you measure the total body metal load which may indicate particles spreading to the lymph nodes, liver and spleen?

5.  Given the ASR system affixes itself to the bone and is designed so that the bone grows into the implant, how much bone is lost when you replace this implant?

6.  If MRIs are best means for detecting metal and other problems from the implant, why are patients not given this test in conjunction with the soft tissue scan?  What are the risk vs reward?

7.  It seems that the protocol for correctly administering an MRI for the purpose of detecting the issues surrounding the implant is complex.  Shouldn’t a radiologist be used who has considerable experience administering the test for detecting hip issues given the complexity of the protocal required to detect the problems?

8.  What is the size of the cup used in your surgery?
  • cups with a smaller size fail at a higher rate
  • femoral head sizes less than 44 mm have  more than 5x the risk for failure over femoral componenets greater than 55 mm.
9.  What kind of clearance is there between the cup and the femoral head?
  • wear could be reduced up to 80% with clearances ranging from 70-100 micron clearance but other implants on the market have clearances between 200 to 400 microns
  • If the cup has been placed exactly at the 45 degree angle you might have low ware but few physcians seem to be able to excute that placement.  It is important that the xray confirms the 45 degree angle placement.  If it is off, the chance of having  metal fragments appear increases significantly.
10.  What does this mean?  What is a poorly performing hip?  Is it x-rays alone that demonstrate metal debris or is it xrays accompanied by symptoms?
 Early revision of poorly performing hip replacements that generate metal debris should give a better revision outcome (taken from the recall notice to orthodpedic surgeons on 8/24/10.)


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