Friday, March 9, 2012

Bristol Hip Meeting 2011 in England: interesting comments

 (I must have missed this meeting...sorry.)

Blog excerpts from the Bristol Hip meeting in December of 2011 (the folks referred to are all MDs)

1. The problems facing the revision hip surgeon are damage to soft tissue, impaired blood supply, bone defects and extended duration of surgery on the infected hip, not unlike facing a Metal on Metal (MoM) bearing surface at revision surgery. At the 2010 meeting, the audience was introduced to the problems with MoM hip implants. This year, the meeting focused on the wear of the bearing surface of MoM resurfacing arthroplasty and total hip arthroplasty (THA), as well as the problems of corrosion at the trunnion femoral head junction and the management of this significant problem.

2. Alister Hart (London) identified that blood tests for metal ions (cobalt and chromium) have been used to investigate MoM hip replacements, but their ability to discriminate between well-functioning and failed hips is not known. The London Bearings Group performed a controlled study and concluded that if they applied a cut-off level of 7 parts per billion, then the maximum of cobalt or chromium gave a sensitivity of 52% and a specificity of 89%. A lower cut-off level increased the sensitivity (ability to identify failures) but decreased the specificity because more well-functioning THA’s will have levels above this cut-off.

3.  In David Langton’s (North Tees/Newcastle) presentation he commented that, in his opinion, all patients should undergo cobalt blood tests, and that 10ug/l identified ‘a good chance of an adverse tissue response’.

4.  We were delighted to welcome our colleagues, Tom Donaldson and Ian Clarke, from across the pond! Tom Donaldson gave a detailed review of the M2a38 MoM bearing surfaces, which to date, had not required revision surgery for Adverse Reaction to Metal Debris (ARMD). He and his research partner, Professor Ian Clarke from DARF, Loma Linda, demonstrated wear patterns on the bearing surfaces and contrasted small diameter Metasul implants with large diameter MoM total hip arthroplasties, and debated why wear damage was so consistent in large diameter MoM hip implants. Ian showed how he mapped the surface damage on MoM implants in simulating a normal functioning total hip replacement. The smaller sized femoral heads show less area of wear in comparison with the larger explanted femoral heads. This original concept was presented for the first time at The Bristol Hip Meeting. Ian was able to identify wear zones in the acetabular cups and femoral heads, as well as areas of abnormal wear and damage to the surface of the hip joint.

David Langton focused on the plastic deformation of the ASR XL bore within the femoral head and highlighted the imprint made by the trunnion. He noted the increased wear at the base of the bore. He informed the faculty and the delegates that the volumetric wear rate was less in the MoM THA’s than in resurfacing hip arthroplasty. The volume of the taper wear is small but possibly initiated a more aggressive biological reaction.

6.  Tony Nargol discussed ‘Investigation and treatment of patients with ARMD’. His presentations encapsulated all the experience that he and David Langton had gained with the MoM bearing hip practice in North Tees/Newcastle. He commented that we should remain aware of this problem in all MoM implants and that the presentation of symptoms should alert the orthopaedic surgeon to the possibility of an adverse tissue reaction. Given that in the past 12 months surgeons from the United Kingdom have published on this problem he could now tell the audience that it was possible that the Pinnacle/Corail 36mm MoM appeared to be a problem in his unit, even though it was still early days. He alluded to cup inclination, size of femoral head and various brands of prostheses. He stated that the MoM THA was a far bigger problem than resurfacing arthroplasty. The findings in Tony’s unit identify a problem, the incidence of which has not yet been established, either in the United Kingdom or abroad.

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