Monday, October 15, 2012

Comparison of Ten-Year Survivorship of Hip Prostheses with Use of Conventional Polyethylene, Metal-on-Metal, or Ceramic-on-Ceramic Bearings JBJS

What does "Comparison of Ten-Year Survivorship of Hip Prostheses with Use of Conventional Polyethylene, Metal-on-Metal, or Ceramic-on-Ceramic Bearings" have to do with total shoulders?

High complements go to the authors from the Valdoltra Orthopaedic Hospital in Ankaran, Slovenia for their long term followup of 487 hips in 469 patients.

This is a most interesting article in that it shows (1) long-term followup is critical for the assessment of the results of joint arthroplasty and (2) "new" is not necessarily better.  As we saw in an earlier post, a large Australian registry showed that some of the newer shoulder arthroplasty designs had higher revision rates than their predecessors. In this article about total hips, the survivorship was determined as the time to revision for any reason.  The authors found that the newer ceramic on ceramic (CoC) bearing surface systems did not outperform conventional metal on polyethylene (MoP). The newer metal on metal (MoM) bearing surfaces had significantly worse survivorship than conventional metal on polyethylene. Their results are nicely summarized in their figure below showing survivorship by year.

Of great importance in this figure is the fact that had the study been concluded at 6 years of followup, it is doubtful than any difference would have been noted. Patients expect long term performance, we need to provide long term followup.

The other important point is that lots of money is spent on developing newer prostheses, for the hip, knee and shoulder - money on research, development, FDA approval, marketing, consultancy and royalties. Imagine what the total figures might be for MoM or CoC hips. These monies are recovered from patients and their insurances. We need to keep a close eye on the value (benefit/cost) of innovation so that health care dollars are spent wisely. New designs bring new risks. CoC bearings introduce the risk of ceramic fracture. MoM bearings introduce the risk of metal debris and increased serum ion levels. 

These authors found a survivorship of 0.984 at ten years for conventional MoP bearings. New designs have to be pretty spectacular to surpass that.

In total shoulder arthroplasty, the principal cause of failure is the glenoid component, yet most 'new' generations of arthroplasty represent changes in the design and increased complexity of the humeral component. It is time to refocus efforts on where the problem lies and to put innovation to the test of long term followup as our colleagues in Slovenia have done for hip arthroplasty.


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