Thursday, February 2, 2012

Polyethylene glenoid component for total shoulders - JBJS

In the February Journal of Bone and Joint Surgery, our colleagues Wirth, Rockwood, Iannotti et al have published a Level IV study on 44 shoulders with primary or secondary arthritis having total shoulder arthroplasty with a new design of all polyethylene glenoid component that has flanges on the central peg.  

The authors were careful to disclose consultancy, speakers bureau, patents, royalties, employment, stock/stock option relationships with the company that makes this glenoid prosthesis, DePuy.

These authors have been avid students of the problems patients experience with total shoulders, having reported previously that component loosening accounted for a large percentage of the complications reported for shoulder arthroplasty. Like many others, these authors again identify glenoid component loosening as ‘the foremost cause of medium and long-term failure of shoulder replacements’. 

The authors used the method we published previously for evaluating the x-rays of these shoulders. Initial post-operative x-rays showed 35 of 44 shoulders had a perfect radiolucency grade (80%). At a mean of three years the number of shoulders with a perfect radiolucency grade had diminished to 20 (45%). Three of the shoulders had glenoid osteolysis. The 24 shoulders with glenoid retroversion had poorer glenoid fixation than the 20 shoulders without glenoid retroversion. 

Although there are no direct comparisions to other arthroplasty systems, this glenoid component may have the advantages of using pegs over keels, pegs offset in the superior/inferior and anteroposterior directions, a central peg with flanges to provide initial fixation, and the need for minimal cement.  It is the component we use here at the University of Washington for total shoulder arthroplasty.

It is concern that even though all of these arthroplasties were performed by the individual surgeon inventor who has extensive experience in this procedure, the radiographic results appear to have worsened over the relatively short mean followup period of three years. We look forward to the medium and long term results with this innovative prosthesis.

In this study, seven of the original 51 shoulders (14%) were lost to followup. For the remainder, mean SST scores improved from 3 to 9.  It is of interest that the improvement in shoulder comfort and function in this series of total shoulder arthroplasties, as indicated by the Simple Shoulder Test, are essentially the same as those that have been achieved with the ream and run procedure that avoids the risks associated with glenoid component failure (SST results with ream and run).

Finally, this paper points out that 33,000 of these glenoid components have been installed whereas outcome information is only available (from this and two other papers) on 100 or 0.3% of them. It is worthwhile considering the 'external validity question':  how generalizable is this sample of surgeries carried out by experts in the field to the remaining 29,900 or 99.7% of the arthroplasties for which the results are unavailable?  This comment is not a specific critique of this paper, but rather a reflection on how little we know about the results of shoulder arthroplasty across the country and world, especially since such a large percentage are performed by 'occasional' shoulder arthroplasty surgeons.


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