Wednesday, December 5, 2018

The international clinical success of a standard all-polyethylene glenoid component - what else is needed?

One and two-year clinical outcomes for a polyethylene glenoid with a fluted peg: one thousand two hundred seventy individual patients from eleven centers.

These authors note that each year more and more total shoulder systems are being cleared by the FDA under the 510(k) mechanism, which requires only that the new system be "substantially equivalent" to a prior legally marketed design.

They point out that clinical shoulder science lacks a benchmark against which the early clinical value of these new systems can be compared. They endeavored to derive such a benchmark from a multicenter study of patients receiving an established, internationally used design of glenoid component.

They obtained data from 11 centers on 1270 patients having total shoulder arthroplasty using an all-polyethylene non-augmented component with a fluted central peg.


They analyzed individual patient outcomes at 1 and 2 years after surgery. They compared the improvement for each patient to the minimal clinically important difference (MCID) and calculated each patient's improvement as a percent of maximal possible improvement (MPI).

The preoperative scores improved from SST 3 ± 2, ASES 37 ± 15, Constant score 36 ± 16, and Penn score 30 ± 19 to SST 10 ± 2, ASES 90 ± 12, Constant 76 ± 13, and Penn 80 ± 24 (p < 0.001 for each). A high percentage of patients improved by more than the MCID (SST 96%, ASES 98%, Constant 94%, Penn 93%) and obtained improvement of at least 30% of the MPI (SST 95%, ASES 98%, Constant 91%, Penn 87%).

Importantly, the clinical outcomes realized with this glenoid design were not worse for the 41% of shoulders with preoperative type B glenoids or for the 30% of shoulders with more than 15 degrees of glenoid retroversion.

Comment: This study demonstrates that individual patients from 11 international practices having total shoulder arthroplasty using a basic glenoid component design can obtain highly significant clinical outcomes, providing a benchmark against which the early outcomes of new designs can be compared to determine whether they provide increased clinical value.

An important finding in this analysis is that with this basic glenoid component design, type B glenoids and glenoids with more than 15° of retroversion did not have outcomes that were inferior to those with less severe glenoid pathoanatomy. While special glenoid components have been marketed for the type B retroverted glenoid, this study points out that the role for these special components has yet to be clarified.

The importance of the type of benchmark established in this article is highlighted by a recent email exchange we (Shoulder Arthritis Blog) had with a senior engineer (SE) at a prominent shoulder implant company:

SE: I have a question that I’m hoping you can help me with. In general, journal articles, and our FDA require a minimum of 2-year clinical follow up for reporting on performance of medical devices. What scientific evidence supports a minimum 2-year duration? Specifically, why is two years an appropriate time point for determining device fixation and longer-term stability? I welcome your thoughts.

SAB: Please see

SE: Thank you. I will review these articles. At first glance they support what I’ve seen in a few other clinical reports. That is, the performance measurement scores tend to peak and plateau around twelve months and then don’t change statistically beyond that point.

SAB: I suggest that the big issue for companies is showing that their new device is any better than what is out there. What are your thoughts on that?

SE: You are correct. Companies are faced with proving evidence that their new device is “equivalent” to a commercially cleared device by FDA. Thus, trying to show substantial equivalency to a predicate device. The FDA has evolved to requesting two-year clinical data to support 510K submissions for some types of devices even if there is a cleared predicate. So my question is, why two years? What specific measurable characteristics are captured at two years that support expected outcomes for the duration of the implanted device? If we can identify these specific characteristics, then can we accurately predict the longer term out come if we are able to identify and measure these same characteristics at one year?

If osseointegration is shown to occur within six months of implantation, and an implanted device shows radiographic signs of osseointegration, and is free of any indications of radiographic loosening at one year, can we successfully predict that proper fixation and implant stability will continue longer term?

SAB: We think the answer to your questions is “YES”, but to us a more important question is, if the new device is equivalent to a prior device, why do we need it? It seems that companies need to show that their device yields better outcomes that what is current there before selling a new device.

SE: I don’t disagree at all with you. In fact, this past year I had both of my hips replaced due to osteoarthritis. I selected a surgeon that used hip devices that have been around for decades and not the latest technologies. What companies face is as younger surgeons come into practice, they want new technologies for their patients. If a company doesn’t continue to innovate, even incrementally, they get left behind.

SAB: We totally understand.We are aware, however, of the cost of bringing new technologies on line (R&D, FDA clearance, marketing, learning curves and unanticipated complications).

As a surgeon, these issues require that companies show that the new stuff provides better outcomes than the old stuff. As an example, is there any evidence that you know of supporting an incremental benefit in terms of patient outcomes from the use of PSI, Short Stems, Stemless, Augmented glenoids, Platform prostheses? If so, We’d love to see it!

SE: I think that answer might come to us in ten years or so

SAB: But it seems you're suggesting that in ten years we will no longer be using the implants for which we have a decade of followup. If we keep changing the implant how will we be able to tell patients about the long term results they are likely to achieve? How will we know if the costs of the "innovations" are offset by benefit to the patient?

We have a new set of shoulder youtubes about the shoulder, check them out at this link.

Be sure to visit "Ream and Run - the state of the art" regarding this radically conservative approach to shoulder arthritis at this link and this link

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