Saturday, October 22, 2016

Metal backed glenoid components and failure rate.

The weak link in metal-backed glenoid implants is the polyethylene

These surgeons have authored a most thoughtful letter regarding the metal backed glenoid. We encourage reading of the complete letter (see this link) and their original article (see this link).

Here we paraphrase their letter. "the results this clinical study, showing poor results with metal backed (MB) glenoid implants at medium- to long-term follow-up, are in accordance with other long-term clinical studies reporting on a high number of patients and with a recent systematic review showing that the revision rate with MB glenoid components is 3 times higher than with all-PE components (see this link). Finally, biomechanics studies have demonstrated the problems created by the metallic interface in anatomic TSA on both the plastic side and the bone side. All these are good reasons, published in the literature, that do not encourage the use of MB glenoid components for anatomic TSA. Careful consideration of the inherent risks is warranted if future exploration of MB anatomic glenoid components is undertaken. The success of MB glenoid components for reverse TSA should not lead to confusion of surgeons: the biomechanical environment is very different in reverse TSA, in which a metallic sphere is associated to a metallic baseplate."

Comment: We have posted some informative links on this topic (see here, and here). In a recent post (see here) we point out that in addition to problems of thickness and back side wear, the issue is in large part the mismatch in the material properties of polyethylene and the metal backing.

Additional data on the difficulties associated with metal backed implants can be found from the robust database of the Australian Orthopaedic Association (see here), showing 'higher than anticipated rates of revision' for metal backed glenoid components.

Examples of these components are shown below:

While no prosthetic glenoid component is perfect, the current evidence is that the safest and most durable implants are the pegged all-polyethylene component

 inserted with careful and conservative glenoid bone preparation.