Thursday, December 12, 2013

Glenoid component in total shoulder - evolution of design

Design Evolution of the Glenoid Component in Total Shoulder Arthroplasty (JBJS Reviews, 2013 Dec;1(2):e2.

This comprehensive review concludes that

➢ Higher rates of failure have been reported for metal-backed glenoid components, and cemented pegged polyethylene components currently appear to be the component design of choice.
➢ So-called modern cementing techniques have reduced postoperative radiolucent lines and may improve glenoid implant longevity.
➢ Compensating for altered glenoid morphology and bone loss continues to be a challenge.

It also points out the ongoing concern about the longevity of glenoid components, referring to this as the 'weak link' in total shoulder replacement. The authors again point out the glenoid loosening has been reported as the most common reason for revision after total shoulder arthroplasty.

They remind us that the shoulder is, in fact, a weight / load bearing joint with loads of 3/4 body weight across the joint in hair coming and 1 1/4 body weight in holding a coffee pot. These loads are not applied in the center of the joint, but rather eccentrically (often as much as 1 cm off-center) risking plastic deformation of the polyethylene component. The most commonly direction of off-center loading was posterior-superior where it can lead to what we have described as rocking horse loosening.

The authors point to evidence favoring a moderate mismatch between the diameter of curvature of the glenoid and that of the humeral head to allow some translation and enhance range of motion; however excessive degrees of mismatch is associated with higher contact pressures and risk of material failure.

The literature supports fixation of an all polyethylene pegged component using cement only in the per holes coupled with excellent carpentry to optimize the fit between the glenoid bone and the back of the glenoid prosthesis that eliminates the need for interposed cement between these surfaces. The article finds lack of support for cementless metal backed glenoid components.

While the article refers to so called 'modern' cement techniques, it does not detail the use of sprayed carbon dioxide to remove fluid from the bone cement interface which avoids leaving blood or clot between cement and bone.

The article mentions the challenge of managing the retroverted glenoid, but points out the lack of clinical data supporting posteriorly augmented glenoid designs to address the bad arthritic triad (BAT).

In spite of its shortcomings, we still view total shoulder arthroplasty as a great option for the surgical management of debilitating shoulder arthritis, especially in the person who wants to optimize the speed of recovery of comfort and function and who does not anticipate high levels of physical activity on the reconstructed shoulder.

For those highly motivated individuals who desire high levels of physical activity and who are prepared for what can be a longer rehabilitation period, we consider the ream and run procedure.


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