Tuesday, August 11, 2015

Eccentric anterior reaming vs posterior augmented glenoid components - is this the right way to answer the question?

Posterior Glenoid Wear in Total Shoulder Arthroplasty: Eccentric Anterior Reaming Is Superior to Posterior Augment

These authors compared the use of augmented glenoid components to eccentric reaming with standard glenoid components in a model of posterior glenoid wear with a 12°-posterior glenoid defect  created in 12 composite scapulae.

In the posterior augment group, glenoid version was corrected to 8° and an 8°-augmented polyethylene glenoid component was placed. 
In the eccentric reaming group, anterior glenoid reaming was performed to neutral version and a standard polyethylene glenoid component was placed.

Specimens were cyclically loaded in the superoinferior direction to 100,000 cycles.

Surviving specimens in the posterior augment group showed greater displacement than the eccentric reaming group during superior edge loading and during inferior edge loading.

A greater number of specimens in the eccentric reaming group were able to achieve the final 100,000 time without catastrophic fracture than those in the posterior augment group.

They concluded that "When addressing posterior glenoid wear in surrogate scapula models, use of angle-backed augmented glenoid components results in accelerated implant loosening compared with neutral-version glenoid after eccentric reaming, as shown by increased implant edge displacement at analogous times."

Comment: While we are no fans of posteriorly augmented or stepped glenoid components, we feel misled by a title like "Posterior Glenoid Wear in Total Shoulder Arthroplasty: Eccentric Anterior Reaming Is Superior to Posterior Augment" - thinking that this is a clinical outcome study that grappled with the wide variety of glenod pathoanatomy we encounter in people - and then find out that this is a study of the properties of glenoid components placed in plastic bones that do not duplicate the bone of an arthritic shoulder and then are loaded in the superior / inferior direction which would seem to be of much less interest than the response to posteriorly directed loads which challenges the stability of retroverted glenoids.

Of interest is the statement in the discussion: " Initial testing for this study was performed with cadaveric scapulae but was abandoned because of the substantial variability between samples, which had a greater effect on implant stability than prosthesis design." Folks, we live in a world where there is substantial variability among patients and we need to do studies that recognize that fact.


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