Thursday, June 20, 2013

Glenoid component loosening associated with glenoid retroversion

Welcome to the 600th post on this blog.

Glenoid Component Retroversion Is Associated with Osteolysis

The authors observe that many patients with primary osteoarthritis have increased glenoid retroversion and that glenoid components inserted in retroversion may experience eccentric glenoid loading and an increased risk of component loosening. They reviewed 66 shoulders having total shoulder replacement with an all-polyethylene press-fit pegged glenoid component designed for osseous ingrowth for treatment of osteoarthritis at an average of 3.8 years. Preoperative glenoid retroversion using computed tomography scans or axillary radiographs. Preoperative CT scans were obtained when the preoperative axillary radiograph was not of sufficient quality to make an assessment of glenoid pathology in the axial plane.

The surgeon attempted to correct excessive glenoid retroversion by asymmetric reaming of the anterior part of the glenoid with the goal of achieving a component perpendicular to the plane of the scapula. When a patient had a large amount of glenoid retroversion, the surgeon accepted incomplete correction of retroversion to avoid excessive removal of bone and the resulting inability to insert a glenoid component.

They used post operative AP and axillary views to seek osteolysis around the central peg of the glenoid component. It is important to recognize, as we've pointed out before, that a standardized axillary view is sufficient as well as less costly and safer than a CT scan. The authors had previously assessed the accuracy of measurement of glenoid component retroversion on radiographs and postoperative CT scans and found a precision 95% confidence interval of 10° for version.
While the authors were blinded as much as possible, it is of note that the assessment of postoperative osteolysis and post operative retroversion were made on the same set of radiographs.

Of the fifty-three patients with study-quality preoperative axillary imaging, twenty (38%) had ≤15° of preoperative retroversion, twenty-four (45%) had >15° and ≤25°, and nine (17%) had >25° (range, 26° to 47°).
The early postoperative radiographs (made one to twelve months postoperatively) showed no osteolysis around the center peg.

At final follow-up however, 20 of the shoulders had osteolysis around the center peg as shown here

in contrast to the ideal postoperative findings shown here

This is of importance, because it suggests that with time, the quality of fixation may deteriorate.

Osteolysis around the center peg was not correlated with a worse clinical outcome defined by shoulder scores or a reoperation due to glenoid loosening over the followup period of this study.

The rate of osteolysis and the Lazarus component loosening grade were associated with (1)  the length of time after replacement, (2) preoperative glenoid retroversion, and (3) postoperative glenoid component retroversion. After adjustment for follow-up time, excessive postoperative glenoid retroversion (≥15°) was associated with an odds ratio of >5 for osteolysis.

In comparison to those with no or small amounts of osteolysis, shoulders with substantial osteolysis had higher preoperative retroversion (22.5 as compared to 14.7), higher postoperative version (15.2 as compared to 10.5), and higher degrees of postop-preop correction of retroversion (7.3 as compared to 4.2). Thus it is not clear that version correction solves the problems associated with preoperative retroversion.

As we've pointed out in previous posts, such as this one, glenoid retroversion can increase the risk of glenoid component failure through what we've described as 'rocking horse' loosening. Other factors apparently associated with glenoid component failure include the glenoid type and point of glenohumeral contact, neither of which was reported in this study.

The optimal method for managing the retroverted, B type glenoid with posterior glenohumeral contact when performing a total shoulder remains a topic of active discussion. Substantial anterior high side reaming, posterior bone grafting, and posteriorly augmented glenoid components all have been shown (see prior posts) to have their own risks.

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