Wednesday, October 16, 2013

Glenoid component position and clinical outcome in total shoulder arthroplasthy

Accuracy of Glenoid Component Placement in Total Shoulder Arthroplasty and Its Effect on Clinical and Radiological Outcome in a Retrospective, Longitudinal, Monocentric Open Study

These authors conducted a retrospective study of 68 total shoulder arthroplasties with a mean follow-up of 38+/−27 months in an attempt to correlate clinical outcome with glenoid component position and fixation by CT scan. On average the retroversion of the glenoid was 6°±12°; mean ± SD, the superior tilt was 12°±17°, the rotation of the implant relative to the scapular plane was 3°±14° and the off-set distance of the centre of the glenoid implant from the scapular plane was 6±4 mm. They found that an inferiorly inclined implant was found to be associated with higher levels of radiolucent lines while retroversion and non-neutral rotation were associated with a reduced range of motion.

The issue with this study is that it did not include an analysis of the preoperative glenohumeral anatomy. Thus we do not know if the poorer results seen with 'glenoid malpoition' are related to more severe preoperative pathoanatomy rather than the position of the glenoid component. The range of glenoid version postoperatively was 17 degrees of anteversion to 32 degrees of retroversion. It seems unlikely that this variation is due to the 'accuracy' surgical technique and more likely that it is due to the underlying pathology.

We also observe that severe osteolysis (as seen in their figure 5) is not infrequently associated with Propionibacterium infection.

In this type of study it is often preferable to define a primary outcome variable, for example the Constant score or the Mole score, and then do first univariate and subsequently multivariate analyses of the possibly associated factors (age, gender, diagnosis, preoperative version, postoperative version, etc). In this way clinicians can be informed regarding the factors most influential on the outcome and the problem associated with multiple comparisons can be managed.

Finally, the observation that poorly aligned glenoid components are associated with poorer results should not be taken as trying to 'correct' preoperative glenoid pathoanatomy using asymmetric reaming or bone grafting, in that both of these have also been associated with poorer results.

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