Quantitative Measurement of Osseous Pathology in Advanced Glenohumeral Osteoarthritis
These authors used 3-dimensional computed tomography (3-D CT) imaging analysis to define common pathologic types seen in advanced glenohumeral osteoarthritis in 155 cases having shoulder arthroplasty.
Posterior translation of the humeral head center was made on the 2-D axial image at the level of the glenoid center point and was defined as humeral-glenoid alignment (HGA). Pathologic HGA was measured relative to the perpendicular line drawn from the glenoid center point.These authors used 3-dimensional computed tomography (3-D CT) imaging analysis to define common pathologic types seen in advanced glenohumeral osteoarthritis in 155 cases having shoulder arthroplasty.
They described 2 new glenoid subtypes (B3 and C2). Their B3 glenoid has high pathologic retroversion, normal premorbid version, and acquired central and posterior bone loss that, on average, is greater than that of the B2 glenoid.
They described the C2 glenoid as dysplastic with high pathologic retroversion, high premorbid version, and acquired posterior bone loss, giving it the appearance of a biconcave glenoid with posterior translation of the humeral head. They point out that the C2 glenoid can be confused with the B2 glenoid.
Comment: The percentage of glenoid types assigned by the authors showed the distribution shown below. It appears that there are four glenoid types accounting for over 92% of the shoulders in their series.
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Comment: The percentage of glenoid types assigned by the authors showed the distribution shown below. It appears that there are four glenoid types accounting for over 92% of the shoulders in their series.
Among their patients, types A1, A2 and B1 consistently had glenoid retroversion < 15 degrees (version greater than minus 15 degrees) as shown below.
With respect to humeral decentering on the glenoid, there was substantial variability (see the large standard deviations), but the A1, A2, and B3 glenoids had less decentering than the B1 and B2 glenoids.
Putting these two parameters together, we see the type A glenoids are in the upper right corner with small amounts of average retroversion and decentering. The B2 glenoid is distinguished by having high degrees of retroversion and decentering while the B3 glenoid has high degrees of retroversion but with less decentering, close to that of the A2 glenoid.
As can be seen from the figures from the article shown below, the distinction between glenoid types is challenging. On the left, an A2 was reclassified to a B3, even though the retroversion was on the borderline of 15 degrees (90 - 75). On the right is shown a shoulder with 17 degrees of retroversion that was originally classified as a B2, although the amount of biconcavity seems very small. Both shoulders show a small amount of decentering.
What be concluded from this?
First, the degrees of retroversion, decentering and biconcavity each exist along continua, varying from a little to a lot.
Second, these continua complicate splitting the findings for version, centering and biconcavity into discrete types.
Third, while it is current practice to describe arthritic pathoanatomy in terms of an increasing number of glenoid types, in the future it may make more sense to report the degrees of retroversion, the degrees of decentering and the amount of biconcavity rather than trying to pigeon hole glenoids into discrete types.
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