Monday, January 15, 2018

Will arthritic posterior glenoid erosion get worse with time?

Progression of Glenoid Morphology in Glenohumeral Osteoarthritis

To observe how pathologic changes evolve over time, these authors identified 65 shoulders with glenohumeral osteoarthritis for which at least 2 computed tomography (CT) scans had been performed at least 24 months apart. 

The amount and location of glenoid bone loss were measured using a vault model, and rotator cuff fatty infiltration was calculated as a percentage of cross-sectional muscle area.
The initial CT scans showed 42 Walch A-type glenoids and 23 B-type glenoids. 
CT scans made at an average (± standard deviation) of 74 ± 32 months after the initial scans showed that only 8 of the 42 A1 glenoids had evidence of  pathologic progression (5 to A2 type and 3 to B type) whereas 17 of 19 B1 glenoids had progressed (15 to B2 and 2 to B3).

An example of this progression is shown below; the glenoid vault is shown in blue and the glenoid center axis is shown in white for the same glenoid at initial evaluation (A), four years later (B) and ten years later (C).

The odds of joint line medialization occurring were 8.1 times higher (95% confidence interval [CI]: 2.1 to 31.4) for B-type glenoids (red) than for A-type glenoids (blue) shown in the figure below.

The median percent fatty infiltration in the infraspinatus muscle was higher in association with B-type glenoids than in association with A-type glenoids on both the initial (14% versus 7%; p < 0.001) and the final follow-up (16% versus 10%; p = 0.003) CT scans.

Comment: More retroverted and more medially eroded glenoids are more difficult to reconstruct, this study can inform discussions regarding the timing of surgery shoulders with early stages of posterior decentering and erosion. The degeneration of the infraspinatus is of interest as well in that this muscle normally resists posterior decentering of the humeral head.