These authors examined the risk factors for glenoid component loosening in 471 shoulder arthroplasties with a mean followup of 8.1 years. The authors used a cemented keeled glenoid component iWrightMedicalGroup).
A flat-back glenoid component was used in the first 186 cases and a convex-backed component in the following 285 cases. Preparation of the glenoid was different among surgeons. Some surgeons preferred only a slight reaming and protection of the subchondral bone layer, and some preferred to take down the bone layer.
A total of 137 glenoid components (29.1%) were radiographically judged to be at risk for loosening.
Univariate analysis revealed that
1. Excessive reaming on the native glenoid with removal of subchondral bone was associated with a 3.7-fold higher risk for glenoid component loosening (p< 0.001).2. A glenohumeral mismatch <6mm was associated with higher radiographic loosening rates (p< 0.03), and the risk increased by 19% with every millimeter of less mismatch.
3. The use of a flat-back glenoid component was associated with a 3.1-fold higher risk for radiographic loosening compared to convex-back glenoids (p< 0.001).
4. B2 glenoids were associated with a higher risk for radiographic loosening compared to A1 (2.3-fold), A2 (3.6-fold), and B1 (2.7-fold) glenoids (p< 0.001).
Comment: This is an important long-term followup study. It lends further support to (1) preservation of the subchondral bone by minimizing glenoid reaming, (2) avoiding the overconstraint associated with conforming glenohumeral anatomy (i.e. a small degree of mismatch), and (3) avoiding a flat backed glenoid component.
It would be of interest to see the results of a multivariate analysis to see if the apparent risk associated with a B2 glenoid was actually due to a tendency for surgeons to excessively ream the anterior glenoid bone in an attempt to "correct" the glenoid pathoanatomy (upper figure below). Our approach is to minimize the reaming of the glenoid by accepting glenoid retroversion (lower figure below).
It would be of interest to see the results of a multivariate analysis to see if the apparent risk associated with a B2 glenoid was actually due to a tendency for surgeons to excessively ream the anterior glenoid bone in an attempt to "correct" the glenoid pathoanatomy (upper figure below). Our approach is to minimize the reaming of the glenoid by accepting glenoid retroversion (lower figure below).
We found that insertion of an all polyethylene pegged glenoid component in >15 degrees of retroversion was not associated with inferior clinical results at two years (see Does Postoperative Glenoid Retroversion Affect the 2-Year Clinical and Radiographic Outcomes for Total Shoulder Arthroplasty?)
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