Saturday, December 13, 2014

Glenoid bone density in A2 and B2 glenoids, implications for pathogenesis and treatment

Regional bone density variations in osteoarthritic glenoids: a comparison of symmetric to asymmetric (type B2) erosion patterns.

These authors compared the erosion patterns of 25 symmetric and 25 asymmetric glenoids using computed tomography-based imaging software.

For the symmetric cohort, there were no significant differences in bone density between the four quadrants at depths of 0 to 2.5 mm and 2.5 to 5 mm. For the asymmetric cohort, bone density was significantly higher in the posterior quadrants compared with the anterior quadrants, especially posteroinferiorly at both depths. The bone beneath the pathological posterior concavity also had lower void fraction compared with the bone beneath the normal anterior concavity.

This study demonstrates that osteoarthritic glenoids with symmetric erosion have uniform subarticular bone density. However, asymmetric (B2) erosion patterns have potentially important regional variations in bone density and porosity, with the densest bone with the least porosity found posteroinferiorly beneath the pathological concavity.

Comment: The condensation of bone beneath the pathological posterior glenoid is a response to posterior loading that occurs with functional decentering, that is the posterior subluxation that occurs when the arm is placed in a functional position, a decentering that is not seen on CT scans taken with the arm at the side as further explained here and here. This is one of the many reasons we do not get preoperative CT scans, preferring instead the 'truth view'.
The recognition of the variance in bone quality has lead some to question the advisability of correcting glenoid version. Here is a related post. Taken together, these findings also bring into question the advisability of sacrificing some of the dense posterior bone to accommodate glenoid components with a posterior step off.


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