These authors developed finite element models of reconstructed healthy and osteoarthritic (OA) scapulas with a virtually implanted glenoid prosthesis design. Three models were created: a reconstructed healthy scapula, an OA scapula with retroversion of 18, and a corrected OA scapula inserted after the anterior portion of the glenoid was reamed to reduce the retroversion to about 6 degrees.
Loads were applied at the center and then posteriorly on the glenoid surface.
They found that in the uncorrected retroverted glenoid, little bone was removed to accommodate the implant and in the corrected glenoid, the anterior surface was significantly reamed to re-create the neutral version angle, resulting in the removal of stiff anterior bone.
The model predicted that eccentric loading on the glenohumeral joint would have little effect on load transfer patterns when the component was inserted in retroversion. However, cement stresses would increase and the load transfer pattern would change with eccentric loads when the glenoid implant was inserted after correction of glenoid version by anterior reaming.
Therefore the model suggested that correction of retroversion in OA glenoids may actually increase the risk for stress shielding and cement failure compared with retroverted glenoids. They also found that OA shoulders can accommodate shorter pegs because of the higher glenoid bone stiffness in the OA glenoid than what is found in normal shoulders.
Comment: The conclusions of this paper are interesting to consider in light of an article discussed in a recent post: "…subluxation of the humeral head correlates with glenoid wear, and it is reasonable to suggest that subluxation causes the wear. This presents a problem which must be emphasized: when one corrects the posterior glenoid wear (using a glenoid component with or without a graft) the subluxation is not corrected. This therefore leaves the risk of recurrence and may be responsible for glenoid loosening due to the 'rocking-horse' mechanism described by Franklin et al."
Our practice is consistent with these papers: when the arthritic glenoid is retroverted, we do not attempt to correct the retroversion by anterior reaming or posterior grafting or using a posteriorly augmented components. Rather, we insert the glenoid component in retroversion after reaming just enough to create a conforming concavity as shown here. Stability is managed if necessary by anteriorly eccentrial humeral heads and rotator interval plication.
They found that in the uncorrected retroverted glenoid, little bone was removed to accommodate the implant and in the corrected glenoid, the anterior surface was significantly reamed to re-create the neutral version angle, resulting in the removal of stiff anterior bone.
The model predicted that eccentric loading on the glenohumeral joint would have little effect on load transfer patterns when the component was inserted in retroversion. However, cement stresses would increase and the load transfer pattern would change with eccentric loads when the glenoid implant was inserted after correction of glenoid version by anterior reaming.
Therefore the model suggested that correction of retroversion in OA glenoids may actually increase the risk for stress shielding and cement failure compared with retroverted glenoids. They also found that OA shoulders can accommodate shorter pegs because of the higher glenoid bone stiffness in the OA glenoid than what is found in normal shoulders.
Comment: The conclusions of this paper are interesting to consider in light of an article discussed in a recent post: "…subluxation of the humeral head correlates with glenoid wear, and it is reasonable to suggest that subluxation causes the wear. This presents a problem which must be emphasized: when one corrects the posterior glenoid wear (using a glenoid component with or without a graft) the subluxation is not corrected. This therefore leaves the risk of recurrence and may be responsible for glenoid loosening due to the 'rocking-horse' mechanism described by Franklin et al."
Our practice is consistent with these papers: when the arthritic glenoid is retroverted, we do not attempt to correct the retroversion by anterior reaming or posterior grafting or using a posteriorly augmented components. Rather, we insert the glenoid component in retroversion after reaming just enough to create a conforming concavity as shown here. Stability is managed if necessary by anteriorly eccentrial humeral heads and rotator interval plication.
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