Glenoid erosion is a recognized cause of inferior clinical results in humeral hemiarthroplasty.
While there is much current interest in the use of a pyrocarbon joint surface to reduce glenoid erosion, as the x-ray above demonstrates, glenoid erosion can take place with pyrocarbon as well as with metal humeral heads.
Here we present some approaches to reducing the risk of glenoid erosion that apply no matter what type of joint surface is used.
The gleonoid.
In the great majority of arthritic shoulders, there is loss of the congruency between the humeral and glenoid articular surfaces. Thus, rather than having the load distributed evenly across the joint (below left), the load is concentrated on a reduced area at the back of the joint. The resulting pressure (load/area) causes progressive posterior bone loss and decentering.
Experience suggests that a 2 mm diametral mismatch between the humeral head and the reamed glenoid is optimal.
If glenoid erosion is to be minimized, the maximum amount of the best quality bone (arrows) needs to be preserved.
by conservative reaming
This can be accomplished by accepting, rather than correcting, glenoid retroversion.
The diagrams below show the preservation of quality bone with accepting the glenoid retroversion (left) in comparison to the greater amount of bone removed with correcting glenoid retroversion (right)
In reaming the glenoid, sharp reamers and irrigation can help minimize the risk of thermal injury to the glenoid bone (see Thermal effects of glenoid reaming during shoulder arthroplasty in vivo).
While some surgeons advocate drilling holes in the reamed glenoid surface
it is apparent that this can weaken the glenoid surface making it more prone to erosion. Perhaps this "docking" is more appropriate when making a pie.
Finally, when possible it is desirable to preserve the glenoid labrum recognizing its load bearing and stabilization functions.
Overstuffing: Soft tissues
As pointed out in Practical Evaluation and Management of the Shoulder, overstuffing can not only restrict the range of glenohumeral motion
which increases pressure on the glenoid joint surface when vigorous stretching is carried out.
Thus for that reason, soft tissue releases are important for reducing the pressure on the glenoid and the risk of glenoid erosion.
180 degree releases if there is excessive posterior translation
and that the shoulder meets the 40, 50, 60 rules (40 degrees of external rotation with the subscapularis approximated, 50% posterior translation, and 60 degrees of internal rotation with the arm abducted).
Overstuffing: Implant size and positioning.
While much attention is being paid to pyrocarbon as an alternative bearing surface, glenoid erosion can be seen with humeral heads of any type of material.
(1) Inadequate head cut, leaving a too long neck.
(2) Too large humeral component
When the head is high, it acts like a cam (click here), excessively tightening the inferior capsule when the arm is elevated because the center of rotation is malpositioned. This tightening results in increased pressure on the glenoid surface when the arm is raised.
(5) Head high and medial
From the above it is noted that humeral head malposition can occur with pyrocarbon and with metal heads; humeral head malposition can occur with stemless, short stem and standard length stems.
To avoid overstuffing related to the humeral component, careful attention needs to be paid to the neck cut, head size and component position.
Conclusion
The risk of glenoid erosion can be reduced by preserving and protecting the best bone in the glenoid, balancing the soft tissues to optimize glenoid laxity, along with careful selection and positioning of the humeral component.
Avoiding glenoid erosion appears to depend more on surgical technique than on technology.
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Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).
