Thursday, August 11, 2011

Revision surgery for failed shoulder replacement arthroplasty due to glenoid component failure, Part 11

What if a failed shoulder arthroplasty is associated with instability, that is,  unwanted translation of the humeral head on the glenoid?  Such a shoulder requires a careful  history, examination, and radiographs.  The physical examination of strength in isometric internal rotation with the arm against the abdomen, isometric elevation of the internally rotated arm, and isometric external rotation of the neutrally rotated arm at the side as well as expert shoulder ultrasound can evaluate the integrity of the subscapularis, supraspinatus, and infraspinatus, respectively.  High quality and appropriately oriented anteroposterior and axillary radiographs will reveal the glenohumeral relationship (including the superior/inferior and anteroposterior relationship of the center of the humeral head and the center of the glenoid), the integrity of the tuberosities, the orientation of the glenoid and much about the type and position of the humeral component.  If knowledge of the humeral version is essential, it may be necessary to perform an examination under fluoroscopy, noting the rotational position of the arm that places the humeral neck in greatest profile. 
In terms of treatment options, here are some to consider.

Subscapularis deficiency may not be reconstructable.  If there is good quality muscle and tendon a repair may be possible after a complete release of the medial muscle and tendon.  A hamstring autograft may be useful for extending the tendon length.  

If the glenoid component is in excessive anteversion, its intrinsic balance stability angle does not provide anterior stability due to its misalignment with the net humeral joint reaction force (determined principally by the scapular origin of the scapulohumeral muscles). This etiology of anterior instability is suspected when there is minimal resistance to the anterior load and shift test.  The diagnosis of glenoid component anteversion can be made by examination of a true axillary view of the joint.  The glenoid centerline normally projects out the anterior scapular neck at the centering point.  In the anteverted glenoid, the glenoid centerline projects down the scapular body or behind it.  When anterior instability is associated with glenoid anteversion, reorientation of the prosthetic glenoid centerline is usually indicated.  Because the anterior glenoid lip of a polyethylene component is usually worn by the recurrent instability, the prosthesis often needs to be changed.  Thus, the revision is accomplished either by removal of the prosthetic component and performance of a properly oriented non-prosthetic glenoid arthroplasty or by reinsertion of a glenoid component with its centerline in proper orientation with the scapula. 

If the anterior glenoid bone stock is deficient, an iliac crest bone graft may be secured to the anterior glenoid and then reamed either for a non-prosthetic glenoid arthroplasty or to fit the back of the glenoid prosthesis.

If the glenoid component is in excessive retroversion, its intrinsic balance stability angle does not provide posterior stability.

Clinically, the shoulder will demonstrate diminished resistance to posterior load and shift and instability on cross body adduction.  On the axillary radiograph, the glenoid centerline is seen to project through the bony glenoid more anteriorly than the normal centering point.  As for glenoid anteversion, correction may include re-establishing the normal glenoid centerline and then performing corrective reaming for a non-prosthetic or prosthetic glenoid arthroplasty.

At times it may be necessary to use a posterior bone graft, but it is challenging to obtain secure fixation of the graft to the host glenoid bone.

If there is insufficient glenoid bone for a reconstruction and if an iliac crest autograft cannot be performed because of insufficient quality bone stock to which it can be anchored, a glenoidectomy can be considered as a salvage procedure.  In this procedure the residual glenoid is resected down to the level of the scapular spine.  An appropriately sized humeral head prosthesis is inserted to articulate with the glenoid neck, the scapular spine and the base of the coracoid.


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