Saturday, July 2, 2016

Revision of a dislocated trabeculated metal prosthesis

A middle aged patient had an attempted reverse total shoulder using a trabeculated metal bone ingrowth prosthesis (below left). On insertion of the glenoid component, the anterior glenoid fractured causing the surgeon to abandon the reverse total shoulder and to convert the implant to a hemiarthroplasty (below right).

On presentation to us, the hemiarthroplasty was chronically dislocated into a major anterior glenoid defect.

The patient desired an attempt at conversion of this dislocated implant to a reverse.

After a difficult removal of the dislocated ingrowth humeral component, we used the technique described in a recent article (see this link), exploring with a drill to find the best bone into which  the central screw of the baseplate could be inserted.

We accepted the necessity of anteverting the glenoid component and achieving secure fixation by inserting the screw into the base of the scapular spine.

 And filling in the anterior glenoid defect with bone graft.

After a 36 neutral glenosphere was fixed in place, we cemented the humeral component to achieve control of height and version. The osteotomized proximal humerus was repaired to the humeral component and cancellous allograft added.

Comment: This case illustrates several points. First, trabeculated metal ingrowth prostheses make revision surgery very difficult. We have not found a use for them in our practice, preferring to fix the humeral component with impaction grafting (which facilitates revision should it become necessary). 

Second, care is needed in the insertion of the reverse glenoid component - difficulties in exposure may tempt the surgeon to place the baseplate in an excessively anterior position risking glenoid fracture as occurred here. Third, it is possible to salvage cases of severe glenoid insufficiency using secure fixation of the baseplate screw into the scapular spine. Fourth, because it is a sphere, version of the glenosphere is not critically important to stability as long as anterior and posterior abutment of the humerus against the glenoid is avoided.


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