Wednesday, July 1, 2015

Reverse total shoulder arthroplasty - bone grafting - can we tell if it reabsorbs?

Effectiveness of CT for the detection of glenoid bone graft resorption following reverse shoulder arthroplasty.

Some surgeons use glenoid bone grafting in cases of reverse shoulder arthroplasty (RSA) to manage glenoid bone deficiency or to increase the offset of the glenosphere from the native glenoid bone. Whenever bone graft is used there is a concern about the possibility of the graft reabsorbing, leaving the glenoid component unsupported. When grafts have been employed, computed tomography (CT) has been used to detect glenoid bonegraft resorption- typically identified by a gap between the bone graft and baseplate.

These authors used a cadaver model to ask if a simulated bone graft resorption gap is detectable by CT scan after a RSA with glenoid bone grafting. They performed RSA with glenoid bone grafting on four cadaver shoulders. Glenoid bone graft resorption gaps were simulated by fixing the implant at six different gap widths (0, 1, 2, 4, 6 and 8mm). CT scans were acquired for each gap and gap widths were measured on  DICOM images in the axial and coronal directions.

The sensitivity of CT imaging to positively identify bonegraft resorption was 38%, with an accuracy of 46%.  Observers tended to visualize no-gap for most conditions. Resorption gap width measurements were consistently underestimated. Metal artifact prevented identification of simulated bonegraft resorption gaps and observers most often determined that there was bonegraft-to-implant contact on CT, when in fact a gap was present.

They concluded that CT scanning was not reliable for assessing bone graft resorption following RSA.

Comment:  We prefer to avoid bone grafts in RSA because of the concern that motivated this article: the risk of failure of graft healing and resorption. If we wish to increase the lateral offset, we use a glenosphere with an extended neck. As the case below from this week illustrates, cases of glenoid deficiency often have glenoid sclerosis that can enable secure fixation of a glenoid base plate that has a strong central screw and peripheral locking screws.


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