Thursday, January 19, 2012

Glenoid component loosening after total shoulder replacement for arthritis - JBJS

The current issue of the Journal of Bone and Joint Surgery presents analysis of the Patterns of Loosening of Polyethylene Keeled Glenoid Components  by a group of respected colleagues, including our French friends Walch, Gazielly, Mole and Boileau.  In this study 518 total shoulder replacements performed at one of 10 European centers for primary glenohumeral osteoarthritis had radiographic (x-ray) followup of over five years. The keeled glenoid component was fixed to the bone with cement.  166 (32%) had x-ray evidence of loosening. 136 had migration (shift or subsidence) of the component.

This article points, again, to the risk of glenoid component failure after total shoulder replacement. The authors sought risk factors for each of three different types of component migration. 

Superior tilting of the component was statistically associated with low positioning of the glenoid component, with positioning of the glenoid in a superiorly inclined position, and with superior subluxation of the humeral head (as is seen in rotator cuff insufficiency). Subsidence of the glenoid component was associated with glenoid reaming. Posterior tilting of the component was associated preoperative posterior subluxation and with excessive reaming. This is a problem, because the anatomy described as a "B-2 glenoid" (shown below from their figure 4), is rather typical of the anatomy encountered in shoulder arthroplasty.

The authors conclude that preserving subchondral bone may be important to the survivorship of the component fixation. They also indicate that eccentric loading (especially superior or posterior) is a risk factor for glenoid failure by what we have called the rocking horse mechanism.

Other factors may have contributed to the glenoid failures in this series. For example in figure 2, shown below, the postoperative film (left) showed radiolucent lines around the cement as well as a large volume of cement, which is may cause enough heat to kill the adjacent bone.

The authors have identified a 'catch-22': preoperative posterior tilting predisposes to glenoid component loosening, but correcting this tilting by reaming also predisposes to glenoid component loosening. The authors suggest the possible role of bone grafting in such situations, but the evidence supporting this approach is limited.

It is the concern about glenoid component failure that led us to explore the ream and run procedure. It is of note that in situations of severe posterior glenoid erosion the humerus can be stabilized in the reamed glenoid without sacrificing glenoid bone stock and without undertaking the risk of glenoid component failure.


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