Sunday, August 24, 2014

Reverse shoulder arthroplasty - concentric vs eccentric glenospheres - how big a deal is notching?

A Comparison of Concentric and Eccentric Glenospheres in Reverse Shoulder ArthroplastyA Randomized Controlled Trial

The clinical significance of unwanted contact between the medial aspect of the humeral component of a reverse total shoulder and the bone of the scapula lies in the increased risk of instability, inferior scapular notching, limited adduction range of motion, poorer functional scores, and lower patient satisfaction. These authors conducted randomized, controlled, double-blinded trial of 50 patients with rotator cuff tear arthropathy in an attempt to determine if the use of an eccentric glenosphere diminished these problems.

The mean follow-up period for the groups was forty-three and forty-seven months. Four patients in the concentric group had developed inferior scapular notching ranging in size from 1.1 to 7.4 mm, compared with one patient in the eccentric group (p = 0.36). No notching occurred in any patient with glenoid overhang of >3.5 mm. No significant difference between the groups was seen with respect to functional outcome scores, patient satisfaction, or shoulder motion.

Three of these patients had complications. One having a concentric prosthesis developed instability after a fall and two (one in each group) developed acromial stress fractures. These fractures healed without surgery, but the functional results were poor.

Comment: There are two basic strategies for avoiding unwanted humero-scapular contact in reverse total shoulder. One is the 'South' approach: moving the humeral component distally using some combination of inferior placement of the glenosphere baseplate, use of an inferiorly eccentric glenosphere, or tilting the glenoid component inferiorly. These strategies may increase the risk of over lengthening the humerus with resulting acromial fractures (as shown in this report) and neurologic complications from plexus traction. The other is the 'East-West' approach: moving the humeral component laterally using a glenosphere that offsets the center of rotation from the glenoid bone. This strategy requires very secure fixation of the glenoid component to the glenoid bone.

We use a combination of the 'South' and the 'East-West' approaches to avoid unwanted contact in reverse total shoulder as shown here and here.

While some surgeons are inclined to pass off 'notching' as having no clinical importance, this cannot be the case as explained here.