Monday, April 11, 2011

Total shoulder: the glenoid component, Part I

After some initial work by Stillbrink and Kenmore, the late Charles Neer introduced the concept of prosthetic replacement of the glenoid joint surface in 1974. His insight was that restoring the concave shape of the glenoid surface could help improve centering of the humeral head. He wrote, "Because of the excessive excursion of the head of the prosthesis noted during this study when the glenoid was flattened and enlarged, it was thought logical to resurface the glenoid in a limited series to determine if the fulcrum could be improved." The combination of a humeral prosthesis and a polyethylene glenoid component is known as a total shoulder joint replacement arthroplasty.
A major challenge, as Neer recognized, was securing the polyethylene to the bone of the glenoid. He sculpted the bone surface by hand and used acrylic bone cement to hold the glenoid prosthesis in place.
One element of this securing is good carpentry, as pointed out by our shoulder fellow, David Collins, who showed that spherical reaming around a normalized axis is key for providing a good fit for the polyethlene prosthesis on the glenoid bone. In 1992, he showed that careful bone preparation minimized the wobble and warp of the polyethylene.

This led to our development of a hand-powered spherical reamer that enabled us to contour the bone around a drill hole placed in the center of the glenoid bone. This first glenoid reamer is shown below.
Now, the concept of reaming around the normal centerline of the glenoid is in common use. A modern reamer is shown below.
This reaming assures a precise fit of the polyethylene component (shown below) on the bone.

Our shoulder fellow Clinton has shown that care needs to be exercised during reaming to make sure the bone surface does not become overheated.


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