Operating in Cairns
Shoulder replacement surgery at Cairns Public Hospital in December 2017, with Dr Will Bryceson.
The type C glenoid
Arthritic shoulder sockets do not wear evenly. A widely used classification describes the patterns, and a type C glenoid is one that is severely retroverted, meaning the socket is tilted substantially backwards. In these shoulders the head of the humerus has often drifted backwards with it, a situation described as subluxation.
This matters because a replacement component has to be seated on bone that is both reduced in quantity and abnormally oriented. Fitting a component to the socket as it is found would leave the joint in an abnormal position, which affects how it loads and how long it lasts.
Bone grafting and planning
One approach is to graft bone into the deficient area to rebuild the socket. The head of the humerus, which is removed during the operation in any case, can be used as the graft source, which avoids taking bone from elsewhere. For a severely deficient socket this can mean a substantial graft.
Pre-operative planning software is particularly useful in these shoulders. It builds a three-dimensional model from the CT scan and allows the correction, the graft and the component position to be worked out before the operation rather than judged in theatre. Where this is done, post-operative imaging can be compared against the plan to confirm the retroversion and subluxation have been corrected.
A reverse total shoulder replacement is often the appropriate choice in these shoulders, particularly where the rotator cuff is also compromised. Individual results vary, and which approach suits a particular shoulder depends on the pattern and extent of the bone loss.
Related information
See our post on augmented glenoid components, which addresses the same problem by a different route, and our shoulder arthritis page.