Wednesday, May 11, 2011

Total shoulder: glenoid component wear

The polyethylene surfaces of glenoid components used in total shoulder replacement are more subject to wear than the surfaces of comparable components used in hip replacement surgery. While the reasons for this are not totally clear, it is evident that the ball (the prosthetic humeral head) of the shoulder moves around on the surface of the shallow glenoid component, rather than staying centered as is the case in the hip with its deeper socket geometry.
This wear can wear and flatten the surface of the socket, allowing even more translation of the humeral head as shown in the diagrams below.
Shoulder fellow Scarlat was one of the first to make make observations on retrieved glenoid components.
Residents Braman and Falicov and shoulder fellow Boorman conducted a detailed study of the alterations in surface geometry of glenoid sockets retrieved at the time of revision surgery. In every case the shape and/or texture of the surface was altered by use in comparison to the surface of comparable unused components. In the diagram below the sharp peak in the graph of the radii of curvature indicate that the unused component is smooth and of uniform curvature.
By contrast, in the component represented in the graph below, retrieved after several years of use, the surface is no longer of uniform curvature.

Below are two examples of the glenoid components we have retrieved at the time of revision surgery, each showing wear and loss of the original contour of the manufactured component.

While it is possible that newer forms of polyethylene have better wear characteristics, we continue to find  that retrieved glenoid components show alterations in the surface geometry because of wear.

One of our readers has responded: ""I wonder how that compares to the glenoid wear of a "ream and run" or those that are Biologically resurfaced.". This is an important question. Here are two references that may be helpful in this regard: Humeral head arthroplasty and meniscal allograft resurfacing of the glenoid that shows loss of joint space with time after biological resurfacing and A quantitative method for determining medial migration of the humeral head after shoulder arthroplasty: preliminary results in assessing glenoid wear at a minimum of two years after hemiarthroplasty with concentric glenoid reaming that describes a way to measure wear and applies it to the ream and run procedure.


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