Posterior glenoid osteoplasty for unstable dislocating shoulders. Surgery to build up the back of the glenoid socket using an osteotomy and graft can restore shoulder anatomy and lessen pain and improve function.

Edited By: Winston J. Warme, MD, Frederick A. Matsen III, M.D.
Last updated Monday, October 09, 2006

Figure 1 - The concavity of the normal glenoid requires that the humeral head be lifted out of the socket in order to translate

Figure 2 - Normally the humeral head must climb out of the depth of the glenoid to translate across its face

Figure 3 - When the posterior aspect of the socket is flat, there is minimal resistance to posterior translation of the humeral head across the glenoid

Figure 4 - The posterior glenoid osteoplasty restores the posterior glenoid concavity and the posterior glenoidogram

Figure 5 - The change in glenoid shape and glenoidogram from before to after the surgery is dramatic

Review of the condition

Characteristics of posterior shoulder instability

The normal shoulder is a marvel of mobility and stability. It provides more motion than any other joint in the human body, yet the humeral head (ball of the shoulder joint) remains precisely centered in the glenoid (the socket of the joint) throughout the wide range of shoulder activities. One of the main stabilizing mechanisms is concavity compression, in which the head of the humerus is held into the glenoid concavity by the action of the rotator cuff (much like a golf ball is held into the concavity of a golf tee) (see figure 1). Because of this concavity, the humeral head must rise up over the glenoid lip before it can translate out of the socket. The path taken by the humeral head during this translation is called the "glenoidogram" (see figure 2).

When the rim at the back of the socket is underdeveloped or worn, the humeral head can translate out the back of the joint more easily, without having to lift up over the rim. In this situation, the glenoidogram becomes flattened (see figure 3).

Possible benefits of posterior glenoid osteoplasty

When recurrent posterior instability or dislocations interfere with the comfort and security of the shoulder and when these symptoms cannot be controlled by other means, a posterior glenoid osteoplasty performed by an experienced shoulder surgeon can usually restore the stability of the joint (see figures 4 and 5).

Surgery for posterior shoulder instability at the University of Washington

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