Monday, June 27, 2011

Failed, Unsatisfactory Shoulder Joint Arthroplasty - stiffness

As noted in the previous post, stiffness is a common feature among unsatisfactory shoulder joint replacements. By stiffness we mean that the shoulder is not capable, even with the help of the other arm, to move through a normal range of motion (see March 29 post). Arthritic shoulders are usually stiff (see April 5 post), so it is not surprising that stiffness may remain a problem even after joint replacement. This is why we are so interested in early post-surgical rehabilitation to maintain the range of motion achieved at surgery (see April 18 and 19 posts). In a technically well-done arthroplasty, range of motion is usually restored and maintained by these rehabilitation exercises.

However there are several surgical principles that are important to re-establishing motion to a stiff, arthritic shoulder. First is that the tight capsule around the joint must be released by sharp dissection as shown in the figure below.

Second is that the bone spurs (osteophytes) be removed to make sure they do not block motion. We refer to the inferior aspect of the joint as Pooh Corner (below left), so that we don't forget to check it and remove any possibility of unwanted contact between the inferior humerus and the glenoid.
We also check for unwanted contact in the posterior aspect of the shoulder that blocks external rotation as shown below.

This can be noted at surgery as the 'open book' phenomenon when the arm is externally rotated - the humeral head is levered away from the glenoid as shown below.
And finally, the surgeon must avoid 'overstuffing' the joint, by inserting such a large humeral head that the soft issues are put under excessive tension (bottom of the figure below) rather than one that puts the soft tissues under normal tension (top of figure below).
Overstuffing can also arise from the insertion of a thick glenoid component - this is one of several issues with metal backed components as shown below right

Finally, overstuffing can arise from varus malposition of the humeral component (the prosthesis is angled toward the socket, rather than being inserted straight) in which case the humerus along with its rotator cuff attachments is pushed away from the glenoid (W), tightening the tissues around the joint.
At surgery, we optimize the shoulder range of motion by assuring that the joint is capable of 40 degrees of external rotation
50% posterior translation
and 60 degrees of internal rotation with the arm out to the side

We refer to these as the 40, 50, 60 rules for achieving ideal soft tissue balance and avoiding an unsatisfactory arthroplasty because of intraoperative causes of stiffness. A good rehabilitation program is still essential to a good result.

If a shoulder stays or becomes stiff after a shoulder arthroplasty and if it does not respond to a good rehabilitation program, revision surgery may be considered to re-release the soft tissue, check to make sure no blocking osteophytes are present, and assure that the humeral head is of the proper size.


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