CHAPTER 13 Soft Tissue Balancing
The use of a prosthetic system that adapts to the patient’s anatomy decreases the need for soft tissue balancing. In most cases, little additional soft tissue balancing is necessary after the steps of the procedure are followed as described in this textbook. Two notable exceptions exist. The first is in an individual, usually with a diagnosis of primary osteoarthritis or instability arthropathy, who has marked posterior glenoid wear and posterior glenohumeral subluxation on preoperative computed tomography or magnetic resonance imaging. The second is in an individual with an exceptionally tight posterior capsule, most commonly seen in our practice in patients with juvenile-onset inflammatory arthropathy.
EVALUATING THE NEED FOR SOFT TISSUE BALANCING
In patients with posterior glenoid wear (type B2 glenoid morphology; see Chapter 7), the sequence of surgical steps is altered. After the glenoid component is implanted, we insert the trial humeral prosthesis instead of the final humeral implant. This is helpful in judging prosthetic stability. After the trial humeral component is reinserted, the glenohumeral joint is reduced. With the arm externally rotated 30 degrees, force is applied in a posterior direction to the proximal humerus. There are two keys that allow the surgeon to determine whether the soft tissues are properly balanced. First, the prosthetic humeral head should subluxate posteriorly approximately 30% to 50% of its diameter and spontaneously reduce on release of the posteriorly directed force. If spontaneous reduction does not occur, posterior capsulorrhaphy may be necessary. Second, if posterior translation of at least 30% of the diameter of the humeral head is not possible, posterior capsular release may be necessary.
PERFORMING A POSTERIOR CAPSULORRHAPHY
In many patients with posterior glenoid wear and posterior humeral head subluxation, the posterior capsule has become distended and ineffective in maintaining posterior glenohumeral stability, even after the osseous glenoid deformity has been corrected by reaming (Fig. 13-1
