The authors followed 518 shoulders having total shoulder arthroplasty. They defined 'secondary rotator cuff dysfunction' as superior subluxation of the humeral head on the glenoid revealed by anteroposterior radiographs evaluated by observers blinded to the clinical data. The incidence of this finding was 16% at 10 years after surgery and 55% at 15 years. Shoulders with this finding had worse comfort and function as well as a greater risk of glenoid component failure. Shoulders with preoperative fatty infiltration of the infraspinatus and shoulders having glenoid components inserted with a superior tilt have an increased risk of secondary cuff dysfunction.
It is of note that the average age of the patients in this series was 68 years. This, of course, is an age in which rotator cuff failure becomes quite common, even if these defects are asymptomatic. Thus, progressive cuff failure can be expected in this patient population. In this regard it is interesting that a partial articular-sided tear of the supraspinatus was found in 48 shoulders and a complete full-thickness supraspinatus tear was found in 43 shoulders; 15% of the shoulders had cuff pathology identified at surgery. Twelve shoulders had cuff repairs at the time of arthroplasty.
It is important to keep in mind that the rotator cuff insertion to the humerus is at jeopardy when the humeral cut is made - we have seen cases in which 'secondary cuff failure' resulted from accidental cuff detachment at surgery.
Some of the cases exemplified in this study show evidence not only of superior migration and loosening, but also of glenoid component wear (thinning of the space between the humeral head and the cement at the glenoid bone surface) and of osteolysis or even infection as shown below.
Among the lessons that can be derived from this study are
(1) inform all patients having a 'total shoulder' that the rotator cuff becomes progressively thin, weak and stiff with age, so that cuff failure is a risk - especially since the arthroplasty may enable and encourage active use of a shoulder that has been 'in irons' for quite a while before surgery
(2) take care to protect the cuff insertion during the humeral cut
(3) avoid 'overstuffing' the shoulder with too-large components that put the cuff under increased tension
(4) assure secure and durable fixation of the glenoid component, avoiding superior tilt
(5) encourage gentle progressive rehabilitation of the shoulder after arthroplasty so that the cuff has a chance to accommodate the increased loading
(6) encourage patients to inform their surgeon if there is a loss in function of a previously functional arthroplasty
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