There are several reasons why this might be the case:
(1) both osteoarthritis and cuff tendinopathy are common age-related degenerative conditions of the shoulder, as a result aging patients are at risk for having both conditions (see Asymptomatic Rotator Cuff Tears, Prevalence of symptomatic and asymptomatic rotator cuff tears in the general population: From mass-screening in one village, Age-related prevalence of rotator cuff tears in asymptomatic shoulders, and Shoulder Osteoarthritis).
(2) anatomic shoulder arthroplasty enables postoperative cuff-loading activities that may not have been possible for months or years before surgery due to the limitations in shoulder use imposed by the shoulder arthritis. It can be anticipated that postoperative changes in shoulder motion and patient activity levels would increase the demand on the rotator cuff,
3) technical issues in anatomic arthroplasty may jeopardize the integrity of the cuff. Some of these are well illustrated below in illustrations by Steve Lippitt in Practical Evaluation and Management of the Shoulder (freely available on line at this link).
(a) Overstuffing from excessive component thickness (see "b" below)
(b) Overstuffing from component malposition
(c) accidental injury of the cuff insertion during humeral head resection
(d) loss of concavity compression stability against the upward pull of the deltoid (red arrow) due to the placement of the glenoid component in a superiorly tilted position with the associated absence of a functional superior concavity (similar to the inability of a tilted tee to stabilize the golf ball).
(4) while cuff deficiency may enable the humeral head to subluxate superiorly, superior subluxatiom resulting from superior placement of the humeral head on the humerus may jeopardize the integrity of the cuff.
The authors of Secondary Rotator Cuff Dysfunction Following Total Shoulder Arthroplasty for Primary Glenohumeral Osteoarthritis: Results of a Multicenter Study with More Than Five Years of Follow-up studied 518 shoulders having complete radiographic and clinical followup out of 704 anatomic total shoulders performed for primary osteoarthritis in 10 different European centers. All TSAs were performed with an Aequalis nonconstrained anatomic prosthesis using a cemented all-polyethylene keeled glenoid component. A flat-back glenoid component was used in 263 shoulders, and a convex-back component was used in 333 cases.
A partial articular-sided tear of the supraspinatus was found in 48 shoulders (8.1%) and a complete full-thickness supraspinatus tear was identified in 43 shoulders (7.2%).
The secondary rotator cuff dysfunction was identified indirectly by moderate or severe superior subluxation of the humeral head on the prosthetic glenoid. Proximal humeral superior subluxation was evaluated on the anteroposterior radiograph as the amount of the translation of the center of the prosthetic head relative to the center of the glenoid component. Subluxation was defined as mild if the center of the prosthetic humeral head had translated <25% of its diameter relative to the center of the glenoid component; as moderate if the center of the prosthetic head translated 25%to 50% of its diameter relative to the center of the glenoid; and as severe if the center of the prosthetic head translated >50% of its diameter relative to the center of the glenoid.
The x-ray below shows superior subluxation related to a too-high position of the humeral component on the humerus, a superiorly tilted glenoid component placed in a too-low position with radiographic loosing, thinning of the superior glenoid polyethylene, and a large amount of cement in the glenoid (which can contribute to glenoid component loosening (see this link). Note that a number of different factors can result in superior decentering of the humeral head relative to the glenoid - it is not a specific sign of "secondary rotator cuff dysfunction".
The rate of superior subluxation averaged 16.8%: 0% at five years followup, 16% at ten years, and 55% at fifteen years.
Duration of follow-up had the strongest association with superior head subluxation, followed by implantation of the glenoid implant with superior tilt, and preoperative fatty infiltration of the infraspinatus muscle.
Patients with superior humeral head subluxation had significantly worse Constant scores, range of motion, and radiographic results (radiolucent line score, radiographic loosening, glenoid component migration.
At an average of 8.7 years after shoulder arthroplasty, the rate of revision for glenoid loosening was 4%. 90.3% of patients were either very satisfied or satisfied with their outcome. The rate of revision, either for glenoid loosening or symptomatic massive rotator cuff tear, was not significantly different between patients with superior humeral head subluxation (5.7%) and those without (5.1%).
Comment: It is apparent that rotator cuff failure can compromise the outcome of anatomic total shoulder arthroplasty. From this study it is also apparent that surgeons may be able to minimize this risk by appropriate patient selection as well as by optimal surgical technique, implant selection and implant positioning.
It is of note that each of the four examples in this paper of superior subluxation (see below) show a higher than desired position of the humeral head in respect to the tuberosity - a location that puts extra tension on the cuff as illustrated above as well as risking eccentric loading and rocking horse loosening of the glenoid component (see Glenoid loosening in total shoulder arthroplasty. Association with rotator cuff deficiency)
The position of the head was not considered as a variable in this study and may have accounted for the superior subluxation as well as the associated inferior clinical and radiographic outcomes.
While the use of reverse total shoulder for patients having osteoarthritis and an intact cuff may seem attractive, it remains to be seen whether RSA yields equivalent or better long term outcomes than anatomic TSA (see Glenohumeral osteoarthritis - what type of arthroplasty has the lowest 10 year revision rate? and Long-Term Outcomes of Reverse Total Shoulder Arthroplasty
You can support cutting edge shoulder research that is leading to better care for patients with shoulder problems, click on this link.
To add this blog to your reading list in Google Chrome, click on the reading list icon
Follow on twitter: https://twitter.com/shoulderarth
Follow on facebook: click on this link
Follow on facebook: https://www.facebook.com/frederick.matsen
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/
Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).
To add this blog to your reading list in Google Chrome, click on the reading list icon
Follow on twitter: https://twitter.com/shoulderarth
Follow on facebook: click on this link
Follow on facebook: https://www.facebook.com/frederick.matsen
Follow on LinkedIn: https://www.linkedin.com/in/rick-matsen-88b1a8133/
Here are some videos that are of shoulder interest
Shoulder arthritis - what you need to know (see this link).
How to x-ray the shoulder (see this link).
The ream and run procedure (see this link).
The total shoulder arthroplasty (see this link).
The cuff tear arthropathy arthroplasty (see this link).
The reverse total shoulder arthroplasty (see this link).
The smooth and move procedure for irreparable rotator cuff tears (see this link).
Shoulder rehabilitation exercises (see this link).
