Instability after shoulder arthroplasty: results of surgical treatment.
BACKGROUND
Currently, there is little available information regarding the surgical treatment of instability following shoulder arthroplasty. The purpose of the present study was to review the results of revision surgery performed for the treatment of instability after shoulder arthroplasty to better define the causes of instability and the risk factors for an unsatisfactory outcome.


METHODS
Between 1985 and 1999, thirty-three shoulders (seven of which had had a hemiarthroplasty and twenty-six of which had had a total shoulder arthroplasty) were treated surgically at our institution for anterior instability (nineteen shoulders) or posterior instability (fourteen shoulders). The primary arthroplasty had been performed for the treatment of degenerative arthritis in sixteen shoulders, arthritis of dislocation in six, acute fracture in four, rheumatoid arthritis in three, and other conditions in four.


RESULTS
The instability was attributed to abnormal capsular tension and/or rotator cuff dysfunction in twenty-one shoulders, component malpositioning in one shoulder, and a combination of both in eleven shoulders. One shoulder was treated with removal of the components. In the remaining thirty-two shoulders, each of the elements that was contributing to the instability was specifically addressed at the time of surgery. Revision surgery restored stability in nine of the thirty-two shoulders. Anterior instability was associated with a higher failure rate than posterior instability was (p = 0.04). Although eleven shoulders had additional surgery for the treatment of recurrent instability, only fourteen of the thirty-three shoulders were stable at the time of the final follow-up. According to the Neer rating system, there were four excellent, six satisfactory, and twenty-three unsatisfactory results.


CONCLUSIONS
Soft-tissue imbalance is present in most cases of instability following shoulder arthroplasty, and component malpositioning plays an additional role in some cases. More than one-half of the shoulders in the present study remained unstable despite attempts at revision. Surgical treatment of instability following arthroplasty is associated with only a modest success rate.
Sanchez-Sotelo
Joaquin
J
Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota 55902, USA.
Sperling
John W
JW
Rowland
Charles M
CM
Cofield
Robert H
RH
D000328:Adult; D000368:Aged; D001178:Arthroplasty / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000209:etiology* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D012086:Reoperation / Q000009:adverse effects; D012785:Shoulder Joint / Q000601:surgery*; D017211:Treatment Failure