title: The main cause of instability after unconstrained shoulder prosthesis is soft tissue deficiency.
abstract: BACKGROUND
  Instability is one of the major causes of failures in unconstrained anatomic total shoulder arthroplasty (TSA). This study reviewed the instabilities that may occur in an anatomic shoulder platform system to identify its potential predictors. We hypothesized that soft tissue deficiency was the main cause of instability and that the best treatment option would be conversion to a reverse shoulder arthroplasty (RSA).
  
  
  METHODS
  Between 2003 and 2013, we reviewed 27 patients who experienced postoperative instability, and the overall incidence was 5.07%. There were 8 hemiarthroplasties (HAs), 14 TSAs with metal-backed glenoid components, and 5 TSAs with cemented glenoid components.
  
  
  RESULTS
  We reported 10 isolated subscapularis tears, 6 massive rotator cuff tears, 8 component malpositions, 2 component dissociations or loosening, and 1 humeral shortening. These dislocations occurred early, within the first 6 months postoperatively, in 20 patients and later in 7. Specific procedures were performed in 8 patients, 17 were converted successfully to a RSA, and no surgery was done in 2 patients. At the last follow-up (mean, 36.96 months) Constant scores, Subjective Shoulder Value, and Simple Shoulder Test scores improved significantly to 49.9, 56.4%, and 6.9 of 12, respectively (P < .05). None of the 25 patients who were revised were categorized as failures. Patients who underwent conversion had a better outcome than those who had other specific procedures (P = .001).
  
  
  CONCLUSIONS
  The major cause of instability in our series was soft tissue deficiency. Most of the patients required conversion, and the platform system we used made conversions easier.
authors.affiliation: Shoulder Department, Clinique de l' Union, Saint Jean, France. Electronic address: jean.kany@clinique-union.fr.
authors.forename: Jean
authors.initials: J
authors.lastname: Kany
authors.affiliation: Department of Orthopedics, Lakshmi Hospital, Ernakulam, India.
authors.forename: Jijo
authors.initials: J
authors.lastname: Jose
authors.affiliation: Shoulder Department, Clinique du Ter, Ploemeur, France.
authors.forename: Denis
authors.initials: D
authors.lastname: Katz
authors.affiliation: Paris Shoulder Unit, Institut de la Main, Clinique Bizet, Paris, France.
authors.forename: Jean-David
authors.initials: JD
authors.lastname: Werthel
authors.affiliation: Department of Physiotherapy and Rehabilitation, Sparsh Hospital for Advanced Surgeries, Bangalore, India.
authors.forename: Padmanaban
authors.initials: P
authors.lastname: Sekaran
authors.affiliation: Department of Orthopedics, Arthroscopy and Sports Medicine, St John's Medical College Hospital, Bangalore, India.
authors.forename: Rajkumar S
authors.initials: RS
authors.lastname: Amaravathi
authors.affiliation: Paris Shoulder Unit, Institut de la Main, Clinique Bizet, Paris, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Valenti
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000072228:Arthroplasty, Replacement, Shoulder / Q000009:adverse effects* / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007593:Joint Instability / Q000209:etiology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D011475:Prosthesis Failure / Q000009:adverse effects; D012086:Reoperation; D012189:Retrospective Studies; D000070636:Rotator Cuff Injuries / Q000150:complications*; D012783:Shoulder Dislocation / Q000209:etiology* / Q000601:surgery; D012785:Shoulder Joint / Q000503:physiopathology*; D000072227:Shoulder Prosthesis / Q000009:adverse effects; D016896:Treatment Outcome
keywords: Instability; conversion; platform system; rotator cuff; subscapularis; total shoulder arthroplasty