title: Conversion of hemi into reverse shoulder arthroplasty: implant design limitations.
abstract: OBJECTIVE
  Cranial migration of shoulder hemiarthroplasties due to rotator cuff insufficiency typically requires conversion into a reverse total shoulder arthroplasty. This study was conducted to analyze differences between the height and offset of six implants designed to enable conversion of a hemiarthroplasty into a reverse system.
  
  
  METHODS
  Anteroposterior radiographs of 40 shoulders were taken. An image analyzing software was used to simulate the implantation of the hemiprostheses. Then the implant was dissembled, leaving on the stem within the humeral shaft. Finally, the implantation of a reverse system was simulated using the stem in the same position. Values are reported as ∆-height and ∆-offset ± standard deviation. Significance was assumed for P < 0.05.
  
  
  RESULTS
  The least decrease in height was determined for Implantcast with 11.6 ± 3.3 mm, followed by DePuy (16 ± 5.7 mm) and the greatest for Tornier with 33 ± 5.3 mm. No significant differences were found among Exactech, Mathys and Zimmer. The largest offset-deviation was calculated for DePuy (-21.7 ± 3.7 mm) and the smallest for Implantcast (-3.3 ± 2.8 mm) and Tornier (1.5 ± 5.7 mm).
  
  
  CONCLUSIONS
  Due to the modular stem, the system of Implantcast can be converted in a reverse system with the least changes in height and offset. For the other manufacturers it does not seem possible to convert a hemiprosthesis to a reversed prosthesis without accepting additional tension of the deltoid muscle. Further experimental studies have to analyze the changes in deltoid abduction moments after conversion of a hemi- into a reversed prosthesis.
authors.affiliation: Trauma Department, Hannover Medical School (MHH), Carl-Neubergstraße 1, 30625, Hannover, Germany, hiteschner@freenet.de.
authors.forename: Hilmar
authors.initials: H
authors.lastname: Teschner
authors.forename: Urs-Vito
authors.initials: UV
authors.lastname: Albrecht
authors.forename: Rupert
authors.initials: R
authors.lastname: Meller
authors.forename: Emmanouil
authors.initials: E
authors.lastname: Liodakis
authors.forename: Ulrich
authors.initials: U
authors.lastname: Wiebking
authors.forename: Christian
authors.initials: C
authors.lastname: Krettek
authors.forename: Michael
authors.initials: M
authors.lastname: Jagodzinski
mesh_terms: D000328:Adult; D000368:Aged; D019643:Arthroplasty, Replacement / Q000379:methods*; D057645:Deltoid Muscle; D005260:Female; D062785:Hemiarthroplasty; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007595:Joint Prosthesis; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D011859:Radiography; D016059:Range of Motion, Articular / Q000502:physiology; D012086:Reoperation; D012785:Shoulder Joint / Q000000981:diagnostic imaging / Q000601:surgery*