title: Effect of humeral stem design on humeral position and range of motion in reverse shoulder arthroplasty.
abstract: OBJECTIVE
  The impacts of humeral offset and stem design after reverse shoulder arthroplasty (RSA) have not been well-studied, particularly with regard to newer stems which have a lower humeral inclination. The purpose of this study was to analyze the effect of different humeral stem designs on range of motion and humeral position following RSA.
  
  
  METHODS
  Using a three-dimensional computer model of RSA, a traditional inlay Grammont stem was compared to a short curved onlay stem with different inclinations (155°, 145°, 135°) and offset (lateralised vs medialised). Humeral offset, the acromiohumeral distance (AHD), and range of motion were evaluated for each configuration.
  
  
  RESULTS
  Altering stem design led to a nearly 7-mm change in humeral offset and 4 mm in the AHD. Different inclinations of the onlay stems had little influence on humeral offset and larger influence on decreasing the AHD. There was a 10° decrease in abduction and a 5° increase in adduction between an inlay Grammont design and an onlay design with the same inclination. Compared to the 155° model, the 135° model improved adduction by 28°, extension by 24° and external rotation of the elbow at the side by 15°, but led to a decrease in abduction of 9°. When the tray was placed medially, on the 145° model, a 9° loss of abduction was observed.
  
  
  CONCLUSIONS
  With varus inclination prostheses (135° and 145°), elevation remains unchanged, abduction slightly decreases, but a dramatic improvement in adduction, extension and external rotation with the elbow at the side are observed.
authors.affiliation: Division of Orthopaedics and Trauma Surgery, La Tour Hospital, Rue J.-D. Maillard 3, 1217, Meyrin, Switzerland. alexandre.laedermann@gmail.com.|Faculty of Medicine, University of Geneva, Rue Michel-Servet 1, 1211, Geneva 4, Switzerland. alexandre.laedermann@gmail.com.|Division of Orthopaedics and Trauma Surgery, Department of Surgery, Geneva University Hospitals, Rue Gabrielle-Perret-Gentil 4, 1211, Geneva 14, Switzerland. alexandre.laedermann@gmail.com.
authors.forename: Alexandre
authors.identifier: http://orcid.org/0000-0002-2797-8936
authors.initials: A
authors.lastname: Lädermann
authors.affiliation: Southern Oregon Orthopedics, Medford, OR, USA.|Department of Orthopaedics and Rehabilitation, Oregon Health & Science University, Portland, OR, USA.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Denard
authors.affiliation: Department of Orthopaedic Surgery and Sports Traumatology, Hôpital de L'Archet-University of Nice Sophia-Antipolis, 151, Route de St Antoine de Ginestière, 06202, Nice, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Boileau
authors.affiliation: Division of Orthopaedics and Trauma Surgery, Department of Surgery, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland.
authors.forename: Alain
authors.initials: A
authors.lastname: Farron
authors.affiliation: Tornier SA, Montbonnot Saint-Martin, France.
authors.forename: Pierric
authors.initials: P
authors.lastname: Deransart
authors.affiliation: Laboratory of Biomechanical Orthopedics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Terrier
authors.affiliation: Laboratory of Biomechanical Orthopedics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
authors.forename: Julien
authors.initials: J
authors.lastname: Ston
authors.affiliation: Department of Orthopaedics, Shoulder Unit, Santy Orthopaedic Center and Jean Mermoz Hospital, Lyon, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Walch
mesh_terms: D019643:Arthroplasty, Replacement / Q000379:methods*; D003198:Computer Simulation; D006801:Humans; D006811:Humerus / Q000601:surgery*; D021621:Imaging, Three-Dimensional; D007595:Joint Prosthesis; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D012399:Rotation; D012785:Shoulder Joint / Q000601:surgery*
keywords: Arm position; Complications; Humeral offset; Impingement; Inlay and onlay design; Range of motion; Reverse total shoulder arthroplasty; Reverse tray