title: Bulk effect of the deltoid muscle on the glenohumeral joint.
abstract: BACKGROUND
  There remains controversy on the role of the deltoid on glenohumeral translations during basic and pitching motions. We thus studied the passive effect of the deltoid on the deltoid glenohumeral joint center (GHJC).
  
  
  METHODS
  Six shoulders were tested using an automated mechanical system. A baseline motion pattern of the intact specimen was contrasted with glenohumeral translation after removal of the deltoid. Each condition was evaluated in abduction (ABD) and an abbreviated throwing motion (ATM) using retro-reflective, bone-embedded markers. The absolute trajectory and the area under the curve (AUC) for each motion were calculated and glenohumeral kinematics with respect to the GH translation were compared.
  
  
  RESULTS
  The removal of the deltoid resulted in significant changes of the GH translation. During 30-60° of ABD, it resulted in a superior and more anterior GH translation, while in the 60-90° segment in a more inferior and medial GH translation. During 90-120°, the GH translation was medialized. In the pitching motion from maximum external rotation to 90° of external rotation (ER), the removal of the deltoid resulted in a more superior, anterior and lateral GH translation. Thus limits anterior translation in the abduction-external rotation position. In the remaining segments (90-80° and 80-45° of ER), it resulted in a lateralization of the GH translation.
  
  
  CONCLUSIONS
  Modelling the throwing shoulder, the deltoid has a significant influence on glenohumeral motion. Athletes with deltoid dysfunction and limited range of motion are at risk for injury due to the resulting change in their throwing mechanics.
authors.affiliation: Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA. C.Rosso@arthro.ch.|Orthopaedic Department, University Hospital Basel and University of Basel, Basel, Switzerland. C.Rosso@arthro.ch.|Altius Swiss Sportsmed Center, Rheinfelden, Switzerland. C.Rosso@arthro.ch.
authors.forename: Claudio
authors.initials: C
authors.lastname: Rosso
authors.affiliation: Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA. muelleram76@gmail.com.|Orthopaedic Department, University Hospital Basel and University of Basel, Basel, Switzerland. muelleram76@gmail.com.
authors.forename: Andreas M
authors.initials: AM
authors.lastname: Mueller
authors.affiliation: Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA. bmckenz510@gmail.com.
authors.forename: Brett
authors.initials: B
authors.lastname: McKenzie
authors.affiliation: Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA. ventezari@gmail.com.
authors.forename: Vahid
authors.initials: V
authors.lastname: Entezari
authors.affiliation: Information Engineering Unit, POLCOMING Department, University of Sassari, Sassari, Italy. acereatti@uniss.it.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cereatti
authors.affiliation: Information Engineering Unit, POLCOMING Department, University of Sassari, Sassari, Italy. dellacroce@uniss.it.
authors.forename: Ugo
authors.initials: U
authors.lastname: Della Croce
authors.affiliation: Department of Orthopaedic Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Stoneman 10, Boston, 02215, MA, USA. aramappa@bidmc.harvard.edu.
authors.forename: Arun J
authors.initials: AJ
authors.lastname: Ramappa
authors.affiliation: Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA. anazaria@bidmc.harvard.edu.
authors.forename: Ara
authors.initials: A
authors.lastname: Nazarian
authors.affiliation: Department of Orthopaedic Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, 330 Brookline Avenue, Stoneman 10, Boston, 02215, MA, USA. jpdeange@bidmc.harvard.edu.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: DeAngelis
keywords: Biomechanics; Bulk effect; Deltoid muscle; Motion analysis; Pitching; Shoulder