title: The effects of prosthetic humeral head shape on glenohumeral joint kinematics: a comparison of non-spherical and spherical prosthetic heads to the native humeral head.
abstract: BACKGROUND
  The purpose of this study was to quantitatively evaluate the effect of the prosthetic humeral head shape on rotational range of motion and glenohumeral joint kinematics.
  
  
  METHODS
  Six fresh-frozen cadaveric shoulders were tested in multiple positions under anatomic muscle loading. Specimens were tested for the native head, and then the spherical and non-spherical prosthetic heads were randomly implanted in the same stem to preserve the center of rotation. Rotational range of motion was measured with 3.3 Nm of torque. Glenohumeral joint kinematics was quantified by the position vectors of the humeral head apex (HHA) and geometric center of the humeral head (GCHH) to calculate translation of HHA and GCHH per degree of humeral rotation.
  
  
  RESULTS
  The non-spherical prosthetic head replicated the native head shape more accurately than the spherical prosthetic head. Between the non-spherical and native heads, there was no statistical difference in rotational range of motion (P > .05), but a statistical difference in HHA and GCHH translation was found at 60° of scapular plane abduction in the interval from 30° of internal rotation to neutral rotation and at 30° of forward flexion plane abduction in the interval from 30° of external rotation to maximum external rotation, respectively (P < .05). The spherical head significantly decreased rotational range of motion (P < .05), increased HHA translation per degree (P < .05), and decreased GCHH translation per degree (P < .05) in multiple positions compared with the native humeral head.
  
  
  CONCLUSIONS
  The custom, non-spherical prosthetic head more accurately replicated the head shape, rotational range of motion, and glenohumeral joint kinematics than the commercially available, spherical prosthetic head compared with the native humeral head.
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, CA, USA; Department of Biomedical Engineering, Cleveland Clinic, Cleveland, OH, USA. Electronic address: bongjaejun@gmail.com.
authors.forename: Bong Jae
authors.initials: BJ
authors.lastname: Jun
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Iannotti
authors.forename: Michelle H
authors.initials: MH
authors.lastname: McGarry
authors.forename: Jae Chul
authors.initials: JC
authors.lastname: Yoo
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Quigley
authors.forename: Thay Q
authors.initials: TQ
authors.lastname: Lee
mesh_terms: D019643:Arthroplasty, Replacement / Q000379:methods*; D002102:Cadaver; D006801:Humans; D058430:Humeral Head / Q000601:surgery*; D007592:Joint Diseases / Q000503:physiopathology / Q000601:surgery*; D007595:Joint Prosthesis; D008875:Middle Aged; D016059:Range of Motion, Articular / Q000502:physiology*; D012540:Scapula / Q000601:surgery*; D012785:Shoulder Joint / Q000503:physiopathology* / Q000601:surgery
keywords: Basic Science; Biomechanics; Cadaveric Model; Hemiarthroplasty; geometric center; humeral head apex; kinematics; prosthetic humeral head shape; range of motion