title: The effects of prosthetic humeral head shape on glenohumeral joint kinematics during humeral axial rotation in total shoulder arthroplasty.
abstract: BACKGROUND
  A non-spherical humeral head has been shown to influence kinematics and stability of the glenohumeral joint; yet, most prosthetic humeral head components are designed to be a perfect sphere. The effect of humeral head shape on prosthetic joint kinematics after total shoulder arthroplasty is not well understood. We hypothesized that prosthetic joint kinematics during humeral axial rotation is dependent on humeral head shape, regardless of joint conformity.
  
  
  METHODS
  Four prosthetic configurations were investigated using a spherical and a non-spherical prosthetic humeral head articulated with a conforming and a non-conforming glenoid component. Testing was performed in the coronal, scapular, and forward flexion plane at 0°, 30°, and 60° of abduction. Prosthetic joint kinematics was measured in 10° intervals during a 100° arc of humeral axial rotation. Glenohumeral translation patterns, net glenohumeral translation, and averaged glenohumeral translation were compared for each of 4 configurations.
  
  
  RESULTS
  Non-spherical head configurations increased the net glenohumeral translation during humeral axial rotation in multiple test positions compared with spherical head configurations (P < .05). Spherical head configurations resulted in a relatively small amount of glenohumeral translation, less than 2 mm. The radius of curvature of the glenoid component alone did not affect the net glenohumeral translation within each of the 2 head groups (P > .05).
  
  
  CONCLUSIONS
  During humeral axial rotation, the non-spherical humeral head shape contributes to increased glenohumeral translation during humeral axial rotation. However, the spherical head shape does not show significant glenohumeral translation during humeral axial rotation, regardless of glenoid conformity.
authors.affiliation: Department of Biomedical Engineering, Cleveland Clinic, Cleveland, OH, USA; Department of Orthopedic Surgery, Cleveland Clinic, Cleveland, OH, USA.
authors.forename: Bong Jae
authors.initials: BJ
authors.lastname: Jun
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, CA, USA.
authors.forename: Thay Q
authors.initials: TQ
authors.lastname: Lee
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, CA, USA.
authors.forename: Michelle H
authors.initials: MH
authors.lastname: McGarry
authors.affiliation: Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, CA, USA.
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Quigley
authors.affiliation: Department of Orthopedic Surgery, Ewha Womans University, Seoul, Republic of Korea.
authors.forename: Sang Jin
authors.initials: SJ
authors.lastname: Shin
authors.affiliation: Department of Orthopedic Surgery, Cleveland Clinic, Cleveland, OH, USA. Electronic address: iannotj@ccf.org.
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Iannotti
mesh_terms: D000072228:Arthroplasty, Replacement, Shoulder; D001696:Biomechanical Phenomena; D006801:Humans; D058430:Humeral Head; D008422:Materials Testing; D011474:Prosthesis Design; D012399:Rotation; D012785:Shoulder Joint / Q000503:physiopathology* / Q000601:surgery; D000072227:Shoulder Prosthesis
keywords: Humeral head shape; center of rotation; conformity; kinematics; total shoulder arthroplasty; translation