Humeral head size in shoulder arthroplasty: a kinematic study

Changes in kinematics after hemiarthroplasty of the glenohumeral joint were investigated in nine cadaveric specimens. During experiments the influence of the humeral head size on glenohumeral kinematics was evaluated. A modular prosthesis with five different head sizes and press-fit stems was used. Three-dimensional kinematic measurements during abduction and adduction from 0 degree to 70 degrees showed increased external rotation with increasing head size. Small prosthetic heads translated inferiorly and large prosthetic heads superiorly compared with the intact humeral head. During forced anterior and posterior translation the mobility is restricted with increasing head size. This study found that when a press-fit prosthesis is used, it takes 1.25 times the volume of the intact humeral head to reconstruct the kinematics of the glenohumeral joint.