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 eva luated. A modular prosthesis with five different head sizes and press- fit stems was used. Three-dimensional kinematic measurements during ab duction and adduction from 0 degrees to 70 degrees showed increased ex ternal rotation with increasing head size. Small prosthetic heads tran slated inferiorly and large prosthetic heads superiorly compared with the intact humeral head. During Forced anterior and posterior translat ion the mobility is restricted with increasing head size. This study f ound 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 th e glenohumeral joint.