Relationship between A-P Translation of the Humeral Head and the Function of the Glenohumeral Ligament

Abstract

The purpose of this study was to evaluate the relationships between an A-P translation of the humeral head and the function of the glenohumeral ligament.
Thirty-five shoulders with anterior instability diag nosed by operative findings were examined. The subjects consisted of 10 shoulders with rotator interval lesions without a Bankart lesion (RIL group ). and 25 shoulders with Bankart lesions (Bankart group ). The normal 20 shoulders were evaluated as the control.
In cinerthrography, the joint kinetics of rotational motion in the 2nd plane on axial views were recorded. The motion of the shoulder joint was from the neutral position to maximun external rotation at 90 degrees of abduction. Using an image analyzing system, the displacement of the center of the humeral head and the rotation of the glenohumeral joint were calculated in each position.
Control group : The displacements of the humeral head were small with trends in the posteroir direction by external rotation.
RIL group: The humeral head translated anterioly 60-80 degrees inan external rotation, and posteriorly in the following an ER (rebound phenomenon).
Bankart group: Anterior translations only could be obse rved in the ER However 4 shoulders with normal MGHLs and IGHLs had the reboundphenomenon in 90-100 degrees ER.
At 90 degrees abduction, the IGHL plays a role in limiting anterior tran slation mainly in the late stage of an external rotation, and the MIGL plays the role of anterior stabilizer in the early stagesof an ER.