Correlation of medial/lateral rotation of the humerus with glenohumeral translation.

OBJECTIVES To correlate glenohumeral translation in the anterior/posterior direction with medial and lateral rotation of the humerus. In addition, the length of the anterior and posterior component of the glenohumeral capsuloligamentous complex was varied in order to gain insight into the contribution of each component to limiting translation. All measurements were made with the humerus positioned at 90 degrees of abduction and 0 degrees of flexion/ extension. METHODS Six fresh cadaveric shoulders were used. Each scapula was mounted in a cement pot to rest it in its correct anatomical position. Seven tests were carried out on each shoulder. A series of measurements of translation of the humerus in the anterior direction and posterior direction were taken at 20 degrees intervals of lateral rotation and then at 20 degrees intervals of medial rotation until the limit of lateral or medial rotation had clearly been reached (test 1). The capsuloligamentous complex was then incised and a beaded chain and catches were sutured across the joint to mimic the capsuloligamentous complex at different lengths (tests 2 to 7). RESULTS/CONCLUSIONS (a) When the glenohumeral capsuloligamentous complex is intact, the humerus translates maximally in the glenoid (between 20 and 30 mm) when the humerus is between 40 degrees and 100 degrees of lateral rotation. (b) As the glenohumeral capsuloligamentous complex increases in length, so does the extent of translation. (c) In medial rotation, the length of the posterior capsule, rather than the length of the anterior capsule, has the greater effect on anterior/posterior translation. (d) In lateral rotation the length of the anterior capsule, rather than the length of the posterior capsule, has the greater effect on anterior/posterior translation. (e) The glenohumeral ligamentous complex acts more as a cuff, enclosing the joint, rather than as a sling, as is commonly thought.