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 capsulo ligamentous complex was varied in order to gain insight into the contributi on of each component to limiting translation. All measurements were made wi th the humerus positioned at 90 degrees of abduction and 0 degrees of flexi on/extension. Methods-Six fresh cadaveric shoulders were used. Each scapula was mounted i n a cement pot to rest it in its correct anatomical position. Seven tests w ere carried out on each shoulder. A series of measurements of translation o f the humerus in the anterior direction and posterior direction were taken at 20 degrees intervals of lateral rotation and then at 20 degrees interval s of medial rotation until the limit of lateral or medial rotation had clea rly been reached (test 1). The capsuloligamentous complex was then incised and a beaded chain and catches were sutured across the joint to mimic the c apsuloligamentous 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 rota tion. (b) As the glenohumeral capsuloligamentous complex increases in lengt h, 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 rotat ion the length of the anterior capsule, rather than the length of the poste rior capsule, has the greater effect on anterior/posterior translation. (e) The glenohumeral ligamentous complex acts more as a cuff, enclosing the jo int, rather than as a sling, as is commonly thought.