Variation of the subscapularis tendon at the fetal glenohumeral joint.

We examined the topohistology of the subscapularis tendon at the glenohumeral joint in 10 mid-term (15-16 weeks of gestation) and 10 late-stage (27-32 weeks) human fetuses. At both stages, there were two patterns of terminal course of the subscapularis tendon: 1) the tendon was tightly attached to the medial part of the joint capsule and extended anterosuperiorly along the capsule to the lesser tubercle (7/10 mid-term fetuses; 5/10 late-stage fetuses); 2) the tendon passed superiorly through the joint cavity for a long distance in combination with the subcoracoid bursa opening widely to the joint cavity (3/10 mid-term fetuses; 5/10 late-stage fetuses). The lower glenoid labrum tended to be well developed in the former pattern because the subscapularis tendon did not interfere with the superior extension of the labrum. With only one exception (late stage), the capsule-attaching tendon was seen in fetuses in which the coracoid process was located on the superior side of the lesser tubercle, whereas the intra-articular tendon accompanied the coracoid process at the same supero-inferior level of the tubercle. Thus, the topographical relationship between the coracoid process and lesser tubercle in fetuses seemed to determine the courses of the subscapularis tendon at the glenohumeral joint. The present variation in the subscapularis tendon was likely connected with the adult morphologies of the middle and inferior glenohumeral ligaments or folds, whose variations are well known.