Variation of the subscapularis tendon at the fetal glenohumeral joint

Abstract

Summary: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.

Distally-extending muscle fibers across involved joints: study of long muscles and tendons of wrist and ankle in late-term fetuses and adult cadavers

“…The brachialis is a major muscle that attaches to and stabilizes the anterior aspect of the humeroulnar joint in adults [ 3 , 4 ], whereas the flexor pollicis longus and others muscles cover the joint capsule in late-term fetuses [ 5 ]. In fetuses, the subscapularis muscle belly tends to extend into the glenohumeral joint cavity along the thick tendon [ 6 ]. Because the subscapularis tendon provides high resistance against mechanical stress in adults [ 7 ], the intra-articular muscle fibers should degenerate during shoulder movements in infants.…”

Differences in foetal topographical anatomy between insertion sites of the iliopsoas and gluteus medius muscles into the proximal femur: a consideration of femoral torsion

“…However, in adults, IP muscle fibres are unlikely to attach to the capsule because the IP tendon reinforces the weak anterior aspect of the joint as a dynamic stabiliser, acting as a supporting structure strengthened by muscle contractions, comparable to the relationship between the rotator cuff and the glenohumeral joint [13]. The subscapularis muscle tendon, the strongest rotator cuff tendon, showed a similar morphology [8], with this tendon in late stage foetuses composed of abundant fragments of muscle fibres [2]. Moreover, flexor muscle fibres attached to the capsule in foetal elbow joints were reported to degenerate after birth [5].…”

Oblique cord (chorda obliqua) of the forearm and muscle-associated fibrous tissues at and around the elbow joint: a study of human foetal specimens

“…In adults, musculofibrous tissues from the supinator muscle belly often join the oblique cord [14]. Likewise, thickening of the foetal subscapularis tendon involves degeneration of parts of the muscle fibres [1]. These findings suggested that the oblique cord formed after birth under the influence of individual mechanical stresses during pronation-supination movements.…”