The sternoclavicular joint: variants of the discus articularis

Objective. TO study the anatomy of the sternoclavicular joint, its discus and its variations. Design. Anatomical study (macroscopic dissection). Background Textbooks on manual therapy give different descriptions of the movements of this joint. These apparent contradictions could be due to poor understanding of the anatomy of this joint resulting in ignoring specific movement patterns under particular conditions. Methods. Macroscopic dissection of 22 embalmed sternoclavicular joints. Results. The sternoclavicular and the costoclavicular parts of the discus always were quite distinct in orientation, thickness, surface and consistency. The sternoclavicular part was attached to the dorso-cranial part of the extremitas sternalis claviculae by a broad insertion in which several small blood vessels are visible. This part is grossly vertical, thicker than the lateral part and has a fibrous aspect. The costoclavicular part of the discus is always thinner than the sternoclavicular part. Sometimes it is reduced to a fine translucent pellet or is perforated. Subsynovial vascular arcades run along the insertion of the discus on the joint capsule, both on sternal and on clavicular sides. The costosternal articular surface can be divided into a sternal and a costal segment, separated by a vascular zone. Conclusions. Findings suggest different functions of the distinct parts of the joint. The smooth aspect of the lateral segment of the costosternal articular surface and of the costoclavicular part of the discus could be an argument to consider a functionally distinct costoclavicular compartment. The insertion of the discus on the clavicula strongly suggests that small movements take place between clavicula and discus and that the discus itself is moved only when the increasing amplitude stretches this insertion. We hypothesise that all midrange movements take place between the convex inferior edge of the clavicula and the costoclavicular part of he discus and that larger elevation depression and pro- and retraction movement take place, respectively, between clavicula and discus or discus and sternum. In three specimens we observed a previously not described arterial ramus articularis originating from the left thyrocervical trunk.