Macroscopic and histological observations on the human sternoclavicular joint disc

To know the detailed morphology of the human sternoclavicular joint and its articular disc is essential to understanding the movement of this joint and the functional role of the disc. In the present study, 51 articular discs of the sternoclavicular joint of 29 Japanese cadavers were macroscopically examined and then embedded in paraffin to make a complete series of coronal sections for light microscopic observation. We classified the articular discs into three types, discoid, ring, and meniscoid. The discoid-type disc was flattened and round in shape, whereas the other two types had partial defects in the centers (ring type) or in the periphery (meniscoid type). We found the bony process that protruded from the sternal end of the clavicle and fitted into the defect part of the ring- or meniscoid-type discs. The mean values of this bony process of the clavicle adjacent to the articular disc were 2.1, 4.7, and 6.0 mm, respectively, in the three types of articular disc. The movement between the articular disc and the clavicle may be limited, because the articular disc was directly attached to the clavicle on its medial region. The present histological observation demonstrated that the sternal side of the disc was composed of fibrocartilage and dense connective tissue. The clavicular side of the disc was composed of only fibrocartilage. The clavicular side of the articular disc of the sternoclavicular joint has the function of resisting the compressive load to the clavicular surface.