The costoclavicular ligament contains an anterior and a posterior fasciculus, which arises from the chondral surface of the first rib and inserts on the undersurface of the medial clavicle (Fig. 19.4) [44]. The anterior fasciculus originates on the anterior medial aspect of the chondral surface and its fibers run superolaterally, while the posterior fasciculus originates on the posterior lateral aspect and its fibers run superomedially [44]. The anterior fasciculus of the costoclavicular ligament limits both lateral translation and upward rotation of the clavicle, while the posterior fasciculus limits medial translation and downward rotation [5, 44, 55].

The interclavicular ligament links the superomedial aspects of each clavicle and runs along the superior margin of the manubrium (Fig. 19.4). The ligament functions as a secondary stabilizer of the SC joint, preventing excessive depression of the clavicle [44].

The anterior and posterior SC ligaments represent capsular thickenings, which function as the primary stabilizers of the SC joint, with the posterior ligament being the stronger of the two (Fig. 19.4) [52]. The anterior SC ligament fibers run obliquely from the medial clavicle to the sternum in a downward and medial direction, serving to prevent anterior displacement of the clavicle. The posterior SC ligament fibers cover the posterior aspect of the SC joint, preventing both anterior and posterior displacements of the clavicle [52].

The presence of an intra-articular disk ligament is a matter of debate. Some authors argue that the intra-articular disk ligament complex passes from the dorsal and caudal clavicular head, through the SC joint, to the synchondral junction of the first rib and manubrium [3, 44, 55]. Yet others argue that the disk only inserts on the anterior and posterior capsular ligaments, which then insert onto the bone, and thus is not a ligament itself [50, 57]. Regardless, by virtue of its inferior lateral and superomedial insertions, the disk acts as a tether, preventing medial translation of the clavicular head [44].

Sternocostoclavicular hyperostosis (SCCH) is a rare chronic inflammatory disorder of the anterior chest wall. The disease typically begins with inflammation and calcification of the sternoclavicular ligaments and sternoclavicular perichondritis, which progresses to erosive arthritis [10, 22]. With time, progressive hyperosteotic changes are seen extending to the medial clavicle, sternoclavicular joint, manubrium, first rib, and soft tissue [10, 22]. Occasionally, changes are seen in ribs two through seven [22]. Complete fusion of the sternoclavicular joints can occur after years of chronic inflammation. Biopsy specimens demonstrate nonspecific osteosclerosis with the presence of a round cell infiltrate and granulation tissue [22]. SCCH can be associated with extrasternal manifestations such as sclerosis of the axial skeleton (vertebrae, pelvis, sacroiliac joint), peripheral arthritis, and, most commonly, palmoplantar pustulosis [10, 22, 51]. The etiology of this rare disorder and the overlap between this and others that present with multifocal nonsuppurative periosteitis and hyperostosis, namely, SAPHO (synovitis, acne, pustulosis, hyperostosis, and osteitis) syndrome and chronic recurrent multifocal osteomyelitis (CRMO), is poorly understood [4]

Condensing osteitis is a rare disorder involving sclerosis and enlargement of the inferomedial clavicle, which spares the sternoclavicular joint. The condition was first described in 1974 [8], and only 40 cases have been documented in the literature [27]. The disease typically presents unilaterally in women of childbearing age without a history of trauma. Patients experience an insidious onset of pain, which may radiate to the supraclavicular fossa, and a fusiform swelling over the medial clavicle [8, 34]. Pain is exacerbated with shoulder abduction and forward flexion. The etiology is currently unknown. Some authors argue the disorder is a response to mechanical stress, while others support an infectious etiology [8, 12, 30, 34]. Radiographs and CT scans demonstrate sclerosis, minor expansion of the inferomedial clavicle, and loss of marrow space [25]. Hypointensity in the affected region of the clavicle on T1-weighted SE images and low to intermediate signal on T2-weighted SE images is noted on MRI [41]. Bone scans with technetium-99 m methylene diphosphonate or pyrophosphate demonstrates focal increased uptake in the ipsilateral medial clavicle, while both indium and gallium scans show no focal accumulation of white blood cells at the lesion, arguing against infectious etiology [34]. Imaging typically demonstrates no involvement of the sternoclavicular joint, manubrium, or first rib in this disorder. Biopsy and gross pathology show increase and thickening of the cancellous bone, periosteal reaction, inferomedial osteophyte formation, and enlargement of the clavicular head without evidence of necrosis, bony destruction, or soft tissue involvement [8, 34].

Friedrich’s disease, or avascular necrosis of the medial clavicle, was first described in 1924 [21]. Like most conditions involving the sternoclavicular joint, Friedrich’s disease is a rare disorder with sparse literature describing the condition. The etiology is currently unknown. While the disease has been described in men, most case reports involve female patients with unilateral disease [31, 35]. Patients typically present with insidious onset of localized pain and swelling at the sternoclavicular joint. This pain tends to increase with shoulder abduction and is not associated with a direct history of trauma. Radiographs and CT scans show sclerosis that is predominantly located in the inferomedial clavicle, but may involve the entire medial clavicular head, and an irregular sternoclavicular joint with bony destruction [9, 25]. Histological evaluation demonstrates characteristic findings of avascular necrosis, namely, Haversian systems with empty lacunae and fibrotic bone marrow [19, 35]. Some argue that given the overlap between Friedrich’s disease and condensing osteitis, specifically the presence of inferomedial clavicular sclerosis, these disorders may represent the same disease with age-related radiographic differences [31].