Musculoskeletal Imaging

Clavicle

1. Anatomy

a long thin bone articulating with the sternum and scapula, which forms the anterior part of the shoulder girdle. Also, see clavicle.

2. Pathology

Congenital pseudarthrosis

of the clavicle may be present at birth (true congenital pseudarthrosis) or may sometimes develop in the first few years of life (infantile pseudarthrosis). Some affected persons may have signs and symptoms typical of neurofibromatosis or fibrous dysplasia, although the precise relationships between these three conditions remain unclear. Congenital pseudarthosis of the clavicle occurs almost exclusively on the right side of the body. Blood vessels adjacent to the clavicle, such as the subclavian artery, and cervical ribs may be important in the pathogenesis of this bone defect. In infants the lesion usually is discovered within the first few months of life because of the presence of a painless lump over the middle one third of the clavicle. The absence of pain and visible callus usually allows differentiation from a post-traumatic pseudarthrosis.

 

Fracture

of the clavicle may occur in one of three functional segments: a distal or interligamentous segment (the outer 25 - 30% of the bone), an intermediate segment (the middle 40 - 50%), and an inner segment (the medial 25%).

Fractures of the distal part of the clavicle result from a force applied on the shoulder driving the humerus and scapula downward. These fractures may be divided into type I fractures, in which the coracoclavicular ligaments are intact, and type II fractures, which have a poorer prognosis and in which a portion (conoid portion) of the coracoclavicular ligaments is severed. With type II fractures a characteristic medial flange of bone may sometimes extend from the distal clavicular fragment. Nonunion frequently occurs when a fracture involves the clavicle distal to the coracoclavicular ligament.

Fractures of the middle segment usually result from a fall onto the outstretched hand or a fall on the shoulder. These are divided into intra-articular fractures and transverse fractures; the latter do not become displaced because of ligamentous and muscular attachments.

Although clavicular fractures in children heal rapidly and without significant sequelae, in adults, deformities occur related to extensive callus formation. Delayed union or nonunion after fractures of the lateral portions of the clavicle usually results from rupture of the coracoclavicular ligament.

 

Condensing osteitis

of the clavicle occurs in young and middle-aged women with a history of stress to the region of the sternoclavicular joint. On radiographs bone sclerosis and mild enlargement may be observed at the inferomedial aspect of the clavicle, with osteophytes in the inferior margin of the clavicular head. Scintigraphy, CT scanning and MR imaging are also useful in documenting the extent of bone involvement (Fig.1).

Ischaemic necrosis of the medial clavicular epiphysis is known as Friedreichs disease. It usually occurs in children and adolescents and is thought to result from direct trauma or to an embolic event causing obliteration of the vascular supply to the medial clavicular epiphysis. Another disorder involving the medial end of the clavicle is sternocostoclavicular hyperostosis. In contrast to condensing osteitis of the clavicle, this condition is more common in older patients and in men, is usually bilateral, and often is accompanied by lesions of the palms and soles ((pustulosis palmaris et plantaris). The latter disorder is part of the group of diseases known as SAPHO syndrome.
 
Posttraumatic osteolysis
of the clavicle may lead to progressive resorption of the outer end of this bone (Fig. 2). The pathogenesis of this condition is not well understood, but osteolysis becomes apparent after single or repeated episodes of local minor or major trauma. When untreated, lysis of 0.5–3 cm of bone substance may occur at the distal end of the clavicle over a period of 12–18 months, associated with erosion and cupping of the acromion, soft tissue swelling, and dystrophic calcification. Repair of the alterations takes place over a period of 4–6 months.
The clavicle may also be involved in chronic recurrent multifocal osteomyelitis, a disease of unknown causation, affecting primarily children and adolescents. Radiographic abnormalities include, eventually, sclerosis and periostitis, with expansion and enlargement of the bone.

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Fig.1

Condensing osteitis. a. Frontal tomogram shows sclerosis of the inferomedial aspect of the right clavicle (arrow), a feature characteristic of condensing osteitis of the clavicle. b. Coronal T1-weighted MR image demonstrates low signal intensity in the inferior medial aspect of the clavicle (arrow). Low signal intensity also was observed in this location on the T2-weighted images (not shown) (Courtesy of Guerdon Greenway, MD, Dallas, TX)
Clavicle, Fig.1 (a)
Clavicle, Fig.1 (b)
Clavicle, Fig.2 (a)
Clavicle, Fig.2 (b)
Clavicle, Fig.2 (c)