Capitellum fracture

Capitellum fractures are uncommon, but their prompt diagnosis and management are crucial due to the severity of the consequent functional impairment resulting from these intra-articular elbow fractures.

Epidemiology

Capitellar fractures are relatively rare, with approximately 3-4% of distal humerus fractures falling into this category . 

Pathology

Mechanism

Direct axial compression force applied to the elbow or fall to an outstretched hand are the most common injury mechanisms.

Radiographic features

The extent of capitellar fractures is often underestimated on plain film, while non-displaced or osteochondral lesions can even remain occult. Thus, CT is usually warranted for evaluation and classification, and to aid surgical planning . In case of displaced fractures, McKee's eponymous "double arc" sign is often visible on lateral radiographs where the two separately visible arcs represent the displaced capitellum and the trochlea .

Classification

Multiple systems exist for characterizing fractures of the capitellum, the most commonly used one being the modified Bryan and Morrey's system :

• type I (Hahn-Steinthal fracture): complete osteochondral fracture of the capitellum; the trochlea can also be involved
• type II (Kocher-Lorenz fracture): anterior osteochondral shear fracture with minimal subchondral bony involvement
• type III (Broberg-Morrey fracture): compressed or comminuted fracture of the capitellum
• type IV: coronal shear fracture involving the capitellum and extending to the trochlea

Treatment and prognosis

Since capitellar fractures are intra-articular, open surgical reduction and internal fixation, or excision of the displaced fragment is often warranted. For some non-displaced fractures, conservative management with splint immobilization is considered appropriate . It is important to be aware that capitellar fractures are commonly associated with radial head fractures, and occassionally with a terrible triad injury pattern .