Ultrasound assessment of the elbow joint in infants and toddlers and its clinical significance.

BACKGROUND: Ultrasound can be used for the diagnosis of elbow injuries in infants and toddlers. However, ultrasound is highly operator-dependent and accurate ultrasound examinations require a complete understanding of the complex anatomy of the elbow joint. PURPOSE: To report the normal ultrasound anatomy of the elbow, particularly of the humeroulnar joint, in infants and toddlers. MATERIAL AND METHOD: Thirty subjects aged <3 years with no history of elbow injuries underwent ultrasound examinations of the elbow joint from six directions: (i) lateral to the humeroradial joint; (ii) anterior to the humeroradial joint; (iii) posterior to the humeroradial joint; (iv) medial to the humeroulnar joint; (v) anterior to the humeroulnar joint; and (vi) posterior to the humeroulnar joint. RESULTS: The appearance of the humeroradial joint observed from three directions was similar and resembled a pair of double fists ("double-breast sign"). The appearance of the humeroulnar joint observed from three directions was different, which is related to the irregular morphology of the medial sides of the humerus and ulna. Anteroposteriorly, the coronoid and olecranon epiphyses and coronoid fossa appear anteriorly and the olecranon and trochlear epiphyses and olecranon fossa appear posteriorly, resembling a "check-mark sign". The medial epicondyle, cubital tunnel and distal humerus appear together ("double-hump sign"). The "anterior hump" is the medial epicondyle and is always higher than the "posterior hump", which is the bony protrusion on the articular surface of the distal humerus. The ultrasound signal of cortical bone in the metaphysis of the distal humerus is continuous with that of the epiphysis of the medial epicondyle. CONCLUSION: Ultrasound is useful for the diagnosis of elbow injuries in infants and toddlers.