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The differential diagnosis for a flail, or nonmoving, upper extremity is fairly short and includes neonatal brachial plexus palsy (NBPP), fracture, distal humeral transphyseal separation, and bone or joint infection. The history and physical are usually adequate to make the diagnosis, although imaging and laboratory examinations can help.

Clinical Findings

History should focus on the infant’s delivery and perinatal events. Both brachial plexus palsy and fractures sustained during birth are associated with difficult deliveries, shoulder dystocia, and larger infants; it is important to remember that a patient may have a fracture concomitant with a brachial plexus palsy. For both NBPP and fracture, the lack of movement will have been present since birth as opposed to a patient with infection, who likely had a period, however short, of normal movement of the limb with subsequent pseudoparalysis developing over time. If an infant sustained a fracture after the neonatal period, he or she will also have had a period of normal movement of the limb. Infections may be characterized by increased fussiness or other general manifestations of malaise, but frequently the pseudoparalytic limb may be the only finding.

The physical examination should focus on inspection for any erythema or swelling, which can be seen not only in infection but also in fractures and transphyseal separations, and palpation for any crepitus, which would suggest fracture. Pain with palpation or movement of the limb would be seen in fracture, transphyseal separation, and infection but not in NBPP. In addition, reflex testing should be done. Because fractures, transphyseal separations, and infections are painful, the lack of movement of the limb is because of pain inhibition rather than true paralysis. Therefore, on physical examination, any movement with reflex testing (eg, Moro) is supportive of infection or fracture; patients with NBPP will have no movement, even with reflex testing, because of a true paralysis of the limb. Occasionally, patients with arthrogryposis that affects the upper extremities preferentially will have a similar “waiter’s tip” appearance as NBPP; the difference will be that, early on, patients with brachial plexus palsy will have normal passive range of motion, whereas arthrogrypotic patients will be stiff from the very beginning. In addition, NBPP is almost universally unilateral, whereas arthrogryposis will affect both upper extremities, although involvement may be asymmetric.

Confirmatory Tests

In brachial plexus palsy, x-ray and ultrasound evaluations will be negative (unless the infant has an associated fracture) and are not routinely ordered because the diagnosis can usually be made by history and physical alone. However, imaging, including x-rays and ultrasound, can be helpful in distinguishing between trauma (fracture or transphyseal separation) and infection. Evaluation should include x-rays of the clavicle and arm; fractures will most likely be of the clavicle or humeral shaft. If the elbow looks dislocated on x-ray, it is most likely a ...

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