Reflexes - Deep Tendon Reflexes on Newborn Physical Exam 

Testing deep tendon reflexes is an important part of the newborn neurological exam. They can be technically difficult to do. The first thing is to use a reflex hammer, not a finger or a stethoscope. Ideally, the baby is in a quiet alert state with the head in the midline. The head turned to one side can reinforce the tone and reflexes on that side. I usually start with the knee jerk because is the easiest to obtain. Take control of the leg with the hand under the knee and the leg at about a 90 degree angle at the knee. Then strike the patellar tendon with the reflex hammer using a pendular action rather a chopping action.

Reposition the leg and try several times if you have trouble getting a knee jerk. Next, I go to the ankle jerk. If I can’t get an ankle jerk in the conventional fashion, I place my fingertips on the plantar aspect of the foot, flex the foot slightly, then strike the back of my fingers. For the bicep jerk, have the arm flexed at the elbow, thumb over the bicep tendon, then strike the thumb with a pendular action. Because of the predominantly flexor tone of the newborn, it is rare to obtain a triceps jerk.

Absence of deep tendon reflexes is a much more important finding than hyperreflexia in the newborn. A normal newborn can have hyperreflexia and still be normal, if the tone is normal, but absent reflexes associated with low tone and weakness is consistent with a lower motor neuron disorder. Preserved or exaggerated reflexes associated with low tone is the hallmark of what is called central or cerebral hypotonia and the cause is an upper motor neuron lesion.

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Contributed by

Dr. Gerald Diaz
Board Certified Internal Medicine Hospitalist, GrepMed Editor in Chief 🇵🇭 🇺🇸 - Sign up for an account to like, bookmark and upload images to contribute to our community platform. Follow us on IG:  https://www.instagram.com/grepmed/ | Twitter: https://twitter.com/grepmeded/
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