Reflex hammer

A reflex hammer is a medical instrument used by practitioners to test deep tendon reflexes. Testing for reflexes is an important part of the neurological physical examination in order to detect abnormalities in the central or peripheral nervous system.

Reflex hammers can also be used for chest percussion.

Prior to the development of specialized reflex hammers, hammers specific for percussion of the chest were used to elicit reflexes. However, this proved to be cumbersome, as the weight of the chest percussion hammer was insufficient to generate an adequate stimulus for a reflex.

Starting in the late 19th century, several models of specific reflex hammers were created:

There are numerous models available from various commercial sources.

The strength of a reflex is used to gauge central and peripheral nervous system disorders, with the former resulting in hyperreflexia, or exaggerated reflexes, and the latter resulting in hyporeflexia or diminished reflexes. However, the strength of the stimulus used to extract the reflex also affects the magnitude of the reflex. Attempts have been made to determine the force required to elicit a reflex, but vary depending on the hammer used, and are difficult to quantify.

The Taylor hammer is usually held at the end by the physician, and the entire device is swung in an arc-like motion onto the tendon in question. The Queen Square and Babinski hammers are usually held perpendicular to the tendon in question, and are passively swung with gravity assistance onto the tendon.

The Jendrassik maneuver, which entails interlocking of flexed fingers to distract a patient and prime the reflex response, can also be used to accentuate reflexes. In cases of hyperreflexia, the physician may place his finger on top of the tendon, and tap the finger with the hammer. Sometimes a reflex hammer may not be necessary to elicit hyperreflexia, with finger tapping over the tendon being sufficient as a stimulus.

...
Wikipedia