A reflex hammer is a medical instrument used by physicians to test deep tendon

Tendon

A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...

 reflex

Reflex

A reflex action, also known as a reflex, is an involuntary and nearly instantaneous movement in response to a stimulus. A true reflex is a behavior which is mediated via the reflex arc; this does not apply to casual uses of the term 'reflex'.-See also:...

es. Testing for reflexes is an important part of the neurological physical examination

Neurological examination

A neurological examination is the assessment of sensory neuron and motor responses, especially reflexes, to determine whether the nervous system is impaired...

 in order to detect abnormalities in the central

Central nervous system

The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 or peripheral nervous system.

Reflex hammers can also be used for chest percussion

Percussion (medicine)

Percussion is a method of tapping on a surface to determine the underlying structure, and is used in clinical examinations to assess the condition of the thorax or abdomen. It is one of the four methods of clinical examination, together with inspection, palpation and auscultation...

.

Models of reflex hammer

Prior to the development of specialized reflex hammers, hammers specific for percussion of the chest

Chest

The chest is a part of the anatomy of humans and various other animals. It is sometimes referred to as the thorax or the bosom.-Chest anatomy - Humans and other hominids:...

 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:

• The Taylor or tomahawk reflex hammer was designed by John Madison Taylor in 1888 and is the most well known reflex hammer in the USA. It consists of a triangular rubber
  Rubber
  Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
  
   component which is attached to a flat metallic handle
  Handle (grip)
  A handle is a part of, or attachment to, an object that can be moved or used by hand. The design of each type of handle involves substantial ergonomic issues, even where these are dealt with intuitively or by following tradition...
  
  .
• The Queen Square reflex hammer was designed for use at the National Hospital for Nervous Diseases (now the National Hospital for Neurology and Neurosurgery) in Queen Square, London. It was originally made with a bamboo
  Bamboo
  Bamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....
  
   or cane handle of varying length, of average 25 to 40 centimetres, attached to a 5 centimetre metal disk with a plastic bumper. The Queen Square hammer is also now made with plastic molds, and often has a sharp tapered end to allow for testing of plantar reflex
  Plantar reflex
  The plantar reflex is a reflex elicited when the sole of the foot is stimulated with a blunt instrument. The reflex can take one of two forms. In normal adults the plantar reflex causes a downward response of the hallux...
  
  es though this is no longer recommended due to tightened infection control
  Infection control
  Infection control is the discipline concerned with preventing nosocomial or healthcare-associated infection, a practical sub-discipline of epidemiology. It is an essential, though often under-recognized and under-supported, part of the infrastructure of health care...
  
  . It is the reflex hammer of choice of the UK neurologist.
• The Babinski reflex hammer was designed by Joseph Babiński
  Joseph Babinski
  Joseph Jules François Félix Babinski was a French neurologist of Polish descent. He is best known for his 1896 description of the Babinski sign, a pathological plantar reflex indicative of corticospinal tract damage....
  
   in 1912 and is similar to the Queen Square hammer, except that it has a metallic handle that is often detachable. Babinski hammers can also be telescoping, allowing for compact storage. Babinski's hammer was popularized in clinical use in America
  United States
  The United States of America is a federal constitutional republic comprising fifty states and a federal district...
  
   by the neurologist Abraham Rabiner, who was given the instrument as a peace offering by Babinski after the two brawled at a black tie
  Black tie
  Black tie is a dress code for evening events and social functions. For a man, the main component is a usually black jacket, known as a dinner jacket or tuxedo...
  
   affair in Vienna
  Vienna
  Vienna is the capital and largest city of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.723 million , and is by far the largest city in Austria, as well as its cultural, economic, and political centre...
  
  .
• The Trömner reflex hammer was designed by Ernst Trömner
  Ernst Trömner
  Ernst Trömner was a German neurologist who was a native of Meerane in the Kingdom of Saxony.In 1893 he earned his medical doctorate at Leipzig, and was later director of the neurological department of St. Georg Hospital in Hamburg...
  
   is unique as in looks like a miniature hammer. Trömner's reflex is when the fingers of the patient partially flexed, the tapping of the volar aspect of the tip of the middle or index finger causes flexion of all four fingers and thumb. This phenomenon is associated with pyramidal tract lesions with moderate spasticity.
• Other reflex hammer types include the Buck, Berliner and Stookey reflex hammers.

There are numerous models available from various commercial sources.

Method of use

The strength of a reflex is used to gauge central and peripheral nervous system disorders, with the former resulting in hyperreflexia

Hyperreflexia

Hyperreflexia is defined as overactive or overresponsive reflexes. Examples of this can include twitching or spastic tendencies, which are indicative of upper motor neuron disease as well as the lessening or loss of control ordinarily exerted by higher brain centers of lower neural pathways...

, or exaggerated reflexes, and the latter resulting in hyporeflexia

Hyporeflexia

Hyporeflexia is the condition of below normal or absent reflexes. It can be tested for by using a reflex hammer. It is the opposite of hyperreflexia....

 or diminished reflexes. However, the strength of the stimulus

Stimulus (physiology)

In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....

 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

Arc (geometry)

In geometry, an arc is a closed segment of a differentiable curve in the two-dimensional plane; for example, a circular arc is a segment of the circumference of a circle...

-like motion onto the tendon

Tendon

A tendon is a tough band of fibrous connective tissue that usually connects muscle to bone and is capable of withstanding tension. Tendons are similar to ligaments and fasciae as they are all made of collagen except that ligaments join one bone to another bone, and fasciae connect muscles to other...

 in question. The Queen Square and Babinski hammers are usually held perpendicular

Perpendicular

In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...

 to the tendon in question, and are passively swung with gravity assistance onto the tendon.

The Jendrassik maneuver

Jendrassik maneuver

The Jendrassik maneuver is a medical maneuver wherein the patient flexes both sets of fingers into a hook-like form and interlocks those sets of fingers together. The tendon below the patient's knee is then hit with a reflex hammer to elicit the patellar reflex. The elicited response is compared...

, which entails interlocking of flexed finger

Finger

A finger is a limb of the human body and a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates....

s to distract a patient, 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.