The reflex hammer is a specialized medical tool used by practitioners to evaluate a patient’s neurological health. This instrument, typically consisting of a metal handle and a soft rubber or plastic head, is a standard component in physical examinations. Its primary function is to elicit involuntary muscle contractions, known as reflexes, which provide information about the integrity of the central and peripheral nervous systems.
Nomenclature and Purpose
The most generalized name for the tool is the “reflex hammer,” but it is also commonly referred to as a “percussion hammer” or a “Deep Tendon Reflex (DTR) hammer.” This terminology is directly linked to its purpose: eliciting Deep Tendon Reflexes. A DTR is an involuntary, rapid muscle contraction that occurs when a muscle’s tendon is suddenly stretched. The hammer’s tap delivers a precise strike that quickly stretches the tendon and the attached muscle. This stretch activates sensory nerve endings, initiating a signal that travels through the spinal cord and back to the muscle. The resulting muscle contraction reveals how efficiently the nerve pathways are functioning. The patellar reflex, or knee-jerk, is the most well-known example of this involuntary response.
Distinct Hammer Designs
The tool is not a single, standardized instrument but rather a category of designs, each often named after its designer or place of origin.
- The Taylor hammer, or “Tomahawk” hammer, is the most common design used in the United States. It features a flat, metallic handle and a triangular rubber head, making it relatively lightweight.
- The Queen Square hammer is a European design favored by many neurologists. It features a long, flexible handle and a weighted, circular rubber head, allowing the practitioner to use gravity for a consistent and controlled strike.
- The Babinski hammer often has a telescoping or detachable metal handle and a round head.
- The Tromner hammer features a dual-ended mallet design, reflecting different preferences for weight and balance.
The Babinski and Queen Square designs often include a pointed or tapered end on the handle, which can be used to test for the plantar reflex, also known as the Babinski sign.
The Mechanics of Reflex Testing
The successful elicitation of a deep tendon reflex relies heavily on proper technique and patient positioning. The practitioner holds the hammer loosely, using a fluid, wrist-driven swing rather than a forceful blow from the arm. The goal is to deliver a quick, brisk tap that strikes the tendon perpendicularly, ensuring the muscle-tendon unit is stretched suddenly.
For the patellar reflex, the patient is typically seated with their legs dangling freely over the edge of the examination table. The hammer strikes the patellar tendon just below the kneecap, causing the quadriceps muscle to contract and the lower leg to kick forward.
Patient relaxation is paramount for accurate testing; if the patient is tense, the reflex may be diminished or absent. If a reflex is difficult to elicit, the practitioner may employ a distraction technique, such as the Jendrassik maneuver, which involves asking the patient to clench their jaw or interlock their hands and pull apart. This maneuver helps reinforce the reflex by distracting the higher brain centers that may inhibit the response.