A reflex is a rapid, involuntary response of the nervous system to a specific stimulus. This automatic action occurs without conscious thought, involving a simple neural pathway called a reflex arc. Assessing deep tendon reflexes provides insight into the integrity of the central and peripheral nervous systems, assessing the spinal cord, nerve roots, and associated motor pathways.
Identifying the Key Arm Reflexes
Routine neurological examinations typically focus on three main deep tendon reflexes in the arm. Each reflex tests a specific segment of the spinal cord and a corresponding nerve pathway. Knowing the exact location and nerve involvement is crucial for interpreting the results.
The Biceps Reflex tests the C5 and C6 spinal nerve roots via the musculocutaneous nerve. The target is the biceps tendon, located in the antecubital fossa, or the crease of the elbow. A successful reflex causes an immediate, brief contraction of the biceps muscle, resulting in slight flexion of the forearm.
The Triceps Reflex assesses the C7 and C8 spinal nerve roots, utilizing the radial nerve. The triceps tendon is found on the back of the upper arm, just above the olecranon process, the bony tip of the elbow. Eliciting this reflex causes the triceps muscle to contract, leading to quick extension of the forearm.
The Brachioradialis Reflex, sometimes called the supinator reflex, is mediated by the radial nerve and checks the C5 and C6 nerve roots. To locate the target, the examiner taps the tendon of the brachioradialis muscle, situated near the wrist on the thumb side of the forearm, about one to two inches above the radial styloid process. The expected response is a flexion and slight supination of the forearm.
Executing the Reflex Test
The procedure for eliciting arm reflexes requires a reflex hammer and a relaxed patient to ensure an accurate response. The patient’s arm must be positioned to isolate the target tendon and place the corresponding muscle in a state of slight stretch. This is necessary because the reflex arc is activated by the sudden stretch of the muscle spindle within the tendon.
For the Biceps Reflex, the patient’s forearm should be supported by the examiner, resting midway between flexion and extension. The examiner places their thumb firmly over the biceps tendon in the elbow crease and strikes their thumb with the reflex hammer. Striking the examiner’s digit rather than the patient’s tendon directly helps to focus the force and provides tactile feedback for even subtle responses.
To test the Triceps Reflex, the arm should be slightly abducted, and the forearm should hang loosely and vertically, allowing the elbow to flex about 90 degrees. The examiner then strikes the triceps tendon directly, located just above the elbow’s bony tip, with a brisk, relaxed wrist motion. The force of the strike should be firm enough to elicit a response but never painful for the patient.
The Brachioradialis Reflex is tested with the patient’s forearm resting on their lap or supported by the examiner, with the hand partially pronated. The examiner locates the tendon on the lateral side of the distal forearm and strikes it directly with the reflex hammer. If the patient is having difficulty relaxing, a distraction technique, such as asking them to clench their teeth or count backward, can be used to temporarily increase reflex excitability.
The technique involves using a quick, swinging motion of the wrist, allowing the hammer head to rebound immediately after contact with the tendon. Compare the response in one arm to the corresponding reflex in the other arm, as asymmetry is often a more significant finding than the absolute strength of the response. The goal is to observe the speed, force, and amplitude of the resulting muscle contraction.
Understanding Reflex Grading and Results
Deep tendon reflexes are quantified using a standard five-point scale, which allows medical professionals to document findings. This standardized grading ranges from 0 to 4+, with each number representing a defined level of response. A grade of 2+ is considered the average, expected, and normal reflex response.
A grade of 0 indicates an absent reflex, even when reinforcement techniques are used, while 1+ signifies a diminished response. These reduced responses are collectively termed hyporeflexia and suggest a problem within the reflex arc itself. Hyporeflexia is often associated with issues in the peripheral nervous system, such as peripheral nerve damage, nerve root compression, or muscle diseases.
In contrast, a 3+ grade represents a brisker reflex, and 4+ is a hyperactive response, often accompanied by clonus. These overly active reflexes are known as hyperreflexia and typically point to a disorder affecting the central nervous system. Hyperreflexia suggests a lesion in the upper motor neurons, which are tracts originating in the brain and spinal cord above the level of the reflex arc.
Interpreting the results requires careful consideration of the entire clinical picture. For instance, a symmetrically 1+ or 3+ response in an otherwise healthy person may still be considered within a normal range for that individual. However, an asymmetrical finding, such as a 0 on one side and a 2+ on the other, strongly suggests a neurological issue requiring further investigation.