To elicit a stretch reflex, support the joint being tested so that the muscle is relaxed. Hold the reflex hammer between your thumb and index finger, and swing it by motion at the wrist, not the elbow. In general, the pointed end of a triangular reflex hammer is used. A gentle tap over the tendon being tested should produce muscle contraction. To assess muscle contraction, it is often necessary both to palpate and to observe the muscle. Test each reflex, and compare it with the other side. Reflexes should be symmetrically equal.

There is individual variation in the reflex response. Only with experience is the examiner able to make an adequate assessment of normal reflexes. Reflexes are commonly graded on a scale from 0 to 4+ as follows:

0: No response 1+: Diminished 2+: Normal 3+: Increased 4+: Hyperactive

Hyperactive reflexes are characteristic of pyramidal tract disease. Electrolyte abnormalities, hyperthyroidism, and other metabolic abnormalities may be the cause of hyperactive reflexes. Diminished reflexes are characteristic of anterior horn cell disorders and myopathies. The examiner should always consider the strength of the reflex in relation to the bulk of the muscle mass. A patient may have diminished reflexes as a result of a decrease in muscle bulk. Patients with hypothyroidism have decreased relaxation after a deep tendon reflex, which is termed a hung reflex.

In a patient with a diminished reflex, the technique of reinforcement may be useful. If the patient performs isometric contraction of other muscles, the generalized reflex activity may be increased. When testing reflexes in the upper extremities, have the patient clench the teeth or push down on the bed with the thighs. When testing reflexes in the lower extremities, have the patient lock fingers and try to pull them apart at the time of testing. This procedure, sometimes called Jendrassik's maneuver, is demonstrated in Figure 21-38.

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