Relaxation is critical during the reflex examination. Tendon reflexes are difficult to elicit when patients tense the muscles being tested. It is helpful to distract patients by engaging them in conversation while testing their reflexes.
Tendon reflexes — The biceps, triceps, brachioradialis, knee (patellar), and ankle (Achilles) reflexes are the ones commonly tested. The joint under consideration should be at about 90 degrees and fully relaxed. It is often helpful to cradle the joint in your own arm to support it. With your other arm, hold the end of the hammer and let the head of the hammer drop like a pendulum so that it strikes the tendon:
●Biceps — just anterior to the elbow
●Triceps — just posterior to the elbow
●Brachioradialis — about 10 cm above the wrist on the radial aspect of the forearm
●Knee — just below the patella
●Ankle — just behind the ankle
When a patient has reflexes that are difficult to elicit, you can amplify them by using reinforcement procedures: Ask the patient to clench his or her teeth or (when testing lower extremity reflexes) to hook together the flexed fingers of both hands and pull. This is also known as the Jendrassik maneuver.
Clonus is a rhythmic series of muscle contractions induced by stretching the tendon. It most commonly occurs at the ankle, where it is typically elicited by suddenly dorsiflexing the patient’s foot and maintaining light upward pressure on the sole.
When reflexes are brisk, it is difficult to detect slight asymmetry. For the most sensitive comparison, it is best to reduce the stimulus until it is just barely above threshold for eliciting the reflex. I typically set aside my reflex hammer and use my fingertips for this purpose. I look for two manifestations of asymmetry:
●Is the threshold stimulus the same on each side, or do I consistently need to hit harder on one side than the other?
●If the threshold stimulus is the same on each side, does it elicit the same magnitude of response on each side?
Such subtle distinctions are most readily made by testing the reflex on one side immediately after testing the corresponding reflex on the other side, rather than testing all reflexes in one limb before testing the contralateral limb.
Another technique I use to heighten sensitivity to subtle reflex asymmetry is to place my finger on the patient’s tendon and strike my finger rather than striking the tendon directly. This helps me aim more accurately and allows me to feel the tendon contraction.
Grading reflexes
The most common convention for grading deep tendon reflexes is simple but imprecise:
●0 = absent
●1 = reduced (hypoactive)
●2 = normal
●3 = increased (hyperactive)
●4 = clonus
Some examiners use a grade of 5 to designate sustained clonus, reserving 4 for unsustained clonus that eventually fades after 2 to 10 beats. Some examiners also include a reflex grade of 1/2 to indicate a reflex that can only be obtained using reinforcement.
The obvious limitation of this scheme is that it provides no guidelines for determining when reflexes are reduced, normal, or increased. This is left up to individual judgment, based upon the examiner’s sense of the range of reflexes present in the normal population.
