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BOOK EXCERPT
Chapter 8 Deep tendon reflexes are monosynaptic reflexes, meaning they are composed of an afferent (sensory) limb and an efferent (motor) limb with a synapse between the two at the level of the spinal cord. The afferent (sensory) portion of the reflex is stimulated when a quick stretch is applied to the muscle, which occurs when striking an already partially elongated muscle with a reflex hammer. This stimulation results in an efferent (motor) response, resulting in contraction of the muscle being tested. There are multiple grading scales used when assessing deep tendon reflexes. Each scale assesses for the degree of response of the muscle being tested. Tables 8-1 and 8-2 demonstrate the two most commonly used scales for reflex testing.
The following guidelines should be followed by the clinician when performing assessment of deep tendon reflexes.
Muscle facilitation or reinforcement may be necessary to elicit a deep tendon reflex in some patients. Facilitation or reinforcement involves having the patient perform a strong muscular contraction in a muscle group not being tested. It is important that this facilitation not involve active contraction of a muscle in extremity being tested. Commonly used facilitation techniques for upper extremity deep tendon reflex testing include having the patient press the medial aspects of the feet together (Figure 8-1), pressing the medial aspects of the knees together (Figure 8-2), or having the patient perform isomeric knee extension against the resistance of the contralateral lower extremity (Figure 8-3). The most commonly used facilitation technique for lower extremity reflex testing is to have the patient perform the Jenrassik maneuver— clasp the fingers together and attempt to isomerically pull them apart (Figure 8-4). Alternate techniques for either upper or lower extremity reflex testing include having the patient make a fist with the uninvolved hand or clenching his or her teeth. Muscle facilitation techniques should be performed while the clinician is striking the tendon.
References
Biceps Brachii Reflex (C5 Nerve Root) TestingTest PositionThe patient is positioned in sitting or standing with the elbow positioned in flexion and the forearm supinated. The upper extremity on the test side should be supported by the clinician.
ActionThe clinician places his thumb over the patient’s distal biceps tendon. The clinician strikes the thumb overlying the biceps tendon to elicit a reflex (Figure 8-5). Positive FindingA normal response to this test is elbow flexion. The reflex is graded based on the tendon’s response (see Tables 8-1 and 8-2). Special ConsiderationsSome authors consider this reflex as testing both the C5 and C6 spinal segments. Reflexes should be compared bilaterally, assessing for variations in response that will assist the clinician in differentiating a peripheral nerve injury (unilateral deficits) from a central nervous system injury (bilateral deficits). Specificity.95 - .99 Sensitivity.10 - .24 Positive Likelihood Ratio.80 - 10 Negative Likelihood Ratio.91 – 4.9 References
Brachioradialis Reflex (C6 Nerve Root) TestingTest PositionThe patient is positioned in sitting or standing with the elbow positioned in flexion and the forearm in neutral. The upper extremity on the test side should be supported by the clinician. ActionThe clinician strikes the radial side of the patient's forearm, over the brachioradialis tendon, to elicit a reflex. The clinician may strike the medial side of the forearm just proximal to the radial styloid process (Figure 8-6) or over the proximal third of the medial side of the forearm (Figure 8-7).
Positive FindingA normal response to this test is elbow flexion. The reflex is graded based on the tendon’s response (see Tables 8-1 and 8-2). Special ConsiderationsSome authors consider this reflex as testing both the C5 and C6 spinal segments. Reflexes should be compared bilaterally, assessing for variations in response that will assist the clinician in differentiating a peripheral nerve injury (unilateral deficits) from a central nervous system injury (bilateral deficits). Specificity.95 – .99 Sensitivity.06 – .08 Positive Likelihood Ratio.99 – 8.0 Negative Likelihood Ratio.93 – 1.2 References
Triceps Reflex (C7 Nerve Root) TestingTest PositionThe patient is positioned in sitting or standing with the shoulder abducted to 90 degrees with internal rotation and the elbow flexed to approximately 90 degrees. The upper extremity on the test side should be supported by the clinician. ActionThe clinician strikes the triceps tendon just proximal to the olecranon process (Figure 8-8).
Positive FindingA normal response to this test is elbow extension. The reflex is graded based on the tendon’s response (see Tables 8-1 and 8-2). Special ConsiderationsSome authors consider this reflex as testing both the C6 and C7 spinal segments. Reflexes should be compared bilaterally, assessing for variations in response that will assist the clinician in differentiating a peripheral nerve injury (unilateral deficits) from a central nervous system injury (bilateral deficits). Specificity.93 - .95 Sensitivity.03 - .10 Positive Likelihood Ratio1.05 - 2.0 Negative Likelihood Ratio.95 - 40 References
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