According to Kenneth H. Walker, Professor of Medicine and Associate Professor of Neurology at Emory University, a stretch reflex is the “contraction of a muscle in response to stretching of muscle spindles, which are receptors that lie in parallel…muscle fibers.” The purpose of the reflex mechanism is to keep the muscle fibers adjusted to a certain length and tension, allowing us to maintain muscle tone and posture. Doctors test the deep tendon reflexes to see if there is an absent or hyper-reactive reflex as this is considered to be a sign of a nerve lesion.
Things You'll Need
- Reflex hammer
Instruct the patient to sit on the edge of the table and relax. Place your thumb over the biceps tendon at the elbow, applying slight pressure, and strike your thumb with the hammer. Observe the arm movement. Repeat on the opposite arm and compare the two. This tests the C5 and C6 nerve roots.
Grasp the patient's arm on the inside aspect of the elbow and tell him to relax the arm. Hold the arm so the elbow is flexed at 90 degrees and just below the level of the shoulder. Find the triceps tendon insertion on the point of the elbow and strike the tendon about 1 inch up from that point. Observe the movement of the forearm and repeat on the other side. This tests the C6 and C7 nerve roots.
Have the patient sit on the table with his lower leg hanging off the edge. Locate the quadriceps tendon below the kneecap and instruct the patient to relax. Place one hand above the knee on the patient’s thigh and strike the quadriceps tendon firmly. Watch for lower leg movement and feel for a contraction in the thigh muscles. Observe and repeat with the other leg, comparing the two. This tests the L3 and L4 nerve roots.
Tell the patient to sit with his lower leg hanging off the table. Grab the foot just before the toes and gently hold it while you strike the Achilles tendon with the hammer. Look and feel for the foot to dip downwards (this is called plantar flexion). Compare to the other foot. This tests the S1 nerve root.
Have the patient lie on his back with only his feet hanging over the edge of the table. Use the non-hammer end to press into the bottom of the foot near the heel and drag it upwards towards the toes. Do this on the outside edge of the foot and watch for the toes to curl. If the toes extend and separate, it is called a positive Babinski’s sign.
Grasp the patient’s middle finger between your thumb and index finger, and tell him to relax. Press downward into the patient’s fingernail with the tip of your thumbnail and drag it outward until it "clicks" over the end of the patient’s nail. If the other fingers flex when you do this, it’s called a positive Hoffman’s response. Perform the test on both hands.