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I. General Principles of Reflex Examination

Any reflex action requires a stimulus, a sensory pathway, a link with a motor unit, a motor neuron, and an effector element (muscle). A breach in this arc results in an absent reflex. Higher centers also influence most reflex arcs; a defect in pathways from these centers can fundamentally change reflex behavior.

When examining any reflex, you should determine:

  1. Whether the reflex is present or absent.

  2. If present, whether it is normal or shows signs of defective influence from higher centers.

  3. If absent, whether the arc is breached on the motor or sensory side.

  4. Whether any abnormalities are unilateral, bilateral, affect all reflexes, or if a definite level can be detected in the nervous system where abnormalities first appear, as reflex "levels" can be as helpful as sensory levels.

For clear results, ensure:

  • Use of a good percussion hammer.

  • The examiner has flexible wrists, allowing the hammer's weight to determine the blow's strength.

  • The patient is warm, comfortable, and relaxed.

  • The muscle is placed in the optimum position, slightly on stretch, with plenty of room for contraction.

  • Maintain a constant mental picture of the segmental and peripheral nerve supply of each muscle as its reflex is tested.

II. Deep Tendon Reflexes (DTRs)

Deep tendon reflexes are involuntary muscle contractions in response to a sudden stretch of the tendon. The grading of deep tendon reflexes is as follows:

  • 0: Absent

  • 1+: Diminished

  • 2+: Normal

  • 3+: Exaggerated

  • 4+: Exaggerated with clonus

Commonly tested DTRs include:

  1. Biceps Reflex:

    • Technique: Gently press your forefinger on the biceps tendon in the antecubital fossa and strike your finger with the hammer.

    • Normal Result: Flexion of the elbow and visible contraction of the biceps muscle.

    • Segmental Innervation: C5.

    • Peripheral Nerve: Musculocutaneous.

  2. Triceps Reflex:

    • Normal Result: Extension of the forearm.

  3. Brachioradialis (Supinator) Reflex:

    • Technique: Strike the lower end of the radius about 5 cm above the wrist. Observe the movement of the forearm and fingers.

    • Normal Result: Contraction of the brachioradialis and flexion of the elbow. The biceps often contract as well.

    • Segmental Innervation: C5, C6.

  4. Knee Jerk (Patellar Reflex):

    • Technique: The patient is supine with knees slightly flexed and thighs externally rotated. Place your hand under the popliteal fossa to lift the thigh slightly, allowing the Quadriceps femoris tendon to be on stretch. Strike the tendon just below the patella.

    • Normal Result: Extension of the knee with visible contraction of the Quadriceps.

    • Exaggerated Reflex: Extension of the knee with adduction of the thigh.

    • Segmental Innervation: L2, L3, L4.

    • Peripheral Nerve: Femoral nerve.

    • Patellar Clonus: Grasp the patella between the index finger and thumb and make a sudden, sharp downward displacement. It will produce rhythmic up and down movements of the patella.

  5. Ankle Jerk (Achilles Reflex):

    • Position: Patient is lying supine. Thigh should be abducted, externally rotated, and knee flexed. Dorsiflex the patient’s foot.

    • Normal Result: Plantar flexion of the foot.

  6. Jaw Jerk:

    • This reflex is described under the Vth cranial nerve (trigeminal nerve) and is useful in finding a "level" of reflex abnormality.

III. Superficial Reflexes

Superficial reflexes are elicited by stroking the skin or mucous membranes.

  1. Gag Reflex:

    • Afferent Nerve: 9th cranial nerve (Glossopharyngeal).

    • Efferent Nerve: 10th cranial nerve (Vagus).

    • Normal Result: Present on both sides.

  2. Cremasteric Reflex:

    • Technique: Stroke the upper inner part of the thigh in a downwards and inwards direction, with the patient lying down or standing up. Observe the movement of the scrotum and testicle.

    • Normal Result: Contraction of the cremasteric muscle pulls up the scrotum and testicle on the side examined.

    • Segmental Innervation: L1, L2.

    • Absence: Often absent in elderly men, those with hydroceles, or after scrotal operations. Also absent in any breach of the reflex arc (including impaired thigh sensation) and pyramidal tract disease.

  3. Anal Reflex:

    • Technique: Lightly scratch the perianal skin.

    • Normal Result: Contraction of the external sphincter.

    • Segmental Innervation: S4, S5.

  4. Plantar Reflex (Babinski Sign):

    • This is considered the most important and frequently misinterpreted reflex.

    • Technique: Position the patient with the knee slightly flexed and the thigh externally rotated. The outer aspect of the foot should rest on the bed. Stroke the lateral aspect of the sole of the foot, from the heel towards the toes.

    • Normal Result: Plantar flexion of the great toe (and other toes).

    • Abnormal Result (Babinski's extensor plantar response): Extension (dorsiflexion) of the big toe at the metatarsophalangeal joint, followed by fanning out and extension of other toes. In advanced cases, there may be dorsiflexion of the ankle and flexion of the hip and knee.

    • Significance: Babinski’s response indicates a disturbance of the pyramidal system function.

    • Normal in Infancy: The plantar response is normally extensor below 6 months of age and may persist up to 12 months in about 75% of children. After this, it should be flexor.

IV. Reinforcement Maneuvers

If reflexes are not easily elicited, reinforcement techniques can be used:

  1. Upper Limb Reflexes: Clenching of teeth.

  2. Lower Limb Reflexes: Jendrassik manoeuvre.