Examine the reflexes routinely at the elbow and wrists. Remember that the reflected arc includes an afferent and an efferent pathway. The afferent pathway is stimulated by the tendon stretching (for example after a hammer simulation). The afferent pathway comes into contact in the spinal cord with a motor neuron which gives rise to stimulation of the efferent pathway and causes the contraction of the muscles of the opposite side in order to resolve the stretch of the tendon. The interruption of the efferent or afferent component of the reflex arc prevents the contraction and cancels the reflex. The interruption of the nerve pathways in the spinal cord above the level of the motor neuron (lesion of the superior motor neuron) blocks the ability to inhibit this last and causes an exaltation of the reflection. Reflexes can be normal, exalted or reduced, absent or delayed (the contraction is rapid but the return is slow - as typically happens in hypothyroidism).
The clone is the rhythmic contraction of the muscle that can be perpetuated for as long as a tension is maintained on the tendon. Only clinical practice can give an idea of the range of variation of normal reflexes. In any case, the right side must be compared with the left one.
The tendon reflexes of the upper
limbs are sometimes difficult to elicit in young subjects.
• Bicipital reflex (C5, C6): place the index finger of the left hand on the
biceps tendon and strike it with the hammer. In normal conditions the lively
contraction of the biceps will occur.
• Triceps reflex (CI, C8): support the patient's flexed arm with one hand and
hit the triceps tendon using the hammer. Under normal conditions the contraction
of the triceps and the extension of the forearm will occur.
• Brachioradial reflex (C5, C6): place a few fingers on the lower end of the
radio and strike them. The brachioradial contraction will cause the elbow to
flex.
• Fingers (C8, TI): connect your fingers with those of the patient whose hand is
open with the palm facing up; hit your fingers with the hammer. As a rule,
slight flexion of all the fingers and interphalangeal joint of the thumb will
occur.
• In the patient in whom an injury of the superior motor neuron is suspected,
the Hoffman reflex may also be elicited: the terminal part of the patient's
middle finger is held between the index finger and the examiner's thumb and
pushed down; the reflex will be abnormal if the thumb flexes and becomes
addicted while the other fingers flex. The presence of this reflex indicates a
hyperreflexia but is not pathognomonic of an injury of the superior motor neuron.
The reflection can be recorded as follows:
• 0 (absent)
• + (reduced)
• ++ (normal)
• +++ (increased)
• ++++ (exalted and associated with clone).