Assessment of deep and superficial reflexes provides information on the integrity of reflex arcs at different levels in the central nervous system. They may be abolished by disease of the lower motor neurone or sensory neurones in the reflex arc, and may be modified by central damage, such as in hyper-reflexic upper motor neurone lesions.
A number of reflexes are assessed with the cranial nerves (page 27); these include those of the special senses, as well as somatic motor and sensory function.
When testing limb reflexes, the position of the limb is such as to put slight tension on the stimulated muscle, but supporting the weight to avoid any active tension. Appropriate tendons are struck precisely and gently with a patellar hammer from a few centimetres swing. Asking the patient to clench their teeth, or pull opposing clasped fingers can reinforce sluggish reflexes.
In hyper-reflexia, stimulation of one muscle may produce movements elsewhere, e.g. antagonists or more distal muscles. In marked hyper- reflexia, tension in the muscle alone may produce reflex contraction, and sustained tension can produce repeated jerking movement (clonus), as seen in patellar or ankle clonus (figure 12a,b).
If the stimulated muscle is weak, the stimulus may produce movement in powerful antagonist muscles (paradoxical or inverted reflexes). Hyporeflexia may persist after motor recovery in a peripheral nerve injury; it is not a good indicator of the severity of the lesion. Reflexes may persist until late in the course of muscular disease.
Reflexes are graded by the degree of contraction: 0, not elicited; 1, elicited with reinforcement; 2, normal; 3, brisk; 4 and 5, unsustained and sustained clonus.
Specific reflex nerve root levels are: biceps, C5,6; supinator and triceps, C6,7; knee, L3,4; ankle, S1,2. Specific reflexes are shown in the figures 13a–l.
Of the superficial reflexes, the Babinski response is routinely examined (figure 14a). It is elicited by scratching the outer edge of the sole, from the heel forwards with a key or other implement. A normal response is curling downwards of the toes. A positive (abnormal) response is extension and fanning of the toes. This is present at birth, but after this it is indicative of an upper motor neurone lesion.
Abdominal reflexes are elicited by scratching diagonally across the four quadrants, each normally produces contraction of the underlying muscles (figure 14b).
The cremasteric reflex is contraction of the cremaster muscle of one side, by scratching the adjacent thigh (figure 14c). It is easily elicited in children but less so in later life.
A number of reflexes are only prominent at birth. Examples are the grasp reflex, produced by stroking the palm (figure 14d), and the placing response, elicited by stroking the outer border of the foot.
At the end of the examination of the motor system look for spinal tension signs. Neck rigidity (Kernig’s sign) occurs in meningitis (figure 15).
Pain from nerve root lesion is accentuated by stretch tests. The tension of straight leg raising on the lower spinal roots, is increased by dorsiflexion of the foot and raising the head off the pillow (figure 16a–c).
The femoral nerve stretch test is carried out prone, knee flexion increases tension and associated pain (figure 17).