Procedure
The tone of a muscle is the tension in that muscle when it not being deliberately tensed. The tone is particularly easy to examine in the limbs. Muscle tone in the arms should be investigated as follows:
- The patient should lie on the examination table, as relaxed as possible.
- Take hold of the patient’s forearm by placing your hand around their wrist.
The elbow should be leaning on the examination table. - Place your fingers on the bicep tendon.
- Flex and extend the elbow several times.
- Compare left and right.
Examine the tone of the leg muscles as well, by passively flexing and extending these at the hip and knee joints.
Interpretation
Potential abnormal findings include rigidity, spasticity and hypotonia.
Rigidity. There is resistance throughout the entire movement trajectory (lead-pipe rigidity) [Figure 38] and/or the movement occurs with small jerks (cogwheel rigidity) [Figure 39]. The findings indicate a condition involving the extrapyramidal system.
Figure 38
Figure 39
Spasticity. Resistance only exists through part of the movement trajectory, and the point at which it occurs varies. Upon persistent flexion, the resistance abruptly gives way (clasp-knife rigidity) [Figure 40]. This finding indicates a condition involving the corticospinal pathway (pyramidal system).
Figure 40
Hypotonia. Even when a patient relaxes, the examined muscle is usually slightly contracted. If, however, sensory conduction to the muscle has been interrupted, for example as the result of severe peripheral nerve damage or acute damage to the corticospinal tract, this muscle tone will no longer be present. In this case, the patient will not be able to deliberately tense the muscle.