Limbs: motor

Position and posture

Patients with different types of motor disease assume typical positions. It is worth looking at the position of the patient before examining the limbs at closer quarters. For example, a patient whose arm is held with a flexed elbow, wrist and fingers and whose leg is extended at the knee and ankle has a contralateral hemisphere lesion, typically a stroke. The myasthenic patient has an extended neck to overcome the ptosis, and a droopy jaw. The patient with Parkinson’s disease is stooped with flexed elbows.

Muscle inspection

Look at the bulk of the muscles. Is the bulk normal, decreased (atrophied) or increased (hypertrophied)?

Muscle atrophy is most commonly seen distally in the small muscles of the hands and in the feet and tibialis anterior. Muscle atrophy can be confined to one muscle group or be more generalized. Atrophy usually reflects lower motor neurone abnormalities, though muscles do atrophy from disuse, for example in a longstanding upper motor neurone lesion or with severe muscle disease.

Muscle hypertrophy is much rarer than atrophy. The calves are most commonly affected. This is seen in the Duchenne and Becker muscular dystrophies.

Fasciculations are small movements within the muscle and reflect contraction of a motor unit. These usually indicate a lower motor neurone abnormality. They are widespread in anterior horn cell diseases, typically motor neurone disease. They can occur in the absence of neurological disease, and are quite commonly observed in the calves of people without neurological disease.

Tone

This is usually assessed at the wrist, elbow, hip and knee (Fig. 1). The joint is moved through its range, initially slowly and then at increasing speeds.

Fig. 1 Testing tone.

There are four patterns of abnormality (Table 1). Rigidity is usually easiest to find at the wrist and elbow. Spasticity is best found at the extension of the elbow or pronation and supination of the forearm, and is more marked as the joint is moved more rapidly.

Power testing

Although traditionally called power testing, what is actually being measured, using your arms and hands as strain gauges, is force. It is important to develop a systematic approach to testing the different muscles and movements described here. As you test, try to think of the nerve root and peripheral nerve innervation of each muscle. The muscles routinely tested are shown in Figures 2–8 and 10–14 (pp. 24–25) and the less commonly tested muscles in Figure 9 (p. 24).

Fig. 2 Testing shoulder abduction.

Fig. 3 Testing elbow extension.

Fig. 4 Testing elbow flexion. (a) Biceps; (b) brachioradialis.

Fig. 5 Testing wrist extension.

Fig. 6 Testing finger extension.

Fig. 7 Testing thumb abduction.

Fig. 8 Testing finger abduction.

Fig. 10 Testing hip flexion (a) and extension (b).

Fig. 11 Testing knee extension (a) and flexion (b).

Fig. 12 Testing dorsiflexion (a) and plantarflexion (b) of the foot.

Fig. 13 Testing foot inversion (a) and eversion (b).

Fig. 14 Testing toe extension.

Fig. 9 Less commonly tested muscles in the shoulder.

It is important to isolate the muscle or muscles that you want to test to avoid trick movements. You can do this by holding or fixing the joint that the muscle moves.

The amended Medical Research Council scale is used to record power and indicates the maximal power achieved, no matter how briefly (Box 1).

Limbs motor

Examination of tone provides useful information about the cause of a motor abnormality.

It is important to develop a systematic and reliable approach to motor examination.

Test each muscle in isolation by fixing the joint.