Our motor nervous system is responsible for generation and control of voluntary and involuntary movements. Abnormalities in motor function can be associated with a wide range of diseases, from movement disorders and myopathies to strokes.
Depending on the site of the lesion, the symptoms of motor dysfunction can manifest as muscle weakness, atrophy, abnormal muscle tone, as well as involuntary movements. Therefore, a careful, systematic testing and integration of all the findings can provide an insight to the level at which the motor pathway might be affected. This in turn helps in formulating a differential diagnosis and determining the course of the subsequent evaluation and treatment.
In this first presentation on motor system examination, we will cover observation and inspection for signs of motor disorders, followed by evaluation of the muscle's tone and strength. The assessment of reflexes, gait and coordination will be reviewed in the next chapter on this topic.
Let's start by discussing the observation and inspection portion of the motor exam. Observation should start during the patient interview itself. While taking history, observe for any abnormalities including paucity of movements, hypokinesis, and hyperkinesis, which includes tremors, tics and chorea.
Next, assess the muscle bulk and observe for fasciculations. Start with the inspection of the extremities for signs of atrophy, and asymmetry between sides. Generalized wasting or cachexia may indicate a systemic disease, such as malignancy, while atrophy in specific areas can be due to muscle denervation, as observed in patients suffering from the lower motor neuron disease.
Following that, inspect the intrinsic hand muscles, the shoulder girdle, and the thigh region for fasciculations, which are spontaneous contractions of small muscle fibers. They can be caused by firing of muscle motor units such as with generalized lower motor neuron disorders. Also, try to elicit fasciculations by gently tapping the muscles in these areas.
After observation and inspection, let's review the maneuvers involved in the assessment of muscle tone. Ensure that the patient is fully relaxed for this part of the exam. To achieve this, try to distract them with a conversation.
Start with passively moving the arm through a full range of elbow flexion and extension. Feel for resistance, and assess for the presence of hypotonia that is decreased tone, or hypertonia, which is increased tone. If hypertonia is detected, then determine the pattern as spastic or rigid.
Next, take the patient's hand in yours as for a handshake, stabilize the forearm with your other hand and then passively pronate, supinate and rotate the wrist. Again, check for resistance and feel the tone. Next, place your index and middle fingers over the patient's biceps tendon, and passively extend and flex the arm while simultaneously rotating the wrist. During this movement, palpate the biceps tendon to assess for the presence of ratcheting sensation. This sign is called "cog-wheeling" and is indicative of Parkinsonism. Cog-wheeling can be accentuated by asking the patient to move the contralateral arm in circular motions.
To test the muscle tone in lower extremities, ask the patient to lie down and request them to relax their legs. Then place your hands behind the patient's knee, and lift the leg in a sudden motion. If the muscle tone is normal, the heel will drag along the surface, while with increased tone or spasticity the foot may come off the bed.
Now let's review the maneuvers involved in muscle strength examination, which involves a few screening tests followed by a detailed formal assessment. The first screening test is the pronator drift test. Tell the patient to raise the arms palms up, as if holding a tray. Then ask them to close the eyes and hold this position. In patients with true motor weakness, the weak arm is likely to pronate, flex at the elbow, and drift downwards. Subsequently, ask the patient to walk around the examination room and observe the arm swinging for symmetry. Watch the stride for equal transit time and stride length. Also determine if the patient has a narrow or wide base stance.
Now perform the formal strength testing and grade the strength of each muscle or a muscle group on the scale from zero to five, where zero represents lack of visible contraction and five is normal muscle strength. Ask the patient to sit down on the exam table and have them raise both the arms outward, while you resist the movement. This maneuver provides information about function of the C5 and C6 nerve roots, which, via the axillary nerve innervate the deltoid muscles that are required for abduction.
Next, instruct the patient to flex their arm against your resistance. This movement again tests the C5 and 6 roots that give rise to the musculocutaneous nerve, which supplies the biceps muscles. Repeat on the other side and assess for symmetry. Subsequently, ask the patient to fully straighten their arm, while you resist the movement. Arm extension at the elbow is controlled by C6 and C7, which, via the radial nerve, innervate the triceps muscle. Again, test one arm at a time and compare between the sides.
For the following test, have the patient extend their wrist while you resist this movement by pushing down against the back of their hand. This also tests the C6 and C7 roots, and the corresponding radial nerve, that supplies the wrist extensors. Repeat the maneuver on the opposite side and compare. Next, explain to the patient, that they should try to squeeze two of your fingers as hard as possible, while you attempt to remove them from their grasp. Test both hands simultaneously and compare between the sides. Finger grip is controlled by the C7 and C8 associated median and ulnar nerves that innervate the forearm flexors and the intrinsic hand muscles.
Next, have the patient spread all the fingers on the both hands, while you try to push them back together. Finger abduction is a function of C8 and T1, which give rise to the ulnar nerve that control the dorsal interossei and abductor digiti minimi muscles. Finally, have the patient touch the tip of the thumb to the pinky while you attempt to pry the finger out. This tests the C8 and T1 roots, and the arising the median nerve that provides motor information to the opponens pollicis muscle.
Now ask the patient to lie down and examine muscle strength in the lower extremities. Start with testing the hip flexion. Have the patient raise the thigh while you try to push it down with your palm. Repeat on the other side and compare. This movement is a function of L2, 3, and 4 roots, which, via the femoral nerve, innervate the iliopsoas muscle.
Next, tell the patient to perform hip adduction by bringing the knees together against your resistance. This is controlled by L2, L3, and L4, via the obturator nerve, and requires several muscles, including the obturator externus and the hip adductor group. Subsequently, ask the patient to roll onto one side and spread their knees apart while you provide resistance. This evaluates the L4, L5, and S1 roots, and the arising superior gluteal nerve, which provides motor information to the hip abductors, namely the gluteus medius and minimus muscles.
Next, instruct the patient to extend one of the knees. Then place your hand under the lower leg, and ask the patient to press it down against your resistance. This tests hip extension controlled by the L5, S1, and S2, via the inferior gluteal nerve innervating the gluteus maximus muscle. After that, place one of your hands proximal to the patient's knee and the other on top of the lower leg, and ask the patient to extend the lower leg against your resistance. Repeat on the other side and compare. This maneuver evaluates the L2, 3 and 4, that give rise to the femoral nerve, which in turn supplies the quadriceps muscle.
For the following test, place one hand under the patient's knee and the other under the ankle, and then tell the patient to pull the leg in as hard as possible while you applying resistance at the ankle. This movement requires proper functioning of the L5, S1, and S2 roots and the sciatic nerve innervating the hamstrings muscles. Next, test ankle dorsiflexion. Start by placing your hand on the top of the patient's foot and then telling the patient to pull their foot up toward their head as hard as possible while you resist the movement. This motion is controlled by the L4 and L5 nerve roots through the peroneal nerve supplying the tibialis anterior muscle.
Subsequently, place your hand under the ball of the patient's foot and instruct them to press down as hard as possible against your resistance. This movement, the ankle plantar flexion, is regulated by the S1 and S2 nerve roots via the tibial nerve branches that supply the gastrocnemius and soleus muscles. Finally, ask the patient to extend the large toe by moving it upwards against your resistance. This tests the L5 and the associated deep peroneal nerve that provides the extensor hallucis longus muscle. This completes the formal muscle strength assessment.
You've just watched JoVE's first installment of the motor system examination. In the second chapter, we will explain how to assess gait, coordination and reflexes. As always, thanks for watching!