Examination of Upper Extremity Muscle Strength

By admin Last updated Jun 7, 2023

Ovid: Field Guide to the Neurologic Examination

Authors: Lewis, Steven L.

Title: Field Guide to the Neurologic Examination, 1st Edition

> Table of Contents > Section 2
– Neurologic Examination > Motor Examination > Chapter 25 –
Examination of Upper Extremity Muscle Strength

Chapter 25

Examination of Upper Extremity Muscle Strength

PURPOSE

The purpose of the examination of upper extremity muscle
strength is to localize neurologic pathology by looking for
characteristic distributions of muscle weakness.

WHEN TO EXAMINE THE MUSCLE STRENGTH OF THE UPPER EXTREMITIES

A screen of upper extremity strength (see Chapter 40,
Performing a Complete Neurologic Examination) should be performed on
all patients as part of the routine neurologic examination. If weakness
is suspected or found, a more detailed evaluation of upper (and lower)
extremity muscles is indicated to try to localize the patient’s
pathology.

NEUROANATOMY OF THE UPPER EXTREMITY MOTOR EXAMINATION

The upper motor neuron pathways that control the muscles
of the upper extremities end primarily within the cervical spinal cord,
proceeding no further caudally than the first thoracic level. The lower
motor neurons that innervate the muscles of the arms leave the spinal
cord primarily from the C5 through the T1 levels. Table 25-1
summarizes the major innervation (root and nerve) of some of the most
clinically relevant muscles of the upper extremities, as well as the
functions of these muscles.

EQUIPMENT NEEDED TO TEST UPPER EXTREMITY MUSCLE STRENGTH

None.

HOW TO EXAMINE THE MUSCLES OF THE UPPER EXTREMITIES

Test for Drift

Always start the examination of upper extremity strength by testing for drift:

Ask the patient to hold his or her arms straight in front of him or her with the palms up.
Instruct the patient to close his or her eyes.
Observe the arms for a few seconds while the patient’s eyes are closed.

Testing Upper Extremity Muscle Strength

Test and grade the muscles of the upper extremities according to the method described in Chapter 24, Approach to the Motor Examination. Figures 25-1, 25-2, 25-3, 25-4, 25-5, 25-6, 25-7, 25-8 and 25-9 illustrate and describe how to examine some of the major muscle groups of the upper extremities.

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TABLE 25-1 Major Innervation of the Muscles of the Upper Extremities

Muscle	Function	Major Root Innervation^a	Nerve Innervation
Deltoid	Arm abduction	C5	Axillary
Biceps	Elbow flexion	C5, C6	Musculocutaneous
Brachioradialis	Elbow flexion	C6	Radial
Extensor carpi radialis	Wrist extension	C6	Radial
Triceps	Elbow extension	C7	Radial
Extensor digitorum	Finger extension	C7	Radial (posterior interosseus branch)
Flexor pollicis longus	Thumb tip flexion	C8	Median
Flexor digitorum profundus	Second and third fingertip flexion	C8	Median
	Fourth and fifth fingertip flexion	C8	Ulnar
Dorsal interossei	Finger abduction	C8, T1	Ulnar
Abductor pollicis brevis	Thumb abduction	T1	Median
^a Although muscles share root innervation from several adjacent root levels, this table names the root with the most important, clinically relevant innervation to the given muscle.

NORMAL FINDINGS

Normally, there should be no significant movement
(drift) of the outstretched arms when the eyes are closed, and there
should be no atrophy or fasciculations of the muscles. Strength should
be full (5/5) and symmetric in all muscles tested of the arms.

Figure 25-1
Examination of arm abduction (deltoid) strength. Ask the patient to
hold his or her arm up 90 degrees at the shoulder (“like a chicken”)
and then ask the patient to resist you as you push down on his or her
abducted arm. What you might say as you test the strength: “Don’t let
me push your arm down.”

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Figure 25-2
Examination of elbow flexion (biceps) strength. Ask the patient to flex
his or her arm at approximately 90 degrees at the elbow, with his or
her palm facing the shoulder (“like you are making a muscle”), and then
ask the patient to resist you as you attempt to extend his or her arm.
What you might say as you test the strength: “Don’t let me pull on your
arm.”

Figure 25-3
Examination of elbow flexion (brachioradialis) strength. Ask the
patient to flex his or her arm at approximately 90 degrees at the
elbow, with the patient’s forearm partially pronated so that the radial
wrist is facing his or her shoulder, and then ask the patient to resist
you as you attempt to extend the arm. What you might say as you test
the strength: “Don’t let me pull on your arm.”

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Figure 25-4
Examination of elbow extension (triceps) strength. Ask the patient to
start with his or her arm bent at approximately 90 degrees at the
elbow, and then as you push on his or her arm, ask the patient to try
to push the arm out (by extending at the elbow) against your
resistance. What you might say as you test the strength: “Try to push
your arm out.”

Figure 25-5
Examination of wrist extension (extensor carpi radialis and extensor
carpi ulnaris) strength. Ask the patient to lift (extend) his or her
hand at the wrist, and then ask the patient to resist you as you
attempt to push down on his or her extended hand. What you might say as
you test the strength: “Don’t let me push your hand down.”

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Figure 25-6
Examination of finger extension (extensor digitorum communis) strength.
Ask the patient to lift (extend) his or her fingers, and then ask the
patient to resist you as you attempt to push down on the extended
fingers. What you might say as you test the strength: “Don’t let me
push your fingers down.”

Figure 25-7
Examination of finger abduction (dorsal interossei) strength. Ask the
patient to spread his or her fingers apart, and then ask the patient to
resist you as you use your thumb and middle finger to attempt to close
his or her fingers. What you might say as you test the strength: “Don’t
let me squeeze your fingers together.”

Figure 25-8
Examination of thumb abduction (abductor pollicis brevis) strength. Ask
the patient to lift his or her thumb up (perpendicular to the plane of
the palm), and then ask the patient to resist as you attempt to push
the thumb down. What you might say as you test the strength: “Don’t let
me push your thumb down.”

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Figure 25-9
Examination of thumb flexion (flexor pollicis longus) strength. Ask the
patient to flex the distal joint of the thumb, and then ask the patient
to resist you as you attempt to straighten the thumb. (Similar testing
can be done to test the flexor digitorum profundus that flexes the
distal phalanx of the fingers.) What you might say as you test the
strength: “Don’t let me pull your thumb.”

ABNORMAL FINDINGS

Testing for Drift

The finding of any downward drift of an
arm when the patient’s eyes are closed suggests weakness of that
extremity due to any cause.
Downward drift of an arm can occur with or without pronation. When it occurs with pronation, the term pronator drift is often used. Whether the downward drift occurs with or without pronation, the significance—weakness—is the same.
Rarely, when drift is tested, an arm may
assume unusual posturing at multiple joints, sometimes with significant
upward movement. This finding suggests the possibility of a
proprioceptive problem (see Chapter 30,
Examination of Vibration and Position Sensation), as can be seen from
disorders of the spinal cord, sensory nerves or roots, or contralateral
parietal lobe.

Strength

Any muscle strength in the arms that is less than 5/5 is abnormal.
Any focal muscle atrophy or
fasciculations in the muscles of the arms is abnormal and suggests
dysfunction of the lower motor neuron supplying those muscles.
Look for patterns of muscle weakness (in
the arms as well as the legs) to support or refute your suspicion of
the localization of the cause of weakness to the brain, spinal cord,
root, plexus, or nerve (see Table 24-3).

ADDITIONAL POINTS

The test for drift is an important part
of the motor examination because even subtle downward drift of an arm
suggests weakness in that extremity,

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even
before you perform any individual muscle strength testing. Think of
drift as the sneak preview to the motor examination. Finding drift
suggests there is subtle extremity weakness regardless of whether
further evidence for weakness is seen on muscle testing.
The muscles described in this chapter are
not inclusive of all the muscles of the arms that may need to
occasionally be tested to localize a cause of weakness, but they do
represent muscles that are particularly helpful to have a working
knowledge of for the majority of neurologic examinations.