Authors: Lewis, Steven L.
Title: Field Guide to the Neurologic Examination, 1st Edition
Copyright ©2004 Lippincott Williams & Wilkins
> Table of Contents > Section 2
– Neurologic Examination > Cranial Nerve Examination > Chapter 17
– Examination of Jaw Strength
– Neurologic Examination > Cranial Nerve Examination > Chapter 17
– Examination of Jaw Strength
Chapter 17
Examination of Jaw Strength
PURPOSE
The purpose of the examination of jaw strength is to
look for evidence of dysfunction of the motor component of the
trigeminal (fifth) nerve in patients who are clinically suspected of
having a lesion of this nerve.
look for evidence of dysfunction of the motor component of the
trigeminal (fifth) nerve in patients who are clinically suspected of
having a lesion of this nerve.
WHEN TO EXAMINE JAW STRENGTH
Jaw strength needs to be tested only in patients who are
suspected of having trigeminal nerve dysfunction, such as patients who
complain of facial numbness.
suspected of having trigeminal nerve dysfunction, such as patients who
complain of facial numbness.
NEUROANATOMY OF JAW MOVEMENT
The muscles that move the jaw—the masseters and the
pterygoids—are supplied by motor branches of the trigeminal (fifth)
cranial nerve that originate in the pons and reach the muscles by
traveling through the mandibular (V3) division of the nerve. The action
of the masseter muscle on each side is to close the jaw. The action of
each pterygoid muscle is to pull the jaw forward toward the center; the
left pterygoid muscle, therefore, pulls the jaw to the right, and the
right pterygoid muscle pulls the jaw to the left.
pterygoids—are supplied by motor branches of the trigeminal (fifth)
cranial nerve that originate in the pons and reach the muscles by
traveling through the mandibular (V3) division of the nerve. The action
of the masseter muscle on each side is to close the jaw. The action of
each pterygoid muscle is to pull the jaw forward toward the center; the
left pterygoid muscle, therefore, pulls the jaw to the right, and the
right pterygoid muscle pulls the jaw to the left.
EQUIPMENT NEEDED TO EXAMINE JAW STRENGTH
None.
HOW TO EXAMINE JAW STRENGTH
-
Ask the patient to open his or her jaw. Note whether the jaw is in the midline or deviates to one side.
-
Next, ask the patient to move the jaw
laterally to each side while you try to resist that movement by pushing
on the jaw with your hand. Note whether the strength of jaw movement to
each side appears approximately the same or is significantly more
easily overcome on one side. -
Ask the patient to close his or her jaw
tightly. Palpate both masseter muscles while the patient closes the jaw
and assess for symmetry of bulk of these muscles.
NORMAL FINDINGS
-
Normally, the jaw should stay in the midline when it opens, and it should not deviate significantly to either side.
-
Lateral jaw motion to each side should feel strong and symmetric and not be easily overcome.
-
When the patient closes the jaw tightly, the masseter muscles should have symmetric bulk.
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ABNORMAL FINDINGS
-
Jaw deviation to one side when the mouth
is opened is consistent with weakness of the pterygoid muscles on the
side that the jaw deviates to. In other words, jaw deviation to the
left is consistent with weakness of the left pterygoid muscles and
suggests a lesion of the motor fibers of the left trigeminal nerve. -
Weakness of lateral jaw movement to one
side suggests weakness of the contralateral pterygoid muscle. In other
words, weakness of jaw movement to the left is consistent with right
pterygoid muscle weakness and suggests a lesion of the motor fibers of
the right trigeminal nerve. -
Diminished bulk of a masseter muscle
suggests a lesion involving motor fibers of the ipsilateral trigeminal
nerve, causing atrophy of the masseter muscle.
ADDITIONAL POINTS
-
Unilateral lesions of the cerebral
hemispheres or the brainstem (above the nucleus of the fifth nerve in
the pons) do not cause weakness of the muscles that move the jaw
because of bilateral upper motor neuron innervation to the fifth nerve
nuclei. -
Assessment of motor trigeminal function
is of limited value in the routine neurologic examination; in the
absence of a specific clinical suspicion of a possible trigeminal nerve
lesion, jaw strength does not need to be tested.