While the ulnar
nerve innervates a number of muscles in the
forearm, motor weakness is most evident in
muscles of the hand, such as the adductor
pollices. It is an important muscle in
grasping objects. Consequently, the client
may report difficulty in holding objects in
the hand, or clumsiness when performing
precision activities such as writing.
While many
symptoms of these two peripheral
neuropathies are similar, there are a number
of factors that help distinguish them in the
evaluation process. If the symptoms started
from an acute injury, identify whether the
primary insult was to the elbow or the
wrist. In chronic compression pathologies it
is a little more complex, but a more
thorough assessment provides valuable clues.
If the
symptoms are aggravated by long periods with
the body weight resting on the wrist,
especially if it is in a hyperextended
position, Guyon’s canal syndrome is
implicated. Using a cane for walking is an
example of how chronic compression may occur
in Guyon's canal. If the symptoms occur from
long periods of resting the body weight on
the elbows, or holding the elbows in a
flexed position (not necessarily
weight-bearing) for long periods, then
cubital tunnel syndrome is more likely.
There
are a few visual indicators that may help
identify ulnar nerve compression from either
cubital tunnel syndrome or Guyon’s canal
syndrome. As mentioned above, the ulnar
nerve innervates several muscles in the
hand. Compression of the nerve in either
condition may lead to atrophy of the
hypothenar muscles (those located in the
fleshy bundle on the ulnar side of the
hand). In some cases, cubital tunnel
syndrome is aggravated by a postural
distortion of the upper extremity called
cubital valgus (see Figure 2). In cubital
valgus the nerve may be pulled taut against
structures bordering it within the cubital
tunnel.
Palpation is
helpful for identifying both conditions.
Because the region of entrapment is
superficial in both pathologies, palpating
the involved area may increase symptoms. If
manual pressure directly over the cubital
tunnel reproduces the primary complaint,
then cubital tunnel syndrome is likely.
Similarly, if pressure directly over Guyon's
canal reproduces the complaint, Guyon’s
canal syndrome is implicated.
The
neurological symptoms of cubital tunnel
syndrome or Guyon’s canal syndrome are apt
to be reproduced with certain motions of the
upper extremity. If cubital tunnel syndrome
is the primary problem, neurological
sensations may be reproduced with elbow
flexion either passively or actively. Often
the symptoms are not aggravated by simply
moving the elbow into a flexed position. The
elbow must be held in the flexed position
for some time before symptoms recur.
Attempting to recreate symptoms by holding
the elbow in flexion is demonstrated during
the elbow-flexion test described below.
If Guyon’s
canal syndrome is the problem, pain is
common with wrist hyperextension, either
actively or passively. In hyperextension the
nerve is pulled taut across the carpal
bones, and if damaged from compression, the
increased tension on the nerve will
aggravate symptoms.
There are two
special orthopedic tests commonly used to
help identify ulnar nerve compression. The
first is the elbow-flexion test. It is
primarily used to identify cubital tunnel
syndrome.
This test
begins with the client in a standing or
seated position. With the shoulder laterally
rotated, the client brings the elbow into
full flexion while the forearm is supinated
and the wrist is hyper extended. This is the
position used when carrying a tray, for
example. If the condition is unilateral, it
is helpful to have the client adopt the
position with both sides at the same time so
a comparison with the unaffected side can be
made. Cubital tunnel syndrome is probable if
symptoms are reproduced within about 60
seconds while holding this position.
Another test
commonly used to evaluate both conditions is
Froment's sign. It evaluates weakness of the
adductor pollices that may result from nerve
compression. While it doesn't discriminate
between these two conditions, it is helpful
in clarifying ulnar nerve involvement in
upper-extremity neurological disorders.
In Froment's
sign the client holds a piece of paper
between the thumb and MCP joint of the index
finger. It is best if the paper is folded
several times so it does not tear easily.
The practitioner attempts to pull the paper
out of the client's grasp. If the client is
able to hold it firmly and the practitioner
has a difficult time pulling it from the
client's grasp, there is no perceivable
weakness in the adductor pollex muscle. If,
however, the client is unable to prevent the
practitioner from easily pulling the paper
out (especially compared to the unaffected
side), there is a good chance that motor
impairment of the adductor pollex exists.