|3475 Torrance Blvd., Ste F
Torrance, CA 90503
Office hours: M-F, 9am
– 5 pm
Worker’s compensation, Medicare
and most insurance plans accepted.
In September 2008, we will be moving to a beautiful new 4,400 sq ft,
state of the art dedicated hand center located at 2808 Columbia Ave
in Torrance, CA., which will feature onsite nerve conduction studies,
occupational hand therapy and digital x-ray.
DISTAL ULNAR NEUROPATHY
The ulnar nerve is most commonly entrapped at the elbow (see cubital tunnel
syndrome). There are circumstances however in which it can be compressed
at the wrist level. This syndrome was well described by a Frenchman named
Guyon in the 1900’s and hence now bears his name.
The ulnar tunnel or Guyon’s canal is approximately 4 cm in length,
which begins at the proximal edge of the carpal transverse ligament and
ends at the fibrous arch of the hypothenar arch. It is bounded medially
by the pisiform, and radially by the hamate hook. The floor consists of
the carpal transverse ligament and the roof consists of the continuation
of the deep forearm fascia i.e the volar carpal ligament. The ulnar nerve
has 15 to 25 fascicles at the wrist. It can be clearly divided into a
volar sensory component and a dorsal motor component. At the wrist, the
ulnar nerve passes over the TCL, medial to the ulnar artery, through Guyon’s
canal. The deep motor branch is given off at the pisiform and passes underneath
a fibrous arch to lie on the palmar surface of the interossei. It crosses
the palm deep to the flexor tendons, to terminate in the adductor pollicus
and ulnar head of the flexor pollicus brevis.
The standard teaching divides the sites of compression in Guyon’s
canal into 3 zones. In zone 1, nerve compression leads to mixed motor
and sensory symptoms. In zone II symptoms are purely sensory and in zone
III symptoms are purely motor and restricted to muscles innervated by
the deep ulnar motor branch. Two sites of entrapment distal to the abductor
digiti minimi have also been described. In these cases the ADM will be
preserved while there is weakness and wasting of the intrinsics (link
to guyons 1,2).
The patient may also present with complaints of numbness and tingling
of the small and/or ring finger. The dorsoulnar aspect of the hand however
is not affected. The patient may give a history of repetitive percussion
using the hypothenar eminence which may occur with autobody technicians,
martial artists and percussionists. Bicyclists who ride for extended periods
in the crouch position may entrap the deep motor branch against the hamate
hook while grasping the handle bars. A history of Raynaud’s symptoms
should alert one to the possibility of ulnar artery thrombosis.
There are no characteristic findings of ulnar tunnel entrapment per se.
A tinel’s sign may be present at the wrist but not the elbow unless
there is an associated cubital tunnel entrapment. Intrinsic atrophy may
also occur in chronic compression, but the forearm muscles i.e. the flexor
carpi ulnaris and the flexor digitorum profundus flexor tendons to the
fingers are not affected. There should be a negative tinel’s at
the elbow and a negative elbow flexion test. If there is an associated
ulnar artery aneurysm there may be a palpable thrill and an audible bruit.
With ulnar artery thrombosis the Allen’s test will be positive for
ulnar artery occlusion. With an associated fracture of the hook of the
hamate, there will be localized tenderness in the palm, 1 cm radial and
1 cm distal to the pisiform. Ancillary testing such as ultrasound, CT,
angiography and MRI may be employed to aid in the diagnosis of these associated
Ulnar motor studies are more popular than ulnar sensory studies. The distal
motor latency is determined by recording from an electrode placed over
the midpoint of the abductor digiti minimi (ADM) while stimulating the
ulnar nerve 8 cm proximally (S1). Normal values include a DML # 3.6 ms
and amplitude > 4.0 MV. Alternatively, the latencies can be measured
from the first dorsal interosseous (FDI), which then assesses conduction
through the deep motor branch of the ulnar nerve. The FDI to ADM latency
should not exceed 2.0 ms. The ulnar nerve is then stimulated 4 cm distal
to the medial epicondyle (S2). By subtracting the latency for S1 from
S2 and measuring the intervening distance, the forearm conduction velocity
is obtained. Ulnar nerve conduction across the cubital tunnel is calculated
by stimulating the nerve at S3, which is 12 cm proximal to S2, and subtracting
the latencies. Most labs measure conduction with the elbow flexed between
90 - 135°. Normal forearm NCV is > 48 m/s. Across the cubital tunnel
the NCV should be > 45 m/s. More than 10 m/s of slowing between the
above and below elbow NCV is abnormal. Amplitude drops of > 20% are
a more sensitive indicator of conduction block or axonal loss.
Ulnar nerve sensory studies
Ring electrodes are placed on the small finger and the ulnar nerve is
stimulated 14 cm proximally. Recordings are also taken from the ring finger
after stimulation of both the ulnar and median nerves. This allows for
comparison of the ulnar to the median SNAPs. Normal peak sensory latencies
are # 3.5 ms and < 0.5 ms median - ulnar difference. Mixed palmar orthodromic
studies can be elicited by stimulating the ulnar nerve in the 4th webspace
and recording over the ulnar nerve at the wrist 8 cm proximally. This
measures the sensory nerve conduction through Guyon’s canal. Normal
values are < 2.2 ms.
The usual nerve conduction studies are inadequate at assessing ulnar nerve
entrapment in the palm. Short segment incremental studies (SSIS) is a
sensitive and specific way to assess the deep motor branch since focal
conduction abnormalities also tend to be normalized over the distance
between the ADM and the FDI. The ulnar nerve is stimulated in 1 cm increments
from 3 - 4 cm proximal and distal to the wrist crease. Abnormal values
include a > 0.5 ms jump or a >120% drop in amplitude. When this
is combined with FDI conduction and interosseous-latency differences the
diagnostic yield increases.
Quantitative sensory testing
The 2PS to the small finger is the first to go, followed by an abnormal
1 PS. The dorsoulnar carpus should remain normal unless there is an associated
The mainstay of treatment is activity modification. Bicyclists should
avoid riding in the crouch position with their hands low on the handlebars
since this is a recognized precipitant of symptoms, and change their hand
position frequently. Autobody repair technicians, martial artists and
percussionists should avoid repetitive hammering using the ulnar border
of their palm. Wrist splinting and cortisone injections have no role in
Intrinisic wasting and/or sensory loss are a sine qua non for decompression.
The presence of a mass occupying lesion also mandates surgical treatment.
Ulnar artery thrombosis or aneurym may be treated with ulnar artery repair
Ulnar motor and/or sensory disturbances due to more proximal causes preclude
a distal release. Ulnar sensory disturbances in CTS were a common indication
for release in the 80's, but has now become an infrequent indication for
the release of Guyon’s canal since the majority of patients experience
improvement following a CTR.
The ulnar nerve is identified proximal to the distal wrist crease between
the FCU and the flexor tendons through a curving incision which crosses
the wrist obliquely, and bisects the interval between the pisiform and
the hook of the hamate. The ulnar nerve is followed distally as the volar
carpal ligament is released. The ulnar artery is inspected for thrombosis
or aneurysm. The fibrous arch of the hypothenar muscles is incised and
the floor of the canal is explored for masses, fibrous bands or anomalous
muscles(link to guyons 3). With entrapment in the palm, the deep motor
branch is followed distally as it traverses the palm lying on the interosseous
fascia, deep to the flexor tendons and superficial palmar arch. The dissection
is completed as the motor branch ends in the muscle belly of the adductor
pollicus. I frequently employ intraoperative nerve conduction studies
to ensure that the nerve is completely decompressed (link to guyons 4).
These are mostly related to injury to the branches of the ulnar nerve
or artery. Injury to the palmar cutaneous branches of the ulnar nerve
or the nerve of Henlé (if present) may result in scar tenderness
and hypoesthesiae. Uncommonly injury to the pisiform ligament complex
can result in instability of the pisotriquetral joint.
Clinical recovery is seen in the majority of patients when the ulnar nerve
entrapment is due to a space occupying lesion. Motor recovery is less
predictable when compared to sensory recovery, especially when the compression
is due to a fibrotic hypothenar arch or of a longstanding nature, but
good results can be obtained (link to guyons 5).
Most people can perform one-handed work activity by the 2nd week followed by light duty including clerical work at 6-8 weeks. Heavy manual labor can often be resumed by 8 -12 weeks.