Susceptibility of the Superficial Sensory Branch
of the Radial Nerve to Form Painful Neuromas
A. LEE DELLON and SUSAN E. MACKINNON
From the Curtis Hand Center and Johns Hopkins Hospital, Baltimore and the Division of Plastic Surgery,
University of Toronto.
The superficial sensory branch of the radial nerve appears prone to develop painful neuromas
out of proportion to its likelihood for injury. Based on cadaver dissections and intraoperatlve
observations, an anatomical mechanism for this “predisposition” is suggested. Exit of this
nerve beneath dense fascia and the tendons of brachioradialis and extensor carpi radialis longus
provide a proximal tethering against which tension develops as the distal fixation point
(neuroma) is pulled through the long excursion of wrist arc of motion. This long excursion and
proximal tethering are not present anatomically for the dorsal cutaneous branch of the ulnar
nerve nor the palmar cutaneous branch of the median nerve.
The susceptibility of the superficial sensory branch of
the radial nerve (SSBR) to form painful neuromas has
been well documented
(Hall and Bechtol, 1963,
Lincheid, 1965, Belsole, 1981, Herndon, Eaton and
Littler, 1976, Tupper and Booth, 1976, Rask, 1978,
Laborde, Kalisman and Tsai, 1982, Lluch and Beasely,
1981). Although the incidence of painful neuromas may
be due partly to the greater number of operative
procedures which are done about the dorsal radial
aspect of the wrist, there seems to be universal
agreement that this cutaneous nerve has almost a
predisposition
to develop
a painful
neuroma.
Furthermore,
this neuroma is more refractory to
treatment once established than are neuromas of either
the dorsal cutaneous branch of the ulnar nerve (DCBU)
of the palmar cutaneous branch of the median nerve
(PCBM). The purpose of this paper is to present
evidence in support of an anatomical mechanism for
this susceptibility of the superficial sensory branch of
the radial nerve to form a painful neuroma. This
mechanism was suggested by the proximal tethering of
this nerve at its exit from the deep fascia that was
observed during treatment of patients with more distal
injuries to this nerve.
Method
Four fresh cadaver upper extremities were dissected to
determine 1) the course of each cutaneous nerve with
respect to the axis of dorsiflexion/radial
deviation and
flexion/ulnar deviation of the wrist (figure 1 and 2) the
degree of mobility of the cutaneous nerve as it emerges
from beneath the forearm muscles to enter the subcutis.
The critical findings were subsequently confirmed in
twelve patients, three being treated for neuromas of
multiple cutaneous nerves about the wrist.
Received for publication
March, 1983.
A. Lee Dellon, M.D., The Hampton Plaza, 300 East Joppa
21204, U.S.A.
Funding for this study was through the Dellon Foundation.
Road, Baltimore,
Maryland
Fig. I
course of the superficial sensory branch of the radial nerve
from proximal (to the left) exiting from beneath
brachioradialis muscle, running distally (to the right). Note
constraining overlying deep fascia at the proximal tethered
point.
Results
Course of the nerve with respect to wrist axis:
The SSBR is adherent to the overlying structures along its
course beneath the brachioradialis muscle. As the nerve
passes distally, and exits between the crossed tendons of
the brachioradialis and the extensor carpi radialis longus,
it continues to be tightly constrained beneath the deep
fascia. The nerve is actually “scissored” or “pinched”
between these tendons (figure 1). The SSBR emerges into
the loose subcutaneous tissue only after another,
variable, 2-3 cm. beneath the adherent deep fascia. In
contrast the DCBU lies loosely beneath the flexor carpi
ulnaris, from which point it enters the subcutaneous
tissue directly at the ulnar border of the wrist (figure 2).
The PCBM, like the DCBU, lies loosely deep to the fascia,
coursing distally between and parallel to the palmaris
longus and flexor carpi radialis tendons. The PCBM does
not truly enter the subcutaneous tissue at the wrist level
but enters deeply into the thenar eminence (figure 3).
thus, the SSBR is tethered proximally by surrounding
anatomical structures, and is the most restricted at its
point of entry toward the wrist. The DCBU and the
PCBM are not tethered proximally.
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OF HAND
SURGERY
SUSCEPTIBILITY OF SUPERFICIAL SENSORY BRANCH OF THE RADIAL NERVE TO FORM PAINFUL NEUROMAS
Fig. 2
course of the dorsal cutaneous branch of the ulnar nerve from
proximal (to the right) directly entering the loose subcutaneous
tissue to run distal (to the left). No proximal tethering.
Fig. 4
Fig. 3
course of the palmar cutaneous branch of the median nerve,
lying deep to deep fascia through its course. No proximal
tethering.
Lkgree of mobility of nerve with respect to wrist axis:
The SSBRcrosses the wrist axis dorsally and radially. The
DCBU lies primarily along the ulnar border of the hand
with its dorsal branches becoming dorsal just distal to the
wrist axis. The PCBM crosses volar to the wrist axis and
terminates just distal to the axis. Thus, considering the
stretch required of a nerve throughout the arc of wrist
motion (figure 4), as you would the tendon excursion
required during finger flexion/extension,
the SSBR
requires more (figure 5) than either the DCBU or the
PCBM. The PCBM requires essentially no excursion
throughout this axis of wrist rotation. The PCBM only
requires an excursion during flexion and dorsiflexion
when the wrist is not deviated. An attempt to document
this in the. living arm during surgical exposure is
demonstrated in figures 6,7 and 8.
Discussion
Situated in its superficial subcutaneous position on the
radial dorsal aspect of the forearm, the SSBR may be
more susceptible to traumatic injury than the other
sensory nerves about the wrist. Situated as well in an
the dominant arc of wrist motion during most work is from
dorsiflexion/radial deviation to flexion/ulnar deviation.
area that is common for surgical exploration, it may
sustain more iatrogenic injuries than the other sensory
nerves about the wrist. However, it has been the clinical
observation that the SSBR nerve appears predisposed to
develop painful neuromas out of proportion to this
potential for injury (Hall and Bechtol, 1963, Linscheid,
1965, Belsole, 1981, Herndon, Eaton and Littler, 1976,
Tupper and Booth, 1976, Rask, 1978, Laborde,
Kalisman and Tsai, 1982, and Lluch and Beasely, 1981).
The observations made in this study suggest that
anatomical factors peculiar to the SSBR nerve may be
the basis for this predisposition to the development of
painful neuromas.
The mechanism proposed is that neuroma-inducing
trauma creates a distal point of scar constraint of the
nerve to the skin, subcutaneous tissue, deep fascia,
tendon or bone. As noted (figures 1-3, 6-8), the SSBR,
unlike the PCM and PCU, is also “anatomically”
tethered proximally in the forearm adherent as it is to
the fascia of the brachioradialis and the tendon of the
extensor carpi radialis longus. In the pathological state
(neuroma), this nerve is thus held in a relatively fixed
position at two points, anatomically in the mid-forearm
and pathologically at the wrist level. Analysis of the
angles through which the wrist joint moves (figures 4
and 5) suggests the arc of motion that puts greatest
“stretch” on the SSBR and the DCBU is dorsiflexionulnar deviation. The SSBR in its maximally stretched
position requires greater excursion than the DCBU
(figure 6 versus 7). Thus the SSBR, unlike the DCBU or
the PCBM, is tethered proximally, as well as distally,
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A. LEE DELLON
fig. 5
AND SUSAN E. MACKINNON
theoretical “excursion” required of a) the superficial sensory branch of the radial nerve and b) the dorsal cutaneous branch of the ulnar
nerve throughout the described arc of motion. Note the palmar cutaneous branch of the median nerve would require no excursion
throuahout this arc, while the SSBR would require the greatest.
Fig. 6~ & 6b “excursion”
required of superficial sensory branch of radial nerve during arc of rotation of wrist. Note the greater degree ot
mobility required for this nerve than the DCBU (figure 7) or PCBM (figure 8).
Fig. 70 & 7b “excursion” required of dorsal cutaneous branch of ulnar nerve during arc of rotation of wrist. Note that much less excursion is
required than for SSBR (figure 6).
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OF HAND SURGERY
SUSCEPTIBILITY OF SUPERFICIAL SENSORY BRANCH OF THE RADIAL. NERVE TO FORM PAINFUL NEUROMAS
Fig. 8
“excursion”
“excursion”
required of palmar cutaneous branch of median nerve during arc of wrist motion was almost none. Here even minimal
is required when wrist is moved from flexion to dorsiflexion.
while having a much greater angle to subtend in its
maximal stretched position. This produces tension and
“shearing trauma” during the normal wrist arc of
motion in the pathological state (presence of neuroma).
Such “shearing trauma” has been suggested as a
mechanism of entrapment
neuropathy
(McClellan,
1975). From basic studies in wound healing in general
(Peacock and Van Winkle, 1970, and Hunt, 1980), and
nerve repair in particular (Millesi, Meissl and Berger,
1972, Bora, Richardson and Black, 1980), this increased
tension would cause increased scar formation (collagen
deposition)
and thus promote
larger neuroma
formation. This thesis is supported by recent electron
which
have
demonstrated
microscopic
studies
myofibroblasts in primate neuromas of the SSBR, and
the increased likelihood of these developing in an
environment of scar, subcutaneous tissue and tension
(Mackinnon, 1983).
No doubt the mechanisms of painful neuroma are
multifactorial. It is our supposition that tension with its
concurrent increase in scar formation is one of the
important factors involved in the formation of painful
neuromas. In the case of the SSBR, this is augmented by
anatomical factors that tend to increase this tension.
This mechanism suggests further that part of the basis
for the success rate in treating neuromas by transposing
the end of the nerve to a “quieter location”, i.e., more
proximally
(Tupper
and Booth,
1976, Laborde,
Kalisman and Tsai, 1982, Lluch and Beasley, 1981) is
due to eliminating the distal tethering effect and thus
reducing tension on the neuroma. In a group of patients
with recurrent incapacitating painful neuromas of the
SSBR, we now have included proximal release of this
nerve in the mid-forearm as part of the treatment with
88% good to excellent relief of pain an average of 21
months after surgery (Mackinnon and Hudson 1983).
Recognition of the functional anatomical constraints
associated with the SSBR nerve has allowed us a greater
understanding of the mechanisms associated with the
production of clinically painful neuromas and hopefully
may in the future help us to reach a greater understanding
of the factors which may lead to better management of
this difficult clinical problem.
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