Open carpal tunnel release has been considered the operative procedure
of choice for decompression of the median nerve at the wrist in
patients whvo have idiopathic carpal tunnel syndrome
1-5
. However, while excellent results have been reported, some authors
have suggested that persistent weakness, tenderness of the scar,
and pain in the thenar or hypothenar area (pillar pain) occur frequently
after open procedures
6-10
. In a review of all cases of occupational carpal tunnel syndrome
in the state of Washington between July 1, 1987, and December 31,
1987, Adams et al. reported a mean loss of work time of four months,
with only ninety-seven (67%) of 144 patients able to return to their
original job
11
. Endoscopic release of the carpal tunnel was introduced as an alternative
method in the hope of decreasing the rate of these complications
12-15
. There are two endoscopic techniques for carpal tunnel release:
single-portal and two-portal
12-16
. Both may offer advantages compared with open carpal tunnel release
by diminishing the frequency and severity of tenderness of the scar
and pillar pain and allowing patients to return to work more quickly
12,17-19
. We are aware of two prospective, randomized clinical trials comparing
the endoscopic and open methods. Before releasing a device for the
single-portal method, Agee et al.
12
completed a prospective trial with a three-month follow-up. Brown
et al.
2
performed the only independent randomized trial (to our knowledge)
of the two-portal technique, with an eighty-four-day follow-up.
In both of these preliminary reports, the authors expressed concern
that the endoscopic technique may have a higher rate of complications.
Palmer et al.
19
reported a prospective, nonrandomized study, with a six-month follow-up,
comparing the open method, the single-portal technique, and the
two-portal technique. They noted that both endoscopic techniques
allowed an earlier return to work than the open technique did, but
the two-portal technique resulted in more complications. Since these
initial studies were carried out, there have been technical improvements
in the endoscopic techniques, and subsequent reports have demonstrated
fewer complications
20-22
. However, no independent prospective, randomized trial comparing
the single-portal technique with the open technique has been conducted,
to our knowledge, since many of these technical improvements have
become available. Previous investigators did not use validated outcome
questionnaires that allow an accurate measurement of patient satisfaction
and correlate results with quality of life, return to work, and
physical parameters
23-25
. Furthermore, standardized functional tests that evaluate dexterity
and the ability to use the hand were not used in any prior studies
26-29
.
The purpose of the present prospective, randomized, multicenter,
blind-assessment outcome study was to compare the results of single-portal
endoscopic carpal tunnel release with those of open carpal tunnel
release with use of validated outcome questionnaires, standardized
functional tests, and physical measurements.
One hundred and forty-seven patients, treated at three institutions,
were identified as having idiopathic carpal tunnel syndrome. Forty-five
patients had bilateral involvement, so the study included a total
of 192 hands. The diagnosis of carpal tunnel syndrome was made on
the basis of pain, paresthesias, and/or weakness in the distribution
of the median nerve at the wrist.
The Tinel and Phalen provocative tests were used to assist in the
diagnosis
30
. Electrophysiological confirmation was established with use of
the combined sensory index, which is the sum of three latency differences:
median-ulnar across the palm (palmdiff), median-ulnar to the ring
finger (ringdiff), and median-radial to the thumb (thumbdiff)
31,32
. All patients included in the study met the American Association
of Electrodiagnostic Medicine diagnostic criteria for carpal tunnel
syndrome
31-33
.
All patients either had failure of nonoperative management, consisting
of the use of a wrist splint and/or injections of a steroid compound
into the carpal canal, or refused such a program. The duration of
preoperative treatment, for the patients who consented to it, was
as long as ten years, depending on the presenting symptoms, the
objective findings, and the response to the nonoperative measures
34
. Patients who had recurrent or acute carpal tunnel syndrome, inflammatory
arthropathy, or documented peripheral neuropathy, or who were pregnant,
were excluded from the study. No patient with diabetes had concomitant
evidence of diabetic peripheral neuropathy. Patients under the age
of eighteen years or over the age of seventy-five years were also
excluded, to meet the guidelines of the human subjects committees.
All patients gave written informed consent to participate in the study.
Demographic Data
All patients:
Initially, 161 patients (209 hands) were enrolled in the study. However,
six patients (eight hands) in the endoscopic group and eight patients
(nine hands) in the open-release group were lost to follow-up after
less than one year and were excluded from the study. The average
age of the 147 patients remaining in the study was fifty-six years
(range, twenty-four to seventy-four years). There were ninety-five
women and fifty-two men. The dominant hand was involved in 106 patients.
The duration of symptoms before the operation averaged thirty-two
months (range, four months to eleven years). One hundred and two
patients (127 hands) worked outside the home, and forty-five patients
(sixty-five hands) worked at home or were retired.
Endoscopic group:
There were seventy-five patients (ninety-seven hands) in this group.
The mean age was fifty-six years, and the dominant hand was involved
in fifty-three patients. Forty-eight of the patients were female.
The mean duration of symptoms was twenty-eight months (range, four
months to eight years). Fifty-three patients (seventy hands) worked
outside the home. Forty-four patients (fifty-eight hands) had made
a Workers' Compensation claim that had been approved. Forty-seven patients
had been treated with a splint for six weeks prior to the surgery.
Sixteen patients had been treated with a steroid injection.
Open-release group:
There were seventy-two patients (ninety-five hands) in this group.
The mean age was fifty-six years, and the dominant hand was involved
in fifty-three patients. Forty-seven of the patients were female.
The mean duration of symptoms was thirty-one months (range, four
months to eleven years). Forty-nine patients (fifty-seven hands)
worked outside the home, and forty patients (fifty-one hands) had
made a Workers' Compensation claim that had been approved. Fifty-five patients
had been treated with a splint for six weeks prior to the surgery.
Twenty-one patients had been treated with a steroid injection prior
to the surgery.
Assessment
An observer independent of the surgical team performed an assessment
before each patient was randomly assigned to a treatment group.
For the postoperative assessment, the observer, a research assistant,
was blinded to the type of procedure by placement of a stockinette
over the patient's hand, as described by Brown et al.
2
. Preoperatively, the patients completed the Carpal Tunnel Syndrome
Symptom Severity Score (CTS-SSS) and the Carpal Tunnel Syndrome
Functional Status Score (CTS-FSS)
23,35,36
. These questionnaires ask the patient to rate symptoms on a scale
of 1 to 5, with 1 representing the fewest symptoms or the least
functional difficulty. The mean scores are reported. Overall satisfaction
was rated on a visual analog scale ranging from 1 to 5. Digital
sensibility was measured with use of two-point-discrimination and
Semmes-Weinstein monofilament tests. The patients were assessed
for the presence of thenar atrophy, and the strength of the abductor
pollicis brevis was graded on a scale of 0 to 5, according to the
criteria of the American Orthopaedic Association
37
. The grip strength of the involved and uninvolved hands was measured
with use of all five settings of the Jamar dynamometer (Asimov Engineering,
Los Angeles, California). The maximum grip was used for the statistical
analysis. Key and three-jaw chuck-pinch strength were determined
with a pinch meter (Therapeutic Instruments, Clifton, New Jersey).
To evaluate dexterity, the patients performed a Jebsen-Taylor hand
function test and a Purdue pegboard test prior to surgery. With
the Jebsen-Taylor hand function test, an examiner monitors the time
that it takes for a patient to complete activities that demonstrate
dexterity and coordination using small and large objects
26,38
. The Purdue pegboard test involves the placement of small metal
pegs into a standardized board, with the number of objects correctly
placed in sixty seconds recorded to provide a comparison of preoperative
and postoperative values
28
. Normal values have varied by age and gender in published tables
39-41
.
Postoperatively, the questionnaires and the measurements of strength
and sensibility were repeated, in a blinded fashion, at two, four,
eight, twelve, twenty-six, and fifty-two weeks. In addition, scar
sensitivity was measured with use of a specially constructed plunger
that applies loads of up to 3.0 kg to three regions: at the level
of the distal wrist crease, 2.0 cm proximal to the wrist crease,
and 2.0 cm distal to it (
Fig. 1
). The loads were applied for thirty seconds at each location, and
the lowest load that produced discomfort was recorded.
Randomization
Approval for patient participation in the study was obtained from
the human subjects committee or internal review board of each hospital.
After the decision to proceed with carpal tunnel release had been
made, the procedure to be performed was determined by drawing a
randomly assigned marked slip of paper from an envelope. Patients
with bilateral carpal tunnel syndrome had the procedure that had
been randomly assigned to the first hand performed on the contralateral
hand as well because Agee et al.
12
demonstrated that patients with bilateral disease will not agree
to have a different procedure done on each hand.
Operative Method
Before the initiation of the study, each surgeon had practiced the
technique of endoscopic carpal tunnel release on cadavera and had
also performed the procedure clinically. Three surgeons, one from
each center, were involved in the study. The number of hands operated
on by each surgeon before the study ranged from twenty to 400. The
procedures were routinely performed with regional anesthesia.
Open carpal tunnel release:
The incision is made 2 mm ulnar to the thenar crease, just distal
to the Kaplan oblique line (a line drawn from the apex of the interdigital
fold between the thumb and index finger, toward the ulnar side of
the hand and parallel to the proximal palmar crease, and passing
4.0 to 5.0 mm distal to the pisiform bone), and extended 3.0 to
4.0 cm proximally toward the distal wrist crease (
Fig. 2
). The superficial palmar fascia, transverse carpal ligament, and
antebrachial fascia are divided under loupe magnification. The tourniquet
is deflated after the wound is closed with monofilament sutures.
In this series, neither tenosynovectomy nor neurolysis was performed.
Single-portal endoscopic carpal tunnel release:
A device designed by Agee, to minimize the scarring in a patient
who was dependent on crutches, was used
12
. A 1.0-cm transverse incision is made at the level of the distal wrist
crease in the center of the volar aspect of the wrist. The incision
is centered over the palmaris longus if it is present. The palmaris
longus is retracted radially to protect the palmar cutaneous branch
of the median nerve. Scissors are used to make a distally based
flap in the flexor retinaculum. The median nerve is identified deep
to the retinaculum, and a synovial elevator is used to reflect the
synovial tissue from the undersurface of the transverse carpal ligament
(
Fig. 3
). Dilators are used to provide a space for the Agee device (3M,
St. Paul, Minnesota). The device is inserted to a depth of <3.0
cm to avoid injury to the superficial palmar arch or the common
digital nerve to the fourth web space (
Fig. 4
). The sheath of the device is maintained tightly against the transverse
carpal ligament to protect the median nerve. Once the device is
in place, its trigger is depressed to elevate the blade, and then
the device is withdrawn to release the transverse carpal ligament.
Several passes may be required when the transverse carpal ligament
is very thick. A Ragnell retractor is used to protect the distal
skin edge from laceration by the blade of the device (
Fig. 5
). The forearm flexor retinaculum can be released under direct vision
with scissors. The incision is closed with monofilament sutures.
Time and Cost
The time from inflation of the tourniquet to transport of the patient
from the operating room was recorded for each procedure. Surgeon's
fees, anesthesia fees, and costs of equipment (including endoscopy
blades) as well as operating-room and all other costs incurred by
the patient on the day of the operation were recorded. Intravenous
regional anesthesia was used routinely at all three study sites,
which helped to standardize the costs.
Postoperative Regimen
Postoperatively, the hand was placed in a bulky dressing; no splints
were used. The patients were allowed to use the hand for light activities
for the first two weeks after surgery. At two weeks, the dressings
and sutures were removed and the patients were instructed to perform
a specific written set of hand exercises. No hand therapy was prescribed
unless there were early signs of reflex sympathetic dystrophy; two
patients had such signs after open release.
Statistical Analysis
Analysis of covariance was performed for comparison of outcomes
at each postoperative interval. Repeated-measures analysis of covariance
were used to compare the results of the two groups. Cochran-Mantel-Haenszel
tests were used to compare ordinal values, and Kaplan-Meier survivorship
analysis was used to compare return to work and function. The quantitative
variables are reported as means and standard deviations. The reported
p values are two-sided. Power analysis was performed so that, for
continuous variables, there was an 80% chance of detecting a significant
difference (p < 0.05) if the true difference was as great as
0.4 times the standard deviation.
Patient Demographics
Seventy-two patients (ninety-five hands) had open carpal tunnel
release, and seventy-five patients (ninety-seven hands) had endoscopic
carpal tunnel release. We found no significant differences between
the two groups with respect to age, gender, handedness, duration
of symptoms, electrodiagnostic findings, frequency of outside work,
number of Workers' Compensation claims, or bilaterality.
Electrodiagnostic Studies
Preoperatively, the sensory latency averaged 4.6 msec and the motor
latency averaged 5.6 msec in the endoscopic group. In the group
treated with open carpal tunnel release, the sensory latency averaged
4.9 msec and the motor latency averaged 5.5 msec. Electromyograms
demonstrated positive findings in nine hands (seven patients) in
the endoscopic group and eleven hands (ten patients) in the open-release
group.
Outcome Measurements
Preoperatively, the Carpal Tunnel Syndrome Symptom Severity Score
averaged 3.1 for the patients in the open-release group and 3.2
for the patients in the endoscopic group (
Table I
). In both groups, the scores improved throughout the follow-up
period, with a mean fifty-two-week score of 1.8 in each group. However,
at two weeks, four weeks, two months, and three months, the patients
in the endoscopic group had significantly lower (better) scores
(p < 0.01).
The Carpal Tunnel Syndrome Functional Status Score averaged 2.7
preoperatively in both groups. The score improved continuously throughout
the follow-up period in the endoscopic group. However, in the open-release
group, improvement was not noted until the fourth week and significant differences
from the endoscopic group were noted at the two-week, four-week,
two-month, and three-month follow-up periods (p < 0.01). Ultimately,
the score in both groups improved to 1.7.
The overall patient satisfaction score was quite good, even at the
two-week follow-up point, at which time it was 4.2 in the endoscopic
group and 3.3 in the open-release group, which was a significant
difference (p < 0.05). Both groups had a gradual increase in
satisfaction until the twenty-six-week follow-up interval. At one
year, the patient satisfaction scores were 4.6 in the endoscopic
group and 4.5 in the open-release group, which was not a significant
difference.
Evaluation of Sensation
Prior to surgery, the mean score for the Semmes-Weinstein monofilament
evaluation of the median nerve distribution was 4.17 in the open-release
group and 4.19 in the endoscopic group. Postoperatively, the sensation
in both groups improved significantly (p < 0.05) but no significant
difference was found between the two groups (p = 0.26), a finding
that was similar to that of Agee et al.
12
. The final sensibility measured 3.26 in the endoscopic group and
3.20 in the open-release group.
Scar Sensitivity
Preoperatively, both groups could withstand loads of up to 3.0 kg
without discomfort. Two weeks after surgery, the endoscopic group
tolerated loads of 2.3 kg whereas the open-release group tolerated
loads of 1.3 kg (p < 0.05). In the endoscopic group, the scars
remained significantly less tender than those in the open-release
group until the third postoperative month. Even at a year after
surgery, both groups had equally mild persistent scar tenderness.
Grip and Pinch Strength
Preoperatively, the grip strength averaged 31 kg in the endoscopic
group and 33 kg in the open-release group. Two weeks after surgery,
the grip strength had decreased significantly in both groups (p < 0.05),
to 21 kg in the endoscopic group and to 15 kg in the open-release
group. The patients in the endoscopic group then recovered grip
strength faster than did those in the open-release group until the
three-month follow-up examination (p < 0.05), when the grip
strengths in both groups approached preoperative levels. At the
time of final follow-up, the patients in the open-release group
had a grip strength of 34 kg and those in the endoscopic group had
a grip strength of 32 kg. The findings for key pinch strength paralleled
those for grip strength. Preoperatively, the patients in the endoscopic
group had a key pinch strength of 7.3 kg, and the patients in the
open-release group had a key pinch strength of 7.4 kg. At the two-week
follow-up evaluation, key pinch strength had decreased to 6.2 kg
in the endoscopic group and to 5.7 kg in the open-release group
(p < 0.05). Both groups continued to improve with regard to
this variable, although the patients in the endoscopic group improved
more quickly. By the third postoperative month, the final key pinch
strength (7.9 kg in the endoscopic group and 8.1 kg in the open-release group)
exceeded the preoperative value in both groups.
The preoperative three-jaw chuck-pinch strength averaged 6.5 kg
in the endoscopic group and 4.7 kg in the open-release group. The
endoscopic group had faster recovery of this strength (p < 0.05)
until the third postoperative month, when the strength exceeded
the preoperative measurement in both groups. At the final follow-up
evaluation, the three-jaw chuck-pinch strength was 6.9 kg in the
endoscopic group and 6.7 kg in the open-release group.
Purdue Pegboard and Jebsen-Taylor Dexterity
Tests
Preoperatively, the mean composite Jebsen-Taylor score was forty-one
seconds in the series as a whole. At the two-week postoperative
evaluation, the mean score had increased to fifty-seven seconds
in the open-release group and to fifty-one seconds in the endoscopic
group. The endoscopic group continued to improve more quickly than
the open-release group (p < 0.05) until the three-month follow-up
period, when both groups had a mean score of forty-four seconds.
At the final follow-up evaluation, the endoscopic group had a score
of thirty-nine seconds and the open-release group had a score of forty-one
seconds.
Neither group showed significant improvement in the ability to
perform the Purdue pegboard test until four weeks after surgery.
Prior to surgery, the endoscopic group had a score of sixteen pegs
and the open-release group had a score of eighteen pegs. Two weeks
after surgery, the endoscopic group had a score of eleven pegs and
the open-release group had a score of twelve pegs. At four weeks,
the scores were seventeen and thirteen pegs, respectively, which
was a significant difference (p < 0.05). By the third postoperative
month, both groups had a score of twenty pegs, which did not improve
further during the remainder of the study.
Return to Work
The median time until the patients returned to work was thirty-eight
days (range, fourteen to eighty-four days) in the open-release group
compared with eighteen days (range, three to fifty-six days) in
the endoscopic release group; this was a significant difference
(p = 0.0086). All of the forty-five patients who had bilateral carpal
tunnel release had the procedures performed at different times,
and their ability to return to work after each procedure was rated
separately.
Time and Cost
The mean time from the administration of anesthesia to the removal
of the patient from the operating room was forty-two minutes in
the endoscopic group and forty-nine minutes in the open-release
group. The mean cost was $3940 for the open carpal tunnel releases
and $3750 for the endoscopic carpal tunnel releases. There was no
significant difference in overall cost.
Complications
None of the patients had a nerve or artery injury. Symptoms consistent
with reflex sympathetic dystrophy, with swelling, redness, and increased
sweating, developed in two patients in the open-release group. In
one, the symptoms were mild and resolved after a brief course of
physical therapy. In the other patient, the symptoms were more protracted
and a regular therapy program as well as the use of nortriptyline
was required. The patient ultimately returned to her regular work. One
patient treated with an open carpal tunnel release required revision
surgery because of persistent symptoms, which resolved following
the second operation. Electrodiagnostic studies of this patient
demonstrated latency periods that actually were more prolonged than
the preoperative latency periods. This occurred even though a 1-cm
separation of the segments of the transverse carpal ligament had
been documented at the initial operation.
None of the fourteen patients (seventeen hands) who were excluded
from the study because of inadequate follow-up had complications
that we could determine from a chart review.
Endoscopic carpal tunnel release was introduced to reduce the morbidity
associated with the open method of carpal tunnel release. Several
studies have indicated that the endoscopic method provides relief
of numbness and paresthesias in a similarly high percentage of patients
and that both procedures are highly effective
12-16
.
Analysis of the primary outcomes in this study demonstrates that
the patients who had undergone endoscopic release had greater relief
of symptoms, improvement in function, and satisfaction for the first
three months following the surgery. Furthermore, they had faster
recovery of both grip and pinch strength, findings that agree with
those in the nonrandomized study performed by Palmer et al.
19
.
Previous studies have suggested that open carpal tunnel release
is associated with considerable morbidity, including prolonged tenderness
of the scar and weakness of grip for as long as three to six months
after the operation
7,8,10,42,43
. The rationale for the development of the endoscopic method was
to improve the major functional outcomes (tenderness of the scar,
grip strength, activities of daily living, and return to work).
In our study, tenderness of the scar was found to be greater in
the patients in the open-release group than in those who had undergone
endoscopic release. We presume that a major factor in this regard
is the fact that the palmaris brevis muscle and the palmar fascia
are not divided with the endoscopic technique but are with the open-incision
technique (
Fig. 6
).
One of the most important functional outcomes is the interval between
the operation and the patient's resumption of activities of daily
living and work. In one previous study, industrial employees lost
an average of fifty-four days of work after open carpal tunnel release
43
. In contrast, Chow, who retrospectively studied the results of endoscopic
carpal tunnel release in 456 patients, noted that 269 (59%) returned
to normal activity and work after two weeks and 392 (86%) returned
after four weeks
13
. As in previous studies of endoscopic carpal tunnel release
2,12,13
, our patients with a single-portal endoscopic release returned to
work earlier than did those with an open release.
The safety of the endoscopic technique has been a major concern.
Although one isolated report focused on the risks involved in endoscopic
surgery
44
, these findings were not borne out in larger, prospective, multicenter
trials
12,19,20
. No complications occurred with the endoscopic technique in our
study. Three patients in the open-release group had complications,
but all three had resolution of those symptoms either with therapy
or with revision carpal tunnel release. The two factors that we
think reduced the rate of complications were the achievement of
adequate anesthesia and a team that was familiar with fiberoptic-assisted
surgery.
This study provides evidence that endoscopic surgery can be performed
as fast as open surgery without an increased prevalence of complications.
As a result, endoscopic release does not increase medical expenses
and can decrease socioeconomic costs because the patient returns
to work in a shorter period of time. We concluded that endoscopic
carpal tunnel release is a safe and cost-effective technique that,
compared with open carpal tunnel release, improves patient outcome
in the first three months following treatment.