Abstract
Background: An objective test is needed to evaluate outcome
following carpal tunnel release. A method to evaluate sensory and motor
function related to carpal tunnel syndrome was investigated.
Methods: Thirty-six candidates for carpal tunnel surgical procedures
underwent a physical examination and nerve-conduction studies and completed a
survey regarding symptoms. A battery of psychomotor and sensory tests was
administered bilaterally immediately before surgery and again six weeks after
surgery. The outcome variables included dynamic sensory gap-detection
thresholds and rapid pinch-and-release rates.
Results: The average gap-detection threshold for the index finger in
the surgical-treatment group demonstrated a 43% improvement, decreasing from
0.14 mm preoperatively to 0.08 mm at six weeks postoperatively (p < 0.01).
The average gap-detection threshold for the index finger in the
non-surgical-treatment group demonstrated no significant improvement,
decreasing from 0.10 mm preoperatively to 0.08 mm postoperatively (p = 0.10).
With the upper force level set at 10% of the maximum voluntary contraction,
the average pinch rate in the surgical-treatment group demonstrated a 20%
improvement, increasing from 6.65 pinches per second preoperatively to 7.96
pinches per second postoperatively (p < 0.001). The average pinch rate in
the non-surgical-treatment group demonstrated a 7% improvement, increasing
from 6.89 pinches per second preoperatively to 7.37 pinches per second at six
weeks postoperatively (p < 0.05).
Conclusions: Measurable and significantly greater improvement was
observed when the surgical-treatment group was compared with the
non-surgical-treatment group in terms of these two sensory and psychomotor
functional testing outcomes at six weeks.
Level of Evidence: Therapeutic study, Level II-1
(prospective cohort study). See Instructions to Authors for a complete
description of levels of evidence.
The diagnosis of carpal tunnel syndrome frequently results in surgery and
prolonged work
disability1,2.
In 1999, among major disabling workplace injuries and illnesses, carpal tunnel
syndrome resulted in the highest median number of days away from work
(twenty-seven) in the United States. Nancollas et al. found that six of
twenty-two individuals who reported work-related carpal tunnel syndrome
changed from heavy to lighter work following
surgery3. Katz et
al.4 found that
extended absence from work correlated with a worsening functional status of
the hand as measured with use of a self-administered
questionnaire5. An
objective measure to quantify functional changes associated with carpal tunnel
syndrome could quantify recovery and functional improvement and could permit
quantitative evaluation of the capacity to return to work. The effect of work
modifications on carpal tunnel syndrome could also be monitored.
A computer-controlled battery of tests for measuring subtle sensory and
psychomotor deficits associated with carpal tunnel syndrome was
developed6-8.
The performance measures in these tests were based on functional activities
performed in occupational tasks, such as tactually inspecting a surface for a
defect or repeatedly pressing a key. The sensory test involved detecting a
computer-controlled gap on a highly polished surface with use of the index
finger pad, which is innervated by the median
nerve6. The
psychomotor task was a rapid pinch-and-release task involving specific median
nerve-innervated muscles of the hand, including the index finger and thumb,
that utilize proprioceptive and force feedback from afferent median nerve
branches distal to the carpal
tunnel7,9.
The outcome of these tests can provide a quantitative assessment of function
in manual tasks. Previous studies have demonstrated that this battery of
sensory and psychomotor tests can differentiate patients with well-defined
carpal tunnel syndrome from confirmed normal
subjects7,10
and also can differentiate workers with carpal tunnel syndrome from controls
in an industrial working
population11.
The purpose of the present study was to evaluate the results of these
psychomotor and sensory tests in patients undergoing unilateral carpal tunnel
release in order to quantify functional aspects of rehabilitation aimed at
return to work. The contralateral hand was used as the control. Specifically,
we hypothesized that the hands that received surgical treatment would show
greater improvement in sensory and psychomotor performance than those that did
not receive surgical treatment.
Patients
Participants were recruited sequentially from the office of two hand
surgeons (S.V.Z. and S.L.O.) who assisted in subject recruitment from a clinic
in the Midwestern United States. All subjects were scheduled to undergo
unilateral carpal tunnel release, and all had findings on examination and on
nerve-conduction studies that were consistent with carpal tunnel syndrome. A
distal median sensory latency of >2.5 ms was considered to be abnormal.
Motor and sensory latencies in the distributions of the median and ulnar
nerves were compared. Electromyographic data were used to correlate the
findings regarding nerve-conduction velocities. Patients with proximal
abnormalities were excluded.
Study participants were scheduled to undergo carpal tunnel release in only
one hand during the course of the study. Each hand was used as its own control
for the evaluation of changes that occurred longitudinally following surgery.
The contralateral hand was used as a control to compare the effects of elapsed
time without surgical intervention. Some subjects reported bilateral symptoms
of carpal tunnel syndrome but underwent surgical treatment of only one hand.
Although some subjects may have had other maladies in addition to carpal
tunnel syndrome, all of the patients in the study group claimed that the
carpal tunnel symptoms predominated.
Volunteer participants provided informed consent and were compensated $15
for their service at each session. Subjects were not compensated on the basis
of their performance. The protocol was reviewed and approved by both
university and hospital institutional review boards. Subjects were informed
that the goal of the study was to evaluate their performance and the nature of
the tasks that they were performing, but they were not advised with regard to
how performance was to be quantified or with regard to the expected outcomes
of the study. Subjects were not provided feedback on their performance.
The majority of subjects were tested immediately before or after their
scheduled physician appointments. Subjects were tested one to two days before
surgery and at the time of their scheduled six-week return visit, which took
place six to eight weeks postoperatively. A total of seventy-two hands were
tested in thirty-six subjects (ten men and twenty-six women). The mean age of
the subjects was 49.0 ± 13.5 years (range, twenty-six to eighty-five
years). Five subjects had filed Workers' Compensation claims. Thirty subjects
were right-hand dominant, and six were left-hand dominant. The surgical
procedure was performed on the dominant hand in twenty-three patients (64%).
Fifteen patients (42%) underwent endoscopic carpal tunnel release with use of
the two-portal Chow
technique12. The
remaining twenty-one patients underwent open carpal tunnel release through a
small incision distal to the wrist crease.
Finger motion was encouraged immediately after surgery. Sutures were
removed seven to ten days after surgery. Strengthening exercises with use of
putty were started at three weeks after surgery. Patients were encouraged to
exercise both hands.
Data Collection
Preoperatively and postoperatively, all subjects completed a survey that
included questions about symptoms in the upper extremities, occupation, and
medical history (with specific questions pertaining to diabetes, arthritis,
thyroid disease, cervical disc rupture, and renal failure). Specific
information also was obtained with regard to the frequency, duration, and
magnitude of symptoms (such as numbness, tingling, or pain) in the hand. Each
subject also completed a self-reported hand diagram. The intensity of symptoms
was measured by asking subjects to rate the symptoms on a scale of 1 to 5,
with 1 indicating "no pain at all" and 5 indicating "worst
pain ever." The frequency of symptoms was measured by asking subjects to
rate the symptoms on a scale of 1 to 6, with 1 indicating that the symptoms
occurred "almost never (every six months)" and 6 indicating that
they occurred "almost always (daily)."
The psychomotor and sensory testing apparatus is shown in
Figure 1. The automated
aesthesiometer, fully described in a previous report by one of us (R.G.R.) and
colleagues6,
measured tactile sensitivity as the finger freely probed a tiny gap on an
otherwise smooth
surface6,8.
Gap-detection sensory thresholds were used to estimate the minimum separation
needed to detect the gap. Both the index and the small finger were tested in
each hand. This allowed for comparisons between areas innervated by the median
and ulnar nerves. Subjects probed the gap for five seconds. Gap size was
changed with use of a micropositioner and digital encoder that were controlled
by a microcomputer. Contact force was controlled at 50 g. A white-noise
auditory signal masked the noise of the motor so that the subject would not be
aware if movement of the plates had occurred. As the gap size was changed, the
subject responded verbally if he or she could detect a gap with use of a
converging-staircase method-of-limits psychophysical paradigm in which the
subject is presented with a titrating series of stimuli that ascend and
descend in magnitude by progressively smaller increments every time the gap is
detected by the
subject6. The
threshold is the average of the upper and lower gap sizes. The software was
programmed to randomly introduce catch trials to test whether the subject was
cooperating.
The rapid pinch-and-release test measured psychomotor performance in terms
of speed and force
control7. An
aluminum strain-gauge dynamometer was pinched with use of the index finger and
the thumb13. The
objective of the pinch-and-release test was to pinch the dynamometer with a
force greater than an upper level (Fupper) and then to release at a
force less than a lower level (Flower) as quickly as possible. A
pinch-strength test was first conducted to ascertain the maximum voluntary
contraction level. The subjects then performed the test with use of alternate
hands and completed two tests for each hand (with Fupper being set
at 10% and 20% of the maximum voluntary contraction); Flower was
fixed at 4% of the maximum voluntary contraction for all tests. One-half of
the subjects were tested with Fupper set at 20% of the maximum
voluntary contraction first, and one-half were tested with Fupper
set at 10% of the maximum voluntary contraction first.
Statistical Analysis
The data were analyzed for differences between and within the
surgical-treatment and non-surgical-treatment groups with regard to
gap-detection thresholds and pinch rates. A full factorial analysis of
variance14 with
repeated measures was used to evaluate the significance of the differences in
functional performance variables, gap-detection thresholds, and pinch rates
when the hands in the surgical-treatment group were compared with those in the
non-surgical-treatment group as well as when the preoperative values were
compared with the postoperative values. The level of significance was set at p
< 0.05.
The preoperative and postoperative gap-detection thresholds for the index
finger are shown in Figure 2.
Preoperatively, the average gap-detection threshold for the index finger was
40% larger in the surgical-treatment group than in the non-surgical-treatment
group (0.14 mm compared with 0.10 mm; p < 0.05). In the surgical-treatment
group, the average gap-detection threshold for the index finger improved by
43%, from 0.14 mm preoperatively to 0.08 mm postoperatively (p < 0.01). In
the non-surgical-treatment group, the average gap-detection threshold for the
index finger improved by only 20%, from 0.10 mm to 0.08 mm (p = 0.10).
Postoperatively, no significant difference was observed between the
surgical-treatment group and the non-surgical-treatment group with regard to
the average gap-detection threshold (0.08 for both groups; p > 0.05).
The preoperative and postoperative gap-detection thresholds for the small
finger also are shown in Figure
2. In the surgical-treatment group, the average gap-detection
threshold for the small finger improved by 22%, from 0.09 mm preoperatively to
0.07 mm postoperatively (p < 0.01). In the non-surgical-treatment group,
the average gap-detection threshold for the small finger did not change,
measuring 0.08 at both time-points (p = 0.09).
The preoperative and postoperative pinch rates with Fupper set
at 20% and 10% of the maximum voluntary contraction are presented in
Figure 3. With
Fupper set at 20% of the maximum voluntary contraction, the average
pinch rate in the surgical-treatment group improved by 18%, from 5.62 pinches
per second preoperatively to 6.63 pinches per second at six weeks
postoperatively (p < 0.001). With Fupper set at 10% of the
maximum voluntary contraction, the average pinch rate in the
surgical-treatment group also improved by 20%, from 6.65 pinches per second
preoperatively to 7.96 pinches per second postoperatively (p < 0.001). With
Fupper set at 20% of the maximum voluntary contraction, the average
pinch rate in the non-surgical-treatment group improved by 7%, from 5.76
pinches per second preoperatively to 6.14 pinches per second postoperatively
(p < 0.05). With Fupper set at 10% of the maximum voluntary
contraction, the average pinch rate in the non-surgical-treatment group also
improved by 7%, from 6.89 pinches per second preoperatively to 7.37 pinches
per second postoperatively (p < 0.05). No significant differences in
average pinch rates were observed between the surgical-treatment and
non-surgical-treatment groups before or after surgery (p > 0.05)
(Fig. 3).
No significant changes in maximum voluntary contraction were observed in
either the surgical-treatment group or the non-surgical-treatment group (p =
0.20). Preoperatively, the average maximum voluntary contraction (and standard
deviation) was 42.14 ± 14.6 N in the surgical-treatment group and 45.06
± 16.3 N in the non-surgical-treatment group. Postoperatively, the
average maximum voluntary contraction in the surgical-treatment group
decreased by 8% (to 38.68 ± 15.7 N) whereas that in the
non-surgical-treatment group increased by 2% (to 46.09 ± 15.6 N).
The intensity and frequency of symptoms decreased following surgery. The
average symptom-intensity score in the surgical-treatment group improved
significantly, from 3.35 before surgery to 1.83 after surgery (p < 0.01).
The average symptom-intensity score in the non-surgical-treatment group also
improved significantly, from 2.11 before surgery to 1.71 after surgery (p <
0.01). The average symptom-frequency score in the surgical-treatment group
improved significantly, from 5.81 before surgery to 3.68 after surgery (p <
0.01) (Fig. 4). The average
symptom-frequency score in the non-surgical-treatment group also improved
significantly, from 3.68 before surgery to 2.65 after surgery (p < 0.05)
(Fig. 4). No significant
differences in the intensity or frequency of symptoms were observed following
surgery between the surgical-treatment group and the non-surgical-treatment
group (p > 0.05). The correlations between the intensity of symptoms and
the gap-detection threshold for the index finger (r = 0.371, p < 0.001),
the pinch rate with Fupper set at 20% of the maximum voluntary
contraction (r = —0.314, p < 0.001), and the pinch rate with
Fupper set at 10% of the maximum voluntary contraction (r =
—0.264, p < 0.01) were significant but small. Similar correlations
were observed between the frequency of symptoms and the gap-detection
threshold for the index finger (r = 0.224, p < 0.01), the pinch rate with
Fupper set at 20% of the maximum voluntary contraction (r =
—0.322, p < 0.001), and the pinch rate with Fupper set at
10% of the maximum voluntary contraction (r = —0.262, p < 0.01).
Improvement in the results of both sensory and psychomotor functional tests
was observed six weeks following carpal tunnel release. The magnitude of
change in functional performance on the psychomotor and sensory tests ranged
from 18% to 43% in the surgical-treatment group and from 7% to 20% in the
non-surgical-treatment group. It is interesting to note that many of the
subjects either were on restricted duty or were off work following surgery
(average time to return to work, 3.5 weeks). The sustained rest and reduction
in physical activities following surgery may have contributed to the
improvement in the sensory function of the index and small fingers in the
non-surgical-treatment group.
Although no significant differences between the surgical-treatment and
non-surgical-treatment groups were observed before or after surgery, this
effect may be due to the fact that many of the subjects reported having
symptoms of carpal tunnel syndrome bilaterally. Subjects who were either on
restricted duty or off work following surgery may have had an overall
reduction in stress for both hands.
The level of activity decreased in all patients after surgery because the
patients were kept out of work for two to four weeks. We believe that this
period of rest benefitted the hands in both the surgical-treatment and
non-surgical-treatment groups. The improvements in performance in the
non-surgical-treatment group were not as great as those in the
surgical-treatment group. The benefit was only temporary in most patients who
later went on to have surgery on the contralateral side. Within one year,
eighteen patients (50%) underwent subsequent surgery on the contralateral
hand. The differences and improvements that were observed in the
non-surgical-treatment group indicate that the test battery may be sensitive
to subtle recovery following conservative treatment involving rest. Even
greater improvement was observed following surgery. Future studies should
follow patients for a longer period of time after surgery, particularly in
cases of bilateral carpal tunnel syndrome.
Another possible explanation for the improved performance that was observed
in both the surgical-treatment and non-surgical-treatment groups is that the
improvements that were noted at the time of the retest may have been due to
learning or training effects rather than to improved nerve function. Jeng et
al.7 found no
significant changes in performance when subjects repeated the rapid
pinch-and-release test one week after the initial test. Similar results were
observed for the tactility
test8. Therefore, a
training effect was not anticipated in the current study.
With regard to the sensory improvements that were observed in the small
finger, previous investigators have observed that distal ulnar nerve
compression can be improved with carpal tunnel release, which may improve
function in the ulnar distribution. Silver et
al.15 observed that
patients with carpal tunnel syndrome had sensory abnormalities of both the
median and the ulnar nerve on either two-point discrimination testing,
Semmes-Weinstein monofilament testing, or both. Most patients had improvement
in the function of both the median and the ulnar nerve after carpal tunnel
release alone. The current study affirms that observation.
The current study did not include a control group of healthy subjects;
however, in previous
studies7,8,
healthy volunteers have been extensively evaluated with both of these tests.
Small effects of hand dominance (8%) and age (6%) were previously observed on
the pinch test. These effects are much smaller than the improvements that were
observed after surgery in the current study.
A history, physical examination, and nerve-conduction studies are all part
of the standard evaluation for the diagnosis of carpal tunnel
syndrome16-18.
Nerve-conduction studies are rarely repeated following surgery because of the
perceived noxious nature of the test and its associated costs. The psychomotor
and sensory tests described in the present study may provide an alternative,
noninvasive measure to quantify recovery.
The results of the present study indicate that the battery of psychomotor
and sensory tests may be useful for monitoring functional improvement
following surgical, medical, and ergonomic interventions. This information is
useful because worsening upper-extremity functional status has been reported
to be a predictor of absence from
work4. The observed
changes were measured over a relatively short time-interval (six weeks)
following surgery. Future studies should also measure functional changes for a
longer period (such as six months) following surgery.
Although group differences were observed, the functional importance of
performance in these tests on an individual basis is not yet known. It is
notable that although significant correlations were observed between the
psychomotor and sensory function measures used in this study and the intensity
and frequency of symptoms, these correlations were small. This finding
suggests that functional performance and symptoms are not directly related,
indicating that objective functional measures, such as the psychomotor and
sensory measures used in this study, provide additional information regarding
rehabilitation from surgery.
The ability of patients to return to work, and variables that supported or
prevented patients from returning to work, were not evaluated in this study.
These topics should be investigated in future studies. It is possible that a
quantitative evaluation of functional recovery following surgery for carpal
tunnel syndrome may be beneficial for assessing rehabilitation and the
capacity to work.
Note: The authors thank Dr. Steven L. Oreck, Ms. Becky J.
Rockhill, and Ms. Carol J. Harm for their assistance in this study.
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