Abstract
Purpose
The purpose of this study was to evaluate the association between preoperative ultrasound, nerve conduction studies (NCS), and/or carpal tunnel syndrome-6 (CTS-6) scores and the postoperative courses of patients undergoing carpal tunnel release (CTR).
Methods
This was a retrospective study of all patients indicated for CTR at a single institution between October 2014 and August 2021. Preoperative data, including age, sex, body mass index, and laterality of the involved hand(s), were collected. Ultrasound was performed with a median nerve cross-sectional area (CSA) of ≥10 mm2 considered positive for CTS. Nerve conduction studies evaluated the distal sensory and motor latencies of the median nerve. Carpal tunnel syndrome-6 scores ≥12 were considered positive for CTS. The primary outcome measurement was the Boston Carpal Tunnel Questionnaire (BCTQ). Statistical analysis was performed to assess the correlation of preoperative studies to predict changes in postoperative BCTQ scores following CTR. Statistical significance was set to P < .05.
Results
In total, 106 patients were included in the analysis, of which 69 patients were positive for CTS on US with an average median nerve CSA of 15.2 ± 4.4 mm2, whereas 37 patients were negative with an average CSA of 9.0 ± 1.3 mm2 (P < .001). Female sex, height, and weight were significantly different between the CTS-positive and -negative cohorts (P = .01, P = .02, and P = .01). Preoperative US, NCS, and CTS-6 were not associated with the ability to achieve minimal clinically important difference in change in BCTQ scores after surgery.
Conclusions
Although helpful in establishing a diagnosis of CTS, positive findings on preoperative US, NCS, and CTS-6 alone are not associated with clinically significant changes in BCTQ symptom or function scores up to 1 year after surgery following CTR.
Type of study/level of evidence
Prognostic IV.
Key words: Carpal tunnel, CTS-6, Nerve studies, Patient outcomes, Ultrasound
Carpal tunnel syndrome (CTS) is the most common compressive neuropathy, with a prevalence of approximately 3% in the general adult population of the United States.1,2 Carpal tunnel release (CTR) has become a routine treatment for CTS, being performed over 400,000 times per year.3 Ultrasonography (US), nerve conduction studies (NCS), and the CTS-6 score are all diagnostic tools that have been shown to detect CTS with varying degrees of sensitivity and specificity.4, 5, 6 Although NCS remains the most commonly used test for diagnosing CTS, recent emphasis on patient-oriented and cost effective care has increased the validity of using ultrasound as part of the diagnostic criteria for CTS.7,8 There is evidence that US and NCS together yield the best diagnostic capability than either test alone,9 with US being more accurate than NCS and the preferred confirmatory test for CTS in certain settings.10
Although the diagnostic performance of US, NCS, and CTS-6 has been investigated extensively, the potential for these tests to be used as prognostic tools is less known. The prognostic value of US on patient-reported outcomes (PROs) has been inconclusive, with conflicting evidence of such capabilities of US following CTR.11, 12, 13, 14, 15 Prior literature has identified that preoperative NCS measurements could be a tool to predict improvement of CTS after CTR, but more recent literature has contradicted this conclusion.16, 17, 18 Preoperative clinical diagnostic tools like CTS-6 have been shown to have no predictive value for patients.19 Because of these inconsistencies in the literature, further research with preoperative US, NCS, and CTS-6 measurements and subsequent PROs may demonstrate whether these diagnostic tests are associated with meaningful recovery after CTR.
Therefore, the aim of this study was to analyze for potential associations between preoperative US, NCS, and/or CTS-6 findings and changes in BCTQ scores up to 1 year in patients undergoing CTR. We hypothesized that preoperative US, NCS, and CTS-6 findings are not correlated to improvement in BCTQ scores following CTR.
Materials and Methods
This was a retrospective study of all patients who were indicated for CTR at a single institution by a single surgeon (the senior author) between October 2014 and August 2021. Approval from the institutional review board was granted to retrospectively review patients’ medical records under STUDY2007308. Patients presenting with hand numbness, paresthesias, and/or pain in the median nerve distribution were indicated for the evaluation of CTS and were reviewed for study inclusion. Patients diagnosed with CTS were indicated for CTR if their symptoms failed to resolve with conservative, nonsurgical management or if their symptoms were severely impacting their quality of life. Patients with complete preoperative demographics in addition to US, NCS, and CTS-6 measurements at 6 weeks, 6 months, and 1 year after surgery were included in this study. Patients with incomplete preoperative data or loss to follow-up were excluded.
Preoperative data, including age, sex, body mass index (BMI), and laterality of the involved hand(s), were collected using the electronic medical record. Ultrasonography was conducted by a fellowship-trained hand surgeon, with the patient’s affected arm supine resting on a table at 70° flexion. A 15-16 MHz linear array transducer was used to measure the cross-sectional area (CSA) of the median nerve in square millimeters at the level of the wrist crease using the trace function. Based on previous literature, median nerve CSA of 10 mm2 or greater was considered positive for CTS.4,20 Nerve conduction studies were performed by a board-certified electrophysiologist measuring the distal motor latency (DML) and distal sensory latency (DSL) at 5–13 cm segments over the median nerve. Nerve conduction study measurements were considered positive for CTS if median nerve DML ≥ 4.0 ms or DSL ≥ 3.5 ms.21 Carpal tunnel syndrome-6, a validated diagnostic tool for CTS, was recorded by a board-certified physician, with a CTS-6 score ≥ 12 considered positive for CTS.22
Ultimately, CTS is a clinical diagnosis that combines reported symptoms and physical findings. Although positive findings with any of the preoperative tools can aid in making a CTS diagnosis, for the purposes of this study, patients were divided into CTS-positive and -negative groups based on median nerve ultrasound measurements. Ultrasound was chosen, as this is the senior author’s standard of care to perform ultrasound on each patient presenting for carpal tunnel evaluation.
PRO measures
The primary outcome measurement in this study was the Boston Carpal Tunnel Questionnaire (BCTQ), consisting of an 11-item symptom severity scale (SSS) and an 8-item functional severity scale (FSS).23 The SSS and FSS are calculated by averaging the responses of each survey, giving a score between 1 and 5, to measure patient symptoms and functional hand health. Patients filled out this questionnaire during the preoperative visit and at each subsequent follow-up at 6 weeks, 6 months, and 1 year. The minimal clinically important difference (MCID) for the relative change in scores in the postoperative period compared with a baseline based on previous literature was determined to be 0.46 for SSS and 0.28 for FSS.24
Statistical analysis
Statistical analysis was performed using R (R Core Team. Released 2022). Summary statistics for demographic and clinical variables are shown as n (%) for categorical variables and mean (±SD) for continuous variables. Patients were then split into two groups based on preoperative US median nerve measurements defined as either US-positive or -negative based on a 10 mm2 cutoff. Between these groups, age, sex, height, weight, BMI, US median nerve CSA, NCS-DML, NCS-DSL, NCS-positive, CTS-6 score, CTS-6-positive, and follow-up time were compared using either χ2 tests for categorical variables or two-sample t test for continuous variables. Then, the absolute change of BCTQ scores (absolute change = BCTQ score at “x” time point after surgery—preoperative BCTQ score) was calculated between patients who were preoperatively classified as US-positive or -negative, NCS-positive or -negative, and CTS-6-positive or -negative. Correlation analysis was also used to characterize the relationship between the number of preoperative positive tests and absolute change in BCTQ scores.
Generalized estimating equations logistic regression models were created to assess the association between risk factors and postoperative improvements in repeated measures of BCTQ.25,26 Improvement in repeated measures of BCTQ was defined as whether the relative difference between preoperative scores compared with each of the 6-week, 6-month, and 1-year postoperative time points achieved MCID.24 Separate generalized estimating equation (GEE) logistic regression models were created for both the SSS and FSS components of BCTQ. First, univariate GEE logistic regression analysis was performed to identify variables that were predictive of relative improvements in postoperative SSS and FSS scores that achieve MCID. The variables analyzed in these models included preoperative measurements of median nerve CSA as both a continuous variable and classification as positive or negative for CTS defined by the cutoff value of 10 mm2. For variables that were statistically significant on univariate analysis, multivariate GEE logistic regression models were developed to assess the role of these variables as predictors of achieving MCID for SSS and FSS. For all regression models, odds ratios and 95% confidence intervals were reported. A threshold of P < .05 was set for statistical significance.
Results
A total of 106 patients were included for the analysis, of which 69 patients were positive for CTS on US, with an average median nerve CSA of 15.2 ± 4.4 mm2, whereas 37 patients were negative for CTS on US with an average CSA of 9.0 ± 1.3 mm2 (P < .001). Patient demographics and baseline US, NCS, and CTS-6 scores are presented in the Table 1. Female sex, height, and weight were found to be significantly different between the CTS-positive and -negative cohorts (P = .01, P =.02, and P = .01, respectively). There were no differences in BMI, NCS, or CTS-6 scores before surgery between the two groups.
Table 1.
Comparison of Preoperative Demographics and Baseline US, NCS, and CTS-6 Scores Between US-Positive and US-Negative Patients
| Demographics and Baseline Characteristics | Overall (n = 106) | US-Positive (n = 69) | US-Negative (n = 37) | Significance (P Value) |
|---|---|---|---|---|
| Age, mean ± SD | 56.3 ± 13.6 | 55.8 ± 13.6 | 57.2 ± 13.6 | .61 |
| Sex (% female), n (%) | 82 (77.4%) | 48 (69.6%) | 34 (91.9%) | .01 |
| Height (in), mean ± SD | 64.9 ± 3.6 | 65.5 ± 3.7 | 63.8 ± 3.1 | .02 |
| Weight (lbs), mean ± SD | 199.1 ± 50.9 | 208.9 ± 54.0 | 181.4 ± 39.5 | .01 |
| BMI, mean ± SD | 33.2 ± 7.8 | 34.1 ± 8.1 | 31.5 ± 7.2 | .10 |
| US median nerve CSA, mm2, mean ± SD | 13.1 ± 4.7 | 15.2 ± 4.4 | 9.0 ± 1.3 | < .001 |
| NCS-DML, mean ± SD | 5.8 ± 2.2 | 6.0 ± 2.3 | 5.5 ± 1.9 | .30 |
| NCS-DSL, mean ± SD | 4.5 ± 1.5 | 4.4 ± 1.4 | 4.6 ± 1.6 | .52 |
| NCS-positive, n (%) | 98 (92.5%) | 64 (92.8%) | 34 (91.9%) | .87 |
| CTS-6 score, mean ± SD | 15.2 ± 5.4 | 14.7 ± 5.6 | 16.2 ± 4.7 | .17 |
| CTS-6 positive, n (%) | 76 (71.7%) | 46 (66.7%) | 30 (81.1%) | .12 |
| Average follow-up (wk), mean ± SD | 17.1 ± 11.1 | 18.5 ± 10.9 | 14.5 ± 11.2 | .08 |
Bolded values are significant (P-value less than or equal to .05).
NCS-DML, nerve conduction studies-distal motor latency.
Changes in BCTQ scores following CTR for each preoperative evaluation tool (US, NCS, and CTS-6) are shown in the Table 2. There were no differences in pre- and postoperative BCTQ scores when stratifying patients by median nerve CSA on US. There were also no significant differences in BCTQ scores before and after surgery when patients were grouped by their NCS. However, when divided into CTS-6-positive and CTS-6-negative cohorts, there was a significant difference in the preoperative SSS portion of the BCTQ. There were no significant correlations between the number of positive preoperative tests and BCTQ scores before surgery and absolute change after surgery (Table 3). A breakdown of the number of preoperative positive tests and a specific combination of preoperative positive tests are displayed in the Figure.
Table 2.
Absolute Changes of BCTQ Scores Between Pre- and Post-op Time Points for Preoperatively Classified US, NCS, and CTS6 Cutoffs
| BCTQ Score Evaluated | US-Positive (n = 69) | US-Negative (n = 37) | Significance (P Value) |
|---|---|---|---|
| Pre-op | |||
| SSS | 3.1 ± 0.8 | 3.2 ± 0.6 | .58 |
| FSS | 2.5 ± 0.9 | 2.7 ± 0.9 | .35 |
| Score change | |||
| SSS 6 wk | −1.5 ± 0.8 | −1.5 ± 1.0 | .71 |
| SSS 6 mo | −1.7 ± 0.9 | −1.4 ± 0.9 | .32 |
| SSS 1 y | −1.2 ± 1.0 | −1.9 ± 0.7 | .10 |
| FSS 6 wk | −1.0 ± 1.0 | −1.1 ± 1.2 | .81 |
| FSS 6 mo | −1.0 ± 1.0 | −1.0 ± 1.2 | >.99 |
| FSS 1 y | −1.0 ± 0.9 | −1.2 ± 0.5 | .59 |
| NCS-Positive (n = 98) | NCS Negative (n = 8) | Significant (P Value) | |
| Pre-op | |||
| SSS | 3.1 ± 0.8 | 3.2 ± 0.8 | .81 |
| FSS | 2.6 ± 0.9 | 2.4 ± 0.7 | .54 |
| Score change | |||
| SSS 6 wk | −1.6 ± 0.9 | −1.1 ± 1.2 | .25 |
| SSS 6 mo | −1.7 ± 0.9 | −1.4 ± 1.0 | .59 |
| SSS 1 y | −1.3 ± 1.0 | −1.2 ± 1.4 | .90 |
| FSS 6 wk | −1.1 ± 1.0 | −0.4 ± 1.2 | .10 |
| FSS 6 mo | −1.0 ± 1.0 | −0.4 ± 0.3 | .27 |
| FSS 1 y | −1.1 ± 0.8 | −0.5 ± 1.0 | .25 |
| CTS-6 Positive (n = 76) | CTS-6 Negative (n = 30) | Significant (P Value) | |
| Pre-op | |||
| SSS | 3.2 ± 0.7 | 2.8 ± 0.8 | .01 |
| FSS | 2.7 ± 0.9 | 2.3 ± 0.8 | .06 |
| Score change | |||
| SSS 6 wk | −1.5 ± 0.9 | −1.6 ± 0.8 | .48 |
| SSS 6 mo | −1.6 ± 0.9 | −1.7 ± 0.9 | .67 |
| SSS 1 y | −1.4 ± 1.0 | −1.1 ± 0.9 | .53 |
| FSS 6 wk | −1.0 ± 1.1 | −1.1 ± 0.8 | .74 |
| FSS 6 mo | −0.9 ± 1.0 | −1.2 ± 0.9 | .50 |
| FSS 1 y | −1.1 ± 0.9 | −0.9 ± 0.8 | .51 |
Bolded values are significant (P-value less than or equal to .05).
FSS, functional severity score.
Table 3.
Correlation Analysis Between the Number of Preoperative Positive Tests and Absolute Changes of BCTQ Scores Between Pre-Op and Post-Op Time Points∗
| BCTQ Score Evaluated | Spearman's Rho | P Value |
|---|---|---|
| Pre-op | ||
| SSS | 0.12 | .22 |
| FSS | 0.08 | .39 |
| Score change | ||
| SSS 6 wk | 0.06 | .65 |
| SSS 6 mo | −0.11 | .5 |
| SSS 1 y | −0.01 | >.99 |
| FSS 6 wk | −0.01 | .97 |
| FSS 6 mo | 0.00 | .99 |
| FSS 1 y | −0.16 | .34 |
Number of preoperative positive tests was considered ordinal data and had a value between 1 and 3 depending on the combination of positive preoperative tests between US, NCS, and CTS-6.
Figure.
Breakdown of patients who were clinically diagnosed with CTS based on A number of positive preoperative tests and B specific combination of positive preoperative tests.
Univariate analysis was then conducted for both the SSS and FSS portions of the BCTQ to assess for potential preoperative variable influences on the relative changes in SSS or FSS, as shown in the Tables 4 and 5. Female sex, BMI, and follow-up time were found to be statistically significant regarding changes in SSS (P = .01, P = .04, and < .001), whereas age, female sex, and follow-up time statistically differed when analyzing changes in FSS (P = .002, .02, and < .001). Preoperative NCS-DML also significantly differed for FSS (P = .02).
Table 4.
Univariate Analysis of Relative Changes in SSS to Achieve MCID∗
| Demographic Variable | Odds Ratio | (95% CI) | P Value |
|---|---|---|---|
| US median nerve CSA | 0.95 | 0.88–1.01 | .12 |
| US median nerve 10 mm2 cutoff | 0.72 | 0.37–1.39 | .33 |
| NCS-DML | 0.88 | 0.75–1.03 | .12 |
| NCS-DSL | 1.03 | 0.82–1.31 | .75 |
| NCS ± cutoff | 2.10 | 0.61–7.23 | .24 |
| CTS-6 score | 1.03 | 0.97–1.98 | .36 |
| CTS-6 ± cutoff | 0.99 | 0.49–1.99 | .97 |
| Diabetes | 1.37 | 0.64–2.92 | .42 |
| Age | 0.98 | 0.96–1.00 | .09 |
| Female sex | 2.90 | 1.31–6.42 | .01 |
| BMI | 1.04 | 1.00–1.09 | .04 |
| Follow-up | 1.06 | 1.04–1.08 | < .001 |
Bolded values are significant (P-value less than or equal to .05).
All variables are adjusted for follow-up.
Table 5.
Multivariate Analysis of Relative Change in SSS to Achieve MCID
| Demographic Variable | Odds Ratio | (95% CI) | P Value |
|---|---|---|---|
| Female sex | 2.93 | 1.33–6.45 | .01 |
| BMI | 1.04 | 1.00–1.09 | .04 |
| Follow-up | 1.06 | 1.04–1.08 | < .001 |
Bolded values are significant (P-value less than or equal to .05).
Finally, the statistically significant variables from the SSS and FSS univariate analyses were used to conduct multivariable analyses. For relative changes in SSS, female sex, BMI, and follow-up time continued to significantly differ as shown in Table 6. Age, female sex, and follow-up time continued to be statistically significant for FSS, whereas the pre-op NCS-DML did not remain significant with multivariable analysis (Table 7).
Table 6.
Univariate Analysis of Relative Changes in FSS to Achieve MCID∗
| Demographic Variable | Odds Ratio | (95% CI) | P Value |
|---|---|---|---|
| US median nerve CSA | 0.95 | 0.88–1.01 | .11 |
| US median nerve 10 mm2 cutoff | 0.66 | 0.35–1.24 | .20 |
| NCS-DML | 0.84 | 0.72–0.97 | .02 |
| NCS-DSL | 0.95 | 0.76–1.19 | .648 |
| NCS ± cutoff | 1.40 | 0.45–4.24 | .57 |
| CTS-6 score | 1.01 | 0.96–1.07 | .63 |
| CTS-6 ± cutoff | 1.29 | 0.66–2.52 | .46 |
| Diabetes | 1.29 | 0.63–2.65 | .49 |
| Age | 0.97 | 0.95–0.99 | .002 |
| Female sex | 2.47 | 1.14–5.34 | .02 |
| BMI | 1.00 | 0.96–1.03 | .85 |
| Follow-up | 1.05 | 1.03–1.08 | <0.001 |
Bolded values are significant (P-value less than or equal to .05).
All variables are adjusted for follow-up.
Table 7.
Multivariate Analysis of Relative Change in FSS to Achieve MCID Cutoff Values
| Demographic Variable | Odds Ratio | (95% CI) | P Value |
|---|---|---|---|
| Pre-op NCS-DML | 0.88 | 0.76–1.03 | .10 |
| Age | 0.97 | 0.95–0.99 | .01 |
| Female sex | 2.59 | 1.19–5.60 | .02 |
| Follow-up | 1.07 | 1.04–1.09 | < .001 |
Bolded values are significant (P-value less than or equal to .05).
Discussion
Ultrasonography, NCS, and the CTS-6 questionnaire are tools with comparable sensitivity and specificity that are used to screen for and diagnose CTS.4 However, there remains conflicting evidence on the ability of these tools to predict clinical outcomes, including PROs, following CTR.11, 12, 13, 14, 15, 16, 17, 18, 19 This study demonstrated that preoperative US, NCS, and CTS-6 findings, considered diagnostic of CTS, had no correlation with postoperative changes in BCTQ scores after CTR.
It has previously been hypothesized that preoperative studies suggesting more severe CTS, such as larger median nerve CSA on US, increased latency on NCS, or higher CTS-6 scores, would suggest worse symptoms and thereby less favorable outcomes following CTR. However, recent research has found that this is not the case for all tools used in the evaluation of CTS. Ultrasound has been a rapidly growing method of diagnosing CTS, and there is a current lack of evidence suggesting that median nerve CSA correlates with symptom severity of CTS.4 Although median nerve CSA and symptom severity have no proven correlation, there has been conflicting evidence of the ability of ultrasound to predict clinical outcomes, in the form of PROs, following CTR. Our findings are similar to the recent work of Fowler et al, which demonstrated that even a clear diagnosis of CTS on ultrasound does not predict BCTQ changes after CTR.27
Unlike ultrasound, NCS and CTS-6 have shown better correlations to patient-reported symptom severity.28,29 Similar to ultrasound, there are limited studies evaluating the prognostic value of preoperative NCS and CTS-6 findings on clinical outcomes after CTR. The majority of the literature on NCS dates back 20 years, with conflicting findings on the relationship between preoperative NCS and postoperative BCTQ scores.16,17 Such studies on CTS-6 are even more limited, but the latest data suggest little ability of CTS-6 to predict changes in BCTQ following CTR.19 Again, our findings in this study showed no association between diagnosis of CTS by preoperative NCS criteria or CTS-6 criteria on postoperative BCTQ symptom severity and function score changes.
Our study provides an evaluation of the association between preoperative CTS studies and CTR recovery by BCTQ change up to 1 year following CTR, looking at three separate preoperative diagnostic tools in a sample of 106 patients. This work has the potential to influence the preoperative evaluation of patients presenting with CTS. Given little direct association between diagnostics results and outcomes following CTR, it may not be necessary to use all CTS diagnostic methods. Instead, it may be more beneficial to the patient and provider to opt for the least invasive and least expensive option when establishing a diagnosis of CTS and conducting preoperative evaluation before CTR.
Limitations
There are limitations to this work. The first is the retrospective design of the study. Additionally, although patients were sent BCTQ forms up to a year after surgery, there was limited in-person follow-up at an average of less than 6 months following CTR. There may also be limitations with the BCTQ itself. Although it is the most frequently used outcome measure for CTS, some recent studies have questioned the adequacy of the questionnaire’s ability to assess the severity of median nerve entrapment, thereby failing to differentiate between mild and severe CTS.30,31 Furthermore, given the BCTQ was first published in 1993, the applicability to patients in today’s digital world has also recently been put into question. For example, tasks included in the FSS portion such as holding a book, gripping a telephone handle, and buttoning clothes are less relevant to patients today, which could affect how they choose to answer such portions of the questionnaire. There is also no part of the questionnaire that specifies whether the patient is answering for the dominant or the nondominant hand, making it more difficult to answer the FSS section, especially for the nondominant hand. This lack of differentiation may also affect the results and symptom scoring accuracy. Addressing such concerns would take further investigation, but for now, the BCTQ remains a standard questionnaire in both clinical practice and research endeavors for CTS. Finally, the generalizability of the findings of this study may be limited. Although ultrasound is readily available in our institution’s orthopedic hand clinics, we recognize that this may not be the case for all providers at other institutions. As such, surgeons may have different methods for diagnosing CTS and use other preoperative tools if regular access to ultrasound is not feasible.
Although helpful in establishing a diagnosis of CTS, using preoperative ultrasound, NCS, and CTS-6 diagnostic cutoffs in this cohort was not associated with changes in BCTQ symptom or function scores up to 1 year after surgery following CTR.
Conflicts of Interest
No benefits in any form have been received or will be received related directly to this article.
Footnotes
DISCLAIMER: Given his role as Editor-in-Chief of The Journal of Hand Surgery Global Online, Dr Fowler had no involvement in the peer review of this article and has no access to information regarding its peer review. Full responsibility for the editorial process for this article was delegated to Aviram M. Giladi, MD, MS.
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