
==== Front
Eur J Phys Rehabil Med
Eur J Phys Rehabil Med
EJPRM
European Journal of Physical and Rehabilitation Medicine
1973-9087
1973-9095
Edizioni Minerva Medica

39007786
8491
10.23736/S1973-9087.24.08491-0
Article
Successful evaluation of a new image-based parameter for the diagnosis of carpal tunnel syndrome: ultrasound assessment of longitudinal median nerve gliding in patients, healthy volunteers, and cadavers
ROSSMANN Tobias 1 2
PRUIDZE Paata 1
VELDEMAN Michael 3
WENINGER Wolfgang J. 1
GRISOLD Wolfgang 4
CHANG Ke-Vin 5
MENG Stefan 1 6 *
1Division of Anatomy, Medical University of Vienna, Vienna, Austria; 2Department of Neurosurgery, Neuromed Campus, Kepler University Hospital, Linz, Austria; 3Department of Neurosurgery, RWTH Aachen University Hospital, Aachen, Germany; 4Neurology Consultancy Unit, Division of Anatomy, Medical University of Vienna, Vienna, Austria; 5Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Bei-Hu Branch, Taipei, Taiwan (ROC); 6Department of Radiology, Hanusch Hospital, Vienna, Austria
* Corresponding author: Stefan Meng, Waehringer Strasse 13, 1090 Vienna, Austria. E-mail: stefan.meng@meduniwien.ac.at
Authors’ contributions: Tobias Rossmann: conceptualization, data curation, investigation, methodology, formal analysis, writing - original draft. Paata Pruidze: investigation. Michael Veldeman: formal analysis, visualization, writing – review and editing. Wolfgang J. Weninger: project administration, resources. Wolfgang Grisold: conceptualization, writing – review and editing. Ke-Vin Chang: conceptualization, writing – review and editing. Stefan Meng: conceptualization, data curation, investigation, methodology, supervision, validation, writing – review and editing. All authors read and approved the final version of the manuscript.

15 7 2024
8 2024
60 4 671679
27 6 2024
04 6 2024
04 3 2024
2024 THE AUTHORS
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives (CC BY-NC-ND) 4.0 License.
BACKGROUND

Reduced longitudinal median nerve gliding is a new promising diagnostic feature in carpal tunnel syndrome (CTS). However, the complexity of existing ultrasound analysis protocols undermines the application in routine clinical practice.

AIM

To provide a simple method for assessing longitudinal gliding with ultrasound, without the need for post-hoc image analysis.

DESIGN

1) Retrospective cohort study, validation by external blinded reviewers; 2) proof of concept in body donors.

SETTING

1) Outpatient clinic; 2) anatomy department.

POPULATION

The population included 48 patients with idiopathic CTS diagnosed by electrodiagnostic testing and ultrasound, as well as 15 healthy controls. Twelve, non-frozen, non-embalmed body donors were enrolled.

METHODS

Longitudinal gliding of the median nerve in the carpal tunnel was visualized in all patients with idiopathic CTS and healthy controls. All ultrasound videos were pseudonymized, equipped with a scale, and randomized. Videos were analyzed by four independent radiologists, all blinded to clinical characteristics. The endpoint was gliding rated as millimeters. Validity of the technique was tested by using speckle tracking software, and in body donors, directly measuring nerve excursion in situ, simultaneously to ultrasound.

RESULTS

Gliding differed significantly between controls and patients with CTS, decreasing with incremental CTS severity. A cut-off value of 3.5 mm to identify patients with CTS, yielded 93.8% sensitivity and 93.3% specificity. Intraclass correlation coefficient among senior author and raters was 0.798 (95% CI 0.513 to 0.900, P<0.001), indicating good reliability. Speckle tracking and especially direct validation in body donors correlated well with ultrasound findings.

CONCLUSIONS

First, longitudinal median nerve gliding can reliably be assessed using this simple technique without the need for complicated procedures. Second, a decrease in gliding was found with progressive severity of CTS. Reproducibility for measured distances is good among raters.

CLINICAL REHABILITATION IMPACT

An easy to apply sonography parameter would bolster the diagnostic ability of specialists in physical medicine and rehabilitation in daily routine.

Key words:

Carpal tunnel syndrome
Ultrasonography
Articular range of motion
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pmcNeuromuscular ultrasound may provide a similar diagnostic accuracy to electrodiagnostic testing in diagnosing carpal tunnel syndrome (CTS).1, 2 A major advantage of ultrasound is the possibility to visualize the morphology of nerve and surrounding tissue. Nerve cross-sectional area (CSA) and wrist-to-forearm ratio (WFR) provide the highest sensitivity and specificity.3 The sensitivity of ultrasound may be further increased by assessment of additional features such as echogenicity, vascularity, and gliding,4 the latter of which received increasing attention in recent years. A rising number of publications suggest significant differences in nerve gliding between patients with CTS and healthy controls.1, 2, 5 Different methods have been used to evaluate median nerve gliding;6 however, these are technically demanding as well as time consuming and therefore not feasible in clinical routine. In addition, only few studies7-9 report the absolute extent of nerve excursions and diagnostic cut-off values have not yet been established. Ultrasound as a user-friendly and efficient method in the diagnosis of CTS,10 may be used to follow-up on treatment results after conservative therapy.11

This study set out to prove the feasibility of a simple diagnostic method to examine longitudinal median nerve gliding. We assessed the reliability of rating nerve gliding based on visual inspection, omitting the necessity for external post-hoc image analysis in the future. Reproducibility was tested based on the performance of blinded independent raters and measurements were objectified in a human cadaver study.

Materials and methods

The project has been approved by the institutional research ethics committee of the Medical University of Vienna (EK Nr. 1532/2022), and was conducted in accordance with the principles set forth in the Declaration of Helsinki. Informed consent for patient file review was waived due to the retrospective nature of this study. Healthy volunteers gave written consent to participate. Body donors provided written consent, that their bodies shall be used for medical research or teaching purposes, before they deceased.

Patient cohort

Recruitment of patients and healthy controls is shown in a flow chart (Figure 1). A total of 360 ultrasound examinations for suspected CTS, performed in 241 patients between January 2021 and July 2022, were retrospectively reviewed. All patients had been referred from external healthcare providers for ultrasound workup. Ultimately, only complete ultrasound examinations including nerve gliding assessment in patients with proven CTS based on nerve conduction studies (NCS)12, 13 were included. We excluded known non-idiopathic etiologies, such as previous CTS surgery or anatomical variants. A total of 66 examinations (48 individuals) were available. In the 18 individuals with bilateral examinations, the less affected side was excluded based on NCS-results and, if similar, based on WFR as an imaging feature. This left unilateral ultrasound examinations of 48 patients eligible for final analysis.

Figure 1 —Flow chart of patient selection and video analysis. CTS: carpal tunnel syndrome; NCS: nerve conduction study; US: ultrasound.

Healthy controls

Fifteen volunteers were prospectively recruited via a local public announcement and underwent the same uniform ultrasound protocol as patients. The examined side was chosen randomly using an online randomization tool (List randomizer, random.org). Possible symptoms of CTS were ruled out by physical examination and completion of Boston Carpal Tunnel Questionnaire (BCTQ).14, 15 None of the volunteers was currently pregnant or had relevant comorbidities (diabetes, rheumatoid arthritis, polymyalgia rheumatica, hypothyroidism, acromegaly, amyloidosis, carcinomatosis).

Ultrasound protocol and video production

A uniform protocol was used by the senior author (S.M.) in all volunteers, patients, and cadaver specimens, using the same high-resolution ultrasound system (Aplio i800 and i18LX5 linear transducer, Canon Medical Systems Europe B.V.). Arms were placed supine with the wrist in neutral position. The median nerve was scanned from mid-forearm to the palm and cross-sectional area (CSA) was measured at wrist and mid-forearm, according to current recommendations (CSA at the wrist / CSA at the mid-forarm).3 The median nerve was then imaged longitudinally underneath the flexor retinaculum, ensuring it would not move out of the image during finger movement (Figure 2).

Figure 2 —Ultrasound anatomy of the carpal tunnel in longitudinal plane. Arrowheads: median nerve; asterisks: flexor tendons; daggers: capitate bone. Twin-headed long arrow depicts median nerve gliding.

Patients/volunteers slightly clenched their fist with all five fingers and thereafter returned to the initial position (Supplementary Digital Material 1: Supplementary Video 1, 4 s, 3.01 MB), none showed signs of impaired finger flexion from CTS. Grasping speed or force were not standardized or measured. Care was taken not to compress the palm of the hand with the ultrasound transducer. Ultrasound videos of full nerve excursion during finger flexion were captured and exported to a video editing software (Premiere Pro, Adobe Inc.), then pseudonymized and uniformly sized according to an inserted scale. This guaranteed identical size proportions regardless of individual computer/display settings (e.g. screen resolution, etc.)

Gliding measurement and study endpoints from video analysis

All videos were put in random order (List randomizer, random.org) and distributed by the first author, leaving all raters blinded to clinical and ultrasound parameters (Figure 1). The senior author analyzed all 63 videos (48 patients + 15 healthy controls) included in this study. To assess generalizability, a random sample of 45 videos (30 from patients and 15 from healthy controls) was analyzed by three independent, external raters. All raters are radiologists experienced with ultrasound but not specialized in neuromuscular ultrasound.

The primary endpoint of this study was the extent of longitudinal median neve gliding in millimeters, based on analysis of the ultrasound videos. Measurement of gliding is based on the identification of a clearly distinguishable intraneural structure which is then followed by scrolling back and forth. The start and end points of nerve excursion are marked using the cursor or simply by a finger on the screen. The measurement itself is made as usual on the ultrasound system. Raters in this study were free to use any anatomical ultrasound detail of the nerve to assess the extent of excursion. Usage of any post-processing software as in speckle tracking or other protocols was prohibited for raters.

Proof of concept, cadaver specimens and dissection protocol

To prove our concept of longitudinal gliding measurement, we assessed how ultrasound findings correspond to nerve gliding in an anatomical setting. Upper extremities (five left, seven right) of twelve, non-frozen, non-embalmed body donors were randomly enrolled as they became available to the anatomy department. Donors with known neuromuscular disease, known CTS, signs of trauma or surgery were excluded. The dissection protocol to simulate clenching a fist is provided in Supplementary Digital Material 2 (Supplementary Text File 1). A graphic representation is shown in Supplementary Digital Material 3 (Supplementary Figure 1). A metal pin was inserted via small skin incision into the distal third of the metacarpal bone, ensuring that no tendon or nerve is affixed. A second pin was inserted in the distal ulna. Sutures were applied to flexor pollicis longus tendon and tendons / distal muscle bulks of superficial and deep flexor digitorum muscle. Arrows in the supplementary figure mark 7/0 sutures applied to median nerve and flexor carpi radialis tendon as reference points, to measure longitudinal gliding. While clenching the fist, median nerve excursion was measured with a caliper by an anatomist and simultaneously by ultrasound. Neither investigator was aware of the result of the other (blinding). Ultimately, specimens were fully dissected by an anatomist and a neurosurgeon to rule out pathologies or anatomical variations at the carpal tunnel, undetected by ultrasound.

Validation by speckle tracking

The anonymized videos were converted to sequences of still images and analyzed using the Speckle TrackerJ plugin16 (version 0.87) for ImageJ.17 In all 63 cases, distinct intraneural structures were followed and their distance travelled was measured.

Statistical analysis

Appropriate tests were chosen based on data normality assessed by Shapiro-Wilk Test. Metric parameters were tested using two-sample t-test or Mann-Whitney U Test. Comparison of subgroups based on NCS severity and healthy controls were compared by Kruskal-Wallis Test with additional post-hoc pairwise comparison (Mann-Whitney U). Interrater reliability between all raters was calculated using the intra-class correlation coefficient (ICC) for metric variables, analyzing all 45 cases rated by all reviewers. ICC estimates and their 95% confidence intervals were calculated based on a mean-rating (k=4), absolute-agreement, two-way mixed-effects model.18 Pairwise comparisons of agreement were assessed via Spearman correlation coefficient. Cut-off-values for gliding measurements were assessed by calculating Receiver-operator-characteristic (ROC) curves. A two-sided P value of <0.05 was considered statistically significant. IBM SPSS Statistics 28.0 (IBM Inc.) and Prism 9 (GraphPad Software Inc.) were used for calculation and graphic presentation of data. The study is reported according to guidelines of the STROBE initiative.

Data availability statement

The data associated with this manuscript are not publicly available but may be made available by the corresponding author on reasonable request.

Results

Patient and healthy controls characteristics

A comparison of the groups is shown in Table I. In both groups, roughly two thirds of patients were female, with a mean age of 56.1 years in the patient group and 39.1 years for healthy controls (P=0.001). A median WFR of 2.472 (2.028 to 2.972) was found in patients, whereas values were within normal limits 1.250 (1.000 to 1.430) in controls (P<0.001). WFR did not differ significantly between NCS severity categories (P=0.379). NCS severity was graded as weakly positive in 43.8%, moderate in 31.2%, and strongly positive in 25%. The right side was more often affected (64.6%) in patients. In controls the distribution was 60% right and 40% left arms. BCTQ mean values for the symptom severity scale and functional status scale were 1.0 in all healthy controls.

Table I —Baseline characteristics of patients and healthy controls.

Characteristics	Patients with CTS
(N.=48)	Healthy controls
(N.=15)	P value	
Gender			1.000	
Female	33 (68.8%)	10 (66.7%)		
Male	15 (31.3%)	5 (33.3%)		
Mean age	56.1±16.2	39.1±18.4	0.001*	
CSA (cm2)				
Wrist	0.190 (0.160 to 0.238)	0.100 (0.080 to 0.110)	<0.001*	
Forearm	0.080 (0.070 to 0.080)	0.080 (0.070 to 0.080)	0.973	
Wrist-forearm-ratio	2.472 (2.028 to 2.972)	1.250 (1.000 to 1.430)	<0.001*	
Affected side				
Left	17 (35.4%)			
Right	31 (64.6%)			
NCS severity				
Weakly positive	21 (43.8%)	-		
Moderately positive	15 (31.2%)	-		
Strongly positive	12 (25.0%)	-		
CSA: cross-sectional area; IQR: interquartile range; NCS: nerve conduction study. *Statistical significance.

Assessment of nerve gliding

Blinded assessment of longitudinal gliding in all 63 individuals by the senior author found a median gliding of 5.0 mm (4.0 to 6.0) for healthy controls, versus 2.0 mm (0 to 2.8) in patients with weakly positive NCS results. There was almost no detectable gliding in patients with moderately and strongly positive NCS. Detailed results are shown in Table II and Figure 3. Comparison of gliding measurements between all groups by Kruskal-Wallis Test (P=0.002) and post-hoc pairwise comparison demonstrated significant differences between healthy controls and NCS weakly (P=0.001), moderately (P<0.001) and strongly positive (P<0.001) patients with CTS.

Table II —Assessment of longitudinal gliding grouped by severity based on NCS.

Parameter	Healthy controls	NCS weakly positive	NCS moderately positive	NCS strongly positive	
Senior author (mm) a	5.0 (4.0 to 6.0)	2.0 (0 to 2.8)	0 (0 to 1.0)	0	
Speckle tracking (mm) a	4.9 (4.3 to 7.0)	2.1 (1.7 to 4.8)	2.2 (1.6 to 2.9)	1.1 (0.7 to 1.5)	
Independent raters (mm) b	6.0 (5.0 to 8.0)	4.0 (3.0 to 5.0)	3.0 (2.0 to 5.0)	2.0 (2.0 to 3.0)	
CTS: carpal tunnel syndrome; NCS: nerve conduction study. a Assessment of longitudinal gliding in all 63 individuals, of those 15 healthy controls, 21 NCS weakly positive, 15 NCS moderately positive, 12 NCS strongly positive. b Each rater evaluated the same 45 randomly chosen individuals, of those each 15 healthy controls, 13 NCS weakly positive, 12 NCS moderately positive, 5 NCS strongly positive.

Figure 3 —Comparison of measurements of longitudinal mobility (distance in mm) between groups, as measured by the senior author (Table II). A) depicts difference between healthy controls and all patients with carpal tunnel syndrome (CTS). B) shows differences between healthy controls and patients with CTS stratified according to NCS severity.

In post-hoc pairwise comparison between patients with CTS only, a significant difference existed between weakly and strongly positive NCS (P=0.002) only. Comparison of weakly versus moderately positive NCS groups was close to significance (P=0.050), unlike moderately versus strongly (P=0.876). Thus, the extent of longitudinal gliding on ultrasound differed significantly between healthy controls and patients with CTS; however, it statistically failed to identify subgroups based on NCS severity.

Assessment by blinded raters

Summarized for all three blinded raters, median gliding in controls was 6.0 mm. Gliding distance was 4.0 mm, 3.0 mm and 2.0 mm for patients graded as NCS weakly, moderately and strongly positive, respectively. Gliding significantly differed between controls and patients overall in all three raters (P<0.001 each). Kruskal-Wallis Test among patients still showed significant group differences (P=0.004, P<0.001, P<0.001) for all raters; however, none was able to discriminate between NCS severity subgroups based on pairwise comparison.

Correlation among raters

For gliding measured in mm, the ICC among senior author and all raters was 0.798 (95% CI 0.513 to 0.900, P<0.001) indicative of good reliability.18 However, the 95% CI suggests that this may include cases of both moderate and excellent reliability. In addition, the strength of agreement was tested in pairwise comparisons between each blinded rater and the senior author. Agreement for measurements in mm was almost perfect with two raters (r=0.822 and r=0.863, both P<0.001). Agreement with the third reviewer was only moderate (r=0.578, P<0.001).

Cut-off value

Gliding measurements taken by the senior author, resulted in ROC curves with AUC=0.969 (SD=0.019; 95% CI: 0.931 to 1.000; P<0.001), indicative of excellent discrimination. A cut-off value of 3.5 mm to differentiate controls from patients yields 93.8% sensitivity and 93.3% specificity (Figure 4A).

Figure 4 —A) Receiver-operator-characteristic (ROC) curve of longitudinal gliding as measured by the senior author. B) ROC curves based on measurements of the three blinded raters.

AUC results were excellent in two raters: AUC=.904 (SD=.046; 95% CI: 0.815 to 0.994; P<0.001) and AUC=0.942 (SD=0.032; 95% CI: 0.880 to 0.100; P<0.001), while still good in the third: AUC=0.817 (SD=0.071; 95% CI: 0.680 to 0.956; P=0.001). Corresponding ROC curves are shown in Figure 4B. Using the same cutoff as above would have yielded a sensitivity of 70%, 70% and 26.7%. Specificity would have corresponded to 93.3%, 100% and 93.3%.

Cadaver study

Full details on cadaver specimens are shown in Supplementary Digital Material 4 (Supplementary Table I). Twelve upper extremities (five left, seven right) of four female and eight male body donors, with a mean age of 75.2 years at death, were included. Median WFR was 1.56 (1.28 to 1.68). Median longitudinal gliding measured on the specimen itself was 5.2 mm (4.1 to 6.5) corresponding to a 5.6 mm (4.0 to 6.8) on ultrasound. This resulted in a median difference of 1.0 mm (0.6 to 1.4) existed, which may be attributed to measurement inaccuracy, elastic behavior of tissues and other factors. Of note, two specimens showed bifid median nerve configuration, associated with a median artery in one case.

Speckle tracking

Results from post-hoc analysis by speckle tracking correlate well with our proposed simplified assessment method. Measured nerve gliding distances lie within the range of findings from senior author and blinded raters, showing the same decrease with progressive CTS severity (Table II). A graphic representation of the correlation is shown in Supplementary Digital Material 5 (Supplementary Figure 2).

Discussion

Longitudinal gliding of the median nerve is a promising new morphological feature of CTS.1, 2, 5 Due to the complexity of post-hoc analyses, nerve gliding has not yet been established as a standard diagnostic element. We report a simple method for the assessment of longitudinal gliding using ultrasound, which yields reproducible results that correlate with NCS findings. Thus, it may serve as an image-based assessment criterion for diagnosing CTS in addition to the well-established increase of nerve caliber (CSA).3, 19 As non-surgical treatment is regarded the first-line treatment in patients with CTS,20 an easy diagnostic tool to monitor the effect of treatment is desirable. This would help to establish and adjust individualized treatment regimens.

The semi-quantitative measurement technique validated in our study is based on gray scale ultrasound inspection and simple direct measurement. Any reference point can be chosen by the examiner. This approach is unique, easy-to-handle and differs from already published methods. These previously reported techniques such as speckle tracking, require exporting ultrasound video clips to an external software to track the movement of fine speckle features in single video frames9, 21 or in relation to tendon excursion velocity.22 Another previously reported method is the analysis of the velocity-time integral in Doppler ultrasound, followed by post hoc analysis in an external software.7, 8 Although speckle tracking has proven to be a valid technique23 and its findings have been successfully correlated with clinical interventions,24 a systematic review of nerve gliding methods6 found the reliability of abovementioned techniques to be moderate. Studies using a semi-quantitative approach, similar to our report, are not included in recent systematic reviews.2, 5, 6 While speckle tracking and Doppler techniques are difficult to be applied in daily clinical routine, our method allows a fast and straightforward assessment. An advantage over software-based measurements may be that the disappearance of fine-speckle structures due to slight sagittal displacement of the ultrasound transducer may be negligible as the overall visual impression remains.

The findings of this study indicate that longitudinal gliding of the median nerve is of diagnostic value in the workup for CTS, adding to current literature.1, 2, 5 In our study, longitudinal gliding of less than 3.5 mm, measured at the wrist during full finger flexion, indicates CTS with up to 93.8% sensitivity and 93.3% specificity. However, ultrasound remains a highly operator-dependent imaging modality, and such a cut-off value may in practice vary between investigators and differ from other measuring methods such as speckle tracking. Methodology and results of this study will have to be validated externally in larger cohorts.

Diagnostic sensitivity of neuromuscular ultrasound assessing nerve swelling ranges from 56-98%,3, 25 which may be increased by an additional ultrasound criterion such as nerve gliding.4 While the majority of studies agree that longitudinal gliding differs between patients and healthy controls,2, 5 the extent of gliding shows considerable variation. Yao et al.9 found significantly reduced gliding in patients (0.4±0.11 mm) compared to controls (0.89±0.36 mm). Higher distances of nerve gliding were found by Liu et al.,8 reporting 21.3±10.6 mm in patients while 25.6±10.3 mm were measured in controls. Similar to our data, Filius et al.26 report 4.1±1.8 mm in healthy controls, decreasing to 2.4±1.0 mm in severe CTS based on NCS. The heterogeneity in literature may be caused by different examination protocols: even slight changes to hand postures may have large effects on nerve gliding, as the simple addition of finger adduction and abduction may double the excursion of the median nerve within the carpal tunnel.27 Also compensatory deformation of nerve and fascicles in case of entrapment28 may influence measurements. A systematic literature review29 reported median nerve excursions between 0.1 to 12.5 mm, depending on several factors in relation to the joints moved. Our results are well within that range, suggesting valid measurements. Measurements by the senior author detected a median excursion of 5.0 mm in healthy controls, decreasing to almost zero with incremental severity based on NCS (Table II, Figure 3). The decrease was less pronounced according to the blinded raters (Table II), at 2.0 mm in severe CTS. To validate our technique and measurements we additionally conducted a proof of concept cadaver study. Absolute differences between the two measurement techniques ranged from 0.03 to 1.77 mm. We thus assume that ultrasound measurements correlate well to in-vivo nerve gliding.

To the best of our knowledge, this is the first study to report correlations of CTS severity and longitudinal gliding. Kruskal-Wallis tests detected significant differences between groups; however, based on pairwise comparison between grades of NCS severity, differences were mostly insignificant. One may hypothesize that a larger sample size would have led to significant results. Only few studies report longitudinal gliding, stratifying their patient cohorts along NCS severity. Liu and colleagues8 detected a mild to moderate correlation of BCTQ results, NCS severity, and gliding. Filius et al.26 report decreasing gliding with increasing CTS severity both in terms of NCS and clinical symptoms. Park et al.30 also found lower gliding related to increasing severity of CTS, similar results were published by others.31, 32

Limitations of the study

This study has limitations. Apart from its retrospective nature, the total number of included individuals is limited despite the large source database. A major shortcoming of our manuscript is the lack of standardization of NCS-results, as patients were referred from multiple external health care providers. Although performed by institutions certified for neurophysiological examinations, uniformity of diagnostic procedures and grading of CTS severity may differ. We tried to counterbalance this fact by strict inclusion/exclusion criteria, ensuring a complete set of clinical, NCS, and imaging data. Investigator experience is a general limitation to ultrasound.6 Our imaging data is based on a standardized ultrasound protocol, analyzed by multiple blinded radiologists. These raters were experienced with ultrasound, but not specialized in neuromuscular ultrasound. Thus, our method seems to be reproducible among sonographers of various expertise. Age was different between patients and healthy controls, an imbalance induced by recruitment of volunteers from healthcare/university facilities, similarly to others.7 Age, among other demographic factors, was shown to influence the cross-sectional area of the median nerve.33 However, a recent meta-analysis found age not to be associated with heterogeneity of reported nerve gliding. In the light of our reported reproducibility, age difference may be regarded negligible; however, it may be relevant when interpreting absolute measurements.

Conclusions

We report a straightforward and reliable examination protocol for the assessment of longitudinal nerve gliding in patients with CTS. Here, we found a decrease of longitudinal nerve gliding distance with progressive CTS severity. A cut-off value of 3.5 mm of distance yielded 93.8% sensitivity and 93.3% specificity for the identification of patients with CTS. Reproducibility among raters is good for measured distances. This method may provide an additional tool to diagnose CTS.

Supplementary Digital Material 1

Supplementary Video 1

Ultrasound

Supplemental Digital Material 2

Supplementary Text File 1

Dissection protocol of cadaver specimens.

Supplementary Digital Material 3

Supplementary Figure 1

Dissection protocol to simulate clenching a fist. A metal pin was inserted via small skin incision into the distal third of the metacarpal bone, ensuring that no tendon or nerve is affixed. A second pin was inserted in the distal ulna (A). Sutures were applied to flexor pollicis longus tendon and tendons / distal muscle bulks of superficial and deep flexor digitorum muscle. Arrows in the supplementary figure mark 7/0 sutures applied to median nerve (B, asterisk) and flexor carpi radialis tendon as reference points, to measure longitudinal gliding.

Supplementary Digital Material 4

Supplemental Table I

Table. Characteristics of cadaver specimen and measured mobility.

Supplementary Digital Material 5

Supplementary Figure 2

Graphic representation of the correlation.

Conflicts of interest: Stefan Meng discloses a consultant relationship with Merz GmbH and receives Honoraria for Lectures from - Canon Medical Europe, Juzo, Sanofi-Aventis GmbH, Austrian Society for Ultrasound in Medicine. All other authors certify that there is no conflict of interest with any financial organization regarding the material discussed in the manuscript.
==== Refs
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